Suppose a mold needs to produce parts immediately but it has a damaged texture. This can be an everyday occurrence within a molding facility, as lifters or pins break and hit the tool surface, causing rust to develop or unacceptable texture wear to appear. These situations call for an action plan to help get that mold back up and running. Here, we will review different degrees of mold damage, how texture is affected and proper repair options.

Texture Level Breakdown
Texture problems that occur during the run of a part generally are caused by a wear-related issue that may have developed over an extended period of time, or because a tool is damaged and can no longer produce acceptable parts. To properly approach both of these scenarios, an understanding of texture finish levels is necessary

Level one is the main texture pattern—the profiled details we see and feel. These can be a leather grain, stipple, wood grain or geometric pattern. They are the texture specifications on the part or tool prints, and they typically range from 0.0005 inch deep to 0.012 inch deep.

Level two is the micro-texture. This is applied over the main texture pattern and is typically sandblasted in the final step. There are many sizes and types of blast media, which are often mixed and blended to contribute to very specific gloss results on the part. These micro-textures have depths that range from 0.0001 inch deep to 0.0015 inch deep.

Texture Wear Resolution
Texture wear usually results from the molding material, an additive in the material or a gas from the material. It will first affect the micro-texture, causing the corners of these very fine, shallow profiles to become rounded. This may be noticed on the part as an increase in glossy appearance.

In most cases, micro-textures can be placed directly over the original texture; however, it is important to understand that every time a main texture is sandblasted, it has a wear effect. This means that there are limits to the amount of re-sandblasting a texture can withstand before it is worn down. Fragile textures and textures in soft tooling are especially vulnerable to sandblast damage.
There is a “point of no return” to texture wear, and once that line is crossed, the tool may need to have the texture polished out and re-grained. Therefore, it is important to have a texture expert evaluate specific sandblasting needs.

The main etched texture profile is affected next by wear. If rounded off by molding wear, these larger texture profiles will have a noticeable appearance flaw beyond that of a gloss differential. Some texture patterns (mostly restricted to sand-style textures) may be refurbished with an over-etch if the texture wear is not too extreme. However, once these sand textures become too round, refurbishment is not enough, and they will need to be polished out and re-textured to their original form. Most other texture pattern styles such as leather grains, geometric/technical patterns, wood grains, etc., may not be candidates for an etch refurbishment.

A part/tool review with a texture expert that includes customer expectations will help determine the best process for texture wear resolution.

Texture Damage and Repair Procedures
Texture damage is defined as an impact event on the textured tool surface that left a scar. The following methods (listed in order of effectiveness) are used for initial texture damage evaluation:

• Close-up photos of the damage.

• A molded part that shows the damage.

• A review of the damaged tool.

1. Scuff of the micro-texture. If the surface has received damage only to the micro-texture, then a re-gloss using the original sandblast media formula will remove the scuff and return the surface almost back to the original finish. The term “almost” is used to account for the wear that sandblasting can cause to an etched texture. This wear happens every time a texture is sandblasted or re-glossed, so it is a concern.

Most textures can be re-glossed at least once and still maintain 95 percent of the original profiles, as long as the technician is trained in the process. Overly aggressive sandblasting can and does damage textures.

2. Scrape of the etched texture. When the main etched grain is damaged, the repair will require acid etching to restore the original texture profiles. The area of repair may be prepped by stoning or polishing out the damage, followed by replacing the texture with etchants often engineered specifically for this application.

Many of today’s textures are achieved through multiple layers of etch applications. In the case of repairs, the layers will have to be reproduced. It is important to know the texture specification so that these layers can be reproduced as accurately as possible.

Some of the repair scenarios for damaged textures will require welding to replace the steel that was removed with the scrape or compression event. The tool’s exact steel type must be noted so the weld metallurgy matches as close as possible to the tool metallurgy. Tool steel manufacturers provide specific welding rod recommendations because differences in steel metallurgy will result in differences in texture profiles.

Weld hardness is another critical factor for successful repair. If the weld is too hard, the micro-texture finish will not match that of the parent steel. This will appear as a gloss differential on the part. Pre-heating the area to be welded and post-weld heating can help minimize this hardness.