Prototypes and Production: Benefits of a Prototype Mold for Establishing Production Mold Parameters

There are many ways to produce prototype parts, especially now that additive manufacturing has progressed in equipment, processes, materials and sometimes convenience. When it comes to medical devices and single-use disposable products that utilize the plastic injection molding process however, building a prototype mold or what is sometimes referred to as a “developmental” mold, can provide more benefits than just building prototype parts using an additive manufacturing process.

While it’s true that the additive manufacturing process can produce a prototype part in a day or so, a prototype part that comes from an actual developmental or “pre-production” mold can provide far more information, not only about the part’s form, fit and function, but about its manufacturability.  Ultimately, the goal of developing a mold for an injection molded part is to optimize the production process.
 
Production Molds Benefit from Prototype Molds
For the medical device market, designing a medical product or component requires complex levels of design, development and testing prior to the actual multi-cavity, high-volume mold being built. Because of this, one of the most optimum ways of getting a prototype part, particularly for the medical industry, is to build a prototype mold with a toolmaker that has multiple high-tech manufacturing tools available. This will enable them to produce a core and cavity insert that can be dropped into a mold base which the moldmaker may have on hand for tryouts, and allow parts to be produced fairly quickly.

Parts can be run quite cost effectively in a smaller injection molding press in the specific material required for the application, and permits the engineering team to evaluate the form, fit and function of the parts while also establishing the validity of the mold design for molding optimization. This makes functional testing more accurate and provides the best data for further development of the product and the mold.

Molding single-use or disposable products for the medical market often requires multi-cavity molds that range from a few as 16 cavities up to 192 cavities or somewhere in between. Another benefit to developing a product or component in a single-cavity prototype mold is that portions of the molding process can also be tested. The molding process may not be optimized in a prototype mold, however it does allow the engineering team to determine if there are design issues that would challenge the molding process.

Costs to manufacture and per unit part cost is dependent on cycle time, making that a critical part of the molding process. Every tenth of a second of additional cycle time in a high-cavitation medical mold means additional costs to the parts.  Using a single cavity prototype mold can help you answer questions such as are there features in the part that would inhibit a fast cycle time or cause a part to get “hung-up” in the mold upon ejection? How is the part filling and cooling? 

Additionally, automation may also be required to handle the large numbers of parts coming from the mold that may include pick-and-place robots, conveyor systems, vision systems, sorters and other devices to automate the process. Design for manufacturability then is key to optimizing the molding production.

There are some disadvantages of a single cavity prototype mold. While it allows you to test and evaluate a sample of one piece, it doesn’t give you a range of cavities to predict the balance and quality throughout the entire mold in a high-cavitation production mold scenario. In some instances, Tech Mold favors building pre-production or “pilot” molds, which can range in cavitation from 1-to-16 cavities and are a better predictor of the part’s final characteristics. The pilot mold will mimic the production mold in design, material selection, melt delivery system, surface finishes, plating, venting and cooling. It also will give the engineering team the ability to perform process (molding) development and provide solid data that will be a valuable foundation for the qualification and decision making process—two critical factors when moving forward with the high-cavitation production molds.

With today’s 3-D modeling software and high-speed machining capabilities, a single cavity pre-production mold can take as little as a week to build. The more cavities that are required however, means that timeline will be extended but many multi-cavity pre-production molds can be built in four to eight weeks. The advantage to the pre-production mold is that it permits collaborative engineering, fast changes to the part and rapid turn-around for a revised core and cavity. Additionally, when a program moves to the production stage, the knowledge gained during the developmental stages is invaluable, and in many cases the higher cavitation developmental mold can be used to mold parts until the production mold is completed, validated and online.
This collaboration between the engineering departments of the OEM and the mold builder is valuable to the development of the product, and saves both time and costs in the long run, particularly where medical devices and critical disposable products such as syringes are concerned.

For medical devices and components, the entire process is longer and more intense with a longer mold build and process development timelines. That is why the development phase is critical to the success of the project. Prototyping methods are useful tools, but they are just tools—just first steps in the long process of developing medical components. Choosing a prototyping method that allows the engineering team to retrieve valuable data up front can often shorten this process and optimize the design and build phases. It allows the medical device OEM to gather the best data, enable optimum testing and manufacturability, and ultimately provide faster time to market, which is critical to the success of any project.

Vince Lomax is vice president of Tempe, Ariz.-based Tech Mold Inc. Vince  began his career as a moldmaker, and has been with Tech Mold for 30 years, having risen through the ranks to his current position.