Broaching Machine Solutions for Splines and Face Teeth Processing of Nosing Fork Parts

Introduction

Flange Yoke is a key connection component in the automotive drivetrain, mainly used for the connection and power transmission of universal joint drive shafts (such as drive shafts and half shafts). It is fixed with the gearbox, transfer case or axle at one end by a flange (nosture), and connected to the drive shaft by a universal joint (U-joint or cross shaft) at the other end, realizing the efficient transmission of power at non-linear angles while compensating for the relative displacement and vibration in the vehicle movement.
The broaching process enables efficient and high-precision manufacturing of two key functional features of punch fork parts in automotive drivetrains: internal splines for torque transmission and axial sliding, and face teeth for precise centering. With their precision, efficiency, and consistency, broaching machines have become the go-to machining equipment for high-volume production of these types of parts.

1.Internal Spline Broaching

Purpose: Process high-precision internal splines in the center hole of the prosthesis fork.
Process: Use a specially designed inner spline broach. The broach pulls (or pushes) through a pre-machined hole (usually a round hole), and the cutting teeth on it cut through the metal in turn, resulting in a precise inner spline tooth profile (e.g., involute spline, rectangular spline). Broaching can complete the processing of all internal spline teeth at one time, with high efficiency, good precision and strong tooth shape consistency.
Advantages: extremely high accuracy (tooth profile, tooth orientation, indexing), excellent surface finish, excellent productivity (one stroke completed).

Raw materials for nosing forks

Inner spline broaching

Inner spline tooth profile

2.Face Tooth Broaching

Purpose: Precise face teeth are machined on the flange end face of the nosing fork.
Process: Use specially designed face tooth broaches or combination broaches. The structure of such broaches is usually in the form of a disc or polygonal disc on which multiple circles of carbide teeth of different heights (or the entire cutterhead is made of high-speed steel). During machining, the part is fixed on the table, and the broach rotates and makes a linear feed motion (vertical or near-vertical) along the normal direction of the end face of the part. The teeth cut the face in turn, eventually forming a circle of precise face teeth.
Advantage: Efficient processing of face teeth with extremely high equalization accuracy and consistent tooth depth. This is the key to ensuring high concentricity of the flange connection. Compared with traditional index milling, broaching efficiency is many times higher, and the accuracy is more stable and reliable.

Raw materials for nosing forks

Face tooth broaching

Precision face teeth

3.Analysis of Parts Machining Process

3.1 Difficulties in parts structure and processing
The core processing parts are internal splines (through/blind hole type) and face teeth (annular distribution, tooth patterns are mostly regular trapezoidal), which are vertically distributed and need to ensure strict shape and position tolerances (coaxiality, perpendicularity). Its core processing difficulties are as follows:

• Difficult to unify the datum: In traditional machining, the internal spline and the face tooth are clamped twice, which is prone to datum deviation, resulting in the coaxiality and perpendicularity of the two, affecting the assembly accuracy.
• High requirements for precision machining of face teeth: The uniformity of tooth shape and pitch of the end face teeth is strict, and it needs to be accurately connected with the internal spline.
• Difficult material processing: 40Cr, 20CrMnTi and other medium carbon alloy steels are commonly used for flange forks, with a hardness of HRC28-32 after quenching and tempering, and high cutting resistance during broaching, which can easily lead to tool wear and tooth deformation.
• Poor batch stability: The positioning accuracy of manual clamping fluctuates greatly, making it easy to have batch part size deviations, making it difficult to meet the needs of large-scale production.

3.2 Process route planning
Combined with the advantages of broaching processing, optimize the process route to achieve “unified reference, one-time clamping, and continuous processing”, the specific process route is as follows:
Blank inspection and pretreatment (sandblasting, scaling, hardness testing) → rough hub and positioning end face (establishing a processing reference) → quenching and tempering treatment (quenching + high-temperature tempering to ensure the mechanical properties of the material) → one-time clamping of broaching machine (using the inner hole and end face as the positioning reference) → internal spline broaching (rough drawing → fine drawing) → face tooth broaching (synchronous indexing positioning, rough drawing → fine drawing) → deburring (high-pressure air blowing + brush cleaning) → precision testing (tooth shape, tooth spacing, shape and position tolerance) → finished product warehousing.
Core optimization points: Integrate the inner spline with the broaching process of the end face teeth, and realize the primary clamping through special tooling to avoid the deviation of the secondary clamping reference; Segmented broaching with “rough drawing → fine drawing” is used to reduce the single cutting allowance, reduce tooth deformation, and improve machining accuracy.

4.Optimization of processing process parameters

Combined with the material characteristics of the nosing fork and the precision requirements of the parts, optimize the broaching process parameters to achieve “efficient cutting and precise forming”, and avoid tooth deformation, surface scratches and other defects, the specific parameters are as follows (can be flexibly adjusted according to the actual part size and material hardness):

4.1 Internal spline broaching parameters

• Roughing speed: 1-3m/min, feed 0.15-0.2mm/tooth, cutting allowance 1.2-1.5mm (total allowance);
• Finishing speed: 4-7m/min, feed 0.08-0.12mm/tooth, cutting allowance 0.3-0.5mm;
• Cutting fluid pressure: 0.8-1.2MPa, flow rate 20-30L/min, ensure sufficient cooling and lubrication;
• Broaching temperature: Control at 150-200°C to avoid tooth deformation and tool wear caused by excessive temperature.

4.2 Broaching parameters of face teeth

• Roughing speed: 1-2.5m/min, feed 0.12-0.18mm/tooth, cutting allowance 1.0-1.2mm;
• Finishing speed: 3.5-6m/min, feed 0.06-0.10mm/tooth, cutting allowance 0.2-0.3mm;
• Indexing speed: 0.5-1r/min, indexing pause time 0.2-0.3s to ensure uniform tooth pitch on the end face;
• Cutting fluid pressure: 1.0-1.5MPa, flow rate 25-35L/min, focus on cooling the broaching part of the face teeth, and discharge chips in time.

4.3 Key points of process optimization

1. Segmented broaching optimization: “rough drawing → fine drawing” segmented broaching is used to reduce the single cutting allowance, reduce the cutting force and cutting temperature, and avoid tooth deformation; After rough drawing, a reasonable fine drawing allowance is reserved to ensure the tooth shape accuracy and surface quality after fine drawing.
2. Cutting fluid optimization: adjust the cutting fluid concentration (8% in summer, 5% in winter) according to seasonal changes, and change the cutting fluid regularly (every 3 months) to avoid the deterioration of the cutting fluid affecting the cooling lubrication effect; Regularly clean the cutting fluid filtration system to ensure filtration accuracy.
3. Tool wear optimization: regularly check tool wear and replace wear tools in time; Cutting edge grinding is carried out before use to improve the cutting edge accuracy; Avoid empty pulling of the tool during broaching and reduce tool wear.
4. Clamping optimization: clean the positioning surface of the parts and the positioning mechanism of the tooling before clamping to avoid iron filings and debris affecting the positioning accuracy; Adjust the clamping force to ensure that the clamping is firm and does not damage the surface of the part, and avoid deformation caused by excessive clamping force.

5.Quality Control System

Establish a full-process quality control system, from the entry of raw materials to the delivery of finished products, layer by layer to ensure the processing accuracy and product consistency, the specific measures are as follows:

5.1 Raw material quality control
When raw materials enter the site, strictly inspect the blank material, hardness (to ensure that it meets the requirements of HRC28-32), dimensional allowance and surface quality, and check whether the blank has cracks, folds and other forging defects; Unqualified blanks are strictly prohibited from being put into production, and a raw material ledger is established to trace the source of raw materials.

5.2 Quality control of the machining process

1. First article inspection: Before each batch of production, process 3 first parts, use gear measuring instruments, projectors, dial indicators and other testing equipment to comprehensively detect the tooth shape, tooth pitch, tooth direction tolerance, symmetry, inclination, and contour of the end teeth, as well as the coaxiality and perpendicularity of the two; After the first article passes the inspection, it can be mass-produced.
2. Inspection control: During the mass production process, every 50 parts processed, an inspection is carried out, focusing on detecting key dimensions and shape and position tolerances, timely detecting processing deviations, adjusting process parameters or replacing tools and tooling to avoid batch failures.
3. Online testing: Use the online testing device supporting the equipment to automatically detect each processed part, automatically sort the unqualified parts, and record the testing data at the same time to facilitate follow-up traceability and process optimization.
4. Environmental control: The processing workshop maintains constant temperature (20±2°C) and constant humidity (50±5%) to avoid deformation of equipment and parts caused by temperature and humidity changes, affecting the processing accuracy. The workshop should be kept clean to avoid dust and debris from entering the equipment and tooling.

6.Broaching Machine Selection and Configuration

6.1Why is broaching the first choice for these two features?

• High precision: The broach itself has extremely high accuracy and stable machining process, which can ensure that the accumulation error of the tooth pitch, tooth shape error, tooth direction error of the internal spline, and the equalization accuracy and tooth depth accuracy of the face teeth meet very high requirements (usually in the micron level).
• High efficiency: the entire profile can be machined in one broaching stroke (whether it is all the teeth of the inner spline or a full circle of face teeth), which is much faster than indexing methods such as shaping and milling. This is crucial for high-volume production of automotive parts.
• Good surface quality: Broaching results in a better surface finish.
• Good repeatability: The tool has high durability and stable machining parameters, ensuring highly consistent quality between parts.
• Suitable for complex profiles: Broaches can be designed to process a variety of complex tooth profiles (e.g., involute splines, special face profiles).

Combined with the size of nosing fork parts (the internal spline specification is usually modulus 2-5mm, the number of teeth is 10-20 teeth; Φ80-Φ300mm), processing accuracy and batch requirements, the selection is based on “CNC horizontal broaching machine” (suitable for large-scale processing of small and medium-sized parts, smooth chip removal, stable positioning), and supporting special tooling, tools and control systems to ensure processing stability and accuracy.

6.2 Core broaching machine equipment selection

Recommended model: CNC horizontal internal drawing machine (customized model, adapted to the integrated processing of the fusing fork), the core parameters are as follows, which can be flexibly adjusted according to the actual part size:

Equipment advantages: The integrated design of the base and the bed, after aging and tempering, the overall rigidity is good, the stability is high, and there is no oil and water leakage. The guide rail adopts heavy-duty roller guide rail, which has low rolling friction, low wear and long service life; Integrated automatic chip removal device to avoid chip accumulation affecting processing accuracy, while reducing manual cleaning costs.

6.3 Special tooling design

The core role of tooling: to realize the one-time clamping and precise positioning of the fusing fork, to ensure the unity of the reference of the inner spline and the end tooth, and at the same time to adapt to the indexing requirements in the broaching process, and solve the problem of unqualified symmetry and inclination of traditional clamping. Combined with patented technology to optimize the design, the specific structure is as follows:

1. Positioning mechanism: adopts the dual positioning method of “inner hole centering + end face positioning”, the positioning mandrel and the inner hole of the nossure fork are precisely matched (mating clearance ≤ 0.003mm), the end face positioning plate adopts quenching treatment (HRC58-62), surface grinding and polishing (Ra≤0.8μm) to ensure positioning accuracy and stability; Auxiliary support mechanisms are added, including fixed bottom plates, V-shaped support blocks, compression springs and locking cylinders, locking cylinders drive the diagonal block downward, and push the V-shaped support block close to the spring chuck seat. Improve clamping rigidity to avoid workpiece shaking during broaching.
2. Clamping mechanism: using hydraulic clamping method, supporting composite cylinder (inner cylinder controls spring chuck clamping, outer cylinder controls central axis to move forward and backward), spring chuck is connected with the center piston rod of composite cylinder through adjustable tie rod, clamping force can be adjusted steplessly according to the size of the part and material hardness (adjustment range 5-20kN) to ensure that the clamping is firm and does not damage the surface of the part; The spring chuck is made of elastic material, adapted to different specifications of inner holes, and has strong versatility.
3. Indexing mechanism: According to the needs of annular distribution of end face teeth, a rack and pinion indexing mechanism is designed, including gears fixed on the central shaft, rack and pinion guide sleeves, rack and pinion adapters and single-piston rod double cylinder barrel indexing drive cylinders, and the rack and gear meshing transmission to achieve precise rotation indexing of the central shaft. The supporting angle precise positioning mechanism is composed of a fixed mouse tooth disc (installed in the clamp body) and a movable mouse tooth disc (installed on the central axis), and the tooth shape is a regular trapezoidal (tooth angle 30°), through the meshing of the two mouse tooth discs, the central axis angle is accurately positioned, locked and centered, and the indexing accuracy is ≤ 0.002mm, which is suitable for the processing of different teeth and face teeth.
4. Protective mechanism: A sealing shield is set on the outside of the tooling to prevent chips and cutting fluid from entering the tooling, affecting the positioning accuracy and service life of the tooling; At the same time, an anti-collision limit device is set up to avoid the collision between the tooling and the broach during the broaching process, and to protect the equipment and tooling.
   Tooling advantages: the first clamping completes the processing of internal splines and end face teeth, which solves the problem of secondary clamping reference deviation; The internal spline positioning method improves the symmetry of the end tooth, and the rack and pinion indexing mechanism solves the problem of the inclination of the end tooth. No reaming is required after drilling, reducing the processing process; Adapted to multi-specification nosing fork parts, only need to replace the positioning mandrel and spring chuck, you can quickly switch product models, and the debugging time is ≤ 30 minutes.

6.4 Specialized Tool Setup

The tool is selected with high-performance carbide broach, customized tooth shape for the processing characteristics of internal splines and face teeth, optimized tool geometric parameters, and improved tool life and machining accuracy, the specific configuration is as follows:

1. Inner spline broach: made of integral carbide material (YT15 or YW2), the tooth shape is customized according to the specifications of the internal spline of the part (modulus, number of teeth, pressure angle and parts are matched); The top of the tooth adopts an arc transition design to avoid the chipping angle of the top of the tooth. TiN coating is applied to the tooth surface to improve surface hardness (≥HRC65) and wear resistance, reduce cutting friction, and reduce tool loss. Adopting the “coarse ribbery + fine ripe” segmented design, the coarse rash bears 80% of the cutting allowance, the fine rashed ensures the tooth shape accuracy and surface quality, and the broach life ≥ 5000 pieces/piece.
2. End face tooth broach: also made of integral carbide material, the tooth shape is regular trapezoidal (matching the tooth shape of the rat tooth disc), the tooth pitch is uniform, and it is suitable for the distribution of end face teeth ring; The cutting edge of the tool is passivated to improve the strength of the cutting edge and avoid the chipping of the cutting edge; Cutting angle optimization (rake angle 12°-15°, trailing angle 8°-10°) to reduce cutting resistance and reduce the risk of tooth surface scratches; The broach life ≥ 4000 pieces/piece.
3. Tool auxiliary device: supporting tool guide sleeve and clamping sleeve to ensure accurate broach movement and avoid tooth shape deviation caused by broach offset; Set up a tool wear detection device to monitor tool wear in real time, and automatically send out an early warning signal when the tool wear reaches 0.01mm, reminding the operator to replace the tool and avoid batch scrap.

Summary

This broaching machine solution for internal splines and end teeth processing of fork parts takes CNC horizontal broaching machine as the core, combined with special tooling, customized tools and optimization processes, to achieve “one clamping, two processes, and precise molding”, effectively solving the core pain points such as insufficient precision, low efficiency, poor batch stability, and cumbersome clamping in traditional processing. The solution takes into account processing accuracy and production efficiency, optimizes cost control, adapts to multi-specification and mass production needs, and supports a complete quality control system and after-sales service to ensure long-term stable operation of equipment, help customers improve product quality, enhance market competitiveness, and achieve dual improvement of economic benefits and quality benefits.