Knurling is a process used to create a pattern on the surface of a material by displacing or deforming the surface. The objective is to increase the friction on a surface and is typically performed on a lathe to cylindrical parts.
Diamond knurl seems like a screw or a pin. It’s composed of two main parts. The bottom section with thread, and the upper section with diamond knurl. Diamond knurl is a typical part produced by lathing. During the CNC turning process, a cutting tool removes material from the outer diameter of a rotating workpiece. The main objective of turning is to reduce the workpiece diameter to the desired dimension.
Selection of appropriate knurling tools
The first step of the CNC turning process for diamond knurling involves carefully selecting an appropriate knurling tool tailored to your application needs.
The type of knurling pattern
The type of knurling pattern determines the shape and orientation of the knurl. There are three basic types of knurling patterns: straight, diagonal, and diamond. Straight knurls produce parallel lines on the workpiece, diagonal knurls produce angled lines, and diamond knurls produce a criss-cross pattern.
The choice of knurling pattern depends on the desired appearance and function of the part. For example, straight knurls are often used for cylindrical parts that need to be rotated, such as knobs and handles. Diagonal knurls are suitable for parts that need to be pushed or pulled, such as levers and switches. Diamond knurls are commonly used for decorative purposes or for parts that require a high degree of grip, such as thumb screws and nuts.
The pitch for the knurling
The pitch of a knurl is the distance between two adjacent grooves and should match the workpiece’s diameter to create a clear and uniform pattern. If the pitch is too large or too small, it may result in double tracking or skipping, causing the knurl to not form a complete pattern.
To avoid this, use a pitch-diameter chart or calculator to determine the optimal pitch for a given diameter, or use a variable-pitch knurl that adjusts its pitch according to the workpiece’s diameter.
Setup of CNC turning machines for diamond knurling
Lathing includes many types of processes, for example, turning, step turning, taper turning, chamfer turning, and contour turning. Step turning helps to make the step of knurling, and contour turning helps make the spherical face. In contour turning operation, the cutting tool axially follows the path with a predefined geometry. Multiple passes of a contouring tool are necessary to create desired contours in the workpiece.
The whole knurling process should start with locating, then setting the machine, and getting ready to knurl. To perform this process, several factors and steps must be considered.
Aligning the knurling tool with the workpiece
The knurling tool should be mounted on a tool post or turret, perpendicular to the workpiece axis. The knurling wheel should align with the workpiece’s center or slightly above it, and the face of the knurls is parallel to the workpiece. Check the alignment using a dial indicator or a test cut.
Programming the CNC lathe
The CNC lathe programming for knurling operation can be controlled using G-code commands or CAM software. The spindle speed should be low to prevent heat and vibration.
The feed rate should match the knurling wheel’s pitch, when processed with a medium feed, it is necessary to keep the speed slow. The depth of the cut should be sufficient to create a uniform pattern without plastic deformation or burrs, and the length of the cut should cover the entire knurled area.
Applying sufficient coolant to the knurling tool and workpiece
Coolant is essential for reducing friction, heat, and wear in knurling tools and workpieces, improving surface quality. Water-based or oil-based coolants can be used based on workpiece material and preference. The knurling process can be monitored and checked using magnifying glasses or microscopes to adjust parameters or replace tool accordingly.
Optimization of machining parameters for achieving desired knurl characteristics
- Response Surface Methodology (RSM)
Utilizing RSM, professionals systematically identify optimal machining parameters. RSM involves designing a series of experiments to explore the relationships between various variables, including material properties, tool specifications, and knurling outcomes. By creating predictive models from these experiments, precise machining parameters can be determined, reducing the need for trial and error.
- Finite Element Analysis (FEA)
FEA is a tool that allows for a comprehensive simulation of the knurling process. Experts use FEA to predict the effects of different machining parameters on the knurling operation. It provides insights into how material properties, tool geometry, and process variables interact, enabling professionals to optimize parameters and foresee potential challenges before actual machining.
- Machine Learning Modeling
Machine learning algorithms are employed to develop predictive models that can determine optimal machining parameters based on historical data. These models consider a wealth of information, such as past machining parameters, material characteristics, tool details, and knurling results. By learning from this data, machine learning models become valuable resources for predicting the most effective parameters for specific workpiece materials and knurling tools.
Conclusion
For perfect knurl patterns, experts carefully pick materials and tools, then adjust settings just right. They even use smart techniques like RSM, which is like planning, FEA for predicting, and machine learning for knowing what works best. This makes sure the knurling is just how they want it.
