Maintaining Tight Tolerances & Part-To-Part Repeatability
Michael Liang
Design,Mold design,Mold maker,Injection molding, Plastic injection,Mold solution,Rapid prototype,CNC,3D printing
In general, part-to-part consistency in complex plastic injection molding is a result of careful process control. Assuming a stable process, optimized tooling, and low shrink material, part-to-part accuracy can be very consistent, within ±0.001” for example, and can be held even tighter depending upon a number of variables:
- Part geometry
- Part size
- Feature locations
- Resin type & shrink rate
- Tool design
- Molding process control & machine repeatability
Applications demanding higher levels of accuracy and precision will involve an iterative tooling approach to “dial-in” critical features. Flow modeling is used to establish warp prediction, optimized gate locations, and cooling strategies, and complex injection molds are designed “steel safe,” with part features on the low end of the tolerance.
Once the mold is designed and constructed, a thorough trial is performed to establish and center the molding process window, and to collect data that will allow an understanding of process drift and stability. Armed with this information, decisions can then be made regarding tooling adjustments, such as:
- Removing (or adding) tool steel to center a critical feature in the tolerance zone
- Gate revisions
- Cooling adjustments
- Adding or revising over-flow features
- Vent adjustments
- Cavity geometry “falsifications” to address unpredictable warp or feature size
For each round of adjustments, another molding trial is performed and the results evaluated until the tooling features and molding processes produce acceptable results.
Given all of these complexities, it is obvious that successfully executing close tolerance, complex plastic injection molding is anything but trivial. However, with our knowledge, technical team, and integrated tooling and molding operations, we are uniquely equipped for the task, able to produce results where most others cannot. Contact me to discuss the tolerance requirements on your complex plastic injection molding project.