Requalifying Surface

During processing, when a surface must be returned to a previous condition or state before dimensional control of the workpiece can be regained, a requalifying operation must take place. Such an operation in the sequence is indicated by several factors like :

Strength and Rigidity of the Workpiece

Many parts are fragile and thus are difficult to process without being distorted by the clamping and cutting forces, although the appropriate locating surface was chosen for the workpiece. The design of the part may, however, eliminate this distortion completely.

State of the Material as It is Received

It is not always possible to eliminate all stresses in a piece of material, when the material is machined, certain stresses may be relieved causing distortion of the workpiece. To correct this, the workpiece must be straightened or the surfaces remachined.

Auxiliary Operations

There must be some consideration to changes, which ordinarily take place in the workpiece as a result of auxiliary operations. Operations such as welding and case hardening usually cause some distortion depending upon non- uniformity of workpiece cross section, uneven heating or cooling, etc.