Metal working

Claim 1

A method of drawing a metal workpiece to form in it a hole of non-circular cross-section, the workpiece having an elongate cross-section, the length and width of the cross-section being greater than those required in the cross-section of the finished article, the method comprising the steps of forming in the workpiece a hole which extends longitudinally of the workpiece, applying a tensile load over at least a length of the workpiece including said hole in the direction of the longitudinal axis of the hole, heating the workpiece locally to a temperature lying between upper and lower limits, the lower limit of said temperature being just above the temperature below which the material of the workpiece will neck and fracture or simply fracture rather than elongate, the upper limit of temperature being just below the temperature at which undesirable metallurgical changes such as grain growth or phase transformation occur in the material of the workpiece, said local heating being carried out at a portion of said length of the workpiece to cause local elongation of the workpiece, the temperature and tensile load together being such as to cause said local elongation of the workpiece to take place at a strain rate lying between upper and lower limits, the lower limit of said strain rate being above the strain rate at which the slow working of the material of the workpiece causes undesirable metallurgical changes to occur and the upper limit of the strain rate being below the strain rate at which the material of the workpiece will neck and fracture or simply fracture rather than elongate and causing relative longitudinal movement between the heating means and the work-piece so as to maintain the position of said heating means relative to said workpiece in such manner that the workpiece is deformed into a desired shape of smaller crosssection and said hole is reduced in size and of different crosssection.

Claim 2

A method of drawing a metal workpiece to form in it a hole of non-circular cross-section, the workpiece having an elongate cross-section, the length and width of the cross-section being greater than those required in the cross-section of the finished article, the method comprising the steps of forming in the workpiece a hole which extends longitudinally of the workpiece, applying a tensile load over at least a length of the workpiece including said hole in the direction of the longitudinal axis of the hole, heating the workpiece locally to a temperature lying between upper and lower limits, the lower limit of said temperature being just above the temperature below which the material of the workpiece will neck and fracture or simply fracture rather than elongate, the upper limit of temperature being just below the temperature at which undesirable metallurgical changes such as grain growth or phase transformation occur in the material of the workpiece, said local heating being carried out at a portion of said length of the workpiece to cause local elongation of the workpiece, the temperature and tensile load together being such as to cause said local elongation of the workpiece to take place at a strain rate lying between upper and lower limits, the lower limit of said strain rate being above the strain rate at which the slow working of the material of the workpiece causes undesirable metallurgical changes to occur and the upper limit of the strain rate being below the strain rate at which the material of the workpiece will neck and fracture or simply fracture rather than elongate and causing relative longitudinal movement between the heating means and the work-piece so as to maintain the position of said heating means relative to said workpiece in such manner that the workpiece is deformed into a desired shape of smaller crosssection and said hole is reduced in size and of different crosssection.