Introduction(die casting process Barret)

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Mold textures are an important consideration when designing molds for plastic injection molding using CNC machining. The texture of the mold cavity directly affects the look and feel of the final plastic part. Selecting the right mold texture requires understanding the different types of textures available and how they influence part quality. This article provides an overview of common mold textures and best practices for incorporating textures into molds produced with CNC machining.
Benefits of Mold Textures
Textured mold surfaces provide several benefits compared to polished surfaces. The key advantages include:
- Improved part release - Textures allow air to reach the plastic part surface, which assists with mold release after cooling. This prevents parts from sticking in the mold.
- Reduced ejection force - The reduction in contact area between the textured mold and part decreases the ejection force required. This protects fine features on the molded parts.
- Enhanced appearance - Textures impart aesthetically pleasing finishes to plastic parts, from soft touch finishes to grained leather effects. This removes the need for secondary finishing operations.
- Lower friction - Some textures like dimples reduce contact area, decreasing friction on sliding surfaces. This improves performance for moving part assemblies.
- Part strength - Certain textures allow plastic to flow into small features, improving mechanical interlocking. This increases part rigidity and strength.
Types of Mold Textures
There are many different mold texture patterns that can be added through CNC machining processes. Common options include:
- Satin finish - Parallel polishing lines create a smooth low-gloss finish similar to brushed metal.
- Mesh patterns - A grid of small pyramidal bumps or dimples is produced through chemical etching or EDM.
- Diamond patterns - Intersecting at angles, these geometric shapes have a sparkling appearance.
- Linen textures - Irregular wavy patterns mimic the look of natural fibers like linen.
- Leather grain - Embossing tools imprint realistic leather pores and grains into the mold.
- Pimple textures - Lots of small hemispherical bumps cover the mold surface evenly.
- Orange peel - A bumpy texture like the surface of an orange is produced. It scatters light evenly.
The size, density, and depth of the texture features determine the final appearance and feel. Finer dense patterns generally provide a smooth uniform finish, while heavier textures create a rough surface.
CNC Machining Textured Molds
There are several techniques available for machining mold textures with CNC equipment:
Milling - Ball end mills can imprint 3D textures through an additional roughing pass along the cavity surface. Textured end mills are available to create patterns in a single pass.
EDM - Graphite electrodes shaped with the negative texture profile are used to erode the pattern onto the mold through electrical discharges.
Laser etching - Lasers remove material in precise patterns to produce complex textures quickly with no tool wear.
Chemical etching - Masking certain areas and submerging the tool in an acid bath selectively etches away exposed surfaces.
Plasma texturing - Ionized gas bombards the mold surface to microscopically roughen it and create matte finishes.
Photochemical machining - Using photo masks and chemicals, this selectively removes material to produce textures.
The texturing method is selected based on the mold material, depth of texture required, cost, and availability of equipment. Harder textures to machine like leathers may use EDM, while general mattifying may apply plasma texturing.
Mold Texture Design Considerations
To successfully design and machine textured injection molds, engineers need to consider:
- Part geometry - Where textures are placed impacts mold filling and cooling. Textures can also act as stress concentrators.
- Draw direction - Long parallel textures should align with the direction plastic flows into the cavity. This prevents flow lines perpendicular to the texture.
- Venting - Adding vent channels prevents air entrapment behind textures that can cause burn marks.
- Draft angles - Increased draft assists release from deep textures. Draft is required perpendicular to long directional textures.
- Tool wear - Harder carbide tooling resists abrasive wear from textured milling. EDM eliminates tool wear.
- Gate location - The gate must introduce plastic directly into textured regions to prevent filling issues.
- Ejection system - Textures change release characteristics, so sufficient ejection force and stroke must be provided.
With careful design and tooling considerations, mold textures produced through CNC machining can make injection molded parts stand out with improved aesthetics, handling, and end-use performance.
Mold texturing enabled by CNC machining introduces limitless options for enhancing plastic parts with tailored visual effects and tactile properties. Matching the right texture pattern and machining technique to each mold region allows efficient injection molding with maximized benefits. Considering the impacts on tooling, plastic flow, cooling, and ejection during design allows functional high-quality textured parts to be consistently mass produced. With a thoughtful design approach, intricate textures take plastic parts to the next level. CNC Milling CNC Machining