Introduction to monitoring and control of welding process

Substantial progress has been made in both the determination of control parameters, monitoring techniques and automatic process control.

Principles of process control

In any manufacturing process it is necessary to ensure that the outcome of the operations carried out matches some defined objective. This involves controlling the operation of the process in some way

In order to achieve the desired output it is necessary to:

  • Establish control relationships which enable the effect of the control variables on the process performance to be predicted.
  •  Monitor the process to ensure that it is operating within limits defined by the control relationships.  
  • Compared with other manufacturing processes, welding has established a reputation for being more difficult to control and less likely to achieve consistent quality.
  • This is probably a result of the multiplicity of interrelated control parameters, the complexity of the control relationships and the difficulty of monitoring process performance.
  • It is also difficult to assess weld integrity without careful non-destructive examination and mechanical properties cannot be checked without destructive testing of the fabrication.
  • These difficulties are recognized in international quality standards and welding is classified as a special process in ISO 9000 and the control measures required for welded fabrication are detailed in ISO 3834.

Comparison of control variables for automatic plasma and MMA welding

An indication of the number of control parameters which need to be considered for two contrasting arc welding processes is given in Table below.

The traditional manual control techniques will be outlined in this chapter and the influence of developments in processes and equipment will be discussed. Substantial progress has also been made in both the determination of control parameters, monitoring techniques and automatic process control.

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