Improved Technology Of Induction Heat Treatment Of Motorcycle Shift Fork

1. An overview of the

  Motorcycle shift fork and shift drum, shift fork pin shaft, as well as a spindle, countershaft, shift shaft components together to complete the motorcycle shift function, shift fork function is to transfer shift shaft shift force so that the spindle and countershaft meshing gear into the corresponding gear combination meshing.

  Motorcycle variable: is the work of archives institutions operated clutch handle, after making the clutch will shift from variable gear treadle force through change gear shaft combination dial positioning plate make the shift drum rotation, shift drum rotates, drive the shift fork mobile in the shift drum trip trough, while moving dial the main shaft and the auxiliary shaft gear fork of a radical move to corresponding gear position, the clutch handle, spindle, and gear shaft and the gear meshing began to work, to the gear ratio of transmission power. The gear changing mechanism of the motorcycle is mainly composed of clutch handle, clutch draw line, clutch separating mechanism, shift pedal, shift shaft combination, shift positioning plate, and shift positioner combination, shift cooperate to complete the gear-changing function.

  Shift-shift fork is the part that most directly moves spindle gear and countershaft gear. The common shape of the shift-shift fork is shown in Figure 1.

FIG. 1 A type of motorcycle is illustrated by shifting fork

  When the shift fork is in use, the plane parts on both sides of the Java are in contact with the sidewall of the fork slot of the gear, as shown in Figure 2.

FIG. 2 Assembly diagram of shift-shift fork and claw of a motorcycle

  The shaft end of the shift fork moves in the travel slot of the shift drum, as shown in Figure 3. These conditions of use determines the shift fork must have a certain strength and wear resistance, and toughness, in order to prevent the abnormal change gears in the process of impact, this also means that the heat treatment of the product control is to ensure that match the strength and wear resistance, toughness, in view of the shift fork induction heat treatment here long-term grope for the improvement of experience introduced to you.

FIG. 3 Assembly diagram of the rear end of shift fork of a motorcycle

2. Main manufacturing process of shifting fork

  The shifting fork of a certain motorcycle is made of national standard 45 steel. According to the use and technical requirements of the shifting fork, namely, the strength, wear resistance and toughness of the shifting fork are required to match, the following main technological process is formulated:

  Blanking → heating → forging forming → drilling → turning end face, inner hole and chamfering → milling fork plane → fine grinding end face → milling opening and chamfering → drilling and chamfering → grinding → induction heating and quenching and tempering → non-destructive testing → polishing → electroplating → reaming and burring → cleaning → applying anti-rust oil → packaging → warehousing.

3. Technical requirements and main processes of induction heat treatment

  According to the technical requirements of the shifting fork: the range of the hardening layer of the Java is shown in Figure 4, the surface hardness is 50 ~ 60HRC, and the depth of the hardening layer is 1.0 ~ 1.5mm.

FIG. 4 Technical requirements for hardening layer of a shift-shift fork claw

  Adopt high-frequency induction heating, quenching, and tempering heat-treatment process. The solid-state super audio heating unit, cW-XJH-60B, with the power of 60kW and frequency of 30 ~ 150kHz, is used. The quenching fluid is clean water, the water temperature is 20 ~ 40℃, and the quenching pressure is 0.2 ~ 0.8mpa. Tempering adopts well type tempering furnace with tempering temperature of 180℃. The structure of the heating inductor used is shown in Figure 5.

FIG. 5 Schematic diagram of the heating induction coil in a shift-shift fork claw

4. Existing problems

  Induction heat treatment process using the above out of shift fork part, confirmed by the test of radical hardness, the depth of hardening layer, hardening area, and the shape is not qualified, do not conform to the technical requirements, testing parts as shown in figure 6 ~ 8, test results are shown in table 1 and table 2, the hardness and depth of hardening layer are very uneven, and the local soft point, claw end hardness is low, many points of hardening layer depth is not enough, so we decided to improve the bad phenomenon.

FIG. 6 Detection site

Figure 7. Point location of claws

FIG. 8 Site of web detection

Table 1 Hardness test results of a type of shifting fork after heat treatment

Table 2 Detection results of hardened layer after heat treatment of a type of shift fork

5. Cause analysis and improvement measures for poor hardness and hardened layer

(1) Cause analysis of poor hardness and hardened layer

Distance shift fork claw ends at 2 mm hardness is bad, and the quenching hardness than the lower limit range 26 mm, show hardening range less than the technical requirements for the lower limit of 25 mm, but the width of the quenching inductor design to meet the requirements of the quenching scope width, and considering the end lines of magnetic force attenuation and increased the width size, confirm the scope of products than ever before quenching increased 5 mm, the width of the existing equipment only 60 kW of power, based on the judgment device output power shortage lead to adverse and quenching hardness range, because the structure of this kind of power supply, The design of the heating and quenching cooling water spray rings used by the inductor can only be designed in a separate way, which will lead to greater hardness heterogeneity. The shape of hardening layer shape depends mainly on the structure of the sensor, the sensor and the clearance between heating part more even more beneficial to the uniform of hardening layer, both the shape of hardening layer, the better, but because the ministry product shape is more complex, consider the “Angle effect” of induction heating characteristic, leading to the structural design of the sensor is very difficult.

In addition, due to the structural limitations of such a power supply, the quenched inductor can only be designed with a single-turn structure, resulting in defects in the design of the original inductor and leading to the occurrence of a bad hardening layer after heat treatment (see Table 2).To improve the above defects, we can only fundamentally change the structure of induction heating equipment and sensors. For this reason, we need to re-review these two items, and according to the review results, we bought new induction heating equipment and redesigned sensors.

(2) Improvement measures

New induction heating equipment using MOS type high-frequency power supply, inverter part adopts high power MOS tubes full-bridge inverter circuit, depending on the load resonance frequency converting dc to ac current, maximum power 120 kW power within the 10% to 100% of rated power-adjustable, frequency of 200 kHz, inverter control part adopts phase-locked loop (PLL) which can adjust the frequency tracking, automatic quenching process is controlled by PLC, quenching machine tool using multi-station NC quenching machine tool, as shown in figure 9. The quench induction is designed as an integral inductor, the water spray ring and the effective ring are the same rings, and the quench water cavity is the internal cavity of the quench inductor. At the same time, a new inductor is designed by referring to the experience of the inductor mentioned above and the complex structure of parts.

FIG. 9 Multi-station quenching machine tool

6. Improve results

The above improvement measures were applied to re-induction heat treatment for the shift shifting fork. The improved shift shifting fork was tested at the same testing site as above. The hardness test results are shown in Table 3.The test results of hardened layer depth are shown in Table 4.The surface tissue was grade 6 Martensite, and the heart tissue was grade 3 tempered Soxhlet. The hardness of the improved shift fork was completely qualified, and the hardness uniformity was greatly improved compared with that before the improvement. The depth of the hardening layer met the technical requirements, and the shape of the hardening layer was also significantly improved, as shown in Figure 10.

Table 3 Hardness test results of a shifting fork after improved after heat treatment

Table 4 Detection results of hardened layer after heat treatment of a certain type of shifting fork after improvement

FIG. 10 Hardened layer after improvement of a shifting fork

7. Conclusion

Through to the complicated shape of motorcycle shift fork of induction heat treatment system improvement, further realized in the process of heat treatment process design, not based on the present situation, only by constantly through the theory with practice, combining with the current design heat treatment system, new equipment, new heat treatment technology to make products to meet the requirements of the department of product design technical requirements, achieve the best performance condition.