Tool and mold maker Minimould achieved improvements in quality and fill time as a result of using Moldflow software early in the manufacture of a new range of laryngoscopes. These devices are now in production by medical device manufacturer Penlon and Minimould.

Penlon specializes in equipment related to anesthesia and metal laryngoscopes. These are spatula-like instruments with a light source used by anesthetists during surgery to open patients' throats to allow a breathing tube to be inserted. The devices come in different shapes and sizes to accommodate a variety of patients.

Moldflow and SolidWorks 3D modeling and analysis allowed Minimould to create this laryngoscope.

Penlon migrated to a plastic material for its new laryngoscopes because surgical instruments that may carry bacteria or infection are disposed of after one-time usage. For Penlon, this circumstance meant redesigning the product for manufacture in plastics.

Not having injection molding capability at its plant, Penlon approached Minimould, which operated by manager director and entrepreneur Peter Clark. "One reason we used Minimould is because, although there are many knowledgeable molders, Peter Clark is very helpful and has a number of key facilities, including Moldflow software, which was used extensively during this development cycle," says Penlon technical director Alan Green.

Using Moldflow and SolidWorks, Minimould designed a one-piece blade that afforded the clarity required, yet retained the full properties of the intended polymer. While this gave the most economic production capability, the design was deemed radical in what is an established market. Minimould and Penlon engineers then evolved a design that mimicked the geometry of the stainless steel version. They then used Moldflow to optimize the design and develop a version that addresses the market's need, as well as reduces production costs using the new polymer material.

Minimould engineers designed the tooling from the approved drawings. The design continued to change extensively throughout the development, as attempts were made to manage the implications on moldability of the complex variations in wall thickness and curvature demanded by the optical and medical requirements. Changing the original 'as-machined' design into a smoothly radiused product conducive to manufacture by injection molding altered the path of the guided light to the extent that the position of the lenses had to be moved, while the design was adjusted to reduce or smooth wall thickness changes where possible.

Minimould also converted the straight split-line format in the tooling to that of a complex split-line, to eliminate visual evidence of the split-line and possibly sharp edges. This was particularly helpful where contact would be made with patients' soft internal tissue, tongue, and palate. The final product is a transparent blade with light guide, using a series of built-in lenses to guide the light to the end of the rod. The blade attaches to a universal metal handle and battery holder.

Selecting a material from the limited choices was difficult. Design specifications called for a material that is highly transparent with low haze. The best materials are polycarbonate (PC) and acrylic (PMMA). PMMA is not known for its strength, and some sterilization processes can attack polycarbonates. During prototype trials, PMMA gave improved results for light guidance compared to PC. Careful geometry management improved the flexibility of the PMMA design. The choice of PMMA as the intended production material required a carefully considered design approach. The material eventually selected was PMMA Oroglas V825 T, which offers high optical qualities.

The thicker wall sections also dictated a large gate surface area. The cooling of this cavity was critical. The predicted cycle time exceeded one minute and the material use expected was also excessive.

Using SolidWorks 3D modeling and real-time fine-tuning of gate positions with MPA analyses, further iterations were made to generate a design likely to give the best compromise among molding, mechanical, and medical requirements. During this process, it was determined that the best compromise between function and moldability meant that the wall section thickness should get progressively thinner as the distance from the gate point increased. Some wall sections were modified to force the melt flow to run smoothly along the blade, thereby reducing the possibility of air traps and weld lines.

Thicker sections remained unavoidable due to the optical requirements: sections thinner than six millimeters substantially reduce light collection at the source point and emission from the lens on the blade. Using prototype modeling techniques, the lens position and angle were set by calculation and subsequent trial results.

Overall, design changes based upon advice from the MPA analyses enabled the cycle time to be reduced by 37.31 seconds and the shot size to just 14.86 cc.

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