Mold Textures and CNC Machining(surface finish chart Philip)

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Mold textures play an important role in injection molded parts. The texture of a mold surface can significantly affect the look, feel, and performance of the final plastic part. With advances in CNC machining, mold makers now have more options and control over mold surface finishes.
What is Mold Texture?
Mold texture refers to the small deviations on the surface of a mold. It is the microscopic peaks and valleys that are imparted onto the plastic during the injection molding process. The texture gives plastic parts visual and tactile properties.
Smooth molds will produce glossy plastic with a slick feel. Rough molds create matte finishes and textured feels. The type of texture is important for both aesthetic and functional reasons.
Visual Effects of Texture
Mold texture gives plastic parts a distinctive visual look. Different textures can make parts look soft or hard, matte or glossy, metallic or plastic-like. Texture affects light reflection for a unique aesthetic.
For example, a smooth mold will make plastic look shiny and wet, while a textured mold can give it a matte, brushed metal appearance. Parts can be made to mimic surfaces like leather, stone, wood, and other materials through manipulated mold texture.
Textures can also help hide small defects like sink marks, ejector pin marks, and flow lines. The right texture makes these inevitable molding defects far less noticeable.
Functional Effects of Texture
Surface texture serves functional purposes as well. The right amount of roughness or smoothness improves grip and feel in hand. It affects slip resistance. Visual clarity and light diffusion are also controlled through surface finish.
Textures can be used to hide fingerprints and scratches that would otherwise mar glossy plastic surfaces. Or a smooth finish could be used to minimize dirt buildup compared to a textured surface. In applications where parts need to slide against each other, like in a snap fit, the right texture reduces friction.
How Mold Texture is Created
Mold texture starts with the machining process. The cutting tool forms peaks and valleys in the steel that match its own surface profile. For example, a smooth cutting tool edge will leave a smooth mold surface. A rough cutting edge or insert will leave a coarser finish.
Additional techniques can further enhance surface finishes:
- Polishing smoothes out rough peaks to create ultra-glossy surfaces. Mechanical, manual, and chemical polishing methods are used.
- Bead blasting roughens a surface by bombarding it with fine glass beads. The pressure and bead size affect resulting roughness.
- Etching and EDM textures the steel with sparking electrical discharges. The shape of the electrode determines the pattern.
- Laser texturing uses a focused laser beam to selectively ablate and rough up the metal. Complex patterns are possible.
- Media blasting peens the steel with fine abrasive particles at high pressures to deform the surface.
- Plating and coatings like PVD can impart decorative finishes.
CNC Machining for Optimized Mold Texture
CNC machining offers mold makers precise control over mold surface finishes. By selecting the right tools and dialing in optimal feeds and speeds, machining imparts a controlled texture directly into the steel. No secondary processes are needed.
This efficient single-step texturing is ideal for injection molds. Molders can match the tool surface finish to the requirements of a particular plastic part, whether for aesthetics, ergonomics, or functionality.
Benefits of CNC machining for textures:
- Achieve good surface finish in soft metals like aluminum, brass, copper. Harder tool steels allow even better finishes.
- Current ballnose cutters produce fine finishes, while textured inserts like vortex tools rough up the surface. More textured tool geometries are in development.
- Finer stepovers, higher spindle speeds, and slower feeds result in a smoother mold finish.
- Quick tool changes allow different areas of a mold to have unique finishes as needed. Hybrid machining combines roughing and finishing.
- Reduced hand polishing lowers labor costs compared to older manual texturing methods.
- Flexible and customizable texturing. Any pattern, roughness, or look can be dialed in.
With CNC's precision and efficiency, mold makers can create high quality textures tailored to each mold. Plastic parts benefit with better appearance, feel, and performance.
Common Texturing Methods for Injection Molds
Here is a brief overview of some texturing techniques commonly used in injection mold manufacturing:
- Milling/Machining - Using specialty cutters, milling imparts controlled texture directly into the mold steel. Texture is determined by tool selection, stepover, feeds/speeds, and machine parameters.
- Hand Polishing - Using abrasive compounds and buffers, polishers work the mold surface to remove peaks. Achieves smooth, glossy finishes but is labor intensive. Hybrid CNC reduces polishing.
- Media Blasting - Blasts the mold with small abrasive media at high pressures to deform the steel surface. Glass bead and aluminum oxide are often used. Good for matte finishes.
- Laser Texturing - Focused laser pulses selectively ablate the mold surface to create detailed peaks and valleys. Very controllable but requires special equipment.
- EDM Texturing - An electrical spark erodes craters into the mold surface. The shape of the electrode determines the resulting texture pattern. Good for geometric finishes.
- Etching - Chemicals or acids selectively corrode the mold surface to create microscopic valleys and peaks. Produces uniform matte textures.
- Plating/PVD - Thin metallic or ceramic coatings are applied to impart decorative finishes while smoothing the base mold texture. Provides a protective layer.
Any of these can be used alone or in combination to create the desired look, feel, and performance required. CNC machining complements all methods through hybrid toolpaths.
Examples of Textured Injection Molded Parts
Here are some examples of injection molded products that benefit from intentionally textured surfaces:
- Kitchen utensils - Matte finishes hide scratches while textured grips improve handling when wet.
- Cosmetics packaging - Soft touch textures give a quality feel and improve grip. Glossy accents make colors vibrant.
- Consumer electronics - Soft touch and matte finishes resist fingerprints on cases and controllers.
- Automotive interiors - Grained finishes mimic leather and reduce gloss on components. Textures match vehicle styling.
- Medical devices - Smooth, polished finishes allow easy cleaning and sterilization.
- Toys - Colorful finishes combine gloss and matte textures for tactile play value.
- Sporting goods - Soft touch grips reduce slippage from sweat while providing tactile grip.
- Household items - Matte textures hide scuffs on products used every day.
- Door handles and knobs - Textures improve grip for opening doors, drawers, and appliances.
With the rise of industrial design, even everyday plastic products now feature meticulously engineered textures that improve aesthetics and usability. CNC machined injection molds provide the level of finish control needed to consistently replicate plastic parts with unique textures.
Summary
Mold texture gives injection molded plastic parts distinct visual and tactile properties that improve aesthetics and function. CNC machining helps mold makers intentionally engineer bespoke surface finishes customized to each product’s requirements. With advanced tools and precise parameters, textures ranging from ultra-smooth to highly-roughened can be achieved efficiently across large production molds. Plastics benefit from finishes impossible through secondary processing alone. CNC texturing minimizes manual polishing for faster, higher quality, lower cost molds. CNC Milling