On the one hand, broaching reduces the stability and production efficiency of the production process, and increases the scrap rate of parts. On the other hand, it will cause more serious wear and tear of the die, reduce the life of the die and the precision of the stamping parts, increase the number of die repair and production shutdown time.
The essence of brushing is due to the local adhesion (occlusion) between the workpiece and the die surface. There are many ways to improve the problem of broaching. Its basic principle is to change the nature of friction pair between die and processed parts, so that the friction pair is replaced by non-sticky materials.
After the die enters the stage of debugging at the production site, there are generally the following ways to improve the problem of grooming:
1. Change the die material and increase the hardness of the die.
2. Surface treatment of die, such as hard chromium plating, PVD and TD, etc.
3. Coating nano-coating on die cavity, such as RNT technology, etc.
4. Adding a layer of other substances between the die and the processed parts to separate the processed parts from the die (such as lubricating or special lubricants or adding a layer of PVC, etc.).
5. Use self-lubricating coated steel plate.
As for die materials, die steels SKD11 and CR12MOV are generally recognized as wear-resistant and anti-occlusion materials. After heat treatment, the hardness can reach HRC58-63 degrees. When the die is small and the shape of the part is simple, this kind of material can be used. However, after heat treatment, the material is difficult to process, brittle, fragile, costly, limited in size, and the deformation of this kind of material is large after heat treatment. The research and matching work after heat treatment is tremendous.
The shape of automobile inner panel is more complex and high strength steel plate is used more and more. This kind of part requires higher overall performance of the die. Mosaic structure is usually used. The surface treatment technology of the insert is TD, hard chromium plating, nitriding, PVD and so on.
TD process is short for thermal diffusion carbide cladding treatment. This technology was first developed and patented by Toyota Central Research Institute in 1970s. It is also called Toyota Diffusion Process, or TD Process for short. Our country is also called molten salt infiltration. Whatever its name, its principle is to place the workpiece in a molten borax mixture and form a metal carbide coating on the workpiece surface by high temperature diffusion.
The main characteristics of TD coating treatment are: high hardness, HV up to about 3000, high wear resistance, tensile resistance, corrosion resistance, etc. The service life of TD coating is about 100,000 sets.
However, the requirement of TD cladding treatment for die materials is very high, and the change of thermal stress, phase transformation stress and specific volume during high temperature treatment will make the die deform or crack easily in the heat treatment process. The repaired die will also crack at the weld seam. TD cladding treatment has a high requirement for the processing quality and shape of the die
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