Mold Textures and How They Are Made with CNC Machining(cnc code Page)

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Mold textures play an important role in injection molding and other manufacturing processes. The texture of a mold cavity surface can dramatically affect the look, feel, and performance of molded parts. With computer numerical control (CNC) machining, intricate and precise mold textures can be created to achieve desired results.
What is Mold Texture?
Mold texture refers to the microscopic irregularities and patterns on the surface of a mold cavity. This is different from the overall geometry and design of the cavity. Texture is controlled by the small peaks, valleys, and variations left by the machining process used to create the mold.
The texture left behind by machining impacts how plastic flows into the mold, how much friction and shear stress is generated, how well the part releases from the mold, and the appearance of the final part. By controlling surface texture, manufacturers can fine-tune the molding process.
Common Mold Texturing Methods
There are various methods for texturing mold surfaces:
- Polishing - This smooths the surface using abrasive compounds. It reduces friction and improves release. A polished surface will result in glossy, smooth parts.
- Media Blasting - Blasting the surface with media like sand or glass beads creates a coarse, matte texture. This improves adhesion and allows gases to escape.
- Acid Etching - Chemical etching opens up the surface and creates texture at the microscopic level. It also smooths burrs and other artifacts.
- EDM Texturing - Electrical discharge machining (EDM) uses controlled electrical discharges to erode away material. By tuning the process, precise textures can be etched into the mold surface.
- Laser Texturing - Focused laser energy can also be used to selectively texture or etch the surface as needed.
- Tool Marks - The marks left by cutting tools like end mills will impart some natural texture based on tool feed rates and stepovers.
Advantages of CNC Texturing
CNC machining offers unique advantages for mold texturing. Unlike manual polishing or acid etching, CNC can create much more complex surface textures with tight control and repeatability.
Some benefits of CNC texturing include:
- Precision - CNC machines have excellent precision and can produce intricate textures to tight tolerances. Surface height variations and patterns can be accurately controlled.
- Flexibility - CNC allows textures to vary across the mold surface. Textures can transition gradually or change abruptly as needed by the part design.
- Speed - CNC texturing is fast compared to manual methods. A program can texture an entire cavity surface automatically.
- Consistency - Every mold cavity can have the same texture quickly applied by CNC. This improves quality and yields consistent parts from each cavity.
- Cost-Effectiveness - No manual labor or specialist technicians are required. CNC texturing has a lower overall cost compared to slower manual methods.
Popular CNC Texturing Techniques
There are several proven CNC techniques for creating useful mold surface textures:
Raster Milling
In raster milling, the cutter follows a high-density toolpath moving back and forth across the cavity surface like a raster pattern. This leaves uniform tool marks covering the surface. Parameters like stepover distance and cut depth control the roughness and frictional characteristics.
Helical Milling
Helical milling involves gradually spiraling the toolpath from the inside to outside of a circular area. This leaves circular swirl-like tool marks that help plastic flow smoothly and eliminate knit lines in parts.
Contour Milling
Contour milling traces complex patterns by having the tool follow user-defined curves and vectors. This can create textures that mimic orange peel, leather grain, brushed metal and various other organic patterns that would be impossible to do manually.
Tiny shapes can be engraved across a mold surface using a ball end mill. Different sizes and spacing of engraved textures can be programmed based on plastics flow analysis. The textures allow gases to vent and prevent defects.
EDM Texturing
As a form of EDM, controlled electrical discharges from the electrode to the mold surface vaporize material, leaving behind tiny craters and valleys for texture. Discharge power and duration are tuned to create desired pit size and density.
Laser Texturing
Focused laser energy can ablate away material in locations specified in the program file. Lasers alter surface chemistry and increase bonding. Widely spaced circular pits are often laser etched to aid plastic flow in molds.
Combining Multiple Textures
Mold makers will often combine different texturing methods in a single mold. Critical high wear areas might get a polished finish while main cavities are laser etched. Engraved venting textures might be added to problematic deep ribs or bosses. CNC makes combining textures efficient.
In summary, CNC opens up immense possibilities for imparting the ideal surface finish in molds to improve molded part quality, appearance, and performance. Today's CNC machines have the precision necessary to create micro-level textures tailored to each mold. This level of texturing automation and control is simply not possible using manual approaches. As CNC programming and 5-axis capabilities continue improving, so will the ability to leverage surface textures across the entire moldmaking workflow. CNC Milling