Just as a baker pours their batter into the right baking pan, a skilled machinist pours liquidized plastic into a mold that is in the shape of a part. This mold, typically known as tooling, is the key to the creation of a high-quality precision component.
After the heated material fills the pre-formed mold, it begins to harden as it cools. Then, the hardened plastic and the tool can separate, leaving a new part and a tool that is ready for re-filling.
Here are the essential parts of a tool:
- Cavity half. The cavity half is the side of the tool that is typically attached to the side of the molding machine. It does not move.
- Core half. The core half is the side of the tool that opens and closes with the molding machine against the cavity half. The core half opens when it is being removed from the tool.
- Cooling lines. Cooling lines are channels that help control the cooling of the plastic part.
- Ejector system. The ejector system includes pins on the core half of the tool that help to push the cooled part out of the tool after molding is complete.
- Runner. The runner is the flow path for the plastic resin that the press injects into the mold.
- Side actions. Side actions are the moving pieces within the cavity that allow for undercuts in the part.
Whether the job calls for an intricate or simple part, tooling determines the quality of the plastic injection molding process and the components created.
How are tools designed and made?
Since they are the foundation of the plastic molding process, tool design requires time, effort. And expertise. The suitable mold material is the first consideration. Most plastic injection molds are made of steel, aluminum, or alloys.
Here are factors that come into play when choosing the right material:
- Complexity of the component
- Application of the component
- Production volume of the tool
- Budget
Since steel can tolerate high temperatures and pressure, steel tooling can produce millions of plastic parts. On the other hand, aluminum tooling is less expensive to create but can only produce in the thousands of plastic parts.
Tooling for a plastic injection mold project also includes acquiring all the components and machinery needed for the job, including gauges, jigs, fixtures, and other equipment. The effort and efficiency of this process have much to do with the quality and the cost of the end part.
Plastic injection molding is customizable
Plastic molding tooling can produce molded parts that meet the unique requirements of each project. Tooling design begins with the prototype phase.
Low-volume prototype tools are created through 3D printing, machining, and cast urethane. With these prototype tools, machinists can troubleshoot the tooling design, reducing the chance for error in the manufacturing and assembly process – and saving time and expense — later.
For example, tool design engineers use flow analyses to optimize the mold, including finding the best locations for parting lines, gates, and ejection locations. Design engineers then collaborate with toolmakers in creating a tool sample.
This first tool is put through its paces to test its functions properly and produce the specified part. During this stage, modifications and mold texturing can occur. Once this stage is complete, the samples are sent to the contract manufacturer.
The next step is to place the new design on the production line. Here the tool is carefully observed and validated. After it passes this scrutiny, the mold enters a regular production schedule, where it is routinely monitored for wear and tear and any other issues that could affect part quality.
The process from prototype to production line can take months to complete, but each step creates more value in the long run. In fact, once the design and testing process is complete, the actual manufacturing process is automated and efficient.
What are some potential trouble spots in tooling?
Sophisticated components demand sophisticated tooling. The tooling process requires accurate monitoring for consistent, reliable part production.
In some cases, designers must add features such as
- undercuts
- threads
- rotational hydraulic motors
- hydraulic cylinders
- rotating mechanical racks or gears
- floating plates
- multi-form slides
Sensors placed on the surface of the tool can monitor the cooling rate and the cavity pressure profile. Tooling engineers also pay close attention to the following factors:
- the placement of lines to maximize the cooling process and minimize any warping
- the calculation of runner sizing specifications for the correct filling levels and low cycle times
- the best shut-off methods for tooling durability
- the optimum flow, fill pressure, cooling time, and tolerance
- the prevention of part defects and flawed appearances (flow marks, shrinkage, or warping)
Plastic injection tooling is part art and part science
As you can see, there is more that goes into the manufacture of precision molded parts than meets the eye. Plastic injection tooling is both a scientific and a creative process.
Think about it. Plastic injection molding involves the science of shooting hot, molten resin into the cavity of a mold. However, the design process is undertaken through a process of intuition, technique, and plain old trial and error.
The ultimate goal of this complex interaction is to create a high-quality precision part that is on time and on budget. If you have questions about plastic injection tooling and how it can work for your company, please contact us today.
At ASPM, we showcase our established history of quality tooling and molding by implementing our rigorous approach to plastic product development. We offer complete support from product design and feasibility, through routine injection mold maintenance and repair. Our highly trained staff is prepared to handle plastic projects with varying complexity in our robust 24-hour facility. Contact us today to discuss your next project.
