Everyone in the injection molding industry understands the importance of mold design. As you may know, the mold is the component in plastic injection machinery that determines the appearance and quality of the finished product. This part works together in conjunction with the rest of the components — like runners, gates, sprues, and heat chambers — to produce a high-quality plastic product.
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Keeping this in mind, manufacturers work tirelessly to craft a mold design that meets not only design specifications but also customer expectations for both high and low-cavitation injection molding. The quality and make of the mold allows injection molders to ensure high tolerance, identify defects, maintain precision, choose the right raw materials, as well as, predict the behavior of the product during end-use. After all, only a well-designed mold is capable of satisfying the different standards expected from an injection molding company, Continue reading to learn more.
In manufacturing, tolerance is defined as the leeway allowed between the design and the appearance/functionality of the final product. Tolerances give manufacturers a bit of legroom in making modifications. This is done to get as close to the final product as possible while satisfying the client’s demands.
Typically, injection molds are capable of achieving tolerances of 0.005 inches, give or take. However, this can differ, depending on the specifications of the client or the design of the mold. Crafting a mold design requires an understanding of the resin behavior — i.e. some resins are prone to shrinkage and minor warping during the injection molding processes. But if the tooling mold has been designed to accommodate these tolerances, resin behavior can be easily predicted. This results in a workable plastic mold that won’t have to undergo extensive post-processing.
Some of the factors associated with injection molding defects are the following: mold design, rate of injection, pressure, temperature, runner presence, type of sprue, gate, and the like. Even if many injection molding deformations only have aesthetic implications at best, manufacturers still want to eliminate them. Flow lines and discolored portions of the ejected product are unsightly and may not satisfy the customer’s needs.
To prevent or completely eliminate these defects from happening, manufacturers need to make a series of changes to the injection mold machine or CNC equipment they use. For example, they may need to change the wall thickness of the tooling mold or create rounded corners in order to improve the flow consistency of the molten resin. They may also need to completely redesign the entire tooling mold just to make its shape more symmetrical.
All other factors aside — injection speed, cooling rate, type of thermoplastic/resin — mold tooling are essential in maintaining the precision design in final injection molded products. As manufacturers try to be receptive to the requests of their clients, they also need to consider the injection molding production process as a whole. The mold design determines precision as well as the feasibility in manufacturing.
This is why injection molding companies continue to work closely with their clients to come up with different designs of a mold. Injection molders employ a range of techniques such as prototyping, reverse engineering, and CNC machining just to craft a molding die with the right dimensions, wall thickness, and cavitation.
Although most types of resins can be used in injection molding, they don’t necessarily have similar qualities. As mentioned before, some plastics are prone to shrinkage, more so than others. The reasons for this is due to the difference in density when the product is in solid and molten form. This means that even when the product has already been ejected from the injection mold machine, it may continue to significantly shrink over time as it continues to cool.
To prevent extreme plastic shrinkage, mold design is modified for each kind of resin. Resins that have high shrinkages (like polypropylene) should be used in molds that do not have thick walls. In this case, each of the mold cavities have to be designed in such a way to predict the rate and gravity of the shrinkage for different polymers.
Finally, mold tooling is also important in determining the environmental behavior of the finished product. This simply means that the product still maintains its design and functionality even when exposed to the elements, whether during assembly with other components or on its own.
WIth mold design, it’s far easier to predict how an injection molded product will be affected by its surroundings. Manufacturers may need to change certain aspects of the mold tooling — whether it is by reducing the number of cavities, lowering the wall thickness, or using a different tooling metal/alloy altogether.
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In this simple guide, you’ve learned the importance of mold design in injection molding. Although this is but one component in an injection mold assembly, the mold design affects the plastic product’s appearance, feasibility, environmental behavior, possibility of defects, and tolerance level. Any well-built mold can be engineered to anticipate all of these factors, allowing for a more efficient and high-quality injection molding process.
Tooling is the backbone of plastic injection molding. Without a proper tool design, your plastic part would never scale up properly. A quality tool design can save you enormous amounts of time and money during production. Before you contact a toolmaker, here are a few facts about tooling you should keep in mind.
Tooling, also known as a mold, refers to the negative cavity space where molten plastic resin is injected to create a part. High quantity and quality parts require proper tooling. Since tool design and construction are complex, fabrication requires significant capital investment and enough lead time to create an effective tool.
The tooling design process starts out in the prototype development phase. Here 3D printing, cast urethane, and machining techniques create prototype tools. These low-volume prototypes troubleshoot, develop, and validate the tooling design during pilot production. While this step may seem unnecessary, cutting down on errors in the manufacturing and assembly process early can significantly decrease time and cost later.
Proper tooling design and choices need to accommodate for complexity, lifetime, application, and potential production volume of the tool. Choosing which tooling to invest in is the hardest part of the tooling process. If the part is going straight into high volume contract manufacturing, then it will be most cost-beneficial to invest directly into expensive production tooling for the long term. In other cases, such as low volume manufacturing, using a prototype tool may be more beneficial until production increases significantly.
Toolmakers provide necessary assistance with the tool design process because they are well-versed in fabricating techniques and tooling design. They can run mold flow analyses to optimize the tooling design and choose the best locations for parting lines, gate, and ejection locations. A quality prototype design engineer will work closely with toolmakers to ensure the fabrication of the optimal tool for your application.
After collaborating with the toolmakers on the design, the part is ready and approved for the T1 sampling stage. They will build the first tool with a 2-16-week lead time dependent on design considerations. T1 sampling demonstrates that the tooling functions correctly and produces ideal parts. After the T1 sampling is accepted, any necessary modifications and aesthetic mold texturing can begin. These additional modifications can take 1-2 weeks to complete. The modified molds, referred to as T2 samples, are sent for approval of texture and appearance. Once the T2 samples are approved, the toolmaker releases them to the contract manufacturer.
Once with the manufacturer, the T2 samples are placed into the production line for process development and part qualification. The tooling undergoes a series of molding studies that help outline the optimal conditions and characteristics for creating parts using that tool. The manufacturer runs experiment trials to isolate process inputs and corresponding impacts on part characteristics. This initial testing helps the molder validate an ideal processing window that produces parts within specification.
After initial process development, qualifications, and validations, the tool enters a regular production maintenance schedule. Here the tool is regularly monitored for wear and other potential issues affecting part quality or tooling lifetime.
The entire process from prototype to production can take months and significant investment to properly complete. Therefore it is vital to design your parts for manufacturing throughout product development. A product design prototyped using machining, or 3d printing, may not easily translate to a tooling design for high volume production. We recommend partnering with a product development company intimately familiar with the tooling design and the manufacturing process that will initially incorporate that knowledge into designing your product. If you are unsure how to get started or would like some expert advice on designing your tools, contact us and we would be happy to help.
About Synectic Product Development: Synectic Product Development is an ISO certified, full-scale product development company. Vertically integrated within the Mack Group, our capabilities allow us to take your design from concept to production. With over 40 years of experience in design, development, and manufacturing, we strive for ingenuity, cost-effectiveness, and aesthetics in our designs. Learn more about our new product introduction services and see how we can help your next project.
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