Published 10/1/1995

Machine Shop Finds New Uses For Aerospace Technology

When most machine shops in California's aerospace industry were closing their doors, one machine shop's doors opened wider.

RMI specializes in close-tolerance machining, tool and fixture design and fabrication, developmental parts, and R&D using hard tooling alloys, titanium, plastics and composites. The company continues to grow with work in the aerospace, medical, consumer sports equipment, and oceanographic industries. To make everything come together, the company chose the CAMAND system from CAMAX (now part of UGS Corporation). This software provides an NC-focused solution for programming, verifying and simulating geometrically-complex and high-speed machining applications.

RMI recently produced a mold for a biomagnetometer, a medical device used to measure magnetic fields emanating from electrical activity in the brain. Biomagnetic Technology Inc. (BTI), a leader in Magnetic Source Imaging, designed the biomagnetometer using Structural Dynamics Research Corporation's I-DEAS solid modeling software.

According to Laurence Warden, senior engineer at BTI, the device relies upon a cluster of 148 superconducting pickup coils that are mounted in precise locations around the brain. Complex geometry was required for the composite mounting structure called a coil-dish. Reynolds-Mason translated the solid model, via IGES, to its NC programming system and was able to CNC machine the parts and composite molds without using dimensioned drawings.

According to Rich Reynolds, RMI president and founder, BTI considered other methods and materials for the lay-up molds, but decided that accuracy and durability were their prime considerations. The customer thought the design required a five-axis machining center, at about $100 an hour. "We were able to produce it rather nicely on a three-axis FADAL VMC with the power of our NC software and a skilled programmer," says Mr. Reynolds.

"The five-axis job was done on a three-axis machine by programming a constant tilt, fixturing, or using an articulated head. You can fixture that part and keep it tilting, cut the part and tilt more. These procedures are all programmed and run again. You have multiple uses of CAMAND's coordinate system, including the added indexing capability," says Arnold Goularte, RMI's CNC operations manager.

"The aluminum mold was designed and machined from four sections of plate, each bolted and doweled to each other from the inside, as opposed to machining from a solid billet. This method not only saved considerable material cost, it also let us easily machine the interior of each section to maintain a constant wall thickness of about 1.5 inches for cure considerations," Mr. Reynolds explains.

"The BTI product used a low temperature fiberglass lay-up mold. This was a cure at 240 degrees. The fiberglass cloth is laid up directly onto the tool, folded in, and then a vacuum bag is placed over the entire tool. It is then placed in an autoclave to cure it. After about an hour, the fiberglass shell is lifted off the tool."

RMI designs tooling directly from the CAD model, after it is imported to the programming system, by offsetting surfaces to compensate for material thickness and shrinkage. The system automatically generates parting lines from model geometry. According to Reynolds, however, the lay-up mold consists of either a contoured female cavity or a male plug. The fabric is laid onto the mold, typically an aluminum tool in RMI's case, in multiple plies, vacuum bagged and then cured in either an autoclave or oven. Advanced composite materials (fiberglass or graphite-woven cloth) are pre-impregnated with thermo-setting resins that become liquid when the tool reaches a predetermined temperature. As the mold and lay-up reach a higher temperature, at about 250 degrees, depending on the resin's cure temperature, it solidifies to a strong lightweight shell that is lifted off the tool.

Customers' files are input using IGES, usually from SDRC I-DEAS (now part of UGS Corporation), Parametric Technology's Pro/ENGINEER, and files transferred from CATIA. The company recently did a whole series of tools for a local company that deals with composites for the Comanche helicopter, all from CATIA files. The size of CAD files from customers is also "no problem," according to Mr. Goularte. "Our customers send data files of all sizes, and large files never affect the system."

T Reynolds-Mason is very pleased with the success they are having in making molds, and with their ability to apply their expertise in aerospace machining to toolmaking.

"When your only product is service," states Mr. Reynolds, "especially when you're the new kids on the block, you must provide even the most talented work force with the best possible tools to enhance that pride in workmanship. In this business, nothing sells your product better than performance."