Multi-axis Machine Research Articles

Optimizing Build Orientation for Support Removal using Multi-Axis Machining

Parts fabricated by additive manufacturing (AM) are often fabricated first as a near-net shape, a combination of intended nominal geometry and sacrificial support structures, which need to be removed in a subsequent post-processing stage using subtractive manufacturing (SM). In this paper, we present a framework for optimizing the build orientation with respect to removability of support structures. In particular, given a general multi-axis machining setup and sampled build orientations, we define a Pareto-optimality criterion based on the total support volume and the “secluded” support volume defined as the support volume that is not accessible by a given set of machining tools. Since total support volume mainly depends on the build orientation and the secluded volume is dictated by the machining setup, in many cases the two objectives are competing and their trade-off needs to be taken into account. The accessibility analysis relies on the inaccessibility measure field (IMF), which is a continuous field in the Euclidean space that quantifies the inaccessibility of each point given a collection of tools and fixturing devices. The value of IMF at each point indicates the minimum possible volumetric collision between objects in relative motion including the part, fixtures, and the tools, over all possible tool orientations and sharp points on the tool. We also propose an automated support removal planning algorithm based on IMF, where a sequence of actions are provided in terms of the fixturing devices, cutting tools, and tool orientation at each step. In our approach, each step is chosen based on the maximal removable volume to iteratively remove accessible supports. The effectiveness of the proposed approach is demonstrated through benchmark examples in 2D and realistic examples in 3D.

Joint decision of condition-based opportunistic maintenance and scheduling for multi-component production systems

ABSTRACT In this study, system maintenance and production scheduling are jointly decided to solve the problems of resource idleness and time cost increase due to system maintenance in the processing of production scheduling. For the multi-component system with economic dependence, a joint strategy of condition-based maintenance and production scheduling is formulated, which includes opportunistic maintenance, preventive maintenance, and corrective maintenance. On this basis, a joint decision model is established to minimise the total weighted expected completion time. Subsequently, all possible maintenance requirements and their corresponding probabilities for the multi-component system in the entire production scheduling process are deduced via the deterioration state space partition modelling method. Furthermore, the stationary probability density function of the joint state of the system is derived, and its numerical solution method is provided. Finally, taking the KS5 adjustable multi-axis tapping machine as an example, numerical experiments are conducted to verify the efficacy of the proposed strategy and the established model. Comparisons with previous strategies using different numbers of components and scheduling job scales indicate that the joint decision model yields better results.

Influence of Minimally Invasive Access Cavity Designs on the Fracture Resistance of Endodontically Treated Mandibular Molars Subjected to Thermocycling and Dynamic Loading

IntroductionThe aim of this study was to investigate the fracture resistance of endodontically treated and restored permanent mandibular molars with minimally invasive access cavities subjected to thermocycling and dynamic loading. MethodsForty first and second mandibular molars were randomly assigned to 4 groups (n = 10/group) as follows: group 1, control (intact teeth); group 2, traditional access cavity (TradAC); group 3, conservative access cavity (ConsAC); and group 4, truss access cavity (TrecAC). After endodontic treatment, teeth were restored with SDR core (Dentsply Caulk, Milford, DE) and subjected to thermocycling followed by dynamic and static loading with a multiaxial fatigue testing machine (Instron, Canton, MA). The maximum load to fracture and pattern of failure (restorable/unrestorable) were recorded. Data were evaluated with analysis of variance and the Tukey post hoc test for multiple comparisons. ResultsFracture resistance of the samples in the control group were higher than those in the experimental groups (P < .005). TradAC exhibited the least resistance to fracture (P < .005). There was no statistically significant difference in the fracture resistance of ConsAC and TrecAC (P = .361) Unrestorable fractures were more frequent in the TradAC group compared with all other groups. ConclusionsMandibular molars with ConsAC and TrecAC exhibited superior fracture resistance compared with TradAC. TradAC had the highest number of unrestorable fractures.

High accuracy on-machine inspection based on rotation theory of multi-axis machine tool

On-machine inspection is an important technology for the precision fabrication. Plagued by overlapping structure and positioning error from machine tool, it is a challenge to generate an on-machine inspection path. In this paper, a rotation theory is investigated for balancing efficiency and accuracy. Based on the kinematic chain of the machine tool, an accessible space graph is established to demonstrate this theory. The least rotations, the least direction reversions can be recognized from this graph. In term of these principles, an orientation planning method is proposed for the parts with overlapping free-form surface. At last, the advantages of proposed path generation method are verified on an impeller’s on-machine inspection.

Task-dependent workpiece placement optimization for minimizing contour errors induced by the low posture-dependent stiffness of robotic milling

Because of the low cost, large workspace and high flexibility, industrial robots (IRs) are promising and competitive alternatives of multi-axis machine tools for milling operations. However, the deformation induced by the low posture-dependent stiffness of robot significantly deteriorates the contour accuracy of milling. Existing studies mainly focused on minimizing the deformation errors caused by the low stiffness, while the contour errors which directly affect the form accuracy did not attract enough attention. In order to improve the contour accuracy of robotic milling, a machining performance index is proposed to optimize the workpiece placement in this paper. Firstly, deformation errors induced by cutting forces are estimated based on the robot stiffness model. Secondly, contour errors are calculated according to deformation errors, and a contour error based machining performance index (CEMPI) is defined by integrating the statistical properties of contour errors. Finally, the optimal workpiece placement is achieved by minimizing CEMPI with particle swarm optimization (PSO). The effectiveness of the proposed task-dependent workpiece placement optimization method is validated by simulation and experiments, which shows that the contour accuracy can be significantly improved with the proposed strategy when compared with traditional methods.

Voxel-Based Adaptive Toolpath Planning using GPU for Freeform Surface Machining

Abstract Today freeform surfaces are widely used on products in automobile, aerospace, and die/molds industries, which are generally manufactured using multi-axis CNC machines. Frequent changes in the design of products necessitate creation of CNC part programs which need fast and accurate toolpath generation methods. Traditional toolpath generation methods involve complex computations and are unable to consider multiple surface patches together. The voxel-based CAD model provides the ability to represent the multi-patch surfaces in a discretized manner which can be processed using an advanced parallel computing framework for accurate tool path planning. This paper presents a new method to generate an adaptive Iso-planar toolpath for a 3-axis CNC machine using the voxel-based part model. The algorithm is designed to work on a Graphics Processing Unit (GPU) that allows parallel processing for faster toolpath generation. The proposed approach consists of two main steps, an algorithm to generate gouge free cutter location points from the voxel-based CAD model and an algorithm to find out sidestep and forward step from those cutter location points to create the final CNC tool path. A new image-processing technique has been proposed to identify gouge by detecting the shadow surface voxels and their intersection with the cutting tool. The developed system was extensively tested and compared with the various reported toolpath planning strategies for machining complex freeform surface parts. The results show that the developed method is computationally efficient, robust, and accurate in generating adaptive planar toolpath.

Investigation of isotropic radiation of low energy X-ray intra-operative radiotherapy by MAGAT gel dosimeter

PurposeIsotropy as a quality assurance aspect of intraoperative radiotherapy (IORT) needs to be evaluated accurately. There are some main problems associated with isotropy investigations by two dimensional dosimeters including limited positions and distances in which isotropy can be measured and long irradiation time needed for isotropy evaluation. In this study, isotropic radiation accuracy of spherical applicators of low energy X-ray IORT was estimated by the use of MAGAT gel as a three dimensional gel dosimeter and a specified IORT phantom. MethodsDesigned IORT phantom was manufactured by multi-axis computer numerical control machine (CNC) using Plexiglas. To investigate isotropy, methacrylic acid, gelatin and tetrakis phosphonium chloride (MAGAT) gel dosimeters embedded in the phantom holes were irradiated with a 50 kV X-ray IORT device to 18 Gy at the surface of the vials. Then, relative dose deviations of output doses from their average were extracted from MRI images of the gel vials in different positions and distances from the 50-mm spherical applicator. ResultsThe percentages of relative deviations of output doses from the average value were less than 8% in all positions which are within the 15% acceptance limit of isotropy radiation. Moreover, a Pearson-moment correlation analysis showed a Pearson's r equal to 0.99–1 for different polar and azimuth angles representing isotropic radiation emission of X-ray IORT. ConclusionIsotropy of IORT can be easily investigated using gel dosimeters by applying the produced phantom which solved the issues facing three-dimensional measurement of isotropic radiation of IORT X-ray source (XRS).

Osteoarthritis-Related Degeneration Alters the Biomechanical Properties of Human Menisci Before the Articular Cartilage.

An exact understanding of the interplay between the articulating tissues of the knee joint in relation to the osteoarthritis (OA)-related degeneration process is of considerable interest. Therefore, the aim of the present study was to characterize the biomechanical properties of mildly and severely degenerated human knee joints, including their menisci and tibial and femoral articular cartilage (AC) surfaces. A spatial biomechanical mapping of the articulating knee joint surfaces of 12 mildly and 12 severely degenerated human cadaveric knee joints was assessed using a multiaxial mechanical testing machine. To do so, indentation stress relaxation tests were combined with thickness and water content measurements at the lateral and medial menisci and the AC of the tibial plateau and femoral condyles to calculate the instantaneous modulus (IM), relaxation modulus, relaxation percentage, maximum applied force during the indentation, and the water content. With progressing joint degeneration, we found an increase in the lateral and the medial meniscal instantaneous moduli (p < 0.02), relaxation moduli (p < 0.01), and maximum applied forces (p < 0.01), while for the underlying tibial AC, the IM (p = 0.01) and maximum applied force (p < 0.01) decreased only at the medial compartment. Degeneration had no influence on the relaxation percentage of the soft tissues. While the water content of the menisci did not change with progressing degeneration, the severely degenerated tibial AC contained more water (p < 0.04) compared to the mildly degenerated tibial cartilage. The results of this study indicate that degeneration-related (bio-)mechanical changes seem likely to be first detectable in the menisci before the articular knee joint cartilage is affected. Should these findings be further reinforced by structural and imaging analyses, the treatment and diagnostic paradigms of OA might be modified, focusing on the early detection of meniscal degeneration and its respective treatment, with the final aim to delay osteoarthritis onset.

Laboratory stand for multi-axis control of stepper drives via EtherCAT fieldbus

In this paper a laboratory stand is presented that was developed for a multi-axis machine stepper drive control system. Each stepper drive utilizes an EtherCAT communication module based on a development board with software developed by the authors. The modules are used to exchange process data with a higher level controller. The EtherCAT communication standard is described including it’s utilization for stepper drive control. A functional description of the developed communication module is also presented. The aim of the Laboratory stand is to conduct research of cyclic communication (1 milisecond or less) and synchronization between multiple drive slave devices and a supervisory controller. The main focus of the presented results was to determine EtherCAT communication cycle jitter on the developed modules. The main aim of the research was to verify whether the data exchange via EtherCAT bus has an impact on the synchronous operation of the multi-axis system.

Collaborative optimization of conical cutter sequence for efficient multi-axis machining of deep curved cavities

As an essential part of the composite fan blade, the leading edge protection cap (LPC) has a very narrow and deep cavity which, in order to avoid the interference, requires the conical ball-end cutter to be long and thin. It calls to improve the cutter’s stiffness so to increase the roughing efficiency of the whole cavity. Targeting this important problem, this paper proposes a novel method to collaboratively optimize a conical cutter sequence, the machining ranges, and the cutting parameters for achieving the highest material removal efficiency. The main difficulty is that all the relevant entities – i.e., the LPC cavity geometry, tool size, tool axis, machining ranges, minimum tool length, tool stiffness, and cutting performance – collaboratively affect the total cutting efficiency. To facilitate decoupling them, the 3D LPC cavity is characterized by its medial surface. To identify all the geometrically accessible conical tools of each medial point, an efficient algorithm is proposed, which is featured by searching characteristic points on the cavity surface. By considering both the geometric and physical accessibilities, the tool sequence domain is constructed. To obtain the appropriate cutting parameters, the best cutting performance of a weak conical cutter is modeled under the constraint of deflection due to the cutting force. Finally, the complicated collaborative optimization model aiming for the minimum cutting time is established and solved by a PSO-based algorithm. The experimental results confirm that the proposed model and algorithm are practicable for improving the roughing efficiency of LPC cavity.

Fundamental Investigations in the Design of Five-Axis Nanopositioning Machines for Measurement and Fabrication Purposes

The majority of nanopositioning and nanomeasuring machines (NPMMs) are based on three independent linear movements in a Cartesian coordinate system. This in combination with the specific nature of sensors and tools limits the addressable part geometries. An enhancement of an NPMM is introduced by the implementation of rotational movements while keeping the precision in the nanometer range. For this purpose, a parameter-based dynamic evaluation system with quantifiable technological parameters has been set up and employed to identify and assess general solution concepts and adequate substructures. Evaluations taken show high potential for three linear movements of the object in combination with two angular movements of the tool. The influence of the additional rotation systems on the existing structure of NPMMs has been investigated further on. Test series on the repeatability of an NPMM enhanced by a chosen combination of a rotary stage and a goniometer setup are realized. As a result of these test series, the necessity of in situ position determination of the tool became very clear. The tool position is measured in situ in relation to a hemispherical reference mirror by three Fabry–Pérot interferometers. FEA optimization has been used to enhance the overall system structure with regard to reproducibility and long-term stability. Results have been experimentally investigated by use of a retroreflector as a tool and the various laser interferometers of the NPMM. The knowledge gained has been formed into general rules for the verification and optimization of design solutions for multiaxial nanopositioning machines.

Path optimization for multi-axis EDM drilling of combustor liner cooling holes using SCGA algorithm

Multi-axis electrical discharge machining (EDM) drilling technology is widely used in the manufacture of film cooling and jet cooling holes of combustor liners. However, there can be more than 3000 film cooling holes with variant orientations in a typical combustor liner. Drilling of thousands of holes without process planning will result in a low machining efficiency. Traditional path optimization methods are carried out in a workpiece coordinate system, which is usually not optimal when applied to multi-axis machining processes. Aiming at minimizing the total non-productive time in a combustor liner multi-axis EDM drilling process, a mathematic model, which takes tool traveling time, tool switching time, and compensation moving time into consideration, is firstly derived. To solve the optimization problem efficiently, a spectral clustering/genetic algorithm (SCGA) is applied as the model has a large number of 0–1 variables. To improve the search performance, pairwise inter-reshuffle (PIR) based initial population and modified mutation are utilized. The performance of SCGA is evaluated by solving a 3616-hole optimization problem and the results are compared with those by other heuristic methods. Comparison results show that the SCGA significantly outperforms other comparison algorithms in terms of minimum non-productive time and convergence speed.

Multi-axis NC machining of integral impeller parts based on NX

The Integral impeller is widely used in all kinds of turbine machinery and aeroengine. With the improvement of engine performance, the shape of the impeller becomes more and more complex. It has the characteristics of small blade spacing, large distortion and thin blade, etc. The Integral impeller is more difficult to process. This paper analyzes the NC machining technology of the Integral impeller and discusses the parameter setting of the multi-axis NC machining.

An overview of fused deposition modelling (FDM): research, development and process optimisation

Purpose The purpose of this paper is to review research studies on process optimisation and machine development that lead to the enhancement of final products in various aspects of the fused deposition modelling (FDM) process. Design/methodology/approach An overview of the literature, focussing on process parameters, machine developments and material characterisations. This study investigates recent research studies that studied FDM capabilities in printing a vast range of materials from thermoplastics to metal alloys. Findings FDM is one of the most common techniques in additive manufacturing (AM) processes. Many parameters in this technology have effects on three-dimensional printed products. Therefore, it is necessary to obtain the optimum elements, for example, build orientation, layer thickness, nozzle diameter, infill pattern and bed temperature. By selecting a proper variable range of parameters, the layers adhere strongly and building end-use products of high quality are achievable. A vast range of materials and their properties from polymers to composite-based polymers are presented. Novel techniques to print metal alloys and composites are examined to increase the productivity of the FDM process. Additionally, defects such as shrinkage and warpage are discussed to eliminate the system’s limitations and improve the quality of final products. Multi-axis and mobile machines brought enhancements throughout the process to eliminate obstacles such as staircase defects in the conventional FDM process. In brief, recent developments were identified and a summary of major improvements was discussed in this study for future research. Originality/value This paper is an overview that provides information about research and developments in FDM. This review focusses on process optimisation and obstacles in printing polymers, composites, geopolymers and novel materials. Therefore, machine characteristics were examined to find out the accessibility of printing novel materials for different applications.

Fatigue life prediction of magneto-rheological elastomers in magnetic field

Fatigue life is one of the most important characteristics of materials. Predicting fatigue life in magnetorheological elastomer (MRE) under combined and repetitive loads is an unavoidable step to increase the safety coefficient of MREs. In this study, high-temperature vulcanization silicon rubber (HTVSR) based MREs were fabricated by incorporating the different soft carbonyl iron particles (CIP) that samples with 10%, 20%, and 30% of CIP volume were made. Fatigue behavior of MRE under the combination of compression-tension and torsion loading in the presence and absence of magnetic fields was studied by using the multiaxial fatigue testing machine. The relationship between maximum energy density function (W max) and fatigue life (N) was achieved that it can predict fatigue life in MREs. The results showed that the dissipation energy was smaller in the presence of a magnetic field at the same CIP volume percentage and increased as the CIP volume percentages grew, because the agglomeration in the samples became more. And also with a magnetic field, at the same CIP volume percentages, the strength of the MRE increased that led to the fatigue life of MRE increasing.

A Review of Multi-Axial Fatigue Tests

Nowadays, estimating the fatigue life of almost any industrial component under multi-axial loads is still a very complicated issue. In this paper, models of multi-axial fatigue for various loading conditions depend on damage parameters conditions shown with a comprehensive review of the multi-axial fatigue machines designed to provide proportional and non-proportional combined loading conditions in the laboratory and corresponding models developed to predict specimens fatigue life. A brief of experimental multi-axial fatigue results reported by previous studies is also presented. Especially, the focus here is on combined bending-torsion and axial-torsion conditions. Such a study allows for a better understanding of the effect of the loading path on material fatigue behaviour during their real operations. Also, predicting fatigue life accurately under non-proportional complex loads will give clear data about when this component is a failure during a real process.

Nanosecond pulsed laser irradiation of metal for processing microgroove with vertical sidewalls

Laser processing is widely used in the manufacture of surface patterns. However, it faces new challenges under some industrial demands. For example, the fine cladding circuit requires that the metal layer is precisely etched in depth for slight damage to the substrate and the formed conductive tracks have vertical sidewalls for higher precision. The former can be achieved by a reasonable control of the process parameters, but the latter is difficult to realize by conventional laser milling since the energy distribution of the spot is Gaussian. In this situation, a new laser processing method, pre-etching then sidewall trimming, is proposed to reduce the taper angle of the etched edge. It features an additional trimming process in which the laser process parameters are planned orderly for their relatively independent effect, and the multiaxis machining technology is introduced to realize the etching with oblique incidence. To control the etching depth in pre-etching, the ablation result of microgroove is predicted by building the laser ablation model at vertical incidence. Furthermore, the laser ablation model at oblique incidence is developed and the planning method of process parameters for the sidewall trimming is researched. The operation of the proposed processing method is completed through a five-axis laser processing machine tool. It is demonstrated that the prepared microgroove has the taper angle less than 3° (decrease degree &amp;gt; 90%). The research achievements improve the sloping sidewalls caused by the inherent characteristic of laser, which has practical application value for manufacturing the surface pattern with high-quality edge.

Dexel-Based Simulation of Directed Energy Deposition Additive Manufacturing

Additive manufacturing is typically a flexible alternative to conventional manufacturing processes. However, manufacturing costs increase due to the effort required to experimentally determine optimum process parameters for customized products or small batches. Therefore, simulation models are needed in order to reduce the amount of effort necessary for experimental testing. For this purpose, a novel technological simulation method for directed energy deposition additive manufacturing is presented here. The Dexel-based simulation allows modeling of additive manufacturing of varying geometric shapes by considering multi-axis machine tool kinematics and local process conditions. The simulation approach can be combined with the simulation of subtractive processes, which enables integrated digital process chains.

An optimized algorithm and the verification methods for improving the volumetric error modeling accuracy of precision machine tools

Referring to the error modeling technology used in precision machine tools, it is difficult for machine tool builders to understand the effects of the theoretical modeling accuracy on the precision machining in the designing stages, where error components are represented by parameters. Therefore, this study is proposed to overcome certain theoretical calculation errors for a parametric form of volumetric error modeling and to examine verification method for judging the modeling precision. Based on the mathematical theory, a novel optimized algorithm is presented, as well as its verification methods. With the two new methods, it is effective to identify theoretical calculation errors and verify the accuracy of error modeling. Meanwhile, the proposed algorithm, with a form grinding machine tool being as an illustration example, is tested and validated by means of numerical simulations in the Matlab. The results reveal that the modeling accuracy of the error characteristic matrix is improved and enhanced by the algorithm, and the two verification methods can check the veracity of parametric modeling precision in different ways. Especially, the second method can check and isolate quantitatively the theoretical calculation errors. At the same time, it is a theoretical guidance for choosing a suitable treatment to meet the accuracy of an error model represented by parametric variables during iterations of the characteristic matrices. These two prediction veracity and uncertainty of the modeling precision can be evaluated. Furthermore, the algorithm and checking methods can be extended to ultra-precision multi-axis machine tools.

Hybrid Surgical and Endovascular Approach via the Contralateral Superficial Middle Cerebral Vein to Occlude Cavernous Sinus Dural Arteriovenous Fistula in a Hybrid Operating Room: A Case Report

Most cases of cavernous sinus dural arteriovenous fistula (CS-dAVF) are treated via the inferior petrous sinus (IPS) through the transfemoral vein approach, but there are cases where treatment through the superficial middle cerebral vein (SMCV) is required. A hybrid operating room (OR) is useful because it allows for smooth direct surgery and endovascular treatment in a clean surgical field. We herein report a case of simultaneous treatment for CS-dAVF by coil embolization via a contralateral SMCV and middle cerebral artery (MCA) aneurysm by clipping in a hybrid OR. A 68-year-old woman had been suffering from left chemosis and ptosis for 2 months before visiting our hospital. Digital subtraction angiography (DSA) revealed Borden type II and Cognard type II a+b CS dAVF with parenchymal hemorrhaging and an unruptured left M1/M2 junction aneurysm. Since passing through the CS via the femoral vein was unsuccessful, we decided to access the right CS via the left CS through the intercavernous sinus (ICS) via the left SMCV by the pterional approach in a hybrid OR equipped with a multi-axis working system angiography machine. Endovascular treatment via direct cannulation into the contralateral SMCV following craniotomy in a hybrid OR is an optional strategy for treating complicated CS-dAVF.