When designing tools for injection molding there are many factors that encompass the effectiveness of the tool. Some of these include placement of injection points in respect to material flow, what type of gate to use, wall thickness, textures, and gripper bar design.
ISC’s approach to tooling is modular tooling. Modular tooling enables the use of a mold body with interchangeable loader bars, shut-offs, strain reliefs and gripper bars. Some benefits of modular tooling include:
- reduced tooling costs if an existing mold section exists
- saved tooling time which results in shorter turnaround times
- the ability to repair or remake a section of the tool rather than the entire tool if it gets damaged
When designing a tool for injection molding it's important to understand how material behaves during the molding process. Different materials have different melting points, durometers (hardness), shrinkage, drying specifications and other characteristics that are important to know when designing a tool. For example if you are pre-molding a large part with polypropylene you will have a lot of shrinkage which will cause sinks on the final mold.
Having the proper wall thickness is also crucial in tool designing, if the wall is too thin there will be "blow outs" which are caused when the pressure of the injected material pushes the inserted part against the wall cavity and leaves the internal part exposed.
The design of runners (channel that material flows into mold cavity) is crucial. Since material cools as it flows through the runner "cold slug" a reservoir for that material needs to be integrated into the runner to allow hot material to flow properly. Once it flows through the runner it goes through the gate or injection point. The gates can be designed in many ways such as fan which works best for very thin walled parts.
Once material is in the mold cavity its natural tendency to begin cooling, when designing the tool it important to understand how the material is going to flow and how to design it in such a way that material fills the entire cavity without having knit lines, sinks or other cosmetic flaws.
When molding parts you want to have consistency from beginning to end. Having tools with an effective design is a key element to making quality parts. To learn more about modular tooling visit www.iscengineering.com or speak direct to an engineer 909.203.1125.