Shorter Machining Time Research Articles

INVESTIGATION OF ELECTROEROSION MACHINING PERFORMANCE OF METAL MATRIX COMPOSITE MATERIALS PRODUCED USING STIR AND INDIRECT SQUEEZE METHOD

In this study, metal matrix composite (MMC) materials were made with an aluminum matrix (AA7075 alloy) and reinforcement silicon carbide (SiC) elements using molten metal stir and indirect squeeze casting. SiC was used as a reinforcing element in the making of MMC material in different amounts (10%, 14%, and 18%) by mass. Electro Discharge Machining (EDM), cut depth (0.5 mm), three different pulse-on times, three different discharge current values, and a fixed pulse-off time (20 s) were used to machine MMC materials. The effects of machining parameters on machining time, average surface roughness, hole diameter, and material wear difference after machining were studied. As a result of the study, the composite material with 75 [Formula: see text]s pulse-on time, 6A current value, and 10% reinforcement element had the lowest machining time, the largest hole diameter, and the smoothest average surface. These machining parameters and materials also had the shortest machining time (5 min). Based on the signal-to-noise ratios, the best parameters for average surface roughness, hole diameter, Processing time, and material wear amount (MMC, discharge current value, and impact time) were found to be [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text], respectively. Based on the ANOVA results, the [Formula: see text]2 values for the average surface roughness, hole diameter, machining time, and material wear loss value were 99.3%, 98.7%, 77.8%, and 97.3%, respectively.

PENGARUH JUMLAH DAN ARAH SAYATAN TERHADAP HASIL MILLING ALUMINIUM

The quality of production goods, especially milling on aluminum material, is considered good if it is characterized by good surface quality of the components and efficient (short) machining time. There are various factors that affect this. This study investigated the CNC milling machining parameters, namely depth of cut and step over, which were written as the influence of the number and direction of cuts on the surface quality and machining time of aluminum materials. The purpose was to obtain the appropriate parameters so that the machining process is more efficient and with the appropriate quality. The CNC milling used was CNC Dahlih with a 6mm diameter tool, feed rate of 460 mm/min, and rotational speed of 2800 RPM. The variables were vertical cutting direction (depth of cut 5mm) with variations in step over of 0.5 mm, 1 mm, and 2 mm, and horizontal cutting direction (step over 5mm) with variations in depth of cut of 0.5mm, 1mm, and 2mm. So that the number of cuts can be equalized to 4, 6, and 12 in the vertical and horizontal cutting directions. The results showed that the more cuts, the lower the surface roughness, but it increased the machining time.

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.

Numerical modeling and experimental evaluation of machining parameters for 2-dimensions ultrasonic-assisted micro-milling at low and high-speed machining

Vibration assisted machining (VAM) is one of the hybrid machining processes for improving the machined surface quality. VAM performance is mainly influenced by the combination of machining and vibration control parameters, where surface roughness value (Ra) became the benchmarking indicator. It is difficult to determine the optimum parameter combination to produce high precision products, especially for micro-milling, due to the interconnected correlation among parameters. The benefits of high-speed machining with VAM are high material removal rate and shorter machining time than low-speed machining. VAM operation at high-speed machining is still limited due to the high possibility of chatter occurrence. Therefore, this research aims to evaluate the 2D VAM resonant performance at low-speed and high-speed machining, operated at ultrasonic vibration and amplitude below one μm. The mathematical model and experimental evaluate the vibration effect based on machining mode, amplitude, and spindle speed variation. The mathematical modelling and experiment result complement each other, where the mathematical model can characterize the effect of resonant vibration, amplitude, and spindle speed increment on the tool path trajectory. The 2D resonant vibration at the feed direction causes interrupting cutting and transforms the tool path trajectory from linear to wavy. The mathematical model and experiment result show the dominant influence of spindle speed and feed rate on the toolpath trajectory and Ra, where low spindle speed and feed rate result in better machine surface roughness. The low-speed machining with VAM results in Ra value between 0.1–0.155 μm, which is below the high-speed machining result, between 0.2–0.38 μm

A new real-time trajectory generation method modifying trajectory based on trajectory error and angular speed for high accuracy and short machining time

A computationally efficient FIR-filtering based tool-path (trajectory) modification method, which simultaneously realizes remarkable trajectory error reduction, vibration avoidance, and short machining time, is presented in this paper. Conventional trajectory generation in NC units causes trajectory error by using smoothing filters for limiting acceleration and avoiding vibration of the machines, and this trajectory error is often too large for practical applications. Therefore, a novel trajectory generation method is presented in this paper to remarkably reduce the trajectory error by modifying the trajectory commanded by G-codes on the basis of the trajectory error and angular speed. In order to realize the trajectory modification method, three key components, (i) p-corresponding method, (ii) ω-smoothing filter, and (iii) modification gain function, are developed in this study. The p-corresponding method is required to stably evaluate the trajectory error, while the other two components are used to compute appropriate modification gains for arbitrary trajectories. The proposed trajectory modification method is completed by integrating the components (i) to (iii), and it is verified utilizing a commercial machine tool. It is confirmed that average trajectory error is reduced remarkably by the proposed method without increasing machining time or sacrificing vibration avoidance by the smoothing filter. In particular, the trajectory errors at circular arcs are eliminated almost completely, e.g., the average trajectory error is reduced significantly by about 80% for a trajectory consisting of several circular arcs and corners.

A Cutter Selection Method for 2 1/2-Axis Trochoidal Milling of the Pocket Based on Optimal Skeleton

The trochoidal toolpath is generated based on skeleton. However, several different skeletons can be extracted from one pocket. To improve the efficiency of trochoidal rough milling, a cutter selection method basing the optimal skeleton is proposed. Firstly, for a pocket, preliminary skeleton curves and nodes are extracted according to the principle of medial axis transformation. A skeleton extraction method is given that the skeleton is a combination of skeleton curves generated by randomly connecting the preliminary skeleton curves under nodes constraint. A set of skeletons can be obtained by repeatedly extracting skeleton. Furthermore, an optimization model based on the shortest machining time is established, and then the optimization model is solved by the Genetic Algorithm to determine the optimal tool combination and skeleton. The developed approach is validated in trochoidal milling a pocket for cutter selection. The experimental results show that the method can significantly improve the processing efficiency.

Multi beam microprocessing for printing and embossing applications with high power ultrashort pulsed lasers

Abstract Micro structuring of surfaces is of great interest for various applications, e.g. for the tooling industry, the printing industry and for consumer goods. In suitable mass production applications, such as injection molding or roll-to-roll processing for various markets, the final product could be equipped with new properties, such as hydrophilic behavior, adjustable gloss level, soft-touch behavior, light management properties etc. To generate functionalities at reasonable cost, embossing dies can be augmented with additional micro/nano-scale structure using laser ablation technologies. Despite the availability of ultrashort pulsed (USP) high power lasers (up to several hundred watts), it is still a challenge to structure large areas, as required on embossing rolls, in an acceptable processing time for industrial production. In terms of industrial implementation, direct digital transfer is a limiting factor for ultrahigh resolution. Shorter machining times by further increasing spot or workpiece motion are limited. Enlarging the ablation diameter, and thus the tool diameter, delivers a higher ablation rate with the comparable ablation quality, but entails a reduction in resolution. While maintaining the achieved state-of-the-art performance, upscaling of single modulated lasers provides a less demanding way to increase productivity. In the processing of steel surfaces, an increase in material removal can also be achieved by using pulse burst. In this work, the parallel process of single modulated multi laser sources is compared with a laser source split by diffractive optical elements (DOE) for applications in a cylinder micro patterning system. A newly developed highly compact ps laser with repetition rates up to 8 MHz and an average power of 300 or 500 W was divided into 8 or 16 parallel beamlets by a DOE. The ablation rate of each approach was investigated by typical microstructures on copper surfaces. At surface speeds of 10 m/s and a resolution of 5080 dpi, an ablation rate of up to 27 mm³/min was achieved. Different functional surface geometries were realized on an embossing roll as master, which is used for replication of the structures in roll-to-roll processes. Functional structures, such as friction reduction, improved soft touch or light guiding elements on large surfaces are demonstrated.

The Capabilities of Spark-Assisted Chemical Engraving: A Review

Brittle non-conductive materials, like glass and ceramics, are becoming ever more significant with the rising demand for fabricating micro-devices with special micro-features. Spark-Assisted Chemical Engraving (SACE), a novel micromachining technology, has offered good machining capabilities for glass and ceramic materials in basic machining operations like drilling, milling, cutting, die sinking, and others. This paper presents a review about SACE technology. It highlights the process fundamentals of operation and the key machining parameters that control it which are mainly related to the electrolyte, tool-electrode, and machining voltage. It provides information about the gas film that forms around the tool during the process and the parameters that enhance its stability, which play a key role in enhancing the machining outcome. This work also presents the capabilities and limitations of SACE through comparing it with other existing micro-drilling and micromachining technologies. Information was collected regarding micro-channel machining capabilities for SACE and other techniques that fall under four major glass micromachining categories—mainly thermal, chemical, mechanical, and hybrid. Based on this, a figure that presents the capabilities of such technologies from the perspective of the machining speed (lateral) and resulting micro-channel geometry (aspect ratio) was plotted. For both drilling and micro-channel machining, SACE showed to be a promising technique compared to others as it requires relatively cheap set-up, results in high aspect ratio structures (above 10), and takes a relatively short machining time. This technique shows its suitability for rapid prototyping of glass micro-parts and devices. The paper also addresses the topic of surface functionalization, specifically the surface texturing done during SACE and other glass micromachining technologies. Through tuning machining parameters, like the electrolyte viscosity, tool–substrate gap, tool travel speed, and machining voltage, SACE shows a promising and unique potential in controlling the surface properties and surface texture while machining.

A lightweight interpolation algorithm for short-segmented machining tool paths to realize vibration avoidance, high accuracy, and short machining time

A computationally efficient FIR-filtering based path-smoothing algorithm which simultaneously realizes vibration avoidance, high accuracy, and short machining time is proposed in this paper. Unlike the case of long G-line blocks where only the adjacent blocks affect the cornering error of a specific corner, more than two blocks affect the error in the case of short-segmented blocks. To satisfy the tolerance error, point-to-point (P2P) technique can be applied, but its machining time will be excessively elongated due to full stops at each corner. Alternatively, motions with the delay times of FIR filters fully-overlapped, which are available on commercially-installed NC systems, can realize short machining time, but they cannot satisfy the tolerance error due to the filtered trajectories accompanies by high speed. Other methods such as spline fitting may satisfy the tolerance error and realize short machining time, but they will allow vibration of the machine tool structure since these motions are not allowed to be filtered for satisfaction of the tolerance. Therefore, no method exists which realizes vibration avoidance, high accuracy, and short machining time all at the same time. For the first time in the literature, a method is proposed which realizes all of the above requirements. The proposed algorithm bases on a kinematic smoothing scheme where no spline-fitting based geometric smoothing is required, and the blended path geometry is only controlled by optimizing the feedrate (speed) profiles along a span of short G01 and G02/G03 moves. FIR filtering is applied to avoid the inertial excitation of the machine tool structure, and a novel “block splitting” method is proposed to keep elongation time of the G-line blocks the minimum. The effectiveness of the proposed method is validated through a series of experiments by comparison with conventional methods.

Machinability of Ni-rich NiTiHf high temperature shape memory alloy

Machining of Ni-rich Ni50.3Ti29.7Hf20 (at%) high temperature shape memory alloys was evaluated under flood cooling conditions. Effects of various cutting speeds (between 20 and 120 m min−1), depth of cuts (between 0.4 and 1 mm), and the associated cutting forces on the work-piece surface quality and tool wear of this alloy are presented. Experimental data demonstrates that abrasion and adhesion were the predominant wear mechanisms leading to extreme wear in a short machining time. Thermal softening mechanism dominated the trend of cutting forces until 95 m min−1 cutting speed. Beyond this speed, force components sharply increased resulting from extreme tool wear. Chip breakability of this alloy is much better when compared to NiTi shape memory alloy.

Use of a virtual milling system to generate power-aware tool paths for 2.5-dimensional pocket machining

Traditional (direction-parallel and contour-parallel) and non-traditional (trochoidal) tool paths are generated by specialized geometric algorithms based on the pocket shape and various parameters. However, the tool paths generated with those methods do not usually consider the required machining power. In this work, a method for generating power-aware tool paths is presented, which uses the power consumption estimation for the calculation of the tool path. A virtual milling system was developed to integrate with the tool path generation algorithm in order to obtain tool paths with precise power requirement control. The virtual milling system and the tests used to calibrate it are described within this article, as well as the proposed tool path generation algorithm. Results from machining a test pocket are presented, including the real and the estimated power requirements. Those results were compared with a contour-parallel tool path strategy, which has a shorter machining time but has higher in-process power consumption.

Cutting Insert and Parameter Optimization for Turning Based on Artificial Neural Networks and a Genetic Algorithm

The objective of this present study is to develop a system to optimize cutting insert selection and cutting parameters. The proposed approach addresses turning processes that use technical information from a tool supplier. The proposed system is based on artificial neural networks and a genetic algorithm, which define the modeling and optimization stages, respectively. For the modeling stage, two artificial neural networks are implemented to evaluate the feed rate and cutting velocity parameters. These models are defined as functions of insert features and working conditions. For the optimization problem, a genetic algorithm is implemented to search an optimal tool insert. This heuristic algorithm is evaluated using a custom objective function, which assesses the machining performance based on the given working specifications, such as the lowest power consumption, the shortest machining time or an acceptable surface roughness.

Interaction of tool and workpiece in ultrasonic-assisted grinding of high performance ceramics

Abstract Ultrasonic assisted grinding processes promise high potential for economical machining of brittle hard materials and improved workpiece qualities. Especially in machining of high performance ceramics as well as ceramic matrix composites (CMC) a significant decrease of process forces and increased material removal rates can be achieved. In previous publications the fundamental effect mechanisms related to ultrasonic assistance in grinding processes were described. However, implicit knowledge about the influence of the tool specifications and geometry on the maximum achievable ultrasonic amplitude is lacking. Furthermore, knowledge about the behavior of the high-frequency tool motions during tool engagement could simplify the design of ultrasonic assisted grinding processes. A targeted utilization of ultrasonic effects can be result in lower process forces, less tool wear and shorter machining times which lead consequently to more sustainable processes. The presented work provides results of the interactions of tool design, tool contact conditions and workpiece in the ultrasonic assisted machining of ceramics with mounted points.

An Integrated Smarter Cutting Parameter Selection System with a Case Study for Pocket Milling

This paper develops an integrated smart cutting parameter selection system for pocket milling. Currently, general CAD/CAM systems generate pocket milling tool paths according to user-designated cutting parameters typically including cutting depth, feed rate, and spindle speed. Pocket milling is often used for rough machining, and shorter cutting times are used to increase productivity. Although shorter machining times can be accomplished with deeper cutting, it may result in unstable cutting (chatter). Stability lobe diagrams (SLD) generated from cutting and tapping tests on selected machine tools describe the relationship between cut depth and spindle speed. However, despite offering useful information for selecting cutting parameters for chatter-free cutting, SLD has not been integrated with existed CAD/CAM systems. Therefore, this study integrates SLD in a CAD/CAM system to effectively determine the optimum cut depth and spindle speed for a theoretically chatter free pocket milling tool path. A case study is used to verify the proposed system integration.

Development of smart machining system for optimizing feedrates to minimize machining time

Abstract Feedrate optimization is an important aspect of getting shorter machining time and increase the potential of efficient machining. This paper presents an autonomous machining system and optimization strategies to predict and improve the performance of milling operations. The machining process was simulated and analyzed in virtual machining framework to extract cutter-workpiece engagement conditions. Cutting force along the cutting segmentation is evaluated based on the laws of mechanics of milling. In simulation, constraint-based optimization scheme was used to maximize the cutting force by calculating acceptable feedrate levels as the optimizing strategy. The intelligent algorithm was integrated into autonomous machining system to modify NC program to accommodate these new feedrates values. The experiment using optimized NC file which generates by our smart machining system were conducted. The result showed autonomous machining system, was effectively reduced 26%. Highlights The smart machining system was implemented in the CNC machine. Optimal feed rates enhance machine tool efficiency. The smart machining system is reliable to reduce machine time.

Laser milling of yttria-stabilized zirconia by using a Q-switched Yb:YAG fiber laser: experimental analysis

The present investigation deals with laser milling process of yttria-stabilized zirconia (YSZ), by using a Q-switched 30 W Yb:YAG fiber laser. First, the influence of laser operational parameters, laser beam scan speed, the number of time, and the sample surface is worked (number of repetition) and the scanning strategy was investigated. This first step allowed to identify the most suitable processing window in terms of surface quality and machined depth. Then, a systematic approach based on full factorial design of experiment was developed and successfully adopted to identify and explain the effect of each operational parameter on laser–material interaction and on the process outputs: roughness, machined depth, and material removal rate. The experimental results demonstrate that the laser treatment is suitable for YZS highlighting high repeatability, process accuracy, short machining time, and the possibility to easily control the process outputs.

Special Issue on Multiaxis Control and Multitasking Machining

Machine tools using numerical control (NC) devices are typical mechatronics products, and introducing them is a powerful way to automate plant production. NC machine tools in workshops meet the requirements of high accuracy and efficiency in the machining of a variety of parts and mold dies. Turning centers and machining centers are typical examples of such machine tools. Various cutting processes have been integrated in them to cope with the increase in machine parts that not only have complicated geometries but also must be made with high accuracy, in small quantities, and in a short machining time. In addition, turning and machining centers have been given multitasking capabilities, and the number of control axes has been increased so that complex products may be manufactured efficiently. Given that the strong attention and interest in multiaxis control and multitasking machine tools are rapidly increasing, it is fitting that the current state of the art of these tools and their practical and applicable technologies be presented. This special issue features 16 research articles – one review and 15 papers – related to the latest research results and practical case studies in multiaxis control and multitasking machining. Their subjects cover various advances in machine control, motion accuracy evaluation, machining error analysis, chatter vibration monitoring or suppression, trouble-free tool path generation, process planning, and new applications of the machine tools. We thank the authors for their contributions to this special issue, and we are sure that both non-specialists and specialists alike will find the information the authors provide both interesting and informative. Moreover, we deeply appreciate the reviewers for their incisive efforts. Without these contributions, this special issue could not have been realized. We truly hope that this special issue will trigger further research on multiaxis control and multitasking machining.

TOOL PATH GENERATION OF CONTOUR PARALLEL BASED ON ANT COLONY OPTIMISATION

In today’s competitive market of manufacturing industry, shorter machining time is one of important factor for reducing the manufacturer’s cost. This paper presents the minimisation of machining time of computer numerical control (CNC) by eliminating the uncut region of sharp corner based on contour parallel milling method. Each uncut region at sharp corner is represented by uncut line which consists of two nodes in x and y directions. An Ant Colony Optimisation (ACO) method is used to optimize the tool path length because of its capability to find the shortest tool path length. The optimisation of tool path length based on ACO algorithm ascertained that the cutting tool remove the uncut line once and able to eliminate the uncut region in the shortest tool path length. To observe the effectiveness of the ACO performance, the simulation results are compared with the results obtained by the previous method. Finally the simulation results show the reduction of 5% machining time compared to previous method.

Research on servo feed control of electrostatic induction feeding micro-ECM

This paper researches about the machining characteristics and servo feeding control of micro electrochemical machining (ECM) with the electrostatic induction feeding method. Since current can flow only in the rising and falling time of pulse voltage, short pulses in the order of several tens of nanoseconds can easily be obtained, realizing significantly narrow gap widths. To avoid short circuit in the small working gap of several micrometers, a servo feeding control system based on monitoring the peak of gap voltage was developed. Compared with the old method, which monitors the average gap voltage, controllability of the working gap width with higher response was obtained because of the higher S/N ratio. The influence of the reference voltage on the material removal rate (MRR) and machining accuracy was investigated. The results showed that higher MRR and smoother surface can be obtained with lower reference voltages, due to the higher current density in the working gap obtained with higher current efficiency. However, the MRR decreased when the reference voltage was too low, as a result of the interruption of machining by the frequent retreat of the tool electrode due to short circuit. On the other hand, the MRR increased with increasing feeding capacitance C1, because electric charge per each pulse duration increased in proportion to C1. The inlet side gap width was independent of C1, due to the higher MRR and shorter machining time with larger C1. Based on the preliminary study, through-holes of 50μm in diameter were machined on a stainless steel (SUS304) plate with a thickness of 50μm to investigate the straightness of the holes. The diameter of the hole at the inlet and outlet sides was 58.5μm and 55.5μm, respectively.

Elimination of the over cut from a repaired turbine blade tip post-machined by electrochemical machining

With the wide use of high-strength hardened materials in the repair of turbine blade tip, conventional machining processes are reaching limitations owing to poor surface integrity and high tool wear. Electrochemical machining (ECM) offers a potential alternative for the machining of repaired turbine blade tip. However, an over cut phenomenon often occurs in ECM of repaired turbine blade tip with a conventional tool. To overcome this drawback, this paper proposes an analytical tool correction based on the allowance distribution. Simulations were performed to analyze the current density distribution on the workpiece surface and to predict the shape evolution of workpiece. The effect of the use of conventional and corrected tools on workpiece shape was compared experimentally to verify the simulation. The simulation and experimental results illustrated that the corrected tool is helpful in removing the current density peaks and thus eliminating the over cut. Additionally, the effect of the applied voltage and machining time on the machined shape of turbine blade tip using the corrected tool were investigated experimentally. The results revealed that the machined shape of turbine blade tip using corrected tool is mainly determined by the machining time. A too long or too short machining time generates concave or convex shapes respectively, while only the optimum time produces an acceptable shape. Repeating the experiments with optimum parameters showed that turbine blade tip with desired shape and good surface quality can be reliably ECM machined using the corrected tool in batch repair operations.