Pull rod stress balancing structure and injection molding machine

Abstract

The invention belongs to the field of injection molding machine equipment, and provides a pull rod stress balancing structure and an injection molding machine, the pull rod stress balancing structure comprises a pull rod body, the pull rod body is provided with an external thread used for being matched with a mold locking oil cylinder assembly, and the external thread is composed of a plurality of thread teeth sequentially arranged in the axis direction of the pull rod body; the external thread is provided with a first thread area and a second thread area which are adjacently arranged in the axial direction. Compared with the prior art, the pull rod has the advantages that the thread teeth in the first thread area are obliquely arranged, so that when the pull rod body bears axial tension, the phenomenon that initial loads borne by the thread teeth in the first thread area are concentrated is effectively reduced; meanwhile, the second thread area is matched with a structure that the large diameter is parallel to the central axis, axial shear force from the first thread area can be borne and transmitted in a balanced mode step by step, and the problem of early fatigue failure caused by uneven stress and local stress concentration of threads of a traditional pull rod is remarkably solved through the structure; the overall bearing capacity, the service life and the operation reliability of the pull rod are improved.

Description

Technical Field

[0001] This invention belongs to the field of injection molding machine equipment, specifically relating to a tie rod force-balanced structure and an injection molding machine. Background Technology

[0002] In a two-platen injection molding machine, the clamping system typically uses four tie rods to connect the moving platen and the fixed platen, and transmits huge axial tensile force during high-pressure clamping by engaging the external thread at the end of the tie rods with the clamping cylinder assembly.

[0003] Due to elastic deformation and assembly clearance in threaded connections, axial loads are not uniformly distributed across all meshing threads in actual operation. Traditional thread machining aligns the thread pitch diameter with the centerline, theoretically ensuring uniform clearance for each thread after assembly of the tie rod and nut. However, when the tie rod is under stress, the stress on the threads decreases sequentially from left to right, with no stress occurring after the 10th thread. This uneven stress distribution causes deformation and failure of the first few threads on the left side. This severely uneven stress state results in the front thread teeth being under high stress for extended periods, making them highly susceptible to plastic deformation, flank crushing, or fatigue cracks, which can lead to mold clamping failure, mold plate misalignment, and even safety accidents. Summary of the Invention

[0004] The purpose of this invention is to address the aforementioned problems in the existing technology by proposing a tie rod force balancing structure and injection molding machine that is simple in structure, has good stability, and achieves load gradient distribution and force balance throughout the entire thread engagement section.

[0005] The objective of this invention can be achieved by addressing the following technical problem: proposing a tie rod force-balanced structure, including a tie rod body, wherein the tie rod body is provided with an external thread for cooperating with a mold-locking cylinder assembly, and the external thread is composed of a plurality of thread teeth arranged sequentially along the axial direction of the tie rod body; The external thread has a first thread area and a second thread area arranged adjacent to each other along the axial direction, wherein the first thread area is close to the fixed platen connected to the mold locking cylinder assembly, and the second thread area is located at the end of the first thread area away from the fixed platen. Multiple threaded teeth in the first threaded area are inclined toward the fixed template one by one and set at an angle with the central axis of the tie rod body. This makes the contact stiffness of each threaded tooth in the first threaded area decrease sequentially from the side closer to the fixed template to the side of the locking cylinder assembly when the tie rod body is subjected to axial tensile force, thereby reducing the initial load borne by the threaded teeth in the first threaded area. The major diameters of the multiple thread teeth in the second threaded area are all arranged parallel to the central axis of the tie rod body, so that the axial shear force acting on the multiple thread teeth in the first threaded area is gradually transmitted axially from the side near the fixed template to the multiple thread teeth in the second threaded area, thereby achieving a balanced force on the overall external thread.

[0006] In the above-mentioned tie rod force-balanced structure, each thread tooth in the first threaded area has an inclined surface, and the inclined surfaces on the multiple thread teeth are arranged linearly.

[0007] In the above-mentioned tie rod force-balanced structure, the angle between the inclined surface and the major diameter of the thread teeth in the second threaded area is 3° to 5°.

[0008] In the aforementioned tie rod force-balanced structure, the external thread is a trapezoidal thread.

[0009] In the aforementioned tie rod force-balanced structure, the external thread is a trapezoidal thread that has undergone nitrogen-barrier treatment.

[0010] In the above-mentioned tie rod force-balanced structure, an arc-shaped clearance groove is also formed between the external thread and the tie rod body.

[0011] In the above-mentioned tie rod force-balanced structure, the length of the first threaded area along the axis of the tie rod body ranges from 31mm to 33mm.

[0012] In the above-mentioned tie rod force balancing structure, the angle between the tangent line of the arc-shaped clearance groove and the major diameter of the thread teeth in the second threaded area is 45°.

[0013] In the above-mentioned tie rod force-balanced structure, a central hole is provided at the end of the tie rod body near the external thread, and the central hole is used to install the mold-locking cylinder assembly.

[0014] The technical solution adopted by the present invention to solve its technical problem is to also propose an injection molding machine, including one of the above-mentioned tie rod force-balanced structures.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] (1) The present invention provides a tie rod force balancing structure and injection molding machine. By tilting the thread teeth in the first thread area, the tie rod body can effectively reduce the initial load concentration phenomenon borne by each thread tooth in the first thread area when it is subjected to axial tensile force. At the same time, the second thread area adopts a structure with the large diameter parallel to the central axis, which can gradually bear and evenly transmit the axial shear force from the first thread area. This structure significantly improves the problem of uneven thread force and local stress concentration leading to early fatigue failure in traditional tie rods, and improves the overall load-bearing capacity, service life and operational reliability of the tie rod.

[0017] (2) The angle between the inclined plane and the major diameter of the thread teeth in the second thread area is limited to 3° to 5°, which can effectively achieve the gradient distribution of load, and will not cause significant weakening of thread strength or assembly difficulties due to excessive inclination angle. It takes into account both mechanical performance and process feasibility, and ensures the long-term stable operation of the tie rod under high load conditions.

[0018] (3) Nitrogen inhibition treatment of trapezoidal threads can form a hardened layer with high hardness, high wear resistance and corrosion resistance on the thread surface, which significantly improves the surface fatigue strength and anti-seize ability of the thread pair, effectively prevents thread wear, jamming or fretting damage during frequent disassembly or high load operation, and extends the service life of tie rods and matching components. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the overall structure of this application; Figure 2 This is a structural schematic diagram of the tie rod body; Figure 3 yes Figure 2 A magnified view of a portion of point A in the middle.

[0020] In the figure, 1 is the tie rod body; 10 is the external thread; 100 is the thread tooth; 100a is the inclined plane; 101 is the first thread area; 102 is the second thread area; 11 is the arc-shaped clearance groove; 12 is the center hole; and 2 is the mold locking cylinder assembly. Detailed Implementation

[0021] The following are specific embodiments of the present invention, which are described in conjunction with the accompanying drawings to further illustrate the technical solutions of the present invention. However, the present invention is not limited to these embodiments.

[0022] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indication will also change accordingly.

[0023] like Figures 1 to 3As shown, a tie rod force-balanced structure includes a tie rod body 1. The tie rod body 1 is provided with an external thread 10 for cooperating with a mold-locking cylinder assembly 2. The external thread 10 is composed of a plurality of thread teeth 100 arranged sequentially along the axial direction of the tie rod body 1. Specifically, the external thread 10 has a first thread region 101 and a second thread region 102 arranged adjacent to each other along the axial direction. The first thread region 101 is close to the fixed template connected to the mold-locking cylinder assembly 2, and the second thread region 102 is located at the end of the first thread region 101 away from the fixed template. The plurality of thread teeth 100 in the first thread region 101 are inclined one by one towards the fixed template and are aligned with the center of the tie rod body 1. The axes are set at an angle, so that when the tie rod body 1 is subjected to axial tension, the contact stiffness of each thread tooth 100 in the first threaded area 101 decreases sequentially from the side near the fixed template to the side of the mold-locking cylinder assembly 2, thereby reducing the initial load borne by the thread teeth 100 in the first threaded area 101; the major diameters of the multiple thread teeth 100 in the second threaded area 102 are all set parallel to the central axis of the tie rod body 1, so that the axial shear force acting on the multiple thread teeth 100 in the first threaded area 101 is gradually transmitted axially from the side near the fixed template to the multiple thread teeth 100 in the second threaded area 102, thereby achieving force balance of the overall external thread 10.

[0024] It should be noted that when the injection molding machine closes the mold, the enormous clamping force is transmitted through the mold plate to the four tie rods, causing the tie rods to undergo axial tensile deformation. Due to the continuity of the material and structure, the force is concentrated near the stress end (i.e., Figure 2 The threads on the left side of the external thread 10 shown need to bear a large load, the magnitude of which is determined by... Figure 2 The external threads 10 shown decrease sequentially from left to right (this principle is a well-known technology in the injection molding machine industry and will not be elaborated here). To solve this technical problem, this solution divides the external threads 10 on the tie rod body 1 into a first thread area 101 and a second thread area 102, and makes the thread teeth 100 in the first thread area 101 face the fixed template (which is installed on...). Figure 1 The left side of the clamping cylinder assembly 2 shown (referring to the structure of an existing injection molding machine, not shown in the figure) is inclined. When axial tension is applied to the tie rod body 1, the part that originally first contacts and participates in bearing the load is... Figure 3 The leftmost thread in the first threaded region 101 shown is the threaded tooth. However, because the bearing tooth of this threaded tooth 100 is tilted as a whole, the axial shear force originally concentrated at the front end is no longer entirely borne by the threaded tooth 100 in the first threaded region 101, but is instead guided to be transmitted axially backward along the tie rod body 1 (i.e., Figure 3(Transmitted from left to right) When the load is transmitted to the second threaded area 102, since the major diameter of the thread teeth 100 in this area is parallel to the central axis of the tie rod body 1 (i.e., the thread teeth 100 in the second threaded area 102 are all conventional tooth structures), its contact stiffness is high and uniform, which can stably bear and share the load from the front. It can be seen that this structure effectively reduces the initial load concentration phenomenon borne by each thread tooth 100 in the first threaded area 101 by the coordinated cooperation of different thread teeth 100 in the first threaded area 101 and the second threaded area 102; at the same time, it can gradually bear and evenly transmit the axial shear force from the first threaded area 101 by utilizing the second threaded area 102, which significantly improves the problem of uneven force distribution and local stress concentration leading to early fatigue failure in traditional tie rod threads, and improves the overall load-bearing capacity, service life and operational reliability of the tie rod.

[0025] Each thread tooth 100 in the first threaded region 101 has a chamfer 100a formed on it, and the chamfers 100a on the multiple thread teeth 100 are arranged linearly.

[0026] like Figure 3 As shown, in this design, the multiple thread teeth 100 within the first threaded region 101 adopt a design with decreasing thread depth from right to left, thus... Figure 3 The local load on the leftmost thread tooth 100 (i.e., the position where the external thread 10 bears the greatest load) is significantly reduced. In addition, the linear arrangement of multiple inclined planes 100a further optimizes the contact state between the thread tooth 100 and the internal thread of the mold-locking cylinder assembly 2, so that the load is more smoothly distributed along the axial direction to the second thread area 102. In other words, in the traditional structure (i.e. all external threads 10 adopt the structure of the internal thread tooth 100 in the second thread area 102), only the first 5-6 teeth of the first thread area 101 are effectively loaded, and there is basically no load after the 10th tooth; while the present invention can extend the number of teeth with effective load to the 10th-12th teeth, the load distribution is more uniform, the overall stiffness and stability of the thread pair is improved, and the risk of chain loosening caused by local failure is reduced.

[0027] like Figure 3 As shown, this scheme defines the included angle between the limiting inclined surface 100a and the major diameter of the thread tooth 100 in the second thread area 102 as α. The included angle α ranges from 3° to 5° (the included angle α in this scheme is preferably 4 degrees). In other words, the inclined surface 100a is deflected by 3° to 5° relative to the standard thread tooth (i.e., the thread tooth 100 in the second thread area 102). This angle can effectively achieve the gradient distribution of load, and will not cause significant weakening of thread strength or assembly difficulties due to excessive inclination angle. It takes into account both mechanical performance and process feasibility, and ensures the long-term stable operation of the tie rod under high load conditions.

[0028] Furthermore, such as Figure 2 and Figure 3As shown, this solution uses a trapezoidal thread as the external thread type 10. Compared with the ordinary triangular thread, it has a larger tooth profile angle and bearing area, which can better withstand axial tensile force and shear force. At the same time, it has good self-locking and wear resistance, making it particularly suitable for high-load and repeatedly loaded working environments in heavy machinery such as injection molding machines, further improving the strength and durability of the tie rod structure.

[0029] Preferably, this solution applies nitrogen-blocking treatment (such as nitriding, soft nitriding and other surface strengthening processes) to the trapezoidal thread, which can form a hardened layer with high hardness, high wear resistance and corrosion resistance on the thread surface, significantly improving the surface fatigue strength and anti-seize ability of the thread pair, effectively preventing thread wear, jamming or fretting damage during high load operation, and extending the service life of the tie rod and matching components.

[0030] like Figure 2 and Figure 3 As shown, this solution provides an arc-shaped relief groove 11 between the external thread 10 and the tie rod body 1. This arc-shaped relief groove 11 can provide machining space for the tool when machining the external thread 10, and can also effectively alleviate the stress concentration phenomenon at the root of the thread. In addition, the arc-shaped relief groove 11 connects the thread and the rod body through a smooth transition, avoiding the crack initiation point caused by sharp corners, and improving the overall fatigue resistance and structural safety of the tie rod, especially under alternating loads.

[0031] like Figure 3 As shown, in this design, the length range of the first threaded section 101 along the axis of the tie rod body 1 (i.e., the chamfered section of the external thread 10, which refers to a chamfered conical surface cut axially from the major diameter of the thread at the end of the external thread 10, used to guide engagement or prevent the initial tooth of the thread from chipping) is 31mm to 33mm. Preferably, the chamfered section of the external thread 10 is 32mm. This length ensures sufficient thread engagement length to transmit load and also ensures that the load gradient distribution of the inclined thread teeth 100 reaches the optimal level, avoiding excessive length leading to increased manufacturing costs or insufficient load adjustment due to insufficient length, thus achieving a balance between structural compactness and mechanical performance.

[0032] Preferably, in this scheme, the angle between the tangent line of the arc-shaped clearance groove 11 and the major diameter of the thread tooth 100 in the second threaded area 102 is defined as β, such as... Figure 3 As shown, the included angle β is 45°. This angle design allows the stress flow to transition most smoothly at the root of the thread, minimizing the local stress concentration factor. At the same time, it facilitates processing and forming, taking into account both mechanical optimization and manufacturing processability, and further improving the fatigue life and reliability of the tie rod.

[0033] A center hole 12 is provided at the end of the tie rod body 1 near the external thread 10. The center hole 12 is used to install the mold clamping cylinder assembly 2. Figure 1As shown, this design not only simplifies the overall assembly structure but also enables precise installation of the clamping cylinder assembly 2, reducing the risk of off-center loading. Simultaneously, the presence of the center hole 12 appropriately reduces the mass at the end of the tie rod, optimizing dynamic response characteristics without compromising strength, which is beneficial for improving the synchronization accuracy and stability of the injection molding machine's clamping system. It should be noted that the structure and working principle of the clamping cylinder assembly 2 in this embodiment are the same as those in existing technologies, and will not be described in detail here.

[0034] This solution applies the aforementioned tie rod force-balanced structure to injection molding machines, which can significantly improve the uniformity of force distribution, smooth operation, and long-term reliability of the overall clamping mechanism. Since the tie rod is one of the four core components of an injection molding machine, its performance directly affects the mold closing accuracy, product molding quality, and equipment maintenance cycle. By adopting the tie rod structure of this invention, downtime caused by thread failure can be effectively reduced, maintenance costs can be lowered, production efficiency can be improved, and higher clamping force design requirements can be supported. It is suitable for large, precision, or high-speed injection molding equipment.

[0035] It should be noted that in this invention, the use of terms such as "first," "second," and "a" is for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified. The terms "connection," "fixed," etc., should be interpreted broadly. For example, "fixed" can mean a fixed connection, a detachable connection, or an integral part; it can mean a mechanical connection or an electrical connection; it can mean a direct connection or an indirect connection through an intermediate medium; it can mean the internal communication of two elements or the interaction between two elements, unless otherwise explicitly specified. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0036] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are feasible for those skilled in the art. If the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0037] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

Claims

1. A tie rod stress equalization structure, comprising a tie rod body, the tie rod body being provided with an external thread for cooperating with a lock mold oil cylinder assembly, the external thread being composed of a plurality of thread teeth arranged in sequence along the axial direction of the tie rod body, characterized in that: the external thread has a first thread area and a second thread area arranged axially adjacent to each other, wherein the first thread area is close to a fixed mold plate connected with the lock mold oil cylinder assembly, and the second thread area is located at one end of the first thread area away from the fixed mold plate; the plurality of thread teeth in the first thread area are arranged in sequence to be inclined toward the fixed mold plate and form an angle with the central axis of the tie rod body, so that when the tie rod body bears an axial tension, the contact stiffness of each thread tooth in the first thread area decreases in sequence from the side close to the fixed mold plate to the side of the lock mold oil cylinder assembly, thereby reducing the initial load borne by the thread teeth in the first thread area; the major diameters of the plurality of thread teeth in the second thread area are arranged in parallel with the central axis of the tie rod body, so that the axial shear force acting on the plurality of thread teeth in the first thread area is gradually transmitted to the plurality of thread teeth in the second thread area along the axial direction from the side close to the fixed mold plate, thereby realizing stress equalization of the entire external thread. A bevel is formed on each thread tooth in the first thread area, and the bevels on the plurality of thread teeth are linearly arranged. The included angle between the bevel and the major diameter of the thread tooth in the second thread area ranges from 3° to 5°. The external thread adopts trapezoidal thread.

2. The force equalizing structure of claim 1, wherein, The external thread adopts trapezoidal thread treated by nitrogen blocking.

3. The force equalizing structure of claim 2, wherein, An arc-shaped avoidance groove is further formed between the external thread and the tie rod body.

4. The force equalization structure of a drawbar according to claim 1 or 2, characterized in that, The length of the first thread area along the axial direction of the tie rod body ranges from 31 mm to 33 mm.

5. The force equalization structure of a drawbar according to claim 1 or 2, characterized in that, The included angle between the tangent line of the arc-shaped avoidance groove and the major diameter of the thread tooth in the second thread area is 45°.

6. The force equalizing structure of claim 5, wherein, A central hole is formed in the end of the tie rod body close to the external thread, and the central hole is used for installing the lock mold oil cylinder assembly.

7. The force equalizing structure of claim 1, wherein, A tie rod stress equalization structure according to any one of claims 1-9.

8. The force equalizing structure of claim 6, wherein, ​ 9. The force equalizing structure of claim 1, wherein, ​ 10. An injection molding machine characterized by, ​

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