Abstract: Thin gear shaving tools are prone to warping deformation during the heat treatment process, resulting in uneven tooth thickness and affecting both appearance and service life. By adopting measures such as drilling holes, mechanical pressing, and adjusting the heat treatment process during the manufacturing process, the warping deformation of thin gear shaving tools has been effectively controlled.
1. Introduction
Radial gear shaving tools have a large outer diameter and small thickness, and the material used is mostly W6Mo5Cr4V2. After heat treatment, they are prone to warping deformation, which seriously affects the end face grinding process. The uneven thickness of the teeth not only affects the appearance and shaving life but also impacts manufacturing accuracy, sometimes even preventing subsequent processing.
In response to the above situation, we conducted an investigation into the causes of deformation during heat treatment and conducted deformation tests before and after heat treatment of the gear shaving tools. A large amount of data indicates that deformation is mainly manifested in end face runout, with radial gear shaving tools having a thickness of ≤22mm being the most affected. Deformation in other specifications of gear shaving tools is not significant. Therefore, we focused on analyzing the causes of deformation in radial gear shaving tools with a thickness of ≤22mm and took measures to effectively control the deformation during heat treatment.
2. Measures Taken to Control Deformation
The deformation of gear shaving tools occurs due to thermal stress and structural stress generated during quenching. Thermal stress deformation mainly occurs during the initial cooling stage. At this time, the interior of the workpiece is still at high temperature and has good plasticity. Under the action of instantaneous thermal stress, the core undergoes multiple compressions, prone to plastic deformation. After cooling, the temperature of the workpiece decreases, and the yield strength increases, making plastic deformation more difficult. Upon cooling to room temperature, the uneven plastic deformation produced during the initial cooling stage is retained, causing deformation of the workpiece.
Table 1: Causes and Measures of Gear Shaving Tool Deformation
| Cause | Measure |
|---|---|
| Thermal stress and structural stress during quenching | Drilling stress relief holes on the end face |
| Non-uniform carbide distribution in the workpiece | Proper forging |
| Heat treatment process parameters | Fine-tuning auxiliary heat treatment processes and operations |
| Quick cooling leading to deformation | Isothermal cooling |
| Lack of deformation correction during tempering | Pressurized tempering correction |
2.1. Drilling Stress Relief Holes on the End Face
Due to the large thermal stress and structural stress generated during quenching and cooling, thin gear shaving tools are prone to warping deformation. Through testing, eight Φ30mm through-holes were drilled in the gear shaving tool, evenly distributed around the end face, which not only reduced the weight of the gear shaving tool but also effectively released the stress generated during heat treatment, achieving good results.
2.2. Proper Forging
Since the cutting edge of the gear shaving tool is at the edge, and the carbide requirement in the core is not high, rolling edge forging is adopted, with repeated hammering of the edge and upsetting multiple times to increase the deformation degree of the 1/4 ring belt of the billet. This improves the size and distribution of carbides in the edge area to meet the specified carbide grade and undergoes spheroidizing annealing to uniform the structure, helping reduce quenching deformation of the gear shaving tool.
2.3. Fine-Tuning Heat Treatment Parameters
Since the heat treatment process parameters of the gear shaving tool are basically finalized and should not be changed arbitrarily, fine adjustments are made to the auxiliary heat treatment processes and operations. Specific measures include quenching in an upright position, slow heating, and multi-stage preheating to minimize thermal stress generated by temperature differences. Appropriately lowering the quenching temperature without compromising heat treatment quality is also effective in reducing warping deformation.
2.4. Isothermal Cooling
During quenching of the gear shaving tool, graded isothermal cooling is adopted, and the isothermal time is appropriately extended to increase the transformation amount of bainite and reduce the transformation amount of martensite during quenching and tempering, significantly reducing warping deformation.
2.5. Pressurized Tempering Correction
Despite taking some measures during quenching, thin gear shaving tools may still exhibit slight warping deformation. In the original tempering process, the gear shaving tools were laid flat in the tempering basket, without any correction for warping deformation. Now, for gear shaving tools with significant deformation, a fixture is used for correction during tempering. The fixture has eight Φ30mm through-holes, matching the stress relief holes on the end face of the gear shaving tool. A large screw connects the two in the middle. The deformed gear shaving tool is clamped in the middle and laid flat in the tempering basket. When fixing the bolts, align the holes on the fixture end face with the process holes on the gear shaving tool end face. The salt bath has good fluidity and is heated relatively uniformly during tempering. After cooling to room temperature after quenching, the gear shaving tool is loaded into the fixture for tempering, and the deformation is significantly improved.
3. Data Comparison
The gear shaving tool is placed flat on the testing platform, and a dial indicator is used to slide back and forth and rotate on the end face of the gear shaving tool to find and record the highest and lowest points of runout, and then the same operation is performed on the other side. Since the gear shaving tool undergoes normal heat treatment operations during the heat treatment process, warping deformation is generally large. The test results under normal heat treatment process are shown in Table 2.
Table 2: Test Results Under Normal Heat Treatment Process (mm)
| Specification | End Face Runout Before Heat Treatment | End Face Runout After Heat Treatment |
|---|---|---|
| Φ240×22 | 0.026, 0.03, 0.025 | 0.07, 0.065, 0.09 |
Based on the deformation, a series of specific measures were taken during the heat treatment process, and the warping deformation of the gear shaving tool was effectively controlled. Due to the large amount of test data, two sets of radial gear shaving tool products with the same drawing number are selected for comparison. The test results after taking measures are shown in Table 3.
Table 3: Test Results After Taking Measures (mm)
| Specification | End Face Runout Before Heat Treatment | End Face Runout After Heat Treatment |
|---|---|---|
| Φ240×22 | 0.025, 0.03, 0.025 | 0.04, 0.035, 0.03 |
4. Conclusion
(1) Although high-speed steel has undergone nearly a century of research and development, and the heat treatment process has formed a fixed pattern, the gear shaving tools and heat treatment processes of various manufacturers vary, resulting in significant differences in performance. The heat treatment process is complex, and subtle differences affect product quality. By strengthening control over each subtle aspect and standardizing operations, the gear shaving tool can maximize its effectiveness during use.
(2) Without changing the original heat treatment process of the gear shaving tool, the phenomenon of excessive warping deformation after heat treatment of thin gear shaving tools was solved by adopting effective measures such as increasing stress relief holes and pressurized correction, meeting the subsequent processing conditions of radial gear shaving tools.