Group Machining of Gearbox Housing Parts on Longitudinal Milling Machines

I. I. Ryabovol, B. D. Barlakov

(Presented by the scientific seminar of the departments of mechanical-engineering technology, machine tools, and metal cutting)

Under an economic contract with the Krasnoyarsk Sovnarkhoz, the Department of Mechanical-Engineering Technology is carrying out work on the topic of improving the quality of manufacture of large gearboxes produced by the Sibtiazhmash plant. This work provides for a comprehensive solution to the problems of designing a new progressive technology for the machining of gearbox parts, tooling, and the technology of gearbox assembly.

The Krasnoyarsk plant “Sibtiazhmash” produces gearboxes of a very broad range of types (about 140 designations), used both to complete the plant’s main products and for delivery to outside customers. The broad product range and the small production program for individual types of gearboxes compel the plant to organize their production on a serial, small-batch, and even individual basis. Vertical crane and cylindrical-conical gearboxes are produced by the plant in the greatest quantity, i.e., on a serial basis.

This article considers one issue from the above-mentioned complex: the machining of the flat surfaces of housing parts of general-purpose vertical-crane gearboxes (VK) and cylindrical-conical gearboxes (KTs).

An analysis of the technology currently used at the plant for machining gearbox housings and covers has enabled us to identify a number of its shortcomings, affecting both machining accuracy and productivity. It should be noted that the plant’s current technology for manufacturing the housings and covers of VK and KTs gearboxes, in the operations for machining the split-plane and base surfaces, is not equipped with fixtures and therefore provides for machining them by layout marking, primarily on longitudinal planing machines. Such a technology, naturally, did not provide high productivity or proper accuracy. The desire to reduce labor input and improve machining accuracy led to the decision to reduce to a minimum, or completely eliminate, the labor-intensive and costly layout-marking operation through the use of special fixtures, and to replace planing with more productive face milling on longitudinal milling machines.

Analyzing the principles of designing technological processes, we came to the conclusion that, under the conditions of the Sibtiazhmash plant, which operates according to a multi-product program, the most acceptable prin-

the principle of group machining is used as the standard type. For this purpose, on the basis of the plant’s materials, we carried out a classification of the housings and covers of the VK and KTs reducers, with allowance for which a standard technology of group machining was developed.

It should be noted that, in developing the technology, the design of the reducer housings had a significant influence on the choice of machining schemes according to the group principle. A design feature of the housings of some reducers is the presence of a sump projecting above the base surface, which complicates not only the machining of the base plane itself, but also the setting of the housing on it when machining the joint plane and the seating and fastening holes. In this connection we provided two schemes for machining the base plane of the housings: scheme “A” — for housings without a projecting sump (reducers VK-750; KTs2-500, Figs. 1a and 4a) and scheme “B” — for reducers with a projecting sump (reducers VK-500; VK-850; VK-950; KTs2-750; KTs2-100; KTs2-1300, Figs. 1b and 4b).

Below we give the content and sketches of setups and operations for machining the base and joint planes of housings and covers of reducers on longitudinal milling machines 6642; 6652; 6662; 6672.

VK reducers

1st operation. Simultaneously mill the base plane of the reducer housing and the side surface “a” (for machining schemes see Figs. 1a—b, for the sketch of loading the machine table see Fig. 2).

2nd operation. Drill “n” holes in the base of the housing and countersink two of them, located diagonally. This operation is intended to create locating holes by which the reducer housing is based in fixtures during most subsequent operations.

3rd operation. A. Simultaneously rough-mill the joint plane of the housing, the joint plane of the cover, and the plane of the cover hatch.
B. Do the same as a finishing operation (for the sketch of setting up the parts and loading the table see Fig. 3).

Note. Depending on the width of the housings and covers of the VK reducers, standard face milling cutters with diameters from 400 to 630 mm are used.

KTs reducers

1st operation. 1. Mill the base plane of the housing and its side surface “a” simultaneously with the plane of the cover hatch (for the sketch of setting up the parts and loading the machine table see Figs. 4 and 5).
2. Reset the reducer housing onto the base plane, and the cover onto the hatch plane.
3. Rough-mill the joint planes of the housing and the cover.
4. Finish-mill the joint planes of the housing and the cover (for the sketch of setting up the parts and loading the machine table see Fig. 6).

Note. The choice of machine size, cutter diameters, and machining schemes depends on the type of reducer (see the table).

From the technology presented it is evident that the machining of the planes of reducer housings and covers on milling machines is carried out according to the group principle, which is ensured by an appropriate design of fixtures that make it possible to set different surfaces of different housings and covers at one level and to machine them in a single table pass.

Scheme “B”

Scheme “A”

Fig. 1. Sketch of the fixture and machining schemes for VK gearbox housings.

Fig. 2. Sketch of loading the table with VK reducer housings:
a) machine 6642. Machining scheme B (VK-500, VK-850, and VK-950 reducers);
b) machine 6662. Machining scheme A (VK-750 reducer).

Designations:
1 — Single-position fixture
2 — Part

Fig. 3. Sketches of the installation and loading of the table with housings and covers of VK reducers.

Fig. 4. Sketches of the setup and loading of the table, and unloading of KC reducers during machining of the planes and the hatch.

Visible labels in the figure:

• Setup I
• \(d_{\phi}\)
• Feed direction
• \(D_{\phi}\)
• Fixture
• Part

Installation II

Feed direction

Labels in the drawing: \(D_{\phi}\), \(D_{0}\); Fixture; Part.

Fig. 6. Sketch of the setup for loading the table with housings and covers of KTs1 reducers when machining the joint planes.

Fig. 7. Device for milling the plane of the connector of the VK-500 and VK-750 reducers.

Table for selecting machines, cutters, and machining schemes

Fixtures for machining housings and covers on milling machines

Proceeding from the principle of group machining incorporated in the technology we designed, and taking into account the variety of size types of gearboxes produced by the plant in small batches, when selecting the designs of fixtures we sought to ensure that they met the following basic requirements:

1) simplicity of design;
2) versatility, allowing, with minimal readjustments or without them, the machining in one and the same fixture either of housings and covers of different sizes, or of different surfaces of the same housings and covers;
3) mechanization of the centering and clamping of the housings and covers being machined.

In developing the designs we proceeded along the path of creating single-station readjustable fixtures, which ensures comparatively small overall dimensions and facilitates installation, transportation, and storage. Group machining in such fixtures is achieved, as can be seen from the loading sketches (Figs. 3, 5, 6), by simultaneously mounting on the machine table fixtures both for machining housings and for machining covers.

Below we give typical fixture designs in order to show, by means of them, the principles we followed in designing the tooling.

The fixture shown in Fig. 8 makes it possible to machine in it the cover of a KTs2-500 gearbox both along the hatch plane and along the split plane without any readjustment. The procedure for machining the cover in it is as follows:

1) the hatch plane (1) is machined when the cover is mounted with the unmachined split plane on three supports 1 and clamped with hydraulic clamps 2 and 10;

2) the split plane II is machined when the cover is mounted with the machined hatch plane on raised supports 5 and 8 and clamped with hydraulic clamps 4 and 7. The cutters are set in height by means of gauge template 3 with the aid of a 5 mm feeler gauge.

Figure 7 shows a fixture that permits machining, without readjustment, the split planes of the covers of VK-500 and VK-750 gearboxes. The covers are mounted on previously machined hatch planes. The position of the covers on the inclined plane of the fixture is determined by pins 3 and 4 entering the hatches of the covers. The plane

Fig. 8. Fixture for milling the planes of the hatch and the joint of the cover of the K112-500 reduction gear unit.

“A” is the common reference plane for installing both covers. The covers are secured with hydraulically operated clamps:

the VK-500 cover—with clamps 2 and 5;
the VK-750 cover—with clamps 1 and 2.

The height adjustment of the milling cutters is likewise carried out using master template 6 with the aid of feeler gauges of various thicknesses.

For the VK-500 cover, the feeler-gauge thickness is 5 mm;
for the VK-750 cover, the feeler-gauge thickness is 65 mm.

Control of the hydraulically operated clamps in both fixtures is carried out from hydraulic panels developed by us.

The remaining fixtures used in milling operations are designed according to the same principle.

Conclusion

1. The technological processes and tooling developed by us for the group machining of reducer housings and covers have been accepted by the plant for implementation.

2. The application of group technology reduces the labor input for machining housings and covers by 30–35%.

3. The universalization of fixtures makes it possible to reduce their number and, consequently, the costs for them by half.

References

1. S. P. Mitrofanov. Scientific Foundations of Group Technology. Lenizdat, 1959.

2. M. A. Tolstov. Pneumatic and Pneumohydraulic Fixtures. Mashgiz, 1961.

3. A. Ya. Belchenko and G. G. Yatsenko. Group Methods for Machining Machine Parts. Mashgiz, 1961.

4. M. A. Aiserov. Fixtures for Metal-Cutting Machine Tools. Mashgiz, 1960.