Most production friction welding applications employ 'in-process' monitoring of the major welding conditions as a Quality Control Method which for continuous drive rotary friction welding include: -
- Rotation speed
- Friction force
- Axial displacement (shortening of the two components)
- Forge force
A machine shut down facility or alarm system can be operated by the monitoring system if incorrect welding conditions are indicated, thus avoiding poor weld quality. However, not only are the welding conditions monitored but, Quality Control starts with the raw materials to be joined and the following should be checked:
- Chemical analysis
- Microstructures
- Strength and hardness
- Dimensions, tolerances
- As supplied condition
Following these checks the dimensions of the component are measured for compliance with the specification, and the surfaces are cleaned for welding. The tooling or clamping fixtures holding the components to be welded should also be checked for:
- Accuracy of alignment
- Excessive clamping forces
- Permitted overhang from the fixture
A welding procedure (in accordance with BSEN ISO 15620:2000) is usually agreed between contractor and customer, which will usually involve most of the aforementioned topics. Weld procedure approval usually requires that destructive testing be undertaken after the production of an agreed number of welds. In the event of failure during bend or tensile tests then preceding samples will also be tested until the source of failure is isolated.
Ultrasonic testing has been applied to friction welded components and techniques are being developed which are said to be capable of detecting non-welded regions.
For further information see Joining Technologies or please contact us.