3-axis Milling Machine Research Articles

A novel energy demand modelling approach for CNC machining based on function blocks

Energy efficiency remains one of the major issues in the machining domain. Today's machining systems are confronted with a number of new challenges, such as turbulent product demand and variations in production resources. Rapid and flexible energy modelling in a distributed and collaborative machining environment emerges as a new research area. Energy demand models in such an environment need to be practical, accurate, effective, scalable and reusable. Energy analysis and optimisation cannot be carried out once for all at the beginning. Instead, it is an on-going process. In this paper, the function block technique, i.e. IEC 61499, is used for the development of energy demand models as it brings advantages such as modularity, encapsulation, extensibility and reusability. A brief review on energy modelling and research on function blocks are given in the first part. A novel energy demand modelling approach based on function blocks is then proposed and elaborated. Three types of function blocks have been developed, i.e. machine tool dependent function blocks, state transition function blocks, and service interface function blocks. The first type, as the fundamental building blocks, is divided into two sub-types, machine component function block and machining state function block. Two case studies, based on a small 3-axis milling machine and an industrial production line respectively, are presented to demonstrate the possible applications using the function block-based model. Comprehensive discussions are given thereafter, including a pilot application of a distributed process planning system and a unique energy evaluation scheme. A confidence level associated energy rating system is proposed as the first step to turn energy consumption figures into useful indicators. The energy demand model based on function blocks developed here enhances the energy modelling and their practical implementations.

Adaptive Robust Control of Circular Machining Contour Error Using Global Task Coordinate Frame

The contour error (CE) of machining processes is defined as the difference between the desired and actual produced shape. Two major factors contributing to CE are axis position error and tool deflection. A large amount of research work formulates the CE in convenient locally defined task coordinate frames that are subject to significant approximation error. The more accurate global task coordinate frame (GTCF) can be used, but transforming the control problem to the GTCF leads to a highly nonlinear control problem. An adaptive robust control (ARC) approach is designed to control machine position in the GTCF, while additionally accounting for tool deflection, to minimize the CE. The combined GTCF/ARC approach is experimentally validated by applying the control to circular contours on a three axis milling machine. The results show that the proposed approach reduces CE in all cases tested.

Integrated Dexels Geometric Model and Predictive Force Model for Feedrate Optimization in 03 Axis Milling Machine

Machining of sculptured surfaces engender abrupt variations in cutting forces, excessive tool deflections and undesirable vibrations and therefore poor surface finish. To reduce these problems and to have a stable machining it is more indispensable to select the appropriate cutting conditions. The aim of this paper is to propose an approach for determining the optimum feedrates along tool path during finishing of sculptured surfaces with ball end tools on 03-axis CNC milling machines using a predictive mechanistic model of cutting forces. Its steps are :1) approximation of the workpiece geometric model by dexels, 2) localization of the contact zones between tools and workpiece using machining simulation, 3) prediction of the cutting forces, 4) optimization of the feedrates and 5) updating of the machining program « G-Code ».

Position-Dependent Multibody Dynamic Modeling of Machine Tools Based on Improved Reduced Order Models

Dynamic response of a machine tool structure varies along the tool path depending on the changes in its structural configurations. The productivity of the machine tool varies as a function of its frequency response function (FRF) which determines its chatter stability and productivity. This paper presents a computationally efficient reduced order model to obtain the FRF at the tool center point of a machine tool at any desired position within its work volume. The machine tool is represented by its position invariant substructures. These substructures are assembled at the contacting interfaces by using novel adaptations of constraint formulations. As the tool moves to a new position, these constraint equations are updated to predict the FRFs efficiently without having to use computationally costly full order finite element or modal models. To facilitate dynamic substructuring, an improved variant of standard component mode synthesis method is developed which automates reduced order determination by retaining only the important modes of the subsystems. Position-dependent dynamic behavior and chatter stability charts are successfully simulated for a virtual three axis milling machine, using the substructurally synthesized reduced order model. Stability lobes obtained using the reduced order model agree well with the corresponding full-order system.

Integrated Geometric Error Compensation of Machining Processes on CNC Machine Tool

Kinematic errors due to geometric inaccuracies in machining system cause deviations of tool positions and orientation from being machined point on the workpiece, which consequently affect geometric accuracy of the machined surface. This paper presents an integrated geometric error model of machining system and compensation method on machine tools. Regarding a machine tool, fixtures, workpiece and tool as an assembly, an integrated geometric error model has been established. The integrated error is modeled by the propagation and the accumulation of errors based on Jacobian-Torsor theory. It is different with previous model, in this model, all the geometric errors of machining system are converted into the machine tool instead of the workpiece machining surface. As is well known in the machine tool, there are 21 geometric error of a 3-axis milling machine tool, which can be measured by laser interferometer. Based on this integrated model and machine tool error, the combination of geometric errors of machining system reflect on the machine tool can be predicted. Finally, a new compensation method is proposed to realize the error compensation, NC program is corrected corresponding NC codes according to the predicted errors during virtual machining before it is fed to the actual machining. A case demonstrates the application of how the method could be used in error compensation for machining processes.

Environmental Impact Characterization of Milling and Implications for Potential Energy Savings in Industry

Since machining is a prevalent process in product manufacture this study reviews the accuracy of a specific energy characterization model to predict the electrical energy consumed by a 3-axis milling machine tool during processing. The energy characterization model had an accuracy of 97.4% for the part manufactured under varied material removal rate conditions and highlighted the potential for energy reduction using higher cutting speeds. Interviews with cutting tool manufacturers and end users showed that there is a genuine potential for energy reduction during milling operations due to the extensive use of uncoated cutting tools in industry.

Algorithm for Smooth S-curve Feedrate Profiling Generation

The algorithms for feedrate profile generation,such as linear and S-curve profiles,have been widely used in machinery controllers,and these algorithms can greatly improve the smoothness of motion.However,most of the algorithms lead to the discontinuous acceleration/deceleration and jerk,or high jerk levels,which is very harmful to machine tool or robot in most occasions. This paper presents a smooth S-curve feedrate profiling generation algorithm that produces continuous feedrate,acceleration,and jerk profiles.Smooth jerk is obtained by imposing limits on the first and second time derivatives of acceleration,resulting in trapezoidal jerk profiles along the tool path.The discretization of smooth S-curve feedrate is realized with a novel approach that improves the efficiency without calculating the deceleration point in each sampled time.To ensure that the interpolation time is a multiple of the value of sampled time,the feedrate,acceleration,jerk,and jerk derivative are recalculated.Meantime,to improve the efficiency,the interpolation steps of all regions are computed before interpolation.According to the distance of trajectory,the smooth S-curve acceleration and decelerations are divided into three blocks:normal block,short block type-Ⅰ,and short block type-Ⅱ.Finally feedrate discretization of short block type-Ⅰand type-Ⅱis obtained with considering the efficiency.The proposed generation algorithm is tested in machining a part on a five axis milling machine,which is controlled with the CNC system for newly developed high-speed machine tools.The test result shows that the smooth S-curve approach has the smoother feedrate,acceleration,deceleration,and jerk profiles than S-curve.The proposed algorithm ensures the automated machinery motion smoothness,and improves the quality and efficiency of the automated machinery motion planning.

Experimental and numerical study of a milling machine-based dieless incremental sheet forming

In this paper, some relevant issues concerning an innovative sheet metal forming method, a milling machine-based Dieless Incremental Sheet Forming (DSF) will be analyzed. The experimental setup is based on the replacement of the commonly used dies by a second forming (Slave) tool where the movement is synchronized with the first forming (Master) tool, thus creating a flexible support. DSF can be used on both CNC machines [1] and industrial robots [2]. In this paper, the authors are only focusing on the experiments with a parallel kinematics 3-axis milling (PKM) machine with 3 additional linear actuators. The deformation state of the formed part will be analyzed using the Vialux-AutoGrid optical strain measurement system and will be compared to the results of 3D FEM modelling.

A Soft CNCS on Windows-XP

In this paper, a soft CNCS (Computerized Numerical Control System) works on Windows-XP operating system is presented. The comparison between soft CNC and traditional CNC system is discussed. The structure of soft CNC system is introduced as follow. The realizations of each real time module, such as real time path planning and interpolation, real time close-loop controller, real time safety detection, are introduced in detail. The real time tasks are based on a real time kernel. In the end, an application of the soft CNC system is realized on a 3-axis milling machine. The machining result shows it works well.

Development of a 3-axis desktop milling machine and a CNC system using advanced modern control algorithms

In this paper, we introduce a desktop-size 3-axis milling machine and a CNC system which was developed to operate the 3-axis milling machine. The 3-axis milling machine has a mini-desktop size of 200×300×200 mm3 and its cutting volume is 20×20×20 mm3. The vertically installed XY stage is driven by voice-coil motors, and for the zaxis, a magnetically preloaded air bearing and a linear motor are used. The air spindle runs at up to 160,000 rpm. The gravity force is acting on the y-direction, so a weight balancer using an air bearing cylinder is installed to cancel out the gravity force acting on the XY stage in the y-direction. The CNC system designed for the 3-axis milling machine consists of two parts. The one is a graphical user interface program which runs under Microsoft Windows and the other is a DSP program which is implemented on a DSP board with TI TMS320C6701 chips. A G-code interpreter is included in the CNC system which can interpret and interpolate a basic set of G-codes and M-codes in real-time. To improve the performance of servo control loop in the CNC system beyond the traditional PID-type control, several modern control algorithms have been tested including H∞ control, input shaping control, disturbance observer and cross-coupled control on the 3-axis milling machine. Experimental results show the effectiveness and drawbacks of each control scheme when they are applied to the 3-axis desktop milling machine.

Study on an Open CNC System of 3-Axis Micro Milling Machine Tool

The traditional CNC system is established on conventional machine tool mainly using ball screws. This could not suitable for micro mechanical machining with linear motor which could provide high speed, high precision, fast response and zero backlash. In this paper, a 3-axis micro milling machine tool with an open CNC system has been developed based on motion controller and linear motors. Considering the requirements of micro milling several special functions just like micro cutting tool setting are provided in exploited control software. The system dynamic characteristics are evaluated through experiments with servo parameters adjustments. In the following machining experiments, the whole system is proved economically and effectively.

Custom TMJ Hemi-joint Fabrication Process

Temporomandibular joint disorder afflicts 10 million Americans, many of whom have osteoarthritis of the temporomandibular joint (TMJ). This condition can inflict severe pain and disrupt the lives of sufferers in many ways. Partial or total replacement of the temporomandibular joint is a last resort treatment option. Surgeons at Mayo Clinic believe a new hemijoint implant design coupled with unique surgical technique can improve joint kinematics and reduce pain. They are currently investigating a patent-pending implant design in a series of patient trials. The Division of Engineering at Mayo Clinic has developed a novel process for fabricating TMJ implants for this study. Computed Tomagraphy (CT) images of the surgical site are first converted into a 3D computer model of the mandibular fossa and condyle area. A fused deposition modeling process is used to create a plastic model of the anatomy, and the surgeons use that model to create a wax mold of the implant. The wax mold is laser scanned to create a 3D CAD model that can be machined with a standard four axis milling machine out of implant grade CoCrMo material. Because of the unique shape of the implant, the machining takes place in two phases, with the implant being refixtured between machining phases using a high strength industrial adhesive. Finally, the implant is polished, inspected, passivated and sterilized for surgery. This fabrication process has allowed Mayo Clinic surgeons to quickly and accurately test their unique implant design.

A New Incremental Sheet Forming Process Based on a Flexible Supporting Die System

Nowadays many industrial sectors use forming processes in order to produce sheet metal components. The most widely used processes are stamping and deep drawing, which are based on big, costly dies and presses. These processes require large initial investment and specific dies for each part, which makes them inflexible and only profitable for large batches. A possible approach to small series production is based on the incremental sheet forming technique (ISF), which consists of a gradual plastic deformation of flat sheet metal by the action of a CNC controlled tool. Equipment such as a 3-axis milling machine can be used for ISF, such that the initial investment costs in ISF are around 5-10% of those required to set up a production line for conventional stamping. In its current stage of development, dedicated dies are often used as support tools in ISF. However, due to the fact that the forming forces are low in ISF, the dies can be made out of cheap materials like resin or wood. Although this is an additional advantage over stamping, the need to use additional tools still reduces the flexibility of the process. The present paper details the concept of a truly “dieless” incremental forming process. In the framework of the SCULPTOR EU project, the authors are working on an innovative concept of incremental sheet metal forming which is based on the replacement of the commonly used dies by a second forming tool which moves in a coordinated way with the first forming tool, thus creating a flexible die system, which does not depend on the specific geometry of the part to be formed. The present work summarizes the results obtained up to now in two fields: (i) the development of a prototype for the flexible die system to be included both in milling machines or combined with robots and (ii) process modelling to improve the understanding of the process.

Development of a PC-based Open Architecture Software-CNC System

AbstractAs a key technology in the field of advanced manufacturing, an open architecture controller is studied. In order to develop an open architecture software-CNC system on personal computer (PC) according to open modular architecture controllers (OMAC). First, the software and hardware platform is chosen and software realization methodology for the CNC system is determined. Second, static modeling methods of an open architecture controller inclusive of object-oriented (OO) programming technology, dynamic link library (DLL) technology and system modules partition are investigated. Third, the dynamical behavioral modeling and the data flow representation of open architecture controller are discussed, which are both described in hierarchy finite state machine (FSM) model. Fourth, a reusable software module model is established to develop software function module library. Finally, a 3-axis milling machine tool test-bed, named for HIT-CNC, is successfully designed by means of the constructed software function module library and the system configuring method. The experimental results show that, besides increasing the degree of reusability and openness, application of above-mentioned methodology leads to significant decrease of development time as well as maintenance cost.

Structural Design and Optimization of a 3-Axis Miniaturized Machine Tool with High Precision Positioning Stages

The procedure of structural design on miniaturized machine tool (mMT) is proposed and structural optimization by applying robustness evaluation method is presented in this paper. The design procedure of a kind of mMT which is a 3-axis miniaturized milling machine tool (mMMT) is discussed and three different structures of mMMT are proposed based on previous design procedure. The most suitable structure is selected using robustness evaluation method, which is Taguchi method, due to volumetric error function. The design parameters of selected structure are optimized.

Concave edge-based part decomposition for hybrid rapid prototyping

As one of the solutions to the limitations of the current layered manufacturing, hybrid rapid prototyping systems that perform both machining and deposition are being introduced. In the hybrid rapid prototyping, a part of a complicated shape is realized by adding layers of a simpler shape, each of which is obtained by machining a sheet of constant thickness from its top and bottom surfaces. Thus it is desired to decompose a given part into the minimum number of layers while guaranteeing each layer to be fabricated from the given sheets using a 3-axis milling machine. To satisfy these requirements, a concave edge-based approach is proposed to decompose a part into layers by considering the tool accessibility, the total number of layers, and the allowable sheet thickness. In this approach, for a given build-up direction, the undercut edges, which cause a part to be inaccessible by a tool, are extracted and classified into two types and eliminated in two decomposition steps.

Development of a high-speed 3-axis machine tool using a novel parallel-kinematics X-Y table

In this paper we discuss the development and performance evaluation of a high-speed, 3-axis milling machine using a novel parallel kinematics x-y table. The x-y table is based on a an inversion of the Oldham coupling. The advantages of this kinematic configuration include low inertia, uniform kinematic conditioning, and dynamically matched axes. The design of the x-y table makes this system particularly well suited for high-speed contouring in the x-y plane. The kinematics, dynamics, and mechanical design of the system are described. Linear and circular contouring experiments are conducted to evaluate the system capabilities. The stiffness of both the mechanism as well as the direct drive actuation system are measured and reported. The experimental results demonstrate that the proposed mechanism offers an attractive combination of performance characteristics for high-speed contouring and high-speed machining.

Geometric and force errors compensation in a 3-axis CNC milling machine

This paper proposes a new off line error compensation model by taking into accounting of geometric and cutting force induced errors in a 3-axis CNC milling machine. Geometric error of a 3-axis milling machine composes of 21 components, which can be measured by laser interferometer within the working volume. Geometric error estimation determined by back-propagation neural network is proposed and used separately in the geometric error compensation model. Likewise, cutting force induced error estimation by back-propagation neural network determined based on a flat end mill behavior observation is proposed and used separately in the cutting force induced error compensation model. Various experiments over a wide range of cutting conditions are carried out to investigate cutting force and machine error relation. Finally, the combination of geometric and cutting force induced errors is modeled by the combined back-propagation neural network. This unique model is used to compensate both geometric and cutting force induced errors simultaneously by a single model. Experimental tests have been carried out in order to validate the performance of geometric and cutting force induced errors compensation model.

Timber for High Efficiency Small Wind Turbine Blades

This paper explores technical and other issues arising from using shaped timber for a 1 metre long high efficiency blade for a small 600 W wind turbine. Two readily available Australian grown softwood timber species, radiata pine and hoop pine, were selected. Reasons for selecting these timbers are detailed in the paper. The fatigue life of the both timbers was determined using four point flexural testing. Results show that hoop pine is 25% stronger and 6% more fatigue resistant than radiata pine. A fatigue test procedure for the 1 m blade has been created based on the aeroelastic response of a 2.5 m long composite wind turbine blade and wind data from the Australian Bureau of Meteorology. Blade fatigue-life predictions, using Miners rule for fatigue damage accumulation, indicated effectively unlimited fatigue-life for a blade constructed from hoop pine, with the turbine operating at design performance in wind speeds up to 20 m/s. The blade's life was reduced to a few months when it was constructed from radiata pine for the same operating conditions to 20 m/s. However for an upper wind speed of 17 m/s, the predicted blade fatigue-life is effectively unlimited for both species. Test blades were machined in both radiata pine and hoop pine on a 3-axis milling machine with tool paths created using Pro/Manufacture software. Some of the important issues with respect to creating the blades out of timber are discussed.

Automated tool sequence selection for 3-axis machining of free-form pockets

This paper describes an efficient method to find the lowest cost tool sequence for rough machining free-form pockets on a 3-axis milling machine. The free-form pocket is approximated to within a predefined tolerance of the desired surface using series of 2.5-D layers of varying thicknesses that can be efficiently removed with flat-end milling cutters. A graph-based method finds an optimal sequence of tools for rough machining the approximated pocket. The algorithm used here can be tuned to suit any available tool set and preferred cost models. The tool sequence that is obtained is near optimal, and may take into account tool wear, as well as various overhead costs of the machine shop.