Mold Textures and Finishes Achievable with CNC Machining(galvanneal Leonard)
- source:FANYA CNC Machining
With CNC, very intricate textures with tight tolerances can be machined right into the steel mold surface. This eliminates the need for time-consuming hand polishing or secondary EDM texturing operations. CNC machined textures also tend to have longer tool life compared to perishable tape or Mytex film type texturing.
Here are some of the main mold cavity textures and finishes that can be created with CNC machining:
Satin or Brushed Finishes
Satin or brushed finishes exhibit fine parallel lines running in one direction across the mold surface, imparting a soft glow and smooth feel to the finished plastic part. These finishes hide fingerprints and minor scratches well. Brushed finishes are created on a CNC machine using a special abrasive brush tool rotated at high speeds. By varying the brush pressure, rotation speed, and feed rate, different depths of brushed finish can be achieved, from very fine velvet-like textures to deeper grainy finishes.
Leatherette finishes aim to simulate the look and feel of natural leather. This is achieved by machining a texture of small peaks and valleys into the mold surface. Typical leatherette textures have a roughness ranging from 0.5 to 2 microns. On a CNC machine, a ball end mill is used to machine interlacing circular tool paths at high stepovers to clear out the valleys. The untouched peaks remain, creating the simulated leather grain effect. Deeper valleys result in more pronounced grain patterns.
Diamond Turned Finishes
Diamond turned finishes have a high luster sheen similar to a finely polished mirror surface. They are achieved by using a single point diamond cutting tool on the CNC machine under very fine finishing parameters. The diamond tool forms minimal peaks and valleys - just a few nanometers high - that reflect light evenly to produce the brilliant shine. Diamond turning is used for molds that require perfect optical clarity such as reflectors, lenses, and light covers.
Gloss textures have a pattern embossed into the mold that interacts with the plastic resin to create areas of both high gloss and low gloss contrast. The gloss effect is dependent on the plastic material used. Gloss texturing requires a ball end mill on the CNC to machine smooth peaks and valleys into the mold surface. The smoothness is key - any sharp edges or tool marks will not generate the proper gloss effect. Gloss texturing takes some trial and error to refine based on the chosen plastic.
A matte texture finish scatters reflected light to achieve a low gloss, non-shiny surface. Mate finishes reduce glare and hide fingerprints. Common matte textures made using CNC machining include sandblast type finishes and orange peel finishes. Sandblast textures use aggressive machining parameters to create macro-level roughness and irregularity. Orange peel finishes take a more controlled approach, using tight tool stepovers to generate uniform peaks and valleys resulting in the characteristic orange peel stippling effect.
Custom Logos and Graphics
Using CNC machining, custom logos, text, symbols, and graphics can be embossed or engraved into the mold surface. This allows the design to be physically reproduced onto every production part. CAD/CAM software makes it easy to program unique geometries and contours for machining. Logos and text can be recessed below the main mold surface or protrude above it depending on the effect desired.
Combining Multiple Textures
With CNC machining, multiple textures and finishes can be combined on a single mold to create truly unique designs. For example, a logo or graphic can be enclosed within a brushed rectangle border. Or a plate can have a gloss textured surface while the border is diamond turned. The CAD/CAM programming software allows different areas to have different toolpaths applied. This allows seamless integration of multiple textures tailored to each surface and feature on the mold.
Benefits of CNC Textures vs Manual Techniques
Compared to manual polishing and texturing methods, CNC machining offers several key benefits for mold textures:
- Accuracy and Consistency - CNC machines ensure each mold cavity has identical, repeatable textures and finishes. There are no significant variances with hand polishing.
- Complex Geometries - CNC machines can create textured surfaces on complex freeform shapes and micro-features not possible by hand.
- Speed - Textures are machined much faster compared to manual polishing and texturing which reduces mold production time.
- Durability - CNC machined textures maintain their integrity over longer mold lifespans whereas hand polished finishes degrade after repeated injection cycles.
- Design Flexibility - A wide range of textures can be tested and iterated on easily by modifying the CNC toolpaths. Manual rework is minimized.
When designing injection molds, leverage CNC machining to create unique mold textures and finishes to give plastic parts enhanced aesthetic qualities and durability. CNC expands the possibilities beyond standard hand polishing methods for bringing ideas to reality. CNC Milling CNC Machining