Heavy machine tools--hydraulic systems used for clamping/unclamping tool holders.

Prodan, Dan ; Bucuresteanu, Anca ; Balan, Emilia 等

1. INTRODUCTION

A very strong clamping's tool holders is recomanded for heavy, horizontal and vertical lathes (Botez, 1977) to obtain the necessary accuracy processing because the cutting forces have great values. A combined clamping can be used: mechanical and hydraulical (Bozina, 2006). The unclamping is only hydraulical. The principial scheme of such a system is presented in Figure 1.

The hydraulic scheme uses a pneumohydraulic accumulator Ac to increase the security in operation. The distributor [D.sub.1] actuates the filling of the circuit. If the distributor [D.sub.2] is not actuated, pressured oil will find its way to the inferior face of piston 2 of the MHL--linear hydraulic motor 1. The clamping force is obtained adding the force owing to pressure with the force owing to pre-tension of the assembly disk springs 3. The tool holder 4 is clamped on special pieces. The pressure relays 1RP and 2RP are necessary to keep the pressure in the accumulator circuit. The clamping tool holder is confirmed with aid from the pressure relay 4RP. For unclamping the tool holder the distributor D2 is actuated using under pressure oil on the way P [right arrow] B. The pressure relay 3RP is used to confirm the unclamping. The oil from the room with disk springs is free to go to the tank on the way A [right arrow] T. The clamping/unclamping is also confirmed throught the course with the aid of the two electric limiters.

[FIGURE 1 OMITTED]

The work cyclogram for such a system is presented in Table 1.

2. MODELLING AND SIMULATION OF CLAMPING/UNCLAMPING TOOL HOLDERS

Using mathematical models of components (Prodan, 2006) it can be obtained the simulation of the operating system in dynamic regime (state). The following characteristics are obtained by simulations:

* the characteristic in Figure 2--the pressure in the superior chamber of MHL motor, on the phase of unclamping tool holder;

* the stroke obtained in given conditions, after a delay of 0.4 s, increases to maximum point 9.8 mm, according to Figure 3;

* the unclamping speed decreases, and it is stopped, after achieving the stroke, according to Figure 4.

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

[FIGURE 4 OMITTED]

3. HYDRAULIC UNIT FOR CLAMPING/ UNCLAMPING TOOL HOLDERS FOR LATHES. ACTUAL ACHIEVEMENT (Prodan, 2008).

The actual scheme of a unit for clamping/unclamping tool holders for lathes is presented in figure 5. In actual scheme the pump carries out other functions, such as: unblocking cross rail, indexing/non-indexing cross rail, blocking faceplate (Prodan et al., 2000). In figure 5 these functions are not represented and the same notations as in figure 1 are used.

[FIGURE 5 OMITTED]

[FIGURE 6 OMITTED]

[FIGURE 7 OMITTED]

The accumulator is used only for clamping tool holder and holding the clamp. The unclamping tool holder and the no-show functions are doing only with the help of pump. For assuring the clamping is used direction valve 1Sd1, on way A, unblocking. In fact, the clamping/unclamping tool holder is obtained with unit MOD 1.2. This unit (DN6) is presented in figure 6 and it contains: bed plate, pressure relays 3RP and 4RP, direction valve 1Sd1 unblocking and distributor D2. Linear hydraulic motor MHL for vertical lathe, before its assembling in ram is presented in figure 7. Tool holder is pulled on plate 2 with the connecting piece 1. On ram the body of linear hydraulic motor 3 is centered. The disk springs are adequate pre-loaded with the help of a plate. The piston is closed in body with the help of cover 4. Electric limiters are fixed on place 7 and they approve clamping/unclamping tool holder when cam 5 on rod 6 is actuated. The oil necessary for cooling the tool is coming on pipe 8. When the system is supplied axially the force achieved by pressure is added up with force obtained by disk springs pre-loaded and clamping is strong and sure. When the system is supplied laterally the piston works against disk springs and the unclamping of tool holder is obtained. The operatining pressure for this system is approximatively 60 bar.

4. CONCLUSION

The clamping/unclamping systems of the tool holder are achieved with great cutting forces and specific security conditions in case of heavy lathes. Usually, the systems are mechanic-hydraulic in modular assemblies with apparatus having DN 4 or 6. The presence of pneumohydraulic accumulators is a warranty for operating in conditions of security constrained. For dimensioning and checking calculations it is recommended to use modeling and simulation. The operating pressures are connected with the operation specific conditions, and the technical possibilities of used apparatus.

5. REFERENCES

Botez, E. (1977). Machine Tools, vol. I, Technical Publisher House, ISBN CZ 621.9, Bucharest

Bozina, P. (2006). Handbuch Werkzeug-maschinen, Edit. HANSER, ISBN 10:3-446-40602-6, Berlin

Prodan, D., Dobrescu, T. Bucuresteanu, A. (2000). Hydraulic systems for fixing, clamping and unclamping), Review Hidraulica, Edited by Hydraulic and Pneumatic Researches Institute, pp. 13-18, July, ISSN 1453-7303, Bucharest

Prodan, D. (2006). Machine Tools. Modelling and Simulation of Hydraulic Elements and Systems, Printech Publisher House, ISBN 978-973-718-572-3, Bucharest

Prodan, D. (2008). Heavy Machine Tools. Manufacturing and Rebuilding, Printech Publisher House, ISBN 978-973-718892-2, Bucharest

Tab. 1. The work cyclograme of the system in Figure 1

 Electro- Pressure relays
 magnets

 Phase E1 E2 1RP 2RP 3RP 4RP

 Stop - - + +(-) - +

Load circuit + - + + - +
 Keeping - - + + - +
 pressure + -

 Reload + - + - - +
 + +
 Unclamping -(+) + + + + -
tool holder

 Clamping -(+) - + + - +
tool holder