Gardner Business Media

Methods - Aug 2018

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Mold Manufacturer Tackles LSR Molding Challenges with High Accuracy 5-Axis Machining Rick Finnie, owner and President of M.R. Mold & Engineering Corp. has been working with silicone and liquid silicone rubber (LSR) molds since the early 1980's. Molding silicone is a specialized process which requires molds to be built with high precision machinery. After experiencing inefficiencies with conventional 3-Axis machining in his moldmaking operation, Rick looked to 5-Axis machining as a means to achieving higher quality, higher precision built tools. Conquering Liquid Silicone Rubber LSR has a low compression set and fast cure cycles; coupled with great stability it can resist extreme temperatures of heat and cold. This makes it ideally suitable for the production of parts, particularly those in the medical industry, where quality and accuracy are crucial. LSR remains flexible and elastic down to -70°F and retains its properties up to 450°F. Many thermoplastic materials can be molded with limited flash using fit specifications between inserts of up to 0.002 in. However, LSRs will often flash even with fit requirements as tight as 0.0001 of an inch or less. This necessitates a different level of engineering, machining, processing precision and expertise. Founded in 1985 with Finnie and one employee, M.R. Mold & Engineering Corp. (Brea, CA) currently boasts 30 employees and a 15,000-plus square foot facility complete with a 4,000 sq. ft. Technology Center, home to 6 molding machines for customer required samplings, run offs and automation technology. Today, M.R. Mold is known for its unprecedented expertise in LSR as well as leaders in the education of the silicone industry. The company's core focus (approximately 80%) is within the medical industry where LSR is primarily used for the production of parts ranging from long- term implants, catheters, oxygen and sleep masks, to artificial knuckles. Fit or Flash: 3-Axis Milling Challenges Over the years M.R. Mold has invested in several CNC mills, as well as Wire and Sinker EDMs. The company's core customers require close tolerances, little to no flash and cosmetically perfect parts —difficult to achieve with conventional CNC 3-Axis machines. "In our industry niche, we were machining complex 3D cores and cavities on conventional 3-Axis mills where feeds, speeds and surface finish were being compromised. The EDM process was often required as the 3-Axis mills were unable to accurately perform the needed machining operations. Additionally, 3-Axis machining sometimes required as many as five set-ups for some of the complex geometries M.R. Mold machines. This process proved to be inefficient, wasted valuable time and introduced errors with each new operation, which compromised the accuracy of the work. "Silicone flashes very easily and medical components have critical tolerances and minimal flash allowances," Finnie commented. Achieving a high level of accuracy on complex geometries using 3-Axis equipment was a huge burden to overcome and led to multiple reworks once molds were sampled and evaluated in the press. The main culprit — parting line flash. Finnie knew the time had come to make an investment in a 5-Axis machine; especially since one of the company's largest customers had close tolerance work that required a high level of accuracy. CASE STUDY: PRECISION MACHINING WITHOUT THE FLASH 12

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