The Importance of Mold Texture in CNC Machining(prototype machining Octavia)
- source:DAHLER CNC Machining
In injection molding, extrusion, casting, and other manufacturing processes that involve molds, texture is an important attribute that influences flow of material into the mold, adhesion of the material to the mold, ease of part ejection, and surface finish of the finished parts. Molds with very smooth surfaces can cause problems such as inadequate material flow, sticking, and uneven part surfaces. Introducing strategic texture helps address these issues. Common texturing methods include abrasive blasting, etching, engraving, electrical discharge texturing (EDT), and electrochemical machining (ECM). CNC machining opens up additional approaches for producing controlled mold textures.
CNC allows mold texturing to be programmed just like other machining operations. So texture patterns and parameters can be precisely defined and executed. Texturing is often performed through specialized CNC toolpaths. For example, rastering contours back and forth across a mold surface with a spherical cutter creates a uniform texture of circular arcs. Or helical interpolation can generate a screw thread-like texture for improved material flow. The flexibility of CNC enables tailored textures optimized for particular materials and manufacturing conditions, which is difficult to achieve with traditional texturing approaches.
The main purposes and benefits of textured CNC machined molds include:
Better material flow - Textures allow gases to escape and give the material flow channels, which reduces imperfections in cast or molded parts. Steeper texture angles facilitate this material flow.
Reduced sticking - Mold textures minimize contact area between the mold and material, decreasing surface tension related adhesion forces during part ejection.
Lower friction - Rougher mold surfaces lower friction at the interface between the mold and material. This further improves mold release.
Increased dimensional precision - Textures can help compensate for shrinkage of materials as they cool inside the mold, allowing more accurate replication of mold dimensions.
Stronger bonding - Certain textures provide a mechanical anchoring effect that strengthens bonding between the molded material and mold surface. This is useful for materials like concrete.
Uniform cooling - Textures enhance thermal conductivity at the mold surface, improving cooling consistency and reducing residual stress in parts.
Aesthetic effects - Mold textures directly transfer to the surface appearance of finished parts. So texturing enables production of varied visual effects.
When employing CNC texturing for molds, recommended practices include:
- Match the texture pattern and scale to the molded material and part geometry to maximize flow and release benefits. Linear or convex shapes often work best.
- Maintain a certain level of roughness, but avoid textures too deep or pointed that could damage the mold or machining tools.
- Orient the texturing direction based on the material flow path through the mold. Textures should facilitate this flow.
- Keep textured areas consistent across mold segments. Variations can lead to irregular cooling and sticking.
- Apply release coatings designed for textured molds to further enhance non-stick properties if needed.
- Adjust cutter size and overlap for rastering toolpaths to control texture consistency.
- Utilize climb milling and moderate feeds/speeds to get cleaner textures. Conventional milling or overly fast machining can distort textures.
- Take light finishing passes to smooth any raised edges or artifacts left between textured areas.
Proper CNC machining strategies must also be adopted to generate high quality mold textures efficiently. The process introduces some unique considerations:
- Use smaller stepovers between toolpath passes to avoid excessive tool marks and grooves within textures. Stepovers should be under 30% of cutter diameter.
- Reduce axial and radial depths of cut compared to non-textured areas to avoid tool overload and deflection. Allow more passes at lighter depths of cut.
- Increase tool overlap between passes to minimize uncut remnants between toolpaths that disrupt intended textures. Overlap up to 50% may be helpful.
- Utilize extended reach cutters to eliminate or reduce need to change tools when transitioning between textured and non-textured areas.
- Choose tooling with specialized geometries and coatings designed for high feed rate machining. This enhances tool life in abrasive texturing operations.
- All holders and spindle interfaces must be in excellent condition for smooth running at the high speeds involved.
With the right CNC programming techniques and machine setup, outstanding mold textures can be consistently and rapidly produced to improve manufacturability. The optimized level of control over texturing offered by CNC machining delivers major advantages over more traditional texturing approaches when it comes to injection molds and other tooling. By considering the role of texture and adopting methods tailored to their specific application, manufacturers can gain significant benefits in product quality, productivity, and part cost. CNC Milling CNC Machining