Patent GB-667002-A (GB)
Title: Method and apparatus for controlling heat in hot machining processes for metals and other materials
IPC: B23P25/00
Filed: 1950-01-31
Abstract: 667,002. Machining heated work. WEINGART, R. I. N. Jan. 31, 1950 [Feb. 8, 1949; May 10, 1949; June 25, 1949], No. 2431/50. Class 83 (iii). [Also in Groups XI and XXXV] Apparatus for machining metal and other materials by means of a cutting tool while the material is heated to reduce the shear strength comprises a strain-responsive element affected by strains imposed by the cutting action, and means whereby variations in the element due to increase or decrease in the shear strength effect a corresponding increase or decrease in the applied heat so as to restore to a predetermined amount the shear strength of the heated material. The element may be applied to the cutting tool, tool-holder, to the work, or to some part of the machine which is subject to strains from the cutting action. In the lathe shown in Fig. 2, the work 21 is heated by an induction coil 30 connected to a high-frequency generator 41, and a strain gauge 36 mounted on the cutting tool 16 is in electrical connection with a control circuit 40, a pre-heat switch 42 and a reversible motor 34. The gauge is connected to one arm of a Wheatstone bridge circuit which includes a fixed resistor 45, Fig. 5, and an adjustable resistor 46. An amplifier 48, in circuit with a power supply 50 and an output meter 51 receives an unbalance voltage from the bridge and delivers an amplified current to the armature 49 of the motor. In operation, if the temperature is above or below that desired, the strain gauge resistance will alter and unbalance the bridge thereby applying a current of different magnitude to the armature 49 to move the coil towards or away from the work and restore the temperature, and hence the shear strength, to the desired value. The heating element may entirely surround the work. In a modification, Fig. 6 (not shown), an hydraulic strain gauge is used. In another modification, Fig. 7 (not shown), an electric strain gauge is mounted on the tool assembly, and variations from the gauge are transmitted to a variable resistance in the grid circuit of a triode electron discharge device to vary the power output thereof, coupling means transmitting the power from the discharge device to the induction coil to control the power input of the latter. In a further modification, Fig. 8 (not shown), the heating unit is composed of one or more gas torches. In another modification, Fig. 9 (not shown), an hydraulic strain gauge is connected to a Bourdon tube the movable end of which is operatively connected to an inductance coil rotatable inside a stationary coil, the output of a high-frequency generator being connected to one of the coils and the heating element to the other coil. In a modification of this arrangement, Fig. 10 (not shown), the Bourdon tube is connected to valve controlling the supply of gas to a torch. In a further modification, Fig. 11, the amount of current flowing to a motor 96 driving the machine tool 97 acts as a measure of the cutting strains involved. The input current to the motor is measured by means of a small resistor 98 inserted in the A.C. line. An amplifier 100 amplifies the voltage across the resistor and applies it to a rectifier 53, the output of which may be connected directly to any one of the control devices. An auxiliary balancing circuit 54 is used to provide a null point. Such a device may be used on a milling machine or any other machine tool which uses a revolving cutter. It may also be used on a shaper or any other machine tool using a power drive to cut material. In another modification, Fig. 12 (not shown), an electric strain gauge controls the direct current in the field coils of a highfrequency generator connected to an induction coil. In a further modification, Fig. 13 (not shown), an electric strain gauge is connected to a reversible motor which controls the arm of a rheostat in the field coils of an A.C. generator. In another modification, Fig. 14 (not shown), the strain gauge is connected to a Wheatstone bridge circuit, the output from which is connected to a mirror galvanometer, the light from the mirror being received by two photo-electric cells connected to a differential amplifier and to it control circuit for transmitting electrical power to a variable heat applicator. In a further modification, Fig. 15 (not shown), applied to a milling machine, any one of several strain gauges can be put in circuit with an amplifier and reversible motor which is arranged to operate a valve controlling the supply of gas to a torch for heating the work. In a still further modification, Fig. 16 (not shown), applied to a boring machine, one of several strain gauges is in circuit with an amplifier and reversible motor for controlling the heat supplied by an induction coil. In this connection, means are provided for cooling the tailstock shaft. It is stated that the heat may be applied by electrical resistance means including arc means.