Swaging Tools
In order to fit bearings with a groove around the outer face of a spherical plain bearing you will require a tool of some form. This tooling normally takes the form of either a plain die which is fixed into a hydraulic press which is then brought to bear on the bearing groove, hence forcing the edge of the groove onto the assembly (swaging). The alternative and preferred method is to use a roller swaging tool which is a much more controlled method of swaging the outer ring lip. The animation to the left shows how this is performed. Roller swaging tools take the form of either a two or three roller format which is specifically designed to engage within the groove of one particular bearing size and in such a way that the edge of the bearing is once more swaged over the assembly. Roller swaging tools can take the form of fixed (ie drill fly press mounted) or portable. Obviously portable tools have the advantage of being used “on airframe” and are manually turned using a C wrench or spanner to gently swage the bearing outer ring. The hand force required is very low due to the design of the tool.
Once the bearing has been swaged into the assembly from both sides some form of inspection and testing should be applied to ensure the swage has been conducted satisfactorily. Most manufacturers have specifications on this (see testing tools). Any cracks in the swaged lip will require the bearing to be removed and discarded. The swage operation should be reviewed before a refit operation is started in order to prevent a repeat failure. Testing can be carried out using proof loading tools and/or breakout torque tools. Proof loading tools apply a preset load and measure any deflection on the other side of the bearing. A table of allowable deflections upon certain applied loads should be available from the airframe OEM.
Other forms of swaging tools can be used to peen a “sacrificial bushing” so the end faces of the bushing are swaged over the edge of both the bearing and assembly. Ball staking is another form of swaging but in this instance the assembly is deformed by the use of a hard ball which locates close to the edge of the bearing mounting hole and is then pressed so that the edge of the hole is deformed slightly over the bearing. Whilst this method is simple there is only a limited number of times an assembly can be acceptably and safely be deformed before the assembly ahs to be rejected.
