Keyway Broaching: The Complete Guide

What is Keyway broaching ?

Keyway broaching is a procedure that employs a broach for machining keyways on workpieces. It is appropriate for mass production and is capable of attaining high-precision, high-efficiency and low-cost processing.

Keyway Broaching: The Complete Guide

During the keyway broaching process, the broach will move along the axial direction of the workpiece, and at the same time, the teeth of the broach will cut on the surface of the workpiece to machine the required keyway on the workpiece. Broaching can process keyways of various shapes, such as flat keyways, semicircular keyways, splined grooves, etc.

Keyway broaching is primarily utilized in the fields of automobiles, aviation, machinery, and others, particularly in instances where high-precision keyways are demanded.

6 Steps keyway broaching

  • Step1: Choose the right broaching machine and broaching tool. Select the appropriate broaching machine and broaching tool according to the size, shape and requirements of the workpiece. The size and shape of the broach should match the size and shape of the keyway.
  • Step2: nstall the broach. Install the broach on the broaching machine and make sure the broach is in the correct position and direction.
  • Step 3: Fix the workpiece. Secure the workpiece to the broaching machine to ensure it does not move or rotate during the broaching process.
  • Step 4: Adjust the broaching machine. According to the material and size of the workpiece, adjust parameters such as the speed, feed amount and cutting depth of the broaching machine.
  • Step 5: Start broaching. Start the broaching machine and make the broach slowly cut into the workpiece for broaching. During the broaching process, attention should be paid to observing the cutting conditions of the broach and adjusting the parameters of the broaching machine in a timely manner to ensure broaching quality.
  • Step 6: Complete broaching. The broaching process ends when the broach has completely passed through the workpiece. At this time, the broaching machine should be closed, the workpiece should be taken out, and the workpiece should be inspected and cleaned.
6 Steps  keyway broaching

What Are The Advantages Of Keyway Broaching?

Keyway broaching has several significant advantages:

High-Precision Processing

1.High dimensional accuracy

  • Keyway broaching enables very precise dimensional control. Broaches are precision designed and manufactured tools with a high degree of consistency in the size and shape of their teeth. During the broaching process, each tooth cuts the workpiece in turn, ensuring that the keyway’s dimensional parameters such as width, depth and length are accurate.
  • For some application fields that require extremely high dimensional accuracy, such as aerospace, precision machinery, etc., keyway broaching can meet strict tolerance requirements and ensure the assembly accuracy and performance of parts.

2.High shape accuracy

  • Broaching can achieve good keyway shape accuracy. The tooth shape of the broach completely matches the shape of the keyway to be processed, and can produce a regular and smooth keyway surface on the workpiece.
  • Compared with other processing methods, keyway broaching is less likely to produce defects such as deformation and distortion, ensuring that the shape of the keyway meets the design requirements.

3.High Position Accuracy

  • During the machining process, the broach cuts along a predetermined trajectory, which can ensure the position accuracy of the keyway on the workpiece. This is especially important where multiple keyways need to mate with each other or with other parts for precise assembly.
  • Through precise positioning and clamping devices, the position accuracy of the keyway can be further improved to ensure the overall processing quality of the workpiece.

High-Efficiency Processing

1.One-time molding:

  • Keyway broaching typically produces the keyway in a single pass, eliminating the need for multiple cuts or other auxiliary machining operations. This greatly shortens processing time and improves production efficiency.
  • Compared with traditional milling, planing and other processing methods, the processing efficiency of keyway broaching can be increased several times or even higher.

2.High cutting speed

  • Under the right conditions, keyway broaching can use higher cutting speeds. The cutting edge of the broach is sharp, the cutting force is small, and it can maintain stable processing conditions under high-speed cutting.
  • High cutting speed can further improve processing efficiency and reduce processing time, which is especially suitable for mass production.

3.High degree of automation:

  • Keyway broaching can be combined with automated processing equipment to achieve automated production. Through CNC broaching machines or other automated equipment, various parameters in the broaching process can be accurately controlled, improving processing accuracy and consistency, while reducing manual operations and improving production efficiency.

Good Surface Quality

1.Low surface roughness:

  • Keyway broaching can produce very smooth surfaces with surface roughness values ​​typically in the range of a few microns or even less. This is because the teeth of the broach are finely ground and the cutting process is smooth, leaving even and delicate processing marks on the surface of the workpiece.
  • Low surface roughness can reduce frictional resistance, improve the fitting accuracy and service life of parts, and also help improve the appearance quality of products.

2.High surface hardness:

  • During the broaching process, due to the action of cutting force and cutting heat, a certain degree of work hardening will occur on the surface of the workpiece. This increases the hardness of the keyway surface and enhances the wear resistance and corrosion resistance of the surface.
  • For some parts that need to work in harsh environments, the surface hardness after keyway broaching can improve their service life and reliability.

Wide Scope Of Application

1.Multiple material processing:

  • Keyway broaching can be applied to processing various materials, including metallic materials such as steel, cast iron, aluminum alloy, copper alloy, etc., and non-metallic materials such as plastic, rubber, etc. The processing of different materials only requires selecting the appropriate broach and cutting parameters.
  • For some difficult-to-machine materials, such as high-strength alloy steel, high-temperature alloys, etc., keyway broaching can also exert its advantages to achieve efficient and high-precision processing.

2.Keyway processing of different sizes:

  • Keyway broaching can process keyways of various sizes, from micro keyways on small precision parts to wide keyways on large workpieces, by selecting the appropriate broach.
  • The design and manufacturing of broaches can be customized according to different keyway size and shape requirements to meet the needs of various application scenarios.

What Are The Disadvantages Of Keyway Broaching?

Keyway broaching mainly has the following disadvantages:

High tool cost
Broach manufacturing is complex:
The manufacturing of keyway broaches requires high-precision processing equipment and professional technical personnel. The tooth shape of the broach is complex and requires high dimensional accuracy. The manufacturing process requires multiple processes, such as forging, cutting, heat treatment, grinding, etc.
These complex manufacturing processes make the cost of broaches higher, especially for broaches of some special shapes or sizes, the manufacturing cost may be higher.
Tool material requirements are high:
In order to ensure the cutting performance and life of the broach, it is usually necessary to use high-performance tool materials, such as high-speed steel, cemented carbide, etc. The prices of these materials are relatively high, further increasing the cost of the broaches.
Moreover, different workpiece materials and processing requirements may require the selection of different tool materials, which also increases the cost and management difficulty of the tools.

High requirements for equipment
A special broaching machine is required:
Keyway broaching usually needs to be performed on a special broaching machine, which is relatively expensive, occupies a large area, and requires relatively high processing space.
For some small businesses or situations with smaller processing volumes, purchasing a special broaching machine may increase production costs and equipment maintenance costs.
Equipment accuracy requirements are high:
Broaching requires high accuracy of equipment. The guide rails, transmission systems and other components of the broaching machine need to have good accuracy and stability to ensure the accuracy and stability of the broach during the cutting process.
If the equipment is not precise enough, the dimensional accuracy and shape accuracy of the keyway may be reduced, and the broach may even be damaged.

Poor flexibility
Only keyways of certain shapes and sizes can be machined:
The shape and size of the keyway broach are fixed and can only process the keyway that matches it. If a keyway of a different shape or size needs to be processed, the broach needs to be replaced, which increases processing costs and time.
In contrast, some other processing methods, such as milling, planing, etc., can process keyways of different shapes and sizes by adjusting the tools and processing parameters, with higher flexibility.
Not suitable for processing complex-shaped workpieces:
Keyway broaching is mainly suitable for processing keyways on flat or cylindrical surfaces. For some workpieces with complex shapes, such as curved surfaces, special-shaped parts, etc., broaching may be limited.
In this case, other processing methods, such as CNC machining, EDM, etc., may be needed to meet the processing needs of complex-shaped workpieces.

How To Ensure The Stability Of The Workpiece During Keyway Broaching?

During the keyway broaching process, it is crucial to ensure the stability of the workpiece, which directly affects the machining accuracy and the quality of the final product. Here are some ways to ensure artifact stability:

  1. Use clamps or adequately secure the workpiece: During broaching operations, use clamps to hold the workpiece securely in place to ensure stability and accuracy during the cutting process
  2. Choose the right metal cutting tool: Choose the right tool based on the specific material and job requirements to ensure stability and efficiency during the machining process
  3. Determine the cutting parameters of the tool: set the cutting depth and cutting speed reasonably, and adjust the parameters according to the material hardness, the number of cutting edges and the stability of the machine tool to reduce vibration and improve processing stability.

How To Choose The Cutting Speed During Keyway Broaching?

When keyway broaching, there are many factors to consider when selecting cutting speed. The following is a detailed introduction for you:

1. Consider The Workpiece Material

  • For materials with lower hardness and better plasticity, such as aluminum alloys, copper alloys, etc., you can choose a higher cutting speed. Generally between 10 m/min and 30 m/min. This is because these materials are easy to process, and higher cutting speeds can improve processing efficiency without causing excessive wear on the tools.
  • For materials with higher hardness, such as alloy steel, tool steel, etc., the cutting speed should be appropriately reduced. Usually around 5m/min to 15m/min. Because hard materials cause greater wear on tools, excessive cutting speeds will drastically shorten tool life.

2. Consider Broach Material And Coating

  • High-quality broach materials, such as high-speed steel or carbide, with good coatings that can withstand high cutting speeds. In this case, the cutting speed can be appropriately increased according to the workpiece material and processing requirements.
  • If the broach material is average or uncoated, the cutting speed should be reduced to prevent excessive wear and damage to the tool.

3. Consider Processing Accuracy Requirements

  • If the machining accuracy of the keyway is high, the cutting speed should be appropriately reduced. This reduces cutting forces and vibration, and improves machining accuracy and surface quality. Generally speaking, when precision requirements are high, the cutting speed may be around 5 m/min to 10 m/min.
  • For processing with relatively low precision requirements, a slightly higher cutting speed can be selected to improve production efficiency.

4. Consider Broaching Machine Performance

  • Broaching machines of different models and specifications have different power and stability. If the broaching machine has greater power and good stability, you can choose a higher cutting speed.
  • For broaching machines with lower power or poor stability, the cutting speed should be reduced to ensure the safety and stability of the processing process.

What Are The Common Faults And Solutions In Keyway Broaching?

Keyway broaching is a commonly used machining method, but in practical applications, some common failures may be encountered. Understanding these failures and their solutions is critical to improving processing efficiency and product quality. The following are some common failures and solutions in keyway broaching:

Faults 1: Workpiece spline jacking burrs

When keyway broaching, burrs on the spline key of the workpiece may be caused by damage to the chamfering teeth of the broach. Observe the chamfering teeth of the broach and if any damage is found, repair it in time to eliminate it.

The burr phenomenon not only affects the surface quality of the workpiece, but may also cause increased wear of the broach. By regularly checking and treating the chamfered teeth of the broach, the generation of burrs can be effectively reduced.

Solutions

Observe the chamfering teeth of the broach and repair them promptly if any damage is found.
Regular inspection and treatment of the chamfering teeth of the broach can effectively reduce the generation of burrs and improve the surface quality of the workpiece.

Faults 2: There are scratches on the key side

Scratches on the key side may be caused by the sharp corner of the trailing end of the broach scratching the key side surface of the workpiece. Measure the width of the rear guide spline of the broach. If the width of the rear guide spline is greater than or equal to the width of the calibrated tooth spline, grinding is required.

In addition, when the broach leaves the factory, the key width of the rear guide part is not ground to the end, and an inverted taper appears, which will also cause scratches on the key side. Through precise measurement and grinding, the occurrence of keyside scratches can be significantly reduced.

Solutions

Measure the width of the rear guide spline of the broach. If the width of the rear guide spline is greater than or equal to the width of the calibrated tooth spline, it must be ground. After grinding, the width of the rear guide spline is 0.04 mm smaller than the width of the calibrated tooth spline. Please note that Grind the end corners of the rear guide splines into arc shapes and polish them

Through precise measurement and grinding, the occurrence of key side scratches can be significantly reduced, ensuring that the size and shape of the workpiece meet the design requirements.

Faults 3: Scratched key bottom

The scratches on the key bottom may be due to the fact that the broach has been sharpened many times, the diameter of the precision cutting teeth is large, and the diameter of the calibration teeth is small. Not all calibration teeth are sharpened each time. Initially, only the first calibration tooth is sharpened. When its diameter is reduced by 0.02~0.03 mm, the second calibration tooth is sharpened.

Through reasonable sharpening sequence and amount, the service life of the broach can be effectively extended and the occurrence of scratches on the key bottom can be reduced.

Solutions

Not all calibration teeth are sharpened each time. Initially, only the first calibration tooth is sharpened. When its diameter is reduced by 0.02~0.03 mm, the second one is sharpened, and the subsequent calibration teeth are also sharpened accordingly. similar

Through reasonable sharpening sequence and amount, the service life of the broach can be effectively extended and the occurrence of scratches on the key bottom can be reduced.

Faults 4: Scales appear on the broached surface

The scaly phenomenon on the broached surface may be due to improper broaching speed, tooth lift, improper rake angle or inappropriate cutting fluid. Use a broaching speed lower than 2 m/min or higher than 5 m/min to test pulling, use a smaller tooth lift, increase the rake angle appropriately, change the heat treatment state of the material, and use extreme pressure cutting fluid

The scaly phenomenon seriously affects the quality of the broached surface. This phenomenon can be effectively improved by adjusting the broaching parameters and using appropriate cutting fluid.

Solutions

Use a broaching speed lower than 2 m/min or higher than 5 m/min to test pulling, use a smaller tooth lift, increase the rake angle appropriately, change the heat treatment state of the material, and use extreme pressure cutting fluid

By adjusting broaching parameters and using appropriate cutting fluid, the scaly phenomenon can be effectively improved and the quality of the broached surface can be improved.

Faults 5: The broach swings up and down while broaching the keyway

The broach swinging up and down when broaching the keyway may be due to the insufficient guide length of the broach guide core. Maintain the correct working position of the broach, maintain the perpendicularity between the datum plane of the workpiece and the pre-made hole, and keep the end surfaces of the workpiece and fixture clean and flat.

By optimizing the broach guide system and keeping the workpiece and fixture clean, the broach swing problem can be effectively solved and machining accuracy and efficiency improved.

Solutions

Maintain the correct working position of the broach, maintain the perpendicularity between the datum plane of the workpiece and the pre-made hole, and keep the end surfaces of the workpiece and fixture clean and flat.

By optimizing the broach guide system and keeping the workpiece and fixture clean, the broach swing problem can be effectively solved and machining accuracy and efficiency improved.

By understanding and analyzing common faults in keyway broaching and their solutions, processing efficiency and product quality can be effectively improved. Regularly check and deal with the chamfered teeth of the keyway broaches, the sharp corners at the end of the trailing part and the scratches on the key bottom, adjust the broaching speed and tooth lift, use appropriate cutting fluid, and keep the broach and workpiece clean. Important measures to reduce the occurrence of failures and improve processing quality.

Learn More: Troubleshooting For Broaching Operation

How To Choose A Suitable Keyway Broach?

When choosing a suitable keyway broach, you can consider the following aspects:

One: Selection Based On Workpiece Material

1. Less hard materials:

  • For materials with lower hardness such as aluminum alloys and copper alloys, you can choose high-speed steel broaches. High-speed steel broaches have good cutting performance and toughness, can be processed under low cutting forces, and are not prone to chipping.
  • At the same time, the price of high-speed steel broaches is relatively low and suitable for processing larger batches of workpieces.

2.Harder materials:

  • For materials with higher hardness such as alloy steel and tool steel, carbide broaches should be selected. Carbide broaches have higher hardness and wear resistance, can withstand larger cutting forces, and are suitable for processing materials with higher hardness.
  • However, carbide broaches are more expensive and brittle, so care must be taken to prevent edge chipping during use.

Two: Select According To Keyway Size

1.Keyway width:

  • When selecting a broach, the width of the broach should match the width of the keyway. Generally speaking, the width of the broach should be slightly smaller than the width of the keyway so that the workpiece can be cut smoothly during the broaching process while ensuring the dimensional accuracy of the keyway.
  • If the width of the broach is too large, it may cause excessive cutting force and damage the broach or the workpiece; if the width of the broach is too small, the dimensional accuracy of the keyway may not meet the requirements.

2.Keyway depth:

  • The length of the broach should be determined according to the depth of the keyway. Generally speaking, the length of the broach should be slightly larger than the depth of the keyway so that the workpiece can be completely cut during the broaching process while ensuring the rigidity and stability of the broach.
  • If the length of the broach is too long, the rigidity of the broach may be insufficient, and vibration may easily occur during the cutting process, affecting the processing quality; if the length of the broach is too short, the workpiece may not be completely cut, affecting the machining depth of the keyway. .

Three: Select According To Processing Accuracy Requirements

1.High precision requirements:

  • If the machining accuracy of the keyway is high, a broach with a higher accuracy level should be selected. The dimensional accuracy and shape accuracy of the teeth of high-precision broaches are higher, which can ensure the dimensional accuracy and shape accuracy of the keyway.
  • At the same time, the surface quality of high-precision broaches is also better, which can reduce friction resistance during the cutting process and improve processing efficiency and surface quality.

2.General accuracy requirements:

  • For situations where the processing accuracy is not high, you can choose a broach with a lower accuracy level. This can reduce the cost of the broach and also meet general processing requirements.

Four: Select According To Production Batch Size

1.Mass production:

  • If it is mass production, you should choose a broach with high durability and stable cutting performance. You can choose carbide broaches or coated broaches, which have higher wear resistance and cutting performance, and can maintain stable processing quality during long-term machining processes.
  • At the same time, you can also consider using replaceable blade broaches, so that the blades can be replaced after wear without replacing the entire broach, reducing production costs.

2.Small batch production:

  • For small batch production, you can choose relatively low-priced high-speed steel broaches. The manufacturing process of high-speed steel broaches is relatively simple, the cost is low, and it is suitable for small batch production.
  • In addition, you can also consider using a universal broach, which can process different workpieces and improve the utilization rate of the broach.

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