Mold Textures in CNC Manufacturing(color anodized aluminum Ryan)
- source:WEINBERG CNC Machining
Surface textures on molds can serve both aesthetic and functional purposes. On the aesthetic side, textures influence the visual appearance and tactile feel of molded components. Common mold textures include glossy, matte, soft touch, and metallic finishes. For functional purposes, mold surfaces can be textured to facilitate demolding, increase bond strength with the molded material, and induce favorable flow patterns.
With CNC machining, mold textures are produced through a combination of toolpath strategies, cutter selection, and post-processing methods. Here are some key techniques for generating different mold surface finishes using CNC equipment:
A polished, glossy look requires the mold surface to be exceptionally smooth. This is achieved through a fine finish pass with a ball end mill followed by extensive polishing. Typical polishing steps include coarse wet sanding, fine wet sanding, and then buffing with compounds from coarse to fine grit. The resulting mirror-like surface will impart a glossy aesthetic to molded parts.
For a smooth but low-sheen matte finish, a mold surface can be left with a finely machined ball end mill finish, then lightly bead blasted to knock down the gloss. Bead blasting uniformly abrades the surface using media like glass beads or ceramic particles. This scatters light to produce a consistent matte look without visible tool marks.
Soft Touch Finishes
Soft touch or rubberized coatings applied to molds will give plastic parts a soft, tactile feel. To prepare the surface for coating adhesion, a coarse tool like an engraving cutter can machine diagonal peaks and valleys into the steel. The textured profile provides mechanical bonding when the soft touch material is applied. These coatings contain rubber or silicone additives to flex and compress when handled.
Vapor deposition techniques allow molds to take on metallic aesthetic properties. Physical vapor deposition (PVD) sputters thin films of metals like titanium, chromium, or gold onto the mold surface at the atomic level. This creates an exceptionally smooth metallic look that gets imparted to the molded parts. PVD coatings also improve mold release.
For plastic parts that need a grippy surface for handling, the mold can be textured to create a non-slip finish. Using a tapered ball end mill, a regular pattern of small bumps or waffle-like pockets can be machined across the mold surface. This gets transferred to the parts as indentations that increase grip and friction.
Extremely fine mold surface textures at the micron level influence the flow of molten plastic. Parallel micro grooves allow air to escape and improve flow, while cross-hatched patterns induce turbulent flow that strengthens molded parts. Precision CNC machining with small end mills is required to produce these tiny details.
As an alternative to machining, laser texturing can also be used to create micro and nano-scale surface patterns on molds. This technique focuses a laser beam over the mold surface to melt and reflow steel in precise spots. By controlling beam settings and movements, delicate textures with details smaller than a machining tool can be produced.
Electrical discharge machining (EDM) uses controlled electrical sparks to erode mold steel. By using custom shaped electrodes, EDM can produce very accurate textures unattainable with standard CNC equipment. This specialized technique is ideal for detailed optical surfaces.
While mold texturing adds tangible surface features, polishing works to make surfaces exceptionally smooth by removing defects left behind by CNC machining. Polishing is necessary for glossy finishes and optical clarity. It also improves mold release. Multi-stage abrasive polishing with progressively finer grit combined with buffing produces polished mold surfaces.
Mold texturing takes advantage of the precision, versatility, and programmability of CNC equipment. By applying different toolpaths, cutters, and post-processing techniques, virtually any surface finish can be created on a mold to influence the appearance and functionality of molded parts. CNC’s consistency and repeatability ensures every production part has the same optimized mold texture. With experience and expertise, moldmakers can leverage CNC to deliver innovative solutions to customer surface finish requirements. CNC Milling