Thin Workpiece Research Articles

Effect of the parameters of metal forming processes on the behaviour of thin-walled structures

Abstract The parameters of metal forming processes affect the distribution of material properties through the workpiece. In particular, sheet rolling and drawing processes induce the through thickness gradient of material properties in sheets that are used in thin-walled structures. The present paper studies the effect of this gradient on the product in the shape of two developable shells (circular cylinder and developable helicoids with different screwing degree) obtained from a plane metal workpiece by parabolic bending. The possibility of manufacturing any developable product without creases and tears from a thin metal workpiece is theoretically proved and the influence of metal forming process on the resulting stress-strain in the workpiece is examined. The results of the research can be implemented in different engineering fields as marine design, civil engineering, air-space industry, and in a range of manufacturing processes.

High-Precision Grinding of Thin and Large Optical Workpieces with the Kinematic Support

In fabrication of a thin and large optical element, grinding with the conventional fixture cannot achieve high precision. When such a thin and large workpiece is tightly fixed to the grinder table, the inconsistency in the form of the contact surfaces and thermal expansion of them produce unexpected stress on the workpiece. After finishing grinding with the fixture, the deformation of the ground surface would happen, accompanied by the release of the stress. This paper proposes a stress-free fixture method by removing over-constraint from the fixture structure. Corrective grinding is executed by calculating the deformation of the workpiece due to the load of the grinding wheel. Furthermore, the fixture enables on-machine measurement by an interferometer above the grinder by replicating the same condition as when the optical element is in use. We achieved a precision of RMS 0.30 µm on a one-meter-size glass ceramic of 60 mm in thickness.

Heating Strategies for Efficient Combined Inductive and Convective Heating of Profiles

In this paper, an experimental and numerical study of a novel heating strategy is shown for thin profiled workpieces using induction and convective heating at the same time. A characteristic of induction heating is its potential for achieving efficient local heating due to the direct conversion of electromagnetic fields to thermal energy. One disadvantage of this is the high temperature gradients that occur on the workpiece and, therefore, the uneven distribution. This is even more significant for thin workpieces or workpieces made out of sheet metal due to the lighter mass and, therefore, less conduction away from the heating zone. This paper presents the idea of combining induction heating with convection to obtain a more even distribution of the temperature but with considerable energy savings compared to pure convective heating. The combination of both heating methods has been analysed both experimentally and numerically with different geometries. The multiphysic simulation included both the induction heating and also the convective heat transfer for temperature-dependent material properties. The results of the simulations and the experiments were in good agreement, and both showed that there is a huge potential for energy savings when convective heating is supported by induction heating (up to 53%). This study provides a reference for future industrial applications for heating sheet metal workpieces, e.g., for drying paint.

Investigation of the stability and contact stiffness of workpiece inside fixture in different machining conditions

The dynamic stability of machining processes is influenced by the dynamic stability of the workpiece and fixture assembly. This effect has not yet been sufficiently considered. Achieving dynamic stability by simply applying a large amount of clamping force is a basic method and involves damages such as elastic deformation of relatively thin workpieces, damage to the clamping surfaces, and high wear of fixture components resulting in malfunction. In spite of this, to the best knowledge of the present authors, the contact stiffness between workpiece and fixture as an influencing parameter has not been sufficiently paid attention by researchers and these parameters have not been taken into account in the equations of dynamic stability. The contact stiffness itself is influenced by the machining parameters. In the present study, the changes in contact stiffness in different machining conditions are investigated as a partial undertaking to fill the gap existing in the modeling of the machining dynamics. In this paper, by defining the mathematical model of the workpiece-fixture system and calculating the matrices of contact stiffness and fixture stiffness, the results of changes in various machining parameters in the stiffness of the workpiece-fixture system have been investigated. The results showed that high contact stiffness cannot be provided simply by applying the maximum force of the clamps. Rather, by increasing the spindle speed, the contact stiffness will increase significantly. Furthermore, by increasing the spindle speed, further increase in the contact stiffness will be achieved with lower feed rates, which will not be economically viable.

Investigation of chatter detection with sensor-integrated tool holders based on strain measurement

Machining chatter is one of the most critical issues that restrict the productivity in milling of thin wall workpieces. Sensor-integrated tool/tool holders, which provide data collection during cutting, can be employed for online chatter detection. Recently, there has been an increasing number of strain-measurement-based smart tool holders, which can measure bending moments and/or torque. Although accelerometer-integrated tool holders have been tested, sensor-integrated tool holders based on strain measurement have not been evaluated for the chatter detection in milling. This paper investigates the potential of chatter avoidance using a commercial sensor-integrated tool holder based on strain measurement.

Research on near field sound pressure of circular piston source based on angular spectrum method

The accuracy of ultrasonic nondestructive examination is limited by the limitation of near field diffraction. With the development of nearfield optical, angular spectrum method is introduced into the acoustic field, which provides a significant direction for the ultrasonic diffraction limit resolution detection. The main research of this paper is the transmission of near field ultrasound in thin workpiece and the law of the interaction of tiny flaws. The paper establishes the relationship between the longitudinal wave signal and the structure of the workpiece and the types of flaws. A method is found that whether there are flaws can be determined near field area by analysing the acoustic field characteristics of workpiece surface. Finally, comparing the calculation results with the finite element simulation, they verify each other, the method turns out to be correct in this paper. The model can also be used to improve the ultrasonic noise reduction algorithm and the extraction of minimal defect feature. It has a greatly practical significance.

Numerical study of transient thermal profile and thermally deformed tip shape in Wire EDM of narrow angles

The geometrical error observed in the tip while machining sharp corners in thin workpieces with WEDM is studied numerically. A finite element model is developed to study the contribution of thermal effects in the tip deflection phenomenon. Initially a temperature distribution model is developed by considering formation of kerf gap and time dependent changes in material properties of different zones in the domain. The transient temperature data is fetched from the model and used in a sequentially coupled Thermo-Mechanical model to predict the deformation of tip. Numerically predicted tip deflection and the shape of the profile is validated and compared with experimental results.

High Precision Visual Dimension Measurement Method with Large Range Based on Multi-Prism and M-Array Coding.

The visual dimension measurement method based on non-splicing single lens has the contradiction between accuracy and range of measurement, which cannot be considered simultaneously. In this paper, a multi-camera cooperative measurement method without mechanical motion is proposed for the dimension measurement of thin slice workpiece. After the calibration of the multi-camera imaging system is achieved through a simple and efficient scheme, the high-precision dimension measurement with a large field of view can be completed through a single exposure. First, the images of the edges of the workpiece are compressed and combined by splitting and merging light through the multi-prism system, and the results are distributed to multiple cameras by changing the light path. Then, the mapping relationship between the global measurement coordinates and the image coordinates of each camera is established based on the globally unique M-array coding, and the image distortion is corrected by the coding unit composed of black and white blocks. Finally, the edge is located accurately by edge point detection at the sub-pixel level and curve fitting. The results of measuring a test workpiece with the dimension of 24 mm × 12 mm × 2 mm through a single exposure show that the repeated measurement accuracy can reach 0.2 µm and the absolute accuracy can reach 0.5 µm. Compared with other methods, our method can achieve the large-field measurement through only one exposure and without the mechanical movement of cameras. The measurement precision is higher and the speed is faster.

Research on the Weight Removing Model and Control Method for the Unbalance Vector of Thin Disc Workpiece

Aiming at the structuring characteristics of thin disc workpiece, we propose the weight removing model and control methods to reduce the mass unbalance vector. Based on the material removing and correcting principle for unbalance workpiece, the weight removing model of drilling and reaming hole way and internal and external arc milling is discussed. The iterative control method with variable weight removing rate is proposed to reduce the weight removing material of the first-time correction and improve the ultimate correcting accuracy. The online measuring and correcting feasibility for unbalance workpiece is verified by experimental way. The advantages of the proposed iterative control method are discussed by simulation analysis. The research results can be used for the online correction of the unbalance disc workpiece on the NC machine tools or automatic dynamic balancing machine.

Glass welding with ultra-short laser pulses and long focal lengths A process model

The welding of glasses with ultra-short laser pulses and high-NA optics has matured to a well-established process. The short focal length requires relatively thin work pieces in the order of 1-2 mm, and the short Rayleigh length requires a very precise adjustment of the laser focus relative to the interface to be welded.To make welding of thick samples possible with relaxed alignment requirements, we welded optically contacted fused silica with a focal length of 65 mm. The resulting welding seams can be as deep as 2 mm and more. It turned out, that they grow from the focal point towards the laser source with increasing pulse energy and irradiation time. A thermal model for the growth of the molten zones will be presented and compared to the process with short focal lengths. Furthermore, the results of tensile tests and helium-leakage tests of welded fused silica samples will be presented.

Clamping deformation of thin circular workpiece with complex boundary in vacuum fixture system

With the increasing requirements on the parallelism and flatness of thin-walled flat parts, vacuum fixtures have been widely used in precision manufacturing. While several research studies focus on using the finite element method to predict the clamping deformation in the vacuum clamping system, it is very time-consuming and often unable to obtain the convergent solution with complex boundary conditions. In this paper, based on Kirchhoff plate theory, a new method was proposed to solve the clamping deformation of the thin circular workpiece with various complex boundary conditions subjected to vacuum negative pressure. The improved Rayleigh–Ritz method was applied to solve the spatial partial derivatives. The admissible function was composed of polynomial and trigonometric functions, which explained the unconstrained state of the workpiece. Furthermore, Courant’s penalty method was used to handle the constraint conditions. Simulations and experiments were conducted to verify the convergence, feasibility, accuracy, and applicability of the proposed method. The results showed that the proposed method is well-suited for arbitrary boundary conditions with vacuum fixture system, and its convergence was good compared to the finite element method. Finally, the influence factors of clamping deformation were discussed comprehensively and were optimized to reduce the clamping deformation. The proposed method can quickly calculate the clamping deformation of the thin circular workpiece under different vacuum clamping conditions, which provides the guidance for fixture design and the selection of clamping parameters for researchers in the processing field.

Investigation on the scale effects of initial bulk and machining induced residual stresses of thin walled milled monolithic aluminum workpieces on part distortions: experiments and finite element prediction model

Thin walled monolithic milled aluminum workpieces are commonly used in the aerospace industry, because of their good properties such as a high overall strength-to-weight ratio. After machining those parts distortions occur. Residual stresses (RS) are the main driver for those distortions. Two types of RS, the initial bulk residual stresses (IBRS) and the machining induced residual stresses (MIRS), contribute to the part distortion. In this study, the scale effects of each RS type and their combined effects on the distortion of milled thin walled aluminum workpieces are evaluated for different wall thicknesses, different IBRS conditions and different MIRS. In this context a finite element model (FEM) is developed to predict the distortion due to the measured RS. A 3D linear elastic model, considering both types of RS as input is presented. The simulation outcome is validated by experiments.It was found that both RS types contribute to part distortion. For parts containing high IBRS, those IBRS dominate the distortion. For stress relieved parts, containing low IBRS, the MIRS dominate the distortion. The investigations showed that the shear RS induced by machining are crucial for the distortion. The developed FEM model is able to predict the distortion due to both RS types.

Investigation of the diameter error when turning thin walled workpieces

Every manufacturing process undergoes geometrical deviations from the defined geometry. In order to produce workpieces within the specified quality, a downstream quality assurance is carried out. This quality assurance is expensive and time consuming. If the geometrical error could be estimated during and after the manufacturing process this quality assurance can be reduced. The geometrical error emerges due to different causes. One of these causes is the deflection of tool and workpiece. This alters the depth of cut and therefore causes a radial error on the machined workpiece. An additional cause is the progressing tool wear during continuous machining, also influencing the depth of cut.This paper presents a method to determine the radial error after turning. The method is based on finite difference calculations, suitable for the investigation of the local error of multi-diameter workpieces. Within the developed model the deflection due to shearing and bending of the workpiece and the tool are examined. Furthermore, the tool wear is considered. Additionally, the calculation for a locally varying depth of cut is presented. The results show that by taking the tool wear into account the model error was decreased from 63.08 % to an absolute error of 5.72 %. Using the proposed model, it is possible to generate relevant data about the geometrical manufacturing error immediately after every machining process.

Spajanje raznorodnih metala ultrazvučnim zavarivanjem

The dissimilar metal welding always challenges. The different alloys have different physical and mechanical properties. In the case of the electronic component of the car, it needs to establish a joint between dissimilar metals. The useful metals are for this application are copper and aluminium. Even that has good conductivity, corrosion resistance and formability. By fusion welding technologies these thin metal workpiece joining is not a simple technology. To use a solid state welding technology can be a suitable solution to establish a cohesion joint in case of this task. It well-known much suitable technologies, even that all of them has advantages and disadvantages. The choice of solid-state technology is the ultrasonic welding process. In the case of this process, we use pressure and high-frequency vibration for welding. Besides this process, the friction and vibration generated heat is lower than the metal melting temperature. The base of this technology is the ultrasound-assisted high-level formability. The optimization of this dissimilar joining technology parameters needs many pre-welding and testing process. In this work, we wanted to introduce this empirical optimization process.

Study of phenomena responsible for part distortions when turning thin Inconel 718 workpieces

• A thorough in-situ experimental procedure to measure geometrical errors is presented. • Geometrical errors due to cutting forces and machining induced residual stresses are separated. • In the studied case, the impact of subsurface residual stresses on the total geometrical error is not negligible. • Tool wear dramatically increases the distortions linked to cutting forces and subsurface residual stresses. • The proportion of total errors linked to machining induced residual stresses increase with tool wear. Machining thin workpieces is a challenging task as geometrical errors may result from the combination of several phenomena. Among these, elastic workpiece deformation and machining induced residual stresses may be predominant sources due to low part stiffness. There is a lack of studies trying to quantify the influence of machining induced residual stresses on the total geometrical errors. A thorough experimental methodology is developed to quantify the influence of both phenomena separately by comparing the workpiece shape and dimensions, in-situ , before and after machining, using laser sensors. The proposed methodology can also be used to quantify the geometrical errors linked to clamping or stress rebalancing following material removal. The case study is the finish turning of thin Inconel 718 workpieces using carbide tools. In the studied case, machining induced residual stresses are responsible for 3–32 % of the total geometrical errors depending on tool wear and cutting parameters.

Cutting force validation and volumetric errors compensation of thin workpieces with sensory tool holder

The purpose of this study is to improve the machining precision and processing efficiency in the milling process of thin workpieces. A static analysis is conducted in commercial software ANSYS with the predicted cutting force exerted on the feature points. In this study, the cutting forces are measured by a sensory tool holder and the data coordinate transformation between the tool and workpiece has been established. Modified tool paths for compensation volumetric errors were built according to the deformation data as a CL (cutter location) file. Moreover, three program interfaces are developed based on MATLAB for calculating the cutting constants, predicting cutting forces, and generating the compensated tool path, respectively. A thin workpiece machining example was made for demonstration and verification, including a tool path simulation in NX CAM (computer-aided manufacturing) software and practical machining on a CNC milling machine. The result shows that the presented method successfully improved machining precision and processing efficiency.

A Study of Nonlinear Behavior of Flexible Tool and Workpiece in Turning Operation With Regenerative Effect Under Internal and Primary Resonance Conditions

Abstract In this work, the nonlinear dynamic behavior of turning operation has been studied considering flexible tool and thin cylindrical workpiece. The system is taken as a two-degree-of-freedom system with nonlinear stiffness and is subjected to self-excited vibration because of the regenerative effect. The cutting force is considered to be a combination of a constant and periodic force in addition to the force due to the regenerative effect. The regenerative effect during turning operation is included in the mathematical model, resulting in a nonlinear delay differential equation. Here, the natural frequency of the workpiece is assumed to be closed to that of the tool, leading to 1:1 internal resonance. Further, the frequency of the time-varying cutting force is assumed to be closed to the natural frequency of the workpiece giving rise to primary resonance condition. The nonlinear responses and the stability of the tool and the workpiece have been determined using a higher-order method of multiple scales (MMS) under internal and primary resonance conditions. The solution of the equation of motion using the MMS is validated by comparing the solution obtained using the numerical method. The effect of the tool and workpiece stiffness nonlinearities on steady-state frequency responses and stability is investigated, and system parameters are also identified to have stable turning operation. This work will find applications in estimating the system parameters for chatter-free turning operation with a flexible tool and workpiece when their dynamic compliances are comparable.

DESIGN AND DEVELOPMENT OF PORTABLE VACUUM CLAMPING (PVAC CLAMP) FOR TOOL ROOM

Clamping in tool room usually uses tools and holding devices such as vise to clamp workpieces. However, conventional clamping device such as vise is time consuming, expensive and can not hold thin workpiece. Therefore, this project presents the design and development of portable vacuum clamping (Pvac CLAMP) for tool room to overcome those limitations. To design and develop Pvac CLAMP, the machines used in the process are milling machine and drilling machine. After Pvac CLAMP had been developed, a test were carried on the Pvac CLAMP. The test was surface roughness measurement. The result shows that Pvac CLAMP has better surface roughness than theconventional vise about 40% reduction.

Surface finish improvement using a damping-alloy sleeve-insert tool holder in the end milling process

This study investigates the effect of a tool holder with a metallic damping alloy on both vibration reduction and surface finish improvement for use in an end-milling process. Two different configurations of damping alloys are designed: a collet and a sleeve inside a conventional tool holder. To determine the system characteristics including damping effects, an experimental verification was organized, after that actual machining tests are conducted. The damping effects of each tool holder are compared through machining tests on carbon-fiber reinforced plastics (CFRP) and mold steel respectively. Additionally, a chatter vibration suppression test using thin aluminum workpiece concludes that the metallic damping alloy is comparable to other damping methods. The results show that damping alloy can reduce machining vibration regardless of workpiece materials or the form of it, and the sleeve type tool holder improves the surface roughness significantly in an end-milling process for both workpiece materials.

High precision 3D measurement method of pipeline on complex working conditions research

The research object of this paper is high-precision 3D structure measurement of thin pipe workpiece with working temperature ranged from -50 °C to +70 °C and pipe diameter range from 20 mm to 100 mm. Measurement method is based on the principle of circular structure light vision detection. Due to the strict temperature environment requirement and limited measurement space of the inner surface of pipeline. A CMOS camera module based on customized optical lens is designed. Matched with camera temperature compensation device. Motion guide rail of telescopic arm is equipped with high precision servo motor and grating ruler are used for accurate measurement. Experimental results show that the measurement system meets the design requirements of accuracy ⩽ 0.02 mm, repeatability ⩽ 5% FS (0.5 mm), and strain test error ⩽ 5%.