Mold Textures in CNC Machining for Improved Part Performance(does anodized aluminum wear off Betsy)
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- source:DAHLER CNC Machining
Surface Finish
One of the main goals of mold texturing is to impart a smooth surface finish on the molded parts. The mold surface is either polished, grained, or textured depending on the desired appearance.
Polished mold surfaces reproduce glossy, reflective finishes. CNC polishing is done using progressively finer grit compounds or abrasive brushes. The polished mold steel acts like a mirror to produce plastic parts with a high-luster finish. This is useful for cosmetic parts.
Graining adds uniform shallow lines or dots to roughen the mold surface. This diffuses reflected light to give a matte or low-gloss finish. Different graining patterns like horizontal, vertical, or cross-hatch can be specified. CNC engraving or chemical etching creates the grain texture. Parts molded in grained molds have a soft, scratch-resistant finish.
Texturing imparts deeper macro textures like peaks/valleys. Textures are generated through EDM, CNC engraving, photochemical etching, or laser ablation. Parts replicated from textured molds have unique visual effects ranging from satin, stone, wood grain, leather, etc. Texturing also helps hide weld lines on parts.
Reduced Friction and Wear
The mold texture pattern has a significant effect on the friction and release of the part from the mold. Smooth, polished surfaces can cause molded parts to stick to the mold, resulting in ejection failures. This can prematurely wear down the mold steel over repeated cycling.
By contrast, textured surfaces reduce contact area between the mold and part. This decreases adhesion forces for easier release. Texturing gives the air a defined path to ingress between mold and part to facilitate demolding. Some common anti-stick textures are diamond patterns, pyramids, rounds, hexagons, mesh, etc. applied over the entire cavity surface.
Texturing also acts as a lubrication reservoir that helps reduce abrasive friction. The texture grooves retain and channel lubricants like mold release agents. This forms a fluid cushion layer between mold and part. Random matte textures are especially good at holding lubrication. Reduced friction allows easier part ejection with less wear on the mold over time.
Demolding and Mold Protection
Certain mold texture patterns cater specifically to demolding requirements of parts with complex geometries and deep undercuts. These textures strategically create release channels to aid air venting and part ejection.
For example, molded internal undercuts require side actions and stripper plates to mechanically eject the part. Long shallow lines textured along these slide planes minimize contact and friction during demolding. Dimple textures applied near rigid edges act as stress raisers that compress to eject rather than tear when demolding flexible parts.
Dense uniform textures on areas prone to flash help reduce molded material penetration into the mold. This eases cleanup and prevents damage to the mold surface. Heavy texturing on the parting line weakens adhesion to limit mold sealing and flash generation. Strategic texturing preserves the delicate mold details and improves longevity over extended production cycles.
Enhanced Replication of Details
Molded parts need to accurately reproduce the design intent of the mold. Fine mold details and textures are easily filled by liquid polymer during injection molding. But as the polymer solidifies, it tends to shrink and pull away from the mold surface.
Shrinkage causes molded parts to lose resolution and become amorphous. Parts may lack sharp definition, edges, and textures intended on the mold. This is especially noticeable on micro-features.
By optimizing surface roughness, mold textures can enhance replication fidelity. Texturing creates anchoring profiles for the polymer to mechanically lock into during solidification. This prevents shrinkage related pull-back from mold surfaces. Maintaining intimate contact ensures high-definition reproduction of even the finest mold details on the molded part.
Summary
Mold surface texturing is a highly effective technique in CNC machining for improving the molding process and performance of finished parts.
Different textures patterns can be machined on the mold cavity to control surface finish, reduce friction, facilitate demolding, minimize wear, and replicate finer details from the mold onto the parts. CNC processes like polishing, engraving, EDM, etching, etc. unlock diverse texturing possibilities based on application requirements.
Considering mold texturing early during CNC programming and incorporating the right surface textures based on part geometry, material, and functionality can lead to highly repeatable, efficient, and robust injection molding production. CNC Milling CNC Machining