Basic Study On Hardened Steel Using EHM

Electric Hot Machining(EHM) is a typical composite process, which during the cutting process a dc current is applied to the circuit made up of the tool and workpiece. When dc current passes through the small zone between the tool and workpiece, the high current density generates much heat to increase the cutting temperature. So the material hardness decreases, the material shear strength reduces, so a more smoothly cutting can be obtained. EHM has been regarded as an effective method against the different-to-machine materials.The hardened steel is a typical difficult-to-machine material and has a widely application in the manufacture of bearings and gears. Generally, hardened steel is machined by milling as a finishing. But the milling has some disadvantages, such as low efficiency, high consumed power and environment pollution etc. With the development of super-hard tools, turning can directly machines hardened steel as finishing which is named hard turning. Hard turning has benefited a lot to surface finishing for its flexibility, economy and environmental protection compared to milling. But present hard turning needs high quality lathe and super-hard tool and the high cost make it difficult to extend. So it provides with important theoretical significance and application value to investigate a simple and convenient technique in hard turning. In this paper, theory and technique in EHM for hardened steel is put forward and investigated systematically, in order to explore a new method of hard turning.Firstly, the set-up of EHM is established. Secondly, through the fundamental test, the feasibility and validity are affirmed. Thirdly, the influence of cutting conditions on surface roughness is studied and the optimum cutting conditions is obtained. At last, pick the workpieces with lower surface roughness and measure the degree of work hardening and residual stress. The results show that this method is feasible, it can not only obtain the surface roughness equal to by milling and there isn't work hardening in surface finish.The feature of machining harden steel by means of EHM are: it can utilize the carbide tool to machine the harden steel in engine lathe. It provides a easy and low cost method to machine harden steel and has a brighter prospect.