Workpiece Material Removal Research Articles

Study on the Wear Characteristics of a Lapping Wheel in Double-Sided Lapping Based on the Trajectory Distribution

In the process of double-sided lapping, the surface shape of the lapping wheel changes because of uneven wear, which affects the quality of the workpiece, especially the surface shape accuracy of the workpiece (bow, warp, and total thickness variance). Lapping trajectory is the primary reason for uneven wear on the wheel surface. Therefore, the uniformity of the lapping wheel wear during the double-sided lapping process will be investigated based on the trajectory distribution in this paper. First, the kinematics of double-sided lapping is analyzed, and the lapping trajectory equation is established. Then, the simulation calculation is conducted using MATLAB software to obtain the trajectory distribution characteristics of the wheel surface. The wear uniformity of the wheel surface is analyzed according to the distribution density of the trajectory. The wear model of the lapping wheel surface is established. Finally, double-sided lapping experiments with sapphire slices are carried out. Under varied workpiece material removal thicknesses, the changes of the lapping wheel surface profile are measured, and the wear of the lapping wheel surface along the radial direction is obtained and compared with the calculation results. The calculation results are basically consistent with the experimental results, which proves the correctness of the double-sided lapping wheel surface wear model.

Exergy efficiency optimization model of motorized spindle system for high-speed dry hobbing

High-speed dry hobbing (HSDH) has been regarded as an environmentally benign gear machining technique. Current research on energy efficiency of machine tool focuses on the energy efficiency for workpiece material removal but rarely involves the energy consumption required to control thermal stability. Due to the fact that thermal effect dominates the machining accuracy and accuracy consistency, especially in the dry machining process, the energy consumption for thermal stability control should be taken as useful energy consumption. In view of this, by taking the motorized spindle system (MSS) as the study objective, which is a core subsystem of machine tool enabling HSDH and characterizes intensive and inefficient energy consumption, an exergy-based method is proposed to evaluate the comprehensive energy efficiency of MSS. Furthermore, an exergy efficiency optimization model is proposed to maximize total exergy efficiency and minimize average temperature of MSS. A solution method integrating Pareto Dominant-based Multi-objective Simulated Annealing (PDMOSA) and Technique for Order of Preference by Similarity to an Ideal Solution (TOPSIS) is proposed to search the best solution of the optimization model. A case study is introduced to validate the proposed model and a final optimal solution is obtained at the total exergy efficiency of 53.5% with balanced temperature of 35.4 °C. The cooling water in MSS is identified to be a dominant factor that affects total exergy destruction. The presented model can give a reference to select appropriate process parameters of MSS for green and precision machining.

Subsurface damage and material removal of Al–Si bilayers under high-speed grinding using molecular dynamics (MD) simulation

By performing three-dimensional molecular dynamics (MD) simulations, the effects of the tool radius, depth of cut and grinding speed are thoroughly studied in terms of the workpiece deformation, material removal, dislocation movement, atomic trajectory, grinding temperature and average grinding force. The strength of ductile/brittle (Al/Si) bilayers is largely enhanced, because the interface can hinder the passage of dislocations. The interface in brittle/ductile (Si/Al) bilayers contributes to its ductility by increasing the movability of dislocations when gliding on it. The brittle to ductile transition of bilayers, which strongly depends on the interface debond energy, has a key role in controlling the dislocation slipping mechanism. The investigation also reveals that a larger tool radius, higher grinding speed or deeper depth of cut results in more chipping volume and higher grinding temperature in both bilayers. At the same machining parameters, the above changes in brittle/ductile (Si/Al) bilayers are more apparent than that in ductile/brittle (Al/Si) bilayers, since Si is stiffer and has a higher yield strength than Al.

Material removal mechanism and deformation characteristics of AlN ceramics under nanoscratching

Abstract To investigate the fundamental mechanism of the deformation and fracture behavior of aluminum nitride (AlN) ceramics in ultra-precision grinding, single and double scratches of AlN ceramics were carried out using a Berkovich indenter. Depth-displacement curve and surface morphology of the single varied force scratch revealed that the brittle-ductile transition occurs during scratching. In the brittle deformation stage, the stress below workpiece surface plays an key role in the change of scratch direction, and grains spall due to crack propagation. Depth-displacement curves and surface morphology of the double scratches revealed that the second and first scratches merge into one scratch in the case of the double scratches with distance of 0.5 μm and 1 μm, leading to the increase in the second scratch depth. A double-scratching-induced stress field model under constant force was established using the Boussinesq field, the Cerruti field, and the sliding bubble field to investigate interaction principle of double scratches and the material removal mechanism of AlN ceramics. Results indicated that the interaction of double scratches leads to the increase in the maximum principal stress of lateral cracks; the maximum principal stress reaches the extreme value after the indenter is unloaded; and the interaction of lateral cracks between double scratches leads to in overall removal of workpiece material and the slip of the second scratch.

Milling stability analysis with considering process damping and mode shapes of in-process thin-walled workpiece

As an unfavorable factor of machining process, chatter threatens the machined quality of workpiece, which determines the assembly and fatigue performance of the workpiece. During the interaction between machine tool and thin-walled workpiece, the process damping effect, multiple modes response and dynamic changes caused by the material removal of the in-process workpiece (IPW) will make the machining process more complicated and introduce great difficulties to dynamic modeling and performance prediction. In this paper, we considered the process damping determined by the indentation volume between flank face of milling tool and machined surface, and used multi-mode model to describe this behavior. In order to establish the assembled material removal model of the IPW dynamics with multiple modes, the structure dynamic modification (SDM) and finite element method (FEM) were combined together. The updated third-order full discretization method was applied to solve the dynamic equation in modal space. Then, the three-dimensional stability lobe diagrams (SLDs) with and without material removal along the tool path were obtained respectively by enveloping multiple modes of the IPW and milling tool together. Finally, the cutting tests were carried out. The experiments showed that the assembled model could predict the dynamics of IPW accurately, and the proposed stability analysis model was relatively close to experimental results. Besides, the modes of thin-walled workpiece with weak rigidity do not always play a dominant role in the process of machining. Although the material removal rate is limited by considering the multiple modes of the system, the processing quality can be ensured.

Time-Varying Chatter Frequency Characteristics in Thin-Walled Workpiece Milling With B-Spline Wavelet on Interval Finite Element Method

As the most significant material removal method, milling plays a very important role in the manufacturing industry. However, chatter occurs frequently in milling, which will seriously affect the production efficiency. The accurate prediction of chatter frequency can contribute to chatter monitoring and the design of the controller for chatter mitigation. During thin-walled workpiece milling under chatter, a new phenomenon of time-varying chatter frequency is discovered and explained in this paper. This phenomenon can be explained as follows, with the workpiece material removal, the modal parameters change during thin-walled milling, which can cause the continuous change of chatter frequency. In order to predict the varying modal parameters, this paper provided an efficient tool, the B-spline wavelet on interval finite element method (BSWIFEM), which can possess the material removal problem more accurately and more rapidly. Based on the calculated modal parameters, the time-varying chatter frequency can be obtained with the chatter frequency calculation formulas. To verify the calculated results, a number of milling tests are implemented on thin-walled parts. The experimental results show that the calculated chatter frequency is in good agreement with the measured chatter frequency, which validates the effectiveness of the proposed method.

Impact of physical properties of workpiece material on material removal rate at EDM

The volume stock removal from the workpiece during the EDM is one of the important parameters that characterize the productivity of the electro-erosion process itself. Therefore, in terms of the economic efficiency of the electro-erosion process, it is appropriate that the value of the MRR parameter is as high as possible. The paper describes the results of experimental research to identify the extent of influence of the physical properties of the workpiece material on the workpiece material removal rate at EDM. The experiments were carried out using an Aggregron Hyperspark 3 electro-erosion machine on selected tool steels. As a tool electrode material for experimental purposes, graphite with the designation EX-60 was chosen because of its practical advantages.

Anode Power Deposition in Dry EDM

Dry electrical discharge machining (DEDM) has been developed as an environmentally friendlier alternative to the traditional EDM in oil-based dielectric. Proper understanding of the physics of the DEDM discharges is necessary in order to improve this new manufacturing technology, since its workpiece material removal and tool electrode wear mechanisms are governed by plasma-material interactions. The present work proposes the application of theoretical models, numerical simulations, and advanced diagnostics from the field of plasma physics as effective tools to estimate the electric discharge power deposition onto the anode workpiece in DEDM. Collisional-radiative models are used here to calculate several plasma properties, from which the anode power deposition can be estimated. In addition, electrical circuit simulations, which use a modified Cassie-Mayr model, calculate the fraction of the total electric discharge power that is consumed by thermal conduction into the anode electrode material. The methods proposed in the present work provide fundamental information for further workpiece material erosion modelling and simulation under different DEDM processing conditions.

Changes of cutting performance under different workpiece removal volume during normal speed and high speed milling of compacted graphite iron

Compacted graphite iron (CGI) possesses good mechanical properties and thermal properties in comparison to gray cast iron (GCI) and spherical graphite spheroidal cast iron (SGI). However, the machinability of CGI is poor, and the cutting tool wear is very fast during the machining of CGI, which can lead to the changes of the cutting force and the machined surface integrity. The present study investigates the influence of workpiece material removal volume (Q) on the cutting tool wear, cutting force, machined surface roughness, and morphology under normal (V = 134 m/min) and high cutting speed process (V = 800 m/min). The result shows that Q had a more obvious effect on the value of cutting forces when the cutting speed was 800/min, while the effect was slight when the cutting speed was 134 m/min. However, the effect of Q on the direction of the resultant cutting force was small, and the direction of the resultant cutting force was more likely to be affected by the increase of cutting speed. The effect of Q on the machined surface roughness Ra and Rz was different between normal and high cutting speed process. Dark and bright areas can be found on the machined surfaces obtained under the normal speed cutting process, and the ratio of dark area to total area P can be used as a parameter to measure the machined surface quality. The flank wear of the cutting tool used for normal speed cutting process can be divided into brighter cemented carbide region and darker coating wear region due to the low wear rate, while only the brighter cemented carbide wear region was found on the tool used for high cutting speed process. Cracks could be found on the cutting tool used for both normal cutting speed process and high cutting speed process. However, the crack propagation appeared faster under high cutting speed process, chipping was formed near the crack. The depth and width of the crater wear under normal cutting speed process were larger than that under high cutting speed process.

One-step generation of hybrid micro-optics with high-frequency diffractive structures on infrared materials by ultra-precision side milling.

Hybrid micro-optics of infrared (IR) materials are of great advantage in realizing the function integration and minimization of advanced IR optical systems. However, due to the hard-and-brittle nature of IR materials, it is still challenging for both non-mechanical and mechanical technologies to achieve one-step generation of hybrid infrared micro-optics with high form accuracy. In the present study, a flexible method, namely ultra-precision side milling (UPSM), is first introduced to achieve one-step generation of infrared hybrid micro-optics in ductile mode, and the corresponding reflective diffraction characteristics are analyzed. In UPSM, the reflective/refractive primary surface of the hybrid micro-optics is formed via the removal of workpiece material, and the high-frequent secondary diffractive micro/nanostructures are simultaneously generated by the tool residual marks of cutting trajectories. With the consideration of the changing curvature of the primary surface, the optimal toolpath generation strategy is introduced to acquire the desired shapes of the secondary micro/nanostructures, and the selecting criteria of the machining parameters is discussed to avoid the brittle fractures of IR materials. In practice, two types of hybrid micro-optic components, namely hybrid micro-aspheric arrays and sinusoid grid surface with high-frequent secondary unidirectional phase gratings, are successfully fabricated on single-crystal silicon to validate the proposed method. The method adopted in this study is very promising for the deterministic fabrication of hybrid micro-optics on infrared materials.

Experimental study on hole quality and its impact on tensile behavior following pure and abrasive waterjet cutting of plain woven CFRP laminates

Waterjet cutting of composites has been proven to be feasible with specific advantages compared with traditional machining techniques, while it still possesses several challenges. Experimental data is presented in this paper relating to hole quality and tensile behavior when using water jet cutting of plain woven CFRP laminates with various processing parameters. The effect of typical parameters including transverse speed, waterjet pressure, and with/without abrasive particles on surface integrity was also studied. A full factorial experimental array was employed involving eight trials. The statistical significance of individual cutting parameters was determined using ANOVA analysis. Results showed that abrasive particles played an important role in workpiece material removal process during waterjet cutting. Typical surface defects including severe entry/exit delamination, uncut fibers, and fiber burrs were observed in CFRP laminates cut by pure waterjet, while marginal damage was recorded when using abrasive waterjet with the same processing parameters. Strip marks together with various defects including craters, uncut fibers, and fiber pull-out were observed on the machined hole surface. Tensile strength of CFRP laminate with open hole cut by waterjet was significantly affected by hole quality, which was increased by up to ~22% (130 MPa) with sample cut by abrasive waterjet than the one processed by pure waterjet with the same cutting parameters. Massive delamination, fiber breakage, and splitting bands were the main tensile failure modes.

Temperature Distribution and Stress Analysis of Aluminium Oxide Work-Piece during Laser Micro Machining Operation

The current study investigates the temperature distribution, stress analysis and material removal of aluminum oxide work piece. Temperature distribution of Aluminum Oxide work-piece when a laser beam (of laser cutting machine) is focused on it to create a micro groove as a part of machining process. Present Demand of industry currently focus on ceramics because of its vast and potential use in many fields such as vehicle sector(automobile), aerospace and bio-medical engineering applications, etc. As part of machining process, a micro groove needs to be created on a crude design material. Aiming at this, a laser cutting machine is employed to create a micro groove which works on a principle that when a high power laser beam is focused on a surface of the body, material gets removed as a result of large amount of heat energy released by the laser beam. Achieving a desired groove of specific dimensions is possible by having control over process parameters of a laser cutting machine which in turn governs the amount of material removed. To tackle with this it is essential to study the temperature distribution (due to heat energy released by laser beam) in the body that is responsible for material removal. ANSYS FEA is used to simulate and analyze this temperature distribution. In this paper temperature graphs for 40W,50W, Material removal for 40W, 50W, Equivalent stress for 40W, 50W are shown.

Performance Evaluation of Conventional Abrasive Wheels for Grinding Ti-6Al-4V

The present experimental study represents comparative performances in between aluminium oxide and silicon carbide wheels for grinding Ti-6Al-4V, considering dry environment as well as using alkaline soap water, applied through a newly developed delivery technique, restricted quantity lubrication (RQL) in drop by drop (DBD) mode. Experiments have been performed on a surface grinding machine in up-grinding mode during which the wheels are passed 20 times over the workpiece substrate for each environmental condition with infeed, 10 μm per pass. The variations of tangential and normal force components have been accurately measured using strain gauge dynamometer for each set of experimentations. Grinding ratios have been evaluated after accurately estimating the volume of material removal of wheel and workpiece. The qualities of the ground surfaces are compared based on the surface roughness parameters, measured using contactile mechanical stylus and observations of the ground surface under high resolution microscope. The outcome of the present investigation indicates silicon carbide wheel is superior to alumina wheel for grinding Ti-6Al-4V in terms of grinding force, grinding ratio, surface quality and the form of chips, obtain herein.

Effects of fumed silica weight fraction on rheological properties of magnetorheological polishing fluids

Magnetorheological (MR) polishing fluids with excellent rheological characteristics are efficient in material removal of workpiece. In this study, fumed silica (FS) was used as thixotropic agent in MR polishing fluid with ten different weight fractions to find the proper additive amount for good rheological and sedimentation properties. The rheological behavior of samples at several additive concentrations was determined by examining flow properties using a rotational rheometer connected to an external magneto-cell. Experimental results showed that, by adding FS to MR polishing fluids, apparent viscosity and yield stress exhibited an obvious increase, while the shear-thinning index decreased sharply. Model fitting showed that all the MR polishing fluids exhibited shear-thinning behavior and followed the Herschel-Bulkley model. Further investigations suggested that 0.5–0.6-wt% FS was the most promising additive proportion for proper rheological and sedimentation properties, while a further increase in FS weight fraction greatly increased apparent viscosity and decreased yield stress undesirably.

Influence of metal vapor jets from tool electrode on material removal of workpiece in EDM

This paper shows that the radial flow caused by the collision of the metal vapor jets generated from the surfaces of the tool electrode and workpiece serves as one of the material removal mechanisms in electrical discharge machining (EDM). Material removal per single discharge of a steel workpiece was larger using the tool electrode made of materials with lower boiling point. Observation of the discharge gap using a high-speed video camera showed that molten material on the workpiece was swept away more significantly and larger amounts of debris was removed using the tool electrode materials with lower boiling point. The molecular dynamics simulation showed that the radial velocities of the vapor atoms removed from the workpiece were higher using the tool electrode with lower boiling point because the jets from the tool electrode were more intensive. Furthermore, the discharge reaction force acting on the wire electrode in a single pulse discharge in air was measured from the wire vibration. The results showed a larger discharge reaction force using a zinc coated brass wire compared with a non-coated wire. Thus, it can be concluded that the shear force caused by the jets serves as one of the material removal mechanisms in EDM. Furthermore, one of the reasons for the higher material removal rate obtained using zinc coated wire electrode in wire EDM is the ease of boiling of the zinc coating layer on the wire surface.

Study on cutting burr and tool failure during high-speed milling of compacted graphite iron by the coated carbide tool

Compacted graphite iron (CGI) is considered as the ideal material to make modern fuel-efficient diesel engine. Due to the vermicular or worm-like graphite distributed among the ferrite/pearlite matrix, CGI behaves better physical and mechanical properties in comparison with gray cast iron (GCI) and spherical graphite spheroidal cast iron (SGI). However, these good properties bring about the machining challenges. So it is important to appropriately select cutting parameters to machine this material with economy and efficiency. The present study investigated the influence of cutting parameters, such as cutting speed V, feed rate f, and exit angle Ψ, on workpiece material removal volume Q and cutting burr height on the entrance side H1 and on the exit side H2 during high-speed milling of CGI by the coated carbide tools. On this basis, the relatively optimum high-speed cutting parameters were selected under the research condition. Cutting tool failure mechanism was also investigated with the aid of scanning electronic microscope (SEM) and energy-dispersive system (EDS) (SUPRA55, Germany) analysis. The results showed that Q, H1, H2, and the type of cutting burr on the exit side of the machined surface could be influenced by the cutting parameters. And the relatively optimum cutting parameters are V = 800 m/min, f = 0.25 mm/rev, and Ψ = 60°. Adhesive wear and thermal cracks which were perpendicular to the cutting edge were common wear mechanisms during the cutting process. However, with an increase in feed rate, mechanical cracks which were parallel to the cutting edge could be found on the flank face of the cutting tool.

Microstructural characteristics of Alloy 718 and Waspaloy and their influence on flank wear during turning

The present study deals with the influence of the microstructures of two wrought superalloys on the flank wear of uncoated cemented tungsten carbide tools in turning. Tool life tests have been performed in order to compare the flank wear development during machining of Alloy 718 and Waspaloy. Additionally, microstructural aspects, such as hardness, grain size as well as types and quantities of hard, abrasive phases have been determined and compared for both machined superalloy workpieces.The results show that Alloy 718 is associated with faster flank wear progression as compared with Waspaloy. The difference in wear is not likely to be the result of higher thermal and mechanical loads on the tool during machining Alloy 718. Characterization of obtained flank wear topographies after removal of adhered workpiece material revealed that abrasive wear is the dominant wear mechanism during machining both superalloys with the investigated cutting parameters. Varying extents of abrasive tool wear during cutting of the two alloys are therefore the likely reason for the different wear rates. In connection to that, significantly larger quantities of hard phases, specifically primary MC-type carbides and TiN-inclusions were found in the Alloy 718 workpiece which can explain the faster flank wear progression during machining this alloy.

Formation of the Workpiece Shape and Surface Finish During Electrical Discharge Machining

Electrical discharge machining is a promising non-traditional machining process, which is quite well investigated in relation to the formation of the plasma channel and the formation of single erosional craters. However, the influence of geometrical and energetic heterogeneities of electrodes on the formation of the workpiece shape and surface finish is insufficiently investigated.In this work the analysis of the influence of geometric and energetic heterogeneities of the surfaces of the electrodes on the discharge and its location, the shape and size of the erosion craters is performed.Theoretical studies based on multidischarge numerical simulation of electrical discharge machining, which includes a cyclical execution of the following steps: 1) modeling of thermal processes for a single discharge; 2) modeling of the workpiece material removal and crater formation during the pause; 3) determining of the location of the subsequent discharge, are carried out.For the simulation of thermal processes the equation of transient heat conduction in a medium with variable physical-chemical properties was used. Thus the workpiece material removal was replaced by an anisotropic material with low heat capacity, which allowed to eliminate the necessity of changing the computational domain when this material was removed.The experimental investigation on the distribution of discharges over the workpiece surface at the initial stage of EDM was performed. The emergence of the phenomenon of “nesting” craters in the zones of maximum energy disposition (bulges, zones of differential surface and temperature) was shown. The process of how these zones are distributed over the entire workpiece surface was shown.

Study of flank wear topography and surface-deformation of cemented carbide tools after turning Alloy 718

An investigation is reported on the characterization of an uncoated tungsten carbide tool used for machining of a Ni-Fe based superalloy (Alloy 718). Scanning electron microscopy (SEM) in combination with white-light interferometry (WLI) was applied to study the flank wear surface topographies both directly after the turning test and when the adhered workpiece material was removed by etching. The obtained results show that the thin layers of adhered workpiece material present on the flank wear land can obscure the wear topography. Removal of adhered workpiece material from the worn areas of interest is therefore necessary to reveal features of worn tool surfaces. SEM observations of worn WC grains revealed that abrasion is an active wear mechanism during cutting. Complementary analysis by the electron backscatter diffraction (EBSD) technique revealed that worn WC grains are additionally characterized by significant strain which suggests the contribution of plastic deformation to the flank wear. Plastic deformation of WC is likely caused by high thermal and mechanical loads acting on the tool during machining.

Research on Electrical Discharge Grinding Technics and Tool's Life of Polycrystalline Cubic Boron Nitride Cutting Tool

Electrical discharge grinding is part of the most widely used methods to machine polycrystalline cubic boron nitride cutting tools. Polycrystalline cubic boron nitride compact samples at different granularity size are the research object. Electrode running speed, peak current and pulse duration is selected as the main process parameters. Material removal volume and the electrode wear set as the evaluation index of productive efficiency. Workpiece surface roughness value sets as an evaluation standard of processing quality. Through electrical discharge grinding experiments, combined with scanning electron microscopy observation, energy spectrum analyzer and roughness tester, the influences of the main process parameters on electrical discharge grinding are analyzed, results show that polycrystalline cubic boron nitride crystal granularity size has some effect on the electrical discharge grinding. With the increase of the electrode rotation speed, the workpiece material removal volume is increased, but the increase rate becomes slow. Electrode wear is further increased with the increase of the electrode rotation speed. With the peak current increase, material removal volume and the surface roughness value of the workpiece material increase, electrode wear reduces. Through the turning test, the relationship between service life of polycrystalline cubic boron nitride cutting tools that are machined by electrical discharge grinding and cutting tool flank wide, workpiece surface roughness are discussed. The results showed that to adjust electrical discharge grinding parameter, such as pulse duration and machining electric currents, can reduce the depth of the effect layer and extend the service life of polycrystalline cubic boron nitride cutting tool. The research provides a valuable experimental reference for drawing up electrical discharge grinding technics of polycrystalline cubic boron nitride cutting tool.