Design of special fixture for the hottest CNC vert

Design of special fixture for NC vertical lathe

in order to meet the needs of processing irregular and difficult to machine parts such as "rear wheel hub and brake drum assembly" on the automobile manufacturing production line, a set of hydraulic fixture is added to the ck815e NC single column vertical lathe, so that the machine tool can clamp workpieces quickly, with high production efficiency and reliable centering benchmark, so as to adapt to the characteristics of large variation range of typical workpieces of the same type and different specifications. The machine tool can be connected to the automobile production line to meet the part processing needs of the production line of "mass production, high efficiency and fast beat"

1 clamping process analysis

the maximum diameter of "rear hub and brake drum assembly" is 440mm, the maximum inner hole diameter is 370mm, and the maximum workpiece height is 340mm. The workpiece is in the shape of a tall wine cup, and the upper and lower inner conical holes are taken as the benchmark. The processed inner holes should maintain a coaxiality of 0.06mm with the benchmark, the inner hole cylindricity of 0.087mm, and the average diameter of the upper and lower inner conical holes is 110mm. According to the overall dimensions, the workpiece can be processed on ck815e CNC single column vertical lathe. If the clamping and centering method of clamping the workpiece outside the claw of the original machine tool workbench is still used, the following shortcomings are difficult to overcome: ① since the process datum of clamping the workpiece is separated from the design datum of machining hole, the coaxiality of machining inner hole and datum hole is required to be 0.06mm, which is difficult to ensure. ② Clamping thin-walled parts is prone to deformation, and the cylindricity of the machined hole of 0.087mm is difficult to ensure. ③ The auxiliary time of clamping and alignment is long, which can not meet the needs of "high efficiency and fast beat" of automobile production line. Therefore, it is necessary to add a set of hydraulic clamping device on the basis of the workbench of the machine tool, and the fixture should meet the following requirements: ① ensure the coaxiality requirements of the machined hole and the reference hole and its own cylindricity requirements. ② The clamping is safe and reliable, that is, the clamping force is large enough. ③ Meet the clamping needs of three typical workpieces with different specifications. ④ The disassembly, installation, and identification of the materials we provide have a short auxiliary time for the positive workpiece. ⑤ The maintenance and replacement of vulnerable parts and sealing rings have become the development trend of the industry, which is green, low-carbon and environment-friendly

2 fixture structure

on the basis of repeated analysis and Research on the characteristics of the cold machining process of typical workpieces, the fixture (see the attached figure) adopts the cutting mode of upward opening of the big end of the workpiece and vertical tool rest from top to bottom. The oil distribution device is installed on the upper part of the spindle of the workbench, the clamping oil cylinder is installed on the upper part of the workbench, and the workpiece is located on the upper part of the clamping oil cylinder

1. Spindle 2 Oil distribution shaft 3 Sealing ring 4 Cylinder body 5 Piston 6 Piston rod 7 Brake drum assembly 8 Plug board 9 Upper cone sleeve 10 Lower taper sleeve 11 Centering sleeve

structure diagram of hydraulic fixture

the fixture layout has the following characteristics: ① it meets the requirements of machining inner hole accuracy of typical workpiece. The cone angle of the upper cone sleeve 9 and the lower cone sleeve 10 is matched and ground according to the actual taper of the inner hole of the typical workpiece to ensure that the contact rate reaches more than 80%. The centering seam between the fixture and the workbench is matched with high precision, and the central hole of the workbench is assembled by itself. Through the above measures, the workpiece machining inner hole center, the workpiece upper and lower inner cone reference hole center, and the workbench rotation center are consistent, ensuring the coaxiality requirements between the workpiece machining inner hole and the reference hole and the cylindricity requirements of the workpiece inner hole. ② Clamping is safe and reliable. Because the clamping cylinder is arranged on the upper part of the workbench, the space of the central hole of the workbench is fully used, and the ideal diameter of the clamping cylinder can be selected to meet the needs of the clamping force. The upper and lower taper sleeves 9 and 10 are notched. When pressed, the inclined plane can be closely pressed on the inclined plane of the workpiece to increase friction. ③ It can meet the clamping needs of three typical workpieces with different specifications. Three sets of upper and lower taper sleeves 9 and 10 are designed for the fixture, which can be easily replaced to meet the needs of clamping different workpieces. ④ The auxiliary time for disassembling, installing and aligning the workpiece is short

when the workpiece is clamped, under the control of the hydraulic valve, the upper end of the oil cylinder is filled with pressure oil, and the piston pull rod 6 tightens the upper cone sleeve 9 to firmly fix the workpiece on the centering sleeve 11; When the workpiece is loosened, oil comes from the lower end of the oil cylinder, and the piston rod moves upward to push out the upper cone sleeve 9 at the same time. Remove the horseshoe shaped insert plate 8 on the upper cone sleeve 9, and pull out the upper cone sleeve 9. At this time, the workpiece can be removed. Because the fixture adopts the clamping mode of automatically centering and clamping the workpiece, the auxiliary time of installing and aligning the workpiece is shortened. ⑤ It is convenient to maintain the machine tool. Because the fixture is arranged at the lower part of the workbench, the sealing ring of vulnerable parts can be easily replaced

in addition, the distance between the oil distribution device and the oil cylinder body is small, the cantilever of the oil distribution shaft is short, and the radial runout during rotation is small, which relatively prolongs the service life of the seal ring. ⑥ The spindle of the machine tool is the oil distributor of the oil distribution device, which improves the rigidity of the spindle and makes the pipeline connection simpler. The upper end cover of the oil cylinder is the centering sleeve, and the oil cylinder body is directly closed on the workbench through the centering stop. Through the above ingenious design, the centering accuracy of the fixture is improved and the machining accuracy requirements of parts are met

3 design calculation

1) calculation of cutting force and cutting torque

a. cutting force pz

pz= CPZ · txpz · sypz · K PZ (n)

where T - cutting depth, mm. T=1.5mm

s - feed rate, mm/r. S=0.8mm/r

the typical workpiece is cast iron, and the carbide tool is used to turn the inner hole. Check the coefficients as follows: cpz=902, xpz=1, ypz=0.75, K pz=1, and substitute into formula (1) to get pz=1145n

b. maximum cutting torque M cut

m cut =pz*d workpiece/2

where d workpiece - the maximum machining diameter of the inner hole of the workpiece, D workpiece =0.37m

substituted into formula (2), m cut =211.8n · M

2) calculation of piston rod tension f pull and oil cylinder diameter D oil cylinder

a. friction torque M friction =s · m cut

where s - safety factor, s=1.3

substituted into formula (3), M friction =275.34n · M

b. cone friction f friction

f friction = (M friction/2)/(d cone/2)

in the formula, D cone - the average diameter of the cone, D cone =0.11m

substitute into formula (4) to get f friction =2503n

4. Wire/sheet tensile test C. piston rod tension f pull

f pull = f friction/sin α·

where α—— Cone angle, α= 30 ° - friction coefficient, =0.15

substitute it into formula (5) to get f pull =33373n

d. cylinder diameter D cylinder

d cylinder = [4f pull/π p+d rod 2]

in the formula, D rod - piston rod diameter, after calculation, take D rod =0.04m

p - pressure oil pressure, p=3.5 × 106n/m2

substitute into formula (6) to get D cylinder =0.1172m. In the design, the diameter of oil cylinder D is taken as oil cylinder =0.12m. When D cylinder =0.12m, M friction =284n · M. M friction>m cut

the fixture was successfully assembled with the original machine tool and trial cut the workpiece. It has been successfully delivered. It has been connected to the automobile production line and officially put into production. The average annual spot prices of copper, aluminum, lead and zinc have fallen by 16.8%, 10.2%, 5.5% and 4.1% respectively year-on-year. (end)