Investigation on Residual Stress and Flank Wear of Tool Insert in Hard Turning of Chrome Plated EN24 Substrate

Hard Turning

One of the solutions the researchers proposed was the hard turning which can be considered as an alternate to the grinding. Hard turning is a simple turning operation which operates on the harder material having hardness above 45 HRc. Hard turning is one recent replacement for grinding operation when finishing of the part is concerned. Gaurav Bartarya and S. K. Choudhury (2012) have reviewed the importance of hard turning. It was very clear from the their article that the tool material, cutting edge geometry and cutting parameters have an impact on the process efficiencies such as cutting forces, surface integrity and white layer formation. They have observed that the depth of cut of finish hard turning was normally less than the nose radius of the cutting insert; the forces diverged from the traditional metal cutting. The authors have concluded that hard turned components generally possess tensile residual stresses. They reported that not much literatures available on the way of reducing the tensile residual stresses on the turned surfaces without negotiating the surface finish.

The hard turning machines are normal CNC lathes with more rigid fixtures for workpiece mounting. With close cutting conditions, the hard turning operation produces the surfaces at far with the grinding operation. Hard turning can machine complex workpieces in one step. It is less time consuming, more flexible, and economical process. Although grinding is the typical finishing process employed in industry, in many cases hard turning is a better option for internal and external finishing. Figure 1 shows the set-up of hard turning of hard chrome plated surfaces.

Figure 1.

Hard turning of chrome plated surfaces on Hardinge machine

There are various parameters involved in CBN cutting tool to enhance the machinability of the workpiece. Some of them are the cutting edge, nose radius, rake angle, orientation of the tool tip, etc. Adair, Shiv G. Kapoor and Richard E. DeVor (2011) have studied the effect of the topology on the rake angle and suggested the right topology to reduce the discrepancy of the rake angle.

Youngsik Choi and C. Richard Liu (2009) have studied the behavior of the coated CBN inserts in superfinish hard machining. The experiments were carried out with both solid PcBN inserts and coated CBN inserts of particle size distributions of less than 0.5µm and 2µm. The experimental results showed that the generation of higher compressive residual stresses and least thermal damage on the workpiece with coated CBN inserts with particle size less than 0.5µm.

Engineered Chrome Surface

Chrome plating is a method of electroplating a thin layer of chromium onto the base material. The thickness of chrome plating depends on the applications. The very thin coating is normally called as the decorative coating.