Systems Approach to Finishing

Finishing methods, like any manufacturing operation, can be looked at efficiently using a systems approach (Ref 2). As can be seen from Fig. 2, a systems approach can also be used to consider a finishing operation and its resulting surface integrity:

• Input: Finishing processes involve a vast array of variables pertaining to four categories (i.e., the work material, the machine tool, the processing tool used, and the operational factors).

• Process: The four inputs define the microscopic aspects of a finishing operation, especially the thermal and mechanical interactions that condition the final surface integrity. These microscopic aspects can be measured macroscopically with forces, power, energy, or temperature transducers during the finishing operation.

• Output: The process leads to a finished part that has a given surface integrity and specific visual, dimensional, residual stress, tribological, metallurgical, and other factors (Fig. 1). The resulting surface integrity of the finished part conditions its operational performance.

Fig. 2 Systems approach to the residual effects of finishing methods

As the name implies, finishing methods occur at the end of a manufacturing process, and thus the residual effects they leave on the part are of crucial importance. Manufactured components typically result from a succession of operations, but in most cases it is the last operation that governs the residual stress profile imparted to the component prior to its use or service. Exceptions occur when the final machining operation has a penetration depth smaller than the previous ones (Ref 3). In such situations, the superimposition of residual stress must be considered (Fig. 3). In more conventional cases, the final grinding operations determine the final state of residual stress rather than the turning operation(s) that preceded them.

Fig. 3 Residual stress profiles in internal grinding cycles. Workpiece: 100Cr6; hardness, 62 HRC; diameter, 40 mm (1.6 in.). Table speed: 1 m/s. Corundum grinding wheel: A80K6V; diameter, 30 mm (1.2 in.); width, 8 mm (0.3 in.); speed, 40 m/s. Dressing: D 427 diamond cup wheel; speed ratio, 0.7; overlap, 40; infeed, 2 /'m. Cooling: 4% emulsion. (a) Roughing. Relative metal removal rate (MRR), 6 mm3/mm ■ s; relative volume of material removed, 18.8 mm3/mm. (b) Finishing. Relative MRR, 1 mm3/mm ■ s; relative volume of material removed, 1.6 mm3/mm. (c) Roughing and finishing. Source: Ref 4

Fig. 3 Residual stress profiles in internal grinding cycles. Workpiece: 100Cr6; hardness, 62 HRC; diameter, 40 mm (1.6 in.). Table speed: 1 m/s. Corundum grinding wheel: A80K6V; diameter, 30 mm (1.2 in.); width, 8 mm (0.3 in.); speed, 40 m/s. Dressing: D 427 diamond cup wheel; speed ratio, 0.7; overlap, 40; infeed, 2 /'m. Cooling: 4% emulsion. (a) Roughing. Relative metal removal rate (MRR), 6 mm3/mm ■ s; relative volume of material removed, 18.8 mm3/mm. (b) Finishing. Relative MRR, 1 mm3/mm ■ s; relative volume of material removed, 1.6 mm3/mm. (c) Roughing and finishing. Source: Ref 4

The residual stress effects of finishing processes can have a significant impact on the performance and viability of engineering components. Examples of possible negative effects are presented in Ref 5, which includes case histories of four finished parts that failed due to residual stresses.

0 0

Post a comment