Textures in surface plastic injection molds and patterns applied to plastic injection molded parts are becoming increasingly sophisticated and complex. These advances are exciting because they offer many new design options to product developers and engineers. But before a finished part can be manufactured, the injection molding tool must first be carefully fabricated.

In this post, we explain how we at Gestión de Compras apply textured surfaces in a controlled and repeatable way to get the results designers expect. Our company has more than 20 years of experience designing and manufacturing plastic injection molds, also with texturing.

Let’s take a look at the five most common methods.

Grinding and polishing

Rough machining leaves tool marks on the part. If left uncorrected, these marks are transferred to the product during molding and, of course, this is not desirable.

Therefore, grinding and polishing removes these marks and other small surface imperfections. This is done by skilled technicians using a variety of rotary tools, diamond burrs, sandpaper, files and other abrasives. The textures they can produce range from mirror-like surfaces to coarse grit or anything in between. Sanding requires skill and some degree of craftsmanship, but technicians cannot access deep cavities or very thin sections. In addition, they must be careful not to excessively alter the dimensional tolerances of the mold.

Spark erosion EDM

Spark erosion works on both hard and soft metals and can produce very tight tolerances. It is ideal for making fine, deep grooves, sharp concave corners, raised lettering and other features that would otherwise be difficult or impossible to machine conventionally. In addition, a very fine, smooth finish can be achieved, eliminating laborious and costly hand polishing.

In the old days, large EDM electrodes were used to apply a textured surface to molding tools, known as “sputter finishing,” but this technique has largely been replaced by chemical etching. All that remains is the name.

Shot blasting

High pressure air is used to spray various types of dry or wet abrasive media against the tool wall. For example, silica (sand), aluminum oxide, glass or plastic beads and even walnut shells. This is an excellent way to clean the tool while achieving a uniform matte or satin finish. The type of material used, as well as the air pressure, volume and spray pattern determine the final appearance.

Chemical Photo Etching

Many plastic parts are designed with sophisticated in-mold patterns and textures. Some mimic the look of stone, leather or wood grain, while others produce more abstract geometric designs. But how are these patterns applied to a molding tool? It is done by photo-etching.

First, the wall of the tool is coated with a photoresist substance, which is a light-sensitive chemical. The desired pattern is then projected onto the surface of the tool with an ultraviolet light, which hardens the areas that come into contact with the light. Remaining photoresist is washed away, leaving a film mask.

The mold is then placed in an acid bath that etches the unprotected areas, creating the desired texture. This process must be carefully controlled to take into account the type of base metal, the complexity of the design and the depth of surface penetration caused by the acid.

Etching is fast, cost-effective and can produce very fine textures to achieve almost any look. But it has some limitations. Etching does not work in undercuts or other areas where the optical line of sight is blocked.

Texturing plastic injection molds with laser engraving

Laser engraving makes it possible to reproduce almost any texture in plastic injection molds on any curved surface. The success of this process depends on the combination of two technologies.

The first is 3D computer modeling. This allows a designer to take a texture map and align it with the contours of almost any moldable shape, using sophisticated algorithms to maintain the geometry of the design.

The second technology is 5-axis motion control. This helps the laser accurately track surface topology while reaching undercuts and other areas that are not in line of sight.

Laser engraving is common in the automotive field, where larger shapes, such as a dashboard, need to have patterns that maintain their consistency over a long length. It is more expensive than other methods and takes time to create the necessary 3D CAD models, but for the most demanding applications it really is the best option.

Textures in plastic injection molds have a definite impact on cycle times, gate and runner locations, demolding angles, tool life, cost and many other factors.

Gestión de Compras is specialized in the design and development of plastic injection molds, with high quality and low production costs. We are at your disposal to develop an injection mold design strategy that takes into account your texture needs.