Operation Principles and Constructional Features of a Progressive Multispindle Automatic

The multispindle automatic has a rigid frame base construction, in which the top brace connects the headstock and the gearbox mounted at the right side of the heavy base. The base also serves as a reservoir for cutting fluid and lubricating oil. The headstock has a central bore for the spindle drum with the work spindles.

The gearing diagram of the spindles of a horizontal four-spindle automatic is shown in Figure 8.34. The power is transmitted from an electric motor (7 kW, 1470 rpm) through a belt drive, change gears Z,/Z2, continuously meshing gears Z, and Z4, a long central shaft, central gear Z5, and a gear (Z6) to impart rotational motion to the spindles. The long central shaft should be hollow and strong to have sufficient torsional rigidity. It is evident that all spindles rotate in the same direction at the same speed. Both bar and chucking multispindle automatics are made in a considerable range of sizes. The sizes are mainly determined by the diameter of stock that can be accommodated in the spindles. The following are the main specifications of multispindle bar automatic DAM 6 x 40:

Number of work spindles

6

Maximum bar diameter (mm)

042, Hex. 36, Sq. 30

Maximum bar length (mm)

4000

Maximum length of stock feed (mm)

200

Maximum turning length (mm) Maximum traverses

180

Bottom and top slides (mm)

80

Side slide (mm)

80

Height of centers over main slide (mm)

63

Speed range, normal (rpm)

100-560

Speed range, rapid (rpm)

400-2240

Progressive ratio (rpm)

1.12

Range of machining time per piece, normal (s)

8.9-821

Range of machining time per piece, rapid (s)

5.5-206

Rated power of drive motor (kW)

17

Overall dimensions (L x W x H) (mm)

6000 x 1400 x 2280

Weight (kg)

11.000

A brief description of the machine elements is as follows:

Spindle-drum (carrier) and indexing mechanism. The spindle drum (2) is supported by and indexes in the frame of the headstock (I). It is indexed by the Geneva mechanism (3) through index arm (4) Figure 8.35a), which revolves on the main camshaft (5). The indexing motion is geared to the drum. During the working position of the machine cycle, the spindle drum is locked rigidly in position by a locking pin (6), which is withdrawn only for indexing (Figure 8.35b). A Geneva cross of five parts is preferred to index the drum of four-, six-, and eight-spindle automatics. The

Gearing diagram of a four-spindle automatic. (From Boguslavsky, B. L., Automatic and Semi-automatic Lathes, Mir Publishers, Moscow, 1970. With permission.)

FIGURE 8.34 Gearing diagram of a four-spindle automatic. (From Boguslavsky, B. L., Automatic and Semi-automatic Lathes, Mir Publishers, Moscow, 1970. With permission.)

Drum indexing and locking of a six-spindle automatic

FIGURE 8.35 Drum indexing and locking of a six-spindle automatic: (a) indexing and (b) locking.

division into five parts renders a favorable transmission of acceleration and power, thus granting a light and smooth indexing of the spindle drum.

Spindle assembly. Figure 8.36 shows a section through a typical assembly of one of the machine spindles. The collet opening and closing unit is similar to that of the single-spindle automatic. The spindle is mounted on fixed front bearings and a

Spindle assembly of a six-spindle automatic. (From Pittler Maschinenfabrik AG, Langen bei Frankfurt/M, Germany.)

FIGURE 8.36 Spindle assembly of a six-spindle automatic. (From Pittler Maschinenfabrik AG, Langen bei Frankfurt/M, Germany.)

High-speed drilling attachment. (From VEB-Drehmaschinenwerk/Leibzig, Pittlerstr, 26, Germany, Technical Information Prospectus Number 1556/e/67.)

FIGURE 8.37 High-speed drilling attachment. (From VEB-Drehmaschinenwerk/Leibzig, Pittlerstr, 26, Germany, Technical Information Prospectus Number 1556/e/67.)

floating rear double raw tapered roller bearing; thus, differential thermal expansion between spindle and housing is allowed. The spindle expands only backward, so that its running accuracy is not affected.

  • 8.5.2.3.1 Tool Slides
  • 1. The main tool slide (end working slide) is a central block that traverses upon a round slide on an extension to the spindle drum to provide accurate alignment of the slide with the spindles. The main slide is advanced and retracted (Figure 8.37). The end tools are mounted directly on the main slide by means of T-slots or dovetails. Every tool mounted upon the slide must have the same feed and stroke. These tools are intended for plain turning, drilling, and reaming operations. Special attachments and holders for independent feed tool spindles are used when the feed of any cutting tool must differ from that of the main slide. These attachments and holders are actuated by drum cams. Figure 8.37 shows a holder carrying a high-speed drilling attachment, whereas Figure 8.38 shows an independent feed, high- spindle speed attachment. The drive mechanism of the end tool slide is shown in Figure 8.39 and performs the following steps:
    • • Rapid approach of the tool slide may be either 75 or 120 mm, w'hile the working feed may be adjusted in a range from 20 to 80 mm. The rapid approach is effected by the advance of the carriage (1) with the feed
Independent feed/high-speed drilling attachment. (From VEB- Drehmaschinenwerk/Leibzig, Pittlerstr, 26, Germany, Technical Information Prospectus Number 1556/e/67.)

FIGURE 8.38 Independent feed/high-speed drilling attachment. (From VEB- Drehmaschinenwerk/Leibzig, Pittlerstr, 26, Germany, Technical Information Prospectus Number 1556/e/67.)

Drive mechanism of the end tool slide. (From Chernov, N.. Machine Tools, Mir Publishers, Moscow, 1975. With permission)

FIGURE 8.39 Drive mechanism of the end tool slide. (From Chernov, N.. Machine Tools, Mir Publishers, Moscow, 1975. With permission)

lever (5) held stationary. The carriage is traversed by a corresponding cam of the main slide through the roll (2) (Figure 8.39).

  • • Rapid approach proceeds until the carriage runs against a stop screw (not shown in the figure). The gear (6) travels together with the carriage. This gear meshes simultaneously with the rack (7) of the tie rod (3) and the rack of the main slide (8). As rack (3) is stationary, the rack (8) and correspondingly, the main tool slide travels a distance twice that of the carriage.
  • • At the end of rapid approach, the carriage stops and is held stationary by the stop screw and the carriage driving cam.
  • • Immediately after this, another cam mounted on the camshaft actuates the feed lever (5) (Figure 8.39) through the roll (4). The rack (7) moves the gear (6), which imparts the movement to the rack (8) and to the end tool slide.
  • • The length of the main slide working travel is set up by positioning a link (3) in the slot of the lever (5) with the aid of the scale located on the lever.
  • • Rapid withdrawal is engaged at the end of working feed. In this case, both the carriage (1) and lever (5) return to their initial positions at the same time.
  • 2. Cross slides are intended for plunge-type cutting operations such as facing, grooving, recessing, knurling, chamfering, and cutting. They are directly mounted on the headstock of the machine and move radially to the center line of the work. Figure 8.40a and b show the cross-slide arrangement for bar and chucking six-spindle automatics, respectively. The cross slides are cammed individually; each is driven by its own cam drum. Therefore, the feed rate can be different for each side tool. The side tools feed slowly into the work to perform their cutting operations and then return to clear out spindles for indexing. In general, two slides are allocated for making heavy roughing and forming cuts. The other slides are used to complete subsequent finishing operations to the required accuracy. Except for a stock feed stop at one position, the tools on the main tool slide move forward and make the cut essentially simultaneously. At the same time, the tools in cross slides move inward and make their plunge cuts (Figure 8.41).

Camming and cyclogram. The main camshaft, either directly or indirectly, controls the cam movements. Hence, cams of various machining operations must be selected from a range of standard cams according to rise and feeds required. The cams for the idle motions, such as stock feeding, chucking, indexing, and so on, are standard cams and are not changed. Multispindle cams are generally composed of specially shaped

Simultaneous working movements of main end slide and cross slides of a four-spindle automatic

FIGURE 8.41 Simultaneous working movements of main end slide and cross slides of a four-spindle automatic.

Standard cams of cross overslides. (From Pittler Maschinenfabrik AG, Langen bei Frankfurt/M, Germany.)

FIGURE 8.42 Standard cams of cross overslides. (From Pittler Maschinenfabrik AG, Langen bei Frankfurt/M, Germany.)

segments that are bolted onto a drum to control motions. Figure 8.42 shows the cams of the cross overslides, which reduce the need for special cams.

Figures 8.43 and 8.44 show the developments of the cross overslide and the main tool-slide cam drums of a six-spindle automatic DAM 6 x 40. The working feeds of both drums occupy about 105°, and the auxiliary activities occupy 255° of the total cycle time 360°. Figure 8.45 shows the complete cyclogram of the working and auxiliary cams of a four-spindle bar automatic (on the basis of camshaft rotation angle). The cyclogram show's the sequence of events in the production of a single piece during one complete revolution of the main tool-slide cam or cross-slide cams. Prior to stock feeding, there is a rapid rise or jump toward the work, and at the end of the cut, an equal and rapid withdrawal or drawback is follow'ed by a dw'ell w'hile indexing and stock feeding. The dw'ell is denoted by a horizontal line, while a rising or a falling line denotes movement. Cyclograms may be of circular or developed types. The

Development of the cross overslide in the direction of drum cam rotation. (From Pittler Maschinenfabrik AG, Langen bei Frankfurt/M, Germany.)

FIGURE 8.43 Development of the cross overslide in the direction of drum cam rotation. (From Pittler Maschinenfabrik AG, Langen bei Frankfurt/M, Germany.)

Development of the main tool-slide cam. (From Pittler Maschinenfabrik AG. Langen bei Frankfurt/M. Germany.)

FIGURE 8.44 Development of the main tool-slide cam. (From Pittler Maschinenfabrik AG. Langen bei Frankfurt/M. Germany.)

developed cyclograms are more easily read. Chucking events occur during the rapid drawback of the slide (Browne, 1965).

Setting time and accuracy of multispindle automatics. Setting the multispindle automatic for a given job requires 2-20 h, while a piece can be often completed every 10 s. The precision of multispindle chucking or bar automatics is good but seldom as good as that of single-spindle automatics. Tolerances of ±13 to ±25 pm on the diameter are common (Metals Handbook, 1989), and the maximum out-of-roundness may reach 15 pm.

 
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