Automotive stamping parts burr problem is a difficult problem faced by all related enterprises, some well-known tooling companies such as Toyota trimming burr one-time pass rate of about 90%, and most of domestic enterprises one-time pass rate of only 60-70%. The resulting rework not only limits the production efficiency but also increases the cost and reduces the competitiveness of enterprises. There are many reasons for burrs, such as process defects, unreasonable design, processing precision is not enough, assembly is not standardized, and the basic operation of the tool assembly is not standardized in these aspects of the factors are caused by burrs of the main reasons. Therefore, we will analyze the process design, structural design, CNC machining, tool assembly of all aspects of the main problems caused by burrs analysis is summarized, put forward improvement measures for your reference!
Tooling Process design
1,Defects:
①Currently trimming line, is back-calculated mainly by the Autoform, the overall trim line may be within tolerance, but the local position of the existence of microscopic uneven serrated shape, the difference between the highest and lowest is around 0.2mm, the processing error is large, and at the same time, after the completion of the assembly,if the polishing worker does not pay attention to the peaks will be thrown off easily resulting in a local gap is too large. On the other hand, the irregularity of the curve at the corner of the trimming line with sharp corners is one of the reasons caused the corner burr.
②The trimming blanking angle is also an important factor affecting the trimming burr. Process design due to poor product manufacturability, part trimming punching angle, obtuse trimming will be greater than 30 ° or acute trimming may be greater than 15 ° punching angle is too large or punching angle is too small will cause burr.
2, Improvements
①After the trim line back-calculation is completed, the tool designer combines with the product's key features and the shape of the product corners rounded corners for manual correction to ensure a smooth transition of the product, the corners as far as possible to ensure that it is a rounded curve (rounded corners should be more than R3 to ensure that can be processed), to avoid sharp corners.
②If the local trimming angle is out of the design specification due to poor product workmanship, a risk report should be made if the mold is not increased for better communication during acceptance.
Tooling structures design
1,Defects
①The ribbons are too long and the punch and die edge band design is too long and not according to the design specifications. This caused great difficulties in machining and tool assembly.
②The presence of lateral forces during trimming and the lack of reasonable measures designed to counteract them is also an important factor in the eventual inability to eliminate them completely.
2,Improvement
The length of the ribbons are designed and machined according to below diagram
CNC machining
1,Defects
①The gap clearance is too small or large will cause the burrs during in the tools assembly;
②Inadequate machining of empty cutter, increasing the workload of grinding vertical edge;
③The corners are not cleared properly this will be also easy to get in the burr happen later;
2,Improvement
①Differentiation of machining parameters and margins for different materials of trimming inserts;
②Increase in the number of inspection points after finishing should be reflected directly on the program sheet;
③Detection is not allowed to use the edge finder, you must use the percentage table, increase the authenticity of the self-test table assessment efforts
④Normal insert empty cutter machining is not in 100%, not allowed to turn the sequence
Tools assembly
1.Tooling assembly is one of the most important, due to this process produces burrs for many reasons, mainly for the followings:
①Reduce the procedures and unreasonable gap clearance are the most main reasons
②The edge of the blade is not perpendicular, the datum is not good, the clearance gap will become bigger to produce burrs after repeated stamping or changing machine tools.
③When assembling the trim edge block in the bottom, it is not clean with scraps, and the edge is not perpendicular after disassembling and reassembling, which will result in burrs.
④Positioning pin is not tight, the clearance is not reasonable after reassembly, it will cause burrs
⑤Hardness is not enough, repeated stamping will cause burrs
2, Improvement
①Different material thicknesses will use different clearance gaps.blanking size is based on the lower die size and the clearance gap is taken on the upper die; The punch size is based on the upper die,and the clearance gap is taken on the lower die
②The edge is made vertical and ligaments under 10mm can be cleared in order to reduce the workload
③We have to check carefully if the inserts are all clean before tooling assembly,and also need to check if there are any scraps in the hole of the screws.
④A random inspection for inserts and pins are necessary after finished. If one of them fails, a full 100% inspection need to be carried out and the responsible person is directly supervised to make corrections.
⑤The hardness check should be divided into process check and final check, process check is carried out after quenching, and the final check is carried out after the end of the product and trimming burr pass rate meets the requirements. Avoid insufficient hardness caused by the change of stop or change of burr. Trimming burr problem is not only a problem of the tool assembly, but the quality of the work of all departments is also very important. Need to pay attention to all departments must be taken seriously.
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