1. Design and production of fixtures
1.1 Features of the fixture: The fixture for anodizing after processing aluminum parts is completely different from the hanger for electroplating. It is not suitable to use an hanger with a hook-like hook as an anodizing fixture because the fixture is anodized. An oxide film is formed on the surface of the workpiece very quickly. During this process, the clamp and the workpiece are slightly loose, which will change the position of the contact and impede the flow of current. For this reason, the workpiece must be clamped by a flexible clamp. Only in this way can the anodization process proceed normally.
1.2 Structure of the fixture: The fixture structure is suitable for individual type. If the assembly type is used, the riveting or welding will loosen due to corrosion after several times of use, which hinders the normal circulation of current during the anodization process. At the same time, the fixture must have a certain cross-sectional area. The clamp of a certain section also has sufficient elastic force and clamping force to keep the workpiece and the clamp in good contact, and to ensure the normal flow of the current required when the workpiece is anodized. Avoid burning the workpiece due to poor heat generated by contact.
1.3 Selection of fixture materials: It is better to make fixtures to choose hard aluminum, and the rigid aluminum has good elasticity and is fast and durable.
2. Fixing of the workpiece
2.1 Cleaning the film to the fixture: The film is also produced by the fixture during the anodization process. For this reason, the used film must be removed before reuse. The film peeling can be carried out in an aluminum degreasing solution. The oxide film at the contact point between the fixture and the workpiece can also be removed with a file. This method can extend the life of the fixture for some fixtures.
2.2 Selection of clamping position: The position of the clamping workpiece should be properly selected. The aluminum alloy processing factory should generally be clamped on the secondary side of the workpiece (ie, the non-decorative part). Otherwise, the contact portion between the workpiece and the jig cannot be formed into an oxide film due to being covered by the jig, and of course, the color cannot be dyed, and obvious white spots are formed here, which affects the appearance quality. In addition, problems such as the occurrence of gas in the concave portion suspended in the solution after the workpiece is clamped should also be considered.
2.3 to prevent deformation of the workpiece clamping: the fixture is not the same as the hanger, the clip has a certain elasticity. Special care should be taken when clamping deformed workpieces. Excessive force should be avoided to cause deformation of the workpiece.
2.4 Preventing the clamping from being loose: When the workpiece is loosely clamped, the current between the clamp and the workpiece will be interrupted by time, in which case the workpiece is likely to be burnt.
2.5 One-by-one clamping of the anodized parts to be dyed: Some units are anodized after some small parts are wrapped with screen cloth or otherwise wrapped. Although this method can save man-hours and improve efficiency under certain circumstances, it can only be used for some anodized materials with low quality requirements. Even if a small amount of workpieces cannot form an oxide film at the mutual covering, it is not easy to be recognized. However, for workpieces that need to be black, it is obviously not advisable to use such a clamping method. Must be clamped one by one to ensure the quality of the anodization.
3. Control of anodizing process conditions for precision aluminum alloy parts processing
3.1 The relationship between the temperature and the voltage of the solution: the lower the temperature of the solution within the rated range, the higher the required voltage should be, because the film is formed at a slower rate when the solution temperature is lower, and the film layer is denser, in order to obtain a certain thickness. The oxide film needs to increase the voltage during the anodization process. When the temperature of the solution is high, the dissolution rate of the oxide film is increased, and the generated oxide film is loose, and at this time, the voltage can be appropriately improved to improve the quality of the oxide film.
3.2 Temperature vs. time of the anodizing solution: The lower the temperature of the solution, the longer the required anodization time should be. The formation speed of the oxide film is slow because the solution temperature is low. When the temperature of the solution rises, the rate of formation of the oxide film increases. At this time, the anodization time should be shortened. Otherwise, the film layer is dissolved due to the increase in the outer resistance of the oxide film, and the phenomenon of the change in the size of the workpiece and the roughening of the surface are caused.