What are the commonly used surface treatment methods in the fabrication of automotive sheet metal parts?

Sheet metal fabrication is the technology of fabrication metal sheets. It includes traditional cutting, blanking, bending and forming and other methods and process parameters, as well as various cold stamping die structures and process parameters, and various equipment work. Principles and manipulation methods, as well as some new stamping technologies and new processes. More and more sheet metal fabrication enterprises realize that proper surface treatment can play a good decorative and protective effect on the surface of the product, improve the “appearance” of the product, and then improve the market competitiveness.

There are two kinds of surface treatment methods commonly used in the fabrication of automobile sheet metal parts: electroplating and spraying. Electroplating is divided into zinc plating, nickel plating, chrome plating, etc. The main purpose is to use the principle of electrolysis to form a metal or alloy protective layer on the surface of the sheet metal workpiece to protect and decorate. Spraying is divided into spraying paint and powder spraying. After the material is pre-treated, the paint is dispersed into uniform and fine droplets with spray gun gas, and sprayed on the surface of the sheet metal workpiece to form a coating on the surface of the workpiece. , and then heat and dry. Spraying can protect the workpiece. In addition to the above two methods, there are some other surface treatment methods, such as anodizing, chromating, wire drawing, sandblasting and oxidation.

Precautions for surface treatment of sheet metal workpieces

• One: Pay attention to the state of the workpiece. All electrochemical treatment must be carried out under the loose part of the workpiece. The assembly feels that electrochemical treatment cannot be carried out. Because during the fabrication, the solution will be trapped in the crevices of the assembly and cause corrosion to the workpiece.
• Two: Pay attention to the fabrication sequence. For example, the parts that have been spot welded can be chemically treated, but they must not be electrochemically treated. Electrochemical treatments including electroplating and anodizing will affect the quality of spot welding. For some electroplated or oxidized parts that require riveting, the fabrication procedures must be followed by electroplating or oxidation first, and then riveting.
• Three: Pay attention to the pretreatment before surface treatment. For example, before the steel parts are sprayed, it is necessary to undergo phosphating treatment, which can increase the adhesion of the coating. In order to improve the corrosion resistance of steel parts plated with bright nickel and automotive stamping parts, a layer of copper or dark nickel can be plated first. Zinc-based alloys also have this problem. Before electroplating, they also need to be pre-plated with a layer of copper or dark nickel as a primer, which can improve the bonding force of the electroplating layer.
• Four: Pay attention to the fact that the workpiece material and the treatment method cannot conflict, and the aluminum alloy casting is never allowed to undergo sulfuric acid anodizing treatment.
• Five: Whether it is suitable for electrochemical fabrication should be judged according to the shape of the part. For example, slender tubes with a length greater than twice the diameter are not suitable for electrochemical fabrication, because a high-quality film cannot be formed on the inner surface; Or for parts with a depth greater than twice the diameter of the pores, the inner surface cannot be completely covered by the coating after plating.
• Six: Pay attention to whether there is a conflict between the base material and the coating material. Because most organic gases have a corrosive effect on zinc, the galvanized layer should be carefully selected in the design of sheet metal fabrication to be in contact with the organic material or assembled in the same airtight body.