Modeling dynamics of parallel turning operations

Parallel turning operations are advantageous in terms of productivity since there are more than one cutting tools in operation. However, the dynamic interaction between these parallel tools may create additional stability problems and the advantage of parallel turning may not be utilized to full extent. For that reason, dynamics and stability of parallel turning processes need to be modeled. In this paper, dynamics of two different parallel turning operations where two turning tools cut a common workpiece are modeled. In the first case, the tools are directly coupled to each other whereas in the other case the coupling occurs through the vibration waves left on the workpiece. For these two cases, stability models in frequency and time domain have been developed. The frequency and time-domain solution results are compared and a reasonable agreement is observed. The predicted stability limits are also compared with experimental results where good agreement is demonstrated

Machining stability and machine tool dynamics

Machining is a common manufacturing process in industry due to its high flexibility and ability to produce parts which excellent quality. The productivity and quality in machining operations can be limited by several process constraints one of which is the self-excited chatter vibrations. Under certain conditions, the process may become unstable yielding oscillations with high amplitudes which result in poor surface finish and damage to the cutting tool, part and the machine tool itself. Stability analysis of the dynamic cutting process can be used to determine chatter-free machining conditions with high material removal rate. Since chatter is a result of the dynamic interactions between the process and the structures both cutting and machine tool dynamics are important elements of the stability analysis. In this paper, methods developed for stability analysis of cutting processes and machine tool dynamics will be presented. Implications of these methods in the selection of process parameters and machine tool design will be also discussed with example applications

Analytical stability models for turning and boring operations

In this paper an analytical model for stability limit predictions in turning and boring operations is proposed. The multi-dimensional model includes the 3D geometry of the processes. In addition a model for the chip thickness at the insert nose radius is also proposed to observe the effect of the insert nose radius on the chatter stability limit. Chatter experiments are conducted for both turning and boring in order to compare with analytical results and good agreement is observed

Atomistic aspects of ductile responses of cubic silicon carbide during nanometric cutting

Cubic silicon carbide (SiC) is an extremely hard and brittle material having unique blend of material properties which makes it suitable candidate for microelectromechanical systems and nanoelectromechanical systems applications. Although, SiC can be machined in ductile regime at nanoscale through single-point diamond turning process, the root cause of the ductile response of SiC has not been understood yet which impedes significant exploitation of this ceramic material. In this paper, molecular dynamics simulation has been carried out to investigate the atomistic aspects of ductile response of SiC during nanometric cutting process. Simulation results show that cubic SiC undergoes sp3-sp2 order-disorder transition resulting in the formation of SiC-graphene-like substance with a growth rate dependent on the cutting conditions. The disorder transition of SiC causes the ductile response during its nanometric cutting operations. It was further found out that the continuous abrasive action between the diamond tool and SiC causes simultaneous sp3-sp2 order-disorder transition of diamond tool which results in graphitization of diamond and consequent tool wear

Regenerative chatter in self-interrupted plunge grinding

This research is supported by National Natural Science Foundation of China under Grant Nos.11572224 and 11502048, and Fundamental Research Funds for the Central Universities under Grant No. ZYGX2015KYQD033. We would like to thank Dr. Pankaj Wahi for an initial discussion during YY’s stay in Aberdeen.Peer reviewedPublisher PD

Surface roughness variation of thin wall milling, related to modal interactions

High-speed milling operations of thin walls are often limited by the so-called regenerative effect that causes poor surface finish. The aim of this paper is to examine the link between chatter instability and surface roughness evolution for thin wall milling. Firstly, the linear stability lobes theory for the thin wall milling optimisation was used. Then, in order to consider the modal interactions, an explicit numerical model was developed. The resulting nonlinear system of delay differential equations is solved by numerical integration. The model takes into account the coupling mode, the modal shape, the fact that the tool may leave the cut and the ploughing effect. Dedicated experiments are carried out in order to confirm this modelling. This paper presents surface roughness and chatter frequency measurements. The stability lobes are validated by thin wall milling. Finally, the modal behaviour and the mode coupling give a new interpretation of the complex surface finish deterioration often observed during thin wall milling

Analytical prediction of chatter stability for variable pitch and variable helix milling tools

Regenerative chatter is a self-excited vibration that can occur during milling and other machining processes. It leads to a poor surface finish, premature tool wear, and potential damage to the machine or tool. Variable pitch and variable helix milling tools have been previously proposed to avoid the onset of regenerative chatter. Although variable pitch tools have been considered in some detail in previous research, this has generally focussed on behaviour at high radial immersions. In contrast there has been very little work focussed on predicting the stability of variable helix tools. In the present study, three solution processes are proposed for predicting the stability of variable pitch or helix milling tools. The first is a semi-discretisation formulation that performs spatial and temporal discretisation of the tool. Unlike previously published methods this can predict the stability of variable pitch or variable helix tools, at low or high radial immersions. The second is a time-averaged semi-discretisation formulation that assumes time-averaged cutting force coefficients. Unlike previous work, this can predict stability of variable helix tools at high radial immersion. The third is a temporal-finite element formulation that can predict the stability of variable pitch tools with a constant uniform helix angle, at low radial immersion. The model predictions are compared to previously published work on variable pitch tools, along with time-domain model simulations. Good agreement is found with both previously published results and the time-domain model. Furthermore, cyclic-fold bifurcations were found to exist for both variable pitch and variable helix tools at lower radial immersions

Machining strategy development in 5-axis milling operations using process models

Increased productivity and part quality can be achieved by selecting machining strategies and conditions properly. At one extreme very high speed and feed rate with small depth of cut can be used for high productivity whereas deep cuts accompanied with slow speeds and feeds may also provide increased material removal rates in some cases. In this study, it is shown that process models are useful tools to simulate and compare alternative strategies for machining of a part. 5-axis milling of turbine engine compressors made out of titanium alloys is used as the case study where strategies such as flank milling (deep cuts), point milling (light cuts) and stripe milling (medium depths) are compared in terms of process time by considering chatter stability, surface finish and tool deflections

Toolpath dependent stability lobes for the milling of thin-walled parts

The milling of thin-walled parts can become a seriously complex problem because the parts have variable dynamics. Firstly, the dynamics evolution of the part has been calculated through Finite Element Method (FEM) analysis. Then, the 3D stability lobes have been calculated for the thin walls and the thin floor. Finally, several milling tests have been performed in order to validate the predictions made by the model