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Direct laser ablation removes material by directly focusing the laser on the material surface so its performance highly depends on the surface condition. Laser-Induced Plasma Micro-Machining (LIPMM) removes the material by focusing an ultrashort laser pulse in an auxiliary dielectric layer above the material and inducing dielectric breakdown to achieve more accurate energy deposition. The physical process of LIPMM can be divided into two stages: pulse absorption and material removal. This work focuses on modeling the pulse absorption stage by implementing the Finite Difference Time Domain (FDTD) method to provide a unified simulation framework for the ultrashort laser-matter interaction. The simulation model can be divided into three steps: 1) the evolution of the laser field, which is described by FDTD with current and a tightly focused beam with Gaussian entry utilized to approximate the unperturbed laser field near focus; 2) the metal absorption of a ultrashort laser pulse, where a two-temperature model is used and the current is described by the Drude model with mean free time approximated by a three stage model and 3) the water breakdown, which is described by Kennedy’s first order model. Combining the above approaches, the unified framework demonstrates its utility on the example of the water-aluminum boundary in the LIPMM process.

Incremental sheet forming is a state-of-the-art manufacturing process for the rapid manufacture of sheet metal components without the use of geometry-specific dies. In this paper, a novel ISF machine, based on a unique overconstrained parallel robot called the Tri-pyramid robot, is introduced. The inverse and forward kinematics of the machine are first analyzed and calibrated based on experimental measurements. In turn, to compensate the kinematic and compliance errors of the machine, a linear encoder system, developed to directly measure the end-effector positions, in conjunction with a neural network, trained to map encoder readings and spatial end-effector positions, is used. A feedback control law is then implemented to compensate the errors in real-time. Experimental results demonstrate that after calibration and error compensation the accuracy of the machine is improved tenfold, making it adequate for incremental forming applications.

Compared to the conventional single-point incremental forming (SPIF) processes, water jet incremental micro-forming (WJIMF) utilizes a high-speed and high-pressure water jet as a tool instead of a rigid round-tipped tool to fabricate thin shell micro objects. Thin foils were incrementally formed with micro-scale water jets on a specially designed testbed. In this paper, the effects on the water jet incremental micro-forming process with respect to several key process parameters, including water jet pressure, relative water jet diameter, sheet thickness, and feed rate, were experimentally studied using stainless steel foils. Experimental results indicate that feature geometry, especially depth, can be controlled by adjusting the processes parameters. The presented results and conclusions provide a foundation for future modeling work and the selection of process parameters to achieve high quality thin shell micro products.

Electrohydrodynamic processes were used for direct-writing of bead arrays with controllable bead sizes. Experiments were conducted to align layers of bead-on-string structures in an effort to create three-dimensional patterns. The results show that the jet focuses on previously deposited droplets allowing for the selective deposition of material over already deposited patterns. Jet attraction to already deposited solutions on the substrate is attributed to the charge transport at the liquid ink-metal collector interface and the dielectric properties of the water/poly(ethylene oxide) solution under an electric field. The deposition process consists of 3 steps: (1) deposition of a layer of bead-on-string structures, (2) addition of extra volume to the beads by subsequent passes of the jet, and (3) evaporation of the solvent resulting in an array of beads with varying sizes. Patterns with up to 20 passes were experimentally obtained. The beads’ height was seen to be independent of the number of passes. The process reported is a simple, fast, and low-cost method for deposition of bead arrays with varying diameters.Copyright © 2017 by ASME

Carbon fiber composites have received growing attention because of their high performance. One economic method to manufacturing the composite parts is the sequence of forming followed by the compression molding process. In this sequence, the preforming procedure forms the prepreg, which is the composite with the uncured resin, to the product geometry while the molding process cures the resin. Slip between different prepreg layers is observed in the preforming step and this paper reports a method to characterize the properties of the interaction between different prepreg layers, which is critical to predictive modeling and design optimization. An experimental setup was established to evaluate the interactions at various industrial production conditions. The experimental results were analyzed for an in-depth understanding about how the temperature, the relative sliding speed, and the fiber orientation affect the tangential interaction between two prepreg layers. The interaction factors measured from these experiments will be implemented in the computational preforming program.

Interface characteristics of Al/Cu micro-laminates fabricated by an Electrically-Assisted Roll Bonding (EARB) process were studied to understand the underlying physical/chemical phenomena that lead to bond strength enhancement when applying electrical current during deformation. Peel tests were conducted for the Al/Cu roll-bonded laminates produced with no current and under 50A and 150A applied current. After peel tests using a micro-tensile machine, the fractured surfaces of both the Al and Cu–sides were examined using scanning electron microscopy (SEM) for fractography and SEM-based energy dispersive (EDS) analysis. Results revealed the strong dependence of the fracture path and its morphology on the strength of the bond, which is influenced by various phenomena occurring at the interface during EARB, such as microextrusion through surface micro-cracks, possible formation of intermetallic components and thermal softening during simultaneous application of strain and high current density.

Incremental forming is a flexible dieless forming process. In incremental forming, the metal sheet is clamped around its periphery. One or multiple generic stylus-type tools move along a predefined toolpath, incrementally deforming the sheet metal into a final, freeform shape. Compared with the traditional sheet metal forming process, the incremental forming process is more flexible, energy efficient and cost effective due to lower capital investment related to tooling. However, maintaining tight geometric tolerances in incremental formed parts can be a challenge. Specifically, undesired global bending is usually induced near the region between the tools and fixture resulting in a compromise in geometric accuracy. To address this issue, Accumulated Double-Sided Incremental Forming (ADSIF) is proposed, which utilizes two tools on both sides of the metal to better achieve localized deformation while simultaneously constraining global bending outside the forming area. Moreover, in ADSIF, the two tools are moving from inward to outward, and thus the tools are always forming virgin material and so as to limit forces on the already-formed part. Thus, ADSIF has a higher potential to achieve the desired geometry. Nevertheless, tool deflection due to machine compliance is still an issue that can have a considerable effect on geometric accuracy. In this work, the effect of tool deflection related to part geometry is studied for the ADSIF process. The nature of using two tools, rather than one, in ADSIF inherently implies that relative tool position is a critical process parameter. It is the region near these two tools where local squeezing and bending of the sheet occurs, the primary modes of deformation found in ADSIF. The change of relative tool positions (i.e., tool gap and relative position angle) are studied in detail by first developing an analytical model. It is concluded that the tool gap will be enlarged under the influence of tool compliance while the relative position angle is less affected. Additionally, a finite element simulation capable of modeling tool deflection is established. The comparison between the simulation results using rigid tools and deformable ones clearly demonstrated the significant influence of tool compliance on part geometry. Lastly, an axisymmetric part with varying wall angles was formed, and it was confirmed that ADSIF demonstrates improved geometry accuracy compared with conventional Double-Sided Incremental Forming.

In spite of its inherent advantages as a manufacturing tool, water-jet has not been extensively applied to the field of micro-manufacturing due to its low tolerance and poor control of the position of jet impingement. This paper explores the possibility of using the phenomenon of liquid dielectrophoresis to deflect and control the trajectory of a water jet in air. An approach is suggested using a localized non-uniform static electric field over a micro water jet with diameters in the range of 25–100 micrometers. The water jet has been modelled as a thin dielectric column and the numerical analysis of the electric field distribution has been carried out using COMSOL to analyze the generated forces and predict the scale of deflection of the jet. This unique approach of harnessing the polar nature of water using the phenomenon of dielectrophoresis might be useful in achieving fine control of the water jet’s trajectory especially in micro water jet material processing.

The magnetorheological (MR) control valve is a major component in MR fluid systems to achieve controllable pressure drop or damping characteristics in practice. However, the optimal design of MR control valve is fairly complex due to large extent of design parameters from both magnetic flux generation and mechanical flow characteristics, as well as different requirements or constraints in practical applications. In this paper, the analytical electro-mechanic-magnetic coupling model of the MR control valve with annular-radial flow path is firstly investigated to quantitatively predict the relationship between design parameters and achievable performances such as pressure drop and dynamic range etc.. And then comparison results based on analytical analysis and finite element method are presented to validate the effect model utilized in MR valves. Consequently, a performance-oriented optimization of MR control valves with annular-radial flow path in a non-dimensional design concept is developed through minimizing reciprocal of dynamic range and identifying several optimal internal design parameters subject to predefined constraints under fairly less quantity of combined external design parameters.Finally, the inherent sensitivity of achievable performances with respect to external design parameters is analyzed to provide practical instructions for appropriate specification of the MR control valve.Copyright © 2014 by ASME

Incremental sheet forming has attracted considerable attention in the recent past due to advantages that include high process flexibility and higher formability as compared to conventional forming processes. However, attaining required geometric accuracy of the formed part is one of the major issues plaguing this process. The Double-Sided Incremental Forming process has emerged as a potential process variant which can preserve the process flexibility while maintaining required geometric accuracy. This paper investigates a mixed toolpath for Double-Sided Incremental Forming which is able to simultaneously achieve good geometric accuracy and higher throughput than is currently possible. The geometries of parts formed using the mixed toolpath strategy are compared to the desired geometry. Furthermore, an examination of the forming forces is used to uncover the reasons for experimentally observed trends. Future work in this area is also discussed.Copyright © 2014 by ASME

Uniaxial tension tests were conducted on thin commercially pure titanium sheets subjected to electrically-assisted deformation using a new experimental setup to decouple thermal-mechanical and possible electroplastic behavior. The observed absence of stress reductions for specimens air-cooled to near room temperature motivated the need to reevaluate the role of temperature on modeling the plastic behavior of metals subjected to electrically-assisted deformation, an item that is often overlooked when invoking electroplasticity theory. As a result, two empirical constitutive models, a modified-Hollomon and the Johnson-Cook models of plastic flow stress, were used to predict the magnitude of stress reductions caused by the application of constant DC current and the associated Joule heating temperature increase during electrically-assisted tension experiments. Results show that the thermal-mechanical coupled models can effectively predict the mechanical behavior of commercially pure titanium in electrically-assisted tension and compression experiments.Copyright © 2013 by ASME

Trauma resulting from surgical blade friction can cause several complications and delay the recovery time of a patient. In order to attain optimal tribological properties, an 8 ps pulsed 532 nm Nd:YVO4 laser was used to ablate the cutting edge surface of surgical blades to create micro dimples of ∼110 μm in diameter and ∼30 μm in depth. Additionally, certain arrays of dimples endured an extra laser ablation operation to add a fillet to the dimple rims with the hope of reducing stress concentrations during tissue cutting and reducing friction even further. These surface textures were experimentally investigated through cutting experiments on phantom tissue material. Ultimately, the blades with the cutting surface texture that employed blended dimple rims showed a substantial reduction in friction forces when cutting phantom tissue samples.Copyright © 2013 by ASME

Recently, the technique of Spot-based Laser Induced Plasma Micro-Machining (Spot-LIPMM) has been developed to address the limitations of conventional ultrashort pulse laser micro-machining. Its main advantages are adaptability to a wide range of materials and superior wall geometries. We propose a variation of the Spot-LIPMM process by creating line plasma instead of spot plasma, with the use of suitable optics. This paper describes the experimental setup used to create line plasma and the process used for micro-machining with L-LIPMM. Optics simulations are developed as a means of guiding the choice of optics to be used for line plasma generation and estimating the energy and shape of the plasma created. It is shown that this Line-based LIPMM (L-LIPMM) process is capable of micromachining channels at a much higher speed than conventional Spot-based laser ablation or spot-based LIPMM. Additionally, the effects of process parameters on machined geometry using L-LIPMM are discussed.Copyright © 2013 by ASME

Problems of excessive coil deformation after winding will present difficulties in later material handling. Sheet material with a lower stiffness is more likely to deform than solid sheet coil. In this paper, numerical and analytical methods are used to study the factors causing this problem. The results can be used to estimate the requirement of the supporting core material to prevent this excessive coil deformation.

A straight flange problem is investigated with the expectation that this will lead to a better understanding of the deformation mechanism and to more complicated flanging problems. The “in-die” shape of the part is subdivided into a number of segments and individual springback of each segment is investigated, by releasing the elastic energy element by element, using the Finite Element Method (FEM). Typical distribution of the springback angle along the blank is obtained and found to be quite different from the widely used constant springback assumption for the curved part of the flange. A new model incorporating a non-uniform moment distribution at the curved part is proposed which reflects the above observation. Explicit analytical formulae are derived and the analytical predictions match with the experimental results very well.