Manufacturers process machined parts through various post-processing operations to obtain specific properties. Knurling is one of these additional processing cycles. Provides attractive textured surfaces for many specialty parts, creating patterns such as bumps and depressions on machined parts.
This article explains what knurling is and examines the different types and common errors in knurling operations. You will also learn more about knurling tools and techniques, including tips for successfully knurling metal.
What is serration?
Knurling is a finishing technique that uses hand tools or a lathe to create patterned grooves on the surfaces of machined components. The knurled technology increases friction on the surface of the piece and prevents the product or object from slipping in the hand. It also offers excellent optics, which are generally preferred over smooth surfaces.
Furthermore, knurling is a typical subtractive machining process that creates a textured surface by pressing or scraping material from a workpiece. Knurled tools often have unique patterns that produce similar patterns when pressed against cylindrical machined parts, such as diagonal or straight lines. Therefore, you can create a textured pattern on your products using a knurled tool with a specific pattern.
Types of serrated techniques
There are different types of knurling that product manufacturers use to create the desired patterns on workpieces.
1. Straight knurling
The straight knurling process creates straight lines and groove patterns on the surface of a workpiece. These are usually intersecting parallel or diagonal lines created using a serrated tool with two tempered wheels with diagonal teeth. Additionally, many industries are currently creating serrated processes on products to create a patterned texture that improves grip and handling.
Possible uses and advantages of straight knurling
Decorative purposes
Straight serrations are decorative patterns that make the surface of a workpiece more aesthetically pleasing. They are perfect for cylindrical objects like handles and knobs. Furthermore, they are suitable for applications such as high-quality writing instruments, custom hardware or jewelry and provide an elegant appearance.
Non-slip or improved grip function
Straight knurling creates a rough texture on the surface of an object to improve grip and make the object easier to hold and manipulate. These serrated patterns help increase friction between the hand and the workpiece and prevent slipping. This is beneficial in applications where a firm grip is crucial.
Alignment and positioning
This serrated structure is sometimes used as a reference to align and position components. The patterns serve as a visual indicator of proper component alignment and fit. Therefore, straight knurling is ideal for devices or mechanisms that require precise alignment, including fine-tuning mechanisms, measuring tools, or optical devices.
2. Diamond serration
Another common knurling technique is diamond knurling, which creates small diamond-shaped grooves or depressions on the surface of a workpiece. It usually consists of the intersection of diagonal lines that form several diamond-shaped projections. However, you can also achieve this surface with serrated wheels whose teeth are arranged like a diamond.
Applications and advantages of diamond knurling
durability
Diamond knurling makes the workpiece more wear-resistant and durable. It is often used on machine parts, tools or decorative parts that are subject to constant contact or high friction.
The depression or diamond structure distributes pressure and wears evenly, reducing the risk of wear or damage. Therefore, this feature makes this serrated structure ideal for applications with high durability requirements.
Decorative application
The diamond-shaped depression is unique and extremely decorative. It creates complex, visually appealing knurled patterns on machined parts, such as bicycle parts, lighter housings, or personal accessories, for an attractive, sophisticated appearance.
Improved grip
Diamond knurling allows for a better grip on hand workpieces by creating multiple points of contact between your hand and the workpiece. Because the diamond-shaped indentations provide better grip, you can hold and manipulate an object more easily with this serrated surface.
3. Spiral serrated process
The spiral serration technique creates diagonal lines in a spiral or spiral pattern on the surface of an object. Manufacturers typically use this knurled pattern on cylindrical surfaces, similar to a screw thread.
Possible uses and advantages of spiral serration
Decorative purposes
The spiral knurling process is similar to other knurling processes in that it is also perfect for decorative purposes. You can combine it with decorative techniques such as coating or polishing to improve the overall appearance of your product.
Advanced functionality
The spiral knurling process improves the functionality of cylindrical parts such as shafts, buttons and handles. The spiral serrated surface allows for a firm grip when turning and operating the machined part.
Thread formation
Threads are produced that match certain thread patterns on cylindrical objects. This reduces the need for further threading operations, making it an economical and efficient process for certain applications.
Various serrated tools for knurling
Product engineers use different knurling tools depending on the application and desired results. To obtain excellent knurling results, it is advisable to consider the properties of the chosen material, such as ductility and hardness. Here are some of the main tools used in the metal knurling process.
1. Serrated wheels
Knurling wheels are the most commonly used tools for knurling metal. They usually consist of two or more hardened steel wheels with opposing, slanted serrated patterns. These wheels are typically attached to a serrated tool and pressed against the rotating part to create the desired serrated pattern.
2. Serrated inserts
These are special tools that can be attached to a lathe for machining. Serrated inserts have a special serrated pattern that is programmed to create the desired serrated surface. Inserts usually come in different patterns and sizes and are made from carbide or high-speed steel.
3. Knurled Tools
These dies are tools used on turret lathes or CNC turning services to create knurled patterns on cylindrical objects. Serrated dies are made from high-speed steel and their serrated patterns are cut into the inner surface of an object. You must mount them in a serrated tool holder and rotate it against a workpiece to create the desired serrated patterns.
4. Knurled tools with pressure mechanism
Pressure serrated tools are hand-held serrated tools that use manual force to create serrated patterns. Pressure tools typically consist of a serrated wheel attached to a handle that aids movement along the surface of the workpiece to create the desired serrated texture. They are suitable for small batches or manual operations.
5. Floating serrated tools
This serrated tool is suitable for creating patterns and grooves on contoured or irregular surfaces. These tools adapt to the shape of the workpiece, ensuring consistent and accurate knurling. Floating tools use articulated arms or spring-loaded mechanisms so that the serrated wheels adapt to the contours of the surface.
Common defects in serrated operations
Serrated parts serve decorative and functional purposes in various applications in industries such as jewelry, furniture, automotive and aviation. However, product designers face several challenges during knurling operations.
1. Size under or over
Manufacturers create knurled patterns on an object that reaches a specific diameter or size. Undersizing occurs when the knurled pattern is smaller than the desired size. On the other hand, oversizing occurs when the knurled pattern is smaller than the intended size. However, these inconsistencies arise due to incorrect configuration, incorrect tool selection, or excessive pressure during the knurling process.
2. Superficial damage
The knurling process sometimes results in superficial damage, such as scratches or nicks that deform the surface of a workpiece. This usually occurs when excessive force is applied during the knurling process or when a knurling tool is worn.
3. Tool wear
Serrated tools typically wear out over time, causing a decrease in performance and deformation of the serrated metal. However, the knurled patterns gradually become less obvious and defects such as flat areas and burrs appear as the tool wears.
4. Poor standard definition
In general, serrated patterns should have clear, distinct lines and consistent depth. However, it is useful to note that inadequate lubrication, incorrect tool geometry, or worn serrations will result in poor workpiece pattern definition.
5. Vibration or traces of vibration
Chatter marks are irregular or sinuous patterns created on the surface of a workpiece due to vibration during the knurling process. Common causes of chatter marks include excessive tool pressure, insufficient rigidity, or incorrect tool alignment during machine setup.
Tips for getting the best knurled finish
Below are some helpful tips on how to get the best knurled finish for your parts.
1. Prepare the workpiece carefully
Irregularities, contamination or misalignment can affect the quality of the desired serration patterns. Therefore, clean the part, clamp it correctly, and make sure it is the correct dimensions before starting the knurling process.
2. Choose the appropriate serrated tool
Choosing serrated tools that match the desired patterns and materials is crucial. Knurled tools include different configurations, pitches and tooth patterns. Therefore, it is advisable to use the ideal tool for the hardness of the material and the desired surface finish.
3. Apply lubrication
Make sure the serrated tool and workpiece receive adequate cutting fluid or lubricant during the process. This reduces heat generation, friction and tool wear and creates a smooth, serrated surface.
4. Optimum cutting speed
Serrating the metal at the proper speed reduces tool wear and ensures proper chip formation. Therefore, it is advisable to determine the ideal turning tool and cutting speed based on the metal serration method. Follow the manufacturer's instructions or processing recommendations for a specific material.
5. Appropriate tool pressure
Excessive pressure may damage or deform the serrated part, while insufficient pressure may cause a flat pattern. When knurling a workpiece, you must apply the correct pressure. However, make sure the tool pressure matches the material and specifications of the serrated tool.
Concluding
After discussing the knurling process, you will be able to differentiate between different knurling tools, patterns, and common errors in knurling operations. This knowledge will help you make the best decision for your project. However, working with a reliable manufacturing company will help you improve your results by a large percentage.
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Common questions
Why is aliasing important?
Knurling is important because it improves the physical properties of a part and repairs worn surfaces. It also allows a better grip between the fingers or hand and the grooved object than normally smooth surfaces.
Which machine is suitable for producing serrated surfaces?
A lathe is the standard machining tool for producing serrated surfaces. It rotates the workpiece to the desired angles. It uses a stationary cutting tool that adds features to a workpiece.
What cutting speed is the right choice for serration?
In general, knurling operates at the same cutting speed as turning when using a high-speed steel cutting tool. However, it is advisable to use a maximum surface speed of 150 SFPM (ft/min) or 50 m/min to avoid jamming the rollers on the pin.
