1 Characteristic of rolling deformation of stainless steel sheets
The material of the magneto shield is 1Crl8Ni9, the material thickness is 0.2~0.3mm, and it is a modified stainless steel sheet. 1Crl8Ni9 belongs to austenitic stainless steel, which has the characteristics of toughness, hardness, stickiness, and strong cold-work hardening. During the re-rolling process, as the degree of re-rolling deformation continues to increase, the austenite structure inside it is continuously induced into martensite. This will bring greater difficulties to the rolling forming process.
Common defects in re-rolled stainless steel sheets include wrinkles, scars, cracks, and breaks.
2 Causes and correction methods of wrinkles
2.1 Flange wrinkles
When the sheet material passes through the mold, the flange part is not only affected by the blank holder force but also is affected by radial tensile stress and tangential tensile stress. When the tangential compressive stress is large, plastic instability may occur in the flange part of the sheet, causing tangential bending, causing the flange part of the sheet to appear slightly wavy in the vertical direction, that is, flange wrinkling. The cause of flange wrinkles is that the blank holder force is too small and the die fillet radius is inappropriate. When the blank holder force is too small, the outer edge of the sheet will become thicker due to the compressive force and radial tensile force in the rounded direction and vertical direction. When the stainless steel sheet is re-rolled, the first is Rolling bars can be added to remedy the problem, and the second is to adjust the blank holder force. The blank holder force when the Bestar Steel shield is re-rolled is 0.3~0.5MPa. The size of the die fillet radius directly affects the quality of the rolled parts. Because it can affect the internal stress of the sheet and the required blank holder force, the formation of wrinkles, the thinning of the wall thickness of the sheet, and the number of re-rolling. The smaller the fillet radius, the greater the internal stress generated by the sheet metal, the greater the blank holder force, and the more serious the wrinkles of the rolled parts will be. The larger the fillet radius is, the smaller the required blank holder force is. The compressed part of the sheet is reduced and the range of the compression force in the circumferential direction is increased. The periphery of the flange wrinkles of the rolled part is larger. Therefore, the fillet should be carefully polished to make the surface smoother, which will help prevent the occurrence of flange wrinkles.
2.2 Wall wrinkles
The wall wrinkles of the stainless steel sheet re-rolled parts are mainly caused by the flange wrinkles being re-rolled to the barrel wall. The correction method is to appropriately adjust the re-rolling gap and at the same time give a tension in the direction perpendicular to the re-rolling direction.
3 scars
3.1 Repair scars
When the re-rolled parts pass through the rounded corners of the die, small slip marks, called scratches, may appear. Since the rounded corner of the die is where the maximum deformation force occurs in the sheet material, and the stainless steel sheet is highly viscous during the deformation process, this defect will become more serious as it develops. It will scratch the products and affect the smoothness of the products. Scratches, pitting, dents, etc. will also appear on the working surfaces of the punch and concave molds. In the actual production process, the problem can be overcome by chromium plating the punch, adjusting the rolling gap, and using appropriate lubricants.
3.2 Mold scratches
Because the surface roughness of the working surfaces and fillet parts of the punch and concave molds does not meet the requirements, and the gaps between the molds are uneven due to poor assembly, bright spots are often formed on the surface of the product, which is called scratches. This defect can be solved by mold modification.
4Cracks and breaks
4.1 Bottom take off
During the re-rolling process, cracking at the bottom of the product is a common defect. The ways to prevent it are to increase the corner radius of the convex and concave molds, reduce the anti-wrinkle blank holder force, strengthen lubrication, and finish the working surface of the re-rolled and concave dies. be prevented.
4.2 Bottom depression
When the re-rolled part has not yet cracked, the material in contact with the punch fillet will be necked due to re-rolling, and the bottom of the product will be dented due to the presence of residual stress after the processing is completed. The correction method is to adjust the fillet radius of the convex and concave molds so that the sheet metal is in a reasonable stress state during the rolling process.
5. Selection of lubricants
When selecting stainless steel lubricants, the following two points should first be considered: (1) The lubricant should have a certain relative thermal stability and still maintain a good lubrication effect when the rolling is heated. (2) When the temperature rises at the moment of rolling, the lubricant can still adhere uniformly to the surface of the blank and the mold without accumulating or forming a thick film.
Stainless steel can be re-rolled using re-rolling oil, emulsions containing high-concentration fillers, powdered graphite suspensions, etc. After long-term practical use, Bestar Steel has achieved good results by applying re-rolling oil to the re-rolled surface of the blank.
The rolling forming of stainless steel sheets is a relatively complex process. It is necessary to carefully study its forming characteristics and influencing factors, and explore and accumulate experience in the actual production process, to take corresponding measures to eliminate various defects and improve the quality of the products.
Post time: Jan-11-2024