The ASME Y 14.5M-2009 provides three distinct variants of composite position tolerance constraints to exercise control over the position characteristics of patterns of features of sizes such as holes. The practical implementation of this class of position tolerance constraints is hampered by a distinct lack of information relative to the ease or difficulty involved in the actual production and satisfaction of these constraints. In this research, machining experiments are carried out to produce various patterns of holes on industrial grade machines. Coordinate locations data of the holes are acquired and a nonlinear optimization formulation is developed and used to assess the producibility of these variants. Boundary curves for pattern and feature-to-feature tolerances are developed, plotted and discussed. The influence of various variables on the producibility of these variants is also discussed. These results may help design and manufacturing engineers exercise a more informed approach to the application and production of these composite position tolerance variants for patterns of features of sizes.

Amongst all the materials, diamond turning of heterogeneous materials like CuBe poses serious machining challenges as the heterogeneity in the workpiece affects the quality of generated surface. Therefore, the present study is aimed to understand the effect of tool-workpiece interactions on the surface characteristics of heterogeneous CuBe workpiece material. Experiments and MDS were carried out to analyse the various surface and subsurface interactions during cutting. Results from the experiments on both the materials for whole cutting length show that the average roughness values on CuBe machined surface is found to be ∼48% higher than that of Cu. SEM results show that while deterministic lay pattern is obtained in case of Cu, the CuBe machined surface possesses near random lay pattern, which is also reflected by the FFT spectrum of surface roughness profiles. Experimental and MDS results reveal that the hard precipitate suffers cracks which propagate vertically as well as radially and as the tool travels from Cu rich phase to Be rich phase, ductile to brittle transition in cutting mechanism is observed. Furthermore, it is observed that diamond turned Cu and CuBe surfaces are contaminated by the oxides of C and Cu. MDS results verify the mechanisms involved in the surface and subsurface interactions during diamond turning.

There has been growing interest in integrating gradient porous structures into synthetic materials like polymers. One particular method for making gradient porous polymers is nonisothermal annealing of co-continuous phase structures of immiscible polymer blends under well-defined thermal boundary conditions. In this paper, we report a method to simulate this nonisothermal phase coarsening process for generation of gradient phase structures by combined implementation of phase-field transport and momentum transport. Specifically, a phase-field equation is solved first to obtain a phase structure with phase size comparable to that of the blend to be annealed. This phase structure is then used as an initial geometry in a two-phase moving-boundary flow simulation to gauge into the phase structure coarsening process. Several case studies were performed and the results show that controllable generation of gradient phase structures can be enabled by well-designed geometry and thermal boundary conditions. Using 2D simulations, different types of gradient phase structures experimentally observed were predicted. With increasing power in computation, the capability of 3D simulation may be unveiled for more accurate prediction of the nonisothermal phase coarsening process and may ultimately evolve into a useful tool for design and processing of gradient porous polymers.

Effect of the in-situ post weld heat treatment (PWHT) was investigated on the flash profile, austenite/ferrite phase balance and mechanical properties of the upset resistance dissimilar weld between the Fe-Cr-Ni and Fe-Cr stainless steels rods. In order to explore the effect of the heat treatment on the joint strength, two as-welded samples with the low strength (116 MPa) and high strength (372 MPa) were used. The results showed that in-situ PWHT was beneficial for both welded samples, though in different ways. For the weld with the low strength, PWHT improved the joint strength (∼ 130% in the optimum condition compared to the as-welded sample) due to the increase in the size of the flash and the related bonded area at the joint interface. However, ferrite percent in the weld zone increased from ∼ 50% up to ∼70%. For the sample with the high strength, ferrite/austenite phase balance was restored at an optimum condition of PWHT. However, the joint strength decreased slightly (less than 5%) due to the grain growth in the Fe-Cr rod, i.e. the fracture location. Fracture analysis was used for justification of the variations in the joint strength. For both of the Fe-Cr-Ni side and Fe-Cr side of the welds, in-situ PWHT generally reduced the hardness. This observation was discussed at the light of the simultaneous effects of the grain growth and formation of little martensite.

Chip formation in conventional cutting occurs by deformation that is only partially bounded by the cutting tool. The unconstrained free surface makes it difficult to determine and to control the deformation of chip formation. The constrained cutting employs a constraining tool in the cutting process to confine the otherwise free surface and enable direct control of the chip formation deformation. The presented work is a study of the deformation mechanics of plane-strain constrained cutting using high speed imaging and digital image correlation (DIC) methods. For different constrained levels (including unconstrained free cutting), material flow of chip formation is directly observed; strain rate and strain in the chip as well as the subsurface region are quantified; cutting forces are measured; and surface finish are examined. The study shows that chip formation in constrained cutting can occur in two different deformation modes, i.e., simple shear and complex extrusion, depending on the constrained level. Constrained cutting in the simple shear regime can reduce strain, reduce cutting force and energy, and improve surface finish compared to free cutting, therefore it is more efficient for material removal than free cutting. Constrained cutting in the extrusion regime imposes a high resistance to the chip flow and causes a significant amount of subsurface deformation, and therefore is not suitable for material removal. Furthermore, the mechanics of chip formation in both free cutting and constrained cutting, especially the roles played by the free surface and the constraining tool, are discussed.

The printing resolution and scale of digital light processing (DLP)-based 3D printing are affected by the pixel size and projected light power. An effective and versatile method to print complex constructs with high resolution and large area is still required since light distribution in printing systems is generally non-uniform. Here, we propose a projection-based continuous 3D printing with grayscale display method to serve as an effective and precise way to improve printing resolution and area. The light characterization results demonstrated that the power density presented a non-uniform distribution, and the power values are linear to the excitation power. After modifying the masks into grayscale according to the duty cycle of the digital micro-mirror device (DMD) display, projected light exhibited improved uniformity along with expected light power and uniform ratio. To validate this developed printing process, the grayscale continuous printing of mesh and hexahedron frame constructs enabled a remarkable increase in the printing area and alleviation of under/over curing. This work reveals significant progress in printing of constructs at larger area and higher resolution in projection-based continuous 3D printing under non-uniform light.

In machining processes, chatter suppression is very important for achieving a high material removal rate, good dimensional accuracy and surface finish. With the merits of effectiveness and easy implementation, spindle speed variation (SSV) is regarded as a promising approach for chatter suppression. However, there is little research on the selection of SSV parameters for adaptive chatter suppression. Although the effectiveness of adaptively modulating SSV amplitudes has been recently examined, the simultaneous adjustment of the SSV amplitude and frequency is expected to exhibit stronger adaptability since it achieves greater flexibility. In this paper, an active chatter suppression strategy is presented by simultaneously adjusting the amplitude and frequency of spindle speed modulation. The effect of SSV parameters on stability improvement in turning processes including the tool wear is firstly investigated to demonstrate the necessity of simultaneously adjusting the amplitude and frequency for chatter suppression. Then the proposed chatter suppression system is introduced, where two SSV parameters are simultaneously adjusted with optimal fractional order proportional integral differential (FOPID) controllers to keep the chatter indicator close to a target value. Moreover, the FOPID controller is optimally tuned with the JADE algorithm. The effectiveness of the proposed method is verified by comparing simulated results of different SSV parameters adjusting strategies. Finally, machining tests are conducted to validate that the proposed chatter suppression method outperforms the existing SSV method in flexibility and effectiveness.

Over the past two decades, a considerable amount of work has been done on zirconia toughened alumina (ZTA) to take advantage of the recognized toughening effect induced by ZrO 2 . In fabricating customized or complex-shaped ZTA parts, conventional manufacturing processes, including slip casting and powder metallurgy, are regarded as time-consuming and cost-intensive. In response to these problems, directed energy deposition (DED) has been proposed and utilized to fabricate customized ZTA parts with highly flexible features in a shorter cycle time at a lower cost. Investigations have been reported on studying effects of input variables (such as laser power) in DED of ZTA parts, however, there are very limited investigations on effects of ZrO 2 content. In this investigation, the effects of ZrO 2 content on microstructures and mechanical properties of DED fabricated ZTA parts are studied. Experimental results show that at lower levels of ZrO 2 contents (5 wt.%, 10 wt.%, and 20 wt.%), a novel three-dimensional quasi-continuous network (3DQCN) microstructure is tailored, whereas at higher levels of ZrO 2 contents (30 wt.%, 35 wt.%, and 41.5 wt.%), eutectic microstructure dominates the whole part. Both the 3DQCN microstructure and the eutectic microstructure are beneficial for toughening ZTA parts. In addition, the 3DQCN microstructure contributes to hardening ZTA parts.

This paper investigates the use of a linear time-invariant (LTI) control framework to optimally design multiple tuned mass dampers (TMDs) that minimize unwanted vibrations caused by exogenous disturbance forces to a ram-type structure with varying dynamic characteristics. A key challenge for the development of the LTI control framework is the reformulation of the TMDs' design parameters, which consist of linear and nonlinear parameters as static feedback gains. This paper proposes the use of extra cascade control inputs to reformulate the optimization problem into an LTI control framework for the simultaneous optimization of linear (i.e., stiffness and damping) and nonlinear (i.e., location) parameters. A rigid planar system with multiple attached TMDs is developed as a mathematical model. It is reconstituted as an LTI framework by connecting a control input for the location parameter with control inputs for the stiffness and damping parameters. The model is then optimized using multi-model H ∞ synthesis. A commercial gantry-type machining center is used to validate the proposed approach. Results from the simulation and experiment show that the optimized multiple TMDs systematically designed by this approach improve the system's dynamic stiffness by up to 83% and increase the allowable maximum depth of cut from 1 mm to 1.5 mm.

This paper presents a new dynamic model of aerostatic spindle including the journal and thrust bearings. Reynolds equations are used to model the dynamics of a 4-DOF aerostatic journal bearing and a 3-DOF aerostatic thrust bearing. Finite element model of the spindle shaft is developed based on Timoshenko beam theory considering the centrifugal and gyroscopic effects, and is coupled with the bearing to construct the dynamic model of the whole aerostatic spindle. The effect of shaft tilt motion due to elastic deformation on the dynamic characteristics of the aerostatic bearing is considered for the first time. Finite difference method is used to determine the load capacity and moments provided by the bearings with changing air film thickness due to shaft vibration, and Newmark-β method is used to obtain the dynamic response of the spindle shaft. The simulated natural frequencies of the aerostatic spindle are verified through impact experiments under static and rotating conditions. Based on the developed model, the effects of tool overhang length, rotating speed, air film thickness and supply air pressure on the frequency response function of the spindle are investigated comprehensively. The proposed dynamic model of the aerostatic spindle is able to provide useful guidance for structure design and process planning for micro machining.

The grinding temperature is of great importance for quality and integrity of machined cemented carbide tool. Tool edge surfaces may be damaged by softening or being stressed, hardened, burned or cracked. Former research on grinding temperature prediction often made assumptions to simplify heat convection due to the grinding fluid. However, these simplifying assumptions can sometimes undermine the mathematical relationships between grinding conditions and surface temperature, particularly in low temperature grinding where fluid convection is most important. This paper is an attempt to provide an improved comprehensive thermal model for prediction of contact temperatures and for monitoring and control of thermal damage. Based on previous thermal model research, this paper tackles a key element of the thermal model for temperature prediction. It proposes a convective heat transfer model based on the classic theory of turbulent flow passing a plate. Theoretical predictions from the thermal model of turbulent flow developed in this paper are compared with experimental values. Predictions are further compared with values from a previously published laminar flow model. And it is shown that the new model leads to a significant reduction in predicted temperatures. The results suggest that the thermal model for turbulent flow provides a reasonable estimate of predicted temperature values within the region of the fluid boiling temperature. The estimates appear to be an improvement compared to the laminar flow thermal model. The turbulent flow thermal model is considered to improve estimates of background contact temperatures in grinding cemented carbide.

Micro-textures applied to cutting tool surfaces provide certain advantages such as reducing tool forces, stresses, and temperature hence overall friction between the tool-chip contact and improving chip adherence and associated tool wear. This study explores the effect of micro-texture geometry parameters fabricated on the rake face of tungsten carbide inserts that were tested in dry turning titanium alloy Ti-6Al-4V. The effects of micro-texture geometry on the cutting forces, tool stresses, tool temperatures, tool wear rate and variable friction coefficient were studied with 3D finite element (FE) simulations. The simulation model was validated comparing cutting forces predicted and measured. The results indicated some effects of micro-textured tool geometry parameters being significant and others are not as significant. The experiments reveal that the effects of micro-groove width, depth, and distance from cutting edge are found to be significant on cutting forces, but the spacing is not as much. The effect of increasing feed rate on cutting force and tool wear was significant and suppressed the advantages offered by micro-grooved texture tool geometry. The simulation results indicate that the effect of micro-texture parameters such as groove depth and distance from cutting edge are significant on tool temperature and wear rate. The variable nature of friction coefficient was emphasized and represented as functions of state variables such as normal stress and local temperature as well as micro-texture parameters.

Ultrasonic welding (USW) is one of the joining technologies that can be applied to short carbon fiber thermoplastic composites. In this study, the USW of Nylon 6 reinforced by short carbon fibers created using injection molding is used to investigate the USW process without energy directors. In addition to process parameters and performance parameters, a new category of parameters is introduced to characterize the behavior of base materials to control USW without energy directors. These parameters, named morphological parameters, are the degree of crystallinity (DoC) and the ratio of the crystalline phases of Nylon 6 (α/γ ratio). One method of controlling the morphological parameters is annealing. A design of experiments is carried out using 5 replicates and 7 annealing temperatures above the glass transition temperature (T g ) and below the melting temperature (T m ) of Nylon 6 to investigate the influence of annealing on the morphological parameters. The DoC and α/γ ratio are measured for each replicate by utilizing differential scanning calorimetry and X-ray diffraction. The results show that the DoC becomes uniform and the α/γ ratio increases after annealing. Consequently, the variation in weld strength decreases and the average weld strength increases by controlling the morphological parameters through annealing.

The powder bed fusion-based additive manufacturing process uses a laser to melt and fuse powder metal material together and creates parts with intricate surface topography that are often influenced by laser path, layer-to-layer scanning strategies, and energy density. Surface topography investigations of as-built, nickel alloy (625) surfaces were performed by obtaining areal height maps using focus variation microscopy for samples produced at various energy density settings and two different scan strategies. Surface areal height maps and measured surface texture parameters revealed the highly irregular nature of surface topography created by laser powder bed fusion (LPBF). Effects of process parameters and energy density on the areal surface texture have been identified. Machine learning methods were applied to measured data to establish input and output relationships between process parameters and measured surface texture parameters with predictive capabilities. The advantages of utilizing such predictive models for process planning purposes are highlighted.

Advanced industrial robotic assembly requires the process parameters to be tuned to achieve high efficiency: short assembly cycle (AC) time and high first-time throughput (FTT) rate. This task is usually undertaken offline because of the difficulties in real-time modeling and the lack of efficient algorithms. This paper proposes a support vector regression (SVR)-enabled method to optimize the assembly process parameters without interrupting the normal production process. To reduce the risk of obtaining a local minimum, we consider the trade-off between exploration and exploitation and propose an adaptive optimization process to balance the production processes and the optimization outcome. The proposed methods have been verified using a typical peg-in-hole robotic assembly process, and the results are compared with design of experiment (DOE) methods and genetic algorithm (GA) method in terms of efficiency and accuracy. The experimental results show that our methods are able to maintain the high FTT rate when it drops below 99%, shorten the average AC time by 3.4%, and reduce the number of assembly trials to find the optimized process parameters by 99.6%.

This paper presented a fundamental investigation on the exit-chipping formation mechanisms involved in rotary ultrasonic drilling (RUD) and conventional drilling (CD) of glass BK7. It was found that the mutual tool-material extrusion initially activated the subsurface crack with the maximum depth (incipient crack) at the margin of the machined surface, and its penetration of the undrilled thickness brought about the emergence of the exit-chipping at Region I. Subsequently, the opposite propagations of two ring-cracks along the circumferential direction of the drilled hole were conducive to the collapse of the machined cylinder, thus leading to the appearance of the exit-chipping at Region II. Ultrasonic superposition significantly decreased the actual undrilled thickness of the machined surface, while slightly increased the exit-chipping width. All the exit-chippings, generated with and without ultrasonic, exhibited the elliptic and symmetrical morphologies accompanied by the corrugated stripes winding the entire chipping surfaces. The quantitative relationship between the instantaneous extrusion pressure and the propagation direction of the incipient crack was proposed, revealing that the propagation angle was inversely proportional to the extrusion pressure. Ultrasonic superimposition augmented the extrusion pressure exerted the machined surface, which reduced the propagation angle of the incipient crack. The elliptic morphology characteristics of the exit-chipping were attributed to the parabolic variation of the additional bending moment with the circumferential spreading of the ring-crack. Ultrasonic superposition increased the propagation angle of the ring-crack, thus deteriorating the exit quality of the drilled hole.

In this study, surface error calculations and stability conditions are presented for milling operations in case of slender parts. The dynamic behavior of the flexible beam-type workpiece is modeled by means of finite element method (FEM), while the varying dynamical properties related to the feed motion as well as the material removal process are incorporated in the model. The FEM-generated direct frequency response function is verified through a closed-form solution based on the distributed transfer function method. Relative errors and convergence of the FEM are investigated based on the analytical solutions of the continuum model, from which appropriate element size and mode number can be selected for modal coordinate transformations. The pattern in the variation of the natural frequencies is explored using the analytical model in case of high radial depth of cut relative to the original cross section of the beam-like workpiece. Both the stability conditions and the resulted surface errors are predicted as a function of the tool position. The presented approach and the results are validated by laboratory tests.

The dynamic performance of the steel–Basalt fiber polymer concrete (BFPC) machine tool joint surface (referred to as the joint surface) has a significant impact on the overall BFPC machine tool performance; however, its dynamic characteristics remain unclear. In order to solve this problem, the influence of roughness and surface pressure on the dynamic performance of joint surface was studied experimentally, and a neural network prediction model for the dynamic performance of the joint surface was established. A BFPC bed was designed and manufactured, and BFPC bed’s dynamic performance was tested experimentally. The finite element simulation model of BFPC bed was established with equivalent spring-damper element. The BFPC bed’s dynamic performance without considering the influence of the joint surface and considering the influence of the joint surface was studied separately. The results show that the maximum error of the natural frequency of the BFPC bed was 6.937% considering the influence of the joint surface, which was much lower than the error without considering the influence of the joint surface. The maximum amplitude error of the X-axis and Z-axis acceleration of the BFPC bed was 6.917% and 5.15%, which were much smaller than the error without considering the influence of the joint surface. It proves the accuracy of the neural network prediction model for dynamic performance of the joint surface and the validity of the finite element simulation method for the joint surface. It provides theoretical support for the design analysis of BFPC machine tool.

Polishing of additively manufactured products is a multi-stage process, and a different combination of polishing pad and process parameters is employed at each stage. Pad change decisions and endpoint determination currently rely on practitioners’ experience and subjective visual inspection of surface quality. An automated and objective decision process is more desired for delivering consistency and reducing variability. Toward that objective, a model-guided decision-making scheme is developed in this article for the polishing process of a titanium alloy workpiece. The model used is a series of Gaussian process models, each established for a polishing stage at which surface data are gathered. The series of Gaussian process models appear capable of capturing surface changes and variation over the polishing process, resulting in a decision protocol informed by the correlation characteristics over the sample surface. It is found that low correlations reveal the existence of extreme roughness that may be deemed surface defects. Making judicious use of the change pattern in surface correlation provides insights enabling timely actions. Physical polishing of titanium alloy samples and a simulation of this process are used together to demonstrate the merit of the proposed method.

This research explores the measurement of strain in a machining process on a milling machine. The goal is to develop a simple and easy method to determine the strain in a machine. Compared with other already existing approaches, the presented method separates the measurement locally from coolant and chips, which decreases the risk of a failure in the case of a continuously monitored machine. Furthermore, the measurement method does not influence the machining process itself. The separation of the machining process and the measurement enables the method to gather data without manipulating the process itself. By excluding any influence of the measurement process, the research presented in this article proves the general suitability of the method to increase the accuracy of the machining operation by modifying the toolpath of the machine.