Study of deformations in ram-boring spindle.

Dinu, Gabriela ; Atanasiu, Costica ; Baciu, Florin 等

1. INTRODUCTION

The machine tools are designated to generate the parts surfaces, using the technological process of cutting, following some conditions for dimensional accuracy, for surface quality and for productivity. The technological accuracy of a machine tool is a sum of multiple precision types: geometric, static, cinematic and dynamic accuracy.

The ram type horizontal boring mills with displaceable column are used for the machining of the cast or welded parts from the field of nuclear, energetic, metallurgic or military industry by mean of milling, drilling, boring and threading operations. The machines can be used both for roughing, finishing operations and superfinishings (Gheorghiu et al., 2007, Hadar et al., 2007). The lay-out of the machine is presented in Fig. 1, where the main assemblies are shown.

A simplified section along the machine headstock is presented in Fig. 2.

The mechanical assemblies of different types represent weak parts in the operation of the machine-tools. The forces transmitted by assemblies may lead to concentrations of stress.

Being able to generate strains, this stress affects the accuracy of the machine and is also able to create supplementary contact loads that could produce the breakage of the surface, by fatigue (Hadar et al., 2007).

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

The boring spindle is a pipe type part, guided inside the milling spindle by two bronze sleeves. The ram (box shape) is guided inside the headstock on hydrostatic guide-ways, with controlled pressure on each pocket.

2. NUMERICAL AND EXPERIMENTAL STUDY

The finite elements method study, performed by the COSMOS program, refers to the situation in which the assembly is loaded by its own weight and by the forces resulted in the cutting process, Fx, Fy and Fz, in three positioning cases (Gheorghiu et al., 2006):

CASE 1--The ram slides out by 800mm stroke;

CASE 2--The boring spindle slides out by 1200mm stroke;

CASE 3--The ram is out by 800mm and the boring spindle is out by 1200mm.

The assignment of the deformations that were obtained is:

CASE 1: 0,0133mm;

CASE 2: 0,0288mm;

CASE 3: 0,038mm.

The distribution of deformations is presented in Fig. 3 (for CASE 1), Fig. 4 (CASE 2) and Fig. 5 (CASE 3).

[FIGURE 3 OMITTED]

[FIGURE 4 OMITTED]

[FIGURE 5 OMITTED]

The experimental tests have been performed by a specialized company which made the measurements of the deformations by the help of micro-comparators and laser systems. The field point was in the same location for all situations, which is, at the free socket head of the boring spindle. The values of deformations obtained are given in:

CASE 1: 0,009mm;

CASE 2: 0,031mm;

CASE 3: 0,040mm.

As shown in Fig. 6 and Fig. 7, there are contact stresses along the contact surfaces of the assembly ram-headstock, especially for top and bottom surfaces.

[FIGURE 6 OMITTED]

[FIGURE 7 OMITTED]

The calculated values range between the following limits: 2 x [10.sup.4] - 3 x [10.sup.5] Pa (Buzdugan, 1980). Even those relatively small values affect the precision of machine-tool. For the case when the ram is at maximum stroke out, one can see that the values of the contact stress on the bottom surface in front of the headstock are several times higher than the values on the top surface. The results can be used by the designer or by the machine operator (user) to set higher values of oil pressure for the first bottom pockets of the ram.

3. CONCLUSION

The conclusions are:

* It is to be noticed that deformations in normal limits have been obtained and, in the most unpropitious situation, as CASE 3, with deformations of 3,83T0-2mm;

* CASE 1 has the lowest deformations and CASE 2 has average ones;

* The results obtained by the two methods are comparable, the unwanted situations being noticed;

* The results are useful for the machine-tool's user, because the user can insert corrections so that the machine's accuracy will not be affected;

* The values of contact stress along the contact surfaces of the assembly ram-headstock, especially for top and bottom surfaces range between the following limits: 2 x [10.sup.4] - 3 x [10.sup.5] Pa. Even such relatively small values can affect the precision of machine-tool;

* For CNC machine tools, the value of contact deformations can be adjusted with some electronic corrections.

4. REFERENCES

Buzdugan, Gh. (1980). Strength of Materials, ed. XI-a, Ed. Tehnica, Bucuresti

Gheorghiu, H. & Hadar, A. (2007). Determining Deformations and Existing Tensions in Structures Made from Bedded Composite Materials with Fibers, Proceedings of the 9th International Conference on Management of Innovative Technologies, 9-10 October, Fiesa, Slovenia, p. 191-195 and on C.D

Gheorghiu, H.; Constantinescu, I.N.; Hadar, A. & Petre, C. (2006) . The numerical methods for calculation in strength structural, Ed. BREN, Bucuresti

Hadar, A.; Constantinescu, I.N.; Gheorghiu, H. & Cotet, C.E (2007) . Simulation and models for estimating in mechanics engineering, Ed. Printech, ISBN 978-973-718-759-8, Bucuresti

Hadar, A.; Szabo, A.; Bordeasu, I.; Gheorghiu, H. & Szabo St. (2007). Contributions regarding force differences usage in weighting devices, The 18th INTERNATIONAL DAAAM SYMPOSIUM, "Intelligent Manufacturing & Automation: Globalisation--Technology--Men--Nature", p. 315-316, ISSN 1726-9679