Making injection mold tools for prototypes or low-volume production can be a complex and time-consuming operation, no matter who you use as a manufacturer. To make a tool in the fastest possible time requires cooperation between both the designer and the supplier. There are many steps a manufacturer can take to minimize delays and speed up the production of a finished tool, but the product designer also has a role to play in preparing drawings for optimal production.
Here are four ways that product designers and manufacturers can work together to make rapid-turnaround injection mold tools.
1. Keep the design simple
Although every project will be different, try to avoid unnecessary complications. Simple geometric shapes with uniform wall thicknesses and gently radiused corners are easier to make than complex/compound curves with variable wall thicknesses and tight, right-angled corners. Reduce the number of slots, holes, indentations and other features which, in turn, may require ribs and bosses that complicate the build.
Avoid features that may require the use of sliders or inserts. They increase tooling time and cost and also require more sophisticated cooling circuits in the mold.
Keep tolerances loose unless absolutely necessary. If there are critical tolerances, clearly specify no more than two per build. Highly-polished surface finishes take more time and money, as do heavily textured surfaces. Be generous in the use of draft angles, and be flexible regarding the placement of injector pin marks and parting lines. The more flexibility in the design, the easier it will be for the toolmaker to optimize his own processes to suit. Remember, it is always easier to add more complex features later as time and finances allow, rather than simplifying designs that have grown too expensive and complex.
2. Use common materials
Your choice of plastic resin actually has a large impact on the kind of metal used to make the tool, the design of the tool and the processing parameters that are applied to make the finished part.
For the quickest and easiest build, choose a readily available resin type that will suit most applications. These would include high- and low-density polyethylene, polycarbonate, polystyrene, acetal, nylon and ABS. These compounds are cheap, abundant, easy to color and have stable engineering properties, which are well understood and predictable. This makes it much easier for the manufacturer to design appropriate cooling circuits as well as to purchase the right tool material to suit the resin, part application and volume.
3. Choose a streamlined production service
One of the best ways to speed up tool production is through a streamlined service such as One Man One Mold (OMOM). The idea of this service is to use a single master machinist who makes the entire tool by himself, using whatever processes and steps needed, in any order, that work best for him. In other words, the machinist is free from any prior constraints about how the tool should be made. This approach can eliminate costly setup times and duplications of effort that can happen when a tool passes through several hands.
Over time, we’ve found that this degree of independence allows machinists to discover new ways to do even common tasks that save time and money. And it’s very important to note that this process helps the manufacturer to work out the snags in a given tool design. This can be an enormous time and money saver for the client if a full-on, high-volume production tool is needed later. This process may cost a bit more for the special attention given, but if time to market is critical, then it’s a good option.
4. Listen to design for manufacturing advice from your manufacturer
Once a designer has submitted a workable drawing to the manufacturer it’s important to avoid any changes to preserve speed. All design input should happen before the work begins—not after. Where possible, design for manufacturing advice should be sought to ensure best practices for features like wall thicknesses, draft angles, injector pin locations, hole size and depth, and so forth.
It’s important for the product engineer to know that, once a tool build has begun, even simple modifications can greatly increase costs, introduce production delays, or both. If a customer requests the fastest possible turnaround time for a tool, some manufacturers specify that changes are not allowed once a design has been accepted to ensure the production schedule is met.
Rapid turnaround doesn’t work for every job
Clearly, some designs are going to be more demanding than others, so quick turnarounds aren’t realistic for every job. However, if speed is of the essence, the above tips will help accelerate the process dramatically for the product designer.
Gordon Styles is the founder and president of Star Rapid, a provider of rapid prototyping, rapid tooling and low-volume production services. Utilizing his background in engineering, Styles founded Star Rapid in 2005 and under his leadership the company has expanded to 250 employees. With an international team of engineers and technicians, Star Rapid combines advanced technologies—such as 3D printing and multi-axis CNC machining—with traditional manufacturing techniques and high-quality standards. Prior to Star Rapid, Styles owned and managed the United Kingdom’s largest rapid prototyping and rapid tooling company, STYLES RPD, which was sold to ARRK Europe in 2000.