Multiphysics models for friction stir welding simulation

Purpose: The Friction Stir Welding (FSW) process comprises of several highly coupled (and non-linear) physical phenomena: large plastic deformation, material flow transportation, mechanical stirring of the tool, tool-workpiece surface interaction, dynamic structural evolution, heat generation from friction and plastic deformation, etc. In this paper, an advanced Finite Element (FE) model encapsulating this complex behavior is presented and various aspects associated with the FE model such as contact modeling, material model and meshing techniques are discussed in detail. Methodology: The numerical model is continuum solid mechanics-based, fully thermomechanically coupled and has successfully simulated the friction stir welding process including plunging, dwelling and welding stages. Findings: The development of several field variables are quantified by the model: temperature, stress, strain, etc. Material movement is visualized by defining tracer particles at the locations of interest. The numerically computed material flow patterns are in very good agreement with the general findings from experiments. Value: The model is, to the best of the authors’ knowledge, the most advanced simulation of FSW published in the literature

Multi-physics simulation of friction stir welding process

Purpose: The Friction Stir Welding (FSW) process comprises of several highly coupled (and non-linear) physical phenomena: large plastic deformation, material flow transportation, mechanical stirring of the tool, tool-workpiece surface interaction, dynamic structural evolution, heat generation from friction and plastic deformation, etc. In this paper, an advanced Finite Element (FE) model encapsulating this complex behavior is presented and various aspects associated with the FE model such as contact modeling, material model and meshing techniques are discussed in detail. Methodology: The numerical model is continuum solid mechanics-based, fully thermomechanically coupled and has successfully simulated the friction stir welding process including plunging, dwelling and welding stages. Findings: The development of several field variables are quantified by the model: temperature, stress, strain, etc. Material movement is visualized by defining tracer particles at the locations of interest. The numerically computed material flow patterns are in very good agreement with the general findings from experiments. Value: The model is, to the best of the authors’ knowledge, the most advanced simulation of FSW published in the literature

More than a Million Ways to Be Pushed: A High-Fidelity Experimental Dataset of Planar Pushing

Pushing is a motion primitive useful to handle objects that are too large, too heavy, or too cluttered to be grasped. It is at the core of much of robotic manipulation, in particular when physical interaction is involved. It seems reasonable then to wish for robots to understand how pushed objects move. In reality, however, robots often rely on approximations which yield models that are computable, but also restricted and inaccurate. Just how close are those models? How reasonable are the assumptions they are based on? To help answer these questions, and to get a better experimental understanding of pushing, we present a comprehensive and high-fidelity dataset of planar pushing experiments. The dataset contains timestamped poses of a circular pusher and a pushed object, as well as forces at the interaction.We vary the push interaction in 6 dimensions: surface material, shape of the pushed object, contact position, pushing direction, pushing speed, and pushing acceleration. An industrial robot automates the data capturing along precisely controlled position-velocity-acceleration trajectories of the pusher, which give dense samples of positions and forces of uniform quality. We finish the paper by characterizing the variability of friction, and evaluating the most common assumptions and simplifications made by models of frictional pushing in robotics.Comment: 8 pages, 10 figure

Friction Variability in Planar Pushing Data: Anisotropic Friction and Data-collection Bias

Friction plays a key role in manipulating objects. Most of what we do with our hands, and most of what robots do with their grippers, is based on the ability to control frictional forces. This paper aims to better understand the variability and predictability of planar friction. In particular, we focus on the analysis of a recent dataset on planar pushing by Yu et al. [1] devised to create a data-driven footprint of planar friction. We show in this paper how we can explain a significant fraction of the observed unconventional phenomena, e.g., stochasticity and multi-modality, by combining the effects of material non-homogeneity, anisotropy of friction and biases due to data collection dynamics, hinting that the variability is explainable but inevitable in practice. We introduce an anisotropic friction model and conduct simulation experiments comparing with more standard isotropic friction models. The anisotropic friction between object and supporting surface results in convergence of initial condition during the automated data collection. Numerical results confirm that the anisotropic friction model explains the bias in the dataset and the apparent stochasticity in the outcome of a push. The fact that the data collection process itself can originate biases in the collected datasets, resulting in deterioration of trained models, calls attention to the data collection dynamics.Comment: 8 pages, 13 figure

Multi-wafer slicing with a fixed abrasive

A wafering machine having a multiplicity of wire cutting blades supported by a bladehead reciprocally moving past a workpiece supported by a holder that rocks about an axis perpendicular to the wires at a frequency less than the reciprocation of the bladehead

Study of friction welding

Friction welding(FW) is a fairly recent technique that utilizes a non-consumable welding tool to generate frictional heat and plastic deformation at the welding location, there by affecting the formation of a joint while the material is in solid state. The principal advantage of frictional welding, being a solid state process, low distortion, absence of melt-related defects and high joint strength, even in those alloys that are that are considered non-weldable by conventional welding techniques. Furthermore, friction welded joints are characterized by the absence of filler-induced problems or defects, since the technique requires no filler, and by the low hydrogen contents in the joints,an important consideration in welding steel and other alloys susceptible to hydrogen damage. FW can be used to produce butt, corner, lap, T, spot, fillet and hem joints, as well as to weld hollow objects, such as tanks and tubes or pipes, stock with different thickness, tapered section and parts with 3-dimensional contours. The technique can produce joints utilizing equipment based on traditional machine tool technologies, and it has been used to weld a variety of similar and dissimilar alloys as well as for welding metal matrix composites and for repairing the existing joints. Replacement of fastened joints with FW welded joints can lead to significant weight and cost savings, attractive propositions for many industries. This document reviews some of the FW work performed to date, presents a brief account of mechanical testing of welded joints, tackles the issue of generating joint allowables, and offers some remarks and observation. FW is a leap forward in manufacturing technology, a leap that will benefit a wide range of industries, including transportation industry in general and the airframe industry in particular

Tribological Effects of Metalworking Fluids in Cutting Processes

An understanding of the proper application of metalworking fluids (MWFs) is necessary for their implementation in efficient production processes. In addition, the knowledge of the process-related aspect of chip transport and the macroscopic cooling effect, the characteristics and properties of lubricant film formation, and the cooling conditions in the secondary shear zone on the chip surface, i.e., in the direct vicinity of the material separation, represent a combined fundamental scientific issue within production engineering. The aim is to transfer methods from the field of tribology of machine elements, which have already led to a considerable gain in knowledge in this discipline, to machining and to couple them with already established approaches to machining. In the case of roller bearings, the contact pressure is in the range as the pressure in the contact zone between the cutting insert and chip. Due to this, established methods might be transferred to the cutting process. In addition to classical pin-on-plate and pin-on-ring friction investigations, film thickness measurements were carried out and compared to machining tests. The coefficient of friction determined in the planing test rig is 0.48 for dry cutting, while it is 0.47 for wet cutting. These two values are much larger than the CoF with MWFs measured on the two tribometers. It is shown that the boundary friction of MWF especially influences the machining process. Thus, additives in MWF might have a high significance in machining

Friction stir welding (FSW) simulation using an arbitrary Lagrangian -Eulerian (ALE) moving mesh approach

Material flow in the solid-state Friction Stir Welding (FSW) is quite a complex process. The Investigation of the material flow can be carried out either by experimentation or by numerical simulation. However, compared to experimentation, numerical simulation is inexpensive, efficient and convenient, but quite challenging to model.;This work concerns the choice and development of numerical methods for efficient and reliable simulation of the material flow during FSW. The two objectives of this work are: to develop a mesh motion scheme for simulating the large deformations of the workpieces during FSW and to assess the material flow behavior of the rigid-elastoplastic problem of FSW using the moving mesh approach.;The challenging issue in modeling FSW is to deal with large deformations of the workpiece material. The Lagrangian simulations of FSW show that the severely distorted finite elements are caused due to the large deformation of workpiece material, which makes the Lagrangian approach inappropriate for modeling FSW. Thus, Arbitrary Lagrangian-Eulerian (ALE) formulations are used to overcome the shortcoming of Lagrangian formulations. The basic idea of the ALE approach is that the mesh is not obliged to follow the material flow. Thereby the excessively distorted elements can be avoided.;An important consideration in applying the ALE approach is an advection method which determines the mesh motion in every step of the analysis. Due to the characteristics of FSW, the moving mesh approach based on ALE formulations is developed for the modeling of FSW. Several case studies that document the material flow during FSW are presented using this approach.;Based on the simulation results, it is concluded that the material motion characteristics on the top surface and through the depth (volume) of friction stir welds have been made for the advancing and retreating sides. The motion trends are consistent with the reported experimental evidence. The case studies demonstrate the capabilities and potential of the mesh motion scheme in simulating the FSW process