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Apparatus for controlling the movement of a reciprocatory vacuum forming machine driven element of a metal forming machine between extended and retracted positions including first piston means defined by said element, first reservoir means slidablyreceiving said first piston means therein, said first piston means having a face disposed in fluid communication with said first reservoir means, second reservoir means, second piston means secured to and projecting from said face of said first pistonmeans, said second piston means being slidably received within said second reservoir when said first piston means is substantially retracted and being disposed wholly outside said second reservoir when said first piston is essentially fully extended,said face of said first piston means having a substantially larger working area exposed to said fluid in said first reservoir than the working surface area of said second piston means which is exposed to said fluid in said second reservoir, a source ofpressurized hydraulic fluid, means connecting said source of pressurized hydraulic fluid in fluid communication with said first reservoir, means connecting said source of pressurized hydraulic fluid in fluid communication with said second reservoir. athird reservoir, conduit means connecting said third reservoir in fluid communication with said first reservoir, valve means interposed in said conduit means for controlling the flow of hydraulic fluid between said first and third reservoirs, first andsecond valve means interposed between said source of pressurized hydraulic fluid and said first and second reservoirs, respectively, and means controlling the opening and closing of said first valve means and wherein said first valve means permits avolume of hydraulic fluid to flow from said source of hydraulic fluid into said first cavity at all times except when it is desired to move said first piston means toward its retracted position. In a typical extrusion operation, a metal billet is held within a die cavity. A punch or anvil is inserted in the die cavity to define an annular space therebetween and held stationary while the billet is forced to extrude over and about theanvil, resulting in extrusion of the billet into and then out of the annular space between the die cavity and the anvil. In other embodiments, the anvil is itself moved relative to a stationary die cavity with resultant extrusion of the billet out ofthe die cavity through the annular space between the anvil and the die cavity wall. It has been recognized heretofore that tool breakage, particularly breakage of the anvil, is likely if there is misalignment of the anvil with respect to the die cavity by as much as 0.0005 inch, per inch, for example. Such misalignment canoccur due to "wobble" of the anvil and/or can be caused by defects in the metal billet, etc. For example, hard spots in the billet and/or air inclusions can result in anvil misalignment sufficient to cause breaking of the anvil. As a consequence ofthese and other factors, relative movement of the machine elements has been purposely slow and precise. In certain prior art extrusion operations, in order to utilize a starting billet that has a minimum cross-sectional area (thereby realizing the necessary economies associated with the choice of extrusion as the forming method), the extrusionprocess has included multiple steps wherein the billet is reduced, i.e. extruded, a multiplicity of times, each successive extrusion enlarging the diameter of the product by an amount that is within the heretofore acceptable reduction limit. Obviously,these multiple "hit" operations increase the cost of the process, thereby increasing the cost of the resultant product. The present inventor has found that reductions in excess of one hundred twelve (112%) percent can be obtained, using only a single "hit", thereby opening up the availability of the less expensive cold extrusion forming process to the manufactureof products not heretofore possible. This is accomplished in a single "hit" operation, by establishing and maintaining a force against the extruding billet which is in opposite to the extruding force, thereby controlling the flow of the metal in thecourse of the extrusion. It has been found that the opposing force applied to the vacuum forming machine product appears to rigidify the product with respect to the extrusion apparatus such that the extruding product which is relatively rigidly held at one endwithin the annular space between the anvil and the die cavity and at its opposite outboard end by a member which is applying the extrusion-opposition force to the product as it is being formed, appears to function as a lateral support sleeve for theanvil about which the billet is extruding. Tool breakage has been reduced by the present inventors to a negligible factor, even at production rates of between 30 and 40 products per minute. Further, the product exhibits excellent physical propertiesincluding good dimensional tolerances.
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