The Mucosa Problem of Aluminum Plate Stamping
In order to realize vehicle lightweight, more and more automobile factories (OEMs) begin to stamp body stamping parts with 5000 and 6000 series aluminium sheets.
The typical drawing depth of the inner plate is generally 100 to 200 mm. The traditional oil lubricated aluminium sheet is difficult to pull in the material outside the die because of the galling problem of drawing time, and the cracking problem of stamping parts is serious. The sticking die also causes ugly stretch marks on the surface of the workpiece. In order to manufacture large quantities of stamping parts for aluminum sheet body, GALLING must be solved.
The sticking problem occurs at the interface between sheet metal and die, and the surface of both sides can be improved. In the aspect of sheet metal, surface texture treatment can be carried out to improve the surface morphology, so as to achieve the purpose of oil reservoir on the surface of the sheet. For example, shot peening, electric spark, laser and other methods are used to roughen the surface of finishing roll. Before entering the coiler, the surface of the sheet is like a fingerprint, leaving numerous pits. For stamping process, these pits are countless oil storage pools. The mystery here is that when the surface of the sheet with "micro-hemp shape" slides on the die, more lubricants can follow into the deformation zone; the greater the contact pressure in the deformation zone, the more lubricants will be extruded from the Micro-storage tank. If the surface of finishing roll is not micro-coarsened, or the micro-peaks and micro-pits on the textured surface are grinded after a long time, the oil carrying capacity decreases. When lubricating oil is needed to reduce friction after entering the deformation zone, no oil is available, and viscous die problems may occur.
Another method of reservoir oil on the plate surface is phosphating. After phosphating treatment on the surface of galvanized sheet, the zinc phosphate conversion film on the outer layer is like a porous and seamless sponge under the microscope, which makes the lubricant have many hiding places. When lubricating oil is needed, it can be extruded by higher contact pressure in the deformation zone.
It is also a good way to pre-coat dry lubricant on the surface of aluminium sheet. The so-called dry lubrication (DRY LUBE) is a high viscosity lubricant applied on the front roll of rolled sheet, which is waxy at room temperature. Dry lubricant is really a good thing. It can effectively isolate the contact between sheet metal and die surface, greatly reduce friction. People like it in tube drawing. Dry lubricant also has shortcomings, it has poor fluidity, lubricant is not easy to run to the side of punching trimming die, the side of the die is not protected by oil film, shear debris is easy to accumulate and bond on the top, causing the side of trimming die roughening problem (GALLING). The original aluminum sheet shallow drawing using lubricating oil, there is no problem, each blanking, the splash on the point of lubricating oil is enough to moisten the side of the punch. To solve the GALLING problem, the side of the punching and trimming die must be polished, and the PVD coating treatment must be carried out.
Recently, the trimming dies used many newly developed high hardness and high finish PVD coatings from North America's two die coating companies, which can effectively prevent GALLING problems on the side of the dies. After several years of semi-industrial experiments, OEM on our North American side can now say with confidence that it has found a way to prevent friction and wear on the surface of the sheet-die during mass production of stamping parts for aluminium sheet cars.