SE MEASURING MACHINE (SEMM). 

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... u is the total Specific Energy (SE) [Vyas, A. et al. (1999)], F c is the cutting force (in the direction of the cutting speed, v is the cutting speed, b is the width along the cutting edge and t is the undeformed chip thickness. If the cutting speed is not used in Eq. (1) it becomes the specific cutting pressure SCP ( k s ), which has been extensively used to estimate cutting force, through tables with values supplied for several machined materials and operations. The SE could be a property of the material being machined, but experimental results has shown that it varies, depending on the cutting edge, machining parameters and operation. This is understandable, since the shape and surface conditions of the cutting edge can affect the efficiency of chip removal. The use of computer simulations, with reliable material data, at cutting conditions obtained by the Charpy test applied at several intermediate steps, seems more promising than continuous medium approaches. With the step-by-step simulation approach the process can be further understood. The Charpy test machine can also provide an absolute scale to machinability of metals, through the SE required to make chips in each one. The Charpy test machine uses, basically, a pendulum to evaluate the energy absorbed by the specimen during its rupture by impact. One of its main characteristics is the high speed in which the material is deformed and ruptured. Instead of breaking the specimen, the same principle was used to produce chips, at speeds compatible to those used in common machining operations. During the chip formation, the pendulum spends some energy, which is promptly measured by its lost on the initial potential energy. The adaptation used an original Charpy machine, with a new pendulum design, a precise angular encoder and a piezoelectric dynamometer. The energy can be measured by the rotation of the pendulum and also checked by the forces, supplied by the dynamometer. Figure 1 shows the SE Measuring Machine (SEMM). The SEMM contains an incremental Elcis encoder model 72 with 10,000 point per revolution and a Kistler dynamometer model 9257BA with 5.0 mV/N (Fz) and 10 mV/N (Fx, Fy) of sensitivity. The system is connected to a lap-top computer containing a PCMCIA card DaQ700, making acquisitions at 22K points per second. The specimen to be tested is fixed at the pendulum. The center of mass adjustment process was first made by a CAD system, during design, and later adjusted using two digital scales. A schematic of specimens is shown in Figure 2. The machine contains two cutting edges forming a gap, through which the specimen passes forming the chips. One of the edges is fixed on the dynamometer and the other on the machine structure. The specimen design resulted simple and the lowest stiffness of the system, on the direction normal to the machined surface is 25 N/ m (z direction, according to Figure 2). On the other directions the stiffness was 105 N/ m and 92 N/ m on x and y, respectively). These values allowed low low differences between the depth of cut set and that obtained (less than 15%). The loss of mass, by chip removal, was measured by weighing the specimen in a digital scale, with resolution of 0.5 mg. A tool holder made of hardened steel was made to accommodate a square insert, 12 mm side, by 3.18 mm of thickness, fixed by a bolt in its center. Other tools holders will be provided in the future. The tool holder can be positioned, by a bolt/nut, allowing a fine adjustment of the depth of cut. After this adjustment the tool holders are tightly fixed. For the test, the pendulum is, initially, released free, cutting air, and its angular displacement is measured. Then the edges are positioned and the pendulum is released, making chips. Figures 3 and 4 show the typical graphs obtained. The resulting natural frequency was around 300 Hz on the x direction, which indicates a value very low, compared to that normally found by chip formation process. With these data the loss of energy, can be calculated using the following equation: where E ch is the energy calculated using data coming from the encoder, the m is the mass of the pendulum, g is the gravitational acceleration, r is the length of the pendulum, is the difference in the pendulum angle between cutting air and making chips, is the angle of SC the pendulum when cutting air. In the SEMM the product mg equals to 229.24 N. The energy spent in the chip formation can also be checked using the cutting force ( F c ) measured by the dynamometer. The curve of force against displacement is numerically integrated, using the ...