Hardened steel machining

Figure 7.3 shows the mold for the manufacture of recycled polymer block, made from, 1045 hardened steel, machined surface finished and controlled. 

An alternative to the measurement of the dimensions of the indentation by means of a microscope is the direct reading method, of which the Rockwell method is an example. The Rockwell hardness is based on indentation into the sample under the action of two consecutively applied loads - a minor load (initial) and a standardised major load (final). In order to eliminate zero error and possible surface effects due to roughness or scale, the initial or minor load is first applied and produce an initial indentation. The Rockwell hardness is based on the increment in the indentation depth produced by the major load over that produced by the minor load. Rockwell hardness scales are divided into a number of groups, each one of these corresponding to a specified penetrator and a specified value of the major load. The different combinations are designated by different subscripts used to express the Rockwell hardness number. Thus, when the test is performed with 150 kg load and a diamond cone indentor, the resulting hardness number is called the Rockwell C (Rc) hardness. If the applied load is 100 kg and the indentor used is a 1.58 mm diameter hardened steel ball, a Rockwell B (RB) hardness number is obtained. The facts that the dial has several scales and that different indentation tools can be filled, enable Rockwell machine to be used equally well for hard and soft materials and for small and thin specimens. Rockwell hardness number is dimensionless. The test is easy to carry out and rapidly accomplished. As a result it is used widely in industrial applications, particularly in quality situations. 

The refiner machine used to accomplish this consists of two 1-m diameter stout steel disks fitted with welded hardened steel bars on one face of each (Fig. 15.5). The barred faces of the two disks face each other, and the spacing between the bars of the facing disks is adjusted to control the fineness of the fiber suspension produced. One disk may be stationary and the other rotated, or they may be counterrotating (rotated in opposite directions) in either case by powerful electric drives of up to 10,000 hp (ca. 8,000 kW). 

W-Cu, V-ThO2). Electrical discharge machining allows close dimensional tolerances, accuracy of form, and a high-quality surface finish to be achieved. Both hardened steels and hardmetals can be machined (Fig. 7.12). Tungsten in wire eroding is not only used as a guide and contact for the wire electrodes, but also as erosion wire. 

Moulds must resist high pressures without distortion, and resist wear over 10 cycles or more they are usually made from forged blocks of low-alloy steel, air-hardened after machining. Moulds act as thick-walled pressure vessels, with high tensile stresses in the walls. For a melt pressure of 50 MPa and a cavity diameter that is four times the wall thickness, the average hoop stress in the wall is 100 MPa from Eq. (C.21). Concave corners in the mould cavity act as stress concentrating features, so to... 

Relative tooling cost, single cavity Lowest. Machined aluminum may be variable, depending on quantity required 20 percent more. Hardened-steel tooling 20 percent to 25 percent more. Compression-molding steel tools... 

Using low-content pcBN tools for finishing previous operations often replaces a grinding operation. In many cases, a hardened steel component was finish ground because its hardness meant that it was not possible to machine it in any other way. Many such components may now be turned to final tolerance and surface... 

Table 2. Demands on basic properties of cutting tool ceramics for machining hardened steel . V = important, xx = very important...

As it is also known from other fields of working metals, the different forms of the chips from machining cast iron and steel cause a much more intense interaction with the cutting plate for the latter material. Therefore, the demands concerning the chemical and oxidation stability are more stringent on working hardened steel than on machining hard cast iron (Table 2). 

Machining Hard Cast Iron and Hardened Steel... 

Figure 18. Life time of advanced ceramic inserts on machining hardened steel (see Table 4 for materials characterization). The arrows indicate frequently observed deviations.

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