Machine Tool Users Research Articles

Proposal of a Machining Test to Evaluate Dynamic Synchronization Error of Rotary and Linear Axes With Reversal of Rotation Direction

Abstract The five-axis machining of a free-form surface often contains the reversal of a rotary axis’ rotation direction with linear axis synchronized with it. This paper proposes a new machining test to quantitatively evaluate the influence of the reversal of rotation direction on the surface geometry and roughness. In the five-axis machining, the trajectory of tool position and orientation is first given in the workpiece coordinate system (WCS) by the computer-aided manufacturing (cam) software, and the computerized numerical control (CNC) system converts it to the machine coordinate system (MCS) to calculate command trajectories. This paper clarifies that the tool path smoothing in the MCS can potentially cause a large contour error because of the dynamic synchronization error of rotary and linear axes. Although some academic works in the literature presented the smoothing in the WCS, many commercial CNC systems still employ the smoothing in the MCS, partly because machine tool users or makers do not clearly see how significant this influence can be on the machining accuracy. The proposed machining test enables a user to quantitatively evaluate it. The machining experiment shows that the geometric error of the finished test piece was as large as 0.16 mm under the conventional smoothing in a commercial CNC system, which can be significantly larger than the influence of other typical geometric errors of a five-axis machine tool. This paper shows, by numerical simulation, that the smoothing in the WCS can completely eliminate this contour error.

A Smart Tool Holder Calibrated by Machine Learning for Measuring Cutting Force in Fine Turning and Its Application to the Specific Cutting Force of Low Carbon Steel S15C

Real-time monitoring of the cutting force in the machining process is critical for improving machining accuracy, optimizing the machining process, and optimizing tool lifetime; however, the dynamometers are too expensive to be widely used by machine tool users. Therefore, this paper presents a simple and cheap apparatus—a smart tool holder—to measure the cutting force of turning tools in the finishing turning. The apparatus does not change the structure of the turning tool. It consists of a tool holder and a piezoresistive force sensor foil, and transmits the signal through Bluetooth wireless communication. Instead of dealing with the circuit hardware, this paper uses the Artificial Neural Network (ANN) model to successfully calibrate the warm-up shift problem of the piezoresistive force sensor. Such a software method is simple, and considerably cheaper than the hardware method. For the force measurement capability of the smart tool holder, the cross-interference between orthogonal forces are very small and thus can be ignored. The force reading of the smart tool holder possesses high repeatability for the same turning parameters and high accuracy within the experiment groups. The authors apply the smart tool holder to cut the low carbon steel S15C, and to determine its specific cutting force in fine turning. The resulting fine turning force model agrees very well with the measurement. Its mean absolute deviation is 3.87% and its standard deviation is 1.55%, which reveals that the accuracy and precision of the smart tool holder and the fine turning force model are both good.

A new measurement system to determine stiffness distribution in machine tool workspace

This paper presents an innovative system determining machine tool quasi-static stiffness in machining space, so-called Stiffness Workspace System (SWS). The system allows for the assessment of the accuracy of a machine which has become a vital aspect over past years for machine tool manufacturers and users. Since machine tools static stiffness is one of the main criteria using to evaluate the machines' quality, it is crucial to highlight the relevance of experimental and analytical stiffness determination methods. Therefore, the proposed method is applied to estimate the spatial variation of static stiffness in the machine tool workspace. This paper describes the SWS system—its design, working principle, mounting conditions and signal processing. The major advantage of the system is the capability to apply forces of controlled magnitude and orientation as well as simultaneously measure the resulting displacements. The obtained results give possibility to estimate and evaluate static stiffness coefficients depending on the position and direction under loaded conditions. The results confirm the validity of the analyses of spatial stiffness distribution in the machine workspace.

OPTIMIZATION OF CNC PARAMETERS ACCORDING TO PRODUCTIVITY CRITERIA USING A MACHINE MODEL BASED ON NEURAL NETWORKS

Every machine-tool user wants to maximize the productivity of their machines looking for balance between speed, precision and lifetime of mechanical components. Nevertheless, because CNCs have wide-ranging use, their correct parametrization for each case is key to achieving the desired objectives; on the other hand, minimizing the numbers of experimental tests to be performed on the machine is essential to reduce time and costs of the set-up process. In order to solve both difficulties, this paper presents a tool to give final user necessary information to properly adjust CNC parameters according to productivity criteria. The method makes use of experimental data to obtain a model of the machine based on neural networks. With this model machining time, geometric error and smoothness of any piece to be manufactured can be predicted, and therefore minimizing test on the real machine and recommending the appropriate values for the CNC. Keywords: optimization, CNC, neural network, model, machine tool, productivity criteria.

Accuracy in Detecting Failure in Ballscrew Assessment towards Machine Tool Servitization

Many manufacturers, in particular machine tool builders, aim for service innovation in order to improve their market competitiveness. Machine tool trading companies expect to create a value-added process through shifting from just selling product i.e. machine tools to selling an integrated combination of product and services, so called product-service system (PSS) which in turn competes with other developing companies. This is the process of servitization. The purpose of this work is to explore the benefits of servitizing machine tool industry and identify the effect of such an approach on the performance of engineering companies. As important, is to evaluate the accuracy of components as part of predictive maintenance, to support machine tool sevitization. This paper proposed a case study of ballscrew performance assessment. The purpose was monitoring the degradation of two parallel ball screws in a 5-Axis gantry machine tool, based on data from an acoustic emission sensor and machine learning technology. The significance of this work is that ballscrew performance as part of machine tool accuracy is critical for high value manufacturing. Machine tool users would prefer their machines to be maintained to the required tolerance by the predictive maintenance service warranty offered by the machine trader and keep their machines up to date to reduce unnecessary downtime.

Special Issue on Active and Passive Vibration Damping in Machine Tools

Automation of machine tools has made them more productive, thereby providing an advantage for sustainability and the welfare of mankind. However, in many cases, the successful automation of machine tools requires the avoidance of self-excited chatter vibrations, resulting in a reliable stable state for cutting. Machine tool operators tend to use the machines close to their power thresholds, thereby unknowingly driving them toward the limits of their stability. Much progress has been made in the last few decades concerning the understanding and prediction of such vibrations, and this has led to improvements such as higher cutting rates and chip thicknesses. Several countermeasures such as active and passive damping are available for avoiding chatter vibrations in machine tools. However, their industrial use is not common yet. In fact, the industry is somewhat unfamiliar with many of these countermeasures. The hesitant attitude of the machine tool builders to apply such countermeasures is a result of several factors: active and passive damping devices are additional system components that require design, tuning, and maintenance. Furthermore, they are associated with a risk of failure, resulting in additional down times of the machines. Additionally, if a machine requires such devices to achieve the desired specifications, the customer’s opinion regarding it can be negatively affected. This situation is challenging for machine tool builders, users, and academia as well. Therefore, we decided to dedicate a special issue of IJAT to this topic. This special issue focuses on both active and passive damping measures, particularly the measures that are systematically designed and deliberately implemented to increase the chatter-free depth of cut in machine tools. The papers in this issue identify successful applications or at least a vision for them. Additionally, models demonstrating the effects of the chosen active or passive damping systems are presented. Some of these models can also be used to systematically select the parameters of the system. Some of the systems can be easily applied as low-cost patch-up solutions to improve the behaviors of the machines already in use. I hope that this special issue delivers a valuable overview of the existing approaches to introduce additional damping in machine tools. I would like to sincerely thank all the authors for their dedication and the well written and illustrated manuscripts. I would also like to thank the reviewers for their efforts to ensure the quality of this issue. Finally, I am very thankful to IJAT for their immense cooperation and support. I wish you all the best and hope that you can benefit from the content of this special issue.

Metrological analysis of a mechatronic system based on novel deformation sensors for thermal issues in machine tools

The precision as well as the production rate of machine tools are starkly dependent on thermal issues. In order to minimize this influence, manufacturers are bound to warm-up procedures before production can begin, so that the machine tool thermal state has stabilized. On the other hand, design optimization and cooling techniques cannot eliminate all errors and call for higher investment costs for the machine tool user. Either through acquiring a new, thermally stable machine or through higher energy consumption, these measures are also not always applicable. Hence, it remains the task for a mechatronic system to capture as much information as possible about the thermal state of the machine tool and take corrective measures during production. A novel mechatronic system that measures directly the thermally induced deformations has been developed to fulfil this task. The measurement uncertainty, as well as the reliability of this mechatronic system are the two crucial properties that define whether this can be applied successfully in the industry. This paper summarizes the investigations on the measurement uncertainty of the proposed system, both analytical and experimental. The functionality of the system was verified on a second test rig, as well as on a vertical machining center, which build the basis for future reliability analyses.

Measurement Parameters Optimized for Sequential Multilateration in Calibrating a Machine Tool with a DOE Method

Improving volumetric error compensation is one of the machine tool user’s key objectives. Smart compensation is bound to calibration accuracy. Calibration quality depends largely on its setup factors. An evaluation criterion is thus required to test the quality of the compensation deduced from these setup factors. The residual error map, which characterizes post-compensation machine errors, is therefore chosen and then needs to be evaluated. In this study, the translation axes of a machine tool were calibrated with a multilateration tracking laser interferometer. In order to optimize such measurements, the residual error map was then characterized by two appliances: a laser interferometer and the tracking laser already employed for the calibration, using for that purpose the sequential multilateration technique. This research work thus aimed to obtain a smart setup of parameters of machine tool calibration analyzing these two residual error maps through the Design Of Experiment (DOE) method. To achieve this goal, the first step was to define the setup parameters for calibrating a compact machine tool with a multilateration tracking laser. The second step was to define both of the measurement processes that are employed to estimate the residual error map. The third step was to obtain the optimized setup parameters using the DOE method.

Latest development of a new standard for the testing of five-axis machine tools using an S-shaped test piece

It has been generally recognized that it is very important for industrial users to test the performance of high-accuracy numerical control machine tools before ordering them. Methods based on special devices such as Double Ball Bar and R-test are currently used for kinematic error measurement and compensation of five-axis machine tools. However, these methods need special devices and software, and industrial machine tool users prefer testing machine tools by physically machining a special workpiece, due to its simplicity and intuition, as doing such machining tests are just like manufacturing parts in real production. On the other hand, since existing machining tests such as cone frustum test piece fail to reflect the dynamic performance of five-axis machine tools, it has drawn a lot of attention to the development of a new machining test method to address this issue. This article introduces a new machining test standard that has been proposed for testing the accuracy of five-axis machine tools using an S-shaped test piece. This method has already been accepted by the International Standard Organization and is now under development for inclusion in ISO 10791 Part 7. The advantages of the S-shaped test method in testing machining performance of five-axis machine tools are analyzed and demonstrated in this article. Furthermore, new development has been made to simplify the definition, reduce the testing workload and improve the measurement accuracy of the proposed testing method.

Framework of a Machine Tool Configurator for Energy Efficiency

The energy consumption behavior of installed machine tools and manufacturing systems are nowadays well evaluated and the field of action for comprehensive improvements and optimization activities is open. Despite the possible improvement potential of installed machine tools, its implementation is limited due to constrains such as high investment costs with unknown amortisation time for the machine tool reconfiguration. The planned configuration of components tailored to the machine tool's target use is seen as a promising way to address the expected energetic performance in the configuration phase using detailed multichannel measurements and knowledge of past improvement activities.A modular configuration approach, based on multichannel measurements, in order to improve the energy efficiency of the machine tool, including all auxiliaries, is not present yet. In conjunction with a case study, this paper introduces a concept for a machine tool configurator to integrate the requirements for the energy use during the use phase of the machine tool and its components. Beyond this, the paper provides information for TCO calculations and investment decision.The integrated approach enables machine tool builders to optimize the machine tool configuration, select components in order to increase energy efficiency and achieve cost savings for the machine tool user, in line and validated with the machine tool builder's business case.

A new approach to contour error control in high speed machining

High speed machining technology attempts to maximize productivity through the use of high spindle speeds and axis traverse rates. The technology is dependent upon the development of suitable mechanical hardware, electrical drives and associated control software to ensure that all components are used to maximum advantage. The role of the control software is particularly demanding since one needs to maximize traverse rates while providing the necessary accuracy, and indeed providing a margin of safety to deal with unexpected changes in process, or system parameters. There have been relatively few improvements in commercial CAD or CAM systems that would help machine tool users to take maximum advantage of high speed machining; rather the majority of the approaches have been undertaken at the machine tool controller level. This paper uses circular interpolation and corner tracking to compare several such control techniques, (Cross Coupled Control (CCC), Zero Phase Error Tracking Control (ZPETC), and Realtime Frequency Modulated Interpolation (FMI)), each of which have been proposed in the literature order to improve machining accuracy. None of these approaches are found to be universally successful when used alone and the authors, in this paper, examine the use of these systems in combination. Particular attention is focused upon an extension of a simplified version of cross coupled control together with Frequency Modulated Interpolation. It is shown that the combined system performs extremely well, and is easily actuated at high frequencies with conventional hardware. A custom built high speed x-y table is used to confirm system performance with multiple constraints present.

Research to the Overall Design of 4-Axis VMC Based on CAD and NC Mfg Verification

The author studied the 4-axis Vertical MC (VMC)，designed and created its general layout feature mode in one CAD platform (the author used Solidworks) with the engineer’s natural thought manner: topdown. The 4-axis VMC’s NC machining simulation is also carried out in one NC mfg verification tool (the author selected Vericut), and the conformability and compatibility are confirmed. The following conclusions can be summarized: the modern NC machine tool designer and user can promote their production quality, efficiency, cost reduction goals with the help of the integration between the CAD and NC mfg verification technology.

ANALYSIS OF PARAMETERS AFFECTING THE QUALITY OF A CUTTING MACHINE

The quality of cutting machines is affected by several factors that can be directly or indirectly influenced by manufacturers, technicians and users of machine tools. The most critical qualitative evaluation parameters of machine tools include accuracy and stability. Investigations of accuracy and repeatable positioning accuracy were essential for the research presented in this paper. The aim was to develop and experimentally verify the design of a methodology for cutting centers aimed at achieving the desired working precision. Before working on the topic described here, it was necessary to make several scientific analyses, which are summarized in this paper. We can build on the initial working hypothesis that by improving the technological parameters (e.g. by increasing the working speed of the machine, or by improving the precision of the positioning) the quality of the cutting machine will also be improved. For the purposes of our study, several investigated parameters were set affecting positioning accuracy, such as rigidity, positioning speed, etc. First, the stiffness of the portal structure of the cutting machine was analyzed. FEM analysis was used to investigate several alternative structures of the cutting machine, and also an innovative solution for beam mounting. The second step was to integrate two types of drives into the design of the cutting machine. The first drive is a classic rack and pinion drive for cutting machines. To increase (improve) the working speed of the machine, linear motors were designed as an alternative drive. The portal of the cutting machine was designed for a working speed of 260mmin−1 and acceleration of 25 m. s−2. The third step was based on the results of the analysis. In collaboration with Microstep, an experimental cutting machine in a portal version was produced using linear synchronous motors driving the portal on both sides, and with direct linear metering of its position. In the fourth step, an experiment was designed and conducted to explore the positioning accuracy and the repeatable positioning accuracy.

A morphology proposal in commercial-off-the-shelf reconfigurable machine tools

Global manufacturing is continuously facing changing demands, the unpredictable part family supply that a machine tool user has to deal with needs varying machine morphologies. The reconfigurable manufacturing system paradigm proposes the need for the right capacity, for the right demand with an economical ramp-up period. The machinist needs to have a systematic manner of configuring the machines, given a set of modules that will be configured and reconfigured for the various demands in the lifespan of a manufacturing system. In this article, the author proposes how the machinist can go about identifying the different morphologies in advance. The method is simple and user-friendly in consideration of the main users who may have basic skills being deficient in sophistication and complexity; it further assists in the determination of the capability the manufacturer has with the available modules.

Sustainable Service System for Machine Tools

Quick and correct service is most important for machine tool users. In order to maintain efficiency of machine tools at customers’ sites, remote maintenance and monitoring system, worldwide spare parts supply system, integration of service parts, education system for service engineers, long-term environmental load reduction are necessary. This paper presents current and future activities of machine tool manufacturers for improving the service system.

Machine tool optimization strategies for ecologic and economic efficiency

Optimization activities in manufacturing must be addressed in the multifaceted context that combines economic, social and environmental goals. Research activities of today not only strive to cope with the legislative pressure of the Directive of the European Parliament on Energy Using Products but also strive for economic advantages for the machine tool user by investigating and applying suitable procedures and methods that help to model, forecast and reduce overall energy consumption. A key issue is the reduction of the amount of resources consumed for the same output and the increased machine tool efficiency with the help of selective methods and a minimum investment. A bottom-up approach to identify potential initial points for optimization is given in the presented research work. This article introduces a methodology for detecting and evaluating reasonable investments for retrofit solutions with different approaches. A technical measurement and optimization approach, depending on the actual circumstances, and an economic approach, that is used to detect optimization potentials with the economic evaluation of selected solutions are proposed in this article.

Guest editorial: IJAMT special issue on: product-service systems

Manufacturing industries are shifting their offerings from selling a physical product to sell functions through product-service system (PSS) business model. This enables manufacturing companies to generate more revenue and better satisfying and exceeding customer expectations. The PSS has great impacts on the product life cycle, the customer and the relationship between the product, business processes, organisational structure and cost. Therefore, there is increasing need to understand these challenges and issues that are critical to the success of developing PSS. Scenarios of PSS in different industrial domains are required to illustrate the implementation success factors of such model. Several manufacturing organisations have passed through this transformation and have good insight and knowledge about the challenge. There is a need to enhance multidisciplinary research in the PSS area. This Special Issue of the International Journal of Advanced Manufacturing Technology presents ten selected papers that cover state of the art research in a number of PSS areas. Some of these papers have been selected from the proceedings of the 6th International Conference on Manufacturing Research (ICMR 2008) held at Brunel University, UK on 9–11 September 2008. This special issue commences with two papers on PSS for machine tool industry. Greenough and Grubic’s paper focuses on modelling condition-based maintenance to deliver a service to machine tool users. The paper describes the development and validation of two software tools to explore the relationship between prognostics and health management technologies and servitization in the machine tool industry. The second paper presents the concept of an industrial product-service system for CNC machine tool (mt-iPSS) based on the provision and enhancement of machining capabilities by Zhu et al. An architecture is proposed to enable the mt-iPSS from the aspects of both hardware and software. Huang et al. investigate how the new concept of PSS can be used and extended to transform, elevate and revitalise traditional equipment manufacturing industry such as the mould and die sector. PSS encompasses several challenges in terms of innovation, organisation structure, information flow and uncertainties. Lee and Abu Ali in their paper present an operating system for innovation by offering a methodology for systematic innovative thinking and a toolbox of interconnected tools that can aid in the transformation of core product competencies into effective product-service amalgamations. An approach for a modular organisation structure with the extension of modular organisation units is described by Meier et al. The structure is supporting the flexible use of resources of networking companies. Planning the resources for the integrated PSS delivery is a complex problem that also needs new planning methods. The metaheuristic optimisation strategy is an approach to establish a real-time planning and control. Durugbo et al. present a review of diagrammatic information flow tools which are designed to describe a system through its functions. A case study of selection lasermelting technology implemented as PSS has been employed to show the application of information flow modelling for PSS design. Mittermeye et al. argue that although PSS possess great potential, the health care sector has not given an attention of the research community. They E. Shehab (*) :R. Roy Decision Engineering Centre, Manufacturing Department, Cranfield University, Building 50, Cranfield, Bedfordshire MK43 0AL, UK e-mail: e.shehab@cranfield.ac.uk

Modelling condition-based maintenance to deliver a service to machine tool users

This paper describes the development and validation of two software tools to explore the relationship between prognostics and health management (PHM) technologies and servitization in the machine tool industry. The software tools are based on software tools that were originally developed to analyse the costs and benefits of PHM technology in the aerospace industry. The development was initiated following an extensive review of relevant literature on both servitization and PHM technology. This review revealed the fact that the servitization literature makes almost no mention of the use of PHM technology to support servitization and the PHM literature makes almost no mention of the servitization business model that might justify expenditure on this technology. The tools model the life cycles of two sets of machine tools, with and without PHM technology, before calculating the net present value of the costs and benefits of PHM in the context of a servitization business model. Although the data used in the tools are hypothetical, the approach taken in the models was validated through interviews with a major machine tool vendor. This research extends existing knowledge on servitization as published in the management literature by linking it to research into PHM as published in the systems engineering literature. The paper concludes by indicating the need for more empirical data on the reliability of machine tool subsystems in order to increase confidence in the value of PHM technology to support machine tool servitization.

A mechanism for linking user's operational requirements with reliability and maintenance schedule for machine tool

Historically, designers have done a good job of evaluating the functions and forms of products in the design phase. However, it is only in the past few years that there appears to be an increased focus on evaluating end user's reliability and maintenance requirements at the design phase. Especially in case of machine tools, where the machines are used by different users with different operational requirements, optimal reliability and the corresponding maintenance policies may vary from one user to another user. It is therefore essential for the designer to have mechanisms that link the machine reliability and maintenance parameters with the user's operational requirements. In this paper, we have identified the users' operational requirements through discussion with the managers of machine tool manufacturers and user industries. Inputs from literature survey have also been taken into consideration. A mechanism to link operational requirements with machine tool reliability and maintenance parameters is proposed. Use of such a mechanism in decision making is also demonstrated with the help of examples.

A Comparative Method of Analysis for Evaluating Sheet Metal Machine Tool Flexibility

In the machine tool sector, for production purposes, flexibility and automation are elements that play conflicting roles because greater automation generally means less flexible production. As a result, it is not easy to choose between technologies that have different degrees of automation or may even be manual. We are therefore proposing a comparative method of analysis that can be used to evaluate one machine tool with respect to another, which is used as a reference. This combination leads to the identification of breakeven points on productivity, flexibility and automation that, when taken together, provide criteria for evaluating the economic suitability or unsuitability of the choice in hand. This comparative model rotates around evaluation variables that have long been consolidated and recognized by sheet metal machine tool manufacturers and users.