Solution for Internal Gear Shaving and Internal and External Circular End Face Grinding of Gearbox Needle Tooth Housing

Introduction

The needle tooth shell of the reducer is one of the core components of planetary reducers or cycloidal reducers (such as RV reducers, harmonic reducers, etc.), which is mainly used to support and fix the needle teeth, so that they can accurately mesh, and achieve high-precision and high-torque power transmission. It plays a key role in industrial robots, automation equipment, precision machinery, and other fields
The inner ring of the needle tooth shell is broaching, and the high-precision composite vertical grinder is used to grind the inner circle, outer circle and end face of the needle tooth shell for one clamping.

1.Core Objective of the Plan

This solution takes “precise positioning, efficient processing, strict error control, and stable mass production” as the core, and achieves the following goals for the processing needs of needle and tooth shells (mostly 45# steel, 20CrMnTi or cast iron):

• Internal tooth machining: the tooth shape accuracy reaches IT6-IT7 level, the tooth surface roughness Ra≤0.8μm, the tooth pitch cumulative error ≤±0.02mm, and the concentricity of the internal tooth and bearing position ≤0.005mm.
• Inner and outer circle machining: outer circle dimensional tolerance IT6, inner circle (bearing position) dimensional tolerance IT5-IT6, roundness ≤ 0.003mm, cylindricity ≤0.005mm, inner and outer circle coaxiality ≤0.005mm, meeting the high-precision requirements of bearing assembly;
• End face processing: end face flatness ≤ 0.005mm, end face and inner and outer circular axis verticality ≤0.005mm/100mm, surface roughness Ra≤ 0.8μm to avoid stress concentration and transmission deviation during assembly;
• Efficiency improvement: compared with the traditional threading process, the internal tooth processing efficiency is increased by 4-10 times; Integrate the processing process, reduce the number of clamps, increase the comprehensive efficiency of the overall production line by more than 30%, and increase the processing pass rate from the industry average of 88% to more than 99%;
• Cost control: optimize tool selection and process parameters to reduce tool loss; reduce process connection errors and reduce rework rate; Through the synergy of imported and domestic high-end equipment, cost-effective processing is achieved.

2.Artifact analysis

Needle tooth shell and its inner ring ring:
Pin tooth housing: is a critical component in RV reducers or cycloidal reducers, usually a ring housing with a precision internal gear ring.
Inner Gear Ring: The tooth ring on the inner wall of the needle tooth shell. This ring is not an ordinary involute gear tooth, but a precision groove used to accommodate the pin. The pin and tooth pin meshes with the cycloidal wheel to achieve reduction transmission.
Accuracy requirements: The tooth shape accuracy, accumulation error of tooth pitch, and surface roughness of the inner gear ring are extremely high (usually in the micron level), which directly determines the transmission accuracy, return difference, noise and life of the reducer.

Before needle tooth shell processing

3.Core Processing Technology Implementation Process

The integrated process of “pretreatment→ internal tooth broaching→ internal and external cylindrical grinding→ end face grinding→ inspection →post-processing” is adopted to reduce the number of clamping, reduce the accumulation of errors, and ensure the smooth connection of each process, the specific implementation steps are as follows:

3.1 Internal tooth broaching process (core process)
Internal tooth broaching is the key to the transmission accuracy of the needle tooth shell, the core is to complete the rough and finishing at one time through the special composite broach, avoiding the disadvantages of the traditional tooth shaping process of multiple times and low efficiency, the specific operation process and parameters are as follows:

1. Clamping positioning: put the pre-treated needle tooth shell into the broaching hydraulic fixture, take the outer circle of the needle tooth shell as the positioning reference, start the hydraulic system to clamp the workpiece to ensure that the workpiece does not move and deform, and use a dial indicator to detect the workpiece runout after clamping, the runout amount is ≤ 0.003mm, and if it is unqualified, it will be re-clamped;
2. Broach installation and adjustment: Install the special composite broach on the main shaft of the broaching machine, adjust the coaxiality of the broach and the workpiece, and the coaxiality ≤ 0.002mm to ensure that the broach lead can smoothly enter the inner hole of the needle tooth shell;
3. Broaching parameter setting: broaching speed 1.5-2.5mm/min, feed rate 0.1-0.15mm/tooth, broaching depth gradually increases according to the tooth gradient of the broach, no additional adjustment is required; During the broaching process, the cooling system is turned on, the emulsion is selected as the cooling medium, and the cooling pressure is 0.3-0.5MPa to ensure that the coolant covers the contact part between the broach and the workpiece, reduce the broaching temperature, take away the chips, and avoid scratches on the tooth surface caused by chip residue;
4. Broaching process monitoring: observe broaching sound and current changes in real time, if there is an abnormal noise or sudden increase in current, stop the machine immediately for inspection, and troubleshoot broach wear, workpiece looseness and other problems; After broaching is completed, the broaching machine automatically retracts, the hydraulic clamp is released, the workpiece is taken out, and the chips on the inner hole and tooth surface of the workpiece are cleaned.
5. Intermediate inspection: For every 3 workpieces processed, 1 piece is extracted for internal tooth accuracy testing, focusing on detecting tooth shape accuracy, tooth pitch cumulative tolerance and surface roughness.

broaching process

3.2 Internal and external cylindrical grinding process
Inner and outer cylindrical grinding needs to ensure the concentricity and dimensional accuracy of the inner and outer circles, to provide guarantee for subsequent assembly, and adopt the grinding sequence of “inner circle first and then outer circle” to avoid the damage of cylindrical grinding to the machined inner hole, the specific operation process and parameters are as follows:

Inner cylindrical grinding

1. Clamping positioning: install the broached needle tooth shell on the tensioning mandrel, take the needle tooth shell inner hole as the positioning reference (the accuracy of the inner hole after broaching has reached the standard), adjust the tightening force to ensure that the workpiece is clamped firmly and without movement, and detect the workpiece runout ≤ 0.002mm after clamping;
2. Grinding wheel adjustment: install the inner grinding grinding wheel, adjust the coaxiality of the grinding wheel and the workpiece, start the grinding wheel idle for 3-5 minutes, check whether the grinding wheel runs smoothly, no runout, no abnormal noise;
3. Grinding parameter setting: coarse grinding speed 30-35m/s, feed rate 0.01-0.015mm/revolution, grinding depth 0.03-0.05mm, fine grinding speed 35-40m/s, feed rate 0.005-0.01mm/revolution, grinding depth 0.005-0.01mm;
4. Cooling and monitoring: During the grinding process, the high-pressure cooling system is turned on, and the coolant pressure is 0.4-0.6MPa to ensure that the coolant reaches the grinding area directly and avoids burns and cracks in the inner hole of the workpiece. Observe the grinding status in real time, if the grinding wheel is blocked, stop the machine immediately to trim the grinding wheel;
5. Inner circle detection: After grinding, use an internal micrometer and roundness meter to detect the inner circle size, roundness and cylindrical degree to ensure that the inner circle size tolerance meets IT5 level, the roundness ≤ 0.002mm, the cylindrical degree ≤ 0.003mm, and if it is unqualified, it will be re-finely ground.

Cylindrical grinding

1. Clamping positioning: keep the clamping state of the workpiece on the tensioned mandrel unchanged (no need to re-clamp), ensure that the outer grinding is consistent with the reference of internal grinding, and avoid the concentricity deviation caused by clamping error;
2. Grinding wheel adjustment: Replace the cylindrical grinding wheel, adjust the position of the grinding wheel and the workpiece, ensure that the grinding wheel is parallel to the workpiece axis, and the parallelism ≤ 0.001mm/m;
3. Grinding parameter setting: rough grinding speed 30-35m/s, feed rate 0.015-0.02mm/revolution, grinding depth 0.04-0.06mm, fine grinding speed 35-40m/s, feed rate 0.005-0.01mm/revolution, grinding depth 0.005-0.01mm;
4. Cooling and monitoring: The cooling method is consistent with the inner grinding, focusing on monitoring the surface quality of the outer circle to avoid scratches, burns and other defects;
5. Outer circle inspection: After grinding, use an outside micrometer and dial indicator to detect the outer circle size, roundness and concentricity to ensure that the outer circle dimension tolerance meets IT6 level, the roundness ≤ 0.002mm, the inner and outer circle concentricity ≤ 0.005mm, and if it is unqualified, it will be re-fine-ground.

3.3 End Face Grinding Process

Face grinding requires ensuring the flatness and perpendicularity of the end face to prevent end face wobble from affecting the assembly accuracy of the reducer. The specific operational process and parameters are as follows:

1. Clamping and positioning: Place the pinion housing, which has completed inner and outer cylindrical grinding, into a vacuum chuck fixture. Use the inner hole and outer cylinder of the pinion housing as auxiliary positioning references. Activate the vacuum system to clamp the workpiece, ensuring the end face of the workpiece fits the chuck without gaps or movement; use a dial gauge to check that end face runout is ≤0.002mm;
2. Wheel adjustment: Install the diamond face grinding wheel, adjust the parallelism between the wheel face and the workpiece end face to ≤0.001mm/m, adjust the wheel height to ensure slight contact between the wheel and the workpiece end face;
3. Grinding parameter settings: Roughing speed 25-30 m/s, feed 0.01-0.015 mm/rev, grinding depth 0.02-0.03 mm; finishing speed 30-35 m/s, feed 0.005-0.01 mm/rev, grinding depth 0.003-0.005 mm; perform 2-3 light grinding passes after finishing, light grinding speed 35 m/s, feed 0.002 mm/rev;
4. Cooling and monitoring: Use a high-pressure cooling system with coolant pressure of 0.5-0.7 MPa to ensure the coolant evenly covers the end face grinding area, reduce grinding temperature, and prevent end face burning; continuously monitor surface quality, and if scratches appear, dress the wheel in time;
5. End face inspection: After grinding, use a flatness gauge to check end face flatness and a dial gauge to check perpendicularity to the inner and outer axes, ensuring flatness ≤0.003 mm, perpendicularity ≤0.004 mm/m, and surface roughness Ra ≤0.4 μm; re-finishing is required if not qualified.

4.Advantages of the Solution and Its Application Effects

Solution advantages

• Controllable accuracy: Through special tooling fixtures, optimized processing parameters and three-level detection system, it effectively controls key indicators such as internal tooth accuracy, inner and outer circular concentricity, and end face flatness to meet the assembly requirements of high-precision reducers, and the tooth shape accuracy and shape and position tolerance are in line with industry standards and design specifications.
• Efficiency improvement: Using a special composite broach, the internal tooth coarse and finishing are completed in one broaching, replacing the traditional gear shaping process, and the processing efficiency is increased by 30%-50%; optimize the clamping process, reduce the number of clamping times, shorten the processing time of a single piece by 20%-30% during mass production, and adapt to the large-scale needs of the robot industry;
• Strong stability: Through equipment calibration, tool grinding wheel optimization, and error prevention and control measures, fluctuations in the processing process are reduced, and the pass rate of mass production is increased to more than 99%, reducing rework costs. At the same time, it avoids the problems of time-consuming and unstable accuracy of traditional manual middle search, and reduces the error of manual intervention.
• Cost saving: reduce the loss of tools and grinding wheels, and reduce the cost of manual clamping and inspection; Optimize the process flow, reduce the scrap rate, and avoid the high investment of high-precision special fixtures, reducing the comprehensive production cost by 15%-25%.

Application effect
This scheme has been applied to the mass production of various specifications of reducer needle and tooth shells (GCr15 material), and has been verified in practice:

• Internal tooth processing: the tooth shape accuracy is stable at 2-3μm, the tooth pitch cumulative tolerance is ≤0.03mm, and the surface roughness Ra≤0.6μm to meet the high-precision transmission requirements of RV reducers;
• Inner and outer cylindrical grinding: the inner and outer circular concentricity is stable at 0.003-0.005mm, and the dimensional tolerance meets the IT5-IT6 level, adapting to the assembly requirements of the main bearing to avoid return errors;
• Face grinding: End face flatness ≤ 0.003mm, verticality ≤0.004mm/m, surface roughness Ra≤0.4μm to ensure tight assembly fit;
• Mass production: The processing time of a single piece is shortened to 15-20 minutes, and the pass rate is stable at more than 99.2%, which greatly improves production efficiency and product quality, meets the supporting needs of high-end equipment such as industrial robots and CNC machine tools, and provides process support for the localization of reducers.

Epilogue

This set of reducer needle tooth shell internal tooth broaching and internal and external round end face grinding solutions, through the integrated design of process optimization, equipment selection and quality control, effectively solves the pain points such as insufficient precision, low efficiency and error accumulation in traditional processing, taking into account the processing quality, efficiency and cost, and can be widely used in the mass production of high-end reducer needle tooth shell, providing technical support for the high-quality development of the reducer industry.