Modelling of straight-flute machine tapping

Abstract

As an important internal thread machining method, tapping is frequently among the final operations performed on elaborately transformed manufactures. The added value is often near its peak when the tapping operation is carried out. Consequently, conservative cutting conditions often are employed to avoid costly tap failure. Taps and tapping also are amongst the most complex and least understood cutting tools and processes. In this paper, the geometry and specification of straight flute taps are discussed, followed by an outline of the development of computer-aided predictive models for side force, thrust force, and torque in machine tapping, based on Armarego’s ‘Unified-Generalized Mechanics of Cutting Approach’. This approach allows processes to be modelled based on their cutting action and geometry only, with material properties provided from a generic database. Unlike other tapping modelling approaches, this is a truly predictive methodology. The models allow for the transient and steady stages and they include all the tap and tapping geometrical variables and the tapping conditions, as well as the tool–workpiece material properties. The models are verified through extensive numerical studies and a comprehensive experimental testing programme. Good qualitative and quantitative correlations are found between the predicted and measured average force components and torque. These models allow tool designers and process planners to optimize the generation and use of taps, thereby improving the competitiveness of this vital manufacturing operation. The results provide further evidence of the validity and generic nature of the unified-mechanics of cutting approach.