Method for hydrostatic extrusion of tubes and billets
United States Patent Brunosson Apr. 15, 1975 [54] METHOD FOR HYDROSTATIC EXTRUSION 3,751,957 8/1973 Nilsson 72/60 OF TUBES AND BILLETS 3,807,032 4/1974 Nilsson 72/60 Inventor: Gunnar Brunosson, Vasteras,  
 Sweden Allmanna Svenska Elektriska Aktiebolaget, Vasteras, Sweden Filed: Feb. 8, 1974 Appl. No.: 440,874  
 Assignee:  
 Foreign Application Priority Data Mar. 7, 1973 Sweden 7303176 US. Cl 72/60; 29/1875 Int. Cl B2ld 23/04 Field of Search 72/60, 253, 257, 258;  
 References Cited UNITED STATES PATENTS 8/1973 Stromblad 72/60 FOREIGN PATENTS OR APPLICATIONS 1,058,854 2/1967 United Kingdom 72/60 Primary ExaminerRichard J. l-Ierbst [57] ABSTRACT 10 Claims, 8 Drawing Figures METHOD FOR HYDROSTATIC EXTRUSION OF TUBES AND BILLETS BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing tubes by hydrostatic extrusion and to a billet intended to be used in the application of such method.  
 2. The Prior Art In hydrostatic extrusion of tubes, a tubular billet is inserted into a pressure chamber and is pressed out through a gap between a die opening and a mandrel under the effect of a surrounding pressure medium. The pressure level is high, usually between and kbar. It is therefore necessary to prevent the billet from being completely pressed out, since exposing a die opening involves an explosion-like outflow of the pressure medium, which may cause damage to the die, the mandrel and the finished product and which may involve danger to personnel. At the same time it is desirable that the material in the billet should be utilized to the greatest possible extent, which means that the extrusion should be terminated as late as possible.  
  One purpose of the invention is to make it possible to terminate the extrusion at a very late stage so that the left-over billet is slight. Another purpose of the invention is to cut off a press product in connection with the completion of the extrusion.  
 SUMMARY OF THE INVENTION According to the invention, an annular sleeve of a material which is harder than the material of the billet is applied at its rear part. The sleeve is suitably pressed into the billet. A bore is formed in the billet having a diameter insignificantly smaller than the outer diameter of the sleeve. The sleeve has a larger inner diameter than the mandrel which passes through the billet, thus securing a connection between the gap between the billet and the mandrel and the space in the pressure chamber outside the billet. The thickness of the material of the sleeve should be larger than the width ofthe gap between the mandrel and the die. When the part of the billet where the sleeve is located reaches the opening between the die and the mandrel, the extrusion conditions are affected so that the position of the billet can be indicated. What happens when the sleeve reaches the die depends on its shape. If the sleeve has such a thickness of material at its front part that it is deformed so that it surrounds the mandrel in a sealing manner, the pressure in the pressure chamber will rise since the material of the sleeve is harder than the material of the billet and therefore requires a higher extrusion pressure at a certain extrusion ratio than the material of the billet. The pressure increase can be indicated and used to generate a control signal which interrupts the supply of pressure medium to the pressure generating punch of the pressure chamber. The sleeve may be formed so that it also cuts off an extruded tube when it reaches the die. However, if the thickness of the sleeve is such that it is not pressed into sealing contact with the mandrel and if it has such an inner diameter that there is a thin gap between the mandrel and the sleeve when the sleeve reaches the die, the sleeve can cut off the extruded tube and the pressure medium will press the cut tube out of the die. When the size and length of the gap is suitable, the outflow of pressure medium can be limited to a harmless speed and magnitude. The outflow of the pressure medium or the pressing out of the tube can be indicated and a suitable control signal can be obtained.  
 BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described more closely with reference to the accompanying figures. FIG. 1 shows schematically a pressure chamber with extrusion tools and an inserted billet just after the start of extrusion; FIGS. 2-6 show various embodiments of the sleeve and the location of these in the billet and FIG. 7 and 8 a die with residual billet after completed extrusion.  
 DESCRIPTION OF THE PREFERRED EMBODIMENTS In the figures, 1 designates a part of a stand of an extrusion press, the rest of which is not shown. In the press there is a high pressure cylinder 2 which forms a pressure chamber 5 together with a pressure generating punch 3, projecting into the cylinder, and a die 4. Between the cylinder 2 and the punch 3 and the die 4, respectively, there are seals 6 and 7, respectively. In the pressure chamber 5 there are inserted a spacing collar 8 and a plate 9 having holes 9&#39; therein. A mandrel 10 which is attached to the plate 9 forms a gap with the opening 11 in the die 4. Under the effect of a pressure medium in the chamber 5 surrounding the billet 12, the billet is pressed out through the gap between the mandrel l0 and the opening 11 in the die, thus forming a tube 13. At the rear part of the billet 12, which has a hole therethrough somewhat larger than the mandrel, there is inserted a sleeve 14 of a material which is harder than the material of the billet to be extruded.  
  As shown in FIGS. 2 and 3 a sleeve 14 having relatively thin walls is applied at the rear end of the billet. The wall thickness of the sleeve should exceed the width of the gap between the mandrel 10 and the wall in the die opening 11 in order that the sleeve may be able to stop the extrusion. The sleeve 14 has the same inner diameter as the hole in the billet l2, and thus a somewhat larger diameter than the mandrel 10. It is pressed into a bore 15 or 16, respectively. In the embodiment according to FIG. 2 the bore and the sleeve have the same length, whereas in the embodiment according to FIG. 3 the bore is longer than the sleeve. In the embodiment according to FIGS. 4 and 5, a sleeve 17 having thick walls is positioned in a bore 18 or 19, respectively, in the billet 12. In the embodiment according to FIG. 4 the bore and the sleeve have the same length, whereas in the embodiment according to FIG. 5 the bore is longer than the sleeve. In the embodiment according to FIG. 6 an outwardly conical sleeve 20 is applied in a corresponding way in a bore 21, the sleeve then having a larger diameter at its rear end than at its front end.  
  FIG. 7 shows how, at the end of the extrusion, when the sleeve 14 has moved down to the die 4, the front end of the sleeve makes contact with the die, the sleeve thus cutting off the tube at the die opening. In this case, the thickness of the sleeve wall is such that it is compressed and makes contact with the mandrel in a sealing manner. The cross-section of the sleeve should be so large in relation to the cross-section of the annular opening 11 between the die 4 and the mandrel 10 that the ratio is greater than the possible extrusion ratio with the pressure with which the material in the billet 12 can be pressed into the said gap. The pressing out the sleeve then requires a higher pressure, and a pressure increase caused by the sleeve can be indicated and give rise to a control signal which interrupts the supply of energy to the driving cylinder of the pressure generating punch.  
  H6. 8 shows how a sleeve with great wall thickness makes contact at the end of the extrusion with the die with its front end. The sleeve has cut off the tube 13. The sleeve has such a strength that it is not deformed into making contact with the mandrel 10, but an annular gap 22 remains. When the gap is small and the length of the gap relatively small the pressure drop during the flow of pressure medium from the pressure chamber and the out-flowing amount of pressure medium will be small. The pressure medium flowing out through the gap 22 presses the last part of the tube 13 out of the die.  
  The billet may be, for example, of aluminum or copper and the sleeve of steel.  
 I claim:  
  1. A method for the hydrostatic extrusion of tubes which comprises inserting into a pressure chamber having a die opening and a mandrel passing through the die opening and of less diameter than the die opening a billet having a central hole therethrough and having a bore at the rear end, and a sleeve in said bore formed of a material which is harder than the material of the billet and has a larger inner diameter than the diameter of the mandrel, the sleeve having a greater thickness of material than the space between the die opening and the mandrel and being substantially shorter than the billet, thereby to prevent the billet from being completely pressed out of the die opening.  
  2. A method as claimed in claim 1, in which the sleeve has substantially the same inner diameter as the inner diameter of the hole in the billet.  
  3. A method as claimed in claim 2, in which the bore is longer than the sleeve.  
  4. A method as claimed in claim 1, in which the sleeve has a greater thickness of material at its rear end than at its front end.  
  5. A billet for use in the hydrostatic extrusion of tubes, having a central bore therethrough and having a sleeve inserted in its rear end concentric with the bore and of harder material than the material of the billet and substantially shorter than the billet.  
  6. A billet as claimed in claim 5, in which billet has a bore at its rear end with a larger diameter than the hole in the billet, the sleeve being inserted in such bore.  
  7. A billet as claimed in claim 6, in which the bore is longer than the sleeve.  
  8. A billet as claimed in claim 5 in which the sleeve has a larger diameter at its rear end than at its front end.  
  9. A billet as claimed in claim 5, in which the billet is of copper and the sleeve is of steel.  
 10. A billet as claimed in claim 5, in which the billet is of aluminium and the sleeve is of steel.