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(12) United States Patent 10 US007954357B2 (12) United States Patent (10) Patent N0.: US 7,954,357 B2 Bradley et al. (45) Date of Patent: Jun. 7, 2011 (54) DRIVER PLATE FOR ELECTROMAGNETIC (56) References Cited FORMING OF SHEET METAL U.S. PATENT DOCUMENTS (75) Inventors: John R. Bradley, Clarkston, MI (U S); 3,618,350 A 11/1971 Larrimer, Jr. et a1. Glenn S. Daehn, Columbus, OH (US) 7,069,756 B2 7/2006 Daehn 7,076,981 B2 7/2006 Bradley et al. (73) Assignees‘ GM Global Technology Operations 7,550,189 B1 * 6/2009 McKnight et a1‘ """"""" " 72/59 LLC, Detroit, MI (US); The Ohio State OTHER PUBLICATIONS University Research Foundation, W.H. Larrimer, Jr. and D.L. Duncan, “Transpactor-A Reusable Elec Columbus, OH (US) tromagnetic Forming T001 . ”, Technical Paper, 1973, pp. 1-14, Society of Manufacturing Engineers, Dearborn, MI. ( * ) Notice: Subject to any disclaimer, the term of this * Cited b examiner patent is extended or adjusted under 35 y U-S-C- 154(1)) by 837 days- Primary Examiner * Teresa M Ekiert (74) Attorney, Agent, or Firm * Reising Ethington RC. (21) App1.N0.: 11/867,734 (57) ABSTRACT (22) Filed; Oct 5, 2007 A multi-layer driver plate is disclosed for use in electromag netic sheet metal forming operations. In one embodiment, the (65) Prior Publication Data driver plate comprises a ?rst layer characterized by loW elec trical resistivity and thickness for inducement and application Us 2009/0090162 A1 APT- 9: 2009 of a suitable electromagnetic forming force, a second layer comprising an elastomeric material for compressing a sheet (51) Int_ CL metal workpiece against a die surface and then regaining its B21D 26/00 (200601) original pre-forming structure, and a third layer interposed (52) us. Cl. ......................................... .. 72/466.8; 72/54 between ‘he ?rst layer and the Second layer ‘0 Protect the _ _ _ EMF force providing layer and to provide overall strength (58) Field of Classi?cation Search .............. .. 72/54, 57, and durability to the EMF driver plate. 72/60, 63, 430, 465.1, 466, 466.8 See application ?le for complete search history. 14 Claims, 2 Drawing Sheets 10 / 'I'I'AI'IIII "I'll 1.24 US. Patent Jun. 7, 2011 Sheet 1 012 US 7,954,357 B2 'II/YIIIIIII'II I 11w US. Patent US 7,954,357 B2 ' If‘ A 33 000000 US 7,954,357 B2 1 2 DRIVER PLATE FOR ELECTROMAGNETIC and discard (or restore to their original ?at condition) loW FORMING OF SHEET METAL resistivity driver plates after each forming operation. TECHNICAL FIELD SUMMARY OF THE INVENTION This invention pertains to electromagnetic forming opera A neW multi-layer driver plate is provided for use in EMF tions in Which a thin sheet metal workpiece is driven at high sheet metal forming operations. The driver plate comprises an velocity against a forming surface. More speci?cally, this elastomeric layer for engaging a surface of a sheet metal invention pertains to the use of a laminated driver plate With Workpiece and driving the opposite surface of the Workpiece an elastomeric layer for contacting the sheet metal and against the forming features of a die or other suitable forming momentarily deforming With it as it is shaped against the surface. The driver plate also comprises a loW electrical resis tivity layer for reacting to a momentary electromagnetic ?eld forming surface. of suitable strength and driving the elastomer layer against the Workpiece in the forming operation. The driver plate includes BACKGROUND OF THE INVENTION a rigid layer for structural support betWeen the loW resistivity layer and the elastomer layer. The respective layers may be Sheet metal forming processes are knoWn in the art and attached or unattached as necessary in a particular applica typically include forcing a sheet metal Workpiece against a tion, but the three layers cooperate in their driver plate func forming tool surface, sometimes called a die surface. In elec tion in repeated forming actions on a sheet metal Workpiece or tromagnetic forming (EMF) of sheet metal the Workpiece is 20 forming actions on a succession of many Workpieces. In one rapidly propelled by a momentary electromagnetic force over example, the loW electrical resistivity layer is attached to the a short distance against the forming surface at velocities far in rigid layer and the rigid layer is attached to the elastomer excess of those found in a conventional stamping technique. layer. In another example, the loW electrical resistivity layer is Typically, the movement and deformation of the Workpiece is attached to the rigid layer but the rigid layer is not attached to completed Within a feW tens of microseconds. EMF is usually 25 the elastomer layer. applied to sheet metal Workpieces that have typical sheet or The driver plate may have a general shape that is comple foil thicknesses up to about 3 millimeters thick and frequently mentary in area (i.e., plan vieW) and elevational contour or to Workpieces less than one-half millimeter in thickness. pro?le to the forming surface of the forming tool for the sheet In a practice of EMF, a loW electrical resistivity (e. g., less metal Workpiece. A typical EMF forming tool has forming than about 0.15 micro-ohm meter) sheet metal Workpiece is 30 features that extend a small distance, e.g., a millimeter or so, positioned close to or against a forming tool surface. Such above the general pro?le of the tool surface. For example, materials include, for example, sheets of copper, aluminum, each plate member of a bipolar plate for a PEM hydrogen/ air and some of their alloys. For example, an inductive coil fuel cell is generally ?at With long, sometimes rounded, gas electromagnetic actuator is used. It is positioned close to the ?oW channels formed in a serpentine pattern and extending a opposite side of the highly conductive sheet metal. A strong 35 millimeter or so above (or beloW) the un-deformed plane of electrical current is discharged through the Windings of the the plate (Which is often less than 0.5 mm thick). In such an coil to generate, momentarily, a strong electromagnetic ?eld. application, the layers of the driver plate may be substantially That ?eld induces an opposing electrical current in the Work ?at. In other forming applications, the shape of article may be piece. The opposing magnetic ?elds betWeen the stationary someWhat arcuate, like a bent (but untWisted) ribbon. In this coil and the Workpiece sheet accelerate the Workpiece to a 40 application, the driver plate may have a curved shape comple high velocity and upon impact it stretches the sheet into mentary to the pro?le of the forming tool and like the general conformance With the tool surface. As an example, US. Pat. con?guration of the sheet metal article to be formed. No. 7,076,981 describes a use of electromagnetic forming in The multi-layer driver plate has a layer of elastomeric shaping netWorks of serpentine ?oW passages in thin metal composition and thickness for engaging the surface of the thin ?oW ?eld plates for a hydrogen/oxygen fuel cell. 45 sheet metal and driving it against the surface of the forming In some instances, the desired sheet metal Workpiece may tool and stretching the metal into conformance With the form lack suitable electrical conductivity to respond to the mag ing surface. While the thickness of the sheet metal may be netic ?eld and be driven against the forming surface by the about one-half millimeter or less, upstanding or recessed discharge of the electromagnetic actuator. In this situation, a features of the forming surface may have dimensions of a loW resistivity driver plate may be placed betWeen the elec 50 millimeter or more. The Workpiece-contacting surface of tromagnetic actuator and the sheet metal. The driver plate elastomeric layer of the driver plate accommodates this shap reacts to the electromagnetic ?eld and drives the sheet metal ing of the sheet metal by suitably ?exing and deforming to against the forming surface. Both the driver plate and the push the sheet metal into conformance With the die surface. metal Workpiece are permanently deformed in the process. So The thickness of the elastomer layer Will usually be greater the driver plate must be separated from the formed product 55 than the height of elevated or recessed features of the forming and either discarded or recycled, and the shaped sheet metal surface to ?ex, deform and force the sheet metal Workpiece product is advanced to the next stage in its manufacturing into and against the metal shaping features of the forming process. surface. The elastomer layer may be initially ?at, or may have Electromagnetic forming can achieve strain rates of the the basic contours of the part to be manufactured. This may order of l 05 sec'1 and sheet velocities in the range of 50 to 300 60 reduce the strain in the elastomer and increase its lifetime in m/ s. Such strain rates in sheet metal Workpieces may improve service. Whether ?at or contoured, the ability of the elastomer the formability of the Workpiece material. The high strain layer to deform reduces the requirement for precise alignment rates may increase the ability to make sharp and deep features of the driver plate and forming tool. in the Workpiece While decreasing spring-back of the formed The driver plate further comprises a more rigid layer sheet and Wrinkling of its features. Thus, there is a need for a 65 attached to, or simply positioned to engage, the backside of means of conducting electromagnetic forming of sheet metal the elastomeric layer.
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