Spline Broaching: The Complete Guide

As an important mechanical transmission method, spline connection is widely used in many fields such as automobiles, aerospace, and machinery manufacturing. Spline broaching, as an efficient and accurate method for processing splines, plays a vital role in modern industrial production. This guide will give you an in-depth understanding of the entire process of spline broaching, from principles to applications, from tool selection to process optimization, providing you with comprehensive and detailed guidance.

What is Spline Broaching?

Spline broaching is a process that uses a special-shaped broach to remove metal from the workpiece in sequence under the action of tension, thereby processing the spline shape. The cutting edge of the broach gradually cuts along the contour of the spline, ultimately forming a precise spline tooth profile.

Compared with traditional milling, gear hobbing and other processing methods, spline broaching has the advantages of high processing accuracy, fast production efficiency, and good surface quality. At the same time, spline broaching can process multiple spline teeth at one time, greatly reducing processing time and cost.

Type Of Spline Broaches

There are mainly the following types of spline broaches:

1.Rectangular Spline Broach

Rectangular Spline Broach
  • Features: Used for processing rectangular spline holes or shafts. The shape of the cutter teeth matches the tooth shape of the rectangular spline, usually with multiple rough cutting teeth, fine cutting teeth and calibration teeth. Rough cutting teeth remove most of the margin, fine cutting teeth improve dimensional accuracy and surface quality, and calibration teeth ensure final machining accuracy.
  • Application: Widely used in mechanical transmission fields, such as automobile transmissions, machine tool transmission shafts, etc.

2.Involute Spline Broaches

Involute Spline Broaches
  • Features: Processing of involute splines. The profile of the cutter teeth is designed based on the involute principle and can accurately process the tooth shape of the involute spline. Compared with rectangular splines, involute splines have higher load-bearing capacity and better centering.
  • Application: It is widely used in high-load, high-precision transmission systems, such as aerospace, heavy machinery and other fields.

Read More:Spline Broaching VS. Rectangular Broaching : How to Choose?

3.Triangular Spline Broaches

Triangular Spline Broaches
  • Features: Suitable for processing triangular splines. The shape of the blade teeth is triangular and can be designed according to different triangular spline specifications. Triangular splines usually have a smaller pressure angle and are suitable for light loads and high speed transmissions.
  • Application: It has certain applications in some precision instruments, electronic equipment and other fields.

4.Spiral Spline Broaches

  • Features: Used for processing spiral splines. The cutter teeth are distributed in a spiral shape along the axial direction, which can generate spiral cutting force during the machining process, making the machining more stable. Helical splines have good self-centering performance and high transmission efficiency.
  • Application: Mainly used in situations where large torque and high-speed rotation need to be transmitted, such as automobile steering systems, industrial robots, etc.

5.Combined spline broach

  • Features: It is composed of multiple parts with different functions, which can be combined and adjusted according to specific processing requirements. For example, rough cutting, fine cutting and calibration sections can be designed into independent modules for easy replacement and repair.
  • Application: Suitable for processing splines of various specifications, or when frequent tool changes are required during processing.

Advantages Of Spline Broaching

  1. High processing accuracy: Spline broaching can achieve high dimensional accuracy and shape accuracy. The splines after broaching have small dimensional tolerance and good surface quality, which can meet the requirements of high-precision spline connection. For example, in fields such as automobiles and aerospace that require extremely high precision of parts, the spline broaching process is widely used13.
  2. High production efficiency: The broach can remove the entire margin of the processing surface in one stroke, and can quickly complete spline processing. It is especially suitable for mass production and can significantly improve production efficiency. For example, in the processing of spline holes for automobile transmissions, the broaching process can be used to process a large number of parts quickly and efficiently 136.
  3. The machined surface quality is good: the broaching process is smooth and will not produce defects such as built-up edges and burrs. The machined surface has low roughness and high smoothness, which can effectively improve the matching performance and service life of the spline 35.
  4. Long tool life: Broaches are usually made of materials such as high-speed steel or carbide, which have high hardness and wear resistance. With reasonable use and maintenance, the tool life is long, which can reduce tool costs 34.
  5. Applicable to a variety of materials: It can be used to process various metal materials, such as steel, cast iron, non-ferrous metals, etc., and has strong versatility.

Disadvantages Of Spline Broaching

  1. High cost of broaches: The manufacturing process of broaches is complex and requires high-precision processing equipment and technology, resulting in high manufacturing costs of broaches. Moreover, the broach is a special tool, and each spline specification requires a corresponding broach. For small batch production or when the spline specifications are diverse, the tool cost will increase significantly 16.
  2. High requirements on machine tools: Special broaching equipment is required. The broaching machine is expensive and occupies a large area. It also requires high precision, rigidity and stability of the machine tool, which increases equipment investment and maintenance costs 6.
  3. Not suitable for complex shapes: Spline broaching is mainly suitable for processing splines with simple and regular shapes. Splines with complex shapes and special requirements may need to be combined with other processing techniques to complete.
  4. Difficulty in adjustment and grinding: The structure of the broach is complex. Once worn or damaged, adjustment and grinding are difficult. Professional technicians and equipment are required, and the accuracy of the tool after grinding may be affected to a certain extent.

Structure of Spline Broaches

The spline broach mainly consists of the following parts:

Handle

The handle is the part that connects the broach to the broaching machine and is used to transmit pulling force. The shape and size of the handle are usually designed according to the chuck form of the broaching machine to ensure that the broaching tool can be firmly installed on the broaching machine. Common handle forms include cylindrical, conical, etc.

Neck

The neck is located between the handle and the transition cone, and its main function is to clamp and transport the broach during the manufacturing process. The diameter of the neck is usually smaller than the shank and transition taper to facilitate handling of the clamping tool.

Transition cone

The function of the transition cone is to enable the broach to smoothly enter the prefabricated hole in the workpiece. The angle of the transition cone is usually small, typically between 15° and 30°, to avoid excessive impact when entering the workpiece.

Leading Department

The function of the leading part is to guide the broach to correctly enter the workpiece during the broaching process and to prevent the broach from deflecting when entering the workpiece. The diameter of the leading part is usually slightly smaller than the cutting part of the broach, and its length is generally 0.75 to 1.5 times the length of the pre-made hole in the workpiece.

Cutting Department

The cutting part is the main working part of the broach and consists of several teeth. Each tooth has a specific shape and size and is used to remove excess material from the workpiece to form a spline shape. The teeth of the cutting part are usually divided into three types: rough cutting teeth, fine cutting teeth and calibration teeth.

  • Rough cutting teeth: Rough cutting teeth are mainly used to remove most of the remaining material. The tooth lift is large and the cutting force is also large. Rough cutting teeth usually have a simple tooth shape to facilitate fast cutting.
  • Precision cutting gear: Precision cutting gear is used to further improve the machining accuracy and surface quality. Its tooth lift is small and the cutting force is also small. The shape of the teeth of precision cutting teeth is usually more complex in order to obtain better cutting results.
  • Calibration teeth: The function of the calibration teeth is to perform final calibration on the workpiece to ensure processing size and shape accuracy. The calibrated teeth have zero tooth lift and their tooth shape is exactly the same as the final shape of the workpiece.

Calibration Department

The calibration section is located after the cutting section, and its function is to perform final calibration and trimming of the workpiece to ensure machining size and shape accuracy. The diameter of the calibration section is usually the same as the final dimensions of the workpiece and its length is typically 1/3 to 1/2 the length of the workpiece.

Back-end department

The function of the rear guide part is to guide the broach to withdraw from the workpiece correctly during the broaching process and to prevent the broach from deflecting when withdrawing from the workpiece. The diameter of the trailing part is usually the same as that of the leading part, and its length is generally 0.25 to 0.5 times the length of the workpiece.

Support Department

The supporting part is located at the tail of the broach. Its function is to support the broach during the broaching process and prevent the broach from bending and deforming due to its own weight. The support part usually consists of one or more rollers. The diameter and width of the rollers should be selected according to the size and weight of the broach.

What Details Need To Be Paid Attention To During The Spline Broaching Process?

During the spline broaching process, the following details require special attention:

1.Workpiece Preparation Stage

First, the workpiece needs to be preprocessed, including turning, milling, etc., to ensure that the size and shape of the workpiece meet the requirements.

  • Dimensional inspection: Ensure that the initial size of the workpiece meets the requirements to avoid affecting the broaching effect due to excessive dimensional deviation. Accurately measure key dimensions such as diameter and length of the workpiece, and make appropriate trims if necessary.
  • Surface treatment: The surface of the workpiece should be clean and free of oil, rust and other impurities. Cleaning, sandblasting and other methods can be used for surface treatment to improve the contact quality between the broaching tool and the workpiece.
  • Hardness testing: Understand the hardness distribution of the workpiece in order to select the appropriate broaching tool and determine the broaching parameters. If the workpiece has uneven hardness, it may cause uneven tool wear during broaching and affect machining accuracy.

2.Installation Stage Of Workpiece

Install the workpiece on the fixture of the broaching machine to ensure that the position of the workpiece is accurate.

  • Fixture selection: Select the appropriate fixture according to the shape and size of the workpiece. The clamp should have sufficient clamping force to ensure that the workpiece does not move or deform during the broaching process. At the same time, the design of the fixture should facilitate the installation and disassembly of workpieces and improve production efficiency.
  • Positioning accuracy: Ensure that the workpiece is positioned accurately in the fixture. Auxiliary positioning devices such as positioning pins and positioning blocks can be used to improve positioning accuracy. The positioning error should be controlled within a very small range to ensure the position accuracy of the spline.
  • Clamping method: Choose an appropriate clamping method to avoid workpiece deformation or surface damage caused by excessive clamping force. Hydraulic clamping, pneumatic clamping and other methods can be used to achieve uniform clamping. At the same time, it should be noted that the clamping force should be adjusted according to the material and size of the workpiece.

3. Installation Stage Of Broach

Install the broach on the tool holder of the broaching machine, and adjust the position and height of the broach.

  • Broach selection: Select the appropriate broach according to the material, size and spline specifications of the workpiece. The tooth shape, number of teeth, pitch and other parameters of the broach should match the requirements of the workpiece. At the same time, it is necessary to choose a broach with reliable quality and high precision to ensure the processing quality.
  • Tool installation: Install the broach correctly on the tool holder of the broaching machine, ensuring that the center line of the broach coincides with the axis of the workpiece. When installing, pay attention to the tightness of the tool to avoid loosening during broaching.
  • Tool adjustment: Adjust the cutting parameters of the broach according to the material and size of the workpiece, such as cutting speed, feed, etc. When adjusting, follow the tool manufacturer’s recommendations and optimize based on actual processing conditions.

4.Carry Out Broaching Stage

Start the broaching machine, and the broach moves along the axial direction of the workpiece under the action of tension to perform cutting. During the broaching process, attention needs to be paid to controlling the broaching speed and pulling force to ensure processing quality.

  • Cutting fluid selection: Select the appropriate cutting fluid to reduce cutting temperature, reduce tool wear and improve machined surface quality. The type and concentration of cutting fluid should be selected according to the material and processing requirements of the workpiece.
  • Broaching speed control: The broaching speed should be reasonably selected based on the material, size of the workpiece and the performance of the broach. If the speed is too high, the tool wears too quickly and the quality of the machined surface decreases; if the speed is too low, the production efficiency will be affected. During the broaching process, it is necessary to maintain a stable broaching speed and avoid speed fluctuations.
  • Feed control: The size of the feed directly affects the processing accuracy and surface quality. Too much feed may cause problems such as tool overload and chipping; too small a feed may affect production efficiency. The feed rate should be selected reasonably according to the material and processing requirements of the workpiece and kept stable during the broaching process.
  • Monitor the processing process: During the broaching process, pay close attention to the processing status, such as cutting sound, tool wear, machined surface quality, etc. If any abnormality is found, the machine should be stopped immediately for inspection, and processing should be continued after troubleshooting.

5.Inspection Workpiece Stage

After broaching is completed, the workpiece needs to be inspected, including inspection of dimensional accuracy, shape accuracy, surface roughness, etc. If problems are found, adjustments and corrections need to be made in time.

  • Dimensional accuracy inspection: Use measuring tools to accurately measure the dimensions of the processed splines, including spline diameter, key width, keyway depth, etc. Dimensional deviations should be controlled within the tolerance range required by the design.
  • Shape accuracy inspection: Check the shape accuracy of splines, such as roundness, straightness, parallelism, etc. The shape error should meet the design requirements to ensure the matching accuracy of the splines.
  • Surface quality inspection: observe the roughness, glossiness, etc. of the processed surface to ensure that the surface quality meets the requirements. If necessary, equipment such as a surface roughness meter can be used for testing.
  • Hardness inspection: Conduct hardness inspection on the processed workpiece to ensure that the hardness of the workpiece is within a reasonable range. If the hardness changes too much, it may affect the performance of the workpiece.

What Are The Common Problems And Solutions For Spline Broaching?

The following common problems and corresponding solutions may be encountered during spline broaching:

Rough Broaching Surface

Reason:

  • Broach wear: The tool gradually wears during use, and the cutting edge becomes dull, resulting in a rough machined surface.
  • Unreasonable cutting parameters: For example, the broaching speed is too high, the feed amount is too large, etc., which will increase the cutting force and cutting heat and reduce the surface quality.
  • Improper selection or insufficient supply of cutting fluid: It cannot effectively cool and lubricate the tool and workpiece, resulting in rough surfaces.
  • The hardness of the workpiece material is too high or uneven: it increases the difficulty of cutting and easily causes tool wear and surface roughness.

Solution:

  • Timely replace worn broaches: By observing the quality of the machined surface and measuring the size of the tool, the degree of wear of the broaches can be judged. When the wear is serious, it should be replaced in time.
  • Adjust cutting parameters: reduce broaching speed and feed, and find a suitable parameter combination to reduce cutting force and cutting heat.
  • Select the appropriate cutting fluid and ensure adequate supply: Select a cutting fluid with good performance based on the workpiece material and processing requirements, and ensure that the cutting fluid can be fully sprayed into the cutting area.
  • Pretreatment of the workpiece: If the hardness of the workpiece material is too high or uneven, pretreatment such as annealing can be performed to reduce the hardness and improve material uniformity.

Dimensional Deviation

Reason:

  • Inaccurate broach size: Errors in the manufacturing process or wear during use cause the broach size to be inconsistent with the design requirements.
  • Inaccurate workpiece installation: Poor positioning and clamping of the workpiece in the fixture causes the workpiece to move during the broaching process, affecting dimensional accuracy.
  • Uneven broaching force: The cutting force of each tooth of the broach is uneven, which may cause deformation of the workpiece and lead to dimensional deviations.

Solution:

  • Check and correct the size of the broach: Use a measuring tool to measure the broach. If there is any deviation, it can be corrected by grinding or other methods, or the broach can be replaced with a new one.
  • Ensure the workpiece is installed correctly: Choose a suitable fixture to ensure that the workpiece is accurately positioned and clamped firmly in the fixture to avoid movement during the broaching process.
  • Optimize the broaching process: adjust the cutting parameters and broaching sequence to evenly distribute the broaching force and reduce workpiece deformation. For example, methods such as layered broaching can be used.

The Broach is Broken

Reason:

Excessive broaching force: The broaching force may exceed the strength limit of the broach due to unreasonable cutting parameters, excessive hardness of the workpiece material, or severe broach wear.
There are defects in the broach: cracks, inclusions and other defects generated during the manufacturing process can easily cause the broach to break during use.
Improper operation: such as sudden stop or start during broaching, collision between broach and workpiece, etc.

Solution:

  • Adjust cutting parameters: reduce broaching speed and feed, and reduce broaching force. For workpieces with too high hardness, methods such as pre-processing can be used to reduce the difficulty of cutting.
  • Check the quality of the broach: Strictly inspect the broach before use, and replace any defective broaches promptly.
  • Standard operation: Keep steady during broaching and avoid sudden stops or starts. Be careful when installing and disassembling the broach to prevent collision with the workpiece.

Spline Shape Error

Reason:

  • Inaccurate broach tooth profile: Manufacturing errors or wear cause the broach tooth profile to be inconsistent with the design requirements.
  • The workpiece deforms during the broaching process: reasons such as excessive cutting force and uneven clamping force cause deformation of the workpiece and affect the spline shape.
  • Insufficient precision of the broaching machine: The broaching machine’s guide rails, clamps and other components are not precise enough, causing the broaching tool to shift during the broaching process, affecting the spline shape.

Solution:

  • Check and correct the broach tooth shape: Use a measuring tool to measure the broach tooth shape. If there is any deviation, it can be corrected by grinding or other methods, or a new broach can be replaced.
  • Control cutting forces and clamping forces: Optimize cutting parameters and fixture design to evenly distribute cutting forces and clamping forces and reduce workpiece deformation.
  • Maintain broaching machine accuracy: Maintain and calibrate broaching machines regularly to ensure that the accuracy of guide rails, fixtures and other components meets processing requirements.

Conclusion

Spline broaching is an efficient and high-precision processing method suitable for spline processing of various materials. When selecting a broach and determining processing parameters, factors such as workpiece material, size and accuracy requirements should be fully considered. To learn more about spline broaching, please contact us. Broachingmach will provide you with professional technical support and solutions.

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