Machinery's Handbook, 31st Edition
1204 MACHINING ECONOMETRICS calculate the tangential cutting force, torque and required machining power are found in the section ESTIMATING SPEEDS AND MACHINING POWER starting on page 1143. Specific Cutting Force, Kc: The specific cutting force, or the specific energy to cut, Kc , is defined as the ratio between the cutting force F C and the chip cross-sectional area A . Thus, Kc = F C ÷ A N/mm 2 . The value of Kc decreases when ECT increases, and when the cutting speed V increases. Usually, Kc is written in terms of its value at ECT = 1, called Kc 1 , and neglecting the effect of cutting speed, thus Kc = Kc 1 3 ECT B , where B = slope in log-log coordinates.
10000
V = 300 V = 250 V = 200
1000
0.01
0.1
1
ECT , mm
Fig. 9. Kc versus ECT , Cutting Speed Plotted A more accurate relationship is illustrated in Fig. 9, where Kc is plotted versus ECT at three different cutting speeds. In Fig. 9, the two dashed lines represent the aforementioned equation, which each have different slopes, B . For the middle value of cutting speed, Kc varies with ECT from about 1900 to 1300 N/mm 2 when ECT increases from 0.1 to 0.7 mm. Generally the speed effect on the magnitude of Kc is approximately 5 to 15 percent when using economic speeds.
1
V =300 V =250 V =200
0.1
0.01
0.1
1
ECT, mm
Fig. 10. F H / F C versus ECT , Cutting Speed Plotted Determination of Axial, F A , and Radial, F R , Forces: This is done by first determining the resultant force F H and then calculating F A and F R using the Fig. 8 formulas. F H is
Copyright 2020, Industrial Press, Inc.
ebooks.industrialpress.com
Made with FlippingBook - Share PDF online