Improvement of boring operations by means of mode coupling effect

Boring bars are inherently slender tools which are prone to show chatter problems due to their low dynamic stiffness and damping, being this problem their main limitation in productivity. The onset of chatter is mainly related to the dynamic stiffness of the bending mode of the boring bar when the length L to dia-meter D ratio is higher than 4. Tuned mass dampers (TMD) are effective technical solutions to increase the dynamic stiffness of large ratio boring bars. However, there are many applications where 4-6 L/D ratio tools are required, and the avoidance of chatter without the application of TMDs is interesting due to the high cost of damped tools. This work proposes the use of mode coupling effect to increase the damping and stabilise the machining process avoiding the use of any special device. This effect occurs when the fre-quency of one of the machine's modes is similar to the frequency of the dominant mode of the boring bar. As a result, the shape of the critical mode of the boring bar is mixed with the mode originated in the machine, and the damping and stability will be higher than the one that is not subjected to any dynamic coupling. The main contribution of this work is the application of this concept to increase stability in boring operations. This objective has been achieved by optimising the tool length and material by means of a dynamic model based on Receptance Coupling Substructure Analysis (RCSA). The model combines an analytical model of the elastic body of the boring bar with the experimental characterisation of the effect of the rest of the machine. This way, the shape and materials of the boring bar can be optimised to create an increase of damping. The optimisation procedure has been experimentally validated resulting in an increase of cutting stability and demonstrating that not always a shorter bar supposes a higher stability.The authors thank the collaboration of Markel Sanz from IDEKO. This work has been supported by EUROSTARS FORTH E!12998 pro-ject and the EU Horizon 2020 InterQ project (958357/H2020-EU.2.1.5.1)

Comparison of Modulation-Assisted Machining Strategies for Achieving Chip Breakage When Turning 17-4 PH Stainless Steel

Chip morphology is an intrinsic characteristic of the machining process that determines the quality of the process. When machining low machinability materials, the chips formed are usually long, continuous, and difficult to break. Due to the negative effect of the accumulation of the chip along the process, chip breakage and the correct extraction out of the machining area have become indispensable requirements. Although numerous chip-breaking methodologies have been proposed, modulation-assisted machining (MAM) is one of the most promising approaches, due to its independence from the workpiece material, tool geometry, and cutting conditions. In this work, a comparison of different modulation-assisted machining strategies, based on the modulation of the feed (F-MAM) or the depth of cut (D-MAM), were experimentally evaluated and compared to conventional turning in terms of chip morphology, surface roughness, and tool wear. Results showed that both MAM strategies enabled chip breakage and improved chip evacuation in comparison to conventional turning; however, D-MAM showed a better performance in terms of tool wear and surface roughness.This research was partially funded from the European Union’s Horizon 2020 Research and Innovation. Programme under the project InterQ (grant agreement No. 958357), and it is an initiative of the Factories-of-the-Future (FoF) Public Private Partnershi

Improvement of boring operations through novel chatter suppression and chip breakage techniques.

Los capítulos 5,7, 9, 10 y 11 están sujetos a confidencialidad por el autor. 283 p.El objetivo de este trabajo de investigación es proponer nuevas técnicas para reducir los problemas limitantes de las operaciones de mandrinado: la evacuación de viruta y las vibraciones autoexcitadas.Como herramienta para el desarrollo de soluciones, se ha llevado a cabo un modelado dinámico del proceso de mandrinado, compuesto por un modelo dinámico de barras y un modelo mecatrónico. Por una parte, el modelo de barras tiene en cuenta la rigidez y el amortiguamiento del amarre, lo que permite una estimación precisa de su comportamiento dinámico. Por otro lado, se ha desarrollado un modelo mecatrónico que permite simular la estabilidad del proceso en el dominio temporal, incluyendo las técnicas de rotura de viruta y los actuadores inerciales. El problema de la rotura de viruta se ha abordado mediante la técnica del mecanizado asistido por modulación (MAM), desarrollando un algoritmo automático que selecciona los parámetros óptimos para su aplicación en operaciones de mandrinado pesado. Además de ello, se han estudiado varias técnicas para suprimir las vibraciones autoexcitadas en operaciones de mandrinado. Por un lado, se propone el acoplamiento modal entre los modos de la barra de mandrinar y de la máquina para los casos de esbeltez intermedia. Por otro lado, las soluciones activas permiten cubrir un mayor rango de esbeltez, por lo que se ha diseñado un nuevo actuador basado en fuerzas de reluctancia. Finalmente, se ha realizado una comparación estricta entre el amortiguamiento proporcionado por medio del dispositivos activos y el que proviene de los sistemas de guiado

The curved uncut chip thickness model: A general geometric model for mechanistic cutting force predictions

The curved uncut chip thickness model is introduced to predict the cutting forces for general uncut chip geometries using the mechanistic approach. Classical geometric models assume that the cutting force is distributed along straight elementary sections of the uncut chip area, which has limited physical validity, but makes mathematical treatments easier for simple cases. The new model assumes that the flow of the material on the contact area of the tool is given by a continuous vector field, according to which the curved uncut chip thickness is measured. The cutting force is distributed along these paths, which leads to a mathematically unique and consistent solution for regular and complex cutting edge geometries. These curved paths can be generated by basic mechanical models, which mimic the more realistic motion of the chip segments along the rake face, without the need of explicit time-consuming cutting simulations. The presented computational procedure generalizes cutting force prediction based on geometric parameters, orthogonal cutting data and the orthogonal to oblique transformations only. The effectiveness of the model for various cutting edge geometries (e.g., thread turning inserts) under extreme cutting conditions is presented in case studies, laboratory and industrial experiments

Damping in ram based vertical lathes and portal machines

Chatter vibrations originated by the machine structure are a major limitation for the productivity of ram based machines performing heavy duty operations. Consequently, the damping of the machine structure has a capital importance. It is known that interfaces and guideways are the main origin of damping. Recently, the use of active dampers has been introduced in industry. In this work, the damping of hydrostatic and rolling guideways with and without active damping has been experimentally identified and compared using receptance coupling. The results show that hydrostatic guidance can introduce 3–4 times more damping than a roller based system. However, the introduction of active damping is a game changer enhancing damping more than 30 times.The authors thank the collaboration of Dr. H. Urreta, I. Berrotaran, A. Perez and F. Wahab from IDEKO. This work has been partially supported by EU H2020 COGNIPLANT (869931) and CDTI-CERVERA MIRAGED (CER-20191001) projects