CLOSING THE QUALITY GAP
The automotive industry’s need for textured parts has risen steadily over the past few years.In response to this need, the process of mold cavity texturing has evolved — rapidly.
In the past, the primary concern most mold makers had about texturing was, most likely, its ability to hide surface imperfections. Now, however, with exacting quality standards and process manufacturing philosophies becoming second nature, it has become clear that when preparing a mold to be textured, the entire process should be considered to ensure quality.
Midwest Mold and Texture serves some of the leading manufacturers of highly complex molds in the automotive,electronics and building materials industries.
According to Midwest Mold and Texture’s Rick Verkamp and Mervin Senters, Jr., knowing how surface finishesand texturing are associated can help mold shops better prepare mold cavities and, in turn, increase the quality of their textured molds.
Enhancing Part Value For The Customer
"Texturing enhances the value of a molded part cosmetically and functionally," says Verkamp,assistant general manager of Midwest Mold and Texture. "It gives a part a more attractive look and,in some cases, does actually help it withstand wear, hide scratches and provide an easy-to-grip surface depending on the intended use for the part."Texturing might also be applied on some areas of the mold core to possibly help solve ejection problems in the molding process.
"From a low glare, matte finish pattern to a more exotic, leather grain pattern, texture designs arelimitless," says Senters, supervisor of Midwest Mold and Texture’s texturing division. And with each pattern,various specifications must be met to achieve a quality texture.
"The texture must be applied evenly to a surface without any flaws," says Senters. "If you don’t begin the process with a good surface finish," he warns, "scratches from the polishing stone andsurface flaws will most likely appear through the textured finish."
Well-Prepped Surfaces Respond To Chemical Engraving
Mold texturing begins with the printing of a texture pattern on the mold cavity’s surface.This is done with photographic films. After this application, the mold cavity is treated withvarious chemicals to harden the texture pattern. Once the pattern is hardened, the surface ofthe steel is subjected to corrosive agents which produce a three-dimensional image design by etching the steel that is not protected by the hardened image.
"A smooth, uniform finish is important so the texture has an even depth, free of pocketsor other hills and valleys that will cause problems when creating parts with the mold," says Verkamp. "Generally, a 400 or higher grit paper better ensures that the surface finish will be adequate, and the surface will be uniform for application of the texture."
This is easier said than done when considering some of the more complex mold cavities."The cavity can hide some of the flaws due to its complex shape," says Senters.The mold cavity should be checked closely for any marks or flaws. If the cavity is outside a tolerance levelfor a specific texture, the texturing facility must contact the mold manufacturer and arrange a rework on thesurface finish — wasting valuable production time and money.
Specifications Greatly Impact the Process
The type of surface finish and texture applied to a mold can be impacted by the following variables:
* Materials - The type of steel, density and overall quality of all materials being used are equallyimportant when texturing. Even how the steel is machined must be taken into consideration as the heatgenerated by the machining process can affect texture quality by creating a deviation in the physical properties of the steel.
* Welding - When repairing a mold that will be textured, it is important that the welding rods arecompatible with the mold material. The quality of the weld itself will also impact quality.
* EDM - The recast layer created by most EDMs must be removed prior to texturing. Chemicalsused during texturing cannot penetrate an EDMed surface. This results in non EDMed surfacesbeing etched more than EDMed sections which creates a rougher surface on the mold.This may affect the cavity shape, hiding flaws. Polishing the cavity throughout ensures a true cavity shape for texturing that is free of any EDM.
* Texture - Keep in mind that each texture has different quality tolerances. More complex textures receive more chemical engraving as they are deeper than other, more shallow, textures such as a non-glare, matte finish for a computer monitor case. The pattern removes more material from the mold and, as a result, it may appear that the surface doesn’t necessarily need as fine a finish. However, moving from a complex leather texture to a lighter, simpler texture, the finish becomes even more important.
Some textures can be as shallow as a couple of microns. With such a low level of material removal,the surface finish must be of the highest quality to achieve a good texture. A more precise processis required for this texture than when creating a texture with a greater depth and a much higher material removal rate, like leather grain.
* Gloss - After the texture is applied, the type of gloss being applied to the cavity must be considered. Certain glosses show flaws more easily. Using a lower gloss over a higher gloss depends on several complex variables.
Performed incorrectly or not taken into consideration, these variables will impact the mold quality, showing deviation after the chemical etching process or, even worse, affecting the plastic.
Cutting Through the Confusion
With the seemingly endless amount of variables involved in texturing, Senters recommends workingwith your texturing facility for best results. "This interaction allows sharing of expertise," says Senters. "Together you can close the gap on certain variables and create a higher quality part."
Verkamp agrees. "It’s best to work with the texturing facility early in the process," he says."Understanding design objectives will enhance success of the total project."
Keep in mind the surface finish tolerance levels for each mold, adjusting based on texture: more tolerance for deeper textures and the least tolerance for light, shallow textures. The bottom line is that the texture is only as good as the mold cavity’s finish; there are very low tolerances for surface imperfections.
"If the surface finish has flaws before the texturing facility gets the mold, we can’t providethe highest quality texture," says Senters. The balance between production levels and qualityin a mold shop is always tight, but by considering the texturing process in advance,it becomes clear that an even higher quality mold can be realized.
About Midwest Mold and Texture Corporation:
This mold works and texturing facility brings a vast level of experience to their work. Located at the edge of the Clermont County Airport in Batavia Township, a suburb of Cincinnati, Ohio, Midwest Mold and Texture consists of two independent divisions. Combined activities of the Mold Division and the Texture Division involve building, modifying, repairing and texturing molds. The parent company of the Texture Division, Tanazawa Hakkosha, was established in the early 1900s, and is a pioneer and worldwide leader in the etching industry. Tanazawa Hakkosha is a developer of unique processes for producing textures. For more information, call 513.732.1300.