Before shipping off to the client, all the die cast parts undergo a series of processes. While die casting, the metal molds or dies are preheated and coated in a die release agent before the molten metal is injected. However, the casted components need to undergo numerous coatings, finishes, painting, and polishing before shipping. This process ensures that the finished parts meet the necessary cosmetic requirements, protect against corrosion, and improve its wear resistance. Carrying out this finishes is always in accordance with the die design.
The preparation of the surface requires considering the functional design features of the part. The areas of the part such as the edges may often need special polishing, shave trim, chromate coating, and painting. The geometry of design of specific part features largely influences the type and quality of the final finish. By carrying out small-scale modifications of crucial surfaces and edges, the costs can be reduced along with lesser surface preparation before the final coat is applied.
Aluminum, zinc, and magnesium die castings are subjected to about three of the post casting finishing steps. This is carried out depending on the durability, cosmetic appearance, and protection of the part. Some of the post finishing steps carried out are mentioned below.
Post-Trim Deburring – Several vibratory processes are done to round sharp edges, smoothen surfaces, eliminate burrs, and to release flash and debris. Mechanical deburring is done in most of the die castings before they are subjected to post-trim finishing.
Surface Conversion Coating – Conversion coating is an important post-casting finishing step that will fully remove any oil, die cast part release agents, and other contaminants remaining on the surface. Conversion coating is carried out as a preparatory process, as it can act as a primer when the part is intended to undergo final painting.
Combined Conversion Coatings – Combined conversion coatings are applied when a die cast component requires a specific function such as corrosion resistance, durability, and enhancements in its cosmetic appearance. It can be used as a replacement for surface conversion coating, as it can also serve as a paint base or the final finish.
Final Cosmetic Surface Finish – A final painting or plating of the die cast components is carried out for cosmetic purposes. Maintaining this appearance, a final applied finish will help in increasing the corrosion resistance, as well as boost heat dissipation for improved insulation properties and surface performance.
Powder coating, liquid paint polyurethane, and water-based finishes are some of the final finished applied. An important part of cosmetic surface finish is component masking that ensures that the areas that do not receive finish coating remain protected.
Painting – Painting is done by either powder or liquid. Non-solvent based powder coatings have the advantage of being non-toxic, which enable safe waste disposal, thus being environmentally friendly. It provides uniformity in the surface finish, provides durability, and is available in several surface textures such as from matte to semi-gloss.
The most common final color finishes used for die casting components are polyurethane and other wet paint chemistries. Compared to powder coating, the production costs and lead times are much lower when liquid paints are used in the process.