Development of semi-automatic forming milling mach

2022-08-07
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Development of semi-automatic form milling machine for impeller profile Abstract: the necessity of developing semi-automatic form milling machine for impeller profile is put forward, and the structure of the whole machine and its main components are introduced. The impeller profile is machined by form milling, which ensures the machining accuracy and improves the production efficiency

key words: semi-automatic rough forming and fine milling machine tool for impeller profile

1 problem presentation and scheme formulation

1.1 problem presentation

impeller is a key part of Roots blower, and its profile is an involute surface. The traditional machining method adopts profiling milling or NC single tool planing, which has the following disadvantages:

(1) the surface roughness and dimensional accuracy of the machined impeller surface are low

(2) the consistency of the impeller profile and the symmetry of the axial line of the profile fail to meet the requirements of the product drawing

(3) low processing efficiency. The working time of a single piece is 35 ~ 40min, and one machine tool can not process three varieties L3 ~ L5, 18 specifications and sizes, and the demand for an annual output of 7400 sets

(4) many times of tool walking, fast tool wear, short service life and unstable machining quality

in view of the above situation, a semi-automatic impeller profile forming milling machine is developed

parallelism of any prime line on the impeller profile to the axis: l3:0.08; L4:0.06; L5:0.06。 Symmetry of impeller profile to axis line: metal paint and pearlescent effect spray free materials are mainly used in bumper bottom guard, skirt, anti friction strip, wheel eyebrow, decoration strip and inner door handle l3:0.05; L4:0.05; L5:0.06。

1.2 formulation of scheme

the material of impeller parts is HT250, and the hardness is 180 ~ 220HB. The shape is oval, the unilateral allowance is 5 ~ 6mm, and both sides need to be machined. To ensure the machining accuracy of parts and improve product quality and labor productivity, only the method of forming milling can be used, and the rough and fine can be completed on two machine tools separately. The following technical scheme is formulated in combination with the needs of users and the technical requirements that can be met

(1) separation of rough and finish machining. The unilateral allowance of rough milling machine is about 5mm, and that of fine milling machine is about 0.75mm

(2) it can adapt to 18 specifications of L3 ~ L5

(3) use the forming milling cutter to finish the machining of the whole single-sided profile in one time for rough and fine milling, and the working time of a single piece is ≤ 6min

(4) a magnetic grid digital display measuring system is set on the precision milling machine tool to detect the up and down adjustment position of the tool and ensure the symmetry of the profile to the axis line

because the involute linear surface is processed and formed at one time, the processing depth is more than 5mm, and the processing area is large. The calculated cutting circumferential force is up to 20000n, so it is necessary to specially develop a special forming milling cutter and a machine tool with high rigidity. After more than one year of trial production, one jx2005c and one jx2005j semi-automatic impeller profile rough and fine milling machine tool aiming at the high-end market positioning of Angang have been finally completed. They have been put into use for more than two years and have received good economic and social benefits

2 main structural design of the machine tool

2.1 jx2005c rough milling machine tool

the structural form of the machine tool is shown in the figure

jx2005c rough milling machine structure

1 Main shaft tailstock assembly 2 Ram assembly 3 Headstock 4 Control box 5 and 9 Side seat 6 Workbench

7 Bed 8 Fixture 9 The overall layout of the side seat

machine tool is a frame type. The headstock 3 is fixed, and the tailstock 1 supporting the tool can move axially. After adjustment, it is fixed. The headstock 3 and tailstock 1 are connected together by a ram. One end of the cutter bar equipped with the forming milling cutter is installed in the spindle hole and tensioned by the pull rod, and the other end is installed in the tailstock with rolling bearings. The tailstock and spindle box are installed on the machine body to make them a whole. This structure greatly improves the rigidity and vibration resistance of the machine tool. The main intermediate and polymer will dominate. The structural design of the shaft tailstock is shown in Figure 3

Figure 3 tailstock mechanism

1 Adjusting device 2 Rear gantry 3 Clamping mechanism 4 Beam

5 Tailstock 6 Coat 7 Inner sleeve 8 Forming knife 9 The cutter bar

tailstock is used to support the rotary cutter bar, which is very important to improve the rigidity and vibration resistance of the spindle cutter bar. An inner sleeve is installed at the front support of the tailstock. The outer sleeve is supported by a rolling bearing. The inner hole and the inner sleeve have a taper of 1:10, and three 2mm wide long axial grooves are symmetrically opened on the circumference of the inner sleeve. After the cutter shaft is installed in the inner sleeve, the inner sleeve is axially pulled by the nut at the rear end to adjust the gap between the cutter shaft support and the sleeve, so as to improve the support stiffness of the cutter rod. When the machine tool is working, the tailstock is fixed on the sliding plate, and its upper part is pressed tightly with a screw rod, so that the ram tailstock and the small sliding plate become a whole. When changing the tool, loosen all the above clamping parts, manually rotate the small lead screw to withdraw the tailstock from the support end of the tool shaft, so as to complete the tool change

2.2 jx2005j fine milling machine tool

the structure of the machine tool is shown in Figure 4. The spindle box 1 moves up and down on the column 3 through the stepper motor reducer (i=1:17) - ball screw nut pair. During the processing, the spindle box 1 is firmly locked on the guide rail surface of the column 3 through the joystick, and the workbench 4 makes the feeding movement. The movement of headstock 1 up and down is used to adjust the cutting depth and adapt to the variety change of impeller. The tool bar 6 forms a frame through the spindle box 1, column 3, RAM 9, tailstock 8, bracket 7 and the bed, greatly improving the rigidity of the spindle tool system

Figure 4 structural form of jx2005j fine milling machine tool

1 Headstock 2 Magnetic grid ruler 3 Column 4 Workbench 5 Bed

6 Cutter bar 7 Support 8 Tailstock 9 Ram assembly

2.3 the structural design of rough and fine milling headstock

is shown in Figure 5. The taper hole at the front end of the main shaft is 7:24, with a diameter of 69.85mm. There are two positioning keys at the front end of the main shaft of 25.415mm, which are used to transmit torque. The volatile organic pollutants (VOCs) emitted by the main shaft in the production process are also more and more strictly restricted. There is a pull rod at the rear end, which is used to tighten the cutter shaft

Figure 5 structure of main shaft components

the diameter of the front end of the main shaft of the rough milling machine tool is 150mm, and the fine milling is 100mm. The front support is C and C two-way thrust radial ball bearings, and the rear support is d double row radial short cylindrical roller bearings, with an auxiliary support single row radial ball bearings in the middle. This configuration not only ensures the rotation accuracy of the main shaft, but also can bear large radial load and axial load, and improves the support stiffness and accuracy of the main shaft

the large gears at the front support of the main shaft adopt β= 10 ° helical gear makes the main shaft run smoothly

2.4 design of special fixture

l3, L4 and L5 have three sets of rough and fine milling fixtures for impellers, and the fixture composition is shown in Figure 6

Figure 6 workpiece fixture

1 Slider 2 Base 3 Inclined block 4 Centring shaft5  block

6 Adjusting lever 7 The pressing plate

fixture is installed on the machine tool and positioned by the middle T-groove on the workbench. The workpiece is installed on the fixture, and the centering shaft 4 is inserted into the end face hole for positioning. The four sides of one end of the centering shaft 4 are placed on the block 5 to ensure the left and right limit of the impeller. Both sides of the impeller lean against the end faces at both ends of the centering shaft 4 to ensure the front and rear limit. Manually rotate the lead screw to make the slide block 1 with inclined plane and the inclined block 3 move relatively, and adjust the upper and lower positions of the workpiece so as to adjust the size of the allowance

during rough milling, the average cutting allowance is 5mm, and the cutting force and cutting area are large at one time. Therefore, the key to fixture design is the selection of clamping point and clamping force of parts. The clamping point is selected as the inner hole of the impeller, with two points for each hole (Fig. 7). Four pressing plates and M20 bolts are used to press the impeller on the workbench, and the workpiece is supported by four support plates. Because the hole wall is thick, the workpiece is not easy to deform. The clamping force at each point is calculated to be more than 10kN, and the practice has proved that the clamping force is sufficient

Figure 7 fixture adjustment position diagram

1 Support plate 2 Centring shaft3 Brief introduction to the structure design of workpiece end face

2.5 tool

the tool used for rough milling is 250mm outside and 60mm inside. The tool body is made of 45 steel, and the cutting part is made of carbide indexable inserts. The tools for finish milling are 220mm outside and 50mm inside, made of W18Cr4V integral high-speed steel, and each type has a set of tools. The cutter design is divided into two parts, which is convenient for manufacturing. The involute blade is divided into several segments and approximated by an arc. Practice has proved that the precision after machining fully meets the requirements of part drawings

this machine tool has been put into use in Tianjin blower General Factory for more than two years since march1996, and the effect is very good. The surface roughness and dimensional accuracy of machined parts are improved by one level, ensuring product quality and increasing labor productivity by 8.5 times. Over two years, it has generated 3.49 million yuan of economic benefits for the plant

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