機(jī)械加工外文翻譯-- 先進(jìn)的精密機(jī)械加工的小深孔（原文）

1、ELSEVIER Journal of Materials Processing Technology 68 11997~ 257 26R Journal of Materials p o rocess1ng Technobgy Advances in the predsion machining of small deep holes Z.M. Wang E.O. Ezugwu “,*, D. Su b “ School

2、of Engkwering ~vstems and De.~ign, South Bank Unilcrsio,, Lomtmt SEi 0.4,4, UK h Department ~/ Ah'chanical Engineering, Voltingham Trem l_#tircrsit v. Votlhtgham NG i 4BU, UK Received 20 October 1995 Abstract Based o

3、n the analysis of the forces acting on a deep-hole drilling head and the understanding of the burnishing action of the carbide guide pads, an investigation of the precision drilling method of small deep holes in difficul

4、t-to-cut materials was carried out. The influence of tool geometry and cutting parameters (cutting speeds and feed rates) on the surface quality of the drilled holes was studied, the results of which indicating that ~1

5、0-~20 mm small deep holes of high tolerance grades (IT7 to IT9) and lower surface roughness values (RD in the range of 0.2-1.6 tJm can be achieved and the problem of axial deviation of holes dril!ed minimised under opt

6、imised cutting parameters by means of the new/improved BTA drill. ~“,, 1997 Elsevier Science S.A. Keywords: Difficult-to-cut materials: Small deep holes: Precision drilling: Stability: Burnishing action 1. Introduction D

7、eep-hole machining is recognised as a difficult pro- cess due to the confined cutting space and the poor cutting conditions, difficult chip-breaking and chip-re- moval, and cantilevered cutting action, as well as poor

8、 machining system stiffness. Frazao et al. [1] pointed out that “the machining of holes of high length to diameter ratio to high standards of size, parallelism, straightness and surface finish has always presented pro

9、blems“. Low machinability of difficult-to-cut materials makes it more difficult to achieve the process efficiently and economically, especially in the solid drilling of small deep holes. Currently, there are three ma

10、in techniques available for deep hole drilling, i.e. the gun, the BTA (from Boring Trepanning Association) and the ejector drilling systems [2,3]. The basic principles of each pro- cess are the same, but the BTA proc

11、ess initially devel- oped in Germany during World War Two represents the most economical method for deep-hole drilling with high length-to-diameter ratio [4]. The BTA process can cover a large range of bore diameters

12、(~6-~750 ram) and high length-to-diameter ratios (up to 100) [5]. Small BTA tools (under ~20 ram) normally consist of a single cutting tip with two * Corresponding author. Fax: + 44 171 8157699. 0924-0136/97/$17.00

13、69; 1997 Elsevier Science S.A. All rights reserved. PII S0924-0136(96)00029-5 sell-piloting carbide pads (Fig. 1). When drilling with the self-piloting tool integrated with a high-pressure coolant system which flushes

14、the chip back through the interior of the boring bar, the cutting forces generated at the cutting edges are balanced by guide pads rubbing against the bore wall. This means that there is burnish- ing action of the gu

15、ide pads on the wall of the ma- chined hole. It is due to the burnishing and fixed-size action of the guide pads combined with interior chip-re- moval method of the BTA process and the use of an extremely rigid cylin

16、drical boring bar that high preci- sion deep holes can is achieved in one pass [6,7]. This work is aimed at developing a reliable method for the precision drilling of small deep holes in difficuL ~o-cut materials. g

17、u ; d epads ~e ± r ~ d l n gr~m~ cut±;ng lip/ ~~ Fig. !. The BTA drilling head. Z.M. Wang et al. /Journal ~/“ Materials Processing Technology 68 0997) 257--261 259 3500 3000 2500 2000 '~ 1000 500 3000 2

18、500 2000 1500 and (b) torque. axial force at the outer edge is obtained (period A). When the middle edge enters, the real axial force in- creases to B point. When the inner edge makes contact with the workpiece, a res

19、ultant axial tbrce k T ~with a point C is observed. The axial force increases suddenly as soon as the core is cut and the guide pads enter the machined hole. After a short period, a stable axial force F~a develops. Th

20、e cutting torque T and the resultant torque Ta were measured in the same way. Fig. 4(b) showing a typical torque-time curve. As shown in Fig. 2, the supporting force acting on each of the guides depends mainly on both

21、the magni- tude and the direction of F: and the positional angles qh and q~2 of the guide pads. At qh = 87° and q~2 = 183% the supporting force on G~ nearly equals the cutting force F~, whilst the force on G2 is

22、 about 20% of the cutting force F~ [10]. Therefore it can be considered that the first pad G~ bears the cutting I~rce F~, while the second pad G2 determines the diameter of the drilled hole. 2. Experimental procedure

23、s Based on the careful investigation of the BTA deep- hole drilling process, including the analysis of the forces acting on the deep-hole drilling head, the observation of the drilling stability and the understanding o

24、f the burnishing action of the guide pads, an improved ~ 16 The study indicates that ~10-~20 mm small deep holes of high tolerance grades (IT7 to IT9) (Fig. 6) and lower surface roughness values (Ra) in the range of 0.

25、2 to 1.6 pm (Fig. 7) can be achieved under the optimised cutting parameters by means of the new/improved type of BTA drill. 3.1. Effect of tool geometry Experimental investigation of deep-hole drilling in difficult-to-

26、cut material (CrNi3MoV) indicates that the good surface finish, high dimension accuracy and the improved run-out of the machined deep-holes can be attributed partly to the high stability of the drilling head and the

27、improved burnishing action of the guide pads. The high stability of the drilling head is achieved by arranging the two carbide pads at positional angles of 80-95 ° and 180-190 ° and inserting an assistant p

28、iloting carbide pad at 270-275 ° clockwise from the cuttiffg edges. The vibration resisting pads at the back of drilling head further promote the stability of the drilling head due to their damping action. Anothe

29、r significant contribution of the soft pads is to suppress the axial deviation of hole, which latter is one of the main problems faced in deep-hole drilling, especially in difficult-to-cut materials. When a slender b

30、oring bar bears a high axial force, bending of the bar occurs and the drilling head in the support-piloting bush inclines. In this case, the misguidance of the drilling head will encourage the run-out of the hole. Th