Machinery's Handbook, 31st Edition
1442 High-Energy Rate Metal Forming Processes is immersed in the tank as well. When exposed to the shock wave, the blank is forced to take on the shape of the die. A schematic illustration of the process is shown in Fig. 34. Electrohydraulic forming is a hybrid between explosive forming and electromagnetic forming. The liquid-based shock is very similar to what would be produced by the explo sive method. However, this method uses essentially the same equipment (capacitor banks) that produces the current in electromagnetic forming. Electrohydraulic forming methods are adapted for use in the production of smaller part sizes. On the other hand, these methods are more favorable for automation because of the fine control of energy discharges and the compactness of the system.
Fig. 34. Electrohydraulic Forming Set-Up Lubricants and Their Effects on Press Work
Most sheet metal forming operations use lubricants to protect the die and part from excessive wear caused by scratching, scoring, welding, and galling. The physical charac teristics of the lubricant and metal-forming operation involved determine the application method to be used. Methods for applying lubricant to sheet metal include dips, swabs, brushes, wipers, roll ers, or recirculation. Of these, the three most common are the following: 1) manually wiping lubricant onto a surface with a rag; 2) roll coating, during which metal blanks pass through rollers that apply the compound; and 3) flooding, during which tooling and metal sheets are drenched with lubricant and the excess liquid is recovered via a filtration and recirculation system. Lubricants for Blanking Operations.— Blanking dies used for carbon and low-alloy steels are often run with only mill lubricant, but will last longer if lightly oiled. Higher alloy steels and stainless steels require thicker lubricants. Kerosene is usually used with alumi- num. Lubricant thickness needs to be about 0.0001 inch (0.0025 mm). During successive strokes, metal debris adheres to the punch and may accelerate wear, but damage may be reduced by application of the lubricant to the sheet or strip. High-speed blanking may re- quire heavier applications of lubrication. For sheets thicker than 1/8 inch (3.18 mm) and for stainless steel, high-pressure lubricants containing sulfurs and chlorines are often used. Lubricants for Drawing Operations.— Shallow drawing and forming of steel can be done with low-viscosity oils and soap solutions, but during deep drawing, different lubri cation requirements exist, from hydrodynamic lubrication in the blank holder to bound- ary lubrication at the drawing radius, where breakdown of the film very often occurs. Characteristic of deep drawing is the high pressure involved in the operation, on the order of 100,000 pounds per square inch (690 MPa). To deal with such force, the choice of
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