Search

Featured Application: The algorithm presented in this work could find useful application in advanced toolpath definition for milling operations when non-uniform (i.e., variable) machining allowance is desired. In milling, the advancement of CAM strategies has increased the need for tailored algorithms for semi-finished phase computation. In some cases (e.g., thin-wall milling), variable radial engagement of the tool during the toolpath is desired, leading to the need of non-uniform machining allowance on the component that could be achieved only with a non-uniform offset algorithm, i.e., offset where the distance to the initial contour varies along that input. This work presents a general algorithm for non-uniform offset of polyline curves. The approach is based on 2D polygons and Boolean union operation, following these steps: (i) projection segments are generated, (ii) polygons (trapezoids and circular sectors) are created, (iii) Boolean union of all the polygons is performed, (iv) boundary of interest is extracted. The proposed algorithm is able to handle both internal and external offset and is robust for complexity of both the polyline and variable offset magnitude along that line, as proven by several examples and two applications to thin-wall milling provided. [ABSTRACT FROM AUTHOR]

Among the chatter suppression techniques in milling, active fixtures seem to be the most industrially oriented, mainly because these devices could be directly retrofittable to a variety of machine tools. The actual performances strongly depend on fixture design and the control logic employed. The usual approach in the literature, derived from general active vibration control applications, is based on the employment of adaptive closed-loop controls aimed at mitigating the amplitude of chatter frequencies with targeted counteracting vibrations. Whilst this approach has proven its effectiveness, a general application would demand a wide actuation bandwidth that is practically impeded by inertial forces and actuator-related issues. This paper presents the study of the performance of alternative open-loop actuation strategies in suppressing chatter phenomena, aiming at limiting the required actuation bandwidth. A dedicated time-domain simulation model, integrating fixture dynamics and the features of piezoelectric actuators, is developed and experimentally validated in order to be used as a testing environment to assess the effectiveness of the proposed actuation strategies. An extensive numerical investigation is then carried out to highlight the most influential factors in assessing the capability of suppressing chatter vibrations. The results clearly demonstrated that the regenerative effect could be effectively disrupted by actuation frequencies close to half the tooth-pass frequency, as long as adequate displacement is provided by the actuators. This could sensibly increase the critical axial depth of cut and hence improve the achievable material removal rate, as discussed in the paper. [ABSTRACT FROM AUTHOR]

Tool-tip frequency response function (FRF) is essential to predict chatter vibration in milling. This key input can be acquired by experimental tests, but a new test has to be performed for every tool clamped on the machine. To avoid such time-consuming procedures, receptance coupling methods have been developed, allowing coupling of the experimental dynamic response of the machine to the numerical model of the tool. Such techniques require joint rotation response, which is hard to experimentally identify. Inversion of receptance coupling technique is usually performed on additional experimental measurements to overcome this issue. This procedure amplifies measurement uncertainties, reducing accuracy of the coupling approach. In this article, a novel receptance coupling technique is presented. Machine and toolkit are connected through two distinct points, eliminating the experimental phase and computation of rotational degrees of freedom (DOFs). Only translation responses are required, acquired by a single test setup. Proposed technique was experimentally validated on different case studies. [ABSTRACT FROM AUTHOR]

Tool-tip Frequency Response Function (FRF) represents one of the essential inputs to predict chatter vibration and compute the Stability Lobe Diagram (SLD). Tool-tip FRFs are generally obtained for the stationary (non-rotating) condition. However, high speeds influence spindle dynamics, leading to a reduced accuracy of the SLD prediction. This paper presents a comprehensive method to identify speed-varying tool-tip FRFs and improve chatter prediction. First, FRFs for a screening tool is identified by a novel technique based on a dedicated experimental test and analytical stability solution. Then, a tailored receptance coupling technique is used to predict speed-varying tool-tip FRFs of any other tool. Proposed method was experimentally validated: chatter prediction accuracy was demonstrated through chatter tests. [ABSTRACT FROM AUTHOR]

The mitigation of chatter vibrations in milling has collected the interest of several researches in the last decades. One of the most industrially oriented alternatives is represented by active fixtures, complex mechatronic devices capable of actuating the workpiece during machining operations, with the purpose of stabilizing the process by generating counteracting vibrations. Most of the previous works show different fixture architecture and model based control techniques. This paper deals with the development and testing of such an active fixture, presenting the main design aspects and the features of the black-box control-logic used. Experimental tests are presented to show the achievable chatter mitigation. [ABSTRACT FROM AUTHOR]

Combining Additive Manufacturing (AM) and traditional machining processes is essential to meet components functional requirements. However significant differences arise in machining AM and wrought parts. Previous works highlighted the increasing of tool wear and worse surface finish. In this paper cutting forces are investigated as an indicator of material machinability. Milling cutting force coefficients are identified using mechanistic approach, comparing AISI-H13 wrought and AM specimen. Cutting force behaviour was investigated for two AM technologies: laser deposition (LENS) and wire-arc additive manufacturing (WAAM). Results show a general increase of cutting forces and coefficients of both AM materials, suggesting AM parts reduced machinability. Therefore, different cutting parameters should be selected for the AM material to achieve a sustainable production. [ABSTRACT FROM AUTHOR]

Active fixtures represent one of the most industrially relevant alternatives among active chatter control techniques in milling, even though control logics and actuation strategies could directly reflect on their effectiveness. Closed-loop controls targeted in the chatter frequency range are commonly adopted for this purpose, but this approach lacks of applicability when chatter frequency exceeds the achievable actuation bandwidth. The purpose of this work is to investigate the effectiveness of potential low-frequency actuation strategies in suppressing chatter vibrations. A dedicated time-domain simulation model, developed and validated by authors, is used to test different actuation strategies in order to highlight the most relevant factors in assessing actuation effectiveness. The simulation results demonstrated that employing actuation frequencies close to the first half-harmonic of the tooth-pass frequency could disrupt the regenerative effect. This allows the mitigation and suppression of chatter phenomenon, increasing the critical axial depth of cut, as discussed in the paper. [ABSTRACT FROM AUTHOR]

Receptance coupling substructure analysis (RCSA) allows to estimate tool-tip FRF of different spindle-holder-tool configurations with the minimum set of measurements. This technique requires accurate holder-tool connection modelling. In this paper fully predictive modelling strategies of holder-tool connection are presented. Proposed procedures are implemented in FE environment, without the use of any tuning experimental test, using solid elements to model the most common connection types. The main advantage of proposed approaches is to model the entire toolkit without requiring lumped stiffness and iterative procedures. Resulted toolkit FE model can be used in RCSA providing accurate tool-tip FRF for chatter prediction. [ABSTRACT FROM AUTHOR]

Repairing, remanufacturing, and refurbishing high value metal components are crucial to move towards a more sustainable economy. Nowadays, repairing operations on high value parts, such as dies, are generally performed using time-consuming manual approaches that rely on the operator's expertise. The research idea of this paper is to develop a retrofit kit to provide additive capabilities to an existing milling machine, allowing automatic repairing of components thanks to a fast switch between additive and machining operations without a relevant economic investment such the acquisition of a brand-new machine: the final cost of the solution is lower than 10% with respect to the mean cost of a 5-axis milling machine. The additive technology used in this work is Wire Arc Additive Manufacturing (WAAM) that is characterized by a higher deposition rate and a simpler and cost-effective equipment with respect to other techniques (e.g., laser cladding). The design of the system is illustrated in the paper together with the analysis of the results achieved repairing a test case: a die casting mold made of AISI H13 tool steel. [ABSTRACT FROM AUTHOR]

In 3-axis milling, cutting force analysis represents one of the main methods to increase the quality and productivity of the process. In this context, cutting force shape gives information of both monitoring and prediction of the cutting process. However, the cutting force shape is not unique, and it changes according to the cutting strategy, tool geometry, and cutting parameters. This paper presents a comprehensive approach to predict and classify cutting force shapes in 3-axis milling operations. In detail, the proposed approach starts by classifying the cutting force shapes for a single fluted endmill (i.e., single flute force shape), and, considering how the single flute force shapes may overlap one another, it extends the classification to a general multiple-fluted endmill. Moreover, the method provides, through analytical equations, angles, and magnitude dimensionless parameters of each key point, describing each shape classified. Finally, the proposed approach was experimentally validated through several milling tests in different cutting conditions. [ABSTRACT FROM AUTHOR]

In peripheral milling, surface accuracy is crucial for the quality of the machined components, and it is one of the reasons why milling is still essential in the manufacturing field. Nonetheless, both static phenomena, like tool deflections, and dynamic issues such as forced vibrations, impact on the accuracy of the components causing surface errors. In this context, the prediction of surface error is an important tool to guarantee surface accuracy and increase productivity at the same time. This paper presents a novel approach to predict surface location error in 2.5-axis peripheral milling operations considering the stiffness variation along the axial depth of cut. The proposed approach discretizes the endmill in small discs, and it evaluates analytically the cutting force along the cross-feed direction for each disc in the frequency domain. Then, tool dynamic stiffness, which is expressed in terms of frequency response function (FRF), is computed considering the stiffness variation along the tool axis. Finally, the presented approach couples the cutting forces with the tool stiffness, and it evaluates surface error along the tool axis. The method was experimentally tested in different conditions to verify its effectiveness and its limits. The results obtained show how static and dynamic aspects and stiffness variation contribute to surface errors in peripheral milling operations. [Display omitted] • Surface location error along the axial depth of cut in 2.5-axis milling is accurately predicted. • Analytical formulations for cutting forces in frequency domain are proposed. • A RCSA-based approach to predict tool FRF variation along the axial depth of cut is presented. • The proposed approach considers both forced vibrations and variation of the tool dynamic stiffness. • Accuracy of the method is proven by experimental validation on several milling tests. [ABSTRACT FROM AUTHOR]

Abstract: Due to the urgent need for global reductions of environmental impacts, many studies have been carried out in different fields. One of the most important sectors is manufacturing, particularly due to the high power consumption of the production machines of manufacturing plants. This paper focuses on the efficiency of the machining centres and provides an experimental approach to evaluate and optimize the process parameters in order to minimize the power consumption in a milling process performed on a modern CNC machine. The parameters evaluated are the cutting speed, the axial and radial depth of cut, and the feed rate. A lubrication strategy has been chosen based on previous studies: all the tests have been carried out using dry lubrication in order to eliminate the environmental impact due to lubricant without substantially affecting the energy consumption. The process has been analyzed using a Response Surface Method in order to obtain a model fit for the fine tuning of the process parameters. [Copyright &y& Elsevier]