Properties Of Workpiece Research Articles

Investigation of the influence of surface waviness of aluminium on the burnishing quality of a combined process

Burnishing is an effective chipless finishing process for improving workpiece properties such as: hardness, vibration resistance and surface quality. Recently, the process has been increasingly applied to prismatic workpieces and free-form geometries. Before burnishing can be carried out, a milling process created the shape of the workpiece, especially for free-form surfaces. The application of different milling tools does not only produce different roughnesses, it also creates waviness which can influence the burnishing process. This publication focuses on the relationship between roughness and waviness of the milling process on the following burnishing of ductile workpiece materials. The presented work also considers the different machining directions and tool movements of this process combination. Within the evaluation the interdependence between milling and burnishing parameters are examined and the remaining frequency components of the two processes on the generated surface are compared.

Determination of thermo-mechanical quantities with a sensor-integrated tool for single lip deep hole drilling

To adjust the subsurface workpiece properties, such as hardness and residual stresses as well as surface quality, machining processes are often followed by forming, peening or heat treatment processes. An appropriate setup of the machining process can adjust the desired properties. The work presented here is part of an interdisciplinary research project in the framework of the priority program "Surface Conditioning in Machining Processes" (SPP 2086) of the German Research Foundation (DFG). This research project has the main objectives to determine the actual thermo-mechanical state of the surface and subsurface in single lip deep hole drilling during the process by means of a sensor-integrated tool as well as to control the process parameters to achieve the desired workpiece properties.Preliminary test series are related to the determination of the thermo-mechanical boundary conditions with thermal, material and machining models. From the obtained results, the requirements concerning the sensor-integrated tool can be derived. Further steps include the development of a tool for the in-process determination of the real cutting conditions, the selection and integration of sensor systems as well as the correlation of process states with workpiece conditions. The single lip deep hole drilling tool will be equipped with sensor systems for the acquisition of temperatures, forces, torques and vibrations close to the affected zone. In particular, for the determination of the process temperature close to the cutting zone, a multi-sensor approach was chosen. Effects on the workpiece can then be investigated using material simulations. The elaboration of a control strategy and its implementation in a deep hole drilling machine will finalize the current project phase. The final goal is that the required workpiece surface and subsurface properties can be controlled based on measurement and simulation data.

Interference- and chatter-free cutter posture optimization towards minimal surface roughness in five-axis machining

Five-axis CNC machining of sculptured surfaces plays a significant role in aerospace industry, such as blisk machining. The key issue involved is the determination of cutter posture in tool path planning. As the interference will cause the cutter to intrude the workpiece or machine tool and then seriously damage the cutter or machine tool, cutter posture must be well planned to avoid interference. Meanwhile, as the machined surface quality will be deteriorated inevitably when chatter arises, chatter must be eliminated as well. In this paper, posture accessibility and stability diagram (PASD) is firstly constructed by identifying interference- and chatter-free cutter postures based on geometric analysis and machining dynamic analysis. Furthermore, as surface roughness is an important characteristic to evaluate the surface properties of workpieces and should be generally minimized, its prediction model is also established for optimization. As is well known, surface roughness is mainly affected by cutter deflection due to inevitable cutter deformation force (CDF). By analyzing the relationship between surface roughness and maximum CDF, a novel surface roughness prediction model is proposed from a new viewpoint, i.e., the maximum CDF. Compared with the traditional prediction models considering only geometry, the proposed prediction model is much more straightforward, and the prediction results are more accurate (the average prediction error is only about 9.0%). This study reveals that the cutter posture has a great effect on surface roughness, which implies that surface roughness can be optimized from a new perspective (cutter posture). Finally, based on the proposed PASD and surface roughness prediction model, a new cutter posture optimization algorithm is proposed to minimize surface roughness. The algorithm considers both geometrical and dynamical constraints (interference and chatter) simultaneously, and it is verified by machining experiments under different cutter postures. According to the validation experiments, the proposed algorithm can effectively avoid the interference and chatter while minimizing the surface roughness (the optimized Ra is only 0.3589 μm compared to normal one 0.5476 μm). To the authors’ best knowledge, it is the first time to optimize cutter posture by considering the following three aspects simultaneously: avoiding interference, eliminating chatter and reducing surface roughness. It will greatly improve the machined surface properties, while optimizing the utilization of the machine tool and cutter (extending their service life by avoiding various potential damages). This also will provide a new perspective that optimizes the machining process of complex and precise parts from cutter posture, which is of great significance to aviation and aerospace industries.

Microstructure and mechanical properties of workpieces of the ultrafine-grained two-phase Ti alloy produced by die forging

The paper presents the results of studies of the microstructure and mechanical properties of experimental workpieces of the ultrafine-grained (UFG) VT8M-1 (Ti–5.7Al– 3.8Mo–1.2Zr–1.3Sn in wt%) alloy produced by isothermal die forging (IDF). The UFG structure in the VT8M-1 alloy was formed by a high-performance method, namely rotary swaging (RS). The structural parameters (the shape and size of the α- and β-phases) and the homogeneity of the UFG structure were analyzed in different sections of forgings. It was shown that the fraction of the primary α- phase decreases, and the size of the secondary equiaxed grains of the α- and β-phases increases from 0.3 to 0.9 µm as a result of recrystallization during IDF. The relationship between the microstructure and mechanical properties of the forged workpieces of the UFG VT8M-1 alloy is discussed.

Research on sub-surface recrystallization of single crystal nickel-based superalloy in micro-milling

The micro-structure/parts of single crystal nickel-based superalloy materials are extensively used in high temperature environments. The recrystallization mechanism of the machined workpiece sub-surface is explained through energy storage model. A micro-milling experiment of single crystal nickel-based superalloy DD98 was performed by simulating the working environment at high temperature and setting different heat treatment temperature. By scanning electron microscopy (SEM), the influence of sub-surface structural elements on the properties of micro-milling workpiece was analyzed. Experimental results indicate that the recrystallization layer thickness of single crystal nickel-based superalloy DD98 increases with the increase of heat treatment temperature. When this temperature is between 950 °C and 1150 °C, the recrystallization thickness is 5–20 μm. The recrystallization of sub-surface layer takes the form of equiaxed recrystallization. Those provide basic data for restraining recrystallization of single crystal materials and have good scientific significance.

Characterization of the effects of detector angular misalignments and accuracy enhancement of X-ray CT dimensional measurements

Characterization of the effects of detector angular misalignments and accuracy enhancement of X-ray CT dimensional measurements

Investigation of quenching stress of 42CrMo treated by alternately timed quenching process

ABSTRACTAlternately timed quenching (ATQ) technology includes ATQ process and equipment. ATQ process essentially executes multicycle quenching-partitioning-tempering (MQ-P-T) process by alternative water -quenching and air cooling. Engineering applications indicate that ATQ process not only can replace oil or aqueous polymer solution quenching, but also reach even be superior to the mechanical properties of workpieces quenched by oil or aqueous polymer solution. Since direct water-quenching usually causes the cracking of workpieces, polluting oil quenching or aqueous polymer solution quenching is still used in modern industry. The combination of water-quenching and air-cooling can effectively avoid the cracking of workpieces, but direct water-quenching (DQ) process very easily causes cracking, and this issue puzzles us for a long time. In this work, 42CrMo cylinder with 60 mm in diameter respectively treated by ATQ process and DQ process for comparison is taken an example, and the quenching stress of 42CrMo cylinder is investigated by the finite element simulation (FES) and X-ray diffraction (XRD) measurement, respectively. The results reveals the origin of avoiding cracking of workpieces for ATQ process, that is, ATQ process markedly lowers the quenching tensile stress and raises its uniform distribution compared with DQ process.

Molecular dynamics simulation of dislocation evolution and surface mechanical properties on polycrystalline copper

During the nanofabrication process of polycrystalline materials, the interactions of dislocations in material determine the evolution of subsurface defects. In this paper, the molecular dynamics simulation models of nanocutting polycrystalline copper, which is used to study the relationship between the crystal structure and the cutting force during the cutting process, were established, and the transformation process between grain boundaries and dislocations was studied to get the effects of grain boundary on dislocation slip and stress conduction. The results show that there are obvious rules between cutting force and cutting process and grain boundaries can prevent dislocation slip and shielding stress conduction. The influence of different cutting parameters on the evolution of subsurface defects of workpiece was further analyzed. Finally, the nanoindentation simulations and experiments were carried out to study the influence of cutting parameters on surface mechanical properties of workpiece. It is found that to some extent, the surface hardening effect of the workpiece is remarkable with the cutting depth increase.

Analysis of the Chemical and Tribological Properties of Phosphate Glass Layers Developing during Metalworking Processes on Manual Transmission Synchronizers*

Abstract Optimization of machining processes to improve the tribological properties of surface layers has become a subject of industrial development. The modifications caused by manufacturing commonly include changes of topography, hardness or residual stresses. The present study investigates modification of the tribological properties of gear synchronizers by the formation of chemical layers on the metal surface within the final grinding process. These layers similar to phosphate glass emerge from the metalworking fluid additive zinc dialkyldithiophosphate (ZnDTP), which is applied in the process in different concentrations. The layers generated at the surface were measured by time-of-flight secondary ion mass spectrometry (ToF-SIMS). Tribological experiments were conducted on a special synchronizer test facility. ToF-SIMS depth profiling revealed that higher ZnDTP concentrations in the metalworking fluid led to thicker phosphate glass layers on the machined surface. The layer that was generated by the addition of 5 % ZnDTP to the metalworking fluid led to a more homogenous coefficient of friction and a lower amount of wear in the tribological experiments. However, the addition of further ZnDTP, up to a total amount of 10 %, led to higher fluctuations in the coefficient of friction and increasing wear, likely related to the occurrence of friction oscillations resulting from thicker phosphate glass layers. However, the results indicate a good potential for improving surface layer properties of metal workpieces by adjusting the chemical composition of the metalworking fluid applied in the final machining process.

Research on milling stability of thin-walled parts based on improved multi-frequency solution

Chatter occurs more frequently due to the lower stiffness of the thin-walled parts, which may exert damaging effect on the machined surface of workpiece. To avoid chatter and predict the stable zone more precisely, a relative transfer function was introduced to consider dynamic properties of both milling tool and workpiece, and an improved multi-frequency solution was employed to predict the critical cutting depth in axial direction. Verified by a cutting test and time domain simulation, improved multi-frequency solution had been proven to be more accurate than zero-order analysis. The proposal of improved multi-frequency solution is important for the chatter suppression techniques to improve the processing efficiency and quality in the aerospace industry.

Uticaj termo-električnih svojstava materijala na obradu električnim pražnjenjem sa praškastom mešavinom

Powder Mixed Electrical Discharge Machining (PMEDM) is considered as one of the viable methods to machine the materials which are hard and tough but with appreciable thermo-electrical properties. In PMEDM, it has been established that machinability is enhanced by adding additives in the form of fine powders in the spark gap of EDM process. In this investigation, the role of the thermo-electrical properties of workpiece on PMEDM process has been studied. Materials with distinct thermoelectric property, namely Mild Steel and Aluminium are taken as workpiece with Alumina as additive powder for the PMEDM process. Experiments have been conducted with Taguchi L9 Orthogonal Array (OA) with Material Removal Rate (MRR) and Tool Wear Index (TWI) as responses. Gap current, duty cycle and flow rate of powder mixed dielectric liquid have been taken as process parameters at 3 levels with circular copper rod of 12 mm diameter as tool electrode. Determination of the influence of properties of the workpiece on the machinability has been performed using a custom made PMEDM set-up. ANOVA and main effect plot of data means for the aforementioned conditions have been analysed. The results are noteworthy with significant influence of the properties of the workpiece on the machinability of PMEDM process.

Eccentric rotary swaging variants

Rotary swaging is an incremental cold forming process that changes beneath the geometry also the microstructure and mechanical properties of the workpiece. Especially a new process design with Eccentric Flat Shaped Dies (EFSD) influences both the kind and amount of stress and plastic strain and consequently the material structure, and hence the material and workpiece properties. Eccentric rotary swaging typically provides a helical material flow. According to the process parameters the microstructure features a typical eddy pattern with a spiral shaped grain orientation. The forming process can be carried out in one or more process steps. In a multistage process, it is possible to change the feed direction and, hence, the material flow helix direction. This approach can be used as a possibility to improve the homogeneity of the workpiece and material properties. In addition, for this aims an intermediate heat treatment in multistage forming operations could be realized. Following the goal of optimizing the final properties, the question arises how these mechanical and thermal treatments affect the material microstructure and the forming properties of the workpiece and how they interact. Experiments were conducted with austenitic stainless steel rods of grade AISI304. The effects of the varied feed direction, feed velocity and heat treatment between the forming operations are discussed.

Modeling of Dynamic Links which Characterize Static Properties of Grinding Wheel and Workpiece during Flat Grinding Process

The article considers the results of theoretical and experimental studies of the process of external grinding on the basis of the developed dynamic model. It uses the description of an equivalent dynamic link that converts a standard signal in the form of Gaussian white noise to a random process. For the settings of the forming filter, the results of statistical processing of profilograms of the working surface of the grinding wheel are obtained. The constructed forming filter makes it possible to characterize the statistical properties of the grinding wheel and workpiece. The developed mathematical model of the operation of flat external grinding can be used to assess the quality characteristics of machined parts and systems of automatic process control when solving the problem of intensification of production.

Burnishing of prismatic workpieces on three-axis machine enabled by closed loop force control

Burnishing is an effective chipless finishing process for improving workpiece properties: hardness, vibration resistance and surface quality. The product quality and process stability are significantly influenced by factors such as tool movement and burnishing force. The implementation of a force controlled tool positioning enables integration of finish operations like burnishing into conventional machining centers. This paper shows the realization of this new machine and process technology. The controller structure and tuning are discussed. In addition, the effects on the process forces and the workpiece are examined.

Study on improving surface residual stress of polished blade after polishing based on two-stage parameter method

Surface residual stress is the one of the key factors affecting the mechanical properties of workpiece. Firstly, this article established the two-stage parameter method and analyzed the principle and advantages of two-stage parameter method. Secondly, the influence of the process parameters on the reason factors, the reason factors on the surface residual stress, and the process parameters on the surface residual stress were analyzed in turn through the single factor method. And then, based on the analysis results of single factor method, the influence of the process parameters on the reason factors was analyzed by the Grey relational theory. Finally, the data obtained from the Grey relational optimization method were tested and analyzed. The experimental results show that using the optimal process parameters and cooling the blade by coolant during the polishing process can make the reason factors more reasonable and improve the surface residual stress.

Towards the simulation of Selective Laser Melting processes via phase transformation models

Selective Laser Melting (SLM) – as one of a number of additive manufacturing techniques – is a promising method for the manufacturing of complex structures and may bring about significant improvements in the context of custom-made designs and lightweight constructions. However, the complex multiphysical processes occurring during SLM necessitates the establishment of appropriate constitutive and process models in order to quantitatively predict the properties of the final workpiece. In particular, the accurate determination of process-induced eigenstresses is a challenging yet important task. In this work, a constitutive modelling framework stemming from phase transformations in shape memory alloys is adopted to the modelling of the changes of state during SLM. This model is based on energy densities and energy minimisation in general and specifically serves as a basis for further enhancements such as the consideration of multiple solid phases of the underlying material. This is particularly considered important due to the fact that the cooling rates during SLM are heterogeneously distributed and that thus different solid phases may form out of the molten material pool. As a first step, the present overall model comprises three phases of the material, namely powder, molten, and re-solidified material. The thermomechanically fully coupled Finite-Element-based process model incorporates approaches for, e.g., the laser beam impact zone and the layer construction model.

Experimental investigation and finite element simulation of AISI 304 during electro discharge machining

In this paper, a two-dimensional axisymmetric thermal model using finite element method (FEM) has been established for predicting the temperature distribution profile on the work piece during electro discharge machining (EDM) and obtained material removal rate (MRR) from the temperature isotherm. For prediction of MRR, the model utilizes some important features viz. size and shape of the heat source (Gaussian heat distribution), thermal properties of workpiece, amount of heat distribution among the dielectric fluid, workpiece and tool, material flushing efficiency and pulse off/on time, etc. ANSYS software was used for developing the thermal model for the single spark operation. For this investigation, AISI 304 stainless steel and tungsten carbide was used as workpiece and electrode material, respectively. A comparison study has been carried out for theoretical and experimental MRR for the effect of each process parameter viz. gap voltage, pulse on time and peak current. The temperature distribution along the radial and depth direction of the workpiece has been reported. The model was validated by comparing the theoretical MRR with the experimental MRR and found a good correlation between them.

On the tracking of individual workpieces in hot forging plants

Tracking each workpiece provides two major advantages in forging technology. First, the matching of physical workpiece with the monitored process information facilitates root-cause analysis for product quality. Second, the following process steps can be adapted according to the incoming workpiece properties to improve the robustness of hot forging process chain. The paper presents a general tracking methodology and tagging experiments on aluminium and steel forgings for harsh drop-forging technology. Furthermore, a framework for streaming and processing large amounts of real-time data as well as a multidimensional approach to model and analyse the workpiece information for individual and batch-tracking are presented.

Structure and properties of compact workpieces and bars made of sintered aluminium alloy CAC-1

Structure and properties of compact workpieces and bars made of sintered aluminium alloy CAC-1

Effects of processing parameters on underfill defects in deep penetration laser welding of thick plates

Underfill defect in welding affects not only the surface integrity but also the mechanical properties of workpiece. In this paper, the effects of the process parameters on underfill defects were investigated, and the deep penetration welding by a 10-kW fiber laser on 12-mm-thick stainless steel plates was used as the case study. The correlation of the processing parameters with the formation and elimination of underfill defects was analyzed and discussed. It was found that during the autogenous laser welding of thick plates, the direction of laser beam relative to gravity has a significant effect on the formation of underfill defects, and the preferable direction was an inclination angle of 60° with respect to the gravity. A negative defocus tended to obtain a full penetration weld with underfill and undercut defects. The higher the welding speed was, the lower the underfill depth was on the top surface. This phenomenon was observed on the full penetration welds at a defocus of − 10 mm. With a negative defocus, it became feasible to optimize the combination of the focal position and the welding speed to achieve a satisfactory appearance of welds. In addition, a bottom-shielding ambience helped the full penetration in the laser welding process positively.