Extrusion and drawing, two related, stalwart topics in material forming, are covered from top of punch to bottom of die in more than 200 papers in the SME Technical Paper library. The range of contributors is broad, from companies like Alcoa, Westinghouse, ASEA, Western Electric and General Electric to universities in Japan, Germany and the US, as well as individual entrepreneur metalworking shops.
Papers come from FABTECH, PRESSTECH and NAMRI/SME’s annual North American Manufacturing Research Conference (NAMRC) and from clinics on can manufacturing, tube fabricating and cold forming.
Warm, cold, impact, hydrostatic are among the many types of extrusion techniques developed and still being improved over the years. The Alcoa author of “Impact Extrusion: Is It Reaching Maturity?” pondered the future of the technology by challenging users to broaden their metalworking horizons, but later writers still recognized impact extrusion of nonferrous metals as “one of the fastest and most economical methods of producing hollow parts in an almost unlimited variety of shapes and sizes.”
The first aluminum impact extrusions were introduced by Alcoa in 1921, the culmination of much work on other metals before that time. Through to the 1940s, “considerable engineering talent was devoted to furthering the process and to establishing it as a primary metalworking technique of wide potential—one to be considered along with the more well-known jobbing processes of casting, forging, or stamping.” World War II demands led to stronger, lighter parts in more varied and intricate shapes, as well as more sophisticated tool designs, methods of construction and press equipment, aided also by the ability to accumulate technical data.
By 1987 the process was simply called impacting—rather than impact extrustion, cold pressing, extrusion forging, cold forging, extrusion pressing and the like—and the parts so formed were called impacts. The paper, “Impact Extrusion Technology,” provides a detailed overview of the process and emphasizes the economic breakthrough in metalworking that came from moving weight-saving aluminum instead of removing it, using lower cost materials and eliminating or simplifying subsequent machining or finishing operations.
A sampling of other extrusion papers cover: determining good candidate parts for cold extrusion instead of screw machining, developments in hydrostatic extrusion at ASEA (now ABB), tension-aided cold extrusion, high-viscosity lubricants for hydrostatic forging and extrusion, warm extrusion of TRIP steels, aluminum extrusion based automotive components, experimental investigation into double cup extrusion type tribo-test and modeling of a plastic lumber extrusion process.
Drawing of complex, precision structural shapes of high-strength and high-temperature alloys experienced technical advancement in the 1970s due to the limitations of existing production methods. Drawn and ironed can manufacturing, with reduced weight and metal cost (“a lighter can does not always mean a cheaper can”), resulting in two-piece cans (with bottom and sides as one integral piece, and the lid), replaced conventional three-piece methods consisting of soldered side body seam, top cover and bottom cover. German researchers describe deep drawability of thinner tinplate for food cans and the influences of punch diameters, friction and material behavior.
The interesting history of deep drawing of metals is given in SME Tech Paper TP85PUB192. Deep drawing, originating in the Waterbury, CT, area with manufacturers of brass tubing and parts for gas lamps, has evolved through experience and skill into a technique for most metals depending on the intended use. A 1993 PRESSTECH conference paper covers the principles of deep drawing of large parts using a four-cylinder hydraulic press.
Several papers, among many on the topic of drawing, from the North American Manufacturing Research Conferences (NAMRC) are of interest. SME Fellow Rajiv Shivpuri of Ohio State University (Columbus) and colleagues investigated so-called zipper defects in floating mandrel drawing of small diameter copper tubes. Japanese researchers from Toyohashi University of Technology (Aichi, Japan) looked at prevention of seizure by oxide coatings in multistage deep drawing of pure titanium sheets. University of Siegen (Germany) colleagues B. Engel and M. Hinkel studied the influences of clamp die geometry and friction on the clamping process in rotary draw bending.
The late SME Fellow Klaus Weinmann, a pioneer in metalforming research, presented many papers during his long career. Two of his later papers with colleagues at Michigan Technological University (Houghton) discussed strains and forming limits of metal flow in the drawbead region of a draw die and the use of active drawbeads in the forming of nonsymmetric aluminum panels.
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