1. Deformation characteristics of stainless steel sheet rolling
Magneto cover material is 1Crl8Ni9, material thickness is 0.2~0.3mm, is stainless steel sheet to roll. 1Crl8Ni9 is an austenitic stainless steel, which has the characteristics of endurance, hardness, viscosity and strong hardening during cold working. During the rolling process, with the increasing deformation degree of rolling, the austenitic structure inside the steel is constantly induced into martensite. This will bring great difficulty to change rolling forming.
The common defects of stainless steel sheet are wrinkles, scars, cracks and cracks.
2. The generation and correction of wrinkles
2.1 Flange wrinkles
When the plate passes through the die, the flange part is subjected to the action of both radial and tangential tensile stresses besides the blank holder force. When the tangential compressive stress is larger, plastic instability may occur in the flange part of the plate tangential bending, so that the flange part of the plate in the vertical direction slightly wavy, that is, the flange wrinkle. The cause of flange wrinkles is that the blank holder force is too small and the fillet radius of the die is not appropriate.
When the blank holder force is too small, the outer edge of the sheet will be because of the fillet direction on the same vertical compression force and radial tensile force and thickened when wrinkling, for stainless steel sheet to change the first is to add to change the rolling bar to remedy, the second is to adjust the size of the blank holder force. The blank holder force is 0.3~0.5MPa.
The size of die fillet radius directly affects the quality of rolling parts. Because it can affect the size of the internal stress of the sheet and the required blank holder force, the formation of wrinkles, the thinning of the sheet wall thickness and the number of rolling. The smaller the fillet radius is, the greater the internal stress of the sheet, the greater the blank holder force, and the more serious the wrinkles are. The larger the fillet radius is, the smaller the required blank holder force is, the less the compression part of the sheet decreases and the range of the compression force increases along the circumferential direction, and the larger the periphery of the flange wrinkles of the rolling parts. So should be carefully polished fillet, make its surface more smooth, help to prevent the generation of flange wrinkles.
2.2 Wall wrinkles
The wall wrinkles of stainless steel sheet are mainly caused by the flange wrinkles being rolled into the cylinder wall. The correction method is to properly adjust the rolling gap and give a tension in the direction perpendicular to the rolling direction.
3.1 Change rolling scar
Small slippage scars, called scratches, may occur when the rolling parts pass through the rounded corners of the die. Because the concave die fillet part is the plate to produce the largest deformation force, while the stainless steel plate deformation process in the viscosity is strong, so this defect will be more serious development. It will abrade products, affect products smooth, punch, concave die working surface will also appear abrade, pitting, dent, etc. In the actual production process, it can be overcome by chrome plating of punch, adjustment of rolling gap and use of appropriate lubricant.
3.2 Die scratch
Because the working surface of punch and concave die, the surface roughness of the rounded corner part is not up to the requirements, and the gap is not uniform because of the poor assembly of the die, the surface of the product often forms a bright spot, known as scratch. This defect can be solved by mold repair.
4 Crack and rupture
4.1 Bottom Blurt
In the process of changing rolling, the crack at the bottom of the product is a common defect, which can be prevented by increasing the radius of the convex and concave die fillet, reducing the wrinkle-proof blank holder force, strengthening lubrication and finishing the working surface of changing rolling die.
4.2 Bottom sag
When the rolling parts have not broken, but the material in contact with the punch corner is necked due to the rolling, and the bottom of the product is depressed due to the existence of residual stress after the completion of processing. The correction method is to adjust the radius of convex and concave die fillet, so that the sheet metal is in a reasonable stress state during the process of rolling.
5. Selection of lubricant
When choosing stainless steel lubricants, the following two points should be considered first:
(1) The lubricant should have a certain relative thermal stability, and still maintain good lubrication effect when the rolling is heated.
(2) When the temperature rises at the moment of rolling, the lubricant can still adhere to the surface of the blank and the die evenly, but not accumulate or form thick film.