Anti-cracking method for hole flanging

Abstract

The invention discloses a hole flanging anti-cracking method, which relates to the technical field of metal workpiece processing, and comprises the following steps: step 1, a hole flanging position of a product is enlarged through a packaging process; step 2, through a back-upsetting process, back-upsetting the shape of the expanded convex hull to the shape size required by hole flanging; 3, punching operation is conducted on the plane subjected to pier returning; 4, burr pressing process treatment is conducted on the punched hole opening; and 5, hole flanging is conducted on the punched position. According to the method, the processes of packaging and upsetting are added before punching operation, the product is stretched to exceed the hole diameter required by hole flanging through packaging, the local stress of the material can be balanced, then the shape of the material is gradually changed through upsetting processing, the phenomenon of overlarge one-time deformation is avoided, the risk of cracking is reduced, and the production efficiency is improved. And the subsequent hole flanging operation can be more stable, and the effects of reducing the rejection rate, reducing the cost and improving the production efficiency are finally achieved.

Description

Technical Field

[0001] The invention relates to the technical field of metal workpiece processing, and in particular to a method for punching holes to prevent cracking. Background Art

[0002] Flanging is the process of turning the edge of a hole on a workpiece into a vertical edge, which is a type of flanging process.

[0003] The current hole-turning process usually includes three steps: punching, burr pressing and hole-turning. In this process, the punching operation will cause burrs on the edge of the hole. Although the subsequent burr pressing step can remove the burrs, the direct punching method will cause the edge of the hole to be subjected to a large local impact force, resulting in cracks on the edge of the hole. Finally, the workpiece will crack during the hole-turning process, especially when the workpiece material is thin or hard. The cracking phenomenon is more obvious during hole-turning, which not only leads to a high product scrap rate and increased production costs, but also reduces production efficiency. For this reason, we propose a method to prevent cracking during hole-turning. Summary of the invention

[0004] The purpose of the present invention is to provide a method for punching holes and preventing cracking, so as to solve the problems raised in the above background technology.

[0005] To achieve the above object, the present invention provides the following technical solution: a method for punching holes to prevent cracking, comprising the following steps:

[0006] Step 1: Enlarge the product hole position through packaging process;

[0007] Step 2: Through the back-piercing process, the enlarged convex shape is back-pierced to the shape size required for the hole turning;

[0008] Step 3: Punch holes on the plane after the pier is returned;

[0009] Step 4: Perform burr pressing process on the punching hole;

[0010] Step 5: Flip the holes at the punching positions.

[0011] Preferably, the size of the convex bulge produced by the packaging process in step 1 exceeds the size of the hole diameter required for the punching.

[0012] Preferably, in the re-piercing process of step 2, the re-piercing is performed by setting a protrusion on the lower die, and the upper surface of the protrusion is set to be smaller than the punching hole diameter, and the lower surface is set to be larger than the punching hole diameter.

[0013] Preferably, during the re-piercing process in step 2, lubricating grease is applied to the surface of the protrusion.

[0014] Preferably, in the back-stitching process of step 2, multiple progressive back-stitching steps are adopted, the deformation amount of each back-stitching is controlled within the plastic range of the material, and cooling time is left between each back-stitching process to gradually form the desired shape.

[0015] Preferably, the pressure of the punching operation in step 3 is 70%-90% of the yield strength of the material, and the punching speed needs to be less than 10 mm per second.

[0016] Preferably, the pressure of the burr pressing operation in step 4 needs to be less than 50% of the yield strength of the material, and the depth of each burr pressing operation needs to be less than 0.2 mm.

[0017] Preferably, before the punching operation in step 5, the workpiece needs to be inspected at the location where the hole is to be punched to check whether there are potential cracks and defects at the location where the hole is to be punched.

[0018] Preferably, the detailed steps of punching holes in step 5 include:

[0019] Step 5.1, preheating the workpiece;

[0020] Step 5.2, performing a hole turning operation on the preheated workpiece;

[0021] Step 5.3: Cool the workpiece.

[0022] Preferably, the temperature increase rate of the workpiece during preheating is controlled between 10 degrees Celsius and 20 degrees Celsius per minute, and the workpiece needs to continue to be heated after reaching the target temperature.

[0023] Technical effects and advantages of the present invention:

[0024] (1) The present invention utilizes the process of adding packaging and back-piercing before the punching operation. By first packaging the product to enlarge it and exceed the hole diameter required for punching, the local stress of the material can be balanced, and then the shape of the material is gradually changed through the back-piercing process, thereby avoiding the phenomenon of excessive deformation at one time, reducing the risk of cracking, and making the subsequent punching operation more stable, ultimately achieving the effect of reducing the scrap rate, reducing costs, and increasing production efficiency.

[0025] (2) The present invention utilizes a process of setting a protrusion on the lower die during the re-piercing process, so that the protrusion produces a chamfering effect on the workpiece after the re-piercing, so that when the workpiece is punched at the chamfered position, the edge transition of the hole is smoother, and there is no burr after punching. Then, after the burr pressing process, the punched section will be smoother.

[0026] (3) The present invention utilizes a method of preheating before punching and cooling after punching, so that the workpiece is softer during the punching process and can more easily withstand plastic deformation, thereby reducing the risk of cracking during the punching process. Then, by cooling, the stress inside the workpiece is effectively released, preventing cracks in the workpiece caused by uneven cooling, and further improving the punching quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of the process of the present invention. DETAILED DESCRIPTION

[0028] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] The present invention provides Figure 1 A method for punching holes to prevent cracking is shown, including the following steps:

[0030] Step 1: Enlarge the product hole position through packaging process;

[0031] Step 2: Through the back-piercing process, the enlarged convex shape is back-pierced to the shape size required for the hole turning;

[0032] Step 3: Punch holes on the plane after the pier is returned;

[0033] Step 4: Perform burr pressing process on the punching hole;

[0034] Step 5: Flip the holes at the punching positions.

[0035] Compared with the traditional punching method, the packing and back-piercing operations are added. The product is first packed to enlarge the hole diameter beyond the required hole diameter for punching, and the local stress of the material can be balanced. The back-piercing step gradually changes the shape of the material to avoid excessive deformation at one time and reduce the risk of cracking. Punching after the back-piercing can make the edge of the material smoother and avoid cracks and burrs caused by direct punching. The hole shape is gradually transitioned to the final shape by back-piercing first, which can avoid burrs and cracks caused by direct punching. The hole mouth quality of the punching after the back-piercing is improved, burrs are reduced, and subsequent burr processing is easier, avoiding stress concentration and cracks caused by burrs. In the back-piercing process, the thickness of the material is evenly distributed. The raised mold design of the back-piercing can control the deformation of the material, making the thickness of the material more uniform during punching, avoiding the risk of cracking due to weak parts of the material during the punching process. Through the gradual deformation process, especially the progressive deformation of the back-piercing, the shape change process of the material can be effectively controlled to reduce the risk of large one-time deformation, and each step of the process can be more precise. The process stability has been significantly improved by accurate control. Although the process flow is relatively complicated, the scrap rate caused by cracking, burrs and uneven deformation can be significantly reduced by the way of back-piercing and re-punching. The finely controlled processing technology improves the yield rate and reduces the cost of rework and scrapping, thereby improving the overall production efficiency. The process can adapt to more types of materials, including materials with higher hardness and greater brittleness. At the same time, since the shape of the material is gradually optimized during the back-piercing process, the hole turning of complex shapes can also be achieved more accurately, so that the process can handle more complex product design requirements; compared with direct punching, the main advantage of packaging, back-piercing and re-punching is that through the step-by-step processing process, the deformation and hole quality of the material can be more finely controlled, the risk of cracking can be significantly reduced, the generation of burrs can be reduced, and the stress distribution of the material can be improved, thereby improving the product quality, process stability and production efficiency. Although the process steps are relatively complicated, its significant effect in preventing cracking and improving the qualified rate makes it have important application value in production environments that require high quality and high stability.

[0036] Among them, the size of the convex bulge packaged in step 1 exceeds the size of the aperture required for punching. In order to reduce the shape and size of the workpiece during the punching process and minimize the risk of cracking and deformation, the size is first enlarged to ensure that the material has enough space for deformation during punching, so that the material can flow smoothly and avoid local excessive stress concentration. Enlarging the size can ensure that the force on the entire workpiece surface is more uniform during punching, which helps to reduce the risk of cracking. The packaging operation that exceeds the aperture can ensure that the workpiece can completely cover the mold gap and avoid irregular shape during the punching process. The material will be subjected to greater compressive stress during the punching process, especially during impact and shearing. If the material thickness is insufficient or the force is concentrated, it is easy to cause cracking or tearing. By enlarging the size first, the material has more space to adapt to the pressure and deformation of the mold, reducing the risk of local excessive stress. When the workpiece exceeds the aperture size before drilling, the pressure and stress distribution during drilling can be more uniform, avoiding excessive deformation of the workpiece due to insufficient size, thereby reducing the risk of cracking. During the drilling process, the material will deform to a certain extent due to force, especially in the part around the hole. By enlarging the product size first, it is ensured that the aperture size produced after drilling will not deviate from the original design size due to material shrinkage or uneven deformation. When the workpiece size is large, the material will produce a more uniform stress distribution when drilling, which helps to improve the dimensional accuracy of the hole and ensure that the aperture after drilling is consistent with the required aperture.

[0037] Among them, in the re-piercing process of step 2, the re-piercing is performed by setting a protrusion on the lower die, and the upper surface of the protrusion is set to be smaller than the punching hole diameter, and the lower surface is set to be larger than the punching hole diameter. By setting the protrusion in the re-piercing process, the chamfering effect of the protrusion after the workpiece is re-pierced is actually utilized. This design not only optimizes the re-piercing process, but also has a positive impact on subsequent punching, burr pressing and flanging processes. Specifically, the method of setting the protrusion is equivalent to chamfering the edge of the workpiece during the re-piercing process, thereby providing a better foundation for the subsequent punching process and burr removal process. This chamfering The chamfer can make the edge flow of the material smoother during punching, reducing the burrs caused by uneven force on the material. The chamfer formed after the back-piercing makes the edge transition of the hole smoother, thereby significantly reducing the generation of burrs. After setting the convexity and back-piercing, the edge of the hole has formed a smoother transition surface during punching, avoiding the sharp edges and irregular surfaces that may be generated after conventional punching. This makes the cross-section of the punching smoother and reduces the intensity of burr processing in the subsequent burr pressing process. The existence of the chamfer makes the material flow better during burr pressing and the edge of the workpiece is more Flat, burr removal becomes easier, the thickness and size of burrs are reduced, and the force required for pressing burrs is smaller, thereby improving production efficiency and process stability. Due to the chamfering effect brought by the back-piercing process, the shape of the hole edge becomes more uniform and regular, which is of great significance to the subsequent hole-turning process. When turning the hole, the edge of the workpiece is smoother, and the hole-turning die is more adaptable to the workpiece, which can reduce the risk of cracking and improve the stability of the hole. Chamfering helps the material flow more smoothly and reduces the possibility of cracks or deformation during hole turning. Especially in the processing of high-hardness materials or precision parts, the chamfering design can significantly reduce the risk of cracking caused by irregular force. The formation of chamfers makes the diameter and edge shape of the hole more standardized, the error during punching is effectively controlled, and the final size of the workpiece is more accurate. Due to the reduction of burrs after punching, the appearance quality of the workpiece is improved, the surface of the workpiece is smooth and neat, and the subsequent surface treatment work will be easier and more efficient. Due to the reduction of burrs, the processing difficulty and time of the burr-pressing process are greatly reduced. The chamfering of the workpiece after back-piercing forms a more ideal punching hole wall, reducing the workload of deburring.

[0038] Among them, during the back-stitching process in step 2, lubricating grease is applied to the raised surface. During the back-stitching process, friction will be generated when the material contacts the mold. Excessive friction will not only affect the forming effect, but may also cause damage to the material surface or wear of the mold. Adding a lubricating medium can significantly reduce the friction coefficient, reduce the direct contact friction between the material and the mold, and ensure a smoother back-stitching process. The lubricating grease forms a thin film on the mold surface, which effectively reduces the direct wear on the mold surface and extends the service life of the mold. This is especially important for back-stitching processes with high strength or high precision requirements, and can reduce the frequency of mold maintenance and replacement, and reduce production costs. During the back-stitching process, especially when the metal material is deformed to a large extent, the material may sometimes adhere to the mold surface, resulting in uneven forming, rough surface, and even defects (such as scratches, dents, etc.). The lubricating medium forms a lubricating film between the mold and the material, which can effectively prevent the material from sticking to the mold and ensure that the product surface is smooth and defect-free after back-stitching. Excessive friction may cause scratches, strains or excessive deformation on the material surface. Lubricating oil can effectively reduce this damage, especially for those with high surface quality requirements. Products (such as electronic component housings, automotive parts, etc.), lubrication can improve processing accuracy and the appearance quality of finished products. During the back-stitching process, due to friction, the temperature at the contact point between the mold and the material may rise. High temperature will not only affect the plasticity of the material, resulting in unstable forming, but also accelerate the wear of the mold. The lubricating medium can play a certain cooling role, reduce the heat accumulation caused by friction, and help keep the temperature of the mold and material within the ideal range during the back-stitching process. Proper lubrication helps to reduce the surface temperature of the material, enhance the plasticity of the material, and reduce the cracking or other defects of the material caused by overheating. Especially when there is a large deformation during the back-stitching process, the role of lubrication in temperature control is particularly important. The lubricating film formed by lubricating grease can effectively reduce the direct contact between the mold surface and the material, and reduce the wear caused by friction, which helps to extend the service life of the mold and reduce the maintenance and replacement costs caused by frequent wear. For high-strength and high-precision molds, lubrication can significantly improve the durability of the mold. Due to the improved lubrication effect, the mold has a longer service life, resulting in a reduced maintenance frequency, reducing the probability of production interruption, and thus improving production efficiency and stability.

[0039] Among them, in the back-piercing process of step 2, multiple progressive back-piercing steps are adopted, and the deformation of each back-piercing is controlled within the plastic range of the material, and cooling time is left between each back-piercing process to gradually form the desired shape. A one-time large-scale back-piercing may cause excessive stress in local areas and cause cracks or rupture risks. Through multiple progressive back-piercing, the small deformation applied each time ensures a more uniform stress distribution, avoids stress concentration caused by excessive deformation, and reduces the risk of cracking and deformation. Different parts of the material may have different stress tolerances. Excessive single deformation may cause excessive stretching in certain areas, causing failure. Progressive back-piercing can apply force in steps to avoid excessive deformation in a certain area. The force is applied to ensure that the shape of the entire workpiece changes gradually. The deformation amount each time is controlled within the plastic range of the material, which can ensure that the workpiece will not exceed the yield limit or rupture point of the material during the back-piercing process, avoiding brittle fracture or cracks in the material. Each step is within the tolerable deformation range of the material, so that the material can smoothly pass through each deformation. Multiple progressive back-piercings only perform small deformations each time, which can more finely control the forming process and avoid uncontrollable problems caused by excessive deformation at one time. Through multiple progressive deformations, the pressure and deformation amount applied each time are small, and the workpiece can gradually adapt to the shape of the mold during the forming process, avoiding problems such as uneven deformation, uneven shrinkage or fracture that may occur during large deformation, greatly A single deformation of a certain degree can easily lead to plastic fatigue of the material and affect the subsequent performance of the workpiece. The progressive piercing can effectively avoid fatigue of the material during processing by gradually applying stress and maintain good mechanical properties. Multiple progressive piercings can help to accurately control each step of deformation so that the workpiece can gradually reach the expected shape and avoid irregular shape or exceeding the tolerance range caused by a single deformation, thereby improving the forming accuracy. Due to the small deformation amount, each step of deformation is smoother, which can reduce the risk of cracks, burrs or wrinkles on the surface. In this way, the surface quality of the workpiece is effectively guaranteed and the workload of subsequent processing is reduced. A large one-time deformation is easily affected by material properties, mold errors or improper operation. When the influence of the material is too great, resulting in unqualified processing, the use of multiple progressive back-piercing can better control the processing process, reduce errors caused by excessive or uneven deformation, and improve the stability of the overall process. This multiple progressive process can not only adapt to the characteristics of different materials, but also obtain relatively stable results under different process conditions. It has strong adaptability and is particularly suitable for workpieces with complex shapes or difficult-to-process materials. Large single deformation usually causes greater impact and wear on the mold, especially on materials with higher hardness. Through multiple progressive back-piercing, the burden of the mold gradually increases, which can reduce the impact force during a single large deformation, reduce the wear of the mold and tools, and extend the service life.

[0040] Among them, the pressure of the punching operation in step 3 is 70%-90% of the yield strength of the material, which can ensure that the deformation of the material during the punching process is moderate and avoid excessive plastic deformation or damage of the material due to excessive pressure. Excessive punching pressure may cause the material to locally exceed the yield strength and produce cracks or cracks. The punching speed needs to be less than 10 mm per second. The appropriate punching speed helps to reduce impact and thermal effects and avoid excessive instantaneous stress during the punching process. This helps to uniformly deform the material and reduce the risk of cracks caused by stress concentration. Controlling the punching speed can ensure a smooth deformation process and help reduce the occurrence of cracks.

[0041] Among them, the pressure of the burr pressing operation in step 4 needs to be less than 50% of the yield strength of the material, which can avoid over-pressing the material and prevent cracks, tears or breaks during the burr pressing process. Excessive burr pressing pressure may cause material rupture and affect the quality of the workpiece, and the depth of each burr pressing must be less than 0.2 mm, which helps to gradually complete the burr trimming and avoid irregular deformation or cracks on the workpiece surface caused by excessive pressing at one time. Small-scale burr pressing allows the workpiece surface to have a smooth transition and reduce burrs or rough surfaces. Each small-scale trimming can ensure the stability of the surface quality and reduce the occurrence of surface defects.

[0042] Among them, before the drilling operation in step 5, the workpiece needs to be inspected at the location to be drilled to check whether there are potential cracks and defects at the location to be drilled, so as to avoid waste of workpieces and delaying processing efficiency.

[0043] The detailed steps of punching holes in step 5 include:

[0044] Step 5.1, preheating the workpiece;

[0045] Step 5.2, performing a hole turning operation on the preheated workpiece;

[0046] Step 5.3: Cool the workpiece.

[0047] Among them, the temperature increase rate of the workpiece during preheating is controlled between 10 degrees Celsius and 20 degrees Celsius per minute. After the workpiece reaches the target temperature, it needs to continue to be heated. The workpiece is preheated before punching and cooled after punching, which makes it softer and more easily able to withstand plastic deformation during the punching process, reducing the risk of cracking during the punching process. The stress inside the workpiece is effectively released by cooling, preventing cracks caused by uneven cooling of the workpiece, and further improving the quality of punching.

[0048] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preventing cracking by punching holes, characterized in that: The following steps are involved: Step 1: Enlarge the product hole position through packaging process; Step 2: Through the back-piercing process, the enlarged convex shape is back-pierced to the shape size required for the hole turning; Step 3: Punch holes on the plane after the pier is returned; Step 4: Perform burr pressing process on the punching hole; Step 5: Flip the holes at the punching positions.

2. A method for preventing cracking by punching holes according to claim 1, characterized in that: The size of the convex hull produced by the packaging process in step 1 exceeds the size of the hole diameter required for the punching.

3. A method for preventing cracking by punching holes according to claim 1, characterized in that: In the re-piercing process of step 2, the re-piercing is performed by setting a protrusion on the lower die, and the upper surface of the protrusion is set to be smaller than the punching hole diameter, and the lower surface is set to be larger than the punching hole diameter.

4. A method for preventing cracking by punching holes according to claim 3, characterized in that: During the re-piercing process in step 2, lubricating grease is applied to the raised surface.

5. A method for punching holes to prevent cracking according to claim 1, characterized in that: During the back-stitching process of step 2, multiple progressive back-stitching steps are adopted, the deformation amount of each back-stitching is controlled within the plastic range of the material, and cooling time is reserved between each back-stitching process to gradually form the desired shape.

6. A method for punching holes to prevent cracking according to claim 1, characterized in that: The pressure of the punching operation in step 3 is 70%-90% of the yield strength of the material, and the punching speed needs to be less than 10 mm per second.

7. A method for preventing cracking by punching holes according to claim 1, characterized in that: The pressure of the burr pressing operation in step 4 must be less than 50% of the yield strength of the material, and the depth of each burr pressing must be less than 0.2 mm.

8. The method for preventing cracking by punching holes according to claim 1, characterized in that: Before the punching operation in step 5, the workpiece needs to be inspected at the location to be punched to check whether there are potential cracks and defects at the location to be punched.

9. A method for preventing cracking by punching holes according to claim 1, characterized in that: The detailed steps of punching holes in step 5 include: Step 5.1, preheating the workpiece; Step 5.2, performing a hole turning operation on the preheated workpiece; Step 5.3: Cool the workpiece.

10. A method for punching holes to prevent cracking according to claim 9, characterized in that: The temperature increase rate of the workpiece during preheating is controlled between 10 degrees Celsius and 20 degrees Celsius per minute, and the workpiece needs to continue to be heated after reaching the target temperature.

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