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Virtual mold & process development for medical parts

Wed, 06/13/2012 - 5:00am
Christof Heisser and Matt Proske

Simulation has established itself as an invaluable tool for design engineers in developing new parts and deciding what materials to use in metal casting or plastic injection molding manufacturing processes serving the medical device industry. In the past, such simulation tools were used by analysis groups and the operators of such tools were specialists who would “setup and run” simulations. Today, however, leading design and manufacturing engineers need to be able to provide answers to questions regarding all areas of the manufacturing process, requiring communication between all members of the product development and production team, as well as management and procurement. Conventional design simulation tools, however, do not cover the simulation of the manufacturing process.

 

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Slide tip and mold core temperature after 16s into the 19th consecutive molding cycle

The MAGMASOFT®Casting Process Simulation tool was introduced 23 years ago as a simulation tool primarily for use by process engineers in metal casting operations to move the trial and error process of finding optimum process parameter combinations from the manufacturing floor into the computer. Designers and analysts recognized the benefits of using such process chain integrated simulation tools, either by using it themselves or in collaboration with in-house manufacturing engineers or with their suppliers. Using such simulation software, suppliers and designers can work together from the beginning of the development of a new part to design parts that are optimized for performance, castability and costs. Process simulation becomes, thereby, an invaluable communication tool between designers and production engineers in an environment of ever shorter product development processes. Indeed, many OEMs now require their casting suppliers to use MAGMASOFT® and often refuse to procure parts from foundries not utilizing this technology.

While simulation has been established as a product design tool in the plastics industry serving the medical device segment, process simulation tools have not been adopted by manufacturing overall. The main reason is that the simulation tools that were originally intended to be used only in the design process lacked the ability to consider the complexity of the entire injection molding process. SIGMASOFT® was introduced by SIGMA®, a fully owned subsidiary of MAGMA®, to provide process simulation software for polymer injection processes. It even simulates the elastomer injection process, i.e. for LSR’s (liquid silicone rubbers), a material category not covered by traditional design simulation tools. This process chain, integrated simulation makes simulation accessible to everyone, not only “simulation and meshing specialists.” SIGMASOFT® has been lauded as “The Next Generation of Polymer Simulation” because of its unique combination of ease-of-use and its capability to consider all details of the entire mold making and molding process. This opens the utilization of this technology to designers with product responsibilities and production engineers, as no finite element meshing experience is required to use it. Based on the success and vast experience of its parent company MAGMA®, SIGMA® is determined to provide comprehensive, accurate yet easy-to-use software to product producers and buyers of plastic and rubber parts.

End User Results
Tessy Plastics, a global contract manufacturer serving the medical device industry, decided to implement this new approach and has been using SIGMASOFT® for a year and the benefits are clear: the predicted cost and time savings estimates have been met or exceeded. “First shot success” is becoming a regular occurrence at Tessy and doesn’t happen by accident. The optimization of current production processes is accomplished daily. Process simulation software must be comprehensive to meet the challenge of easily combining so many material, process and design variables. As with any advanced technology, training is required to facilitate successful implementation quickly. The processor has fully trained five engineers in its use. Having a group of people trained, who work as a team, eases the implementation of such new technology. It is very important to be able to share information and bounce ideas between the team to speed up that learning process. Besides teaching the functionality of the software, the provider (SIGMA®) also offered onsite implementation assistance within the existing engineering team.

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Mold temperature simulation result after several cycles superimposed on real mold

The following is one example of the many successes that the company realized in its medical business since the addition of SIGMASOFT® one year ago:
Tessy was challenged by its customer to reduce the cycle time of a product. One of the options discussed was to consider adding conformal cooling.A common method for implementing conformal cooling is to build the cavities using DMLS (Direct Metal Laser Sintering). This process is costly in comparison to more conventional tooling practices, so, before proceeding, the company ran a thermal analysis to both optimize the cooling design and to evaluate the conformal cooling against the original conventional cooling. This would help Tessy determine if the added cost in tooling would result in enough savings in cycle time to pay for the production changes.

A multi-cycle thermal analysis was run on the original tooling design with conventional cooling to determine the number of cycles required to stabilize the mold temperature. The simulated process was based on the actual current production process. An analysis was run on both the original and the conformal designs to determine the difference in solidification time. The simulation of the initial design for the conformal cooling revealed that the original water layout did not control the temperature in the location that had the greatest impact on cycle time and, therefore, the design could be improved with conformal cooling. Without using process simulation and its multi-cycle capability, this would have been a very costly and time-consuming exercise for Tessy. Using process simulation, however, the company was able to quickly determine the root cause of the problem and engineer an optimum design.

Conclusion
The utilization of comprehensive process simulation like MAGMASOFT® and SIGMASOFT® has an impact on almost every department of a metal casting or molding operation. At Tessy, SIGMASOFT® is located in the process engineering department and essentially allows the engineers to visualize every detail of the mold or part at any point in the overall process. Within the engineering department, it drives the user to be very specific about the process inputs which, in turn, improves the overall understanding and knowledge of the outcome. Its position within the company also allows for the simultaneous development of process and tooling as well as the documentation of those developments. This is one aspect of how process simulation not only improves the communication within the process engineering department, but also improves the communication to the shop floor, explaining why the use of specific parameters to stay within a defined process window is necessary to assure the production of good parts, from the beginning to the end of the production run.

Matt Proske is an application sales engineering manager for Sigma Plastic Services Inc., based in Schaumburg, IL. A graduate of Kent State University in Manufacturing Engineering, Matt assists customers in the application of SigmaSoft, the company's advanced process simulation software for injection molders of thermoplastics, elastomers and TPE's. Christof Heisser is the President of MAGMA Foundry Technologies, Inc.

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