In the machinery production and metal processing industries, knurling technology is regarded as a common and crucial surface processing method. Knurling can not only significantly improve performance indicators such as surface finish and gloss, but also improve product quality. Whether it is the handle of a tool, the knob of an instrument, or various other mechanical parts, knurling can significantly improve the performance and appearance quality of the product. Therefore, knurling is widely used in various fields and has achieved great results. This article will discuss in depth the application scenarios, technical characteristics and uses of the knurling process.
What is knurling in a mechanical sense?
Mechanical knurling is a cold working process, which applies pressure on the surface of metal or plastic, and forms a concave and convex texture through plastic deformation, so as to enhance the functions of anti-slip, grip, etc., and has a decorative effect, which is widely used in tool manufacturing, automobiles, instrumentation and other fields.
The core mechanism of mechanical knurling
- Double roller extrusion system: Customized knurled wheels such as straight wheels or mesh wheels are used and installed in pairs on special equipment. The workpiece is extruded at a high pressure of 500 – 1500 N/cm², and the pressure is adjusted according to the hardness of the material and the depth of the tread.
- Plastic deformation of the material: After compression, the surface of the material flows plastically, forming a concave and convex structure with a depth of 0.1 – 0.5mm, and the shape of the pattern is determined by the drum tooth shape, including straight knurling, diamond knurling and customized pattern knurling.
- Chipless machining features: Different from traditional cutting, knurling is formed by cold extrusion, no waste chip generation, and material utilization rate is nearly 100%.
Improvement of physical properties by mechanical knurling
| Performance indicators | Improved effect | Test standard |
|---|---|---|
| Surface friction coefficient | Increased by 200%-300% | ASTM D1894 (plastic friction) |
| Anti-slip strength | Reach ISO 1307 Class B (≥5kN/m²) | ISO 1307 |
| Abrasion resistance | Extend service life by 30%-50% (high-frequency contact scenario) | ASTM G99 |
Typical application scenarios for mechanical knurling
- Tool and equipment handles: used for wrenches, screwdrivers, etc., to improve grip stability and comfort.
- Precision instrument adjustment parts: such as touch knobs, dials, improve operation accuracy.
- Mechanical transmission parts: press-fit bushings, couplings, etc., to enhance the strength of interference fit.
- Consumer electronics: mobile phone frames, camera lenses, both beautiful and enhance the texture, grip feel.
Process advantages and industry value
- Cost-effective: Single-pass processing, no subsequent coating or non-slip components, reducing costs and increasing efficiency.
- Functional integration: to meet the multiple needs of anti-slip, beautiful, touch optimization, etc., to improve the comprehensive performance of products.
- Material compatibility: suitable for steel, aluminum, copper alloy and other metals and ABS, nylon, POM and other engineering plastics.
What is the purpose of knurling?
In the fields of mechanical manufacturing, tool design and consumer goods, knurling, as a classic surface treatment technology, has always occupied an important position. Whether it is the anti-slip texture of the screwdriver handle or the exquisite texture of the high-end instrument knob, knurling plays an irreplaceable role silently. LS will deeply analyze the core purpose of knurling and reveal how it can achieve dual upgrades in function and aesthetics through simple processes.
The 5 core purposes of knurling
(1) Enhance friction and prevent slippage
The primary purpose of knurling is to significantly increase the coefficient of friction (up to 300%) through the uneven texture of the surface and ensure operational stability:
- Tool handle: hand tools such as wrenches and screwdrivers, which are more firmly held after knurling, and are not easy to get rid of even if they are stained with oil.
- Adjustment parts: instrument knobs, valve switches, etc., knurled patterns provide precise control feedback to prevent accidental touches.
- Industrial parts: transmission shafts, couplings and other mechanical parts, knurled surface can increase the friction of the contact surface and prevent relative sliding.
- Data support: Tested by ASTM D1894, the coefficient of friction of knurled surface can reach 0.8-1.2, which is far higher than the 0.2-0.4 of smooth surface.
(2) Optimize the human-computer interaction experience
Knurling improves efficiency and comfort through haptic design:
- Haptic feedback: The uneven texture provides a clear “grip confirmation” and reduces operator fatigue.
- Labor-saving design: The diamond-shaped knurling pattern makes the rotation operation more labor-intensive, especially for components that require frequent adjustments (e.g. microscope focal length knobs).
- Blind operation support: Specific knurled patterns can be used as tactile markers to help users quickly locate features when visual vision is not possible.
(3) Replace complex structures and reduce costs
Knurling can replace high-cost processing methods with simple processes:
- Alternative spline/rack: In low-torque scenarios, the knurled shaft can be pressed directly to the sleeve, eliminating the need to cut the spline.
- Fewer add-ons: There is no need to install additional rubber grips or stickers, and the functionality is integrated directly through knurling.
- Processing efficiency: single roll forming, the speed is 5-8 times faster than laser engraving, and the cost is reduced by more than 40%.
(4) Enhance the aesthetics and added value of products
In modern industrial design, knurling has evolved from a purely functional process to an aesthetic design language:
- High-end texture: Precision knurled patterns (such as sunburst patterns and sunburst patterns) are often used in luxury parts such as watch crowns and camera lens rings.
- Brand identity: Customized knurling patterns can become a visual identity for the product (e.g., specific grid density or cross angle).
- Tactile marketing: Consumers can directly perceive the quality of product craftsmanship by touching the knurled texture and enhance their purchase decisions.
(5) Strengthen the mechanical fitting performance
In precision assembly, knurling improves component connection reliability:
- Interference fit enhancement: The knurled shaft has a 20%-30% increase in the contact area with the hole, and the tensile strength is increased to ISO 1307 Class B (≥5kN/m²).
- Stress distribution optimization: The cross-knurled pattern can disperse the pressure matching stress and reduce the risk of local deformation.
- Anti-loosening design: additional knurling is attached to the threaded connection to prevent the nut from loosening spontaneously (especially in vibrating environments).
3 major technical advantages of knurling process
| Advantage dimensions | Comparison with traditional processes | Knurling solution |
|---|---|---|
| Anti-slip performance | Rubber sleeves are prone to aging and falling off | Permanent texture, life is synchronized with the base material |
| Processing cost | Laser engraving unit price ￥0.5-1.2/cm² | Knurling cost is only ￥0.1-0.3/cm² |
| Environmental protection | Electroplating/spraying produces chemical pollution | Cold processing has zero emissions |
In the field of industrial manufacturing and product design, knurling technology meets a variety of functional requirements with different texture designs. As the three mainstream types, diamond knurling, cross knurling and straight knurling have their own characteristics in terms of friction, bearing strength and operation experience. The following is an in-depth analysis of their structure, performance and application, so that you can choose the right knurling solution.
1. Diamond knurling
- Structural features: Diamond-shaped concave and convex lines composed of 30° – 45° staggered twill, which has a 40% increase in surface contact area compared to linear knurling, and has multi-directional anti-skid performance.
- Performance Advantages: The twill design allows the knurling to maintain a stable coefficient of friction at any grip angle, tested by ASTM D1894 with a coefficient of friction of up to 1.2; At the same time, the moderate texture density brings a pleasant touch, which is suitable for long-term hand-held operation, which can effectively reduce hand fatigue.
- Typical applications: often used in medical tools, such as surgical forceps, bone drill handles, to ensure that there is still good anti-slip performance in wet environments; It is also suitable for precision instruments, such as optical equipment focusing rings and laboratory instrument knobs; In the field of consumer electronics, high-end camera lens rings and smart wearable device adjustment knobs are also often knurled.
2. Cross knurling
- Structural features: 90° orthogonal grid shape is presented, forming a uniform square concave and convex structure. Tested according to ISO 1307, its load-bearing strength is 25% higher than that of diamond knurling.
- Performance advantages: the orthogonal structure can effectively disperse pressure, has ultra-high strength, and the compressive strength is ≥8kN/m², which is suitable for high load scenarios; The large grid gap is not easy to accumulate impurities, which is easy to clean and maintain, and has anti-fouling characteristics.
- Typical applications: In the field of industrial valves, hand wheels and pressure regulating valves certified according to EN 12516 – 1 are often cross-knurled; In addition, this type of knurling is also used in crane control levers and hydraulic equipment handles of heavy machinery, as well as ship steering wheels and locomotive brake handles in transportation equipment.
3. Straight knurling
- Structural features: the knurling line is a parallel straight line, and the direction is consistent with the axis of the workpiece, and its surface friction resistance is unidirectionally distributed, which is suitable for linear sliding operation.
- Performance advantages: The unidirectional texture makes it only 0.6 – 0.8 friction coefficient when sliding, and the operating resistance is small, which is very suitable for precision adjustment; At the same time, because it can be rolled in a single shot, the processing speed is 30% faster than other types of knurling, and the efficiency is higher.
- Typical applications: commonly found in measuring tools such as micrometer sleeves, vernier caliper thumb wheels; It is also suitable for sliding parts, such as machine tool guide rail adjustment knobs and telescopic devices; In electronic devices, volume sliders, linear potentiometer knobs, etc., are also used for linear knurling.
Comparison table of key parameters of three knurlings
| Parameters | Diamond knurling | Cross knurling | Straight knurling |
|---|---|---|---|
| Texture angle | 30°-45° staggered twill | 90° orthogonal grid | 0° parallel straight line |
| Contact area | +40% (compared to straight line) | +20% (compared to straight line) | Base value |
| Bearing strength | 5-7kN/m² | 8-10kN/m² | 4-5kN/m² |
| Applicable operation type | Multi-directional rotation grip | High-strength pressing operation | One-way sliding adjustment |
| Industry standards | ISO 9001 | EN 12516-1 | DIN 82 |
How to choose the type of knurling?
In machining and product design, the selection of knurling type needs to take into account the function, cost and aesthetics to ensure that knurling is practical and economical and beautiful.
1. Choose according to functional requirements
Anti-slip scene: In humid environments, such as medical operations and laboratory operations, the staggered twill of diamond-shaped knurling is multi-directional anti-slip and can be held stably; Heavy-duty operations such as industrial valves and heavy machinery rely on cross-knurled orthogonal grids to withstand heavy pressure and ensure safety.
Precision adjustment: straight line knurled unidirectional friction resistance, suitable for straight line sliding precision adjustment, often used in micrometer sleeve, volume slider, etc.
2. Weigh in from the processing cost
The diamond-shaped knurled twill processing is complex, and the tool loss is large; Straight knurling single roll forming, high mass production efficiency, low cost, significant advantages.
3. Customized according to aesthetic requirements
High-end consumer goods: diamond-shaped knurling has a unique texture and texture, which is suitable for high-end watch crowns and camera lens rings to enhance the delicacy of products.
Industrial equipment: The cross-knurled orthogonal mesh shows a tough industrial style, which meets the practical and rugged design standards of industrial equipment.
Which materials require special knurling parameters?
The success or failure of the knurling process is closely related to the accurate matching of material properties and process parameters. For special materials such as aluminum alloy, stainless steel, engineering plastics, etc., conventional knurling parameters can easily cause problems such as sticky knives and blurred patterns, and even lead to scrapping of workpieces. The following is an in-depth analysis of the six categories of materials that require special parameter control and provides practical process optimization solutions to help achieve the desired knurling effect.
1. 6 kinds of materials that need to adjust knurling parameters
(1) Aluminum alloy (6061-T6)
Processing difficulties
The viscosity of aluminum alloy material is large, and aluminum chips are easy to adhere to the roller during processing; Its coefficient of thermal expansion is high, and it is difficult to ensure grain accuracy at high temperatures.
Special parameter settings
| Parameters | Standard knurling parameters | Optimized parameters for aluminum alloy |
|---|---|---|
| Workpiece precooling temperature | Normal temperature | -10℃ (liquid nitrogen spray treatment) |
| Feed speed | 0.15-0.3mm/rev | ≤0.1mm/rev |
| Roller hardness | HRC 58-60 | HRC 62+ (titanium coating) |
Operational recommendations
After every 20 pieces of processing, the roller cogging is cleaned in time; Compressed air is used to cool the machining area in real time.
(2) Austenitic stainless steel (316L)
Difficult to process
Austenitic stainless steels exhibit significant work hardening when machined, and the hardness can be increased by 30% to 50%; Local temperatures of up to 800°C during machining accelerate roller wear.
Special parameter settings
| Parameter item | Standard parameter | Stainless steel optimization parameter |
|---|---|---|
| Knurling pressure | 800-1000N/cm² | 1200-1500N/cm² |
| Lubricant | Ordinary cutting oil | Molybdenum sulfide cutting oil (concentration 1:10) |
| Roller tooth profile angle | 90° | 75° (sharp-angle teeth break through the hardened layer) |
Operational recommendations
Two calendering processes are used, the first time with a pressure of 800N/cm² and the second with a pressure of 1200N/cm² for fine pressing; After each piece of processing, check the wear of the roller tooth tip, and the allowable wear amount ≤ 0.02mm.
(3) Engineering plastics (POM/Delrin)
Difficult to process
Engineering plastics are prone to stress cracking when they are cold-rolled; The material has strong toughness and low granulation rate.
Special parameter settings
| Parameter item | Metal processing parameters | POM optimization parameters |
|---|---|---|
| Roller temperature | Normal temperature | 80-100℃ (hot rolling) |
| Grain depth | 0.3-0.5mm | ≤0.2mm |
| Rolling speed | 20-30rpm | 50-60rpm (fast shaping) |
Operational recommendations
Use electric heating rollers and control the temperature accuracy at ±2°C; After the processing is completed, the shape is immediately set with cold air to prevent the workpiece from rebounding and deforming.
2. Other materials that require special treatment
(1) Titanium alloy (Ti-6Al-4V)
Processing in a nitrogen protected environment can effectively prevent high-temperature oxidation; Reduce the pressure to 700 N/cm² to avoid lattice distortion.
(2) Copper alloy (H62 brass)
Change the rake angle of the roller to -5° to inhibit the accumulation of material flow; Increase the feed rate to 0.25mm/rev to improve machining efficiency.
(3) Ultra-thin wall parts (wall thickness < 1mm)
The double roller pressing method is used to offset the radial deformation force; Control the bevel depth to 15% of the wall thickness, e.g. a 1mm wall thickness for ultra-thin wall pieces, and the bevel depth is limited to 0.15mm.
Comparison of effects before and after process optimization
| Material | Problem phenomenon | Optimization solution | Yield improvement |
|---|---|---|---|
| Aluminum alloy | Grain adhesion, burrs | Precooling + low-speed feeding | 82% → 98% |
| Stainless steel | Roller tooth collapse, uneven grain | Sulfurized oil lubrication + step pressurization | 65% → 93% |
| POM plastic | Cracks, rebound deformation | 80℃ hot rolling + cold air shaping | 70% → 95% |
How Does CNC Knurling Revolutionize Precision?
In machining, the traditional knurling process is not very accurate, and CNC knurling breaks this situation. Through CNC technology, the knurling depth fluctuation has been reduced from ±0.1mm to ±0.02mm, and the processing efficiency has been increased by more than 30%. This is mainly due to closed-loop pressure control and multi-axis synergy technology.
1. Dynamic pressure compensation system: the key to improving accuracy
(1) Precise suppression of pressure fluctuations
The high-precision sensor monitors the roller pressure in real time at 0.01 second intervals, and the closed-loop control accuracy can reach 50N, which can control the pressure change more stably than the 200N pressure fluctuation of the traditional hydraulic system, and the groove depth consistency is improved to ±0.02mm, far exceeding the ±0.1mm of the traditional process.
(2) Smart material adaptive technology
The system automatically recognizes materials in the HB50 – 600 hardness range and adjusts the pressure profile according to the material properties. For example, aluminium alloys are machined with gradient pressurization of 900 – 1100 N/cm² and stainless steel with 1200 – 1500 N/cm² step pressurization to ensure high-precision knurling of different materials.
2. Multi-axis synchronization technology: innovate the processing of complex parts
(1) Turning and knurling compound machining
The CNC machine realizes the real-time linkage between the spindle (C-axis) and the knurling cutter (Y-axis), and can perform turning and knurling simultaneously. For example, crankshaft oil seal knurling, the traditional process requires three processes: turning, transfer, and knurling, while the CNC solution can be completed in one clamping, and the man-hours are shortened by 35%.
(2) Non-circular cross-section knurled breakthrough
For oval parts, such as the knurling of automobile piston pins, CNC knurling can dynamically match the spindle speed and feed rate, and the pattern spacing error is ≤0.03mm, breaking through the limitations of traditional technology.
3. Comparison of accuracy and efficiency data
| Indicators | Traditional knurling | CNC knurling | Improvement |
|---|---|---|---|
| Depth consistency | ±0.1mm | ±0.02mm | 500% |
| Changeover time | 45-60 minutes | 8-15 minutes | 70% |
| Complicated parts qualification rate | 68%-75% | 95%-98% | 35% |
| Energy efficiency | 0.18kW·h/piece | 0.12kW·h/piece | 33% |
4. Industry Application Cases
(1) Medical Implants (Titanium Alloy Bone Screws)
Titanium alloy bone screws need to be knurled with φ2mm threads, and the depth tolerance is required to be ±0.015mm. CNC knurling utilizes a 0.001° indexing accuracy C-axis paired with a micro knurling wheel to reduce the defect rate from 12% to 0.3%.
(2) Motor shafts for new energy vehicles
The knurled depth-diameter ratio of the inner wall of the blind hole of the motor shaft of new energy vehicles is 18:1, which is difficult. The CNC solution with B-axis oscillating turret and internal coolant knurled tools reduces machining time from 22 minutes to 9 minutes, significantly increasing efficiency.
Conclusion
As an economical and efficient surface finishing process, knurling plays an irreplaceable role in the field of mechanical manufacturing. From functional anti-slip to aesthetic decoration, from simple tools to precision instruments, knurling technology continues to add value to various products. Understanding the true purpose and application scenarios of knurling will help engineers and designers use this process more reasonably to create products with better performance and better experience.
With the advancement of material science and processing technology, knurling technology is also constantly developing and innovating, and will surely show broader application prospects in the future.
📞 Phone: +86 185 6675 9667
📧 Email: info@longshengmfg.com
🌐 Website: https://www.longshengmfg.com/
Disclaimer
The content appearing on this webpage is for informational purposes only. LS makes no representation or warranty of any kind, be it expressed or implied, as to the accuracy, completeness, or validity of the information. Any performance parameters, geometric tolerances, specific design features, quality and types of materials, or processes should not be inferred to represent what will be delivered by third-party suppliers or manufacturers through LS’s network. Buyers seeking quotes for parts are responsible for defining the specific requirements for those parts. Please contact to our for more information.
Team LS
This article was written by various LS contributors. LS is a leading resource on manufacturing with CNC machining, sheet metal fabrication, 3D printing, injection molding,metal stamping and more.
FAQs
What is Knurling? What is its purpose?
Knurling is a kind of knurling tool through rotation or linear motion on the metal surface to press out a precise diamond, straight or reticulated concave and convex texture of the cold working process, its core purpose is to permanently change the surface characteristics of the workpiece through mechanical deformation without additional materials, not only to enhance the friction (friction coefficient can be increased by 300%-500%) and to achieve anti-slip function, but also to cover up the surface of the raw material micro defects, widely used in tool handles, instrument knobs, Hydraulic fittings and other occasions where reliable manual operation or mechanical connection is required.
What is the importance of knurling?
The importance of the knurling process is reflected in its irreplaceable engineering value: it meets strict standards such as MIL-STD-1913 in the military field, ensures no slippage when operating with blood in medical equipment, and maintains the reliability of pedals in extreme weather in automobile manufacturing, this surface treatment not only improves functionality (such as a 72% increase in grip after knurling a certain type of aviation wrench), but also achieves aesthetic unity of industrial products through standardized textures (such as the German DIN82 standard), It directly affects the service life and operational safety level of the product.
What are the two reasons for knurling?
From an engineering point of view, knurling is mainly based on two rigid needs: the first is the functional rigid demand, such as the hydraulic joint knurled without additional anti-slip structure can transmit higher torque (the torque capacity of a certain type of joint is increased by 40%), and the second is the process economy, compared with laser engraving or micro sandblasting, the knurled single piece processing time can be shortened to 3-5 seconds and the tool life is more than 50,000 pieces, especially suitable for mass production, At the same time, the surface texture depth (usually 0.1-0.3mm) that meets the requirements of IP54 protection level can only be reached by knurling at one time.
What are the advantages of knurling?
The knurling process integrates multiple advantages: outstanding cost-benefit ratio (60% cost savings compared to spraying anti-slip layer), excellent physical properties (the texture has the same life as the substrate, and 85% effectiveness is maintained after 2000 cycles of wear resistance test), wide adaptability (all kinds of metals up to HRC35 can be processed), and high process flexibility (12 standard patterns such as straight/anilox/twill can be quickly switched by changing rollers), which make it the most economical and reliable surface texture solution in the field of mechanical engineering. In particular, it occupies a leading position in the fields of auto parts and power tools, which need to balance function and cost.
