Cutting and forming taps - Resources and practices

Screw connection is widely used in the mechanical engineering sector, as this solution meets serviceability requirements in terms of strength and rigidity, and allows for operational constraints such as the possibility of disassembly. The field of screw connection is vast and relatively complex, as it combines a number of technological elements: different thread geometries, steel grades, coatings, tolerances, dimensioning and assembly conditions. The manufacture of screwed assemblies requires the production of internal threads, and the above-mentioned elements need to be taken into account when obtaining them. The machining entity that is the thread is therefore not a surface like any other, since its function - assembly - is clearly defined, and its production must meet numerous specifications.

Over 80% of internal threads are currently manufactured using a tapping technique, which can be either cutting or forming. Mastering a tapping technique is therefore essential for the manufacture of mechanical parts. What's more, this operation generally takes place at the end of the machining process, or even at the end of the manufacturing process. As a result, any failure during the tapping process results in a loss of both the value of the raw part itself, and the value added by all previous operations. For parts with very high added value, which it is therefore unacceptable to scrap, it is therefore necessary to carry out the necessary rework following a failed tapping operation. These rework operations are delicate and costly, which is why precautions are generally taken when tapping, in particular by reducing the criticality of the operation by lowering operational parameters such as cutting speed.

Tapping techniques are tricky to master in many respects. On the one hand, the kinematics of the process are not straightforward, and there are many different types of tool, differing if only in their geometry. On the other hand, the study of tapping requires the consideration of technological parameters other than the tool and its conditions of use, namely: the pilot hole, the attachment, the machine and its programming, as well as the workpiece pick-up.

This article focuses on tapping methods and the different tapping practices that exist. It lays the foundations for the analysis that will be carried out in the second part. , on tapping techniques at the tool tip.