Meaning
Custom holding devices secure molded plastic parts in a precise position to allow accurate drilling, tapping, or milling operations after the molding cycle. In high precision polymer manufacturing, secondary machining fixtures prevent part deflection and vibration during machining by supporting thin walls and complex geometries. These fixtures are often made of aluminum or polyurethane to avoid scratching the plastic surface.
They ensure that post-molding modifications achieve the required dimensional tolerances.
Fixture Design
The fixture must match the contour of the molded part to provide uniform support and prevent deformation under the forces of machining. Quick release clamps are used to speed up part loading and unloading. This reduces cycle time and improves operator efficiency.
Process Variables
Molded parts shrink as they cool, which means the fixture must be designed to accommodate the part’s dimension at the time of machining. If the parts are machined too soon after molding, they may still be warm and expand, which leads to incorrect dimensions. Fixture alignment must be checked regularly to prevent machining errors.
Quality Consequence
Inadequate holding can cause the part to slip, resulting in misaligned holes or surface defects. This leads to rejected parts and increased scrap costs. Utilizing robust fixtures is therefore critical for achieving high yields in secondary operations.
