Editor’s note: This week, which is also known as Career Week, The Banner will run a guest column each day from a local manufacturer. The columns were an initiative of Bennington County Industrial Corp. and coincide with a host of Career Week activities.
At Kaman we help solve weight problems. Anything that needs to move or be carried can benefit from shedding pounds. A lighter vehicle can travel further and faster, carry a bigger payload and consume less fuel thus reducing its cost to operate and impact on our environment. And it isn’t just planes, trains and automobiles that get better the lighter they are. Machines from the mundane to the complex can operate faster and more economically if their moving parts are lighter. Everything from windmill blades to robot arms benefit from less mass.
Here in Bennington we design and build lightweight components for aircraft and other machines using carbon fiber reinforced composites. These materials are almost half the weight of aluminum yet can be as strong as steel. They have been used for many years in military aircraft, exotic sports cars and expensive sail boats. You are probably familiar with them in tennis rackets, golf clubs and fishing rods but they are about to take off in a big way, quite literally, since they form the bulk of the airframe on the new Boeing 787 Dreamliner and soon to fly Airbus A350.
A composite material is a mixture of two or more materials with each complementing the properties of the others. Reinforced concrete is a man-made example and wood is nature’s own. At Kaman we use very light and strong carbon fibers embedded in plastic resin. The fibers give strength and the resin helps to form and retain the shape of the product while binding and protecting the fibers and distributing loads evenly among them.
Carbon fibers are about one half of one millionth of an inch across. They consist of almost pure carbon and at a molecular level are formed from sheets of atoms joined in a hexagonal pattern like a honeycomb. In this respect the material is similar to the graphite in your pencil but instead of the sheets being stacked in tidy layers that can slide easily over each other to be deposited on paper they are randomly folded and scrunched over and around each other to form tightly bound and very strong filaments. Depending on the grade anywhere from 3,000 to 60,000 of these filaments are bundled into untwisted threads called tows that can then be embedded in resin. Tows that are first woven into a fabric create that highly marketable black weave look we all associate with carbon fiber.
Making parts from carbon fiber composite is similar to building a fiberglass canoe, but at Kaman instead of layering dry material into a mold and wetting it out with resin applied by brush, we use a form of the material called prepreg. We buy this in rolls from a range of suppliers who pre-impregnate the fibers with a precise and evenly distributed quantity of resin that is partially cured to form a tacky sheet.
Our production process starts by cutting the prepreg into a carefully designed jigsaw puzzle of shapes on a computer controlled machine.
Technicians place these into molds in a predetermined position and sequence and once this laminate is complete it is covered with a flexible plastic bag that is evacuated to compact the material, similar to vacuum packing coffee. The molds are then placed in a large pressurized oven called an autoclave where over two or more hours the laminate is further compacted and the resin fully cooked to form a solid product.
When removed from their molds the parts are trimmed on computer controlled machines with some being built into larger assemblies and painted. After a final inspection they are delivered across the USA and around the world for incorporation into products as diverse as the USMC’s Osprey tilt-rotor aircraft and a high-speed machine that threads elastic into babies’ diapers.
Jim Sharkey is the general manager of Kaman Composites of VT.