Knurling is a machining process used to create grooves on the surface of metal components. In the past, it was used to restore worn mating surfaces on shafts and hubs. However, with the spread of mass production and the reduction in the cost of spare parts, this use has declined.
Yet, knurling still allows the recovery of play between worn couplings and has specific applications where static or dynamic sealing is required. Some of the most common sectors in which it is used include the automotive industry, mechanical engineering and watch manufacturing.
Let's find out below what knurling is, how it works and what it is used for.
What is Knurling and what is it for?
As you can read in our Glossary, knurling is a production process for engraving the surface of a metal part. Its main purpose is to create a knurling, which provides a better grip and offers a more finished aesthetic appearance. It is a special kind of machining, as no chip removal occurs in the recess variant.
In the design phase, it is essential to ensure the feasibility of the work. It is not uncommon to receive drawings that propose knurling patterns that are almost impossible to realise, due to the geometry of the design or the type of material chosen. Close collaboration between the designer and the machine operator is therefore required to ensure that the end result is feasible and meets the desired specifications.
From a technical point of view, knurling is performed using knurling rollers and CNC lathes. The machining parameters must be carefully defined according to material and fit. After machining, dimensional checks certify the conformity of the knurling.
How Knurling is Done
The correct execution of knurling requires special attention to detail. The lathe speed must be kept low to avoid imperfections. The use of the tailstock is essential to prevent possible deformation or breakage of the workpiece due to fatigue. In addition, it is essential to lubricate the rollers, or wheels, with oil to ensure smooth rotation.
When it comes to knurling tools, it is essential to consider several factors such as robustness, precision, stability and technological know-how. Only high-quality tools guarantee optimal results, provided they are used by highly qualified personnel.
Knurling can be performed through two main methods: roughing and knurling.
The removal method is a process in which material is physically removed from the surface of the object in question. This process is generally carried out through the use of cutting tools or other abrasive methods.
Choosing the excision route results in very precise surfaces, at the cost of some discomfort. Although the quality of the result is not to be questioned, the production of waste is an element to be considered. In addition, it has some practical limitations: it is only possible to resort to stock removal when facing knurled items from the mouth, and then only for RAA and RGE knurling.
The tracing method, as the name suggests, does not involve removing material from the surface. Rather, it works by deforming and displacing existing material to create a desired design or pattern. This is often achieved by pressing a tool or mould onto the surface.
The tracing method can be likened to processes such as engraving or stamping. One of its most striking features is that it preserves the integrity of the material, minimising waste. It is particularly effective when you want to create surface details or patterns without altering the overall geometry of the object.
However, it is essential to ensure that the material in question can withstand deformation without being damaged or creating internal stresses that could compromise its structural integrity.
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