Method and apparatus for fabricating articles from metals having a hexagonal close packed crystal structure

Abstract

A method and apparatus for fabricating articles from metals having a hexagonal close packed (HCP) crystal structure is described. The method comprises a two-stage process: specialized hot deep drawing and pneumatic coining within a single press cycle. The apparatus includes a drawing chamber in which the environmental temperature is sufficient to impart enough ductility to the metal or alloy blank to allow it to be drawn about a plug into an outline shape of the finished part. More detailed features are then added by increasing the gas pressure inside the chamber, thereby forcing the drawn blank more closely against the contours of the plug. Use of pneumatic pressure avoids the use of matched dies, which are prohibitively complex and expensive to use to shape parts from such HCP metals.

1 . A method of fabricating an article from a metal or alloy having a hexagonal close packed crystal structure, the method comprising a draw stage followed by a coining stage, wherein
 the draw stage comprises the steps of:
 a) providing a blank of a metal or alloy having a hexagonal close packed crystal structure; 
 b) mounting the blank in a deep draw press adjacent a draw ring; 
 c) heating the environment of the blank to a predetermined temperature; and 
 d) moving a heated shaped plug at a predetermined speed onto the blank and through the draw ring so as to draw the heated blank into a drawing chamber as the plug advances through the draw ring; and wherein 
   the coining stage comprises the steps of:
 e) holding the plug stationary; 
 f) clamping a flange of the drawn blank so as to form a seal between the blank and the drawing chamber; and 
 g) passing a gas into the drawing chamber so as to increase the pressure therein, thereby applying a pneumatic force to the drawn blank to force the drawn blank to mate closely with the plug. 
   
     
     
         2 . A method in accordance with  claim 1  wherein the alloy is magnesium or a magnesium-rich alloy. 
     
     
         3 . A method in accordance with  claim 1  wherein the plug is a helmet-shaped plug, the method thereby resulting in creation of a helmet-shaped article. 
     
     
         4 . A method in accordance with  claim 1  wherein the draw ring is mounted on a first clamping plate and a stripper plate is mounted on a second clamping plate, the blank being located between the first and second clamping plates. 
     
     
         5 . A method in accordance with  claim 4  wherein the first and second clamping plates are arranged to maintain a gap of predetermined size therebetween during the draw stage and to close that gap about the flange of the drawn blank in order to form the seal during the coining stage. 
     
     
         6 . A method in accordance with  claim 4  wherein the method is followed by a step of retracting the plug through the draw ring, whilst retaining the formed blank on the stripper plate. 
     
     
         7 . A method in accordance with  claim 6  wherein the method is followed by the steps of solution treating, quenching and then ageing the formed blank. 
     
     
         8 . An apparatus for fabricating an article from a metal or alloy having a hexagonal close packed crystal structure, the apparatus comprising:
 a drawing chamber having a gas inlet;   first and second clamping plates between which a heated blank may be located, a draw ring being mounted on the first clamping plate; and   a heater for controlling the environmental temperature of the blank;   a heated shaped plug suitable for insertion through the draw ring to draw the heated blank onto the plug and into the drawing chamber as the plug is advanced, wherein:   the clamping plates are operable to clamp a flange of the drawn blank so as to form a seal between the blank and the drawing chamber; and   the gas inlet is for passing pressurized gas into the drawing chamber such that the pressure therein is increased, thereby causing a pneumatic force to be applied to the drawn blank to force the drawn blank to mate closely with the plug.   
     
     
         9 . A apparatus in accordance with  claim 8  wherein the alloy is magnesium or a magnesium-rich alloy. 
     
     
         10 . A apparatus in accordance with  claim 8  wherein the plug is a helmet-shaped plug, the apparatus therefore being for fabrication of a helmet-shaped article. 
     
     
         11 . A apparatus in accordance with  claim 8  including a stripper plate mounted on the second clamping plate. 
     
     
         12 . A apparatus in accordance with  claim 11  wherein the first and second clamping plates are moveable to adjust the separation therebetween, the separation being such as to maintain a controlled gap whilst advancing the plug and to close around the flange of the drawn blank in order to form the seal thereafter.