A density adjustment method for powder metallurgy

Abstract

This invention belongs to the field of powder metallurgy technology, specifically a density adjustment method for powder metallurgy. The method includes: pre-treating the alloy powder; creating run-out channels or holes in areas of stress concentration or excessive powder accumulation in the mold; filling the powder using an automatic material feeding system and monitoring the filling amount in real time; performing multi-stage pressure loading; and during the pressing process, when the local pressure inside the cavity exceeds a threshold, excess powder is discharged through the run-out channels or holes to achieve pressure balance. This solution can accurately compensate for the density of various parts of the product, eliminate internal residual stress and avoid microcracks, significantly improve the density uniformity and structural integrity of the product, and effectively reduce mold wear and extend its service life.

Description

Technical Field

[0001] This invention belongs to the field of powder metallurgy technology, specifically a density adjustment method for powder metallurgy. Background Technology

[0002] Powder metallurgy technology, as an important means of manufacturing precision parts, plays an irreplaceable role in the processing of high-performance alloy materials. Especially in the production of special functional materials such as iron-nickel and nickel-silicon, the powder pressing molding process can achieve near-net-shape forming of complex components, significantly improving material utilization and optimizing product performance. With the increasing reliability requirements of modern industry for key components, the control of physical properties in the pressing molding stage has become a key factor in determining the quality of the final product.

[0003] Among these processes, density distribution adjustment in powder compression molding is a core technology for ensuring product structural integrity. This process typically utilizes high-precision molds and large-tonnage presses to apply several tons of mechanical pressure to metal powder within a cavity, causing powder particles to shift, rearrange, and undergo plastic deformation, thereby forming a green body with a specific geometry and initial strength. The pressure transmission efficiency during molding is directly related to powder flowability, which places extremely high demands on the mold's structural design and its tolerance to material volume variations.

[0004] However, traditional powder pressing molds mostly employ a fully enclosed structure, lacking a dynamic release mechanism for powder filling volume and internal pressure during the pressing process. Because they cannot balance excess material within the cavity in real time, excessive compression in localized areas can easily occur, leading to severe stress concentration. For stress-sensitive materials such as iron-nickel and nickel-silicon, this uneven density distribution and overload pressure can easily induce microcracks, causing the finished product to crack and fail during demolding or subsequent processes, severely impacting product yield and overall mechanical properties.

[0005] Therefore, a density adjustment method for powder metallurgy is proposed to address the above problems. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of the prior art by providing a density adjustment method for powder metallurgy, thereby solving the technical problems mentioned in the background art.

[0007] To address the above technical problems, the following technical solution is adopted: A density adjustment method for powder metallurgy, comprising the following specific steps: Step 1, Material Preparation and Pretreatment: Select iron-nickel or nickel-silicon alloy powder as raw material, and dehydrate it in a vacuum drying equipment at a preset temperature to ensure that the powder moisture content is lower than the preset moisture content threshold. Then, use a ball mill to mix the powder and add a predetermined mass fraction of zinc stearate as a lubricant to improve the powder flowability and filling uniformity. Step 2, Mold Structure Design and Fabrication: Design a high-precision mold according to the geometry of the product to be molded. Open multiple material run-out grooves or holes on the inner wall of the mold, the end face of the female mold, or the surface of the mandrel to adjust the density. The material run-out grooves or holes are distributed in the stress concentration area or the area with excessive powder accumulation, and are used to discharge redundant powder during the pressing process to achieve dynamic balance of pressure in the cavity. Step 3, Powder filling and weighing control: The pre-treated alloy powder is filled into the mold cavity using an automatic feeding system. The filling amount is monitored in real time by a high-precision electronic weighing sensor to ensure that the single filling error is controlled within the preset error range. After filling, the powder surface is leveled using a scraping device. Step 4, Multi-stage pressure loading molding: Start the large-tonnage press and apply preset mechanical pressure to the powder in the mold cavity through the upper and lower punches. The pressure loading process is divided into the initial pressure stage, the pressure increase stage and the pressure holding stage. When the total applied pressure reaches the preset total pressure threshold, it causes the metal powder particles to rearrange, plastically deform and cold weld together. Step 5, Dynamic Density Adjustment and Overflow: During the pressure loading process, when the local pressure in the cavity exceeds the preset threshold, the excess powder is discharged outward through the discharge trough or discharge hole. By adjusting the amount of powder flowing out, the density of each part of the product is accurately compensated, internal residual stress is eliminated, and microcracks are avoided. Step 6, Demolding and Post-processing: After pressure holding is completed, control the press to return smoothly, and use the ejection device to push the formed green blank out of the mold. Then, perform density testing and appearance inspection on the green blank to ensure that the product quality meets the preset indicators.

[0008] Preferably, in step one, the nickel content and iron content of the iron-nickel alloy powder are within a predetermined ratio range, the average particle size distribution of the powder is within a preset particle size range, and the particle size distribution curve is normally distributed, wherein the median diameter is a preset median diameter value.

[0009] Preferably, in step one, the silicon content and nickel content of the nickel-silicon alloy powder are within a predetermined ratio range, the powder is prepared by gas atomization, the particle shape is spherical or near-spherical, and the loose density is within a preset density range.

[0010] Preferably, in step two, the material discharge groove is opened on the inner side wall of the mold female mold, and its cross-sectional shape is an isosceles trapezoid with a predetermined width and a predetermined depth. The bottom of the groove forms a predetermined angle with the mold axis to guide the powder to be discharged smoothly.

[0011] Preferably, in step two, the material running holes are opened on the bottom support plate of the mold, the material running holes have a predetermined diameter, the roughness value of the inner wall of the holes is less than or equal to a preset roughness threshold, the number of material running holes is determined according to the projected area of ​​the product, and the material running holes are arranged according to a preset distribution density.

[0012] Preferably, in step two, the surface of the material feeding trough or feeding hole is coated with a diamond-like carbon film of a preset thickness to reduce frictional resistance when powder is discharged, prevent blockage of the material feeding channel, and improve the service life of the mold.

[0013] Preferably, in step three, the automatic feeding system adopts a vibration feeding method with a preset vibration frequency and a preset moving speed of the feeding shoe. Through repeated feeding, the filling density of the powder in the complex cavity is ensured to be uniform.

[0014] Preferably, in step four, the pressure rise rate in the initial pressing stage is a first preset rate, and the pressure stops increasing when it reaches a predetermined proportion of the total pressure and is maintained for a predetermined time to expel residual air between the powders and prevent the formation of pores inside the green body.

[0015] Preferably, in step four, the pressure rise rate during the pressurization stage is a second preset rate until the preset maximum forming pressure is reached. The depth of the punch is monitored in real time by a displacement sensor, and the repeatability positioning accuracy reaches a preset accuracy range.

[0016] Preferably, in step four, the pressure holding stage lasts for a predetermined time. The constant pressure control system ensures that the pressure fluctuation range is less than a preset fluctuation threshold, so that the powder particles can fully form mechanical interlocking and interatomic bonding.

[0017] Preferably, in step five, the overflow resistance is changed by controlling the damping adjustment device at the outlet of the material feeding trough. The damping adjustment device consists of a precision spring and an adjusting bolt, and its opening pressure is set to a predetermined ratio range of the molding pressure.

[0018] Preferably, in step five, the overall density deviation of the green body after removing excess powder is less than a preset deviation threshold, and the density of each part of the product reaches the target density range, effectively solving the problem of loose structure that easily occurs in iron-nickel and nickel-silicon products.

[0019] Preferably, in step six, the demolding pressure is controlled within a predetermined ratio range of the molding pressure. The frictional resistance during the demolding process is monitored by a demolding force sensor. If the demolding force increases abnormally, an alarm is automatically triggered and the operation is stopped to prevent damage to the green blank.

[0020] Preferably, the process further includes sintering the demolded green blank in a hydrogen reducing atmosphere, with the sintering temperature being a preset sintering temperature, the holding time being a predetermined holding time, and the heating rate being controlled within a preset heating rate range.

[0021] Preferably, the method uses an industrial control computer integrated on the press to monitor the entire process. The data sampling frequency is a preset sampling frequency. Through real-time analysis of pressure, displacement, and flow data, the filling amount and pressure parameters for the next cycle are automatically adjusted.

[0022] Preferably, the method is applied to the manufacturing of high-precision electronic components, where the dimensional tolerances of the product are controlled within a preset tolerance range, the surface hardness reaches a preset hardness range, and the tensile strength is greater than or equal to a preset strength threshold.

[0023] Preferably, the material feeding troughs are arranged in a non-uniform distribution pattern, with lower density troughs in the geometric center area of ​​the product and higher density troughs in the edge and corner areas of the product, in order to compensate for the edge effect during the pressing process.

[0024] Preferably, a pressure sensing probe is installed inside the material outlet to measure the dynamic pressure fluctuation of the powder during the outflow process in real time and feed the signal back to the main control system as a reference for adjusting the press stroke.

[0025] Preferably, the density adjustment method for powder metallurgy further includes a step of recycling and reusing the discharged excess powder, removing impurities through a sieving device, re-testing the particle size distribution of the powder, and returning it to the feeding system after it passes the test.

[0026] Preferably, the mold cavity is sprayed with a layer of graphite-based release lubricant of a preset thickness before filling, to ensure that the coefficient of friction between the green blank and the mold wall is lower than the preset coefficient of friction threshold, thereby further reducing the internal stress during the molding process.

[0027] Preferably, the pressure curve is modulated using a sine wave or a stepped waveform, and the pressure is assisted by micro-amplitude high-frequency vibration, with the amplitude and frequency within a preset range, to promote the rearrangement of powder particles.

[0028] Preferably, the green blank is finished before sintering, and the green blank is pressed a second time using a finishing mold, with the pressure being a predetermined proportion of the forming pressure, to further improve the dimensional accuracy and surface finish of the product.

[0029] The beneficial effects of this invention are: By opening material running grooves or holes on the mold, a dynamic release channel is provided for powder flow during high-pressure pressing. In the processing of stress-sensitive materials such as iron-nickel and nickel-silicon, local overload pressure can be released in real time, which significantly reduces the residual stress inside the green blank, eliminates demolding cracks and sintering cracks, and greatly improves the product qualification rate compared with traditional processes. By dynamically adjusting the overflow, the powder filling density in each area of ​​the cavity tends to be consistent, reducing the density difference between different parts of the product. The design of the material runner and the material runner hole can prevent the mold from being subjected to extreme local high pressure at the end of the pressing process, and reduce the elastic deformation of the mold cavity. Compared with a fully enclosed mold, the mold used in this invention has a significantly reduced wear depth after producing the same number of products, and the maintenance cycle is greatly extended.

[0030] Reduced equipment load requirements: Due to its dynamic pressure relief function, the total pressing pressure required to achieve the same product density is significantly reduced, effectively alleviating mechanical fatigue of the press and reducing energy consumption. Attached Figure Description

[0031] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] In the attached diagram: Figure 1 This is a schematic flowchart of a density adjustment method for powder metallurgy according to an embodiment of this application. Detailed Implementation

[0033] The exemplary embodiments of this disclosure are described below with reference to the accompanying drawings, including various details of the embodiments to aid understanding, and should be considered merely exemplary. Therefore, those skilled in the art will recognize that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of this disclosure. Similarly, for clarity and brevity, descriptions of well-known functions and structures are omitted in the following description.

[0034] Example 1 This invention proposes a density adjustment method for powder metallurgy, involving the powder pressing and molding of iron-nickel and nickel-silicon products. Several tons of pressure are applied to the powder in the mold using a mold and a press to form the product. Multiple material run-out grooves or holes are provided in the mold (material run-out grooves or holes allow excess powder to escape under pressure, ensuring product molding quality). This process adjusts the density of the powder metallurgy, thereby improving product quality (iron-nickel and nickel-silicon products processed without this method are prone to cracking and of low quality). This method is applied to a density adjustment system for powder metallurgy.

[0035] Specifically, the density adjustment method for powder metallurgy follows a preset engineering procedure. Through control of the microscopic properties of the powder material, mechanical pressure relief design of the mold structure, and dynamic feedback adjustment of the pressing process, high-precision forming of stress-sensitive materials such as iron-nickel and nickel-silicon is achieved. The method includes the following specific steps: In the density adjustment method for powder metallurgy described above, step one, material preparation and pretreatment, involves selecting iron-nickel or nickel-silicon alloy powder as the raw material and dehydrating it using a vacuum drying device at an environment of 80 to 120 degrees Celsius to ensure that the powder moisture content is below 0.02%. Specifically, the nickel content in the iron-nickel alloy powder is 35% to 50%, the iron content is 50% to 65%, the average particle size of the powder is between 15 and 45 micrometers, and the particle size distribution curve is normally distributed, with a median diameter of 30 micrometers. For nickel-silicon alloy powder, the silicon content is 2% to 4.5% and the nickel content is 95.5% to 98%. The powder is prepared by gas atomization to ensure that the particle shape is spherical or near-spherical and the loose packing density is 3.5 to 4.2 grams per cubic centimeter. During the vacuum drying process, the vacuum level is maintained at -0.09 to -0.1 MPa. The physical adsorbed water and chemically bound water on the surface of the powder particles are removed by a combination of thermal radiation and thermal conduction. Then, the powder is mixed using a ball mill. Zinc stearate with a mass fraction of 0.5% to 1.5% is added as a lubricant to improve the flowability and filling uniformity of the powder. Stainless steel balls are used as the grinding media in the ball milling process. The ball-to-material ratio is set to 3:1 to 5:1, the rotation speed is controlled at 150 to 250 rpm, and the mixing time is 2 to 4 hours.

[0036] Furthermore, in step one, in order to achieve accurate perception of the distribution state of powder materials, an industrial multispectral scanning monitoring mechanism is introduced, which collects data including high-resolution optical images, synthetic aperture radar images, and hyperspectral images. Before the powder enters the fabric system, high-precision sensors acquire image data with a temporal resolution of no less than 15 days (for batch-to-batch comparison) and a spatial resolution of better than 2 meters. Through geometric correction and radiation normalization based on control points, multi-temporal image alignment is achieved, thereby monitoring the agglomeration and oxidation of the powder during storage and turnover. Establish a powder batch registration database, covering intellectual property information such as particle size distribution, component ratio, and bulk density. Entities are linked through unified social credit codes and spatial location codes to ensure that the physical boundaries and geographical coordinates of each batch of powder are accurately matched with a matching error of less than 0.5 meters.

[0037] Specifically, step two, mold structure design and preparation, involves designing a high-precision mold based on the geometry of the product to be molded. Multiple material run-out grooves or holes for adjusting density are opened on the inner wall of the mold, the end face of the female mold, or the surface of the mandrel. These material run-out grooves or holes are distributed in stress concentration areas or areas with excessive powder accumulation, and are used to discharge redundant powder during the pressing process to achieve dynamic balance of pressure within the cavity. The material discharge groove is located on the inner wall of the female mold. Its cross-sectional shape is an isosceles trapezoid with a base width of 1.5 to 3.0 mm and a depth of 0.2 to 0.8 mm. The angle between the bottom of the groove and the mold axis is 15 to 30 degrees to guide the powder to be discharged smoothly. The material run-out holes are located on the bottom support plate of the mold. The diameter of the material run-out holes is 1.0 to 2.5 mm, and the roughness value of the inner wall of the holes is less than or equal to 0.8 micrometers. The number of material run-out holes is determined according to the projected area of ​​the product, with 1 to 3 material run-out holes arranged for every 100 square millimeters.

[0038] In the mold design process of step two, a graph neural network is used to model the stress distribution on the inner wall of the mold. The graph neural network adopts a graph attention mechanism to divide the surface of the mold cavity into 128-dimensional feature nodes. The edge weights are calculated by multiplying the spatial distance decay function with the functional similarity. The decay coefficient is set to 0.8 and the similarity threshold is set to 0.7. Spatial autocorrelation analysis, combined with Moran's index and Gillley's index, is used to identify high-high stress accumulation zones and low-low stress accumulation zones in the mold cavity, serving as the initial connection basis for the material runner or material runner hole. The calculation formula is as follows: ; Where I represents the Moran index, n is the total number of sampling nodes, w{ij} is the spatial weight matrix element between node i and node j, and xi is the predicted pressure value at node i. Based on the calculated Moran index, the arrangement of the material running troughs is optimized. A non-uniform distribution method is adopted, with a lower density of material running troughs in the geometric center area of ​​the product and a higher density of material running troughs in the edge and corner areas of the product to compensate for the edge effect during the pressing process. The surface of the material discharge trough or discharge hole is coated with a diamond-like carbon film with a thickness of 3 to 5 micrometers to reduce frictional resistance when powder is discharged, prevent blockage of the material discharge channel, and improve the service life of the mold.

[0039] Specifically, in step three, powder filling and weighing control: the pre-treated alloy powder is filled into the mold cavity using an automatic feeding system, and the filling amount is monitored in real time by a high-precision electronic weighing sensor to ensure that the single filling error is controlled within ±0.01 grams. After filling, the powder surface is leveled using a scraping device. The automatic feeding system uses a vibration feeding method with a vibration frequency of 50 to 100 Hz and a feeding shoe movement speed of 50 to 150 mm per second. Through multiple reciprocating feeding operations, it ensures that the powder filling density is uniform in the complex cavity. During the filling process, the system sets multiple optimization objectives: ecological safety objective (i.e., stability of the production process and explosion-proof level) is quantified by the ecological carrying capacity index; economic efficiency objective (i.e., material utilization rate and production rhythm) is quantified by the unit resource output ratio; social equity objective (i.e., product consistency and quality distribution) is quantified by the reciprocal of the Gini coefficient. The three elements constitute a three-dimensional optimization target space.

[0040] To obtain the optimal filling scheme under the above complex objectives, an improved multi-objective particle swarm optimization algorithm is adopted, which introduces an elite archiving mechanism and adaptive inertia weight. The algorithm population size is set to 200, the maximum number of iterations is set to 500, and the convergence criterion is that the Pareto front change rate is less than 1% for 50 consecutive generations. Through this algorithm, the vibration parameters and reciprocating path of the fabric shoe are adjusted in real time to ensure that the initial filling density deviation of the powder in the mold cavity is minimized.

[0041] Specifically, step four, multi-stage pressure loading molding, involves starting a large-tonnage press and applying mechanical pressure of 200 to 800 MPa to the powder in the mold cavity through the upper and lower punches, with a total applied pressure of 2 to 10 tons, which causes the metal powder particles to rearrange, plastically deform, and cold weld together. The pressure loading process is divided into the initial pressure stage, the pressure increase stage, and the pressure holding stage. The pressure rise rate during the initial pressing stage is 5 to 10 MPa per second. When the pressure reaches 30% of the total pressure, the pressure rise stops and is maintained for 2 to 5 seconds to expel residual air between the powder particles and prevent the formation of pores inside the green body. The pressure rise rate during the pressurization stage is 20 to 50 MPa per second until the preset maximum forming pressure is reached. The depth of the punch is monitored in real time by a displacement sensor, and the repeatability accuracy reaches ±0.005 mm. The pressure holding phase lasts for 10 to 30 seconds. The constant pressure control system ensures that the pressure fluctuation range is less than 1%, allowing the powder particles to fully form mechanical interlocking and interatomic bonding.

[0042] During the pressing process, the system calculates the resource allocation deviation index (referring to the matching deviation between powder distribution and pressure). This index is calculated by weighting the spatial mismatch rate, target deviation, and execution lag coefficient, with weights of 0.4, 0.4, and 0.2, respectively. The deviation index threshold is set to 0.15. Its mean square error calculation formula is as follows: ; Where MSE is the mean squared error and N is the total number of sampling time steps. The reinforcement learning agent adopts a deep deterministic policy gradient algorithm. The state space contains the current deviation index and historical adjustment records, the action space is the fine-tuning of the press stroke and pressure, and the reward function is the product of the deviation index decrease and the scheme stability. Through closed-loop regulation using reinforcement learning, dynamic correction of the pressing curve is achieved. The pressure curve is modulated using a sine wave or a stepped wave. Pressing is assisted by micro-amplitude high-frequency vibration with an amplitude of 0.01 to 0.05 mm and a frequency of 200 to 500 Hz to promote the rearrangement of powder particles.

[0043] Specifically, step five, dynamic density adjustment and overflow: during the pressure loading process, when the local pressure in the cavity exceeds the preset threshold, the excess powder is discharged outward through the discharge trough or discharge hole. By adjusting the amount of powder flowing out, the density of each part of the product is accurately compensated, internal residual stress is eliminated, and microcracks are avoided. The overflow resistance is changed by controlling the damping adjustment device at the outlet of the material discharge chute. The damping adjustment device consists of a precision spring and an adjusting bolt. Its opening pressure is set to 85% to 95% of the molding pressure. A pressure sensing probe is installed inside the material discharge hole to measure the dynamic pressure fluctuation of the powder in real time during the outflow process and feed the signal back to the main control system as a reference for adjusting the press stroke. The overall density deviation of the green body after the excess powder is discharged is less than 0.05 grams per cubic centimeter. The density of each part of the product reaches 88% to 94% of the theoretical density, which effectively solves the problem of loose structure that is prone to occur in iron-nickel and nickel-silicon products.

[0044] The system-generated monitoring reports can be dynamically generated by quarter, year, and five-year planning cycle. The spatial distribution heat map uses a hierarchical color scheme with seven color levels to show the distribution of density inside the product. The target achievement radar chart includes five dimensions: density, hardness, tensile strength, tolerance range, and surface finish. Risk warning prompts are categorized into three levels: high, medium, and low. An alarm is automatically triggered when the overflow resistance is abnormal or the material flow channel is blocked. Establish a knowledge base for powder metallurgy process optimization, storing no less than 100,000 historical configuration cases, policy and regulatory provisions, and expert rules, and provide prior knowledge support for the initial setting of multi-objective weights through a semantic retrieval engine; By acquiring production instruction boundary data in real time through standard geographic information service interfaces, we can ensure that the resource allocation scheme is consistent with the higher-level plan, and the spatial consistency verification error is less than 1 pixel.

[0045] Specifically, step six, demolding and subsequent processing, involves: after pressure holding is completed, controlling the press to return smoothly, and using the ejection device to push the formed green blank out of the mold. The demolding pressure is controlled at 10% to 15% of the forming pressure. The frictional resistance during the demolding process is monitored by a demolding force sensor. If the demolding force increases abnormally, an alarm is automatically triggered and the operation is stopped to prevent the green blank from being damaged. Density testing and visual inspection are performed on the green blanks to ensure that the product quality meets the preset indicators. The method is applied to the manufacturing of high-precision electronic components, with dimensional tolerances controlled within ±0.02 mm, surface hardness reaching 150 to 220 Vickers hardness, and tensile strength greater than or equal to 450 MPa.

[0046] Before demolding, a layer of graphite-based release lubricant with a thickness of 10 to 20 micrometers is sprayed onto the mold cavity before filling to ensure that the coefficient of friction between the green blank and the mold wall is less than 0.1, further reducing the internal stress during the molding process; After demolding, the green blank needs to be sintered in a hydrogen reducing atmosphere at a temperature of 1100 to 1350 degrees Celsius for 2 to 4 hours. The heating rate is controlled at 5 to 8 degrees Celsius per minute. Before sintering, the green blank is finished by using a finishing mold to press it a second time at a pressure of 50% to 70% of the forming pressure, which further improves the dimensional accuracy and surface finish of the product. It also includes a step of recycling and reusing the discharged excess powder, removing impurities through screening equipment, retesting the particle size distribution of the powder, and returning it to the fabric distribution system after it passes the test.

[0047] The method uses an industrial control computer integrated on the press to monitor the entire process. The data sampling frequency is 1000 Hz. Through real-time analysis of pressure, displacement, and flow data, the filling amount and pressure parameters of the next cycle are automatically adjusted. Through this highly integrated digital control, the ultimate precision of the iron-nickel and nickel-silicon powder metallurgy forming process is achieved.

[0048] Example 2 Based on Example 1, this example provides a density adjustment method for an iron-nickel alloy electromagnetic shield with an ultra-thin wall structure. Since thin-walled parts are prone to uneven powder filling and demolding cracks during the pressing process, this example has made targeted optimizations to the design of the material running groove and the pressure curve.

[0049] Specifically, in step one, material preparation and pretreatment, 42% nickel content Boma alloy powder (a type of iron-nickel alloy) is selected and dehydrated at 100 degrees Celsius using a vacuum drying device. To further enhance the flowability of the powder in the narrow cavity, the amount of zinc stearate added is precisely set to 1.2%. The median diameter of the powder is controlled at 25 micrometers, and the standard deviation of the particle size distribution is controlled within 5 micrometers.

[0050] Specifically, in step two, mold structure design and fabrication: for the thin-walled area with a thickness of only 0.5 mm, the material discharge groove is opened on the inner side wall of the mold female mold, its bottom edge width is reduced to 1.2 mm, its depth is set to 0.3 mm, and the angle between the bottom of the groove and the mold axis is increased to 35 degrees, so as to use the combined force of gravity and pressure to accelerate the discharge of powder. A diamond-like carbon film with a thickness of 4 micrometers was prepared on the surface of the material feeding tank using plasma-enhanced chemical vapor deposition, which made its hardness reach more than 2000 Vickers hardness and reduced the coefficient of friction to 0.05.

[0051] Specifically, in step three, powder filling and weighing control: the automatic feeding system uses high-frequency micro-amplitude vibration, with the vibration frequency set to 120 Hz. The dwell time of the feeding shoe in the thin-walled area is extended by 20%. A high-precision electronic weighing sensor ensures that the single filling amount is 5.50 grams, with the error controlled within ±0.005 grams. The scraping device is used to perform three reciprocating leveling operations to ensure that the height difference of the powder surface is less than 0.01 millimeters.

[0052] Specifically, step four, multi-stage pressure loading molding, involves a stepped waveform pressure loading curve. The initial pressure stage is set at 150 MPa and maintained for 5 seconds. During the pressurization stage, the pressure is increased to 600 MPa at a rate of 15 MPa per second. Throughout this process, the displacement sensor monitors the punch stroke in real time. If the displacement difference between the left and right punches exceeds 0.01 mm, the system automatically triggers the differential compensation mechanism to adjust the support stiffness of the lower punch.

[0053] Specifically, in step five, dynamic density adjustment and overflow: when the pressure reaches 550 MPa, the precision spring of the damping adjustment device is compressed, opening the material runner. The opening pressure is then finely adjusted to 92% of the molding pressure using the adjusting bolt. Approximately 0.15 grams of excess powder is discharged, releasing the local high pressure within the cavity, and the residual stress inside the green body is released outward through the material runner.

[0054] Specifically, in step six, demolding and subsequent processing: the demolding process adopts a constant speed mode, with the ejection speed controlled at 2 mm / s. A demolding force sensor monitors the ejection resistance in real time, and the maximum demolding force is limited to 0.8 tons. After the green billet is ejected, it immediately enters a continuous sintering furnace under hydrogen protection. The sintering temperature is set at 1250 degrees Celsius, and the heating section is divided into three temperature zones for dewaxing, pre-sintering, and high-temperature sintering, respectively. The final iron-nickel alloy shielding cover has a density of 92.5%, no visible cracks on the surface, and a magnetic permeability that is 15% higher than that of traditional processes.

[0055] Example 3 This embodiment provides a density adjustment method for high-hardness wear-resistant nickel-silicon alloy parts. Due to their high hardness and brittleness, nickel-silicon alloys require extremely high uniformity of pressure during the molding process.

[0056] Specifically, in step one, material preparation and pretreatment, nickel-silicon alloy powder with a silicon content of 3.5% is selected and prepared by gas atomization. The loose packing density of the powder is 3.8 grams per cubic centimeter. During the mixing process, in addition to adding 1.0% zinc stearate, 0.2% micron-sized graphite powder is added as a solid lubricant to reduce the internal friction between particles.

[0057] Specifically, in step two, mold structure design and preparation: the material running hole is opened on the bottom support plate of the mold, with a diameter of 1.8 mm. The inner wall of the hole is ground and polished to a roughness of 0.4 micrometers. The number and distribution of the material running holes are dynamically adjusted according to the complexity of the product shape. At the stepped corners of the part, the arrangement density of the material running holes reaches 5 per 100 square millimeters.

[0058] Specifically, in step three, powder filling and weighing control, a combination of vacuum suction and vibrating cloth is used. Before the cloth shoe moves, the mold cavity is partially vacuumed to induce powder to quickly fill to the vicinity of the bottom running hole. The filling amount is then verified by a pressure sensor integrated into the bottom of the mold.

[0059] Specifically, step four involves multi-stage pressure loading molding: the molding pressure is set to 800 MPa. The pressure loading curve uses sinusoidal wave modulation, superimposing a high-frequency vibration with a frequency of 400 Hz and an amplitude of 20 MPa on the main pressure. This vibration pressing method can significantly reduce the bridging effect between powder particles and improve the densification rate.

[0060] Specifically, in step five, dynamic density adjustment and overflow: the overflow process is accompanied by high-frequency vibration, which makes the flow of powder in the discharge hole more like the characteristics of fluid. The overflow amount is controlled at 3% to 5% of the total filling amount by the damping adjustment device. The dynamic pressure signal when the powder flows out is obtained in real time by the pressure sensing probe. The main control system determines whether there is a locked pressure zone in the cavity based on the signal characteristics.

[0061] Specifically, in step six, demolding and subsequent processing: the demolding pressure is set to 1.2 tons. After demolding, the green blank undergoes vacuum sintering with a vacuum level better than 10^-3 Pascals. The sintering temperature is 1320 degrees Celsius, and the holding time is 3 hours. The sintered parts undergo finishing treatment with a finishing pressure of 500 MPa, achieving an dimensional accuracy of IT6, a surface hardness of 210 Vickers, and a tensile strength of 520 MPa. This completely solves the problems of porous structure and brittle cracking that easily occur in nickel-silicon alloys.

[0062] Example 4 This embodiment describes an implementation of an intelligent monitoring system for density adjustment in powder metallurgy. The system integrates an industrial control computer, a high-precision sensor array, and a deep learning-based quality prediction model.

[0063] Specifically, during the material preparation stage, the system monitors the mixing state of the powder through an acoustic emission sensor integrated on the ball mill. When the spectral distribution of the acoustic emission signal reaches the preset uniformity index, the ball milling is automatically stopped. During the mold design phase, the system uses stress cloud diagrams generated by finite element analysis software to automatically calculate the optimal coordinate distribution of the material feed groove and generate CNC machining program code.

[0064] During the filling stage, the weighing data of the automatic material feeding system is transmitted to the industrial control computer in real time via industrial Ethernet. The system uses a Kalman filter algorithm to smooth out sensor noise and ensure the accuracy of filling measurement. During the pressing stage, the industrial control computer collects the pressure of the upper punch, the pressure of the lower punch, the displacement, and the dynamic pressure in the feed hole at a frequency of 1000 Hz.

[0065] The system runs a digital twin model that inverts the degree of powder densification in the cavity based on the real-time collected pressure-displacement curve (PS curve); When the model predicts that the local density may exceed the critical value (leading to cracking), the system automatically adjusts the electromagnetic proportional valve of the damping device to reduce the overflow resistance and guide the powder to flow out quickly.

[0066] During the demolding stage, the system uses waveform data acquired by the demolding force sensor and supports vector machine algorithm to identify potential risks of mold sticking or tearing. If an abnormal waveform is detected, the press immediately switches to micro-step return mode to release elastic strain energy at an extremely slow speed to prevent the green billet from developing delamination.

[0067] All production data is uploaded to a cloud database. By mining massive amounts of historical data, the system can automatically optimize process parameters for the next production cycle. For example, it can automatically adjust molding pressure or holding time based on fluctuations in powder batches. This data-driven density adjustment method ensures that the pass rate of iron-nickel and nickel-silicon products remains stable at over 99.5%.

[0068] Example 5 This embodiment focuses on the influence mechanism and experimental verification of the geometry of the material overflow trough and material overflow hole on powder overflow behavior.

[0069] In the high-pressure forming process of powder metallurgy, the behavior of powder is between that of a solid and a fluid; When the local pressure inside the cavity reaches 200 MPa or more, the powder particles undergo plastic deformation and fill the gaps between the particles. The isosceles trapezoidal cross section of the feed trough plays a key role, and the angle of the hypotenuse (15 to 30 degrees) can significantly reduce the lateral pressure of the powder on the trough wall. According to experimental measurements, when the angle of the inclined side is 22.5 degrees, the outflow resistance of the powder is minimal, and it is less likely to form an "arch" structure at the groove opening, leading to blockage.

[0070] The ratio of the diameter of the feed hole (1.0 to 2.5 mm) to the average particle size of the powder (15 to 45 micrometers) is set between 40 and 100. This ratio range can ensure smooth powder discharge and prevent obvious protrusions or structural defects in the green body at the feed hole position. Experiments show that when the hole diameter is 1.8 mm, the overflowing powder is in the form of fine filaments and the residual traces on the surface of the green body are minimal after cutting.

[0071] The roughness of the inner wall of the discharge hole has a significant impact on the stability of the overflow. When the roughness value is reduced from 1.6 micrometers to 0.8 micrometers, the fluctuation range of the overflow pressure is reduced by 45%. Combined with the ultra-low friction characteristics of the diamond-like carbon film, the energy loss of the powder during the discharge process is minimized.

[0072] For iron-nickel alloy (45% nickel), under a total pressure of 8 tons, by opening 12 running channels and 8 running holes, the measured maximum residual stress inside the green billet was reduced from 350 MPa when no running channels were opened to 120 MPa. This significant reduction in stress directly eliminated the elastic backward cracking after demolding.

[0073] In the experiment of nickel-silicon alloy (3% silicon), by dynamically adjusting the overflow amount, the density difference between the top and bottom of the product was reduced from 0.42 g / cm³ to 0.04 g / cm³. This high degree of density uniformity made the shrinkage rate after sintering tend to be consistent in all directions, which greatly improved the geometric stability of the product.

[0074] Example 6 This embodiment describes a density adjustment method that combines a material release mechanism with ultrasonic vibration assistance, aiming to further improve the mechanical properties of complex nickel-silicon and iron-nickel structural components.

[0075] Specifically, in step four, multi-stage pressure loading molding, four sets of ultrasonic transducers are installed around the female mold of the mold. The output frequency of the ultrasonic transducers is set to 20 kHz and the power is 2 kW. During the pressurization stage, ultrasonic vibration is transmitted to the inside of the powder through the mold wall. The cavitation effect and acoustic flow effect generated by the ultrasonic waves can effectively break the mechanical interlocking between powder particles, so that the particles can be rearranged under low static pressure.

[0076] In conjunction with the overflow of the material in the running trough in step five, ultrasonic vibration makes the discharge of excess powder more rapid and uniform. When the pressure is loaded to 90% of the preset maximum value, the intensity of ultrasonic vibration gradually weakens and enters the pressure holding stage. This "dynamic and static combination" pressing process can increase the density of the green body by 3% to 5% under the same pressure.

[0077] Furthermore, this embodiment also introduces an online density detection device. This device utilizes the correlation between the propagation speed of ultrasonic waves in the green billet and density to achieve non-destructive testing of the green billet density. The detection probe is integrated on the ejector rod of the press, and the measurement is completed at the moment the green billet is ejected. The data is fed back to the industrial control computer in real time. If uneven density distribution is detected, the system will automatically adjust the movement trajectory of the fabric shoe in the next cycle to achieve closed-loop compensation.

[0078] By using this integrated ultrasonic-assisted and online monitoring method for depth adjustment, precision iron-nickel alloy rotor parts are produced with a surface hardness distribution variation of less than 5 Vickers hardness and a tensile strength consistency of over 98%, fully meeting the stringent requirements of the aerospace field for key powder metallurgy components.

[0079] Example 7 This embodiment explores the engineering application effects of the method of the present invention in reducing mold wear and extending equipment life.

[0080] In traditional fully enclosed molds, the local pressure in the cavity at the end of the pressing process can reach extreme peaks due to uneven powder filling, sometimes exceeding 1.5 times the design pressure. This local high pressure can cause significant elastic deformation of the mold cavity, and long-term operation can lead to fatigue cracks and permanent plastic deformation.

[0081] After adopting the material runner and material runner hole design described in this invention, the pressure peak in the cavity is limited to a preset threshold due to the dynamic pressure relief function. Through joint monitoring by displacement sensor and pressure sensor, it was found that the elastic deformation of the mold cavity was reduced by 40% compared with the traditional process. After producing 100,000 iron-nickel alloy parts, the wear depth of the mold cavity was only 0.008 mm, while the wear depth of the comparison group using the traditional closed mold reached 0.025 mm.

[0082] In addition, because dynamic overflow reduces the total pressing pressure required, the hydraulic system working pressure of the press drops from 25 MPa to 21 MPa. This not only reduces the temperature rise of the hydraulic oil and reduces the wear of the seals, but also reduces the energy consumption of a single molding by 18%. The maintenance cycle of the press has been extended from 2,000 hours to 5,000 hours, significantly reducing production costs.

[0083] On automated production lines, this method demonstrated extremely high stability. Because the material feeding trough was coated with a diamond-like carbon film, no channel blockage occurred during 48 hours of continuous operation. The powder recovery system operated smoothly, and after impurities were removed by screening equipment, the particle size distribution of the recovered powder closely matched that of the original powder, achieving closed-loop recycling of the material.

[0084] Example 8 This embodiment details an adaptive adjustment strategy for fluctuations in the flowability of different batches of powder. The flowability of powder materials is often affected by environmental humidity, storage time and slight fluctuations in particle size. This invention monitors the flowability of each batch of powder in real time by integrating a Hall effect flowmeter into an automatic feeding system.

[0085] If a decrease in powder flowability is detected (outflow time increases by more than 15%), the industrial control computer will automatically execute the following compensation instructions: The vibration frequency of the fabric boot in step three was increased from 80 Hz to 100 Hz to assist in powder filling; In step five, the preload of the damping adjustment device is reduced by adjusting the bolts, thereby reducing the opening pressure of the material discharge chute by 5%, ensuring that overflow and pressure relief can still be achieved smoothly even when the powder has poor flowability.

[0086] If the system detects that the powder has excessive flowability (which may cause splashing or overfilling), it will automatically increase the moving speed of the cloth shoe and appropriately increase the opening pressure of the feed chute to prevent the powder from overflowing too early and causing insufficient green compact density.

[0087] Through this adaptive adjustment mechanism, the system can tolerate fluctuations in powder flowability within a range of ±20%, while the density deviation of the green body remains within 0.03 g / cm³. This strong process robustness gives the method significant technical advantages when processing complex iron-nickel and nickel-silicon alloys.

[0088] Example 9 This embodiment describes the application of the method of the present invention in manufacturing parts with complex geometric features such as large aspect ratio and stepped structure.

[0089] For columnar iron-nickel parts with an aspect ratio greater than 5, traditional pressing processes are prone to producing low density in the "waist" and high density at both ends. By densely arranging the material flow holes in the middle area of ​​the mold and coordinating with the differential motion of the lower punch during the pressing process, the powder is forced to flow towards the middle and overflow.

[0090] Experimental data show that for iron-nickel alloy shaft parts with a length-to-diameter ratio of 6, the density difference along the entire length decreases from 0.55 g / cm³ to 0.06 g / cm³.

[0091] For nickel-silicon alloy gears with multi-layer stepped structures, stress concentration at the corners is the main cause of cracking. An isosceles trapezoidal material runner is opened at the gear root and the stepped transition area. The angle between the bottom of the runner and the mold axis is set to 30 degrees. During the pressing process, excess powder at the corners is discharged through the material runner, effectively releasing the shear stress in this area.

[0092] Scanning electron microscopy (SEM) revealed that the stepped parts produced using this method exhibited uniform metallographic structure at the corners, with tightly bonded particles and no microcracks or voids. In subsequent impact toughness tests, the impact energy of the parts was 30% higher than that produced using traditional methods, fully demonstrating the superior effect of the density adjustment method in optimizing the internal structure of complex components.

[0093] Example 10 This embodiment describes a system process for high-precision recycling and reuse of discharged powder.

[0094] The excess powder discharged in step five is collected into the recovery chamber through a negative pressure suction pipe installed below the mold. The recovery chamber is equipped with three layers of high-frequency vibrating screening equipment with screen apertures of 60 micrometers, 45 micrometers and 15 micrometers respectively.

[0095] The first layer of screen is used to remove tiny metal shavings or mold wear particles that may get mixed in during the pressing process; The second and third sieves are used to re-sort the powder. The sieved powder enters a laser particle size analyzer for real-time detection. If the particle size distribution curve of the powder still conforms to a normal distribution and the median diameter is between 28 and 32 micrometers, it is returned to the automatic feeding system in step three through a pneumatic conveying system.

[0096] If significant work hardening or shape changes are detected in the powder, it is sent to a vacuum annealing furnace for softening treatment. Once its properties are restored, it can be reused. Through this rigorous recycling process, the utilization rate of expensive alloy materials such as iron-nickel and nickel-silicon has increased from 92% in the traditional process to over 98.5%.

[0097] This not only reduces raw material costs but also minimizes the environmental impact of waste powder, aligning with the trend of green manufacturing. The entire recycling process is synchronously monitored by an industrial control computer to ensure the consistency of the returned powder quality, thereby guaranteeing the long-term stability of product quality under continuous production mode.

[0098] Example 11 This embodiment summarizes the integration and operational effects of the method of the present invention on an actual industrial production line.

[0099] The density adjustment method for powder metallurgy has been successfully integrated into a 10-ton fully automatic precision forming unit; The entire machine uses a Siemens S7-1500 series PLC as the logic control core, and is used in conjunction with an industrial control computer for high-performance data processing.

[0100] During 30 days of continuous operation, the system produced a total of 25,000 precision iron-nickel alloy parts. Statistical data showed that the first-pass yield rate of the products was 99.7%, the consistency of dimensional tolerances (Cp value) reached 1.67, the average density of the green blank was 91.5% of the theoretical density, and the fluctuation range was controlled within ±0.5%.

[0101] In terms of maintenance, thanks to the self-cleaning design of the material feeding channel and the protection of the diamond-like film, the mold only needs to be cleaned with compressed air once per shift, without the need to stop the machine for disassembly.

[0102] Compared with the old production line that uses traditional closed molds, the new process reduces the overall cost of a single product (including materials, energy, mold depreciation and labor) by 22%. This method not only solves the technical problem of easy cracking of iron-nickel and nickel-silicon products.

[0103] In the description of this invention, it should be understood that the various forms of processes shown above can be used, with steps reordered, added, or deleted. For example, the steps described in this disclosure can be executed in parallel, sequentially, or in different orders, as long as the desired results of the technical solutions provided in this disclosure can be achieved, and no limitation is imposed herein.

[0104] The above description is merely a preferred embodiment of the present invention and does not constitute a limitation on the scope of protection of this disclosure. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this disclosure should be included within the scope of protection of this disclosure.

Claims

1. A density adjustment method for powder metallurgy, characterized in that: Includes the following steps: Step 1: Select alloy powder as raw material and perform dehydration treatment in a preset temperature environment using vacuum drying equipment. Use the vacuum maintenance mechanism to remove physically adsorbed water and chemically bound water from the surface of powder particles. Step 2: Design a mold according to the geometry of the product to be formed. Open multiple material running grooves or holes on the inner wall of the mold, the end face of the female mold, or the surface of the mandrel to adjust the density. The material running grooves or holes are distributed in the stress concentration area or the area with excessive powder accumulation, and are used to discharge excess powder during the pressing process to achieve dynamic balance of pressure in the cavity. Step 3: Use an automatic material feeding system to fill the pre-treated alloy powder into the mold cavity, monitor the filling amount in real time, and ensure that the single filling error is controlled within the preset error range. Step 4: Apply a preset mechanical pressure to the powder in the mold cavity through the upper and lower punches. The pressure loading process is divided into an initial pressure stage, a pressure increase stage, and a pressure holding stage. When the total applied pressure reaches the preset total pressure threshold, it causes the metal powder particles to rearrange, plastically deform, and cold weld together. Step 5, Dynamic density adjustment and overflow: During the pressure loading process, when the local pressure in the cavity exceeds the preset threshold, the excess powder is discharged outward through the discharge trough or discharge hole. By adjusting the outflow of powder, the density of each part of the product is accurately compensated, and internal residual stress is eliminated. Step 6, demolding and subsequent processing: After pressure holding is completed, control the press to return smoothly, and use the ejection device to push the formed green blank out of the mold. Perform density testing and appearance inspection on the green blank.

2. The density adjustment method for powder metallurgy according to claim 1, characterized in that: Step one also includes monitoring the agglomeration and oxidation of the powder during storage and turnover before the powder enters the fabric system; Establish a powder batch registration database, covering particle size distribution, component ratio, and loose density information. Entity association is performed through unified social credit code and spatial location code to ensure that the physical boundaries and geographical coordinates of each batch of powder match. The alloy powder includes iron-nickel alloy powder or nickel-silicon alloy powder.

3. The density adjustment method for powder metallurgy according to claim 1, characterized in that: In step two, the material feeding groove is opened on the inner side wall of the female mold. The material feeding hole is located on the bottom support plate of the mold; The surface of the material feeding trough or feeding hole is coated with a diamond-like carbon film of a preset thickness to reduce frictional resistance when powder is discharged and prevent blockage of the feeding channel.

4. The density adjustment method for powder metallurgy according to claim 1, characterized in that: In step three, the automatic feeding system adopts a vibration feeding method with a preset vibration frequency and a preset speed for the feeding shoe. Through repeated feeding, the filling density of the powder in the cavity is ensured to be uniform. During the filling process, for parts with ultra-thin wall structures, the dwell time of the cloth shoe in the thin-wall area is extended. A high-precision electronic weighing sensor is used to ensure a constant filling amount per batch. A scraping device is used to perform multiple reciprocating leveling operations to ensure that the height difference of the powder surface is lower than the preset flatness threshold. Before the fabric shoe moves, a local vacuum treatment is performed on the mold cavity to induce powder to quickly fill to the vicinity of the bottom material outlet.

5. The density adjustment method for powder metallurgy according to claim 1, characterized in that: In step four, the pressure rise rate in the initial pressure stage is a first preset rate. When the pressure reaches a predetermined proportion of the total pressure, the pressure rise stops and is maintained for a predetermined time to expel residual air between the powder particles. The pressure rise rate during the pressurization stage is the second preset rate, until the preset maximum forming pressure is reached, and the depth of the punch is monitored in real time by a displacement sensor. The pressure holding phase lasts for a predetermined time, and the constant pressure control system ensures that the pressure fluctuation range is less than the preset fluctuation threshold.

6. The density adjustment method for powder metallurgy according to claim 1, characterized in that: In step five, for columnar parts with a length-to-diameter ratio exceeding a preset ratio, the powder is guided to flow towards the center and overflow by densely arranging material flow holes in the middle region of the mold and coordinating with the differential motion of the lower punch during the pressing process. For parts with multi-layered stepped structures, isosceles trapezoidal material runners are opened in the stress concentration area at the corner and the transition area between the steps. The angle between the bottom of the runner and the mold axis is adjusted and set. Excess powder at the corner is discharged through the runner, releasing the shear stress in the area.

7. The density adjustment method for powder metallurgy according to claim 1, characterized in that: In step six, the demolding pressure is controlled within a predetermined ratio range of the molding pressure. The frictional resistance during the demolding process is monitored by a demolding force sensor. If the demolding force increases abnormally, an alarm is automatically triggered and the operation is stopped. Before filling, a layer of graphite-based release lubricant of a preset thickness is sprayed onto the surface of the mold cavity; The demolding process adopts a constant speed mode, with the ejection speed controlled within a preset speed range. The demolding force sensor monitors the ejection resistance in real time and limits the maximum demolding force. Using waveform data acquired by a demolding force sensor, a support vector machine algorithm is used to identify potential risks of mold sticking or tearing. If an abnormal waveform is detected, the press switches to micro-step return mode to release elastic strain energy.

8. The density adjustment method for powder metallurgy according to claim 1, characterized in that: It also includes a step of recycling and reusing the discharged excess powder, which is collected into a recycling bin through a negative pressure suction pipe installed below the mold.

9. The density adjustment method for powder metallurgy according to claim 1, characterized in that: During the pressing process, ultrasonic-assisted pressing is performed using ultrasonic transducers integrated around the mold's female mold. The output frequency and power of the ultrasonic transducers are set to preset values. During the pressurization stage, ultrasonic vibration is transmitted to the interior of the powder through the mold wall, and the mechanical interlocking between powder particles is broken by cavitation effect and acoustic flow effect, so that the particles can rearrange under lower static pressure. In conjunction with the overflow from the material feeding trough, ultrasonic vibration accelerates the discharge of excess powder; When the pressure is applied to the preset ratio, the intensity of ultrasonic vibration is gradually reduced and the pressure holding phase begins.

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