Design of automatic indexing tool table for the ho

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CNC lathe automatic indexing tool table design

1 introduction

at present, the speed of railway trains is greatly increased, and the imbalance of a single wheel of the wheel after speed increase is required to be 70g · M. the rotating surfaces of the wheel, such as the web plate and wheel hub, which were not processed before, need to be processed. At present, the original hydraulic profiling machine tool that can only process the inner and outer rim surfaces, flange surfaces and tread surfaces of the wheel can no longer meet the processing needs of the wheel after speed increase. After repeated research on the wheel processing process route, it is decided to carry out numerical control transformation on the basis of hydraulic profiling machine tool, and design a set of four station automatic indexing tool table on the vertical tool rest of the original machine tool, so as to meet the production needs of full processing of wheel surface. The unilateral allowance of the wheel is 8 ~ 10mm. After calculation, the main cutting force of the machine tool is 25kn. Considering the overload cutting in wheel processing, the main cutting force is set as 30KN. At present, in domestic CNC lathes, the four position automatic indexing tool table with a main cutting force of 30KN is not available from stock. The maximum main cutting force of the existing automatic indexing tool table in our factory is 20KN. According to the needs of the market, it is decided to develop and develop a four position automatic indexing tool table with a main cutting force of 30KN on the basis of the existing tool table. The cutter head shall meet the following requirements: (1) the positioning accuracy and repeated positioning accuracy shall meet the accuracy standard of CNC vertical lathe; (2) The cutter head has good rigidity and meets the requirements of 30KN main cutting force

2 cutter head structure

this cutter head adopts a multi tooth disc positioning device, which is composed of two end face toothed discs 4 and 5 with the same number of teeth and tooth shape. The fixed toothed disc 5 is connected with the ram 8, and the movable toothed disc 4 is fixedly connected with the rotary cutter head 3. During indexing and indexing, the movable gear plate 4 is lifted and disengaged from the fixed gear plate 5. Under the action of pressure oil, the piston rack 10 is axially displaced, driving the shaft gear 9 to rotate for one cycle. The shaft gear 9 engages with the internal teeth of the movable gear plate 4, drives the movable gear plate 4 to rotate a station, and then the two gear plates 4 and 5 re engage and compress under the action of the Belleville spring. Under the action of the pressure oil of the clamping cylinder, the two gear plates 4 and 5 are further compressed, and most of the teeth are in close contact, which can obtain high positioning accuracy and repeated positioning accuracy. Finally, the piston rack 10 is reset under the action of pressure oil, and the control mode adopts full digital pulse control to complete an automatic indexing cycle

1. Belleville spring 2 Piston 3 Rotary table 4 Movable toothed disc 5 Toothed discs 6, 7 Locating plate 8 Ram 9 Shaft gear 10 Plug rack 11 The buffer pin

multi tooth disc positioning device has the following characteristics: (1) high indexing positioning accuracy, up to ± 3, and high repeated positioning accuracy, up to ± 2,. (2) Automatic centering. (3) The tooth surface wear has little effect on the positioning accuracy. With the continuous use of running in, the positioning accuracy may be improved and the accuracy retention is good. (4) Strong bearing capacity and good positioning rigidity. This cutterhead is equipped with coarse positioning plates 6 and 7. When the movable gear plate 4 is lifted, when the shaft gear 9 is not meshed with the internal teeth of the movable gear plate 4, the coarse positioning plates 6 and 7 do not disengage first. After the internal teeth of the movable gear plate 4 are meshed with the shaft gear 9, the coarse positioning plates 6 and 7 are completely disengaged. The rough positioning plate is installed with a tool holder on the tool table Cutter bar (Michael Li, the mechanical design manager of minmi technology, said: "there is a large eccentric load in the process of project research and development) In case of sudden power failure in the free state and during the rotation of the cutter head, it plays a protective role in preventing the cutter head from rotating or not in place. In the automatic indexing device of the cutter head, the 0.02 ~ 0.03mm hydraulic damping gap between the cutter head and the piston rack 10 is controlled by grinding the buffer pin 11 to ensure the smooth rotation of the cutter head. During the downward rotation of the cutter head under eccentric load, it plays a role in preventing the piston rack 10 and the shaft gear 9 from being affected by impact and large wear

3 cutter head design calculation

1) calculation of clamping force

clamping force w should ensure that the tight fit of the gear disc is still maintained under the working load. However, the clamping force should not be too large, otherwise it will cause the deformation of the toothed disc and reduce the positioning accuracy

The clamping force W at

tangent is calculated as

where s - safety factor, which is generally taken as s=1 ~ 1.5. If the working conditions are stable and the impact load is small, Then s is taken as the small value (s=1.3 in this paper)

pz - cutting force (px=py=0.5pz=15000n)

mn torque borne by the toothed disc (mn=0.3-py-0.23px=1050n · m)

mr - overturning torque borne by the toothed disc

fr - radial force borne by the toothed disc (in the meshing pitch plane) [fr= (px2+py2] =20 237n

f0 - toothed disc.Axial force borne (f0=fz=30 000n)

r - pitch circle radius of gear disc (r-180mm)

β—— Tooth angle( β= 60°)

ρ—— Friction angle( ρ= 3 °)

the above formula is substituted into the value, and w=47.3kn when tangent. The actual clamping force W is 50kN, of which the clamping force of the Belleville spring is 30KN; The clamping force of the clamping oil cylinder is 20KN, and the clamping mode of disc spring mechanical clamping and hydraulic clamping is used as auxiliary to ensure the safety and reliability of the clamping of the cutter head

2) check and calculate the extrusion stress of the tooth surface of the multi tooth disc

one of the key parts of the cutter head is the multi tooth disc. Its rigidity can bear one of the National 863 projects. Whether it meets the design requirements will directly affect the positioning accuracy and service life of the cutter head. Extrusion stress of the tooth surface of the gear disc σ The calculation formula of ij is

, where σ Ij -- extrusion stress of tooth surface, n/mm2

z'-- calculated number of teeth (z'=0.5 z=0.5 × 120=60)

b - tooth width (b=25mm)

h0 - meshing height of teeth (h0=4.2mm)

w - clamping force, n

ss - safety factor (taking ss=1.3)

[ σ] Ij -- allowable extrusion stress of tooth surface (taken as the value of tooth surface hardening)[ σ] Ij=40n/mm2)

substitute into the value, σ ij=34.2(N/mm2)

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