Guidelines for plastic part design
When designing plastic parts, there are several key guidelines to consider to ensure that the part is manufacturable, functional, and cost-effective. These guidelines span across material selection, part geometry, tooling, and production methods. Here’s an overview:
1. Material Selection
Consider material properties: Choose the material based on the required mechanical properties (e.g., strength, flexibility, temperature resistance, etc.). Common plastics include ABS, polypropylene (PP), polycarbonate (PC), and nylon.
Consider environmental factors: Is the part exposed to UV light, moisture, or extreme temperatures? Choose materials that can withstand these conditions.
Consider processing capabilities: Different plastics are suited for different processes like injection molding, blow molding, or extrusion.
2. Design for Manufacturability (DFM)
Minimize undercuts: Undercuts make molding more complex and can require specialized tooling. If they are necessary, consider using side actions, slides, or inserts.
Draft angles: Include draft angles (typically 1-3 degrees) on vertical walls to make part removal from the mold easier and reduce wear on the mold.
Uniform wall thickness: Aim for uniform wall thickness (typically between 1.5-4 mm) to avoid issues like warping, sink marks, or voids. If varying thicknesses are required, use fillets to ease transitions.
Ribs and gussets: Use ribs or gussets to add strength without increasing wall thickness. Ensure they are not too thick, as this can cause molding problems.
Avoid sharp corners: Use radii at corners and edges to improve moldability, prevent stress concentrations, and ensure uniform material flow during molding.
3. Tooling and Mold Considerations
Mold flow: Design the part so that the material flows evenly from the gate to all sections of the mold. Avoid sharp transitions and areas where material might pile up.
Gate location: Choose an appropriate gate location that minimizes cosmetic defects and ensures uniform material flow.
Parting lines: Ensure parting lines are placed strategically to avoid visible marks and reduce the need for extra finishing work.
Shrinkage allowance: Account for material shrinkage during cooling. Different plastics have different shrinkage rates, so ensure this is factored into the design.
4. Tolerance and Fit
Standard tolerances: Set realistic tolerances based on the plastic material and manufacturing process. Plastic parts typically have looser tolerances than metal parts due to the way plastics behave when cooled.
Assembly considerations: If the plastic part will be assembled with other parts (plastic or metal), ensure the design allows for easy assembly (snap fits, screw holes, or clips).
5. Surface Finish
Texture: Specify the surface texture (smooth, matte, or textured) based on the part’s function and aesthetics. Textures can also hide imperfections from molding.
Aesthetics: Consider the need for color, gloss, and other finishes, which can affect both the part’s function and the consumer’s perception.
6. Cost-Efficiency
Minimize complex geometry: Complex shapes may require more expensive molds and longer cycle times. Simplified geometries tend to reduce costs.
Optimize part count: If you can integrate multiple parts into a single molded piece (through snap fits or over-molding), this can reduce assembly costs and improve strength.
Consider material and cycle time costs: Lighter parts that use less material, and designs that reduce cycle time, can lower production costs.
7. Sustainability
Material recyclability: Consider using recycled materials or designing for easy disassembly if the part needs to be recycled.
Design for minimal waste: Optimize part design to reduce scrap and waste during manufacturing.
By following these guidelines, you can optimize plastic part design for functionality, manufacturability, and cost-effectiveness.