What are the common surface treatment methods in automobile sheet metal processing?

2021-02-02 15:51:16

Sheet metal processing is the technology of processing sheet metal. It includes not only the traditional cutting, blanking, bending and forming methods and process parameters, but also various cold stamping die structures and process parameters, various equipment working principles and operation methods, as well as some new stamping technologies and processes. More and more sheet metal processing enterprises realize that proper surface treatment can play a good role in decoration and protection of the product surface, improve the "appearance value" of the product, and then improve the market competitiveness.

There are two kinds of surface treatment methods commonly used in automobile sheet metal processing: electroplating and spraying. Electroplating is divided into zinc plating, nickel plating, chromium plating, etc. the main purpose is to form a metal or alloy protective layer on the surface of sheet metal workpiece by using the principle of electrolysis, so as to protect and decorate it. Spray painting is divided into spray painting and powder spraying. After the material is pretreated, spray gun gas is used to disperse the coating into uniform and fine droplets, which are sprayed on the surface of sheet metal workpiece to form coating on the surface of workpiece, and then heated and dried. Spraying can protect the workpiece. In addition to the above two methods, there are other surface treatment methods, such as anodization, chromate, wire drawing, sandblasting and oxidation.

Precautions for surface treatment of sheet metal parts

1： It should be noted that the state of the workpiece, all electrochemical treatment must be carried out in the bulk of the workpiece, assembly feel that electrochemical treatment can not be carried out. Because in the process of treatment, the solution will be trapped in the gap of the assembly and cause corrosion to the workpiece.

2： Attention should be paid to the processing sequence, such as the parts after spot welding can be treated by chemical treatment, but electrochemical treatment must not be carried out, including electroplating, anodizing and other electrochemical treatment will affect the quality of spot welding. For some electroplated or oxidized parts with riveting requirements, the processing procedure must follow the principle of electroplating or oxidation before riveting.

3： Attention should be paid to the pretreatment before surface treatment. For example, it is necessary to phosphatize the steel parts before spraying, so as to increase the adhesion of the coating. In order to improve the corrosion resistance of bright nickel plated steel parts and automobile stamping parts, a layer of copper or dark nickel can be plated as the base. Zinc based alloy also has this problem. Before electroplating, a layer of copper or dark nickel should be pre plated to improve the adhesion of the plating layer.

4： It should be noted that there should be no conflict between workpiece material and treatment method, and sulfuric acid anodizing is not allowed for aluminum alloy castings.

5： It should be judged whether it is suitable for electrochemical machining according to the shape of the parts. For example, it is not suitable to conduct electrochemical processing for the long and thin tubes with the length greater than twice the diameter, because the high-quality film can not be formed on the inner surface of the parts. For the parts with deep grooves or pores with the depth greater than twice the diameter, the inner surface can not be completely covered by the coating after electroplating.

6： We should also pay attention to whether there is a conflict between the substrate material and the coating material. Because most organic gases have a corrosive effect on zinc, we should carefully select the zinc coating to contact with the organic material or assemble it in the same sealed body in the design of sheet metal processing.