Building-up Cutting Tools Saves High-speed Steel
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ASAVING of 250 tons of high-speed steel. in a year is effected -by one concern alone—according to an official publication—by employing butt welding in the manufacture of certain tools, such as drills, reamers, milling cntters and lathe tools. Vurther valuable economies can be realized by repairing worn, chipped or broken cutters, and in the manufacture by a different rgethod of tools in this class by atomic hydrogen welding and arc welding respectively.
In the first-named process the method is to build-up the tool from two pieces of steel of different quality—one for the shank and one for the cutting portion. These are electrically butt-welded together ^ with entirely satisfactory result. To take the case of a twist drill, the shank may be of mediumcarbon steel and, the other part a highspeed-steel blank, which will ultimately become the cutter.
The two pieces are joined by flash butt welding, are taken from the machine with the minimum of loss of time so that the temperature does not appreciably fall, and are normalized in a furnace. After this the blank is subjected to an annealing process for machining, and, when this operation is completed, the tool is hardened. In doing this, the shank is first toughened and then the whole is tempered.
In the ' repair of tools—milling cutters, for example—by atomic hydrogen welding, metal is deposited on the chipped edges of the teeth or is used to replace broken teeth; the welding rods being possibly made up of discarded. portion's of high-speed-steel drills 'and taps. No flux is required, nor subsequent heat treatment, the teeth merely being finished by grinding to form and size. Before welding, however, the cutterg are pre-heated to avoid local stressing. .
A similar process can be applied to manufacture by depositing a tool-steel cutting edge by electric arc welding on to mild-steel 0r_3 per cent, nickelsteel cutter bodies. The saving in highspeed steel in such cases may amount to 90 per cent, and this represents a big economy in tungsten, which is particularly important.
There are numerous other applications of these processes in the rnanufac-, ture and repair of tools, and full instructions are contained in two leaflets issued by the Controller of Jigs. Tools and Gauges, Machine Tool Control, 35, Old Queen Street, London. S.W,1.