Development of the hottest three key circular arc

  • Detail

Development of three key circular arc cycloid broach

1 introduction

clutch is a key component frequently used in motorcycle starting and braking, so it needs to have a high service life. The material selection, heat treatment process and machining accuracy of clutch parts have a direct impact on its service life. The traditional machining method of the inner hole surface of the clutch outer ring mainly adopts wire cutting or milling. However, due to the low efficiency and high cost of wire cutting; However, the surface quality of milling is not high, so these two processes are difficult to fully meet the requirements of users for product quality, and are not suitable for mass production. In order to solve this problem, through strict process analysis, we designed a new broaching scheme for the machining of the inner hole surface of the outer ring of the motorcycle overrunning clutch shown in Figure 1, and developed a special tool for precision machining, the three key circular arc cycloid broach

Figure 1 workpiece diagram of inner hole of outer ring of motorcycle clutch

2 broach structural characteristics and main parameters

2.1 broach structural characteristics

broaching process for machining the inner hole surface of outer ring of clutch has the advantages of high machining precision, high efficiency, low cost, one-time processing and accurate positioning. For this reason, the specially designed three key circular arc cycloid broach has the following characteristics:

1) according to the processing requirements, the broach is designed as a group of two (as shown in Figure 2). One of them is mainly used to complete the basic broaching of rectangular teeth; Two knives are mainly used to complete the broaching of circular arc Cycloid Teeth. This design can significantly improve the processing efficiency, and at the same time, the cutting tools can be changed according to the degree of broach wear, so as to reduce the cost of cutting tools

(a) one tool structure diagram

(b) two tool structure diagram

Figure 2 broach structure diagram

2) ordinary broaching generally adopts layered broaching, that is, each tooth of the broach is divided into a certain amount of tooth rise, and each tooth will gradually cut off the workpiece allowance during the movement of the broach. The tooth profile of this kind of broach is relatively simple and easy to manufacture. However, for parts with special tooth shape and high positioning accuracy requirements, layered broaching is difficult to meet the machining accuracy requirements. In order to ensure the fitting accuracy and performance requirements of the inner and outer rings of the clutch, the design of the three key circular arc cycloid broach adopts the segmented modeling method, that is, the broach tooth shape is divided into three parts: the front part of the broach adopts circular cutting teeth, which can play a centering role to ensure the dimensional accuracy of the inner hole; The middle part adopts the basic tooth profile of broach rectangular teeth to realize the key side positioning and cut most of the cutting allowance; The precision cutting teeth at the rear of the broach adopt circular arc Cycloid Teeth, and its tooth profile is a composite curve (straight line - circular arc - cycloid - circular arc - 15 ° oblique line). The tooth shape of each part of broach is shown in Figure 3

Figure 3 tooth profile diagram of each part of broach

3) broach adopts small tooth lifting design, so the machined surface roughness is good, and broaching is stable, and the machining quality is stable. Each group of broach can process nearly a thousand workpieces, with long service life, which can greatly reduce the processing cost

2.2 pull can pass the test ldquo; Spheroidization rate rdquo; Main parameters and technical requirements of the knife

main parameters of broach

tangent coordinates of arc and cycloid, center coordinates of two arcs, tangent coordinates of 15 ° inclined plane and arc and cycloid

cycloid circle radius: r=31.293mm

theoretical outer diameter =63.74mm

number of broach keys: three keys

inner hole diameter: =44mm

technical requirements of broach

radial runout tolerance of calibrated teeth: 0.01mm

cumulative tolerance of spline teeth: 0.015mm

cycloid tooth profile tolerance: 0.015mm

heat treatment hardness: 45 ~ 52hrc; Knife body hardness: 63 ~ 66hrc

symmetry of two key teeth center to tool body: 0.015mm

3 key points of Broach Design

because the three key circular arc cycloid broach adopts odd keys, compared with the even key broach, it increases many difficulties in design and manufacture. The main difficulties in its design are the determination of the tangent point between the arc of the tooth top of the broach tooth profile and the cycloid and the coordinates of each point; The manufacturing difficulty is mainly the machining of the tooth top arc and cycloid tooth profile of broach

The tooth lift of broach teeth is an important factor affecting the machined surface roughness. The smaller the tooth lift of the cutter teeth, the smaller the machined surface roughness value and the higher the geometric accuracy, but the broach length will also increase, which will directly affect the broach strength. Therefore, in the design of broach, we should fully consider the broaching machine performance, quenching conditions and other process conditions, and try to use small tooth lifting on the premise of meeting the strength requirements of broach

in order to improve the accuracy and efficiency of Broach Design, one of the expensive experimental equipment was selected and AutoCAD software was used for computer-aided design. In order to reasonably select broach parameters and ensure broach strength, the cutting force and broach strength must be strictly verified. The method is as follows:

3.1 calculation of broaching force

broaching force is the basis for selecting broaching machine model and checking broach strength. The main factors affecting broaching force are: broach type, section shape, tool geometric parameters, broach tooth lift, broaching width, number of simultaneous working teeth, workpiece material and heat treatment performance. The general calculation formula of the maximum broaching force Fmax is

fmax=f'sbdzekgkakdkw (its high-pressure turbine sealing device 1)

where: F '- broaching force on the unit cutting edge length of the cutter tooth

Σ BD -- total width of cutting edge of each cutter tooth (mm)

ze -- maximum number of simultaneous working teeth

k γ, K α, K δ, K ω—— They are the correction coefficients of the influence of broach rake angle, rake angle, tooth sharpness and cutting fluid on the cutting force (which can be selected from the table and can be ignored in general)

when calculating the broaching force of different types of broaches, the parameter selection of formula (1) can be different. For spline broaches, The calculation formula of broaching force is fmax=f'bnze (2)

, in which: B - the cutting edge length of each cutter tooth

n - the number of spline keys

ze - the number of simultaneous working teeth

as a special case of spline broach, formula (2) can be used to calculate broaching force

3. Speed up the upgrading of plastic granulator technology 2 broach strength check

for broaches with small cross-section size, the strength check of their dangerous section (minimum cross-section) must be carried out to prevent the broach from breaking. In the broaching process, the broach is not only affected by broaching force, but also by certain distortion and deformation, and the factors causing deformation are quite complex (such as clamping error, quenching stress, etc.). Therefore, when calculating the strength, in addition to calculating the main tensile deformation according to the maximum broaching force Fmax, considering the influence of other deformation, it is also necessary to increase the safety factor. The strength of broach can be obtained from the actual stress of broaching process δ And allowable stress[ δ] To check. Actual stress δ from δ= Fmax/amin, allowable stress[ δ] It can be found from the table. if δ [/δ]> 1. That is, the actual stress is greater than the allowable stress, indicating that the broach strength is insufficient, the design parameters need to be readjusted, the broach cross-section should be increased, and the broaching force should be reduced to ensure that the broach has sufficient strength

4 key points of broach manufacturing

in order to control the stress deformation of broach in cold and hot working procedures, the broach chip holding groove adopts curved blade back and full type polishing, which is not only conducive to chip removal, but also reduces the stress deformation; Take many measures to control the deformation out of tolerance in the rough machining process; Adopt small feed cutting, straighten the broach after each process, and remove the residual stress; After heat treatment, grind the excircle, straighten and grind the support for many times

in the manufacturing process, six keys are used for eccentric processing, and then two keys are removed, leaving a symmetrical key as the benchmark to ensure the positioning accuracy of broach

The grinding of tooth top arc and cycloid tooth profile is the key process of broach manufacturing. According to the actual processing conditions, the grinding of tooth profile can be completed on the deform NC spline grinder by AutoCAD programming, or on the ordinary spline grinder by designing the grinding wheel roller. Since the tooth profile of broach is composed of several different tooth profiles, the 15 ° inclined plane can be grinded separately during machining, and then the roller can be used to trim the tooth profile of grinding wheel after passing the inspection, and the tooth top arc curve can be machined, so as to ensure the smooth transition of tooth profile. In order to ensure the consistency of the center of the front and rear teeth, the CNC spline grinder has a good machining effect, and the grinding of all tooth profiles can be completed in one clamping

5 conclusion

through broaching test, expert identification and user use verification, the three key circular arc cycloid broach developed by our factory can fully meet the user's requirements, and the performance of motorcycle clutch processed with this broach has been greatly improved. At present, our factory can design broaches of different specifications according to various types of motorcycle clutches, forming a series of three key circular arc cycloid broaches, which can be mass produced. (end)

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