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3376 深孔实体钻削附件的设计

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3376 深孔实体钻削附件的设计 实体 附件 设计
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3376 深孔实体钻削附件的设计,3376,深孔实体钻削附件的设计,实体,附件,设计
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COMBINED MACHINING OF DEEP HOLES IN BLANKS OF ViSCOPLASTIC MATERIALS V. A. Gorokhov UDC 669.715:669.245:62-472 Machining of small diameter (d = 2o5-12 mm) deep (s 10d) holes in blanks of nickel, iron-nickel, titanium, and aluminum alloys, copper, and other viscoplastic materials in- volves significant difficulties, which may be explained by their specific properties I, 2. To provide high quality of machining of holes and simplification and an increase in effec- tiveness of production of parts combined machining by vibrodrilling and burnishing is used 2. In this case special drills and devices for deep drilling, chrome-plated sulfidized burnishing tools, precision mechanical-hydraulic chucks, and special Model VU-I-VU-5 vibro- machines built on a base of standard metal cutting tools are used. Let us consider further features of the microgeometry of the surfaces and also the accuracy of the form and the condition of the surface layer of the material in combined ma- chining of small diameter long holes in blanks of precision parts of various difficult-to- machine materials. The surface finish Ra was taken as the criterion for evaluation of the microgeometry. The relationships of Ra to the method and conditions of machining (Fig i) were obtained with use of the following tools: drills and burnishing tools with a diameter of 5 , an angle at the tip of the drill of 140 , and angles of the lip 81 and reverse taper 2 5 and 4 , respectively. Drilling and vibrodrilling were done with a rate of rotation of the spin- dle (blank) of n b = 1200 rpm, a speed of the blank of v = 18.8 m/min, a feed of s = 0.008 m/n/ rev, a frequency of vibration of fv = 75 Hz, a ratio of the frequency of vibration to the rate of rotation of the blank of i = 15/8, an amplitude of vibration of 2A 0.05 mm, and the cutting fluid a solution of Akvoi-10. The measurements of Ra were made on a Model 253 profilograph-profilometer. The increase in Ra in operation with special drills without vibration of them may be attributed to the negative influence?9 of formation of a built-up edge and a continuous chip, which is not flushed away by cutting fluid supplied under a pressure of p = 12.5 MPa, and scratches of the surface in machining and repeated removal of the drills from the hole for removal of the chip accumulating in their longitudinal channels. If the change in surface finish of the hole for a single blank (d = 5 ran, Z = lld) is considered then at the moment of entry of the drill into the blank for 2-3 ram and for a distance of 1-2 mm before removal of it from the blank Ra is 10-15% and 4-8%, respectively, more than Ra of the main channel of the hole. As has been established, the presence of a gap in mating of the jig bushing with the drill and also deviation of from coaxiality of the drill relative to the spindle of the vibromachine have an influence on the increase in Ra at the start and finish of drilling Further investigation showed (Fig. I) that the surfaces of holes of blanks of difficult- to-machine materials produced by drills without vibration of the tool possess undercut rough- nesses (form 5, when the density of distribution of the undercutting roughnesses N u = 260- 280 mm -l and the excess of undercutting roughness over the level of Rz h u = 0.4 Rz). With an amplitude of vibration of 2A 0.bs a surface of form 4 with N u = 220-260 mm -I and h u = 0.3 Rz is provided, with 0.bs 2A s a surface of form 3 with N u = 160-220 ram -l and h u = 0.2 Rz, with 2A = s a surface of form 2 with N u = 80-160 mm - and h u = 0-0.i Rz, and with s 2A l.bs a surface of form 1 with N u = 80 mm -I and h u = 0. A surface on which under- cutting roughness is absent (form 0) is reliably provided in combined machining by vibro- drilling with subsequent burnishing with chrome-plated sulfidized burnishing tools 3. With use of precision attachments, the development of vibromachines using highly accu- rate equipment such as the Model IE61MT (VU-2) screw-cutting lathe, and provision of other factors Translated from Khimicheskoe i Neftyanoe Mashinostroenie, No. 4, pp. 27-30, April, 1993. 0009-2355/93/0304-0191512.50 ?9 1993 Plenum Publishing Corporation 191 R, J.IIl 1,z o,g g , / , , o I: ! i z li s II II s I b Fig. 1 Fig. 2 Fig. 1 Change in average arithmetic deviation of the profile Ra of the surface in relation to method and conditions of ma- chining of holes: a) VT3-1 alloy; b) KhN67VMTYu alloy; c) 45 steel; i) drilling with a spiral drill of R6M5 steel, supply of cutting fluid by flooding; 2) drilling with a spiral drill of VK8 cemented carbide, cutting fluid by flooding; 3) drill- ing with a special drill coated with VK8, cutting fluid under pressure; 4) vibrodrilling with a special drill, cutting fluid under pressure; 5) burnishing with a chrome-plated sulfidized burnishing tool, cutting fluid by application with a brush. Fig. 2. Roundness patterns of a hole in a sleeve. 2000 a) after vibrodrilling, A = 8 Dm; b) after combined machining, A = 4 Dm. Here A is out-of-roundness. it is possible to not only successfully control the microgeometry and form of the surface in accordance with service requirements for parts but also to produce holes of high accuracy in difficult-to-machine materials. The accuracy of the diameter of holes (d = 5 mm, s = 54 mm) was investigated on blanks of tubes from a bar of MIN-T copper. The parameters of vibrodrilling were s = 0.035 mm/ rev, n b = 2000 rpm (v = 31.4 m/min), fv = 75 Hz, 2A = 0.08 mm, and i = 9/8, where i = if + i r (here if is the full number of vibrations and i r is the fractional remainder). After drilling the hole diameter is .measured with a low-pressure (0.5 MPa) pneumatic gauge. Of the 50 blanks 48 were not beyond the hole diameter tolerance T (according to drawing T = 12 Dm). The deviation from roundness was also checked on a Model 218 roundness gauge. As follows from Fig. 2, the maximum out-of-roundness in vibrodrilling is 8 Dm. The deviation from cylindricity determined from the taper of the hole by measurement of its diam- eter at the entry of the drill, in the center of the hole, and at the exit of the drill was from 6 to i0 m (that is, within the diameter tolerance). The drilling was done with a radial gap between the drill and the jig bushing of 0.04 mm. With a decrease in the gap to 0.02 mm the field of scatter in the deviations of dimensions and the form of the holesdropped by 1.7 times. The curvature (deflection) of the axis of the hole y was investigated on specimens of highly plastic ADI aluminum alloy bars. The investigation included determination of the re- lationship of y to the drilling method (rotation and feed of the drill, rotation of the blank and feed of the drill), te depth of the hole, and the design of the drill (elongated 192 TABLE 1 /qx f z 3-J) 4 ,/ A =T=/ m 1oo I 1 / / f200 :000 - t / 800 - 600 / o. I/ / / 200 20 0 60 80 4 nm Fig. 3 Fig. 4 Fig. 3. Plan of measurement of the wobble of the hole: i, 4) centers; 2) section of a specimen; 3) indicator with di- visions of 0.002 mm. Fig. 4. Curvature (deflection) of the axis of the hole y in relation to the depth of drilling s with spirai (i) and special (2) drills: solid line) with rotation of the drill; dashed line) with rotation of the drill and the blank. Drill Machine Drilling method Wobble of the hole, mm at the I at the entry I exit of of the the drill drill Curvature (deflection) of the hole, mm Spiral Model 2A125 vertical drilling machine Spiral Model IK62 screw-cutting lathe Special VU-I vibro- drilling machine Drill rotates, part 0.13 0.47 0.17 does not rotate Drill does not rotate, 0.12 0.36 0.12 part rotates Drill does not rotate but does vibrate, part rotates 0.I 0.12 0.01 spiral, special with internal delivery of the cutting fluid, a 5% emulsion of ET-2 self- emulsifying oil, and with a diameter of 5 mm). After drilling the specimens were placed in centers and the plane in which the axis of the longitudinal section of the hole has the greatest deviation was determined from the wob- ble of the outer cylindrical surface on them. This plane was marked on the outer surface of specimens with a longitudinal scribe mark. For the purpose of investigation of the relation- ship of the increase in deviation of the hole specimens ( = i00 mm) were cut into i0 por- tions (sections) about 9.5 mm long which were numbered. After this the wobble of the outer cylindrical surface of each section relative to the hole was measured (plan shown in Fig. 3). The investigation results (Fig. 4) showed that the smallest deflection of the axis of the hole is observed with feed of the drill when only the blank is rotated. The use of special drills even under normal operating conditions reduces deviation of the axis of the hole by about eight times The positive aspects of the method in which the blank is rotated and the drill is fed appear most clearly in vibration drilling with use of a precision chuck 62 and an attach- ment for drilling 4. For example, in drilling with a spiral drill and vibrodrilling with a special drill of a 3 mm diameter 36 mm long hole (s = 12d) in blanks of VT3-1 titanium al- loy with different methods different deviations of the axis of the hole occur (Table i). As may be seen, vibrodrilling on high-accuracy machines such as the VU-2 and others may provide a deviation of the axis of the hole no greater than 0o015 m 193 #z, Im f 8 If zo 8, deg Fig. 5 Fig. 6 Fig. 5. Relationship of the height of the roughnesses Rz of the surfaces of holes to the angles of the burnishing tools 81 and 82. Fig. 6. Microstructure of the surface layer of MIN-T copper tubes. 200 a) bored; b) combined machining. After burnishing the out-of-round of the holes drops from 8 to 4 Dm, or in half (Fig. 2a, b). The deviation from cylindricity of the holes, the taper of ten blanks of MIN-T cop- per (d = 5 mm), burnished after vibrodrilling drops on the average from 8.9 to 7.2 Dm or by 19%. There is practically no change in the deviation of the axis of the holes in burnishing although there is a tendency toward an insignificant decrease. In burnishing with sulfided burnishing tools the surface roughness of holes in blanks of titanium and nickel alloys and 12KhI8NgT steel drops from 0.3-0.5 Vm to 0.1-0.2 Bm, or by 2.5 times (Fig I). The surface finish of the holes depends upon the parameters of the burnishing tools to a significant degree, particularly upon the angles of the lip 8 and reverse tapers 82 (rig. 5) 4. From Fig. 5 it follows that to provide the lowest value of Rz it is necessary to use 81 = 4-6 and 82 = 2-6 . Combined machining leads to a change in the microstructure, microhardness, and degree and depth of hardening of the surface layer of the material of parts. Figure 6 shows the microstructure of the surface layer of material in machining of the holes of tubes. From a study of the microstructure it follows that the depth h o of the strengthened layer is 5 m for bored blanks and 61 Dm for vibrodrilled and burnished. The microhardness H was determined on oblique specimens with an angle to the axis of the hole of 3 50 min, which provides a magnification of the investigated zone of 15 times, and HB was measured on a Neophot-2 tester. The distribution of the microhardness in relation to depth of the strengthened layer in drilling and vibrodrilling is shown in Fig. 7a, from which it may be seen that with approach to the surface of the hole (a decrase in h o) HB in- creases from 74 to 96 (curve i) and to 98 (curve 2). In this case the maximum degree of strengthening of the metal reaches 29.7% in drilling and 32.4% in vibrodrilling. Figure 7b illustrates the change in microhardness in relation to the form of machining and material after vibrodrilling of 6 mm diameter holes in blanks of KhN67VMTYu and VT3-1 alloys. Burnishing with chrome-plated sulfidized burnishing tools was done with a decrease in surface Ra from 0.7 to 0.17 m. From a study of the relationships it follows that com- bined machining provides the greatest microhardness Hp, degree of strengthening, and depth 194 r zo ,o o -o N. gm 00 -c- , 760 32O N x 280 , zo o 60 8o oo h, m b Fig. 7. Change in surface micro- hardness H in relation to depth of the hardened layer ho: a) tubes of MIN-T copper; b) KhN67XfMTYu and VT3-1 alloys; i) drilled; 2) vibro- drilled; 3) combined machined; solid line) KhN67MVTYu alloy; dashed line) MIN-T copper. of the hardened layer h o and then follow vibrodrilling and drilling. In drilling the follow- ing parameters were obtained for KhN67VMTYu and VT3-1 alloys, respectively: Hmax 386 and 339; homax 80 and 72 Dm; and degree of strengthening of the metal 13.5 and 21%; in vibro- drilling of them Hmax 400 and 352; h omax i00 and 80 Dm; degree of strengthening up to 17.6 and 25.7%, and in burnishing of them Hmax is 428 and 380, h omax 130 and 116 Dm, and degree of strengthening up to 26 and 36%. These investigation results indicate the significant possibilities of combined machin- ing. With use of high-accuracy attachments, devices, and tools 2-4 combined machining of holes by vibrodrilling and burnishing leads to a decrease in Ra from 0o3-0.5 to 0.1-0.2 m, makes it possible to produce No. 7 quality hole diameters and levels A and B relative geo- metric accuracy, and makes it possible to control the surface microgeometry and to provide forms of them (from 0 to 5) with a presence exceeding the level of Rz and density of dis- tribution of undercutting roughness 5. An analysis of the results indicates the high strengthening capacity of combined ma- chini
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