Laboratory Analysis of Cutting Forces and Surface Finishes
Part I
Objective:
To determine the effects of velocity and feed on the cutting forces.
Procedure:
A piece of aluminum pipe was dimensioned and mounted in a lathe set up for orthogonal cutting. The cutting tool was equipped with a strain gauge. The work piece was cut with constant speed, variable feed and constant feed, variable speed. Measurements of the forces were recorded and the chip thickness was measured.
Summary:
The data collected is provided below along with the results of the calculations of other aspects of machining. Two graphs are provide the data explaining various relationships. The first graph describes the effect on cutting forces as the cutting velocity increases. The slope of the lines are approximately 0.6, which suggests that the force increases less compared to the increase of velocity. This relationship exhibits linearity over the measured range. This relationship also shows that there is an optimal cutting speed for a particular feed rate at which the increase in horse power required to cut is minimized for an increase in the mmr. In the second graph we see the relationship between feed and cutting force. Again we can see an increase in force as the feed rate increases. More horse power is required to remove more material. However, we again can see an optimal feed rate at which the increase in horse power is less than the increase in volume of metal removed. It was also interesting to note that the horse power consumed in cutting per cubic inch was varying from the listed value in the book and that at one point the Hpu value was 0.300 for each condition.
feed Fc Fc Ft Ft Resultant t1 t2
speed
in/rev N lbf N lbf lbf in in
RPM
90.000 0.005 452.000 101.614 665.000 149.498 180.762 0.005 0.013
140.000 0.005 520.000 116.901 731.500 164.448 201.764 0.005 0.015
215.000 0.005 639.000 143.653 795.000 178.723 229.299 0.005 0.016
330.000 0.005 743.000 167.033 812.300 182.612 247.482 0.005 0.017
140.000 0.001 218.000 49.008 278.300 62.564 79.474 0.001 0.004
140.000 0.002 347.000 78.009 415.000 93.296 121.612 0.002 0.007
140.000 0.005 445.000 100.040 632.400 142.169 173.839 0.005 0.012
140.000 0.007 770.000 173.103 1012.600 227.642 285.981 0.007 0.022
140.000 0.010 1346.000 302.593 1332.000 299.446 425.711 0.010 0.025
phi alpha Fs Fn F Vc Vs Vf
rc
rad rad lbf lbf lbf ft/m ft/m ft/m
0.408 0.399 0.087 35.580 177.226 15.754 52.903 55.367 21.584
0.333 0.330 0.087 53.319 194.592 17.585 82.293 84.446 27.431
0.319 0.316 0.087 63.651 220.288 19.985 126.379 129.255 40.283
0.305 0.303 0.087 71.727 236.860 21.569 193.977 197.821 59.238
0.343 0.339 0.087 20.312 76.834 6.927 82.293 84.637 28.215
0.309 0.306 0.087 34.863 116.507 10.599 82.293 83.985 25.414
0.391 0.384 0.087 36.814 169.897 15.151 82.293 85.716 32.202
0.327 0.324 0.087 77.136 275.382 24.925 82.293 84.329 26.939
0.408 0.399 0.087 83.794 417.383 37.103 82.293 86.127 33.576
Ws Wf Q Ps Hp(cuttin Hpu Hpu c
Wc g)
Hp Hp in^3/min psi Hp/(in^3/ tables tables
Hp m)
0.163 0.060 0.010 0.793 6775.095 0.294 0.245 0.300 1.200
0.292 0.136 0.015 1.234 7794.357 0.359 0.299 0.300 1.200
0.550 0.249 0.024 1.895 9578.066 0.435 0.362 0.300 1.200
0.982 0.430 0.039 2.909 11136.937 0.499 0.415 0.300 1.200
0.122 0.052 0.006 0.290 13887.446 0.621 0.443 0.300 1.400
0.195 0.089 0.008 0.508 12631.570 0.573 0.441 0.300 1.300
0.249 0.096 0.015 1.089 7559.527 0.330 0.275 0.300 1.200
0.432 0.197 0.020 1.767 8063.341 0.367 0.350 0.300 1.050
0.755 0.219 0.038 2.468 10087.697 0.410 0.400 0.300 1.025
Part II
Objective:
To determine the surface texture achieved at various speeds and feed rates on various materials.
Procedure:
To begin we must verify that the equipment is functioning properly. The lathe should be operating at the appropriate feeds and speeds and the profilometer should be measured against a standard. Then the work piece was mounted in the lathe and the cutting was started. The surface roughness and the feeds and speeds were recorded for each material and tool.
Summary:
The data collected contains information on roughness as a function of feed rate and material. As to be expected, an increase in feed causes an increase in roughness (see graph). In this operation the increase in feed causes the tool to travel less on the work piece. Thus, we are increasing our area of cut per revolution. This decreases our amount of material removed and the amount of surface area touched by the tool as a whole.
The comparison between the steel and the brass is somewhat inconclusive since the RPMs vary between each material. The increase in roughness may be caused by the decrease in RPMs.
