Tooling Precision is Key to Micromolding Success

After losing four babies, Jamie McDonald was overjoyed to learn she was expecting twins. But her happiness abruptly ended when she gave birth to the tiny pair at 24 weeks. “We felt pretty positive we were never going to bring them home,” she recounted to “The Doctors” syndicated talk show.
 
McDonald’s babies—Everly and Maverick—weighed 1.9 pounds at birth and both were diagnosed with patent ductus arteriosus (PDA), a potentially life-threatening congenital heart condition triggered by an opening between two cardiac blood vessels. The sixth most common defect, PDA occurs in 5-10 percent of all children born with congenital heart disease, and is twice as likely to occur in girls than boys.
 
The condition is treatable with therapy, minimally-invasive catheter-based interventions, and minimally-invasive surgical solutions. Doctors chose the latter option for Everly and Maverick, implanting a pea-sized wire mesh device between their pulmonary arteries and aortas to prevent blood from mixing and straining their tiny hearts and lungs.
 
The device, made by Abbott Laboratories, is inserted through a small leg incision and guided to the afflicted cardiac vessels. Manufacturing such a diminutive object most certainly entailed micromolding, a type of injection molding that produces extremely tiny parts, often with micron tolerances. The process uses special equipment that can produce intricate designs and details.
 
Medical Product Outsourcing’s October feature, “Little Big Parts,” addresses the latest trends and challenges shaping the fast-growing medical micromolding market. Justin Strike, product manager at Trelleborg Healthcare & Medical, was among the various experts interviewed for the story. His full input is provided in the following Q&A.
 
Michael Barbella: What are the latest innovations in micromolding technology?
Justin Strike: Silicone: Shot size control is critical for low viscosity LSR and is therefore a major focus with newer micromolding equipment. Without tight control over shot size, 5-10 percent of micro part cavity volume could easily be “leaked.”
Thermoplastics: In thermoplastic micromolding systems, the focus is on material quality. Molders are investing in custom injection units and bespoke material delivery systems that reduce material volume to minimize degradation prior to shot.
 
Barbella: What market forces are fueling the need for micromolding technology and services?
Strike: The miniaturization of medical devices is driving the need for micromolding of smaller components.
 
Barbella: How is the need for smaller, more complex medical devices/components challenging micromolding suppliers and providers?
Strike: For process validation, micromolding suppliers need machines that can process very small-scale components with tight control and quality inspection equipment with the same limits to measure and assess that control. Operators typically must manipulate and inspect finished parts, which at these smaller sizes, can be quite difficult. Therefore, molders are moving to more automated visual evaluation for post mold inspection and processing.
 
Barbella: What factors must be taken into consideration in designing tooling for micromolded parts?
Strike: Micromolding with silicone requires tools that deliver a high degree of precision in shut-off surfaces. Thermoplastic tools need consistent cooling and precision. Regardless of the material, surface finishes are limited since conventional tool polishing could wipe out micro geometry. Finally, tools should exit the machining center or EDM bath ready for resin.
 
Barbella: Should micromolding tooling design be outsourced? Why or why not?
Strike: Micromolding challenges are universal. Device manufacturers with one or two micro forms to mold would benefit from outsourcing those programs to a molder that has implemented universal solutions to avoid excess capital and personnel expense. This is true for the tooling, but perhaps more importantly for the processing of those tools. Tool design for micromolding should take the processing equipment into consideration. Therefore, when outsourcing tool design, the molder should make the tooling designer or manufacturer aware of the processing equipment that will be used.
The tool design and/or build strategy will utilize the machining equipment to minimize fit error. It begins with the equipment being used to manufacture the tooling and ends with the injection molding machine being used to process the tool. Because of the unique challenges facing micromolded components, we found it beneficial to accomplish the tool design, build, and processing under one roof. This will help reduce the time to a successful molding.
 
Barbella: What are customers demanding or expecting in their micromolded products?
Strike: Flaws in injection molding are typically fixed in size. For instance, flash is a result of the tool steel fit, cavity pressure and material viscosity. Those factors still exist in micromolding, except the size of the flash formed is proportionally larger on the micro part. Our customers would like to see defects reduce in size proportionally to the size of the part. To achieve that, tooling improvements and greater process control is needed than for conventional-sized parts.
 
Barbella: How are minimally invasive and point-of-care applications affecting micromolded device design and development?
Strike: The use of microparts/components in minimally invasive procedures enables more elements to be included in the device for deployment during surgery. The smaller the device, the more that can be accomplished during the procedure or the less invasive the procedure. Our customers are generally looking for thinner walls and longer flows. Gate vestige needs to be planned for and managed as it becomes a dominate feature of the micropart.
 
Barbella: What new micromolding technologies (if any) are on the horizon?
Strike: Tool quality still dictates part quality for all sizes of medical components. For micromolding, the focus has been on improving tooling precision to ensure micromolding success. Higher quality 5-axis machining centers (priced generally between $500k – $1M) deliver the precision and function needed for managing feature detail and tool fit for micro parts. However, the high cost of this equipment will likely limit micromolding to specialized players. Also, specialized material delivery systems and injection units are required to manage resin stability in thermoplastic micromolding.