Numerical simulation of ultrasonic spot welding of superelastic NiTi alloys: Temperature distribution and deformation behavior

Ultrasonic spot welding (USW) has attracted increasing attention due to its high- throughput solid-state bonding mechanism, which shows great potential in the semiconductor and automotive industry for the joining of metal sheets. However, the short welding cycle makes it challenging to effectively monitor the temperature history and deformation of the workpieces during the USW process, especially for the materials with some special properties. In this study, a three-dimensional (3D) finite element analysis model for USW of superelastic NiTi shape memory alloy (SMA) with Cu interlayer was developed using ANSYS Workbench. The thermal-stress coupled phenomena including the heat generation and stress distribution during the welding process was simulated and analyzed. Firstly, the superelastic constitutive model of NiTi SMAs was constructed. The distribution of temperature and stress field was then obtained by thermal-stress analysis using the direct coupling method, and the superelasticity of SMAs was observed. The simulation results showed that the highest temperature occurred in the center of the welding area during USW, which is proportional to the welding time and inversely proportional to the clamping pressure. In addition, the maximum stress occurred at the center of the contact surface between upper NiTi and Cu interlayer. After that, the validity of the simulation results was verified by setting up a thermocouple temperature measurement platform to collect the temperature data, which exhibited a good agreement with the simulated results. The simulation procedure demonstrates its potential to predict temperature and stress distribution during USW process.

A Review of Advances in Modeling of Conventional Machining Processes: From Merchant to the Present

This paper presents a review of recent advances in modeling and simulation of conventional metal machining processes, which continue to dominate a significant part of all machining processes, and in recent years, the need for predictive models for machining processes has grown in importance in the digital manufacturing age. Significant advances have been made in modeling the mechanics of cutting in conventional machining, driven by industrial need and enabled by rapid advances in computational power. The paper surveys the state-of-the-art in analytical and numerical modeling of conventional metal machining processes with a focus on their ability to predict useful performance attributes including chip geometry, forces, temperatures, tool wear, residual stress, and microstructure. Also included in the review is a discussion of the industrial use of modeling and simulation tools for conventional machining. Additionally, the practical applicability, implementation benefits, and methodological limitations of conventional machining process modeling have been examined. The paper concludes with a summary of future research directions in modeling and simulation of conventional metal machining processes.

FEA model based cautious automatic optimal shape control for fuselage assembly

In a half fuselage assembly process, shape control is vital for achieving ultra-high precision assembly. To achieve better shape adjustment, we need to determine the optimal location and force of each actuator to push and pull a fuselage to compensate for its initial shape distortion. The current practice achieves this goal by solving a surrogate model based optimization problem. However, there are two limitations of this surrogate model based method: (1) Low efficiency: Collecting training data for surrogate modeling from many FEA replications is time-consuming. (2) Non-optimality: The required number of FEA replications for building an accurate surrogate model will increase as the potential number of actuator locations increases. Therefore, the surrogate model can only be built on a limited number of prespecified potential actuator locations, which will lead to sub-optimal control results. To address these issues, this paper proposes an FEA model based automatic optimal shape control (AOSC) framework. This method directly loads the system equation from the FEA simulation platform to determine the optimal location and force of each actuator. Moreover, the proposed method further integrates the cautious control concept into the AOSC system to address model uncertainties in practice. The case study with industrial settings shows that the proposed Cautious AOSC method achieves higher control accuracy compared to the current industrial practice.

Five-axis trajectory generation considering synchronisation and nonlinear interpolation errors

This paper presents a novel real-time interpolation technique for 5-axis machine tools to attain higher speedand accuracy. To realize computationally efficient real-time interpolation of 6DOF tool motion, a joint workpiece-machine coordinate system interpolation scheme is proposed. Cartesian motion of the tool centre point (TCP) isinterpolated in the workpiece coordinate system (WCS), whereas tool orientation is interpolated in the machinecoordinate system (MCS) based on the finite impulse response (FIR) filtering. Such approach provides several ad-vantages: i) it eliminates the need for complex real-time spherical interpolation techniques, ii) facilitates efficientuse of slower rotary drive kinematics to compensate for the dynamic mismatch between Cartesian and rotary axesand achieve higher tool acceleration, iii) mitigates feed fluctuations while interpolating near kinematic singulari-ties. To take advantage of such benefits and realize accurate joint WCS-MCS interpolation scheme, tool orientationinterpolation errors are analysed. A novel approach is developed to adaptively discretize long linear tool movesand confine interpolation errors within user set tolerances. Synchronization errors between TCP and tool orienta-tion are also characterized, and peak synchronization error level is determined to guide the interpolation parameterselection. Finally, blending errors during non-stop continuous interpolation of linear toolpaths are modelled andconfined. Advantages of the proposed interpolation scheme are demonstrated through simulation studies and vali-dated experimentally. Overall, proposed technique can improve cycle times up to 10% while providing smooth and accurate non-stop real-time interpolation of tool motion in 5-axis machining.

Rotordynamics of an Improved Face-grinding Spindle: Rotational Stiffness of Thrust Bearing Increases Radial Stiffness of Spindle

The support is a key factor affecting performance of face-grinding spindle. However, advantage of traditional rolling element bearing is not highlighted when it is for large-size face grinding. This technical brief aims to develop a combined support for the face-grinding spindle consisting of a water-lubricated hydrostatic thrust bearing and two types of radial rolling bearings, and the flexible rotor dynamics of the spindle with the combined support is analyzed using the modified transfer matrix method. The results show that the rotational stiffness of water-lubricated hydrostatic thrust bearing can increase the radial stiffness of the face-grinding spindle, so the small-size rolling bearings can be utilized as the radial support for the spindle by aid of such rotational stiffness. A comparative study of comprehensive performance between the spindle supported by rolling bearings and the replacement spindle designed with our proposed combined support shows that the proposed one has technical advantage of large axial load-carrying capacity, low frictional power loss, low temperature rise and etc.

3D Permeability of Thick-Section Glass Fabric Reinforced Polymer Composite by Vacuum-Assisted Resin Infusion Molding

Determination of permeability of thick-section glass fabric preforms with fabric layers of different architectures is critical for manufacturing large, thick composite structures with complex geometry, such as wind turbine blades. The thick-section reinforcement permeability is inherently three-dimensional and needs to be obtained for accurate composite processing modeling and analysis. Numerical simulation of the liquid stage of vacuum-assisted resin infusion molding (VARIM) is important to advance the composite manufacturing process and reduce processing-induced defects. In this research, the 3D permeability of thick-section E-glass fabric reinforcement preforms is determined and the results are validated by a comparison between flow front progressions from experiments and from numerical simulations using ANSYS Fluent software. The orientation of the principal permeability axes were unknown prior to experiments. The approach used in this research differs from those in literature in that the through-thickness permeability is determined as a function of flow front positions along the principal axes and the in-plane permeabilities and is not dependent on the inlet radius. The approach was tested on reinforcements with fabric architectures which vary through-the-thickness direction, such as those in a spar cap of a wind turbine blade. The computational simulations of the flow-front progression through-the-thickness were consistent with experimental observations.

Prediction of Surface Profile Evolution of Workpiece and Lapping plate in Lapping Process

Lapping has a history of hundreds of years, yet it still relies on the experience of workers. To improve the automaticity and controllability of the lapping process, a modeling method of friction and wear is developed to predict the surface profile evolution of the workpiece and lapping plate in the lapping process. In the proposed method, by solving the balance equations of resultant force and moment, the inclination angles of the workpiece can be calculated, thus more accurate contact pressure distribution of the workpiece/lapping plate interface can be calculated. Combined with the material removal rate model, the continuous evolution process of the workpiece and lapping plate can be predicted in the lapping process. The modeling method was validated by a lapping test of a flat optical glass (Φ 100 mm) with a composite copper plate. The results show that the proposed method can predict the evolution of the surface profile of the workpiece and lapping plate with high accuracy. Consequently, the lapping plate can be dressed at the right time point. Benefit from this, in the validation test the PV value of the workpiece (with 5 mm edge exclusion) was reduced from 5.279 μm to 0.267 μm in 30 min. The proposed surface profile evolution modeling method not only improves the lapping efficiency but also provides an opportunity to understand the lapping process.

Resistance spot welding of additively manufactured maraging steels Part II: Failure behavior

Application of maraging steels via selective laser melting process in the automotive industry was unavoidably involved in the resistance spot welding with conventional steels. Due to the rapid cooling rate of welding process, selective laser melted maraging steels with unique chemical components and stack microstructure could induced the different microstructural evolution, resulting in the complicated fracture behavior in the spot welds. This paper developed a FEA model to predict the fracture mode of spot welds of DP600 to maraging steel and the effect of test conditions and printing orientations were studied. A method was proposed to calculate the material properties of fusion zone by introducing the combined effect of melting DP600 and maraging steels via selective laser melting, resulting in the accurate prediction of fracture mode and strength of spot welds. An interlayer with lower strength was found around the fusion zone and the fracture path propagated in the region, resulting in the partial interfacial failure of spot welds. Meanwhile, the printing orientation had no significant effect on the fracture mode and strength of spot welds, but the different material properties of maraging steels could affect the fracture displacement of spot welds. These findings could pave a way to guide the application of maraging steels via selective laser melting process in multiple industries, especially in the automotive industry.

Resistance spot welding of additively manufactured maraging steels Part I: Nugget formation

Application of additively manufactured steels is unavoidably involved in the resistance spot welding with conventionally manufactured steels. However, the microstructural evolution of an additive manufactured steel at high temperatures is still unknown, especially for the rapid solidification process. This paper investigated the microstructural evolution of a selective laser melted maraging steel during the rapid solidification process via resistance spot welding. Asymmetrical fusion zone with boat shape was found in the spot weld due to the rougher surface and larger electrical resistance of maraging steel via selective laser melting process. The rapid expansion of fusion zone at end of welding process was caused by the carbide formation at the heat-affected zone of maraging steel via selective laser melting process. Besides, printing orientation affected the surface roughness of a selective laser melted maraging steel and subsequently significantly influence the early stage of formation of fusion zone of additively manufactured maraging steel. We expect that our findings will pave the way to the future application of additively manufactured steels in the industries.

Effect of process parameters on interfacial temperature and shear strength of ultrasonic additive manufacturing of carbon steel 4130

Ultrasonic additive manufacturing (UAM) is a solid state manufacturing process capable of producing near-net-shape metal parts. Recent studies have shown the promise of UAM welding of high strength steels. However, the effect of weld parameters on the weld quality of UAM steel is unclear. A design of experiments study based on a Taguchi L16 design array was conducted to investigate the influence of parameters including baseplate temperature, amplitude, welding speed, and normal force on the interfacial temperature and shear strength of UAM welding of carbon steel 4130. Analysis of variance (ANOVA) and main effects analyses were performed to determine optimal weld parameters within the process window. A Pearson correlation test was conducted to find the relationship between interfacial temperature and shear strength. These analyses indicate that the highest shear strength of 392.8 MPa can be achieved by using a baseplate temperature of 400°F (204.4°C), amplitude of 31.5 μm, welding speed of 40 in/min (16.93 mm/s), and normal force of 6000 N. The Pearson correlation coefficient is calculated as 0.227, which indicates a weak positive correlation between interfacial temperature and shear strength over the range tested.