Chatter in machining process is one of the common failures of a production line. For a cantilever tool, such as a boring bar, the rule of thumb requires the overhang length of the tool to be less than 4 times the diameter. The reason is because longer overhang will induce severe tool vibration in the form of chatter during machining. When a longer overhang than 4 times diameter is necessary for performing special machining operations, damping methods are needed to suppress tool chatter. One of the methods is the constrained layer damping method. Materials, such viscoelastic material, are applied in the vibration node regions of the structure to absorb the concentrated vibration strain energy and transform the mechanical energy to heat. With a cantilever tool clamped in a tool holder, the clamping interface is usually the vibration node region. The friction in the joint interface with low normal pressure became another source of damping and can be used for tool chatter suppression in mechanical structures. Joint interfaces are well known to possess normal pressure dependent stiffness and damping. The normal pressure’s effect on the structures frequency response function had been observed by H. Åkesson [1] et al, and L.Mi [2] et al. However, the direct effect of the joint interface normal pressure on machining process stability hasn’t been investigated. In this paper, a cantilever tool with 6.5 overhang length to diameter ratio is investigated. The direct effect of the tool clamping interface’s normal pressure on the machining process stability is studied. Three different levels of clamping normal pressure are tested with an internal turning process. The machining results indicate another adaptable solution on shop floor for suppressing tool chatter.

Machining dynamic stability has been enhanced through a damping coating based on a novel carbon-based nanocomposite material. The coating was synthesized using a plasma enhanced chemical vapor deposition method, and deposited on to the round-shank boring bar used for internal turning and tested during machining. Comparisons between an uncoated and a coated boring bar were carried out at 0.25 mm and 0.5 mm depth of cut using a five times length to diameter ratio overhang, which are typical conditions known to generate detrimental mechanical vibrations. From sound pressure measurement it was found that the measured absolute sound level during process could be reduced by about 90% when using the tool coated with damping layer. Surface roughness measurements of the processed workpiece showed decreased Ra values from approximately 3-6 mu m to less than 2 mu m (and in 50% of the cases < 1 mu m) when comparing an uncoated standard tool with its coated counterpart. Moreover, it was found that the addition of an anti-vibration coating did not adversely affect other tool properties, such as rigidity and modularity.

A computation model based on inverse receptance coupling method is presented in this paper aiming for obtaining the joint interface's stiffness and damping properties using frequency response functions measured on assembled structures only. In the model, it is emphasized that the joint stiffness and damping should be modeled with frequency dependency. The model's validity is checked both through finite element (FE) simulation and experimental analyses. In the FE simulation example, the computation model gives more accurate results with noise-free data. In the experimental example, where noise in the data is unavoidable, the computation model is explored further for its applicability in the real industrial environment. Results from applications of the computational model show that it is even capable of obtaining the joint interface stiffness and damping values over the structure's resonance frequency. A viable process of predicting behaviors of workpiece with receptance coupling method through identifying the joint interface properties is presented in the end of the paper. The applicability of this computation model and the factors that influence the accuracy of the model are discussed in the end of the paper.

Multi-layered nanostructured Cu and Cu-CNx composites synthesized by plasma-enhanced chemical vapour deposition were applied in the clamping area of a milling tool to suppress regenerative tool chatter. Scanning electron microscopy analysis showed a multi-layered nanostructure with excellent conformality, i.e. coating is not only uniform on planar surfaces but also around corners of the substrate. Cu:CuCNx nanostructured multilayers with thicknesses of approximately 0.5:1.6 mu m were obtained. With a diameter of 20 mm, the milling tool performed slotting processes at an overhang length of 120 mm. Modal analysis showed that a coating, with a thickness of approximately 300 mu m, can add sufficient damping without losing stiffness of the tool, to increase the critical stability limit by 50% or 100% depending on cutting direction.

A hybrid joint interface module (HJIM) was developed using viscoelastic materials’ (VEM) “incompressible” property. The HJIM composes VEM layers compressed by screws. Its static stiffness and damping had been characterized by inverse receptance method. The analysis result showed that its static stiffness increases by nearly 50 % with increasing compression preload without compromising its loss factor. A comparison study of HJIM with a viscoelastic material joint interface module (VJIM) revealed that the change of the screws mechanical contact conditions affected the HJIM’s stiffness. Compression preload by fastening the screws, however, did not significantly affect the damping property of the HJIM. On the contrary to shear pre-strain, compression preload did not affect the VEM’s properties shown by studying the VJIM case. A workpiece was studied while fixed on the HJIM. Varying compression preload affected the stiffness of HJIM and that resulted in increased shear strain in VEM for certain modes while decreased shear strain in VEM for other modes. The affected shear strain in VEM altered the vibrational strain energy distribution and changed the receptance amplitude of different modes. In addition to apply the VEM where it is significantly strained, the analysis revealed that constraining the shear strain in VEM resulted in reduced receptance amplitude for different modes. The changes of receptance will further affect the vibration conditions in machining.

Nanostructured Cu:CuCN_x composite coatings with high static and dynamic stiffness were synthesized by means of plasma-enhanced chemical vapor deposition (PECVD) combined with high power impulse magnetron sputtering (HiPIMS). Scanning electron microscope (SEM) images and energy-dispersive X-ray spectroscopy (EDS) mapping from cross-sectioned samples reveals a multi-layered nanostructure enriched in Cu, C, N, and O in different ratios. Mechanical properties of the coatings were investigated by Vickers micro-indention and model tests. It was observed that copper inclusions as well as copper interlayers in the CN_x matrix can increase mechanical damping by up to 160%. Mechanical properties such as hardness, elastic modulus and loss factor were significantly improved by increasing the discharge power of the sputtering process. Moreover the coatings loss modulus was evaluated on the basis of indentation creep measurements under room temperature. The coating with optimum properties exhibited loss modulus of 2.6 GPa. The composite with the highest damping loss modulus were applied on the clamping region of a milling machining tool to verify their effect in suppressing regenerative tool chatter. The high dynamic stiffness coatings were found to effectively improve the critical stability limit of a milling tool by at least 300%, suggesting a significant increase of the dynamic stiffness.