【正文】 power demand and machining time was analyzed to confirm that the increased loads due to faster material removal was not increasing the total energy consumed. 2 POWER DEMAND FOR VARIED .’ S Since machine tool programmers and operators have an array of options when defining the process plan for part production, this analysis strives to reduce energy consumption by process parameter selection of a machine tool. Specifically, the parameters concerning material removal rate (.) were varied on a Mori Seiki NV1500 DCG while selecting appropriate tooling. The power demand was measured with a Wattnode MODBUS wattmeter. In previous work, experiments we re conducted in which spindle speed, feed rate, feed per tooth, and cutter type were varied to analyze the change in energy consumption while milling a low carbon steel, AISI 1018 steel [5]. Also, [6] conducted experiments on face milling, end milling, and drilling operations in which the energy consumption, machining cost, and tool wear were pared for increased cutting speeds. Tool wear and, consequently, cutting tool cost increased significantly when the process parameters veered away from the remended cutting conditions. So in the following experiments the cutting tool type was changed to maintain the remended process parameters, but reduce energy consumption while machining, noheless. Width of Cut Experiments Given the energy savings from changing the cutter type this project focused on varying material removal rate. First the width of cut was increased while machining with a: 1. 2 flute uncoated carbide end mill, 2. 2 flute TiN coated carbide end mill, and 3. 4 flute TiN coated carbide end mill. Peripheral cuts were made along the yaxis at a depth of cut of 2 mm with an 8 mm diameter end mill over a length of 101 mm in a 1018 steel work piece. The width of cut was varied by 1 mm increments between 1 mm and 7 mm, in addition to a mm width of cut. Table 1 summarizes the cutting conditions used. The chip load was maintained at approximately mm/tooth to avoid excessive tool wear and breakage. 4 Table 1: Process parameters for width of cut experiments. Once the power was measured for each width of cut experiment,the power demand was measured for the machine tool while air cutting, that is, while running the tool path without material removal. This way the power associated with the material removal process could be extracted, known hereafter as the cutting power demand. The average air cutting power demand was found to be 1510 W for the cutter (2) process parameters, so it was subtracted from the average total power demand. Figure 1 shows the cutting power demand as a function of the . for cutter (2). This plot has a slightly parabolic trend with a point of inflection at approximately 75 mm3/s. The cutting power demand for the mm width of cut was almost nine times greater than the 1 mm width of cut. Since the total air cutting power demand was only 1510 W, though, the resulting increase in total power demand of the machine tool was only 28%. Thus in terms of energy consumption, the operator still experiences energy savings with the increase in . Figure 1: Cutting power demand using cutter (2) while cutting 1018 steel. Figure 2 shows the average power demand of the NV1500 DCG for cutters (1)– (3). The relationship between power and . shifts from parabolic to linear in moving from the conditions imposed on cutter (1) to cutter (3). The increase in power demand is the greatest for cutter (3), but the load on the spindle motor and axis drives is also much greater than that of the 2 flute cutting tools since the feed rate is twice as large or greater. 5 Figure 2: Average total power demand as a function of . Depth of Cut Experiments Depth of cut experiments were also conducted on a 1018 steel work piece 101 mm in length. Cuts were made along the yaxis using 8 mm diameter, 2 flute uncoated and TiN coated carbide end mills under near slotting conditions (a width of cut of mm). The power demand was measured at depths of cut of 1, 2, 4, and 8 mm. The chip load was maintained constant across the various cutters at mm/tooth. The spindle speed and feed rate were varied, though, to account for higher loads on the machine tool during the depth of cut experiments (see Table 2 for a summary of the processing conditions). Table 2: Process parameter ranges for depth of cut experiments. Figure 3 summarizes the power demanded by the NV1500 DCG for the 2 flute TiN coated end mill (cutter (2)) and the energy consumed as a function of material removal rate. Although the power demand increases with load the energy consumption still drops drastically with the increase in material removal rate. The machine tool experiences a power demand increase of approximately twothirds, whereas the energy consumption reduces to less than onethird of its original value. This shows that the decrease in processing time effectively dominates over the increase in power demand due to increased loads. Since the power demand was shown to increase with load, and experimentally this increase in load was not enough to increase the overall energy consumption, the tradeoff between power demand and processing time will be analyzed. 6 Figure 3: Energy and power demand as a function of . for depth of cut experiments with cutter (2). Tradeoff Between Power Demand and Processing Time The machine tool’ s electrical energy consumption is dependent on the power demand, p avg, and processing time, ?t, as seen in Equation（ 1） . Since the power demand shows some variability due to the internal cooling unit of the machine tool, the average power demand, p avg , will be used. As was mentioned previously, the average power demand is posed of a cutting, p cut, a