Gaps at part interfaces pose a major challenge for laser transmission welding (LTW) of thermoplastics due to the reliance on contact conduction between the absorptive and transmissive parts. In industrial applications, gaps between parts can occur for a variety of tolerance and process control reasons. Previous experimental and modeling work in LTW has focused on gap-free joints, with little attention to bridging a gap with thermal expansion of the absorbing material. A two-dimensional comprehensive numerical model simulated bridging gaps in LTW. Using the model, operating parameters were selected for welding across a 12.7 μ m gap and a 25.4 μ m gap by creating sufficient thermal strain to bridge the gap and form a weld. Using these operating parameters, PVC samples were welded in a T -joint geometry with a designed gap. The quality of the welds was assessed visually, by destructive force testing and by measuring the weld size to quantify the weld strength. All the experimental samples, for the two gap sizes, bridged the gap and formed welds. The average weld strength of the 12.7 μ m gap samples was 16.1 MPa , while the 25.4 μ m gap samples had an average strength of 10.0 MPa . Gaps were successfully bridged with LTW by using a two-dimensional model to design the operating parameters. To achieve higher modeling accuracy, a three-dimensional model might better simulate the thermal diffusion in the direction of laser travel.

Gas metal arc welding (GMAW) is the most widely used process for metal joining because of its high productivity and good quality, but analysis shows that the fundamental characteristic restricts conventional GMAW from further increasing the welding productivity. A novel GMAW process, refereed to as double-electrode GMAW or DE-GMAW, thus has been developed to make it possible to increase the melting current while the base metal current can still be controlled at a desired level. This fundamental change provides an effective method to allow manufacturers to use high melting currents to achieve high melting speed and low base metal heat input. A series of experiments have been conducted to uncover the basic characteristics of this novel process. Results obtained from analyses of high-speed image sequences and recorded current signals suggest that DE-GMAW can lower the critical current for achieving the desired spray transfer, shift the droplet trajectory, reduce the diameter of the droplet, and increase the speed and (generation) rate of the droplets.

A general precision motion control methodology for complex contours is proposed in this paper. Each motion servomechanism dynamic model is divided into a linear portion and a portion containing nonlinear friction, unmodeled dynamics, and unknown disturbances. A full state feedback controller, based on a state space error system model, is developed to track general reference trajectories. The lumped static, Coulomb, and Stribeck friction effects are described using the Tustin friction model. Unmodeled dynamics and unknown disturbances are estimated using a Kalman filter that employs a first-order stochastic model. The nonlinear friction, unmodeled dynamics, and unknown disturbances are directly canceled by the controller. In the proposed motion control methodology, complex contours (i.e., contours whose radii of curvature constantly change along the contour) do not need to be decomposed into line segments and arcs and the reference signals do not need to be prefiltered. Also, the controller structure does not need to be adjusted to track different types of contours. Experiments are conducted on a two-axis laboratory grade machine tool for elliptical, limacon, and free-form contours. The results demonstrate the excellent tracking performance of the proposed motion control methodology. They also demonstrate that the performance is independent of the contours’ complexity.

In recent years, scientific interest on friction stir welding (FSW) has grown more and more since such a joining technique allows one to weld lightweight alloys that are rather difficult to weld or even “unweldable” with the classic fusion welding operations. Furthermore, few industrial applications of the process are already known in different manufacturing fields. In this paper, the optimization problem of a FSW lap joint for automotive applications is investigated, taking into account process parameters such as the tool rotating speed and the tool feed rate; a numerical gradient technique is applied for the optimization procedure reducing the number of experimental tests to be developed.

This paper proposes a comprehensive quality prediction framework for multistage machining processes, connecting engineering design with the activities of quality modeling, variation propagation modeling and calculation, dimensional variation evaluation, dimensional variation analysis, and quality feedback. Presented is an integrated information model utilizing a hybrid (feature/point-based) dimensional accuracy and variation quality modeling approach that incorporates Monte Carlo simulation, variation propagation, and regression modeling algorithms. Two important variations (kinematic and static) for the workpiece, machine tool, fixture, and machining processes are considered. The objective of the framework is to support the development of a quality prediction and analysis software tool that is efficient in predicting part dimensional quality in a multistage machining system (serial, parallel, or hybrid) from station level to system level.

The process of coincident wire and powder deposition by laser has recently emerged in research work as a layered manufacturing method with a higher deposition rate than the established laser direct metal deposition technique and as a means of creating functionally graded metallic surface layers in a single pass. This work analytically models the process by accounting for the incoming wire and powder as virtual negative heat sources. The major assumptions of the model are confirmed experimentally and the predicted temperature profiles compared with values measured using contact and pyrometric methods. Model accuracy outside the molten zone is excellent, but this solution does not account for latent heat and intrapool circulation effects so it gives only moderate precision when extrapolated to within the melt pool. Increasing the mass feed rate to the melt pool reduces its depth and the temperature surrounding it—these effects can be quantified in three dimensions by the model.

This paper presents an experimental study on the drilling characteristics of an E-glass fabric-reinforced polypropylene composite and aluminum alloy 6061-T6. Both materials have many similar structural applications, especially in the automotive industry. The drilling characteristics considered were axial thrust force, torque, temperature increase during drilling, and chip morphology. Both axial thrust force and torque were significantly higher for the aluminum alloy but were independent of the cutting speed for both materials. However, both increased linearly with increasing feed rate for the composite, but nonlinearly for the aluminum alloy. The Shaw-Oxford equation for predicting axial thrust and torque worked well with the aluminum alloy but did not fit the composite’s axial thrust and torque characteristics. Both materials exhibited temperature rise at locations close to the drilled hole. The temperature rise decreased with increasing feed rate as well as increasing cutting speed; however, the maximum temperature rise in the composite was significantly lower than that in the aluminum alloy. There was also a significant difference in the morphology of chips of these two materials.

The spatial and temporal distribution of tool temperature in drilling of commercially pure titanium is studied using the inverse heat transfer method. The chisel and cutting edges of a spiral point drill are treated as a series of elementary cutting tools. Using the oblique cutting analysis of the measured thrust force and torque, the forces and frictional heat generation on elementary cutting tools are calculated. Temperatures measured by thermocouples embedded on the drill flank face are used as the input for the inverse heat transfer analysis to calculate the heat partition factor between the drill and chip. The temperature distribution of the drill is solved by the finite element method and validated by experimental measurements with good agreement. For titanium drilling, the drill temperature is high. At 24.4 m/min and 73.2 m/min drill peripheral cutting speed, the peak temperature of the drill reaches 480°C and 1060°C, respectively, after 12.7 mm depth of drilling with 0.025 mm feed per cutting tooth. The steady increase of drill temperature versus drilling time is investigated.

A 3D rigid assembly modeling technique is developed for stream of variation analysis (SOVA) in multi-station processes. An assembly process is modeled as a spatial indexed state transition dynamic system. The model takes into account product and process factors such as: part-to-fixture, part-to-part, and inter-station interactions, which represent the influences coming from both tooling errors and part errors. The incorporation of the virtual fixture concept ( Huang et al., Proc. of 2006 ASME MSEC ) and inter-station interaction leads to the generic, unified SOVA model formulation. An automatic model generation technique is also developed for surmounting difficulties in modeling based on first principles. It enhances the applicability in modeling complex assemblies. The developed SOVA methodology outperforms the current simulation based techniques in computation efficiency, not only in forward analysis of complex assembly systems (tolerance analysis, sensitivity analysis), but it is also more powerful in backward analysis (tolerance synthesis and dimensional fault diagnosis). The model is validated using industrial case studies and series of simulations conducted using standardized industrial software (3DCS Analyst).

In two-dimensional (2D) free-form contour machining by using a straight (flat) end mill, conventional contour parallel paths offer varying cutting engagement with workpiece, which inevitably causes the variation in cutting loads on the tool, resulting in geometric inaccuracy of the machined workpiece surface. This paper presents an algorithm to generate a new offset tool path, such that the cutting engagement is regulated at a desired level over the finishing path. The key idea of the proposed algorithm is that the semi-finish path, the path prior to the finishing path, is modified such that the workpiece surface generated by the semi-finish path gives the desired engagement angle over the finishing path. The expectation with the proposed algorithm is that by regulating the cutting engagement angle along the tool path trajectory, the cutting force can be controlled at any desirable value, which will potentially reduce variation of tool deflection, thus improving geometric accuracy of machined workpiece. In this study, two case studies for 2D contiguous end milling operations with a straight end mill are shown to demonstrate the capability of the proposed algorithm for tool path modification to regulate the cutting engagement. Machining results obtained in both case studies reveal far reduced variation of cutting force, and thus, the improved geometric accuracy of the machined workpiece contour.

In this paper, the results of experiments conducted to investigate the friction coefficient existing at a brass-steel interface are presented. The research discussed here is the second of a two-part study on the size effects in friction conditions that exist during microextrusion. In the regime of dimensions of the order of a few hundred microns, these size effects tend to play a significant role in affecting the characteristics of microforming processes. Experimental results presented in the previous companion paper have already shown that the friction conditions obtained from comparisons of experimental results and numerical models show a size effect related to the overall dimensions of the extruded part, assuming material response is homogeneous. Another interesting observation was made when extrusion experiments were performed to produce submillimeter sized pins. It was noted that pins fabricated from large grain-size material ( 211 μ m ) showed a tendency to curve, whereas those fabricated from billets having a small grain size ( 32 μ m ) , did not show this tendency. In order to further investigate these phenomena, it was necessary to segregate the individual influences of material response and interfacial behavior on the microextrusion process, and therefore, a series of frictional experiments was conducted using a stored-energy Kolsky bar. The advantage of the Kolsky bar method is that it provides a direct measurement of the existing interfacial conditions and does not depend on material deformation behavior like other methods to measure friction. The method also provides both static and dynamic coefficients of friction, and these values could prove relevant for microextrusion tests performed at high strain rates. Tests were conducted using brass samples of a small grain size ( 32 μ m ) and a large grain size ( 211 μ m ) at low contact pressure ( 22 MPa ) and high contact pressure ( 250 MPa ) to see whether there was any change in the friction conditions due to these parameters. Another parameter that was varied was the area of contact. Static and dynamic coefficients of friction are reported for all the cases. The main conclusion of these experiments was that the friction coefficient did not show any significant dependence on the material grain size, interface pressure, or area of contact.

In this part of the paper series, chatter experiments are conducted in order to verify the proposed stability models presented in the first part ( Ozlu, E., and Budak, E., 2007, ASME J. Manuf. Sci. Eng., 129(4), pp. 726–732) . Turning and boring chatter experiments are conducted for the cases where the tool or the workpiece is the most flexible component of the cutting system. In addition, chatter experiments demonstrating the effect of the insert nose radius on the stability limit are presented. Satisfactory agreement is observed between the analytical predictions and the experimental results.

In this paper an analytical model for stability limit predictions in turning and boring operations is proposed. The multidimensional model includes the three-dimensional geometry of the processes resulting in an eigenvalue problem. In addition, a model for the chip thickness at the insert nose is proposed to observe the effect of the insert nose radius on the chatter stability limit. The model represents a development over existing ones due to accurate treatment of the multidimensional process dynamics and geometry, and resulting practical formulas for stability limit predictions. Chatter experiments are conducted for both turning and boring in order to verify the model predictions, and overall, an acceptable agreement is observed.

A three-dimensional finite element model was developed to predict the temperature distribution and phase transformation in deposited stainless steel 410 (SS410) during the Laser Engineered Net Shaping (LENS™) rapid fabrication process. The development of the model was carried out using the SYSWELD software package. The model calculates the evolution of temperature in the part during the fabrication of a SS410 plate. The metallurgical transformations are taken into account using the temperature-dependent material properties and the continuous cooling transformation diagram. The ferritic and martensitic transformation as well as austenitization and tempering of martensite are considered. The influence of processing parameters such as laser power and traverse speed on the phase transformation and the consequent hardness are analyzed. The potential presence of porosity due to lack of fusion is also discussed. The results show that the temperature distribution, the microstructure, and hardness in the final part depend significantly on the processing parameters.

The relatively new technique of fluidized bed assisted abrasive jet machining (FB-AJM) is applied to finishing the inner surfaces of tubular Inconel 718 components. The effects of abrasive size, jet pressure, and machining cycle were evaluated, and the behavior of abrasive cutting edges acting against the surface during the process to remove material is accounted for. The finished surface was found to be highly dependent on jet pressure because it affects the abrasive contact against the surface as well as the finishing force acting on the abrasive, on the abrasive grain size, which controls the depth of cut, and on machining cycle, which controls the interaction time between the abrasives and the surface being finished. By altering these conditions, this process achieves surface roughness ( R a ) as fine as 0.1 μ m and imparts minimal additional residual stress on the surface. This study also reveals the mechanisms that determine the smoothing of the inner surface of Inconel 718 tubes and improve the form accuracy, i.e., the internal roundness of the Inconel 718 tube.

Lubricants in hot forging are applied to the heated die surface by spraying dilute water based graphite suspensions through high-pressure nozzles. To avoid undesirable steam formation, these lubricant droplets need to completely dry before deformation begins. This paper presents an analytical model to estimate evaporation time for the impacting drops at surface temperatures above Leidenfrost, 300 – 450 ° C . It is based on the suspension of deformed droplet on a vapor cushion sustained by a continuous supply of water from the drying droplet. Model predictions are validated by single droplet experiments with different surface temperatures, dilution ratios, and impacting speeds.

A stream-of-variation analysis (SOVA) model for three-dimensional (3D) rigid-body assemblies in a single station is developed. Both product and process information, such as part and fixture locating errors, are integrated in the model. The model represents a linear relationship of the variations between key product characteristics and key control characteristics. The generic modeling procedure and framework are provided, which involve: (1) an assembly graph (AG) to represent the kinematical constraints among parts and fixtures, (2) an unified method to transform all constraints (mating interface and fixture locators etc.) into a 3-2-1 locating scheme, and (3) a 3D rigid model for variation flow in a single-station process. The generality of the model is achieved by formulating all these constraints with an unified generalized fixture model. Thus, the model is able to accommodate various types of assemblies and provides a building block for complex multistation assembly model, in which the interstation interactions are taken into account. The model has been verified by using Monte Carlo simulation and a standardized industrial software. It provides the basis for variation control through tolerance design analysis, synthesis, and diagnosis in manufacturing systems.

This paper is aiming at development of an analytical approach for computation of the geometrical parameters of cutting edges of an involute hob. It is well recognized that the involute hob geometry strongly affects the cutting tool performance, as well as the efficiency of gear hobbing operation. It is proven experimentally and by industrial practice that the optimal value of every geometrical parameter of the tool cutting edge exists and, thus, it can be found out. A method for computation of the cutting edge geometry is necessary for optimization of parameters of a gear hobbing operation. In this paper, an analytical method for the computation of the cutting edge geometry of a gear hob is reported. The method is based on wide application of elements of vector calculus and matrices. The analysis is performed in the tool-in-use reference system. An equation of the penetration curve is derived. The machining zone is partitioned onto several different sectors. The roughing sector and the generating sector are distinguished. Generating of the work-gear tooth profile occurs within the generating sector that is bounded by the penetration curve. The derived equations, as well as the worked-out computer codes are applicable for computation of the cutting edge geometry at any point of the cutting edge of the hob, and at a any instant of time. The equations and the computer codes enable one estimating the impact of (a) the hob diameter, (b) the hob number of starts, (c) the work-gear number of teeth, (d) the hob feed rate, and (e) the hob rotation onto the actual values of the geometrical parameters of the hob cutting edges. Numerical results of the investigation are computed using commercial software MATHCAD-SCIENTIFIC . The results of the computation of the cutting edge geometry of the involute hob enable the user (a) to avoid not-feasible values of any and all geometrical parameters of the cutting edge of the hob teeth, (b) to develop parameters of the hob grinding and reliving operations, which guaranteed the optimal values of any and all geometrical parameters of the hob cutting edges. Ultimately, the application of the hobs with optimal geometry of the cutting edges will result in an increase in the cutting tool performance and in the efficiency of the gear hobbing operation. The latter is of critical importance for high volute production of involute gears for the needs of the automotive industry. The reported research results are ready to be put into practice.

Hard roller burnishing is a cost-effective finishing and surface enhancement process where a ceramic ball rolls on the machined surface to flatten the roughness peaks. The ball is supported and lubricated by hydrostatic fluid in a special tool holder. The process not only improves surface finish but also imposes favorable compressive residual stresses in functional surfaces, which can lead to long fatigue life. Most research in the past focused on experimental studies. There is still a special need for a reliable finite element method (FEM) model that provides a fundamental understanding of the process mechanics. In this study, two-dimensional (2D) and three-dimensional FEM models for hard roller burnishing were established. The developed 2D FEM model was used to study the effects of process parameters (i.e., burnishing pressure, feed rate) on surface finish and residual stresses. The simulation results were evaluated and compared to the experimental data. Results show that the established FEM model could predict the residual stresses and provided useful information for the effect of process parameters. Both FEM and experiments show that burnishing pressure is the most influence, where high burnishing pressure produces less roughness and more compressive residual stress at the surface.

A fast method called the “inverse approach” for sheet forming modeling is based on the assumptions of the proportional loading and simplified tool actions. To improve the stress estimation, the pseudo-inverse approach was recently developed: some realistic intermediate configurations are geometrically determined to consider the deformation paths; two new efficient algorithms of plastic integration are proposed to consider the loading history. In the direct scalar algorithm (DSA), an elastic unloading-reloading factor γ is introduced to deal with the bending-unbending effects; the equation in unknown stress vectors is transformed into a scalar equation using the notion of the equivalent stress, thus the plastic multiplier Δ λ can be directly obtained without iterative resolution scheme. In the γ -return mapping algorithm, the equivalent plastic strain increment estimated by DSA is taken as the initial solution in Simo’s return mapping algorithm, leading to a stable, efficient, and accurate plastic integration scheme. The numerical experience has shown that these two algorithms give a considerable reduction of CPU time in the plastic integration.