Metal fusion bonding – Process – Using dynamic frictional energy
Patent
1986-12-30
1988-04-05
Godici, Nicholas P.
Metal fusion bonding
Process
Using dynamic frictional energy
228113, 228 2, 228 443, B23K 2012
Patent
active
047353538
DESCRIPTION:
BRIEF SUMMARY
The invention relates to methods and apparatus for friction welding.
In conventional friction welding, relative rotation between a pair of workpieces is caused while the workpieces are urged together. Typically thereafter once sufficient heat is built up between the workpieces relative rotation is stopped and the workpieces are urged together under forging force which may be the same as or greater than the original urging force.
One of the problems with conventional friction welding arises when the two workpieces are initially brought together. At this stage, there is significant dry friction between the workpieces and a considerable increase in energy is required to overcome this dry friction. For example, when welding a 10 mm diameter stud the initial frictional torque may be in the range 30-40 Nm. This problem has been overcome in the past by designing a drive motor capable of supplying sufficient driving torque to overcome dry friction. Such a drive motor is acceptable in relatively stationary friction welding apparatus but is not a satisfactory solution when it comes to the design of portable friction welding apparatus. There is a requirement now to be able to carry out friction welding at the site at which the welded workpieces are to be used. This should be contrasted with prior arrangements in which the workpieces are brought to the friction welding apparatus where they are welded and then are transported back to their position of use. However, drive motors suitable for portable welding apparatus typically have a driving torque of the order of 8 Nm. Thus in the example mentioned, when welding a stud of 10 mm diameter, on touchdown there is a net resistive torque of over 20 Nm. The effect of this is to rapidly decelerate the motor so that the heat of rubbing is reduced and no flux forms. The motor thus stalls before the weld is initiated. The motor rating would therefore need to be increased by a factor of 3 or 4 thus rendering the concept of portability impractable.
In accordance with one aspect of the present invention, a method of friction welding comprises actuating drive means coupled to a primary source of energy to cause relative rotation between a pair of workpieces, the drive means also being coupled to an auxiliary source of energy; and bringing the workpieces into contact with one another under pressure, the auxiliary source of energy being adapted to supply the drive means with sufficient additional energy such that the drive means overcomes the effects of resistive torque between the workpieces on initial contact between the workpieces.
In accordance with a second aspect of the present invention, friction welding apparatus comprises drive means for coupling to a primary source of energy in use and for causing relative rotation between a pair of workpieces; an auxiliary energy store coupled to the drive means; and means for urging the workpieces into contact with one another, the auxiliary store being adapted to supply the drive means with sufficient additional energy such that the drive means overcomes the effects of resistive torque between the workpiece of initial contact between the workpieces in use.
The invention enables a compact, more efficient and much cheaper method and apparatus to be achieved as well as enabling portable friction welding apparatus to be designed. The problem of overcoming the high resistive torque experienced during initial touchdown is dealt with by coupling the drive means to an auxiliary source of energy which supplies additional energy during the touchdown phase. Sufficient additional energy is supplied such that the deceleration of the drive means on initial contact between the workpieces is limited to acceptable limits until the resistive torque has fallen to a level which is substantially equal to or less than the capacity of the drive means. In other words, an equilibrium between the driving torque of the drive means and the resistive torque between the workpieces is reached before the drive means stalls. After this phase, the drive means is capable o
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Heath Thomas V.
Thomson Allan R.
Godici Nicholas P.
Heinrich Samuel M.
Thomson Welding & Inspection Ltd.
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