Tool Clamping Research Articles

A Time Domain Simulation Approach for Micro Milling Processes

Prediction of Process Machine Interactions (PMI) can be achieved using models for conventional milling processes in the time and frequency domain. However, instabilities such as regenerative chatter can also be observed in micro milling processes using filigree cemented carbide end mills. The dominant chatter frequencies are basically related to the end mills eigenfrequencies. Nevertheless, the dynamic characteristics of the machine tool structure and the work piece must not be neglected. In this paper a comprehensive time domain process model is presented. The machine tool dynamics are considered as non-coupled oscillators based on measured frequency response functions at the tool holder. The end mill is modeled as rotating Euler-Bernoulli beam with variable boundary conditions at the tool clamping. At first, the parameter identification for a geometric cutting force model is described. It contains the cutting edge radius as a time-depended parameter. Thereafter, the modeling and parameter identification of the structural parts are presented. A stability criterion is defined with special regard to the tool deflection at the TCP. Finally, simulation results at different stable and unstable operating points for full immersion cutting are discussed in detail and compared to experimental tests.

A shape memory alloy based tool clamping device

The traditional collet-chuck mechanism for tool clamping is a significant source of errors in spindles due to stack-up tolerances. This, in turn, adversely affects the tool's error motions particularly in demanding micro-cutting operations performed with ultra-high-speed miniaturized spindles. Hence, novel thought for miniature tool clamping is needed to minimize tool run-out and error motions in order to meet the necessary cutting speeds and accuracy requirements. In this paper a couple of Shape Memory Alloy (SMA) based solutions for the clamping of miniature tools will be explored. For clamp actuation the so-called Two-Way Shape Memory Effect (TWSME) property of NiTi SMAs will be exploited. The basic principles, design requirements, analysis and physical realization of these devices will be discussed. It will be shown through experimental verification tests that clamping forces in excess of tens of Newtons are possible, confirming thus the feasibility of the proposed solutions.

Experimental Analysis of the Deviation from Circularity of Bored Hole Based on the Taguchi Method

In this study, the effects of cutting parameters, boring tool material and the overhang ratio of boring tool (tool clamping length) on the deviation from circularity of a bored hole were examined experimentally. The optimal cutting condition can be estimated by the analysis of the signal to noise (S/N) ratio in Taguchi method. The individual contributions of each factor on the deviation from circularity were calculated by using the Analysis of Variance (ANOVA). Therefore, at the determined condition, it could be observed whether a factor is significant or not. Also, it was observed that the values of deviation from circularity increased significantly with an increase in the effective tool length at the lower depth of cut values. In addition, the circularity could be improved with increasing the depth of cut values for the same tool clamping lengths.

Evaluation of the stiffness chain on the deflection of end-mills under cutting forces

This study presents the investigation of the stiffness of the system formed by the machine-tool, shank and toolholder, collet and tool. Cutting forces induce the deflection of the system, and consequently an error appears on the machined surface. Comparing values obtained from cantilever beam models applied to the cutting tool, analytical or FEM, with those experimentally obtained, large differences have been observed, which in some cases are more than 50%. For this reason, we have proceeded to evaluate the stiffness of each of the existing elements between the machine bed and the tool tip. Thus, deflections of the machine-tool, toolholder and toolholder clamping in the spindle, tool clamping in the toolholder, and tool itself, were measured experimentally under the effects of known forces. The final application is the ball-end milling of complex surfaces, an operation commonly performed in the finishing of moulds or forging dies, where errors of more than 70 μm are not unusual. A great part of this error comes from the deflection of the machine-tool assembly, spindle, shank and tool, due to the high cutting forces of the high speed machining of tempered steels. Cutting forces can be estimated using a semi-empirical approach, and from here some values of probable errors may be taken into account to check if the CNC programs are sufficiently adapted. However, a previous study of the deflection chain in the cutting process is needed, as is presented in this work. Results show that stiffness of the slender and flexible tools is 15 times lower than that of the machine and toolholder system. But this correlation is only 5–7 times lower for shorter and thicker tools.

Tooling Structure: Interface between Cutting Edge and Machine Tool

With a significant progress achieved both in new cutting materials and in machine tool design, the weakest link in the machining system is, in many cases, the tooling structure serving as an interface between the cutting insert and the machine tool. Inadequacy of the tooling structure results in excessive static deflections limiting the achievable accuracy, and in forced and self-excited vibrations limiting the cutting regimes and surface finish of the machined surface. In order to advance the tooling structures' technology, it is important to assess the state of the art, keeping in mind that the majority of publications on the subject is not in English. This paper provides a worldwide analytical survey on six important subjects related to tooling structures. 1) Influence of machining system parameters on tool life and process stability; 2) Stiffness and damping of tools; 3) Tool/toolholder interfaces (tool clamping devices); 4) Modular tooling; 5) Tool-machine interfaces; 6) Tool balancing for high speed machine tools

Dynamic performance improvement of an electrical discharge machine using an experimental design method and experimental modal analysis

An orthogonal array method is used in the design of experimental variables for the identification of their effects on the dynamics of the tool-head system of an electrical discharge machine. The purpose of the identification was to develop formulae for the prediction of resonant frequencies under a given configuration of the machine, so that the servo motor driving frequency at which the tool-head system was excited in the vertical direction could be maximized. Modal tests were carried out on the tool-head system to determine the weakest point of the most problematic dynamic mode and it was found to be the tool clamping device, which was therefore modified. The improvements are shown in terms of the resonant frequencies, the vibration magnitudes and the mode shapes.