Workpiece Holder Research Articles

Investigation of the Surface Treatment Process of AISI 304 Stainless Steel by Centrifugal Disc Finishing with the Use of an Active Workpiece Holder.

This article presents the results of experimental studies of the centrifugal disc finishing (CDF) process of 304 steel elements with the use of an active workpieces holder, that allows workpieces for additional rotational and oscillation movements. The main aim of the research was to evaluate the mechanism of formation of the surface texture and to assess the intensity and effectiveness of the machining process. It is shown that additional movements of the workpiece significantly affect the formation of the machining traces generated by the elementary phenomena of micro-cutting, scratching, grooving, etc. As a result, these combined and complex interactions lead to the formation of the surface topography of the workpieces. Based on the research results, it can be concluded that the use of an active workpiece holder in the CDF process allows changes in the intensity of the machining process. Moreover, the active holder allows modification of the surface smoothing process. The intensity of the treatment process depends primarily on the location of the workpiece holder in the appropriate energy area of the work charge. On the other hand, the efficiency of the workpiece surface smoothing depends on the parameters of the oscillation and rotational movements of the workpiece mounted in the active holder. The presented research results show that the use of an active holder, enabling rotation and oscillation of the workpiece, may lead to a more effective use of smoothing processes in CDF machines. The analysis of the results shows that the values of the Sdr and Sa parameters are more strongly dependent on the vibration frequency and increase with its increasing frequency. This is undoubtedly the result of the concentration of smoothing marks on the smoothed surface. However, with regard to the rotational speed of the object, this relationship is non-monotonic, and its greatest influence occurs at its intermediate values. It follows that this activity does not have a significant impact on the generation of the number of smoothing marks and the degree of their concentration. The research methodology proposed in the work allows the initial determination of the dependence of the results of the CDF process on the machining parameters, including the parameters of the active holder. This methodology can also be used for machining materials other than AISI 304 steel.

Cutting of Rock by Wire-Sawing in Vacuum (2nd Report)

This paper deals with the measurement and simulation of the saw wire temperature during machining a rock sample in vacuum. It is expected for wire-sawing to keep cutting performance by successive supply of cutting edges. The performance of wire-sawing in vacuum has been investigated for lunar and planetary explorations. To clarify the deterioration due to the nickel adhesion on the rock, the temperature rise was investigated. In the experiment, the saw wire was reciprocated with slider-clank mechanism to machine a rock sample. A workpiece holder was mounted on a lever though an octagonal load cell with strain gauges to measure the principal force and thrust simultaneously. The saw wire temperature was measured by its electric resistance during machining. In vacuum, the saw wire temperature rose about 30°C at a wire speed of 0.16 m/s. The generated heat during machining was conducted to the rock sample as well as the saw wire. The temperature rise of a saw wire during machining in vacuum was analyzed by a three-dimensional finite difference model. In the simulation, the saw wire temperature rose about 55°C at the same wire speed as the experiment. The trend of the simulated temperature rise coincided with the measured one. The generated heat during machining affected little on the nickel adhesion and the performance of wire-sawing in vacuum.

Optimization of Jet Impingement Erosion Process of Alumina-Titania coated stainless steels

The mineral processing industries depend on conveying feed stocks in slurry form. Slurries erode the carriers as well as the pumps which are used in the process. Material loss due to erosion is a serious problem in transporting solid liquid mixture. The pump impellers are generally made of stainless steel. The efficiency of the stainless steel impellers decreases due to erosion even though the pump continues to work. These impellers are damaged or lose its efficiency roughly during 250–300 h of operation. Stainless steel materials used for impellers are taken to the required dimension and are given Alumina-Titania coating using detonation spray process. The thickness of the coating is 250 µm. The coated specimen is mounted in the work piece holder and subjected to erosion test using water Jet erosion tester.The parameters that are varied are exposure time, velocity of the jet and angle of impingement. Through this study it was found out that the most influencing factors of Liquid impact erosion are impact Angle and exposure time. It is observed that maximum erosion takes place when the impact angle is 90 degrees The SEM images reveal that the material removal takes place due to chipping and micro cutting. This occurs when the angle of impingement is 90° and the velocity of impingement is reasonably higher.

Vibration reduction during milling of highly flexible workpieces using active workpiece holder system.

The milling of highly flexible workpieces, such as thin-walled structures used in turbine blades, aerospace equipment, and jet engine compressors, requires vibration compensation to improve the quality of the workpiece surface. Vibration can be reduced by selecting appropriate cutting parameters. However, this approach reduces system productivity. This paper presents an active workpiece holder that controls the vibration of general computer numerical control machine tools. The proposed holder, which comprises a flexible guide mechanism, driver, and sensor, measures vibration and actively controls it using piezoactuators. A high-rigidity flexure mechanism was designed for the holder, and finite element method simulation and modal analysis were performed. Finally, the proposed system was fabricated, and experimental verification indicated that the system reduced vibration. The surface quality obtained using the controlled system was ∼50% better than that obtained using the uncontrolled system.

Thermal and technological aspects of double face grinding of C45 carbon steel

In grinding, the contact zone temperature is a decisive factor influencing the achievable surface quality and the grinding tool wear. In contrast to other grinding processes, only few information regarding double face grinding with planetary kinematics when processing steel is known up to date. Since the successive substitution of industrial double-sided lapping processes by double-sided grinding, it has become necessary to the conducted research in order to provide deeper understanding of the process and factors that influence it. To determine the workpiece temperature during grinding of C45 components, silicon temperature sensors were integrated into the workpiece holders and technological investigations were carried out. The influences and interactions of the mean cutting speed, cooling lubricant flow rate and cutting ability of the grinding wheels on the resulting workpiece temperature were analysed. Subsequently, modelling enabled an empirical estimation of the resulting workpiece temperature for processes in the investigated test area. With regard to the design and optimization of processes for machining plane-parallel workpiece surfaces, this model is a helpful tool for avoiding thermally induced workpiece damage and reduction of tool wear. Furthermore, the method can be used to conduct further examinations on the grinding process and to reduce the amount of cooling lubricant used, to improve life cycle assessment.

Design and fabrication of Automated mechanism for chemical pre-treatment process in Powder coating

The paper is intended to design and fabricate an automated mechanism for chemical pre-treatment process in powder coating for avoiding the manual handling of metal substrates in chemical pre-treatment processing in order to remove dust, to avoid corrosion and to provide good adhesion for powder coating. For this, a gantry crane structure is proposed where two vertical columns and a horizontal beam setup are designed to which a movable carriage is mounted across the horizontal beam. The movable carriage is fitted with a pulley mounted by a rope, the end of the rope is connected to a hanger which has a workpiece holder to which a metal substrate is hanged. The process is controlled by a programmable controller which is programmed with appropriate delays and according to the process designated, the hanged workpiece will move up and down and get dipped into the chemical tank. Once the delay was completed, the carriage automatically moves horizontally to the next tank. The gantry crane structure with movable carriage having pulley and programmable controller are well suited for automating pre-treatment process and it can safeguard manual workers' hands from hazardous chemicals in the tank and also achieving the exact delay operations of each tank process.

Optimal selection of process parameters to reduce vibration during end milling of Al 356/SiC metal matrix composite

Machining performances are strongly influenced by vibration which occurs due to the dynamic nature of machine toolstructures. A self excited vibration commonly known as chatter is frequent debacle occurs during milling operations whichcause worsening outcomes such as excessive tool wear, poor surface finish and reduced tool life. In this paper an effort hasbeen tried to optimize the machining and geometrical parameters for reduced vibration using Taguchi method with greyrelational analysis during end milling of Al356/SiC metal matrix composites. The twin channel piezoelectric accelerometerhas been used to measure vibration. Acceleration amplitudes at two different positions, one in spindle and another in workpiece holder have been recorded for each experiment. Analyses of variance (ANOVA) have been applied to find theprominent parameters and the optimal parameter combination for best average response and signal to noise (S/N) ratio.Grey relational analysis has been implemented to find the optimal permutation of machining and geometrical parameters byconsidering both responses (acceleration amplitude taken at two different positions) simultaneously. Confirmation testsestablished that the grey-based Taguchi method has been successful in optimizing the process parameter for reducedvibration.

Low-Cost Piezoelectric Transducer for Ceramic Grinding Monitoring

This paper presents a performance assessment of the low-cost thin-disk piezoelectric diaphragm (PZT) for the surface integrity monitoring in the grinding operation. PZT diaphragms are flexible, low-cost, and smart devices, making them promising for applications in manufacturing fields, such as in the grinding operation. To accomplish this, experimental grinding tests were carried out on workpieces of ceramic material covering from slight to severe machining conditions. A low-cost thin-disk PZT diaphragm was assessed, which was attached to the workpiece holder using a cyanoacrylate glue. In addition, a commercial and consolidated acoustic emission (AE) sensor was used as a baseline for comparative purpose. Likewise, the surface roughness measurements were performed after grinding each workpiece to support the sensor monitoring system. Feature extraction using frequency spectrum and time domain analysis were applied to the sensor signals by means of fast Fourier transform (FFT), digital bandpass filters, root mean square (RMS) value, and power deviation (DPO) metric. The results indicate a clear relationship between the thin-disk PZT diaphragm and the conventional AE sensor for surface integrity monitoring in grinding, which proves the effectiveness and reliability of an innovative sensing device for the present application.

Optimization of Machining and Geometrical Parameters to Reduce Vibration While Milling Metal Matrix Composite

During end milling of metal matrix composite (MMC), it is subjected to varying impact load and cutting force. This action induces vibration during machining, which results in poor surface finish and increased tool wear. In this study, an attempt has been made to determine the optimum level of geometrical parameters such as helix angle, nose radius and rake angle and machining parameters such as cutting speed, feed rate and depth of cut to obtain minimum vibration amplitude during end milling operation using particle swarm optimization (PSO). Machining was carried out on aluminum (Al 356)/silicon carbide (SiC) particulate MMC using high-speed steel end mill cutter. The experimental design adapted for conducting the experiments was L27 orthogonal design array. The experiments were conducted using vertical machining, and the vibration amplitudes were measured at two positions (spindle and workpiece holder) using a twin-channel piezoelectric accelerometer. The empirical regression model was developed by relating the input parameters and the output vibration amplitudes, and optimization of process parameters to obtain minimum acceleration amplitude was done using PSO. Scanning electron microscopic images of the milled surfaces were examined, and it indicated the presence of cracks and holes due to pulling out of SiC particles.

Open-loop linearization for piezoelectric actuator with inverse hysteresis model

For developing an active workpiece holder, piezo actuators are used to apply compensation forces and displacements. These actuators suffer from hysteresis effects which impair accuracy and performance. The focus of this work is the modelling of the actuator’s hysteresis and establishing a corresponding inverse model to compensate the effect in an open-loop approach. The model, on the basis of easy to calculate sigmoid functions, is shown to yield good linearization of the actuator’s behavior.

Study on influential parameters of hybrid AFM processes: a review

The abrasive flow machining (AFM) processes are ultra-precise finishing techniques widely used as finishing solutions for micro/nano finishing of inaccessible contours on difficult to machine components. The AFM processes use highly visco-elastic properties of the abrasive laden medium as a cutting tool for deburring, edge rounding and polishing the surface. Due to the design of workpiece holder and hybridization of basic AFM, the complex shear modulus of the abrasive laden medium can locally be influenced and thus a targeted removal of material from workpiece can be achieved, as a result, there was improved performance, productivity, surface integrity, and texture. This article addresses the detailed classification of AFM processes based on the use of different energy and tooling and highlights the critical outcomes in each category. The objective of this article is to review and summarize various process parameters of AFM processes like extrusion pressure, medium flow volume, medium flow rate, number of cycle, viscosity, workpiece geometry, etc. and their effects on roughness value and material removal rate. Key capabilities and noted findings concerning various AFM processes in addition to their applications and future challenges are also discussed in this paper.

A Novel Concept of CNC Machining Center Automatic Feeder

Machining operations are extremely relevant in the current metalworking scenario. Many efforts have been made by researchers in order to optimize machining trajectories and automatic machine feeding systems. However, only the large companies with huge productions have capacity enough to invest in sophisticated feeding systems. This project intends to present a solution to extend the autonomy of machining centers by using a 6-axis robot to replace the operator on work piece feeding operation. The system consists in a robot embedded in the same structure as a small warehouse positioned on one side of the machine, maintaining the possibility of operating in a standard manner. With the modular construction of the warehouse it is possible to accommodate numerous work piece sizes and engraving a Quick Response code at the work piece holder allows its identification and therefore brings flexibility to the system. It is expected that a milling machine equipped with this system present an extended working capability without human intervention, becoming possible to extract more useful process control information, in line with the Industry 4.0 needs.

Modelling and Simulation of a New Variable Stiffness Holder for Milling of Flexible Details

Abstract Modern industry expectations in terms of milling operations often demand the milling of the flexible details by using slender ball-end tools. This is a difficult task because of possible vibration occurrence. Due to existence of certain conditions (small depths of cutting, regeneration phenomena), cutting process may become unstable and self-excited chatter vibration may appear. Frequency of the chatter vibration is close to dominant natural frequency of the workpiece or the tool. One of the methods of chatter vibration avoidance is matching the spindle speed to the optimum phase shift between subsequent cutting edges passes (i.e. the Liao-Young condition). However, the set of optimum spindle speeds from the point of view of vibration reduction may be not optimum one from other points of view. For example milling efficiency or machine tool capabilities cannot be assured. This article presents the idea of a workpiece holder with adjustable stiffness and discusses a new variant of its realization. In the holder, milling process is performed at constant spindle speed and feed speed. In order to avoid vibration the holder stiffness is modified. Stiffness changes modify natural frequencies of the workpiece and thus it is possible to modify dynamic properties of the workpiece in such a way that arbitrary chosen, constant spindle speed will be optimum, due to the Liao-Young condition performance. Calculation of the optimum stiffness is performed before milling, based on the workpieces modal identification results and the finite element model simulations.

Compensation of tool deflection in micromilling using workpiece holder control device

This paper presents a real-time tool deflection compensation technique to improve micromilling machining accuracy. Lateral and axial errors of the cutter location (CL) caused by tool deflection were estimated using the cutting force and compensated by applying an additional feed to the workpiece that is equivalent to the estimated CL errors. To evaluate the proposed method, a workpiece holder comprising a three-axis stage and a tool dynamometer was installed on the work table of a machine tool. A proportional derivative (PD) position controller with a model-based tool deflection estimator was designed and implemented on a real-time computer to control the workpiece holder. Lateral and axial machining errors in side milling and radii errors in circular slot milling are discussed to demonstrate the effect of tool deflection compensation.

Design of An Active Workpiece Holder

Milling is one of the most used machining processes thanks to its high flexibility and high achievable quality. The performance of milling machines is constantly increasing, improving the convenience and increasing the competitiveness of this operation. However, the trend of performance improvement has found a technological limit: self-excited vibrations due to the dynamics of the system machine-workpiece-tooling (i.e. chatter). Chatter is the most dangerous dynamic phenomena that could happen during milling; due to its regenerative nature, it could lead the machine and the tooling system to a heavy fault or to the disruption of the workpiece. This paper develops an active workpiece holder that avoids chatter vibrations by a smart actuation of the workpiece. The design of the workpiece holder is a difficult task due to strict product requirements and the need to create a decoupled structure. The decoupling of the structure is a fundamental requirement of the product because this affects the controllability of the system. Axiomatic Design Theory is used to support the definition of the product requirements and the product architecture. After the definition of the optimal structure of the workpiece, the design features are integrated in order to obtain a functional decoupled structure.

Chip root analyses in peripheral longitudinal up-grinding by means of a new quick-stop device

Due to its specific process characteristics the micro geometric contact conditions in grinding cannot be directly observed. An approach to visualise and analyse the mechanisms in the contact zone in grinding is constituted by quick-stop experiments. These are state-of-the-art in geometrically defined machining processes but were not yet successfully applied in geometrically undefined machining processes like grinding. In this article, a newly developed quick-stop device is presented that is suitable to analyse the micro geometric contact conditions in peripheral longitudinal up-grinding. This device mainly consists of carrier components with impactors on both sides of the grinding tool and a pneumatically extendable stopper that is integrated into a pivot-mounted work piece holder. In initial experiments with this new quick-stop device the chip formation mechanisms and the number of active grains along the contact zone were identified.

An experimental investigation into resonance dry grinding of hardened steel and nickel alloys with element of MQL

Current policies on environmental issues put extra pressures on manufacturing processes to be resource efficient and eco-friendly. However, in grinding processes, large amounts of cutting fluids are used. These fluids are not environmental friendly thus require proper management before disposal with associated cost. Hence, this work sets to explore low-frequency vibration in grinding in order to improve coolant application in conventional grinding at the first stage with the aim to introduce this into high efficiency deep grinding (HEDG) at latter stage. An attempt is made to grind nickel alloys with minimum quantity lubricant (MQL) as oppose to flood cooling. To achieve this with minimum alterations to the machine tool, a piezo-driven workpiece holder was developed for surface grinding. This simple innovative workpiece holder allowed oscillating during actual grinding process. However, this paper presents the results of low-frequency oscillatory grinding in dry and near-dry conditions. The response of the machine tool spindle unit is presented alongside with the workpiece holder response. In this investigation, hardened steels and nickel alloys were ground with vibration assistance. The grinding forces are illustrated together with the surface finish. The wheel performance is given in terms of grinding ratio.

New Design “Duplo-headstock”

The quality of machine tools is critical in determining their productivity and the accuracy of the finished work piece. The headstock of the machine tool has the greatest impact on these parameters. The tool or work-piece holder must meet specific demands for maximum speed and rigidity. These two parameters are variable, but always in contradiction, and depend mainly on the Spindle-Bearings System (SBS). In this context, SBS are increasingly being produced in combination with roller bearings, and with various combinations of radial ball bearings. This is mainly because the radial ball bearings allow groupings of different combinations to achieve the optimal compromise between the required maximum speed and the desired stiffness of the SBS. Stiffness, especially in ball bearings, is not constant but dependent on the magnitude of the load. The SBS is a statically indeterminate system, and an accurate calculation of the bearings and its nodes, as well as the whole system, is only possible using iterative methods. The exact calculation of SBS stiffness cannot be achieved without the use of powerful computers and high-quality software. Selection of the optimal configuration is achieved by analyzing a number of potential, alternative SBS solutions. The exact calculation of a large number of variants, and manufacturing their prototypes, is time consuming and very expensive. The solution is to quickly determine, with sufficient reliability, the parameters of the bearing nodes, which are influenced by the radial ball bearings. It is only in the final variation that an accurate calculation using iterative methods can be made, followed by subsequent production of a prototype for verification. At our workplace, we dedicate our time to intensive research into bearing nodes and the complete SBS.

Process Plans and Manufacturing Dimensions for the Steering of Machining: The Copilot-Pro® Methodology

To set the machining, the technique commonly used is to measure dimensions between each machined surface and the one which locates the workpiece into the workpiece holder. This technique leads to dimensions with much smaller tolerances than the ones specified on the design drawing and to long time setting. On an example of a screw machining process we present the first stage of the Copilot-Pro® methodology. It consists in identifying the groups of manufacturing operations which must be done before extracting the workpiece from the machine-tool to measure the surfaces achieved. Thus, the number of workpieces extracted from the machine-tool is minimized which reduces the setting times, the number of unfinished and rejected workpieces and which permit to select manufacturing dimensions with higher tolerances.

Development of High-precision Micro CNC Machine with Three-dimensional Measurement System

This study aims at developing a machine center consisting of high-speed micro-milling machine, micro-EDM and coordinate measuring machine. The machine center uses a commercially available PC-Based CNC controller and micro-EDM power supply. The structure design is based on an open L-shaped granite base, where a Z-axis platform is mounted on the top of an L-type base, while X and Y-axis platforms are assembled by stacking. Additionally, a fuel tank, WEDG winding mechanism and a work piece holder were fixed to the X-axis work platform. Three-axis positioning stages use servomotors to drive lead screws for motion control. Equipped with a commercially available PC-Based CNC controller, any processing path and precision motion control can be achieved. In addition, the Z-axis platform includes a commercially available rapid adapter for the rapid assembly of C-axis rotation, high-speed micro-milling spindle and three-dimensional measuring probe. This means that the machine can quickly switch between micro-EDM, high-speed micro-milling and three-dimensional measurement. The machine center successfully produced micro probes with a front-end sphere with a diameter of less than 100 μm. Combined with a self-developed trigger circuit, it also completed a three-dimensional touch trigger probe. The measurement software was developed with Borland C++ Builder. Integrating the three-dimensional touch trigger probe with the three-axis linear scale, the three-dimensional coordinates of the measured values were calculated and processed. It has been successfully applied to the measurement of point, line, circle and angle.