Horizontal Multispindle Bar and Chucking Automatics

The principal advantage of the multispindle automatics over the single-spindle automatics is the reduction of cycle time. In contrast to single-spindle automatics, where the turret face is working on one spindle at a time, in multispindle automatics, all turret faces of the main tool slide are working on all spindles at the same time.

Multispindle automatics are designed for mass production of parts from a bar stock or separate blanks. The distinguishing characteristic is that several WPs are machined at the same time from bars or blanks. According to the type of stock material of the WP, they are classified as bar- or chucking (magazine)-type automatics. Chucking machines have the same design of bar automatics, with the exception of stock feeding mechanisms. Typical parts produced by these machines are illustrated in Figure 8.30.

Special Features of Multispindle Automatics

Multispindle automatics have the following distinctive features:

• • They may be of parallel or progressive action.
• • Simultaneous cutting by a number of tools is possible.
• • A nonindexable central main tool slide has a tooling position for each spindle, serving the same function as the turret of a single-screw automatic. It provides one or more cutting tools for each spindle and imparts axial feed to these tools (Figure 8.31).

FIGURE 8.30 Typical parts produced on multispindle automatics. (From Acherkan, N.. Machine Tool Design, Mir Publishers, Moscow, 1969. With permission.)

FIGURE 8.31 Nonindexable central main tool slide of a multispindle automatic. (From Pittler Maschinenfabrik AG, Langen bei Frankfurt/M, Germany.)

• • Progressive-action automatics are available in four, five, six, or eight spindles. Six-spindle automatics are the most common. The equispaced work spindles are carried by a rotating drum (headstock) that indexes consecutively to bring each spindle into a different working position (Figure 8.31).
• • Parallel-action automatics are simpler than progressive-action automatics in construction, as no indexing is required.
• • Multispindle automatics (parallel or progressive) have a nonindexable cross slide at each position, so that an additional tool can be fed crosswise (Figure 8.32).
• • Cams are used to control the motions of the cross slides and the main tool slide. They are either specially designed or selected from a standard range at some sacrifice of optimum output.

The advantages and limitations of multispindle automatics are given here.

Advantages:

• • More tooling positions and resultant higher productivity
• • Greater variety of work that can be produced

FIGURE 8.32 Cross slides of a progressive-action multispindle automatic. (From Acherkan,

N.. Machine Tool Design, Mir Publishers, Moscow, 1969. With permission.)

• • Possibility of producing two pieces per cycle
• • More economical use of floor space when continuous high output is required
• • Simplicity of cams controlling the movement of different parts of the machine

Limitations:

• • Higher loss when the machine is not running, according to its higher capital cost.
• • Setup of the machine is rather tedious and requires a long time, as the space of the head stock and main tool slide is crowded by many tools and attachments.

Characteristics of Parallel- and Progressive-Action Multispindle Automatic

Figure 8.33 illustrates a multispindle automatic with parallel and progressive action.

A parallel-action multispindle automatic is characterized by the following:

• 1. Its spindles are arranged vertically (Figure 8.33a), and it is usually a four- spindle machine.
• 2. The same operation is performed simultaneously in all spindles.
• 3. During one operating cycle, as many WPs are completed as the number of spindles.

FIGURE 8.33 Multispindle bar automatics: (a) parallel-action and (b) progressive-action. (From Chernov, N.. Machine Tools, Mir Publishers, Moscow, 1975. With permission.)

• 4. Each spindle has usually two cross slides. The first is used for forming or chamfering and the other for cutting off the stock.
• 5. The machine can be equipped with multiple-tool spindles for drilling, boring, or threading operations.
• 6. Such a machine produces comparatively short parts of simple shape from bar stock. This type is also known as a straight four-spindle bar automatic.

A progressive-action multispindle automatic is characterized by the following:

• 1. The arrangement of spindles is radial about the axis of the spindle drum.
• 2. Four, five, six, or eight spindles are mounted in the spindle drum, which indexes periodically through an angle equal to the central angle between two adjacent spindles.
• 3. Only one machining stage is performed at each spindle position, and each WP passes consecutively through all positions according to the sequence of operations established in the setup (Figure 8.33b).
• 4. The setup is designed so that the WP is completely machined in one full revolution of the spindle drum, one part being completed at each indexing.
• 5. One of the positions is the loading or feeding position. In the bar-type automatic, the finished WP is cut off in this position, and the bar is fed out to the stop and then clamped by the collet chuck. In the chucking type, the finished part is released by the chuck; in the loading position, a new blank is loaded into the chuck from the magazine and clamped.

TABLE 8.1

Switching Sequence for Six- and Eight-Spindle Bar and Chucking Automatics

Automatic	Progressive Bar/Chucking	Parallel/Progressive
		Bar	Chucking
Loading and Feeding Stations	(6) (8)	(3) -(6) (4) —(8)	(1)—(2) (1)—(2)
Six-spindle	1—2—3—4—5—<6)
Eight-spindle	1—2—3—4—5—6—7—(8)

From Technical Data, Mehrspindel-Drehautomaten, 538-70083. GVD Pittler Maschinenfabrik AG, Langen bei Frankfurt/M, Germany.

A parallel- or progressive-action multispindle automatic is characterized by the following:

• 1. Sometimes, provision may be made in the design of six- or eight-spindle machines for two loading (or feeding) positions, usually diametrically opposed in the case of bar automatics and adjacent in the case of chucking automatics. Table 8.1 illustrates the switching sequence for six- and eight- spindle bar and chucking automatics.
• 2. Single indexing is required in the case of a bar automatic; double indexing is required in the case of a chucking automatic (Table 8.1).
• 3. Two WPs are completely machined during one full revolution of the spindle drum in a bar automatic, whereas two revolutions of the spindle drum are needed to produce two WPs in the case of a chucking automatic.
• 4. Parallel/progressive action is applicable for machining parts of simple shape at a high rate.