5-axis Machining Research Articles

Decreasing ramp-up durations of ultraprecision machine tools using reinforcement learning

Ramp-up phases in machining processes are often required to enable the desired workpiece quality. Within conventional CNC processes these phases mainly depend on the corresponding CNC program. But, especially in the field of ultra-precision manufacturing these ramp-up phases require adaptions deep within the control system of the machine tools. The control parameters of the axis servo-drives need to be optimized regarding the corresponding manufacturing process. This process inhibits an iterative nature, which causes multiple rejects because of not sufficient workpiece quality. Naturally this optimization process adds up to the overall manufacturing time. One of the main factors to reduce this time span is the machine operator's experience. But within the currently expanding industry of high-tech products, which require functional workpiece surfaces inhibiting complex geometries, requirements in workpiece tolerances are constantly increasing, resulting in individual and mostly unknown axis control settings for most newly developed workpieces. In a first approach of automating and accelerating the ramp-up phase, an artificial intelligence solution, based on reinforcement learning techniques is introduced. One of the main advantages of using reinforcement learning (RL) based models for this problem is their capability to adapt to feedback from their environment. The installed machine drives can serve as learning environments, but this approach results in extraordinary high training durations. The behavior of the machine axis can be efficiently simulated by applicating techniques from the field of control theory, which results in a drastic reduction of training times while the behavior of the real axis can still be emulated.

Fault monitoring and diagnosis of motorized spindle in five-axis Machining Center based on CNN-SVM-PSO

A spindle fault diagnosis method based on CNN-SVM optimized by particle swarm algorithm (PSO) is proposed to address the problems of high failure rate of electric spindles of high precision CNC machine tools, while manual fault diagnosis is a tedious task and low efficiency. The model uses a convolutional neural network (CNN) model as a deep feature miner and a support vector machine (SVM) as a fault state classifier. Taking the electric spindle of a five-axis machining centre as the experimental research object, the model classifies and predicts four labelled states: normal state of the electric spindle, loose state of the rotating shaft and coupling, eccentric state of the motor air gap and damaged state of the bearing and rolling body, while introducing a particle swarm algorithm ( PSO) is introduced to optimize the hyperparameters in the model to improve the prediction effect. The results show that the proposed hybrid PSO-CNN-SVM model is able to monitor and diagnose the electric spindle failure of a 5-axis machining centre with an accuracy of 99.33%. In comparison with the BP model, SVM model, CNN model and CNN-SVM model, the accuracy of the model increased by 10%, 6%, 4% and 2% respectively, which shows that the fault diagnosis model proposed in the paper can monitor the operation status of the electric spindle more effectively and diagnose the type of electric spindle fault, so as to improve the maintenance strategy.

Rectilinear strain sensing framework for real time compensation of structural distortions in precision machinery

Precision machinery such as machine tools use heavy duty structural elements to provide high accuracy and repeatability. However, external forces and thermal effects can still cause significant errors. Machine builders put significant emphasis on good design for error avoidance and more recently, utilise software-based error compensation methods to further improve performance. For geometric errors which result from build tolerances, and which normally only vary slowly over time, most Numerical Control systems provide functionality for pre-calibrated error compensation. For compensation of thermal errors, temperature sensors are often used to provide data for a model which calculates the effect of the temperature field on the machine structure. Although this method is widely researched, there is often significant residual error due the time-variant non-linear relationship between temperature and the error between the tool and workpiece. This may be exacerbated by introducing multi-material structural elements to reduce weight. Direct measurement and combining temperature with direct measurement can enable more precise modelling but can add significant cost of additional sensors. In this research a direct measurement method is applied using a series of short-range, ultra-low-cost displacement sensors, exploiting a particular arrangement of compact slotted photo-microsensors. These are organised in a novel rectilinear framework to enable detection of the bending of a machine tool structure. The design provides high resolution measurement of strain over arbitrary lengths and cost-effective hardware for permanently embedding on a machine. The system was applied to the ram of a high precision 3-axis machine tool and used to compensate the thermal error caused by running the integrated high-speed spindle. The residual error was reduced from 10 to 4 µm, even reducing the magnitude of the effect of the chiller cycles.

Analysis of the Impact of Circular Contour Error Based on CNC Machine

To improve the processing accuracy of the CNC machine, the errors caused by uneven pitch spacing between the servo feeding axes of the NC machine are analyzed. With the combination of the principle of plane circular contour motion track synthesis, the influence of the pitch errors produced by the X and Y axes on the circular contour errors is analyzed. Finally, the experimental platform is adopted to analyze the data before and after screw pitch error compensation with a spherical rod. The results verify that the screw pitch errors impact the outline errors, and the proportion of mismatch errors was reduced by 96.88% after screw pitch errors compensation.

A New Approach of Modelling Bottom Edge Cutting in 4-Axis Rough Milling of Complex Parts and Its Application on Feed Rate Optimization.

Complex mechanical parts such as a blisk of aero-engines are commonly used in aerospace industry. These parts are complex in shape and their rough machining are conducted in 4-axis machine tools with end mills. The end mills are fully engaged into the workpiece material to be removed. Because of the complex cutter motion in 4-axis milling, the bottom edges of the end mills are involved in cutting with high possibility, resulting in an undesirable increase of cutting forces, tool deflection, and quick tool wear. To address this technical challenge, an analytical method is proposed to identify and evaluate the bottom edge cutting in 4-axis milling in this work. The motion of the cutter's tool tip with respect to the workpiece is analyzed and the equations are formulated based on a basic interpolation algorithm. An approach to identifying and evaluating the bottom edge cutting is proposed. The increment of the cutting forces caused by the bottom edge cutting is taken into consideration to precisely evaluate the overall cutting forces. A feed rate optimization model is then established to control the cutting forces. The simulation and the experiment of rough milling of a blisk verify that the bottom edge cutting can be identified and the cutting force can be controlled by optimizing the feed rates without losing much machining efficiency.

Shaping of the Fresnel lens array on roller molds by 6-axis diamond machining

The Fresnel lens arrays are rapidly developing with the increasing demand for better optical performances and capabilities. For the roll-to-roll embossing of optical films, direct diamond machining of the Fresnel lenses on roller molds has been realized by installing an additional goniometer on the 5-axis ultra-precision machine tool in the previous study. However, this method owns two shortcomings, i.e., the communication delay between the machine tool and the goniometer and the poor positioning accuracy of the goniometer. In this paper, a 6-axis diamond shaping method is proposed to fabricate the Fresnel lens array on the roller periphery by utilizing a commercial 6-axis ultra-precision machine tool. It is ensured that the side cutting edge of the diamond tool matches the Fresnel lenses profiles during shaping. Also, the tool rake face is always perpendicular to both the roller tangent plane at the cutter location point and the cutting velocity relative to the roller via the synchronized rotations of the A-, B- and C-axes to avoid the tool–workpiece interference. The process to calibrate installation errors is introduced and utilized. The tool path is generated according to the cutting tool geometry, the lens parameters and the machine tool configuration. Experiments are carried out by machining the designed Fresnel lens array on a roller mold, which consists of lenses with different feature heights. The surface qualities of the lens arrays are evaluated and the influence of the block time to run the CNC code are also analyzed. The experimental results verify that the proposed method is effective and flexible for machining of the Fresnel lens array on roller molds.

Error assessment and correction for extrusion-based bioprinting using computer vision method.

299Bioprinting offers a new approach to addressing the organ shortage crisis. Despite recent technological advances, insufficient printing resolution continues to be one of the reasons that impede the development of bioprinting. Normally, machine axes movement cannot be reliably used to predict material placement, and the printing path tends to deviate from the predetermined designed reference trajectory in varying degrees. Therefore, a computer vision-based method was proposed in this study to correct trajectory deviation and improve printing accuracy. The image algorithm calculated the deviation between the printed trajectory and the reference trajectory to generate an error vector. Furthermore, the axes trajectory was modified according to the normal vector approach in the second printing to compensate for the deviation error. The highest correction efficiency that could be achieved was 91%. More significantly, we discovered that the correction results, for the first time, were in a normal distribution instead of a random distribution.

Spatial angle error equivalence principle and on-machine detection method for 5-axis machine tools

Spatial angle error equivalence principle and on-machine detection method for 5-axis machine tools

Evaluation of zirconia crowns restoring endodontically treated posterior teeth with 2 finish line designs and 2 occlusal reduction schemes: A randomized clinical trial

Statement of problemPreparation design has been linked to restoration survival, and the finish line geometry, such as a deep chamfer or shoulder, has been linked to marginal integrity. However, limited data are available for restoration success with the feather-edge finish line when used with monolithic zirconia crowns with different occlusal reduction schemes. PurposeThe purpose of this randomized clinical trial was to evaluate the clinical performance of 2 finish line designs (feather-edge and rounded shoulder) in relation to 2 occlusal designs (flat and planar) in endodontically treated teeth restored with monolithic zirconia crowns. Material and methodsSixty-six complete-coverage monolithic zirconia crowns were provided for posterior endodontically treated teeth. The participants were divided into 3 groups based on the preparation design: the control group (PS) had a planar occlusal scheme with a rounded shoulder finish line; the first intervention group (FF) had a flat occlusal scheme with a feather-edge finish line; and the second intervention group (FS) had a flat occlusal scheme with a rounded shoulder finish line. The crowns were designed with the exocad software program and milled with a 5-axis machine. After cementation, clinical performance in terms of marginal adaptation, marginal discoloration, fracture, and secondary caries was evaluated by using the modified United States Public Health Service (USPHS) criteria. The gingival index score system was used to evaluate the gingival response. The scores were recorded immediately after cementation and at 3 subsequent follow-up visits every 3 months for 1 year. The chi-square test was used in all comparisons of outcomes and follow-up durations (α=.05). ResultsIn terms of marginal adaptations, the control group (PS) demonstrated the best marginal adaptation scores during follow-up visits, followed by intervention 2 (FS), and lastly, intervention 1 (FF), which was scored mostly with Bravo. At the third follow-up visit, the intervention 1 (FF) group reported the most gingival responses of all groups. No significant difference among the groups was found in terms of marginal discoloration, fracture, or secondary caries at any of the follow-up visits. Each group received a perfect Alfa score of 100% on all 3 follow-up assessments. ConclusionsIn this 1-year randomized clinical trial, all evaluated preparation schemes and corresponding crowns were clinically successful. The clinical performance of monolithic zirconia crowns of the novel preparation design (FF) was successful in terms of marginal adaption, fracture, secondary caries, and marginal discoloration.

A positioning correction method for turbine blade film cooling holes

It is significant to improve the machining accuracy of film cooling holes on aero-engine turbine blades. This paper presents a method to correct the position of film cooling holes on turbine blades. In this method, the pre-positioning algorithm and the precise positioning algorithm are proposed. The pre-positioning algorithm introduces the blade structure information. In the precise positioning algorithm, 3D coordinate transformation, ∠B and ∠C of 5-axis machine tool updating, iteration points creating based on the normal vector are designed. The operation of the gas film cooling hole correcting by the method is given. Experiment shows that, after 7 iterations, the error is reduced to 0.0344mm, achieving high-precision positioning of turbine blades. Furthermore, the coordinates are corrected to realize the high-precision machining of the film cooling holes, which can improve the cooling performance of turbine blades.

Based on NXUG10 Research on automatic programming and simulation machining of integral split impeller

Taking the programming and simulation processing of integral split impeller in nxug10.0 software as an example, this paper introduces a method that can realize the automatic programming of parts and components to call out five axis machine tool for simulation processing in ug10.0 software. This paper introduces the whole process of ug10.0 impeller machining module from automatic programming parameter setting of integral split impeller to generating tool path files for machining integral split impeller parts and calling out five axis machine tool for simulation machining. The correctness of the automatic programming program is verified. The phenomenon of Tool Collision and interference in the machining process is avoided, and the machining efficiency of the impeller is greatly improved.

State identification of a 5-axis ultra-precision CNC machine tool using energy consumption data assisted by multi-output densely connected 1D-CNN model

State identification of a 5-axis ultra-precision CNC machine tool using energy consumption data assisted by multi-output densely connected 1D-CNN model

A Dual-Arm Robot That Autonomously Lifts Up and Tumbles Heavy Plates Using Crane Pulley Blocks

This paper proposes a combined planning and optimization method that enables a dual-arm robot to lift up and flip heavy plates using crane pulley blocks. The problem is motivated by the low payload of modern collaborative robots. Instead of directly manipulating heavy plates that collaborative robots cannot afford, the paper develops a planner for collaborative robots to operate crane pulley blocks. The planner assumes a target plate is pre-attached to the crane hook. It optimizes dual-arm action sequences and plans the robot’s dual-arm motion that pulls the rope of the crane pulley blocks to lift up the plate. The crane pulley blocks reduce the payload that each robotic arm needs to bear. When the plate is lifted up to a satisfying pose, the planner plans a sliding-pushing motion for one of the robot arms to tumble over the plate while considering force and moment constraints. The article presents the technical details of the planner and several experiments and analysis carried out using a dual-arm robot made by two Universal Robots UR3 arms. The influence of various parameters and optimization goals are investigated and compared in depth. The results show that the proposed planner is flexible and efficient. This paper is motivated by a cleaning process in a factory that produces sewage press machines. The pressboard of sewage press machines could be as heavy as 1000 kg. Human workers need to flip and clean both sides of the board before installing them to the main axis of a sewage machine. Their solution is using a gantry crane. They attach the board to the crane hook using bearing belts, activate the crane to lift up the board. When the board is raised to a satisfying pose, the workers turn the board over by pushing it. Motivated by human workers’ actions, we developed the planner presented in this paper. We assumed crane pulley blocks in the experiments and analysis, but in practice, they may be replaced with electronic ones to improve effort and efficiency. Using the electronic ones will be a sub-problem since there is no need for pulling ropes. The proposed method is expected to help a company’s technicians better judge if they need a heavy payload manipulator or keep their current crane equipment while employing several intelligent collaborative robots to operate them. As a result, it may help to accelerate the upgrade of manufacturing sites while reducing reforming budgets. Note to Practitioners—This paper is motivated by a cleaning process in a factory that produces sewage press machines. The pressboard of sewage press machines could be as heavy as 1000 kg. Human workers need to flip and clean both sides of the board before installing them to the main axis of a sewage machine. Their solution is using a gantry crane. They attach the board to the crane hook using bearing belts, activate the crane to lift up the board. When the board is raised to a satisfying pose, the workers turn the board over by pushing it. Motivated by human workers’ actions, we developed the planner presented in this paper. We assumed crane pulley blocks in the experiments and analysis, but in practice, they may be replaced with electronic ones to improve effort and efficiency. Using the electronic ones will be a sub-problem since there is no need for pulling ropes. The proposed method is expected to help a company’s technicians better judge if they need a heavy payload manipulator or keep their current crane equipment while employing several intelligent collaborative robots to operate them. As a result, it may help to accelerate the upgrade of manufacturing sites while reducing reforming budgets.

Hybrid Manufacturing Process Planning for Arbitrary Part and Tool Shapes

Hybrid manufacturing (HM) technologies combine additive and subtractive manufacturing (AM/SM) capabilities in multi-modal process plans that leverage the strengths of each. Despite the growing interest in HM technologies, software tools for process planning have not caught up with advances in hardware and typically impose restrictions that limit the design and manufacturing engineers’ ability to systematically explore the full design and process planning spaces. We present a general framework for identifying AM/SM actions that make up an HM process plan based on accessibility and support requirements, using morphological operations that allow for arbitrary part and tool geometries to be considered. To take advantage of multi-modality, we define the actions to allow for temporary excessive material deposition or removal, with an understanding that subsequent actions can correct for them, unlike the case in unimodal (AM-only or SM-only) process plans that are monotonic. We use this framework to generate a combinatorial space of valid, potentially non-monotonic, process plans for a given part of arbitrary shape, a collection of AM/SM tools of arbitrary shapes, and a set of relative rotations (fixed for each action) between them, representing build/fixturing directions on 3-axis machines. Finally, we define a simple objective function quantifying the cost of materials and operating time in terms of deposition/removal volumes and use a search algorithm to explore the exponentially large space of valid process plans to find “cost-optimal” solutions. We demonstrate the effectiveness of our method on 3D examples.

A review on additive/subtractive hybrid manufacturing of directed energy deposition (DED) process

Additive manufacturing (AM) processes are reliable techniques to build highly complex metallic parts. Direct energy deposition (DED) is one of the most common technologies to 3D print metal alloys. Despite a wide range of literature that has discussed the ability of DED in metal printing, weak binding, poor accuracy, and rough surface still exist in final products. Thus, limitations in 3D printing of metal powder and wire indicate post-processing techniques required to achieve high quality in both mechanical properties and surface quality. Therefore, hybrid manufacturing (HM), specifically additive/subtractive hybrid manufacturing (ASHM) of DED has been proposed to enhance product quality. ASHM is a capable process that combines two technologies with 3-axis or multi-axis machines. Different methods have been suggested to increase the accuracy of machines to find better quality and microstructure. In contrast, drawbacks in ASHM still exist such as limitations in existing reliable materials and poor accuracy in machine coordination to avoid collision in the multi-axes machine. It should be noted that there is no review work with focuses on both DED and hybridization of DED processes. Thus, in this review work, a unique study of DED in comparison to ASHM as well as novel techniques are discussed with the objective of showing the capabilities of each process and the benefits of using them for different applications. Finally, new gaps are discussed in ASHM to enhance the layer bonding and surface quality with the processes' effects on microstructures and performance. The development of a revolutionary additive/subtractive hybrid manufacturing (ASHM) process makes use of both simplex additive manufacturing (AM) and subtractive machining. The technique improves the part's surface quality and geometric and dimensional accuracy via directed energy deposition (DED) combined with the machining process. This review paper offers a comprehensive and detailed analysis of the benefits and state-of-the-art ASHM of DED process.

Simulation of Toolpaths Using 3D Method Strategies for Complex Shape in Milling Application

Several strategies can be used for machining complex 3D shapes on a 3-axis CNC vertical milling machine in Autodesk Inventor Professional software. However, it is challenging to determine suitable strategies without guidance. Among the strategies involved are Scallop, Radial, Spiral, and Morphed Spiral. The purpose of this study is to compare the toolpaths strategy in terms of machining time by using high-speed machining parameters. A hemisphere shape and a fillet feature in the part are considered complex shapes due to their convex and concave surfaces. There are two step machining processes involved, which are roughing and finishing. Comparison time is focused on finishing the process using those strategies. Actual fixed machining parameters like tool diameter, feed rate, spindle speed, stepover, and cutting depth are used to make simulations of the toolpaths. Based on the simulation, the radial strategy has the shortest machining time and cutting length by more than fifty percent (50%) compared to other strategies. This is due to the fact that this technique generates passes along the arc's radii, which are subsequently projected down on the surfaces. The passes can be linked in a zig-zag pattern between the outer and inner radius, either from inside to outside or outside to inside. However, collisions between the cutting tool and the workpiece must be closely monitored. As a result, cutting length must also be addressed when deciding to use this strategy. In conclusion, high-speed machining with the right machining strategy is essential for increased productivity.

Improvement in the efficiency of the five-axis machining of aerospace blisks.

Blisks are not easily machined because of their complex curved surfaces and the high-precision requirements of surface machining. Lightweight alloy materials with superior mechanical properties, such as titanium alloy and stainless steel, are popular material choices for manufacturing turbine blisks. However, these materials are difficult to cut and require advanced machine tools and processing technologies. Because aerospace-grade parts are complex and require precise dimensions and high surface quality, machining these parts by using three-axis machine tools is difficult. Using multi-axis machine tools for the machining of complex parts can cause the achievement of precise dimensions, high quality, and the required surface roughness. In the multi-axis machining of aerospace blisks, tool path planning is considered the most difficult task. In this study, we examined the implementation of five-axis machining technology for the manufacturing of an aerospace blisk. Processing modules from computer-aided manufacturing software (NX10) are used for five-axis tool path generating, and 5-axis machining numerical control code is generated through post-processing calculations. Solid cutting simulation software (VERICUT) is used to verify whether tools exhibited overcut or interference. A sensory tool holder (SPIKE) is used to analyze cutting force during the rough machining of a blisk. The sensory tool holder is also adopted to evaluate the spindle runout and tool holding status. In order to obtain a consistent cutting allowance and surface accuracy, the online measurement system is used to generate a measurement path for semi-finish and finish machining. The real cut is performed with SUS304 and demonstrates the practical application. Through improvements in process planning, the machining time was shortened by 16.5%.

NEW DEVICE FOR RAPID MEASUREMENT OF MACHINE TOOL GEOMETRIC ERRORS

Control systems of modern machine tools are equipped with a number of functions for volumetric accuracy enhancement. These functions can compensate for all the geometric errors of the axes, which are characterized by 21 errors for a 3-axis machine tool. Compensation data are stored in compensation tables and the control system calculates actual compensation based on these tables and actual machine tool position. Geometric errors are measured within the machine tool maintenance plan and it presents a time-consuming process. Measurement is mainly based on interferometric devices, where the precise setup of laser source and detector is challenging. This article introduces an original system for automatic interferometer set up to speed up the measurement of geometric errors. The system is designed for the interferometer Renishaw XM-60, which simultaneously measures all 6 degrees of freedom. The developed control software identifies interferometer position and transforms the measured data into a machine coordinate system. Numerical simulation verified the proposed solution.

Development of the real-time winding angle measurement device for the laboratory-scale 3-axis winding machine

It is well-known that an automatic system can reduce errors to a great extent, which increases productivity and reduces labor costs. The existing filament winding machines or equipment lack the winding angle detection or measurement system, which cannot provide high precision and stable winding angle. This paper proposes a real-time winding angle device that can detect and measure the fiber orientation of filament wound composite products. The real-time winding angle measurement system consists of an Arducam 5MP OV5647 camera and OpenCV software. It is developed as the programming function for processing the real-time image of the winding angle. Furthermore, the traveled movement slider and the winding angle measurement image can be acquired during the dry/wet process. The laboratory-scale 3-axis winding machine integrated with the real-time winding angle measurement device is successfully developed, assembled, and tested.

An action-oriented teaching approach for intelligent and energy efficient precision manufacturing

Thermal errors of machine tools are a major contributor to inaccuracies of produced workpieces. Especially, the reduction of thermal errors without increasing the energy consumption of the machine tool and the shop floor due to exact air conditioning has a great social, scientific, and industrial relevance. Therefore, the Institute of Machine Tools and Manufacturing (IWF) at ETH Zürich set up a series of three lab courses to increase the awareness of undergraduate students on this important topic. In the first lab course the students elaborate how the carbon footprint of machine tools can be minimized over the whole live cycle including the manufactured products. Specifically, the students measure the energy demand and analyze the energy efficiency of the most important components of a 5-axis machine tool in different operating conditions. The second lab course focuses on the thermal chain of causes, which describes the physical fundamentals leading to the thermal deformations of machine tools. Temperature and displacement measurements as well as finite-element simulations of a purpose-built test bench visualize the characteristics of the thermal chain of causes. The third lab course completes the topic by dealing with model-based thermal compensation strategies, which enables a shift from resource-based towards intelligence-based reduction strategies for thermal errors. The students evaluate the thermal behaviour of a 5-axis machine tool with an on-machine measurement cycle and learn how to create physical and data-based thermal error compensation models.