Metal Cutting Dynamics

  Metal cutting is one of the most commonly used methods of producing the final shape of manufactured products. Improved productivity is of essence for the industry in order to stay cost effective at a competitive market. Vibrations in metal cutting constitute a large part in hindering the productivity during machining. Excessive vibrations can lead to for example: accelerated tool wear, tool breakage, poor surface finish of the machined component and damage to the spindle bearings. Fast and accurate simulation routines and measurement methods for machining dynamics are very important in the development of new cutting tools.

  The research is carried out by an industrial PhD student working 50% with AB Sandvik Coromant and 50% with the structural analysis group, ensuring a close cooperation between industry and university. The project focuses on methods for simulation and measurements of both linear and nonlinear dynamics within metal cutting. Vibration damping is often a key factor in increasing productivity. Most damping materials used today show some form of hysteretic behavior. 

  Therefore, measuring and modeling of nonlinear systems with hysteresis is an important part of the research (figure 1).

Figure 1 – Nonlinear hysteretic damper used to attenuate vibrations in a cutting tool

  To aid the product development, computer based simulation routines for nonlinear mechanical systems incorporating both structural nonlinearities as well as nonlinear behavior originating from the cutting process (for example: cutting forces and regenerative/self‐exciting vibrations) are developed. These simulation models are continuously verified by experimental measurements. An important factor when validating simulation models is reliable estimation of cutting forces. Correct measurements of cutting forces can be difficult to obtain because of unwanted dynamic effects from the measurement setup (force dynamometer and work piece). These dynamic effects can lead to erroneous results and make it difficult to validate the model. A method to remove unwanted dynamic effects while still keeping information related to the true cutting forces have been developed and tested with good results.

  Examples of currently ongoing projects are, surface error prediction of a machined component using dynamic simulations and optimization of differential pitch cutters.