Mold Textures and CNC Milling(medical injection molding Marina)

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  • source:CLAREY CNC Machining
Computer numerical control (CNC) milling has revolutionized the process of creating molds used for casting and molding parts. The ability to precisely machine complex geometries with tight tolerances has enabled molds with intricate details and surface finishes that were previously difficult or impossible to achieve manually. One area where CNC milling shines is in replicating realistic textures on mold surfaces.
When a liquid material is cast into a mold, it picks up every small detail of the mold's surface. Things like bumps, grooves, pores, grains and other irregularities get imprinted onto the cast part. These surface features are collectively referred to as the mold's "texture."
Realistic surface textures are important for aesthetic reasons in products like jewelry, toys, sculptures and decor items. But texture is also functional - it can help with grip, improve wear resistance, facilitate lubrication and more. CNC milling provides unparalleled control over mold textures.
There are several techniques for adding texture during CNC milling:
Direct Engraving - The required texture can be engraved directly into the mold material using small end mills. Things like text, logos, patterns and general roughening can be added. The scale and depth of textures is limited by the size of tooling available.
EDM Texturing - Electrical Discharge Machining (EDM) uses controlled electrical discharges to erode material. By scanning the EDM head over the mold surface, intricate textures with undercuts can be produced.
Chemical Texturing - Etching the mold material with acids/chemicals produces a rough surface. The chemical attack can be modified to create distinct patterns.
Laser Texturing - Powerful laser beams can be used to melt, ablate and alter mold surfaces to impart texture. Non-contact processing allows for accuracy.
Media Blasting - Fine abrasive media directed at high pressures onto mold surfaces imparts controlled roughness. Media selection and blasting parameters determine the resulting finish.
Plasma Texturing - Energized gases rapidly etch the mold material in the desired texture pattern. Contains undercuts and high detail.
Photochemical Machining - Using photoresists, masks and chemical etchants, very precise and complex textures can be produced through a process similar to PCB manufacturing.
Each of these techniques has its pros and cons. EDM and Plasma texturing allow the most detailed control of texture geometry, while laser and chemical texturing excel at tuning surface roughness. Photochemical machining produces the most consistent results for intricate high resolution patterns. And media blasting is most suitable for overall roughening or adding randomized textures.
The CNC machining process itself can also be adjusted to inherently produce textured surfaces on mold cavities:
Optimized Tool Paths - Tool paths can be programmed to leave behind a rough surface finish, depending on factors like path overlap, stepover distance and climb vs conventional milling.
Specialized Tooling - Using extra-coarse diamond engraving tools or PVD-coated end mills with special fluting designed to leave faint tool marks.
Mold Vibration - Introducing controlled vibrations in the mold during machining can cause the cutting tool to leave behind a textured trail.
Adjusting Parameters - Higher feed rates and lower spindle speeds will result in coarser surface finishes. Low pressure and flow when coolant drilling also increases surface roughness.
Post-Processing Operations - Additional light manual polishing, media blasting or chemical etching can be performed after CNC machining to further enhance texture.
The most realistic mold textures often use a combination of techniques. CNC machining might first produce the overall mold cavity shape along with any larger engraved textures. Then the mold gets transferred to a secondary process like EDM or laser texturing to add finer details. Or a primary roughing routine is followed by optimized finishing toolpaths.
Advanced CAM software makes programming even highly complex texturing strategies for CNC machining very intuitive. The texturing mode allows you to "draw" textures directly on the CAD model. These are then converted into toolpaths using specialized algorithms. Additional options like texture libraries, manipulation tools and simulation allow for unparalleled control.
When designing textures for CNC milled molds, considerations include:
- Purpose - Is the texture functional, cosmetic or both? This affects the geometry and scale.
- Material - The mold material (tool steel, aluminum, etc) will impact the feasible methods for adding texture.
- Release - More intricate textures can cause ejection difficulties and require draft angles or coatings.
- Accuracy - Very precise textures require stable fixturing and vibration dampening during machining.
- Cost - Less tool wear generally occurs with smoother finishes, affecting machining time and tooling expenses.
With the right CNC equipment, CAM software and approach - realistic surface textures that fully replicate the design intent can be machined into molds. The finished cast or molded parts exhibit all the minute details in a repeatable and cost-effective process. Whether for ergonomics, aesthetics or functional performance - CNC's texture control truly empowers mold designers. CNC Milling