Virtual prototypes, e.g., finite element models, are commonly used to reduce the development times of a new machine tool generation. However, the accuracy of these models is often limited by their representation of damping effects and the possibility to efficiently simulate the dynamic behavior in different axis positions. This paper shows the changing local damping distribution within a single-axis machine tool configuration for different axis positions. Based on this investigation, an approach to accurately model the position-dependent dynamics, while keeping the calculation times small, is presented. The virtual model of the machine is divided in several substructures, which consider the local damping behavior of each dissipation source. The reduced mass, stiffness, and damping matrices are coupled in the desired machine position by using multipoint constraints, which are generated at the desired machine position after the reduction of the substructures. Four different approaches to apply multipoint constraints on reduced substructures are compared, followed by an investigation of their influencing parameters. The most promising approach is compared with a model without local damping representation as well as a model without substructuring. By considering the local damping effects within the finite element model and coupling the reduced models of each component in arbitrary axis positions, an efficient analysis and optimization of the dynamic behavior of a machine tool over the whole workspace can be conducted.

Additive manufacturing (or three-dimensional (3D) printing) is constantly growing as an innovative process for the production of complex-shape components. Among the seven recognized 3D printing technologies, fused deposition modeling (FDM) covers a very important role, not only for producing representative 3D models, but, mainly due to the development of innovative material like Peek and Ultem, also for realizing structurally functional components. However, being FDM a production process involving high thermal gradients, non-negligible deformations and residual stresses may affect the 3D printed component. In this work we focus on meso/macroscopic simulations of the FDM process using abaqus software. After describing in detail the methodological process, we investigate the impact of several parameters and modeling choices (e.g., mesh size, material model, time-step size) on simulation outcomes and we validate the obtained results with experimental measurements.

Deformation machining (DM) is a combination of thin structure machining and single-point incremental forming/bending (SPIF/SPIB). This process enables the creation of complex structures and geometries, which are probably difficult or sometimes impossible to manufacture employing conventional manufacturing techniques. Geometrical discrepancies in thin structure or sheet metal bending and forming are a major obstacle in manufacturing quality components. These discrepancies are more prevalent and complex in nature in incremental or generative manufacturing. In the present work, a comprehensive experimental and numerical study on the parametric effects on various geometrical inaccuracies in DM process has been performed. This study would help in giving an insight in providing necessary geometrical compensation, ensuring a quality product over a wide range of process parameters.

In recent years, the requirements for high dimensional precision on Z-bent shaped parts have become increasingly stringent. To attain these requirements, the suitable selection of the Z-die bending type has to be considered much more strictly. In this research, two types of Z-bending processes, offset Z-die bending and wiping Z-die bending, were investigated using the finite element method (FEM) to identify the spring-back characteristics and dimensions of Z-bent shaped parts. In the case of offset Z-die bending, the spring-back characteristics on both bend angles were similar. In contrast, in the case of wiping Z-bending, the spring-back characteristics on both bend angles were different. In addition, the dimensions of the Z-bent shaped parts were investigated. It was found, in the case of wiping Z-bending, that web thinning was generated and the outer bend radius was out of tolerance. To validate the FEM simulation results, experiments were carried out. The FEM simulation results showed good agreement with the experimental results in terms of the bend angles and the overall geometry of the Z-bent shaped parts. To achieve precise Z-bent shaped parts, the suitable selection of Z-die bending type in the Z-die bending process is very important.

Incremental sheet forming (ISF) is a low cost, die-less forming process suitable for low volume production. In case of components with multiple features, the accuracy of formed component depends on the sequence in which the features are formed. In addition, sheet spring-back, tool deflection, and rigid-body displacement (RBD) also affect the accuracy of formed components. Predicting the component geometry using finite element analysis (FEA) is computationally expensive and time consuming. Simple mechanics-based methodology is presented in this work to predict the geometry of components having single, multiple features, and high-wall angle components formed using single and/or multistage forming. Predictions using proposed methodology are used to select the best forming sequence in case of multiple feature components. Results presented show that the formed component geometry can be predicted with an average error of 225 μ m and maximum error of 700 μ m. In addition, a methodology is developed to achieve uniform thickness distribution with good accuracy in high wall angle components formed using multistage strategy. Hemispherical component is formed with 100 μ m variation in thickness except at the component opening and maximum profile deviation of 350 μ m. This thickness prediction capability helps the designer to choose intermediate stages and to form components with engineered thickness with reasonable accuracy.

Electric impact wrench is an important tool used in manufacturing and maintenance services. It has complex mechanism and its operation involves dynamic events occurring at vastly different time scales, which poses challenges for efficient and accurate modeling to facilitate design optimization and control. This investigation establishes a first principle-based, system-level model of a representative impact wrench. The model explicitly incorporates the dynamic flexibility of gear transmission, spindle shaft, and impacting components into the kinematic relations that connect them together. The nonlinear impact and contact events, coupled with the rotational and translational motions of all components, are explicitly analyzed, and systematic parametric identification is performed based on a multi-objective optimization (MOO) approach. The model prediction is correlated with experimental studies.

An improved “mass–spring” model to analyze the entire short-circuiting transfer (SCT) dynamic process based on the association between the arcing and circuiting phases has been proposed. This paper analyses the basic characteristics of displacement of the droplet mass center and oscillation velocity of droplet variation. In addition, the effect of welding current on the short-circuiting frequency is studied. The results of the simulations conducted agree well with the experimental results obtained. An analysis method for optimal welding current during SCT is also proposed, and the droplet transport stability is discussed. Simulation results demonstrate that the relative displacement of the droplet mass center and the average equivalent diameter of the transfer droplets are at a minimum under the optimal welding current condition. This research provides a reference for further simulation of the SCT process and useful guidance for the selection of optimum technics parameters.

In this work, a four high cold rolling mill is modeled as a spring-mass-damper system considering horizontally and vertically applied time-dependent forces due to the interaction between the strip and the working rolls. The effect of vibration of the moving strip on the work roll vibration is also considered for developing the governing equation of motion of the system which is found to be that of a nonlinear parametrically excited system. The governing equation of motion is solved by using the method of multiple scales to find the instability regions and frequency-response curves of the system. The critical amplitude of horizontal load in roll bite is calculated and the frequency-response is studied in detail considering the effect of various process parameters, such as velocity, thickness of strip, time delay, amplitude, and frequency of horizontal load in roll bite. This work can find application in the design and development of high speed and chatter free rolling mills.

Increasing demands and concerns for reliable supply of liquid transportation fuels make it important to find alternative sources to petroleum-based fuels. One such alternative is cellulosic ethanol. However, several technical barriers have hindered large-scale, cost-effective manufacturing of cellulosic ethanol, such as low density of cellulosic feedstocks (causing high transportation and storage costs) and low efficiency of enzymatic hydrolysis (causing longer processing time and low sugar yield). Ultrasonic vibration-assisted (UV-A) pelleting can increase the density of cellulosic materials and sugar yield in enzymatic hydrolysis. At present, effects of process variables in UV-A pelleting on pellet quality (density, durability, and spring-back) and sugar yield have not been adequately investigated. This paper reports an experimental investigation on UV-A pelleting of wheat straw. A 24 factorial design is employed to evaluate effects of process variables (moisture content, sieve size, pelleting pressure, and ultrasonic power) on output variables (pellet density, durability, spring-back, and sugar yield).

The excessive stresses during the coiling of helical springs could lead to breakage of the rod. Moreover, the high level of residual stress in the formed helical spring reduces considerably its fatigue life. For the practical estimation of residual and coiling stresses in the helical springs the analytical formulas are necessary. In this paper the analytical solution of the problem of elastic–plastic deformation of cylindrical bar under combined bending and torsion moments is found for a special nonlinear stress–strain law. The obtained solution allows the analysis of the active stresses during the combined bending and twist. Moreover, the residual stresses in the bar after springback are also derived in closed analytical form. The results of this analysis are applied to the actual engineering problem of determination of stresses during the manufacturing of helical coiled springs. A practically important example, describing the manufacturing of helical coiled spring is worked out to illustrate the simplicity achieved in determining the plasticization process and residual stresses. The obtained results match the reported measured values. The developed method does not require numerical simulation and is perfectly suited for programming of coiling machines, estimation of loads during manufacturing of cold-wounded helical springs and for dimensioning and wear calculation of coiling tools.

In this research, a simulated annealing algorithm was used to minimize the spring-back in V-die bending process. First, an adaptive neuro-fuzzy inference system (ANFIS) model was developed using the data generated based on experimental observations. The output parameter of the ANFIS model is spring-back and the input parameters are sheet thickness, sheet orientation, and punch tip radius. The performance of the ANFIS model in training and testing sets is compared with those observations. The results indicated that the ANFIS model can be applied successfully for prediction of spring-back. Then, the ANFIS model was used as a function in simulated annealing algorithm to minimize the spring-back. The results showed that the proposed model has an acceptable performance to optimize the bending process.

Abrasive waterjet peening (AWJP) has been conceived as a new surface treatment process capable of achieving desired changes in surface texture, chemistry, and residual stress simultaneously. In the present investigation, the influence of elastic prestress on the residual stress resulting from AWJP was studied. Treatments were conducted on steel, as well as nickel and titanium alloy targets subjected to an elastic prestress ranging from 0% to 75% of the material’s yield strength. The results showed that a tensile elastic prestress increases the surface residual stress and the depth of the compressive stress zone. The surface residual stress in each metal increased nonuniformly with magnitude of prestress; the maximum surface residual stress was obtained at an applied prestress between 45% and 60% of the substrate yield strength. Overall, the increases in surface stress and depth that were obtained reached 100% and 50%, respectively. There were no changes to the surface texture caused by the prestress. According to results of this study, application of an elastic prestress can serve as an effective method for improving characteristics of the residual stress field in components treated using AWJP.

A lumped parameter dynamical model is developed to describe the metal transfer for gas metal arc welding in the globular mode. The oscillations of molten drop are modeled using a mass-spring-damper system with variable mass and spring coefficient. An analytical solution is developed for the variable coefficient system to better understand the effect of various model parameters on the drop oscillations. The effect of welding drop motion on the observed current and voltage signals is investigated, and the model agrees well with the experimental results. Furthermore, the effect of wire feeding rate (or welding current) on the metal transfer cycle time is studied, and the model successfully estimates the cycle times for different wire feeding rates. Possible regions of unstable metal transfer are investigated both by the model and experiments. The model can be used to identify the range of welding wire feed rates that results in stable metal transfer during the globular mode of metal transfer.

Milling of thin-walled aerospace structures is a critical process due to the high flexibility of the workpiece. Current practices in the fixture design and the choice of cutting parameters rely solely on conservative guidelines and the designer’s experience. This is a result of the lack of computationally efficient dynamic models to represent the dynamic response of the workpiece during machining, and the interaction between the workpiece, fixture and the cutting forces. This paper presents a novel dynamic formulation of typical thin-walled pockets encountered in aerospace structures. It is based on an analytical description of a five-sided pocket using a plate model. An off-line calibration of the model parameters, using global and local optimization, is performed in order to match the dynamic response of the pocket structure. The developed simplified model is based on Rayleigh’s energy method. Various pocket shapes are examined under different loading conditions and compared to finite element (FE) predictions and experimental results. In both cases, the results obtained by the developed model are in excellent agreement. This proposed approach resulted in one to two orders of magnitude reduction in computational time when compared to FE models, with a prediction error less than 10%.

Drill chatter degrades hole roundness, hole size, and tool life. This wastes time and money in tools, scrap, and hole rework. Chatter prediction in milling and turning has shown significant benefit to industry; however, researchers have been unable to accurately predict chatter in drilling applications. In the past, the drill, including the chisel edge, was modeled as either a fixed-fixed or fixed-pinned beam (Tekinalp, O., and Ulsoy, A. G., 1989, “Modeling and Finite Element Analysis of Drill Bit Vibrations,” ASME J. Eng. Indust. 111 , pp. 148–154), but more recent research (Dilley, D. N., Bayly, P. V., and Schaut, A. J., 2005, “Effects of the Chisel Edge on the Chatter Frequency in Drilling,” J. Sound Vib., 281, pp. 423–428) has shown that a fixed-embedded model using springs improves frequency matching. The effects of the drill margins on dynamics have not been studied. The fixed-fixed or fixed-pinned model will be shown to be inappropriate for modeling the effects of margin engagement, while the spring-end boundary condition can better approximate the frequency increase observed experimentally as the drill margins engage deeper into the hole. In addition, the shifted frequency is well below the frequency found from an analytical fixed-fixed or fixed-pinned beam. Evidence that the margins cause the frequency shift is seen in three-dimensional waterfall plots that show this shift for pilot hole drilling (in which the margins are engaged), but not for tube drilling (in which margins are not engaged).

This paper presents a systematic finite element model to predict the fixture unit stiffness by introducing nonlinear contact elements on the contact surface between fixture components. The contact element includes three independent springs: two in tangential directions and one in the normal direction of the contact surface. Strong nonlinearity is caused by possible separation and sliding between two fixture components. The problem is formulated by the penalty function method and is solved by the Newton-Raphson procedure. The model was validated by two cases of analysis of a linear cantilever beam and a simple fixture unit with two components. The results are in agreement with the corresponding analytical solution of beams and the previous experimental results for fixture in the literature.

Material handling of compliant sheet metal parts significantly impacts both part dimensional quality and production rate in the stamping industry. This paper advances previously developed material handling end effector layout optimization methodology for rigid point end effectors [1] by developing a dexterous part-holding end effector model. This model overcomes the shortcomings of the rigid point part-holding end effector model by predicting part deformation more accurately for various modes of deformation and for a set of part-holding end effector locations. This is especially important for handling systems which utilize vacuum cup end effectors widely used for handling of large sheet metal parts. The dexterous end effector model design method and an algorithm for estimation of model parameters are developed. The algorithm combines data from design of computer simulations and from the set of experiments by integrating finite element analysis and a statistical data processing technique. Experimental studies are conducted to verify the developed model and the model parameter estimation algorithm. The developed methodology provides an analytical tool for product and process designers to accurately predict part deformation during handling, which further leads to minimization of part deformation, improvement of part dimensional quality and increase of production rate.

Commercially-available reconfigurable fixtures, used for holding compliant sheet metal, composite and plastic parts during secondary machining operations, are extremely expensive and overly-complicated devices. A computer-controlled, reconfigurable fixturing device (RFD) concept for compliant parts, based on a matrix of individually-stoppable pins lowered by a single rigid platen, has been developed as a simple and low-cost design alternative to commercially-available devices. Two different approaches to stopping and clamping individual pins have been investigated: a combination electromagnet assist and gas springs compressed with a toggle mechanism, and a pneumatic clamp. Simple mechanical models have been developed for predicting the stopping and clamping performance of both designs including pin positioning accuracy, vertical load-carrying capacity of a pin, and deflection of a pin subjected to lateral loads. An RFD prototype, consisting of a single pin actuated by a servoed platen, has been designed, built and tested. It has demonstrated the feasibility of this new RFD design. [S1087-1357(00)02204-8]

This research focuses on real-time position control for draping fabric sliding on a high friction surface. Although fabrics are usually positioned on smooth surfaces with fixed fabric guides to simplify automated handling, a high friction work surface holds the fabric in place after positioning, allowing accurate assembly of multiple fabric parts without specialized jigs or fixtures. A neural adaptive controller with feedforward friction compensation provides asymptotic tracking for a spring mass model with friction. A test stand and an optical sensor are designed to facilitate real time position measurement and control. The neural adaptive controller demonstrates good position tracking and robustness to fabric property variations relative to open loop or PID control.

The accuracy of precision machining operations could be improved through tool force feedback. Tool force is ideally suited for use in a control algorithm because it contains information on the instantaneous depth of cut, feed rate and condition of the tool. A tool force model that could form the basis of this new control technique has been developed. By measuring the shear angle from micrographs of chip cross sections, equations for the forces due to chip formation and the friction between the chip and the tool have been written. Furthermore, the effects of elastic deformation of the workpiece (spring back) on chip formation and the measured forces, which can be significant in precision machining, have been included in the model. Machining experiments were conducted with a 0 deg rake diamond tool and four metals that are commonly diamond turned. For machining with newly lapped as well as worn tools, the calculated forces were in excellent agreement with the measured values for the array of workpiece materials.