Electrical upsetting method and device therefor
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a method and device for electrical upsetting, that is, expanding to increase the diameter of the end part of metal raw material such as rods, pipes, and the like, in the main, by resistive heat generation at that part to soften. 
     2. Description of Prior Arts 
     The electrical upsetting method which has so far been in practice comprises the following four steps, in reference to FIGS. 1A through D of the accompanying drawing, wherein a reference numeral 1 designates a cylindrical shaping die for the upsetting work, a numeral 2 refers to a reinforcing ring for the shaping die 1, a numeral 3 denotes a die holder, 4 designates an anvil electrode having an electrode tip 41 at its distal end and also serving as a knock-out rod, 5 indicates a bushing to guide the forwarding and retracting movements of the anvil electrode 4, and 6 refers to an electrode in a clamping type, for example, to contact with a workpiece W. 
     Step A: The anvil electrode 4 is forwarded to position its distal end part 41 at the entrance opening of the shaping die 1, and the end face of the workpiece W clamped by the clamp electrode 6 is butted to the abovementioned electrode tip 41. 
     Step B: Electric current is caused to flow across the anvil electrode 4 and the clamp electrode 6, and, as the anvil electrode 4 is being gradually retracted, the workpiece W is pushed into the shaping die 1 under a strong pressure, during which the end part W&#39; of the workpiece becomes softened by heat generated to contact the inner peripheral surface of the shaping die 1. 
     Step C: The workpiece W is further pushed into the die 1 until the electrode tip 41 reaches the bottom (or the innermost) part of the shaping die 1, when the upsetting work is terminated. 
     Step D: The clamp electrode 6 is released from the workpiece W, and the anvil electrode 4 is forwarded to thereby knock out the thus upset workpiece W from the shaping die 1. 
     In more detail, the end part W&#39; of the workpiece increases its diameter and upset during the abovementioned steps B and C to contact the inner peripheral surface of the shaping die 1, and slide-moves along the contacted surface. In this case, the inner peripheral surface of the shaping die 1 for shaping the end part W&#39; of the workpiece W, which has been softened by heat generation into an intended or predetermined shape is brought to a high temperature condition along with heating of the workpiece W, and is also subjected to vigorous frictional force with the result that it tends to be readily worn out. As the consequence of this, the service life of the shaping die 1 is generally short, and frequent exchange of the part is unavoidable. On account of this, a number of spare shaping dies have to be provided beforehand in preparation for such exchange. 
     Moreover, since the inner peripheral surface of the shaping die is more or less exposed to the external atmosphere, or air, it tends to be readily oxidized, which accelerates wear and tear in a rather short period of service. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide an improved method for the electrical upsetting work of the tubular or rod-shaped metal material, which is free from the above-described disadvantages inherent in the known upsetting methods. 
     It is another object of the present invention to provide an improved electrical upsetting device having good durability against oxidation due to exposure of the shaping die to the external atmosphere, and also against vigorous frictional force caused to the inner peripheral surface thereof during the upsetting work. 
     According to the present invention, in one aspect thereof, there is provided an electrical upsetting method of a cylindrical metal material which comprises steps of: causing an anvil electrode and an end face of a workpiece to contact each other in a shaping die; conducting electric current across electrodes to generate heat at the end part of said workpiece to soften the end portion; pushing said workpiece to the anvil electrode under vigorous pressure, while withdrawing the anvil electrode toward the bottom or the innermost part of said shaping die, to upset the end part following said shaping die; and discharging said workpiece out of said shaping die by forwarding said anvil electrode. 
     According to the present invention, in another aspect thereof, there is provided an electrical upsetting device for upsetting cylindrical metal material, which comprises in combination: an anvil electrode, to which an end face of a workpiece is butted; another electrode to be connected with said workpiece; a shaping die provided between said anvil electrode and said another electrode with the anvil electrode constituting the bottom or the innermost part of the shaping die; and an inert gas feeding source, a space gap being formed between the outer peripheral surface of said anvil electrode which moves back and forth in an along said shaping die and the inner peripheral surface of said shaping die to be communicatively connected with said inert gas feeding source through passage grooves. 
     There has thus been outlined, rather broadly, the more important feature of the present invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional features of the invention that will be described hereinafter and which will form the subject of the claim appended hereto. Those skilled in the art will appreciate that the conception, upon which this disclosure is based may readily be utilized as a basis for the designing of other structure for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent construction so far as they do not depart from the spirit and scope of the present invention. 
    
    
     BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING 
     Specific embodiments of the present invention have been chosen for the purpose of illustration and description, and are shown in the accompanying drawing, forming a part of the specification, in which: 
     FIGS. 1A through 1D are respectively schematic side views, in longitudinal cross-section, showing the sequential steps in the conventional electrical upsetting method; 
     FIGS. 2A through 2F are respectively schematic side views, in longitudinal cross-section, showing the sequential steps in the electrical upsetting method according to the present invention; 
     FIGS. 3A through 3D are respectively schematic side views, in longitudinal cross-section, showing the improved construction of the electrical upsetting device according to the present invention as well as the sequential steps of the electrical upsetting work using the same; 
     FIG. 4 is a cross-sectional view of the electrical upsetting device according to the present invention taken along a line A--A in FIG. 3A; and 
     FIG. 5 is also a cross-sectional view of the electrical upsetting device according to the present invention, taken along a line B--B in FIG. 3A. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     In the following, the preferred embodiments of the electrical upsetting method and device according to the present invention will be described in speicific details in reference to FIGS. 2A through 2F as well as FIGS. 3, 4 and 5 of the accompanying drawing. 
     The electrical upsetting method according to the present invention, in contrast to the afore-described conventional upsetting method, comprises the following steps. 
     Step A: The anvil electrode 4 is forwarded to position its distal end part 41 at the entrance opening of the shaping die 1, and the end face of the workpiece W clamped by the clamp electrode 6 is butted to the abovementioned electrode tip 41. 
     Step B: In a state of the workpiece W being butted to the electrode tip 41, the anvil electrode 4 is retreated for a certain definite distance, after which electric current is caused to flow across the anvil electrode 4 and the clamp electrode 6. A clearance S is present between the workpiece W and the inner peripheral surface of the shaping die 1. After lapse of a certain time period, the end part W&#39; of the workpiece generates heat to become softened. 
     Step C: Subsequently, in the state of the head-to-head contact of the workpiece and the anvil electrode and the current conduction across the anvil electrode and the clamp electrode as mentioned above, the anvil electrode 4 is withdrawn until the electrode tip 41 reached the bottom (or the innermost) part of the shaping die 1, while the workpiece W is being pushed into the shaping die under a vigorous pressure force, whereby the end part W&#39; of the workpiece W becomes gradually swollen and the upsetting work starts. 
     Step D: The workpiece W is continued to be pushed under a vigorous pressure force into the shaping die 1, whereby the end part W&#39; of the workpiece W contacts the inner peripheral surface of the shaping die 1. 
     Step E: The end part W&#39; of the workpiece W fully expands within the interior of the shaping die 1 and shaped into predetermined size and shape. 
     Step F: The clamp electrode 6 is released or relaxed from the workpiece W, and then the anvil electrode 4 is forwarded to knock out the thus upset workpiece W from the shaping die 1. 
     Since the electrical upsetting method according to the present invention is performed in the above-described sequential process steps, the clearance S present between the outer peripheral surface of the end part W&#39; of the workpiece W and the inner peripheral surface of the shaping die 1 prevents or delays direct heating of the shaping die 1 during the steps B and C, due to heat generation in the workpiece W, and this space gap S diminishes to extinction during the step D by swelling or upsetting of the distal end of the workpiece W through its diametrical increase due to pushing under vigorous pressure into the shaping die. 
     Accordingly, while the upsetting work is being performed, there takes place no slide-movement between the outer peripheral surface of the end part W&#39; of the workpiece and the inner peripheral surface of the shaping die 1, which results in the least wear in the shaping die 1 and produces a remarkable effect of improving the durability of the shaping die. 
     In addition, since the distal end of the workpiece W first generates heat due to the electric current conduction to increase the electrical resistance at that part from the heat as generated and the current flows rearward from the distal end of the workpiece W, the heat generation and softening of the workpiece at the distal end W&#39; thereof is favorable, whereby the end part W&#39; can be easily upset. 
     In the following, the electrical upsetting device according to the present invention will be described in reference to the accompanying drawing. As illustrated in FIGS. 3 to 5, the electrical upsetting device of the present invention is basically constructed with the cylindrical upsetting die 1, the reinforcing die 2 for the shaping die 1, the die holder 3, the anvil electrode 4 having the electrode tip 41 at its distal end and also serving as the knock-out rod, the bushing 5 to guide the forwarding and retracting motions of the anvil electrode 4, and the clamping type electrode 6 to be connected with the workpiece W. A space gap S is formed between the inner peripheral surface of the shaping die 1 and the outer peripheral surface of the anvil electrode 4 by reducing, to a slight extent, the diameter of the anvil electrode 4 at its portion to be inserted into, and extended through, the shaping die 1. 
     The abovementioned space gap S is communicatively connected to an inert gas feeding source 7 such as, for example, nitrogen gas feeding source, through a radial groove T1 formed at the end face of the bushing 5, an axial groove T2 defined in the inner peripheral surface of the reinforcing ring 2, and annular groove T3 formed at a portion where the inner end face of the reinforcing die 2 and the die holder 3 meet, and a groove T4 radially extending through the die holder 3 and reaching the abovementioned annular groove T3. It is to be noted that the inert gas is continuously fed under a constant pressure. 
     In the following, the upsetting steps using the above-described upsetting device according to the present invention will be described in reference to FIGS. 3A to 3D. 
     Step A: The anvil electrode 4 is forwarded to position its distal end part 41 at the entrance opening of the shaping die 1, and the end face of the workpiece W clamped by the clamp electrode 6 is butted to the abovementioned electrode tip 41. The inert gas flows into the space gap S between the outer peripheral surface of the anvil electrode 4 and the inner peripheral surface of the shaping die 1 through the grooves T1, T2, T3 and T4, respectively. 
     Step B: Electric current is caused to flow across the anvil electrode 4 and the clamp electrode 6, and, as the anvil electrode 4 is being gradually retreated, the workpiece W is pushed into the shaping die 1 under a vigorous pressure, during which the end part W&#39;of the workpiece becomes softened by heat generated to contact the inner peripheral surface of the shaping die 1. 
     Step C: The workpiece W is further pushed into the die 1 until the electrode tip 41 reaches the bottom (or the innermost) part of the shaping die 1, when the upsetting work is terminated. 
     Step D: The clamp electrode 6 is released from the workpiece W, and the anvil electrode 4 is forwarded to thereby knock out the thus upset workpiece W from the shaping die 1. 
     In the above-described steps B and C, since the space gap between the inner peripheral surface of the shaping die 1 and the outer periphery of the anvil electrode 4 is filled with the inert gas immediately before the end part W&#39; of the workpiece 1 contact thereto by expansion, there occurs no oxidation of the shaping die 1. In addition, the shaping die 1 is sufficiently cooled by the inert gas to be well protected from overheating. 
     Furthermore, at the time of knocking out the workpiece from the die at the step D, and even thereafter, the inert gas continues to flow through the space gap S, so that no air possibly intrudes into the gap. In other words, since the inner peripheral surface of the shaping die 1 does not contact air during the upsetting work, the shaping die 1 can be well prevented from wear and tear to the substantially perfect extent to be ascribable to oxidation, as well as from deterioration due to the high temperature generated during the upsetting work. Consequently, in conjunction with the cooling effect of the inert gas, the durability of the shaping die 1 improves remarkably and effectively.