The features of your final part should determine the kind of surface finishes you require on a mold. So, you must put sufficient time and effort into the mold-making process to get the right surface finishes for your final parts. Without the right surface finishes, your plastic parts won’t feel correct or function properly.

To create perfectly finished plastic parts, you must select the right types of surface finishes. What surface finish types and standards will yield the best results? Let’s explore.

Pick the Right SPI Standard

Wondering which molds are right for your injection molding project? The Society of Plastics Industry (SPI) sets standards for all plastic industries in North America (now known as the Plastics Industry Association).

Use their pre-defined standards to determine the aesthetic qualities of the plastic materials you use. You have four different categories of SPI grades to choose from –

  • Shiny Finish – If your plastic product needs to be shiny and reflective (e.g., an optical part), your product will need an extremely hardened steel mold. These types of molds are typically made of steel.
  • Semi-Gloss Finish – Plastic products with semi-gloss surface finishes are also made using hard, steel molds. Manufacturers polish these molds with sandpaper to provide semi-gloss finishes. Plastic parts with high-grade semi-gloss finishes rarely show any molding-related defects.
  • Matte Finish – Matte finishes are very popular in the plastics manufacturing industry. These finishes don’t show any signs of machining or tool defects. 
  • Textured Finish – The textured finish grade is ideal for parts that need to have smudge-free features. Glass beads, dry pasts, and advanced molders are used to give the parts textured finishes.

Speak to your design engineers to guarantee you know what types of textures you need for the parts you’re manufacturing. Use this chart to determine what type of mold is ideal for your job at hand. Using mold grades to assess the right mold type is vital for achieving quality and cost objectives.

Pick the Right Technique

Your parts can have the best possible surface finishes right off your Computer Numerical Control mill (CNC). Make sure to select the right cutting techniques. Use adaptive constant scallop-height toolpath planning algorithms to overcome poor-precision issues. Keep these details in mind before running your Computer-Aided Manufacturing (CAM) system to create molds.

Choose the Right Materials for the Project

Different materials have different chemical structures. Hence, they all have slight but notable effects on the surface finish. To get the desired surface finishes, you must choose the right materials. Assess details like the material’s heating point, flexibility, etc., before selecting materials.

Discuss these details with your design and engineering team. There are some additives that can enhance the quality of your surface finish. But, always avoid using too many additives as they’re quite expensive. The goal should be getting the perfect surface finish right off the CNC mill.

Create Well-Defined Tool Libraries for Your CAM

Manufacturers must always know the geometries of their tools. More importantly, their CAM systems must know the specific geometries of their tools. Or else, they won’t understand how different mold geometries relate to different toolpaths.

The best way to ensure your CAM system always knows the specific geometries of your tools is by setting up proper tool libraries. With the right CAM tool libraries, you can outsource much of the heavy lifting to your software tools.

By creating well-defined tool libraries, manufacturers can eliminate manufacturing errors and produce at faster rates.

Machine Maintenance

To achieve the best possible surface finishes for mold making, the CNC machines or CNC stepper motor you use need to be up to the mark. They should function like well-oiled machines. Without regular cleaning or maintenance, small clippings can get into their systems. The ball screws, motors, etc., may start vibrating and kill decent surface finishes.

You must also set up the CNC machine on a solid, strong surface. It’s the only way to eliminate vibration risks. CNC machines on poor, non-rigid setups also tend to break faster. Any issues with the CNC machine will lead to shoddy surface finishes.

Injection Speed of the Material 

The injection speed of the material will also determine the quality of the surface finish. For example, for glossy finishes, fast injection speeds are required. Discuss these details with your design team.

Always have a clear strategy before launching your plastic injection molding process. If possible, partner with surface molding and finishing experts for expert guidance and assistance.

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