Abstract: The main component of linear bearings, the steel outer hub frame, is generally produced using conventional mechanical cold processing methods, which are cumbersome in process, high in energy consumption, long in production cycle, and poor in quality stability. To overcome the above shortcomings, this article analyzes the plastic forming process of the outer hub frame of linear bearings, and uses a die stamping to form the part. A precision punching scheme for uniformly distributed side long grooves from the outside to the inside is determined, and a die that can be used for precision punching of the side long grooves of the outer hub frame of linear bearings is designed. The working principle of the die is explained, and the design points are pointed out. Practice has proven that the designed mold has high punching efficiency and the quality of the parts fully meets the requirements for use.
Keywords: Linear bearings; Side groove; Precision punching; mould design
1. Introduction
Ball linear bearings are widely used in aerospace, machine tools, mechanical equipment, processing control, robots, automation equipment, material control, packaging, medical and entertainment equipment, and other production or mechatronic integrated products due to their high motion speed, small damping, flexibility, reliability, stability and accuracy. The main component of traditional linear bearings, the steel outer hub frame, is produced using conventional mechanical cold processing methods, which are cumbersome in process, high in energy consumption, long in production cycle, and poor in quality stability. To overcome these shortcomings, this article developed a stamping die for the steel outer hub of linear bearings, achieving non cutting machining of the steel outer hub of linear bearings. The forming of the steel outer hub frame can be divided into two processes: first, the forming of the cylindrical blank, which includes basic processes such as cutting, drawing, and punching bottom holes; Next is the punching forming of the long groove on the side of the outer hub frame. Due to the difficulty of precision punching the long groove on the side of the outer hub frame, the mold design is quite unique. This is introduced here.
2. Analysis of forming process
The formed parts are shown in Figure 1, made of 08F steel with a thickness of 1mm. The 7 long grooves in the circumferential direction of the parts must be evenly distributed, and the rolling of the balls in the grooves must be smooth, with minimal wear, and there should be no burrs on the inner walls of the grooves.
Figure 1 Parts
The main difficulty in forming parts is how to ensure the uniform distribution of multiple long grooves in the circumferential direction, improve the punching quality of the parts, and reduce burrs and deformation. According to the technical requirements of the parts, there are three process options available for selection. Option 1: Use a indexing device, and the direction of movement of the press slider is the cutting direction. The cylindrical part is installed flat on the mold. After each groove is punched, use the indexing device to punch the next groove, and then punch 7 grooves in sequence. Its advantages are simple mold design, convenient processing and manufacturing, low punching force, easy control of punching clearance, and easy guarantee of the smoothness of individual grooves. The disadvantage is that a precision indexing device must be designed, which makes it difficult to clamp and position the workpiece. The work efficiency is low, and the accumulated error is large, making it difficult to achieve uniform distribution of 7 side grooves. Option 2: The movement direction of the press slider is the same as the axis of the cylindrical part, and the punch simultaneously punches 7 side long grooves from the inside out. Its advantages are that it is easy to meet the technical requirements of the parts, high production efficiency, and the punching burrs are outside, making it easy to clean. But the disadvantage is that the mold structure is complex, and the lateral punching motion is limited by the size of the workpiece. Parts with too small dimensions cannot be processed using this method. Option 3: The sliding block of the press moves in the same direction as the axis of the cylindrical part, and the punch simultaneously punches 7 side long grooves from the outside to the inside. Its advantage is that lateral movement is easy to achieve, and lateral movement is not limited by the size of the workpiece, making it easy to achieve uniform distribution of 7 grooves in the axial direction. The disadvantage is that the mold structure is complex, and the punching burrs are on the inner wall, making it difficult to clean. After analysis and argumentation, it has been decided to adopt the third solution. In order to reduce burrs and deformation during punching and meet performance requirements, precision punching is adopted.
3. Mold Design
3.1 Mold structure design
According to the third scheme, the precision punching die for the long groove on the side of the outer hub of the linear bearing is designed as shown in Figure 2 [2-5]. The concave mold 21 and the concave mold fixing plate 2 are in an interference fit, and a polyurethane rubber 25 with a spline shape is placed in the concave mold for unloading and providing counter pressure. The convex mold 38 is connected to the slider 8 through a cylindrical pin, and the edge pressing ring 22 and edge pressing rubber 23 are connected to the slider with screws. The slider drives the convex mold, edge pressing ring, and edge pressing rubber to slide together in the guide groove 5 to complete the punching process. The inner surface of the edge pressing ring is processed into a cylindrical surface to better press the material. The wedge 9 is fixed to the upper mold seat 12 by screws and pins, and the punch pressure acts on the upper mold seat. The inclined surface of the wedge contacts the inclined surface of the slider, driving the convex mold to move towards the concave mold and completing the stamping process.
Figure 2 Schematic diagram of precision punching die
1. Lower mold seat; 2. concave mold fixing plate; 3. Guide groove; 4. Rear stopper; 5. Guide plate; 6. Mandrel; 7. Spring; 8. Sliding block; 9. Diagonal wedge; 10. 30. Guide pillar; 11. 24. Guide sleeve; 12. Upper mold seat; 13. 15, 18, 37. Screws; 14. 16, 39. Pins; 17. Diagonal wedge cushion plate; 19. 23. 25. Rubber; 20. Pressing plate; 21. Concave mold; 22. Edge pressing ring; 26. Push plate; 27. Pushing plate and cushion plate; 28. Support bracket; 29. Nut; 31. Support block; 32. Support; 33. Rotary shaft; 34. Handle; 35. Top plate; 36. Top rod; 38. Convex mold
The working process of the mold is as follows: position the blank on the concave mold 21, lower the upper mold, and move the pressure plate 20 and the inclined wedge 9 downwards. The inclined wedge contacts the sliding block 8, driving the sliding block to slide towards the concave mold. When the upper mold descends to a certain distance, the pressure plate contacts the spline rubber 25 inside the concave mold and begins to compress. At this time, the upper mold continues to descend. When the rubber inside the concave mold is compressed to a certain extent, the shoulder of the pressure plate contacts the spline rubber on the upper surface of the concave mold and stops compressing. The upper mold continues to descend, The slider continues to move towards the concave mold, and the edge pressing rubber 23 compresses the edge pressing ring to press the blank. The convex mold continues to move forward and completes the precision punching process under the counter pressure generated by the spline rubber 25. The upper mold moves upwards, the wedge detaches from the slider, and under the action of rubber 19, the pressure plate 20 does not move. The spline rubber is still in a compressed state, and under the action of edge pressing rubber 23 and pull rod spring 7, the slider moves backwards. The convex mold comes out of the blank, and the spline rubber pushes out the punching waste. The upper mold continues to move upwards. When rubber 19 is released to a certain extent, the pressure plate moves upwards, the spline rubber is released, and the upper mold moves upwards to the upper dead center position. Shake the handle 34, Push plate 26 out of the workpiece and complete one punching.
3.2 Key points of mold design
The design points of the precision punching die for the long groove on the side of the outer hub of the linear bearing are as follows.
(1) The material of the convex and concave molds is Cr12, and the heat treatment hardness is 58-62HRC. In order to facilitate machining and improve machining accuracy, they are designed as a combination structure. The convex mold is used as the reference part to match the concave mold. After assembly, it is necessary to ensure that the double-sided punching gap is 0.01mm and the gap is uniform.
(2) The selection of the inclination angle between the wedge and slider should consider two aspects: the pressure of the press and the stroke of the punch. While ensuring the stroke of the punch, the required pressure of the press should be minimized as much as possible. Balancing two factors here, the inclination angle is taken as 30 °.
(3) The wedge and slider, as well as the slider and slide, are prone to wear and tear, and the surface should be coated with lubricating oil during operation. The material and heat treatment requirements require high wear resistance, with material W18Cr4V and a heat treatment hardness of 60-63HRC. After working for a period of time, there will be some wear and tear on the mold. By increasing the vertical stroke of the mold and modifying the size of the limit piece, normal operation can be restored.
(4) To ensure precision punching, a toothed edge pressing ring is used during punching. The edge pressing ring not only has the function of pressing the edge, but also guides the convex mold, enhancing its stiffness. After the punching is completed, the edge pressing ring acts as a discharge plate to smoothly remove the workpiece from the convex mold, preventing deformation of the workpiece.
(5) In order to ensure the smooth discharge of waste, when designing rubber, attention should be paid to the compression force of rubber 19 on the pressure plate after compression, which should be greater than the compression force of spline rubber 25. To achieve the effect of precision punching, it is necessary to wait for the spline rubber to be compressed and press the blank from the concave mold before starting the punching process.
Therefore, it is necessary to strictly control the relationship between the distance of upper and lower mold movement and the horizontal sliding distance of the slider.
4. Conclusion
Punching the side groove of the outer hub frame of a linear bearing is a difficult point in the stamping process of the outer hub frame of a linear bearing. In order to ensure uniform distribution of circumferential side grooves and meet the quality requirements of the punching section for performance. This article designs a set of molds that use a wedge slider mechanism to simultaneously laterally punch uniformly distributed side grooves, and adopts precision punching technology. Practice has proven that this set of molds has high punching efficiency, fully meets the quality requirements of the parts, has stable performance, and reduces the production cycle and cost of the linear bearing outer hub frame. It has now begun to promote production. The mold designed in this article has a certain reference value for the forming of similar parts.
2024 March 1st Week VAFEM Product Recommendation:
A linear-motion bearing or linear slide is a bearing designed to provide free motion in one direction. There are many different types of linear motion bearings. Motorized linear slides such as machine slides, X-Y tables, roller tables and some dovetail slides are bearings moved by drive mechanisms. Not all linear slides are motorized, and non-motorized dovetail slides, ball bearing slides and roller slides provide low-friction linear movement for equipment powered by inertia or by hand. All linear slides provide linear motion based on bearings, whether they are ball bearings, dovetail bearings, linear roller bearings, magnetic or fluid bearings. X-Y tables, linear stages, machine slides and other advanced slides use linear motion bearings to provide movement along both X and Y multiple axis.
2024-03-02