Hardness control of grind-hardening and finishing grinding by means of area-based specific energy

The grind-hardening process uses the heat generated within the grinding zone in order to produce surface hardening of the workpiece. However, after the process, workpieces present dimensional inaccuracies and poor surface roughness. Thus, a final grinding operation has to be performed. For an industrial implementation of the whole process, two problems need to be solved. On the one hand, on-line control of the hardness penetration depth (HPD) should be achieved. On the other hand, excessive softening of the workpiece has to be avoided during the finishing grinding. This paper, firstly, investigates the feasibility of using the area based grinding energy (Ec″) for the prediction of the HPD. Surface grind-hardening tests carried out on 100Cr6, 42CrMo4 and AISI 1045 steels have shown that, for all the tested parameter sets, a linear correlation exists between Ec″ and HPD. Furthermore, the slope of this linear relationship can be estimated from the chemical composition of the hardened steel based on the equivalent carbon number. On the other hand, the influence of varying wheel dressing conditions on the Ec″-HPD relationship is analysed. Secondly, it has been found that a relationship exists between Ec″ and the surface softening during the finishing grinding operation. This relationship is independent of the grinding parameter combination when the maximum undeformed chip thickness is over a threshold value. Thus, Ec″ is a very appropriate parameter to control both the hardening and the finishing process of grind-hardened workpieces.