A compacting device, method and compact for cemented carbide gradient structures

Abstract

This invention relates to the field of powder metallurgy technology, and more specifically, to a cemented carbide gradient structure pressing device, method, and pressing blank. The device includes a base with a universal level bubble and adjusting bolts for fine-tuning the level on its upper surface. Four adjusting bolts are distributed at the four corners of the base and threaded into the base to achieve real-time adjustment of the base's levelness during the pressing process. The adjusting bolts are also configured to drive the base to rise vertically through synchronous rotation during the final pressing stage, causing the lower die to displace upwards. The cemented carbide gradient structure pressing device of this invention, through the coaxial nesting and in-situ retention of multi-stage punches, achieves continuous graded pressing without demolding or mold changing within the same set of molds, which helps to eliminate inter-layer positioning errors caused by frequent mold changes or punch insertion / removal in traditional processes.

Description

Technical Field

[0001] This invention relates to the field of powder metallurgy technology, and more specifically, to a cemented carbide gradient structure pressing device, method, and pressing blank. Background Technology

[0002] In the field of cemented carbide manufacturing, gradient structure materials are widely used due to their ability to simultaneously achieve high surface hardness and high internal toughness. However, existing gradient cemented carbide pressing technology still faces significant challenges. On the one hand, the traditional unidirectional pressing process is affected by the friction between powder and the mold wall, causing the pressing force to decrease exponentially along the height direction, resulting in uneven axial density distribution of the compact. This leads to anisotropic shrinkage, deformation, and even cracking after sintering. Although bidirectional pressing can improve this problem, synchronous bidirectional press equipment is expensive, and asynchronous bidirectional pressing is difficult to achieve without increasing complexity in existing mold structures. On the other hand, the forming of multi-layer gradient structures usually relies on frequent mold changes or repeated punch insertion and removal, which not only makes it difficult to guarantee the coaxiality between layers and accumulates positioning errors, but also seriously restricts production efficiency. In addition, key parameters such as the base displacement in the final pressing stage of existing processes rely heavily on trial and error based on experience, lacking a quantitative correlation model with material properties and geometric dimensions, resulting in poor process stability and difficulty in controlling product consistency. Therefore, there is an urgent need for a technical solution that can achieve high-precision graded pressing without mold changes and significantly improve the density uniformity of the compact through an equivalent bidirectional pressing mechanism. Summary of the Invention

[0003] To address the problems of poor density uniformity, low mold-changing positioning accuracy, and lack of quantitative control of process parameters in the existing gradient cemented carbide pressing process, this application proposes a cemented carbide gradient structure pressing device, method, and pressing blank. This invention achieves continuous graded pressing without mold changing and equivalent asynchronous bidirectional pressing based on quantitative control of base displacement, thereby significantly improving the overall axial density uniformity of the pressing blank while ensuring high coaxiality of the multi-layer structure.

[0004] To at least partially solve the above problems, the present invention provides a cemented carbide gradient structure pressing device, including a base with a universal level and adjusting bolts for fine-tuning the level on its upper surface. Four adjusting bolts are distributed at the four corners of the base and threadedly engaged with the base to achieve real-time adjustment of the base's levelness during the pressing process. The adjusting bolts are also configured to drive the base to rise vertically through synchronous rotation during the final pressing stage, causing the lower die to move upwards. A die sleeve is embedded in a stepped groove in the middle of the base and positioned by the stepped groove. A lower die is nested with the base and the die sleeve and moves relative to them. A support column is threadedly fixed to a threaded hole on the upper surface of the base, and its other end is fixed to an upper platform by bolts. Multiple stepped grooves are formed in the middle of the upper platform. The stepped groove includes at least a first step and a second step. The first step is used to assemble the outer shell limiter, and the second step is used to assemble the intermediate layer limiter. Both the outer shell limiter and the intermediate layer limiter are sleeve-shaped structures, and both have pin holes on their rods for detachable connection with the outer shell punch and the intermediate layer punch respectively by fixing pins. A pressure plate is connected to the upper platform by locking bolts and presses the outer shell limiter and the intermediate layer limiter into the stepped groove of the upper platform. An inner core punch is detachably inserted into the inner cavity of the intermediate layer blank in the mold sleeve. An upper die is detachably set above the blank in the mold sleeve. A presser has its rod passing through the central through hole of the upper platform for contacting any one of the outer shell punch, the intermediate layer punch, the inner core punch, and the upper die to transmit pressing force. This invention constructs a detachable and coaxially nested foundation for the limiter and punch by cooperating with the multi-level stepped grooves and fixing pins on the upper platform. This allows the preceding punch to be retained in place as the cavity boundary of the subsequent level after pressing, so that continuous graded pressing can be achieved without demolding or replacing the entire set of molds.

[0005] Optionally, the universal level bubble has an accuracy of 0.02 mm / m, and the adjusting bolt has an adjustment accuracy of 0.01 mm / revolution. These two components work together to achieve real-time monitoring and fine-tuning of the base's levelness. This high-precision level monitoring and fine-tuning mechanism ensures that the base remains level throughout the pressing process, preventing uneven powder filling and skewed compact density caused by equipment tilt. This lays the foundation for uniformity in subsequent equivalent bidirectional pressing.

[0006] Optionally, the intermediate layer limiter is sleeved inside the outer shell limiter, and the intermediate layer punch is sleeved inside the outer shell punch. The first and second steps of the upper platform are concentrically arranged, and the outer shell punch and the intermediate layer punch are respectively fixed to the corresponding outer shell limiter and intermediate layer limiter by fixing pins to form a multi-level coaxial nested structure. This invention, through a multi-level coaxial nested structure, ensures strict alignment of the punches at each level of the outer shell, intermediate layer, and inner core during the pressing process, effectively eliminating the cumulative positioning error caused by multiple clamping operations, and ensuring the coaxiality and interface bonding quality between the gradient structure layers.

[0007] The present invention also provides a method for pressing a cemented carbide gradient structure, which is applied to the cemented carbide gradient structure pressing device described in the above scheme. The same set of cemented carbide gradient structure pressing device is used to achieve graded sequential pressing by changing the combination of limiters and punches. The method includes: adjusting the base to a horizontal state by adjusting bolts in conjunction with a universal level. An outer shell limiter and an outer shell punch are installed in the mold cavity formed by the base, mold sleeve and lower mold. The outer shell limiter is fixed to the first step of the upper platform by a pressure plate, and the outer shell punch is suspended and fixed to the outer shell limiter by a fixing pin. After the outer shell powder is evenly filled, the outer shell part is pressed by the presser. After pressing, the outer shell punch is retained in the mold cavity, and its lower end face is flush with the upper end face of the outer shell blank, naturally forming an intermediate layer pressing mold cavity. Without demolding, remove the pressure plate, and leave the outer shell punch inside the mold cavity with its lower end face flush with the upper end face of the outer shell blank. Install the intermediate layer limiter on the second step of the upper platform. The intermediate layer limiter is fitted inside the outer shell limiter and fixed again by the pressure plate. The intermediate layer punch is suspended and fixed to the intermediate layer limiter by a fixing pin and passes through the inner side of the outer shell punch. After uniformly filling the intermediate layer powder, the intermediate layer punch is driven by the presser to press the intermediate layer part. After pressing, the intermediate layer punch is left inside the mold cavity with its lower end face flush with the upper end face of the intermediate layer blank, naturally forming the inner core pressing mold cavity. Without demolding, the inner core powder is evenly filled into the inner core cavity formed by the inner side of the intermediate laminate blank. The inner core is then inserted into the inner core cavity along the axial direction, and the inner core part is pressed by the inner core punch driven by the presser. No demolding is required. Remove the limiters and punches of each layer, and adjust the adjusting bolts to raise the base by a distance L. The distance L is determined based on the target product height, the relative density of the pressed blank after grading, the target relative density of sintering, the compensation coefficient, and the friction correction function. Install the upper mold and drive the upper mold through the presser to press the formed multi-layered blank as a whole. This causes the lower mold to move upward relative to the upper mold, forming a constraint reaction force from the bottom up. This force, combined with the pressing force from above, constitutes an equivalent asynchronous bidirectional pressing. After demolding, a cemented carbide gradient structure compact is obtained.

[0008] The above solution achieves continuous forming without mold replacement through the in-situ retention mechanism of the punch, avoiding interlayer misalignment. More importantly, in the final pressing stage, the lower mold generates an upward reverse pressing force by driving the base to rise a preset distance L, which, together with the downward pressure of the upper mold, forms an equivalent asynchronous bidirectional pressing, effectively compensating for the insufficient bottom density caused by unidirectional pressing and significantly improving the uniformity of the axial density of the pressed blank.

[0009] Optionally, in the equivalent asynchronous bidirectional pressing, the distance L that the base rises is determined based on the following formula: ; In the formula: L is the distance the base rises. Here, H is the compensation coefficient, and H is the target product height. This is a friction correction function, with values ​​ranging from 0.8 to 1.2, and is related to the friction coefficient. And related to the height-to-diameter ratio H / D of the pressed billet, To achieve the target relative density during sintering, The relative density of the compact after graded pressing is given. This invention establishes a quantitative correlation model between the base lifting distance and the product geometry, material compression characteristics, and friction state. This transforms the previously experience-based process parameters into calculable physical control quantities, ensuring the accuracy of the equivalent bidirectional pressing compensation and avoiding density fluctuations caused by over- or under-pressing.

[0010] Optionally, in the WC-Co cemented carbide system, when the friction coefficient μ satisfies 0.15≤μ≤0.25 and the billet height-to-diameter ratio H / D satisfies 0.5≤H / D≤2.0, the ratio L / H of the base lifting distance L to the target product height H is in the range of 0.02~0.08. The above scheme provides a simplified engineering application range for typical WC-Co cemented carbide systems, reducing the complexity of process calculations while ensuring the pressing effect, and improving the practicality of this method in industrial production.

[0011] Optionally, the pressing stroke and height of the outer shell punch, the intermediate layer punch, and the inner core punch are designed through collaborative calculation to ensure that when the staged pressing is completed, the blank height of the outer shell portion, the intermediate layer portion, and the inner core portion is consistent with the target blank height calculated based on the following relationship, and the relative density of each blank layer is the same. The target blank height for each punch layer is calculated based on the following formula: For the i-th layer, the powder loading height With the target compact height satisfy: ; Where i = 1, 2, 3 correspond to the outer shell portion, the intermediate layer portion, and the inner core portion, respectively. To determine the relative density of loosely packed materials, the target compact height for each layer is... Equals the corresponding layer height of the target product multiplied by the target relative density of sintering. Relative density of the compact after staged pressing The ratio of the punch heights of each layer can be calculated to ensure that each layer of compacted blank has the same relative density after staged pressing. This allows for isotropic shrinkage during sintering, avoiding interfacial stress concentration, warping, or cracking caused by density differences between layers, and ensuring the integrity and dimensional accuracy of the gradient structure.

[0012] Optionally, the staged pressing pressure in the pressing shell, the pressing intermediate layer, and the pressing inner core is 100~200MPa, and the holding time is 5~15s; the final pressure in the equivalent asynchronous bidirectional pressing is 250~400MPa, and the holding time is 15~30s; the equivalent asynchronous bidirectional pressing improves the density uniformity index of the pressed blank along the height direction. Improved to above 0.95, of which and These are the actual densities of the lower and upper ends of the compact, respectively. By optimizing the pressure and holding time parameters of the staged pressing and final pressing, the axial density uniformity index of the compact reached above 0.95 while ensuring the interlayer bonding strength, thus verifying the effectiveness of the equivalent bidirectional pressing mechanism.

[0013] Optionally, the method further includes: after demolding, degreasing and sintering the obtained compact at a temperature of 1350~1450℃ for 30~90 min to obtain a cemented carbide gradient structure product with a relative density of 85%~95%. The above scheme completes the entire process chain from pressing to sintering, ensuring the stability of the gradient structure during densification through a matched sintering regime, ultimately obtaining high-performance cemented carbide products.

[0014] Optionally, the powders for the pressed outer shell, the pressed intermediate layer, and the pressed inner core are all WC-Co based cemented carbide powders, wherein: the powder for the pressed outer shell is WC-6wt%Co powder with a particle size of 1~3μm; the powder for the pressed intermediate layer is WC-10wt%Co powder with a particle size of 2~4μm; and the powder for the pressed inner core is WC-15wt%Co powder with a particle size of 4~6μm. The above scheme clarifies the typical material system and composition gradient design of each layer suitable for this method, providing a concrete material basis for preparing cemented carbide tools with wear-resistant surfaces and strong cores.

[0015] Furthermore, the present invention also provides a cemented carbide gradient structure compact, which is prepared by the method described above. The compact has a three-layer gradient structure, with each layer having a relative density of 60% to 80%, and the maximum density difference along the pressing direction within any layer is [not specified]. This compact has the characteristics of consistent interlayer density and minimal intralayer axial density difference, making it a key intermediate for subsequent sintering to obtain high-quality gradient cemented carbide products.

[0016] Compared with existing technologies, this invention achieves the following significant technical effects through the combination of a nested in-situ retention graded pressing mechanism and an equivalent asynchronous bidirectional pressing mechanism based on quantitative control of base displacement: First, by using coaxial nesting and in-situ retention of multi-stage punches, continuous graded pressing without demolding or mold replacement is achieved within the same mold set. This helps eliminate inter-layer positioning errors caused by frequent mold changes or punch insertion / removal in traditional processes, keeping the coaxiality of the gradient structure layers within 0.05mm. Second, by adjusting the bolts to drive the base to rise a preset distance L, equivalent asynchronous bidirectional pressing is achieved on a single-action press. The reverse constraint reaction force at the bottom effectively compensates for the axial density attenuation caused by unidirectional pressing, increasing the density uniformity index η of the pressed blank along the height direction to over 0.95, and ensuring that the density difference Δρ within any layer is ≤0.05g / cm³. 3 Third, this invention establishes a quantitative correlation model between the base lifting distance L and the product height, the density difference between the green body and the sintered body, and the friction characteristics. This transforms the process parameters from empirical trial and error to scientific calculation. Combined with the coordinated design of the height of each punch, it helps to ensure that the relative density of each layer of pressed blank is consistent, achieves isotropic shrinkage during sintering, and significantly reduces the risk of product deformation and cracking.

[0017] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0018] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Figure 1 This is a schematic diagram of the shell pressing state structure according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the intermediate layer pressing state structure according to an embodiment of the present invention; Figure 3 This is a schematic diagram of the core pressing state structure according to an embodiment of the present invention; Figure 4 This is a schematic diagram of the overall final pressure state structure according to an embodiment of the present invention; Figure 5 This is a longitudinal sectional view of the pressing device according to an embodiment of the present invention.

[0019] Among them, 1-base; 2-adjusting bolt; 3-universal horizontal bubble; 4-lower mold; 5-mold sleeve; 6-support column; 7-upper platform; 8-locking bolt; 9-pressure plate; 10-outer shell limiter; 11-fixing pin; 12-outer shell punch; 13-intermediate layer limiter; 14-intermediate layer punch; 15-inner core punch; 16-upper mold; 17-presser. Detailed Implementation

[0020] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments, so that those skilled in the art can implement it based on the description. The following description, in conjunction with the accompanying drawings... Figure 1 - Appendix Figure 5 The present invention will be described in further detail below.

[0021] Example 1:

[0022] like Figure 1 and Figure 5As shown, this embodiment provides a cemented carbide gradient structure pressing device, which forms the hardware foundation for realizing continuous pressing of multi-layer gradient structures without mold changes and equivalent bidirectional pressing. The cemented carbide gradient structure pressing device includes a base 1, on the upper surface of which is provided a universal level bubble 3 and adjusting bolts 2 for fine-tuning the level. Four adjusting bolts 2 are distributed at the four corners of the base 1 and threadedly engaged with the base 1 to achieve real-time adjustment of the levelness of the base 1 during the pressing process. The adjusting bolts 2 are also configured to drive the base 1 to rise vertically through synchronous rotation during the final pressing stage, so that the lower mold 4 generates an upward displacement. In this invention, the base 1 serves as the bearing reference for the entire device. The adjusting bolts 2 distributed at its four corners not only provide support but also convert rotational motion into linear lifting motion through precision threaded pairs. This dual-function configuration allows the same set of adjusting bolts 2 to both eliminate installation errors and ensure the horizontal reference of powder filling during the pressing preparation stage, and to act as an active driving element during the final pressing stage, precisely controlling the rise of the base 1. Thus, without relying on a complex double-action press, it provides the necessary bottom reverse displacement source for the equivalent asynchronous bidirectional pressing described in subsequent embodiments. The mold sleeve 5 is embedded in the stepped groove in the middle of the base 1 and positioned by the stepped groove; the lower mold 4 is nested with the base 1 and the mold sleeve 5 and moves relative to each other. The stepped groove in the center of the base 1 provides radial limit and axial support for the mold sleeve 5, ensuring the coaxiality of the mold cavity assembly and the base 1. The lower mold 4 slides in the inner hole of the mold sleeve 5. When the adjusting bolt 2 rotates and rises synchronously, the base 1 and the lower mold 4 move upward synchronously. The base 1 is driven to rise by the adjusting bolt 2 through the threaded pair, and the lower mold 4 subsequently generates a controlled axial displacement within the mold sleeve 5. This linkage is the mechanical prerequisite for realizing dynamic mold cavity depth adjustment and final pressure reverse force application. The support column 6 is threaded to the threaded hole on the upper surface of the base 1, and the other end is fixed to the upper platform 7 by bolts. In this embodiment, the support column 6 is preferably four high-strength alloy steel columns, evenly distributed on the outer periphery of the base 1, to construct a rigid frame structure. The upper platform 7 has a multi-level stepped groove in its middle section. This stepped groove includes at least a first step and a second step. The first step is used to assemble the outer shell limiter 10, and the second step is used to assemble the intermediate layer limiter 13. Specifically, the multi-level stepped groove of the upper platform 7 is the core positioning interface for the present invention to achieve graded pressing without mold changing. The first step and the second step are arranged in concentric circles and have high machining accuracy. The structured hierarchical design allows limiters of different specifications to be quickly switched and positioned based on the same physical reference, fundamentally eliminating the cumulative alignment error introduced by changing the entire set of molds or repeatedly disassembling and assembling the press head in traditional processes, and providing rigid guarantee for the interlayer coaxiality of the multi-layer gradient structure. Both the outer shell limiter 10 and the intermediate layer limiter 13 are sleeve-shaped structures, and both have pin holes on their rods for detachable connection with the outer shell punch 12 and the intermediate layer punch 14 respectively by fixing pins 11.The sleeve-like structure allows the outer shell limiter 10 and the intermediate layer limiter 13 to be installed independently or nested together when needed. A fixing pin 11 passes through a pin hole to suspend and fix the punch to the corresponding limiter; this pin connection method combines accurate positioning with convenient assembly and disassembly. When switching pressing levels, simply pull out the fixing pin 11 to separate the punch and limiter, or quickly replace the limiter and punch as a single module, greatly simplifying the operation process and shortening auxiliary time. The pressure plate 9 is connected to the upper platform 7 by locking bolts 8, and presses the outer shell limiter 10 and the intermediate layer limiter 13 into the stepped groove of the upper platform 7. The locking bolts 8 are M6 bolts, and the pressure plate 9 acts as an axial locking element. The preload applied by the locking bolts 8 tightly presses the flange face of the limiter against the stepped surface of the stepped groove, limiting the axial movement of the limiter under the pressing reaction force and ensuring the dimensional accuracy of the mold cavity depth. The inner core punch 15 is detachably inserted into the inner cavity of the intermediate laminated blank within the mold sleeve 5; the upper die 16 is detachably positioned above the pressed blank within the mold sleeve 5. The inner core punch 15 is used for forming the innermost layer of powder, and its outer diameter is adapted to the inner hole of the intermediate laminated blank; the upper die 16 is used for overall densification in the final pressing stage. Both adopt a modular design and can be flexibly replaced according to product specifications, further enhancing the versatility of the device. The rod of the presser 17 passes through the central through hole of the upper platform 7 and is used to contact any of the outer shell punch 12, the intermediate layer punch 14, the inner core punch 15, and the upper die 16 to transmit pressing force. Specifically, the presser 17 serves as the power transmission interface for an external hydraulic press or mechanical press, and its rod passes through the center of the upper platform 7, enabling it to sequentially align and drive different punches or upper dies 16 located on the same axis. This single-point power input, combined with the design of the multi-station mold assembly, allows a single-action press to complete complex multi-stage sequential pressing and final pressing processes, significantly reducing equipment investment costs. This embodiment constructs a pressing device integrating high-precision positioning, rapid module switching, and bidirectional pressing functions. The cooperation between the multi-level stepped grooves of the upper platform 7 and the fixing pins 11 establishes the physical basis for in-situ retention and nested assembly, making it possible to continuously complete the graded pressing of multi-layer gradient structures without demolding or mold changing; while the dual-function configuration of the adjusting bolts 2 transforms the traditional static base 1 into a dynamic pressing execution unit, laying a solid hardware foundation for subsequent equivalent bidirectional pressing through displacement compensation of the base 1.

[0023] Example 2:

[0024] Based on the cemented carbide gradient structure pressing device described in Example 1, this embodiment further specifies the precision of the horizontal fine-tuning mechanism. In this invention, the precision of the universal level bubble 3 is 0.02 mm / m (i.e., 0.02 millimeters per meter), and the adjustment precision of the adjusting bolt 2 is 0.01 mm / revolution. The two work together to achieve real-time monitoring and fine-tuning of the levelness of the base 1. This combination of precision parameters is not arbitrarily selected, but determined based on the stringent requirements of the cemented carbide powder pressing process for the flatness of the reference surface. As a visual feedback element, the 0.02 mm / m precision of the universal level bubble 3 means that it can keenly perceive a height difference of only 0.02 millimeters over a 1-meter span. This provides the operator with a high-resolution indication of the level status, ensuring that the vertical deviation of the upper surface of the base 1 relative to the gravity plumb line is controlled within a very small range. Correspondingly, the adjusting bolt 2 adopts a precision threaded pair design, and its 0.01 mm / revolution adjustment precision ensures that the axial displacement generated by each rotation operation is only on the order of 10 micrometers. This precise execution resolution allows operators to quantitatively compensate for minute bubble offsets in the universal horizontal bubble 3, avoiding repeated over- or under-adjustment caused by excessively large adjustment steps. From a microscopic perspective, this precision combination plays a decisive supporting role in subsequent process steps. First, in the powder filling stage before staged pressing, the high levelness of the base 1 directly determines the flatness of the bottom of the mold cavity. For hard alloy mixed powders with poor flowability, even a slight tilt of the bottom surface can lead to uneven thickness of the loose powder layer, resulting in differences in compression ratios in different parts after pre-pressing, forming an initial density gradient. Through the aforementioned high-precision fine-tuning mechanism, the horizontal error of the base 1 can be stably controlled within 0.02 mm / m, eliminating systematic density deviations introduced by equipment posture issues at the source. Second, in the equivalent asynchronous bidirectional pressing process of the final pressing stage, the base 1 is no longer just a static support component, but transforms into an active force-applying unit that moves upward. At this time, the levelness of the upper surface of the base 1 becomes the reference surface for the upward lifting of the lower mold 4. If the reference surface is tilted beyond the aforementioned accuracy range, the lower die 4 will apply a non-uniform constraint reaction force to the bottom of the compact during its ascent, resulting in additional shear stress inside the compact. This will not only damage the interface bonding quality of the formed gradient structure but may also cause warping deformation of the compact after demolding. Therefore, the universal horizontal bubble 3 and the adjusting bolt 2 essentially provide a dynamically controllable and precise mechanical boundary condition for equivalent bidirectional pressing, ensuring the uniform transmission of the reverse pressing force along the axial direction. This is an indispensable hardware guarantee for achieving the overall density uniformity index η≥0.95 of the compact.

[0025] It should be understood that although this embodiment provides specific preferred values ​​of 0.02 mm / m and 0.01 mm / revolution, in actual engineering applications, this precision configuration can be adaptively adjusted according to product size specifications and density tolerance requirements. For example, for large-size blanks or non-critical components with relatively low requirements for density uniformity, the precision can be appropriately relaxed to 0.05 mm / m and 0.02 mm / revolution; while for extreme applications such as micro-precision cutting tools, the precision can be further increased to 0.01 mm / m and 0.005 mm / revolution. However, for the typical WC-Co graded cemented carbide forming problem solved by this invention, the above combination of 0.02 mm / m and 0.01 mm / revolution has been experimentally verified to be the process window that achieves the best balance between cost, operating efficiency, and product quality.

[0026] Example 3:

[0027] Based on the cemented carbide gradient structure pressing device described in Example 1, this embodiment further specifies the multi-level coaxial nested assembly structure. The intermediate layer limiter 13 is sleeved inside the outer shell limiter 10, and the intermediate layer punch 14 is sleeved inside the outer shell punch 12. The first and second steps of the upper platform 7 are concentrically arranged. The outer shell punch 12 and the intermediate layer punch 14 are respectively fixed to the corresponding outer shell limiter 10 and intermediate layer limiter 13 via fixing pins 11, forming a multi-level coaxial nested structure. This structural design is the physical foundation for achieving high-precision forming of multi-layer gradient structures. Figure 1 , Figure 2 and Figure 5As shown, the upper platform 7 serves as the installation reference for the entire mold cavity assembly, and its first and second steps are manufactured with strict coaxiality tolerances. When the outer shell limiter 10 is installed on the first step and the intermediate layer limiter 13 is installed on the second step, their geometric center lines theoretically coincide completely. Based on this, the fit between the intermediate layer limiter 13 and the inner side of the outer shell limiter 10 is not a simple spatial overlap, but a precision guide and support based on a common axis. Similarly, the intermediate layer punch 14 is fitted inside the outer shell punch 12, so that the outer shell punch 12 not only undertakes its own forming function, but also acts as the internal guide mandrel of the intermediate layer punch 14. This core-fixed, nested assembly logic fundamentally ensures the spatial uniformity of each level of forming components. The fixing pin 11 passes laterally through the pin hole of the limiter rod and the corresponding mating hole of the punch, suspending and fixing the punch on the limiter. After the entire nested assembly is assembled, the working end faces of each layer of punches naturally maintain extremely high coaxiality and parallelism. This multi-level coaxial nested assembly structure effectively eliminates the cumulative errors caused by multiple clamping operations. In traditional gradient pressing processes, after each layer is pressed, it is often necessary to disassemble the current mold and replace it with the next layer mold, or pull out the inner layer press head and insert the outer layer press head. Each disassembly and assembly operation introduces new positioning deviations, which accumulate linearly with the number of layers, eventually leading to misalignment between gradient structure layers, uneven wall thickness, and even interface cracking. In this invention, the outer shell punch 12 is retained in place after the outer shell pressing is completed, directly serving as the inner mold boundary for intermediate layer pressing; the intermediate layer limiter 13 and the intermediate layer punch 14 can be directly fitted and installed. The entire process requires no movement or recalibration, and the positioning of all subsequent layers is based on the already pressed inner layer components as self-alignment references. This positioning method based on structural self-consistency controls the interlayer coaxiality error within a very small range allowed by machining accuracy, which is significantly better than the traditional process that relies on repeated manual alignment, providing a reliable structural guarantee for the preparation of high-quality, clearly interfaced gradient cemented carbide blanks.

[0028] Example 4:

[0029] like Figures 1 to 4 As shown, this embodiment provides a method for pressing a cemented carbide gradient structure. This method uses a cemented carbide gradient structure pressing device as described in any one of Embodiments 1 to 3, achieving graded sequential pressing by changing the combination of the limiter and the punch. The core of this method lies in utilizing the same set of mold devices to complete the step-by-step forming of multi-layer structures through the in-situ retention and nested assembly of the punch without demolding. In the final pressing stage, equivalent bidirectional pressing is achieved through the controlled displacement of the base 1, thereby solving the problems of large mold-changing positioning errors and uneven density in unidirectional pressing in traditional processes. This pressing method includes the following steps: In step S100, the base 1 is adjusted to a horizontal position using adjusting bolts 2 and universal leveling bubble 3. Before loading powder, the operator needs to observe the position of the bubble in the universal leveling bubble 3 and fine-tune the adjusting bolts 2 distributed at the four corners of the base 1 until the upper surface of the base 1 reaches the preset levelness requirement. This pre-treatment action ensures the absolute flatness of the bottom of the subsequent mold cavity, avoids uneven powder loading thickness caused by equipment tilting, eliminates the potential for initial density gradient in the pressed blank from the source, and lays the foundation for the dimensional accuracy of subsequent pressing layers.

[0030] In step S200, a housing limiter 10 and a housing punch 12 are installed in the mold cavity formed by the base 1, mold sleeve 5, and lower mold 4. The housing limiter 10 is fixed to the first step of the upper platform 7 by a pressure plate 9, and the housing punch 12 is suspended and fixed to the housing limiter 10 by a fixing pin 11. After uniformly filling the housing powder, the housing punch 12 is driven by the presser 17 to press the housing part. After pressing, the housing punch 12 is retained in the mold cavity, and its lower end face is flush with the upper end face of the housing blank, naturally forming an intermediate layer pressing mold cavity. Figure 1 As shown, at this stage, after the outer shell punch 12 has completed the compaction of the outer shell powder, it is not pulled out or retracted as in traditional processes, but remains stationary at the pressing endpoint. At this time, the lower end face of the outer shell punch 12 not only marks the forming height of the outer shell layer, but also directly serves as the rigid bottom mold of the next level (intermediate layer). This state transition mechanism of retaining the punch in situ ensures that the formation of the intermediate layer mold cavity depends entirely on the compacted upper surface of the outer shell blank, which guarantees a tight fit between the layers and avoids the cumulative height error introduced by repositioning the bottom mold.

[0031] Step S300: Without demolding, remove the pressure plate 9. The outer shell punch 12 remains in the mold cavity, with its lower end face flush with the upper end face of the outer shell blank. Install the intermediate layer limiter 13 on the second step of the upper platform 7. The intermediate layer limiter 13 is sleeved inside the outer shell limiter 10 and fixed by the pressure plate 9. The intermediate layer punch 14 is suspended and fixed to the intermediate layer limiter 13 by the fixing pin 11 and passes through the inner side of the outer shell punch 12. After uniformly filling the intermediate layer powder, the intermediate layer punch 14 is driven by the presser 17 to press the intermediate layer portion. After pressing, the intermediate layer punch 14 remains in the mold cavity, with its lower end face flush with the upper end face of the intermediate layer blank, naturally forming the inner core pressing mold cavity. Figure 2As shown, this step embodies the essence of the nested in-situ retention of this invention. Throughout the entire operation, the formed outer shell blank remains under the protection and constraint of the mold sleeve 5, without any relative displacement. The intermediate layer limiter 13 and the intermediate layer punch 14 are positioned using the second step of the upper platform 7 and are directly fitted inside the already positioned outer shell assembly. This assembly method utilizes the multi-level coaxial nesting structure described in Embodiment 3, ensuring that the centering reference of the intermediate layer pressing completely coincides with the outer shell layer. Similarly, after the intermediate layer pressing is completed, the intermediate layer punch 14 is also retained in its original position, with its lower end face flush with the upper surface of the intermediate layer blank, naturally constructing again an annular or cylindrical space for accommodating the inner core powder, completely eliminating the intermediate demolding or mold changing process, and greatly improving the interlayer coaxiality and production efficiency.

[0032] In step S400, without demolding, after uniformly filling the inner core mold cavity formed by the inner side of the intermediate laminate blank with inner core powder, the inner core punch 15 is inserted axially into the inner core mold cavity, and the inner core part is pressed by the presser 17 driving the inner core punch 15. Figure 3 As shown, this is the final stage of graded pressing. Since the previous steps have precisely constructed the sidewalls (i.e., the inner surface of the intermediate laminate) and bottom (i.e., the lower end face of the intermediate layer punch 14 or the lower end face of the outer shell punch 12, depending on the specific structural design), the inner core punch 15 only needs to be inserted axially to begin operation. At this point, the three-layer gradient structure powder has completed step-by-step pre-pressing within the same mold cavity. The relative positions of each layer are maintained by mechanical interlocking and interfacial friction, and each layer punch is in a pressure-holding or limiting state, together forming a complete composite compact assembly.

[0033] Step S500: Without demolding, remove the limiters and punches from each layer. Adjust the adjusting bolts 2 to raise the base 1 by a distance L. The distance L is determined based on the target product height, the relative density of the pressed blank after grading, the target relative density for sintering, the compensation coefficient, and the friction correction function. Install the upper mold 16. Drive the upper mold 16 through the presser 17 to press the formed multi-layered pressed blank as a whole, causing the lower mold 4 to move upward relative to the upper mold 16, forming an upward constraint reaction force from the bottom. This, combined with the pressing force from above, constitutes an equivalent asynchronous bidirectional pressing. Figure 4As shown, this is another core step that distinguishes this invention from existing technologies. After completing the graded pressing, all internal limiters and punches are first removed, leaving only the mold sleeve 5 and lower die 4 that enclose the multi-layered pressed blank. In terms of the operation sequence, the fixing pin 11 should be pulled out first to separate the punches from the limiters, then each layer of punches and limiters should be removed in sequence, and finally the adjusting bolt 2 should be adjusted to raise the base 1. This sequence can prevent the punches from disturbing the formed pressed blank as the base 1 rises. Each punch and its corresponding pressed blank are in dry pressure contact, and the surface of the punch is polished. When the punch is slowly pulled out axially upward, the multi-layered pressed blank remains stable under the lateral constraint of the mold sleeve 5 and the bottom support of the lower die 4, and will not be disturbed or damaged due to the removal of the punches. Subsequently, the base 1 and the lower die 4 are precisely driven to rise upward by rotating the adjusting bolt 2 by a preset distance L. The distance L is not arbitrarily set, and its size takes into account the current degree of densification of the pressed blank, the shrinkage rate required for final sintering, and the friction characteristics between the powder and the mold wall. When the upper die 16 presses down for final pressing, since the base 1 has been pre-raised, the lower die 4 applies a continuous and controlled upward support force to the bottom of the compact. It should be noted that the mechanical essence of this equivalent asynchronous bidirectional pressing is that by pre-setting the upward displacement L of the base 1, the initial stress state and neutral surface position of the compact before final pressing are changed, so that the subsequent unidirectional pressing of the upper die 16 is equivalent to asynchronous bidirectional pressing. The surface with the highest density (neutral surface) of the compact shifts from the top in traditional unidirectional pressing to near the middle, thereby significantly improving the density uniformity along the height direction. This synergistic effect of the bottom reaction force and the top active pressure simulates the mechanical effect of a bidirectional press on a single-action press, effectively overcoming the density gradient problem caused by the pressure attenuation along the height direction in unidirectional pressing, and making the overall density of the compact tend to be uniform.

[0034] In step S600, a cemented carbide gradient structure blank is obtained after demolding. After completing the equivalent bidirectional final pressing, the pressure is released, and the blank is disengaged from the mold sleeve 5 by the ejection mechanism or the reverse adjustment base 1.

[0035] Through the above-described process, this invention achieves a seamless transition from graded forming to overall densification within the same apparatus. The in-situ retention and nested assembly of the punches solves the problems of difficult positioning and low efficiency in multi-layer structures; while the equivalent bidirectional pressing based on the controlled displacement of the base 1 significantly improves the density uniformity and quality stability of the gradient cemented carbide billet without increasing the complexity of the equipment.

[0036] Example 5:

[0037] Based on step S500 of the cemented carbide gradient structure pressing method described in Example 4, this example further specifies the method for determining the rising distance L of the base 1. In the equivalent asynchronous bidirectional pressing, the rising distance L of the base 1 is determined based on the following formula: ; In the formula: L is the distance that base 1 rises. Here, H is the compensation coefficient, and H is the target product height. This is a friction correction function, with values ​​ranging from 0.8 to 1.2, and is related to the friction coefficient. And related to the height-to-diameter ratio H / D of the pressed billet, To achieve the target relative density during sintering, The formula represents the relative density of the pressed blank after graded pressing. The above formula is an engineering model used in this invention to guide the physical displacement control of the adjusting bolt 2. In actual operation, the calculation result of this formula is directly converted into the number of rotations of the adjusting bolt 2 or the pulse signal of the servo motor, thereby driving the base 1 to generate a precise axial displacement L. This control strategy, which strongly binds material property parameters, geometric dimension parameters, and mechanical execution actions, is the core technical means to achieve precise equivalent bidirectional pressing. Each parameter in the formula has a clear physical meaning and engineering basis for its value. This term characterizes the theoretical linear shrinkage rate of the pressed compact from the green state to the sintered densified state, forming the benchmark value for the compensation amount of base 1. However, in the actual pressing process, the densification behavior of the powder is not an ideal linear process and is affected by various non-ideal factors such as die friction and elastic aftereffect. Therefore, a compensation coefficient is introduced. The theoretical shrinkage rate mentioned above is corrected. The value typically ranges from 0.15 to 0.30, depending on the compressibility of the powder and lubrication conditions. For example, for WC-Co mixed powders with added forming agents such as paraffin wax, due to their good flowability and low internal friction, A lower value can be used; however, for powders without added lubricant or with a wide particle size distribution, a higher value is required. This value is used to compensate for additional energy loss. More importantly, the friction correction function... In unidirectional or simple bidirectional pressing, due to the friction between the powder particles and the inner wall of the die sleeve 5, the pressing force decreases exponentially along the height direction, resulting in a significant density gradient inside the compact. This frictional effect is related not only to the coefficient of friction between the powder and the die wall. It is directly related to, and also significantly affected by, the geometry of the compact, i.e., the height-to-diameter ratio (H / D). When H / D is large, the cumulative effect of friction is enhanced, and the pressure transmission efficiency is reduced. In this case, a larger bottom reverse displacement is required to compensate for the insufficient density at the bottom. The value should approach the upper limit of 1.2; conversely, when H / D is small or the coefficient of friction is low, the value should be lower. At lower pressure levels (e.g., when using high-efficiency lubricants), pressure transmission is more uniform, and the required compensation is relatively smaller. The value can approach the lower limit of 0.8. By... Set as By incorporating the H / D function, this invention can adaptively adjust the compensation strategy for products of different specifications and materials, avoiding the risks of overvoltage or undervoltage caused by using a fixed ratio compensation. In practical engineering, The specific values ​​can be selected according to the following typical values ​​based on the operating conditions: when , (Low friction, short and stout parts). Take 0.85; when , (Medium operating conditions) Take 1.00; when , (High-friction, slender parts). Take 1.15. For operating conditions falling between the above typical values, linear interpolation can be used to determine... Value. Through the above quantitative control model, this invention transforms the final pressure compensation process, which originally relied on trial and error based on operator experience, into a calculable and predictable scientific control process. In specific implementation scenarios, operators or automated control systems only need to input the target product height H and the preset sintering density. Measured green body density And selected according to working conditions and The optimal rising distance L of the base 1 can be calculated in real time. Then, by synchronously rotating the adjusting bolts 2 distributed at the four corners of the base 1, the base 1 is precisely raised by this distance L. This controlled upward displacement allows the lower die 4 to apply a reverse constraint force to the bottom of the compact during the final pressing stage, matching the main pressure at the top. This effectively counteracts the axial pressure attenuation caused by friction, thus making the density distribution of the compact more uniform along the height direction. Experimental data shows that using this model to control the rising distance L of the base 1 for equivalent bidirectional pressing can improve the density uniformity index of the compact. The stability was improved to over 0.95, which is significantly better than the traditional process level that relies on experience for adjustment. This lays a solid foundation for obtaining gradient cemented carbide products with high dimensional accuracy and no deformation or cracking during subsequent sintering.

[0038] Example 6:

[0039] Based on the empirical correlation described in Example 5, this invention further provides a simplified engineering application scheme for specific material systems and geometric size ranges. Specifically, in WC-Co cemented carbide systems, when the coefficient of friction μ satisfies 0.15≤μ≤0.25 and the aspect ratio H / D of the compact satisfies 0.5≤H / D≤2.0, the ratio L / H of the rising distance L of the base 1 to the height H of the target product is in the range of 0.02~0.08. This scheme is based on the relatively stable tribological properties and compression behavior exhibited by WC-Co cemented carbide powder in industrial production. For WC-Co mixed powder with added conventional forming agents (such as paraffin wax, PEG, etc.), under standard mold lubrication conditions, the coefficient of friction μ between it and the inner wall of the steel mold sleeve 5 usually falls stably in the range of 0.15 to 0.25. At the same time, the aspect ratio H / D of most industrial graded cemented carbide products (such as drill bits, end mills, top hammers, etc.) is also concentrated between 0.5 and 2.0. Within this specific parameter space, the complex friction correction function in Example 5 The product of the density difference term exhibits a high linear correlation, allowing the base 1 rising distance L, which originally required multivariate coupled calculations, to be approximated with high precision as a fixed proportional range to the target product height H. This simplification is not a coarsening of the theoretical model, but rather a safe process window extracted from massive industrial measurement data. It significantly reduces the complexity of on-site process control while ensuring the pressing effect. From an engineering implementation perspective, this ratio L / H within the range of 0.02 to 0.08 has significant technical advantages. First, it transforms abstract mathematical formulas into intuitive proportional relationships that are easy for operators to understand and execute. On the production floor, technicians no longer need to measure the friction coefficient or perform tedious function calculations every time; they can quickly estimate the range of distances that base 1 should rise based on the target product height H. For example, for a typical product with a height of 50mm, the base 1 rising distance L is locked between 1mm and 4mm. The simplified control logic significantly reduces process deviations caused by human calculation errors and improves the stability of the production cycle. Secondly, this range provides standardized boundary conditions for the parameter preset of the automated control system, enabling the equipment to converge to the optimal process point with fewer debugging attempts when switching between products of different specifications, thereby improving the overall uptime of the equipment. When selecting specific values ​​within this range, the engineering principle of using the upper limit for large height-to-diameter ratios and the lower limit for small height-to-diameter ratios should be followed. Specifically, when the height-to-diameter ratio (H / D) of the compact is close to 2.0 (i.e., slender parts), the axial pressure attenuation effect caused by unidirectional pressing is more significant due to the longer powder column, and the problem of insufficient bottom density is relatively prominent. In this case, an upper limit value close to 0.08 should be selected to provide a larger bottom reverse compensation displacement. Conversely, when H / D is close to 0.5 (i.e., short and stout parts), the pressure transmission is more uniform, and the required compensation is smaller. A lower limit value close to 0.02 can be selected to avoid excessive reverse displacement leading to overpressure at the bottom of the compact or interlayer interface shear failure. For example, when preparing a three-layer gradient drill bit blank with a diameter of 20 mm and a height of 50 mm (H / D=2.5, slightly outside the range but the upper limit trend can be referenced), selecting L / H=0.06 (i.e., L=3.0 mm) can obtain the best density uniformity; while when preparing a wear-resistant liner with a diameter of 40 mm and a height of 30 mm (H / D=0.75), selecting L / H=0.03 (i.e., L=0.9 mm) can meet the process requirements.

[0040] Example 7:

[0041] In the context of the graded sequential pressing process described in Example 4, to ensure the dimensional stability and interface integrity of the multi-layer gradient structure during subsequent sintering, this invention further provides a collaborative calculation mechanism for the height of each layer's punch. Specifically, the pressing stroke and height of the outer shell punch 12, the intermediate layer punch 14, and the inner core punch 15 are collaboratively calculated and designed to ensure that, upon completion of graded pressing, the compact heights of the outer shell, intermediate layer, and inner core are consistent with the target compact height calculated based on the following relationship, and the relative density of each compact layer is [missing information]. The target blank height for each punch layer is calculated based on the following formula: For the i-th layer, the powder loading height With the target compact height satisfy: ; Where i = 1, 2, 3 correspond to the outer shell portion, the intermediate layer portion, and the inner core portion, respectively. To determine the relative density of loosely packed materials, the target compact height for each layer is... Equals the corresponding layer height of the target product multiplied by the target relative density of sintering. Relative density of the compact after staged pressing The ratio. This design is not a simple geometric matching, but rather based on the principle of mass conservation in powder densification behavior, aiming to eliminate the risk of sintering deformation caused by interlayer density differences from the molding source. Under the premise of a constant mold cross-sectional area, the volume change of the powder is inversely proportional to its density change. The loose relative density in the formula... The relative density refers to the density of powder in its natural packing state. Its value is affected by powder particle size distribution, particle morphology, and forming agent content, and is usually obtained through actual measurement using a standard loose packing density meter or a Hall flow meter. The relative density of the compact after graded pressing... This is the key control target set by this process, and in this embodiment, it is preferably a fixed value within the range of 60% to 80%. It should be emphasized that although the powder composition (such as Co content) and particle size of different layers may differ, leading to differences in their compression characteristic curves, this invention adjusts the powder loading height of each layer... This ensures that after experiencing their respective hierarchical suppression pressures, all levels can ultimately converge precisely to the same preset value. Value. For example, for core powders with poor flowability and low bulk density, the calculated powder filling height. The filling height will increase accordingly; and for loosely packed powders with higher density, the filling height will increase accordingly. The density is relatively small. This differentiated powder loading strategy based on material properties is the mathematical basis for achieving uniform final density of each layer. This collaborative calculation mechanism directly determines the sintering quality of gradient cemented carbide products. During liquid phase sintering, the linear shrinkage rate of the compact is significantly negatively correlated with the green compact density. If the initial relative density of each compact layer is... Inconsistencies exist; for example, if the outer shell layer has a density of 75% while the inner core layer has a density of only 65%, then at the same sintering temperature, the shrinkage rate of the inner core layer will be significantly greater than that of the outer shell layer. Since the gradient structure is a unified whole, this differential shrinkage will generate enormous shear and tensile stresses at the interlayer interfaces. This can lead to product warping and dimensional deviations, or even interface delamination and cracking, rendering the product unusable. This embodiment uses the above formula to forcefully constrain each laminated preform to achieve uniformity. This ensures that each layer has nearly the same shrinkage driving force during sintering, thereby achieving true isotropic synchronous shrinkage. This not only effectively avoids the problem of interface stress concentration, but also ensures the smoothness and bonding strength of the gradient component transition zone, making the performance gradient distribution of the final product more in line with design expectations.

[0042] Example 8:

[0043] Based on the cemented carbide gradient structure pressing method described in Example 4, this example further defines the specific parameters of the pressing process and the resulting compact quality indicators. Specifically, the staged pressing pressure in the outer shell, the intermediate pressing layer, and the inner core is 100~200MPa, and the holding time is 5~15s; the final pressure in the equivalent asynchronous bidirectional pressing is 250~400MPa, and the holding time is 15~30s. This parameter window is not an arbitrary choice based on experience, but is determined based on the rheological characteristics and densification kinetics of cemented carbide powder in the multi-stage forming process. In the staged pressing, a relatively low pressure (100~200MPa) and a short holding time are used to allow each layer of powder to initially form and obtain sufficient green strength to maintain its shape, while retaining a certain porosity and plastic deformation capacity. This is crucial for the subsequent nested pressing of layers and the mechanical interlocking of the interlayer interfaces. If the staged pressure is too high, the first pressed layers will experience severe work hardening, leading to a decrease in interlayer bonding during subsequent pressing, and even microcracks at the interface. Conversely, if the pressure is too low, the green compact density will be insufficient to support the weight and positioning accuracy of the subsequent nested components. In the final pressing stage, a higher pressure (250~400MPa) and a longer holding time of 15~30s are used to fully activate the plastic flow and rearrangement of powder particles within the equivalent bidirectional stress field constructed by the rising distance L of the base 1 described in Example 5, completely eliminating the density gradient and weak interfacial bonding areas left by the staged pressing. The longer holding time also helps release the elastic strain energy accumulated during pressing, reducing elastic after-effect expansion after demolding, thereby ensuring the dimensional accuracy and internal structural integrity of the compact. More importantly, the above combination of process parameters works synergistically with the equivalent asynchronous bidirectional pressing mechanism, which improves the density uniformity of the compact along the height direction. Improved to above 0.95, of which and These represent the actual densities at the lower and upper ends of the compact, respectively. By optimizing the pressure and holding time parameters of the staged pressing and final pressing, the axial density uniformity index of the compact reached above 0.95 while ensuring the interlayer bonding strength. This verifies the effectiveness of the equivalent bidirectional pressing mechanism, which is significantly superior to the traditional unidirectional pressing process. In this definition, the density uniformity index η is a dimensionless ratio used to quantify the consistency of the axial density distribution of the compact. This typically corresponds to the density of the bottom region, which is far from the punch and most affected by frictional losses in traditional unidirectional pressing. This corresponds to the density of the top region, which is closest to the punch and directly subjected to force. In this invention, due to the introduction of the bottom reverse constraint reaction force generated by the upward distance L of the base 1, the bottom region, which originally had the lowest density in unidirectional pressing, receives effective compaction compensation, thus... Significantly improved and approaching When η≥0.95, it means that the density difference between the upper and lower ends of the compact is controlled within 5%. This high degree of uniformity is a prerequisite for achieving isotropic shrinkage and avoiding product warping or cracking during subsequent sintering.

[0044] To verify the technical effectiveness of this parameter combination, the applicant conducted a comparative experiment. Using the same WC-Co three-layer gradient powder system and the same mold assembly, the comparative example employed a traditional unidirectional pressing process (i.e., the base 1 does not rise during the final pressing stage, only the upper mold 16 presses down), with the stage pressing pressure set at 150 MPa and the final pressing pressure at 300 MPa. The test results showed that the compact prepared in the comparative example had a higher density at its upper end. Approximately 11.8 g / cm³ 3 The lower end density Only 10.2g / cm 3 The calculated density uniformity index η≈0.86, far below the threshold of 0.95. This significant density gradient led to obvious taper deformation in the sintered product, and micropore aggregation was observed at the interlayer interfaces. In contrast, the compact prepared using the parameters and equivalent biaxial pressing method described in this embodiment showed a lower density at its upper end. It is 11.9 g / cm³ 3 lower end density Increased to 11.5g / cm 3 The density uniformity index η reached 0.966. This data strongly demonstrates that simply increasing the final pressure cannot solve the problem of axial density non-uniformity. Only by combining specific pressure-time parameters with the controlled displacement of base 1 can a better synergistic effect be achieved, resulting in unexpectedly high uniformity molding. In practical engineering applications, the above parameters can be finely adjusted according to the specific powder characteristics. For example, for powders with fine particle size, large specific surface area, and high internal friction, the upper limit of the grading pressing pressure range (e.g., 180~200MPa) should be selected to ensure initial densification, and the final pressure holding time should also be appropriately extended (e.g., 25~30s) to fully degas and creep densify. For coarse-particle powders with added high-efficiency lubricants and excellent flowability, the grading pressure can be appropriately reduced (e.g., 100~120MPa), and the final pressure holding time can be shortened to 15~20s to improve production efficiency. Regardless of the adjustment, the final measured density uniformity index η≥0.95 should be used as the criterion for process qualification.

[0045] Example 9:

[0046] After obtaining the cemented carbide gradient structure compact through demolding in step S600 of Example 4, this example further specifies the subsequent post-processing steps to complete the entire technology chain from powder pressing to final product manufacturing. Specifically, the method further includes: after demolding, degreasing and sintering the obtained compact at a sintering temperature of 1350~1450℃ for 30~90min to obtain a cemented carbide gradient structure product with a relative density of 85%~95%. The setting of these post-processing parameters is highly compatible with the nested in-situ retention graded pressing and equivalent asynchronous bidirectional pressing processes used in the aforementioned examples. Specifically, the degreasing process is usually carried out at a low temperature stage (e.g., 300~600℃) before sintering, aiming to slowly and thoroughly remove organic forming agents such as paraffin and PEG added to the compact. Because the gradient compact prepared by this invention has the characteristics of consistent relative density (60%~80%) in each layer and uniform axial density distribution (η≥0.95), the gas discharge channels are unobstructed and the stress distribution is balanced during the degreasing process, effectively avoiding degreasing cracks or local abnormal carbon content caused by density differences, thus laying a good microstructure foundation for subsequent high-temperature sintering. During the sintering stage, the temperature range of 1350~1450℃ is the optimal densification window determined for the liquid-phase sintering characteristics of WC-Co cemented carbide. When the temperature is below 1350℃, the amount of liquid phase generated is insufficient, making it difficult to completely fill the intergranular gaps, resulting in excessively high residual porosity in the product, failing to meet the relative density requirement of over 85%. When the temperature exceeds 1450℃, although the densification rate accelerates, it easily triggers abnormal growth of WC grains and excessive migration and aggregation of the binder phase cobalt. This not only weakens the mechanical properties of the material but may also destroy the carefully designed gradient composition distribution, leading to blurred or even disappeared gradient transition zones. In this embodiment, the preferred sintering temperature can be adjusted according to the specific cobalt content gradient. For example, for a structure with a low cobalt outer shell (e.g., WC-6Co) and a high cobalt inner core (e.g., WC-15Co), a medium temperature range of 1380~1420℃ can be used. This ensures sufficient densification of the high cobalt layer while suppressing grain coarsening of the low cobalt layer. Simultaneously, a holding time of 30~90 min ensures sufficient time for the liquid phase to rearrange and fill the pores through capillary force, and also provides kinetic conditions for the diffusion of gradient elements, resulting in metallurgical bonding at the interlayer interface rather than simple mechanical interlocking. It is particularly noteworthy that the highly uniform axial density of the compact is achieved through quantitative control of the rising distance L of the base 1 in the preceding pressing process, enabling all parts of the compact to shrink linearly at nearly the same rate under this sintering regime. If a traditional unidirectional pressing process is used, the density difference between the upper and lower ends of the compact is often greater than 0.15 g / cm³. 3Differential shrinkage will inevitably occur under the same sintering conditions, resulting in products with bulging, taper, or even cracking. However, the uniform compact obtained by the present invention through the aforementioned process can achieve true isotropic shrinkage under the sintering regime. The resulting cemented carbide gradient structure products not only have a stable relative density of 85%~95% at a high level, but also have a dimensional accuracy of within ±0.05mm. The interlayer bonding strength is significantly improved, which fully meets the stringent requirements of high-end cutting tools and wear-resistant parts.

[0047] Example 10:

[0048] Based on the cemented carbide gradient structure pressing method described in Example 4, this example further specifies the specific composition and particle size of each layer of powder. Specifically, the outer shell powder, the intermediate layer powder, and the inner core powder are all WC-Co based cemented carbide powders, wherein: the outer shell uses WC-6wt%Co powder with a particle size of 1~3μm; the intermediate layer uses WC-10wt%Co powder with a particle size of 2~4μm; and the inner core uses WC-15wt%Co powder with a particle size of 4~6μm. This composition gradient design is determined based on the requirements of cemented carbide tools for a performance gradient from the surface to the core. The outer shell layer uses low-cobalt (6wt%Co) fine-grained (1~3μm) powder, which can achieve high hardness (HV30≥1600) and excellent wear resistance after sintering, making it suitable for cutting edges or working surfaces; the inner core layer uses high-cobalt (15wt%Co) coarser-grained (4~6μm) powder, which has high fracture toughness and bending strength after sintering, providing strong mechanical support for the overall structure; the intermediate layer uses powder with medium cobalt content (10wt%Co) and medium particle size (2~4μm) as a transition zone between the outer shell and the inner core, which mitigates the abrupt change in hardness and toughness and reduces stress concentration at the interface.

[0049] Example 11:

[0050] This embodiment provides a complete parameterized working example. Taking the preparation of a three-layer gradient cemented carbide drill bit blank with a diameter of 20 mm and a height of 50 mm as an example, this embodiment specifically illustrates the process of achieving equivalent bidirectional pressing using the device and method of the present invention.

[0051] 1. Material and mold preparation; Powder material: WC-Co series cemented carbide powder, with a three-layer structure designed as follows: Outer shell layer (wear-resistant layer): WC-6%Co, particle size 1-3μm, theoretical density 15.0g / cm³ 3 Intermediate layer (transition layer): WC-10%Co, particle size 2-4μm, theoretical density 14.5g / cm³ 3 Inner core layer (toughening layer): WC-15%Co, particle size 4-6μm, theoretical density 13.8g / cm³3 After each layer of powder is ball-milled and dried, 2wt% paraffin forming agent is added to prepare the powder to be pressed.

[0052] 1.2 Mold and Equipment Parameters; Mold sleeve 5 inner diameter: 20.2mm (considering sintering shrinkage); graded pressing relative density coefficient: k=0.70 (i.e., 70% of theoretical density); sintering target relative density: =0.92 (i.e., 92% of the theoretical density); Calculation of the rising distance of base 1: Based on ; Let α = 0.25, =k=0.70, L=0.25×50×(0.92-0.70) / 0.92≈3.0mm, that is, L / H=6.0%, which is within the optimization range of 2%~8%.

[0053] 2. Device debugging and leveling: Place base 1 on the hydraulic press workbench and install mold sleeve 5 and lower mold 4. By observing the universal spirit level 3, adjust the adjusting bolts 2 distributed at the four corners of base 1 to ensure that the levelness error of the upper surface of base 1 is ≤0.02mm / m. Install support column 6 and upper platform 7, ensuring that the parallelism between upper platform 7 and base 1 is ≤0.05mm.

[0054] 3. Hierarchical suppression; 3.1. Shell Lamination: Install the shell limiter 10 on the first step of the upper platform 7 and fix it with the pressure plate 9; suspend and fix the shell punch 12 to the shell limiter 10 with the fixing pin 11 and insert it into the mold sleeve 5; calculate the powder loading: the shell layer is designed to be 15mm thick with a relative density of 0.70, and the required powder mass is: m1 = (π × (20mm)) 2 / 4)×15mm×15.0g / cm 3 ×0.70≈49.5g; After uniformly loading the powder, apply pressure of 150MPa through the press 17 and hold for 10s; After pressing, the outer shell punch 12 is retained in the mold cavity, with the lower end face flush with the upper end face of the powder, forming an outer shell laminate blank with a depth of 15mm (relative density≈70%), and the middle layer mold cavity is naturally formed inside. 3.2. Intermediate Layer Pressing: No demolding is required. Remove the pressure plate 9, leaving the outer shell punch 12 inside the mold cavity. Place the intermediate layer limiter 13 inside the outer shell limiter 10, install it on the second step of the upper platform 7, and fix it with the pressure plate 9. Suspend and fix the intermediate layer punch 14 to the intermediate layer limiter 13 using the fixing pin 11, and pass it over the outer shell punch 12. The intermediate layer is designed to be 15mm thick, with a powder filling amount of: m² = (π × (20mm)) 2 -(14mm) 2 ) / 4)×15mm×14.5g / cm3 ×0.70≈27.3g (Note: 14mm is the inner diameter of the outer shell layer); After uniformly filling the powder, apply a pressure of 150MPa and hold for 10s; After pressing, the intermediate layer punch 14 is retained in the mold cavity to form an intermediate layer blank (relative density ≈70%), and the inner core mold cavity is naturally formed inside; 3.3. Core Layer Pressing: No demolding required. The core layer is designed to be 20mm thick. Powder content: m3 = (π × (14mm)) 2 / 4)×20mm×13.8g / cm 3 ×0.70≈29.7g; After uniformly filling with powder, install the inner core punch 15, apply pressure of 150MPa, and hold for 10s; After pressing, the relative density of the inner core laminate is ≈70%, and the total height of the three-layer laminate is about 71.4mm (50mm / 0.70).

[0055] 4. Equivalent bidirectional pressing final pressure, key steps are as follows: Keep the blank in the mold cavity, remove the pressure plate 9, outer shell limiter 10, intermediate layer limiter 13 and each layer punch; adjust the adjusting bolt 2 to raise the base 1 by L=3.0mm (i.e. 6% of the product height); install the upper die 16 so that its lower end face contacts the upper end face of the blank; apply a final pressure of 300MPa through the presser 17 and hold for 20s; at this time, the upper die 16 applies pressure from top to bottom, while the base 1 provides upward support displacement L from the bottom through the lower die 4, forming a asynchronous bidirectional pressing effect. According to the asynchronous bidirectional pressing principle, the slight reverse pressing of the subsequent action die punch (base 1 rises) (3mm / 71.4mm≈4.2% relative displacement) effectively compensates for the insufficient bottom density caused by unidirectional pressing, making the density distribution of the blank along the height direction tend to be uniform.

[0056] Final pressing results: The total height of the compact decreased to approximately 54.3 mm (close to the target height before sintering); the relative density of each layer increased to approximately 78-80%; the density difference between the upper and lower ends of the compact Δρ ≤ 0.04 g / cm³. 3 (Superior to uniaxial compression Δρ≥0.15g / cm) 3 ).

[0057] 5. Demolding and sintering (S6); Release the pressure, adjust base 1 to descend, and push lower die 4 to eject the pressed blank; measure the density of the pressed blank using Archimedes' method (ISO 3369 standard): outer shell layer: 11.85 g / cm³ 3 (Relative density 79.0%); Intermediate layer: 11.31 g / cm³ 3 (Relative density 78.0%); Inner core layer: 10.77 g / cm³ 3(Relative density 78.0%); After degreasing, the compact was sintered in a vacuum sintering furnace at 1380°C for 60 min; The height of the sintered product was 49.8 mm (shrinkage rate of about 8.3%, which is in line with expectations); Density: Outer shell: 13.65 g / cm³ 3 (Relative density 91.0%); Intermediate layer: 13.19 g / cm³ 3 (Relative density 91.0%) Inner core layer: 12.56 g / cm³ 3 (Relative density 91.0%).

[0058] 6. Performance test results;

[0059] Technical Effect Analysis: Through the equivalent bidirectional pressing of the base 1 rising L=3mm (6%H), this embodiment achieves a significant improvement in density uniformity, reducing the density difference between the upper and lower parts of the compact from 0.15g / cm³ under unidirectional pressing. 3 The above decreased to 0.04 g / cm³. 3 The following results approach the ideal bidirectional pressing level; controllable sintering shrinkage is achieved, as the density of each pressed blank is uniform and consistent (around 78%), resulting in isotropic shrinkage after sintering and improved dimensional accuracy; interlayer bonding is strengthened, and the overall densification during final pressing ensures tight bonding at the three-layer interface, increasing shear strength by nearly 30%; furthermore, process efficiency is improved, with staged pressing without mold changes combined with equivalent bidirectional pressing, shortening the single-piece production cycle by nearly half. This embodiment verifies the synergistic effect of L / H=6% (within the 2%~8% optimization range) and k=0.70, achieving high-quality and high-efficiency forming of cemented carbide gradient structures.

[0060] Example 12:

[0061] This embodiment provides a cemented carbide gradient structure compact, which is an intermediate material prepared by the above-described method. The compact has a three-layer gradient structure, with each layer having a relative density of 60% to 80%, and the maximum density difference along the pressing direction within any layer is [not specified]. In this embodiment, the three-layer gradient structure refers to an outer shell layer, an intermediate layer, and an inner core layer that are distributed radially or axially from the outside to the inside (or from the surface to the core). The chemical composition (such as binder phase content, carbide grain size, etc.) of each layer exhibits a step-like or continuous variation. For example, in a typical WC-Co gradient cemented carbide compact, the outer shell layer can use low-cobalt (such as WC-6Co) fine-grained powder to obtain high hardness and wear resistance, the inner core layer uses high-cobalt (such as WC-15Co) coarse-grained powder to ensure strength and toughness, and the intermediate layer serves as a transition zone to mitigate abrupt performance changes.

[0062] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. Other modifications can be easily made by those skilled in the art. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. A cemented carbide gradient structure pressing device, characterized in that, include: The base (1) has a universal level (3) and multiple adjusting bolts (2) for fine-tuning the level on its upper surface; the mold sleeve (5) is embedded in the stepped groove in the middle of the base (1) and is positioned by the stepped groove; the lower mold (4) is nested with the base (1) and the mold sleeve (5) and moves relative to each other; the support column (6) is fixed to the upper surface of the base (1) and the other end is connected to the upper platform (7); the upper platform (7) has a multi-level stepped groove in the middle, the stepped groove includes a first step and a second step, the first step is used to assemble the outer shell limiter (10), and the second step is used to assemble the intermediate layer limiter (13); the outer shell limiter (10) and the intermediate layer limiter (13) are both sleeve-shaped structures, and both of them have pin holes on their rods for passage The fixing pin (11) is detachably fixed to the outer shell punch (12) and the intermediate layer punch (14) respectively; the pressure plate (9) is connected to the upper platform (7) by the locking bolt (8) and presses the outer shell limiter (10) and the intermediate layer limiter (13) into the stepped groove of the upper platform (7); the inner core punch (15) is detachably inserted into the inner cavity of the intermediate layer blank in the mold sleeve (5); the upper mold (16) is detachably set above the blank in the mold sleeve (5); the presser (17) has its rod passing through the through hole in the middle of the upper platform (7) and is used to contact any one of the outer shell punch (12), the intermediate layer punch (14), the inner core punch (15) and the upper mold (16) to transmit pressing force; When using the same set of hard alloy gradient structure pressing device to achieve graded sequential pressing by changing the combination of limiter and punch, after uniformly filling the outer shell powder, the outer shell punch (12) is driven by the presser (17) to press the outer shell part. After pressing, the outer shell punch (12) is retained in the mold cavity, and its lower end face is flush with the upper end face of the outer shell blank, naturally forming the intermediate layer pressing mold cavity; after uniformly filling the intermediate layer powder, the intermediate layer punch (14) is driven by the presser (17) to press the intermediate layer part. After pressing, the intermediate layer punch (14) is retained in the mold cavity, and its lower end face is flush with the upper end face of the intermediate layer blank, naturally forming the inner core pressing mold cavity.

2. The cemented carbide gradient structure pressing device according to claim 1, characterized in that, Four adjusting bolts (2) are distributed at the four corners of the base (1) and threaded with the base (1) to realize the real-time adjustment of the level of the base (1) during the pressing process; the adjusting bolts (2) are also configured to drive the base (1) to rise in the vertical direction by synchronous rotation during the final pressing stage, so that the lower mold (4) will produce an upward displacement; the adjustment accuracy of the adjusting bolts (2) is 0.01mm / revolution, and the accuracy of the universal level bubble (3) is 0.02mm / m. The two work together to realize the real-time monitoring and fine adjustment of the level of the base (1).

3. The cemented carbide gradient structure pressing device according to claim 1, characterized in that, The intermediate layer limiter (13) is sleeved inside the outer shell limiter (10), and the intermediate layer punch (14) is sleeved inside the outer shell punch (12). The first step and the second step of the upper platform (7) are concentrically arranged. The outer shell punch (12) and the intermediate layer punch (14) are respectively fixed to the corresponding outer shell limiter (10) and intermediate layer limiter (13) by fixing pins (11) to form a multi-level coaxial nested structure.

4. A method for pressing a cemented carbide gradient structure, applied to the cemented carbide gradient structure pressing device as described in claim 1, characterized in that, Using the same set of cemented carbide gradient structure pressing devices, staged sequential pressing is achieved by changing the combination of limiters and punches, including: Adjust the base (1) to a horizontal position by adjusting the bolt (2) in conjunction with the universal level (3); Install a shell limiter (10) and a shell punch (12) in the cavity formed by the base (1), the mold sleeve (5) and the lower mold (4). The shell limiter (10) is fixed to the first step of the upper platform (7) by the pressure plate (9). The shell punch (12) is suspended and fixed to the shell limiter (10) by a fixing pin (11). After the shell powder is filled evenly, the shell punch (12) is driven by the presser (17) to press the shell part. After pressing, the shell punch (12) is retained in the cavity, and its lower end face is flush with the upper end face of the shell blank, naturally forming an intermediate layer pressing cavity. Without demolding, remove the pressure plate (9), and leave the outer shell punch (12) in the mold cavity. Its lower end face is flush with the upper end face of the outer shell blank. Install the intermediate layer limiter (13) on the second step of the upper platform (7). The intermediate layer limiter (13) is sleeved inside the outer shell limiter (10) and fixed by the pressure plate (9). The intermediate layer punch (14) is suspended and fixed to the intermediate layer limiter (13) by a fixing pin (11) and sleeved inside the outer shell punch (12). After uniformly filling the intermediate layer powder, the intermediate layer punch (14) is driven by the presser (17) to press the intermediate layer part. After pressing, the intermediate layer punch (14) is left in the mold cavity, and its lower end face is flush with the upper end face of the intermediate layer blank, naturally forming the inner core pressing mold cavity. Without demolding, after uniformly filling the inner core powder into the inner core mold cavity formed by the inner side of the intermediate laminate blank, insert the inner core punch (15) into the inner core mold cavity along the axial direction, and drive the inner core punch (15) to press the inner core part through the presser (17); Without demolding, remove the limiters and punches of each layer, adjust the adjusting bolt (2) to raise the base (1) by a distance L. The distance L is determined based on the target product height, the relative density of the pressed blank after graded pressing, the relative density of the sintering target, the compensation coefficient and the friction correction function. Install the upper mold (16), and drive the upper mold (16) to press the formed multi-layer pressed blank as a whole through the presser (17), so that the lower mold (4) will have an upward displacement relative to the upper mold (16), forming a constraint reaction force from the bottom to the top, which, together with the pressing force from above, constitutes an equivalent asynchronous bidirectional pressing. After demolding, a cemented carbide gradient structure compact is obtained.

5. The method according to claim 4, characterized in that, In the equivalent asynchronous bidirectional pressing, the distance L from which the base (1) rises is determined based on the following formula: ； In the formula: L is the distance the base (1) rises. Here, H is the compensation coefficient, and H is the target product height. This is a friction correction function, with values ​​ranging from 0.8 to 1.2, and is related to the friction coefficient. And related to the height-to-diameter ratio H / D of the pressed billet, To achieve the target relative density during sintering, The relative density of the compact after graded pressing.

6. The method according to claim 5, characterized in that, In the WC-Co cemented carbide system, when the friction coefficient μ satisfies 0.15≤μ≤0.25 and the height-to-diameter ratio H / D of the pressed blank satisfies 0.5≤H / D≤2.0, the ratio L / H of the rising distance L of the base (1) to the height H of the target product is in the range of 0.02~0.

08.

7. The method according to claim 4, characterized in that, The pressing stroke and height of the outer shell punch (12), the intermediate layer punch (14), and the inner core punch (15) are designed through collaborative calculation to ensure that when the staged pressing is completed, the blank height of the outer shell part, the intermediate layer part, and the inner core part is consistent with the target blank height calculated based on the following relationship, and the relative density of each layer blank is 100%. The target blank height for each punch layer is calculated based on the following formula: For the i-th layer, the powder loading height With the target compact height satisfy: ； Where i = 1, 2, 3 correspond to the outer shell portion, the intermediate layer portion, and the inner core portion, respectively. To determine the relative density of loosely packed materials, the target compact height for each layer is... Equals the corresponding layer height of the target product multiplied by the target relative density of sintering. Relative density of the compact after staged pressing The ratio of .

8. The method according to claim 4, characterized in that, The graded pressing pressure in the pressing shell, the pressing intermediate layer and the pressing inner core is 100~200MPa, and the holding time is 5~15s; the final pressure in the equivalent asynchronous bidirectional pressing is 250~400MPa, and the holding time is 15~30s.

9. The method according to claim 4, characterized in that, The powder used for the pressed outer shell, the powder used for the pressed intermediate layer, and the powder used for the pressed inner core are all WC-Co series cemented carbide powders. Specifically, the powder used for the pressed outer shell is WC-6wt%Co powder with a particle size of 1~3μm; the powder used for the pressed intermediate layer is WC-10wt%Co powder with a particle size of 2~4μm; and the powder used for the pressed inner core is WC-15wt%Co powder with a particle size of 4~6μm.

10. A cemented carbide gradient structure compact, characterized in that, The compact is prepared by the method described in any one of claims 4-9, wherein the compact has a three-layer gradient structure, each layer having a relative density of 60% to 80%, and the maximum density difference along the pressing direction within any layer is [not specified]. .

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