Not taking the time to properly determine shrink rate can have a big impact on the quality of an injection molded part's geometry, performance, and appearance.
To facilitate this calculation, materials suppliers typically provide shrink rate numbers based on ASTM Standard D955 and a .125-inch thick plaque with a specific gating size and location. Although a good place to start, this value is usually not accurate enough for many products, especially critical, highly complex parts.
Almost any reasonable design looks good on paper or even as a prototype, but that doesn’t mean it’s a sure thing when it comes to manufacturing it. On the other hand, using Design for Manufacturability (DfM) to improve part design, injection molding processes and material selection ensures a product or component can be manufactured in a streamlined, efficient, validated, and repeatable way — saving time and money.
Cooling is one of the most critical parts of the injection molding process. Not only is it the longest part of the process — taking up more than 80 percent of the cycle time — but it's not smart to cut corners when it comes to cooling. In order to achieve precise, tight tolerances, the cooling rate must be carefully controlled — not rushed to completion.
There is more than one way to produce an effective plastic injection-molded part. The question is: is complex tool design the answer or is it better to utilize machining technologies to complete the task?
Tooling is arguably the most important part of the entire injection molding process. Not only does the tool need to be perfect to ensure all design specifications are met, but it’s also one of the most expensive, time-consuming fixes if something isn’t right—especially if you’re working with a third-party toolmaker. Working with an outside toolmaker for projects requires a lot of back and forth communication, leaving room for misinterpretations and sometimes delayed responses.
Injection molding is a dynamic, complex process that, simply by the nature of its many variables, requires some testing and adjustments to get it just right before you can start production. Some manufacturers, however, choose to focus on completing the the mold first and then build the process around the finalized mold, thinking this saves time and money. However, this approach typically results in production problems that slow the whole process down, and reduces quality and repeatability.
Success in the injection molding business isn’t just about having the right equipment or the latest technologies. This is a good start, of course—but to completely meet the ever-evolving needs of clients who make complex products under challenging time and cost constraints, injection molders must have top tool makers in their supply chains that embrace the same vision of manufacturing excellence and customer service. Core to this philosophy is that tool makers must treat the injection molders’ clients as their own.
Complex injection molding projects are, by nature, an expensive undertaking. Part development and injection mold tooling design/build often account for the majority of the budget, particularly in the case of intricate components. The consistency and quality of the part produced hinges on optimizing part development and injection mold tooling performance, as does overall project cost. Missteps can lead to expensive setbacks, product defects and quickly evaporating profits.
Injection molds are a necessary and typically expensive part of any critical use plastic component project. Oftentimes, protecting this considerable tooling investment is overlooked until the mold breaks down or experiences another serious problem that bottoms out the bottom line. With good reason—emergency repair expenses on top of the time, productivity and product lost can be staggering.