Research Papers

J. Manuf. Sci. Eng. 2013;135(2):021001-021001-12. doi:10.1115/1.4023708.

In this study, a practical identification method for process damping is presented for milling, and the information obtained from identification is used for modeling purposes. In the proposed approach, the process-damping coefficients in x and y directions are identified directly from the experimental stability limits. Then, they are used in identification of the indentation constant through energy balance formulation. The identified indentation constant is further used in modeling of process damping and estimation of stability limit for different cutting conditions and tool geometries. Milling tools with two different types of flank geometries, namely, planar and cylindrical, are considered in this study. The predictions are verified by time-domain simulations and experimental results. It is shown that the presented method can be used for identification and modeling of process damping in milling to determine chatter-free cutting depths at relatively low cutting speeds.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2013;135(2):021002-021002-11. doi:10.1115/1.4023374.

A system has been developed to measure the three-dimensional weld pool surface geometry in the gas metal arc welding (GMAW) process. It utilizes the specular nature of the weld pool surface by projecting a five-line laser pattern onto the surface and imaging its reflection. Specifically, the laser reflection is intercepted by an imaging plane and captured using a high speed camera. The reflected pattern is used to reconstruct the weld pool surface based on the law of reflection. Two reconstruction algorithms, referred to as center-points reconstruction and piece-wise weld pool surface reconstruction algorithm, are applied to sequentially reconstruct the weld pool height and three-dimensional surface geometry. Reconstructions has been conducted using simulated weld pool surface to provide a method to compare the reconstruction result with a known surface and evaluate the reconstruction accuracy. It is found that the proposed method is capable of reconstructing weld pool surface with acceptable accuracy. The height error of reconstructed center-points is less than 0.1 mm and the error of estimated weld pool boundary is less than 10%. Reconstruction results from images captured in welding experiments are also demonstrated.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2013;135(2):021003-021003-6. doi:10.1115/1.4023376.

A new technique was proposed and experimentally verified for the cavity pressure acquisition in the injection-compression molding (ICM). The surface strain of the fixed mold half and the cavity pressure were monitored simultaneously during ICM. In the compression stage, a directly proportional relationship between the cavity pressure and mold surface strain was found and determined via the regression analysis. By taking the advantage of this relationship, the cavity pressure profile with high accuracy was indirectly obtained from the nondestructive measurement of the mold surface strain. Moreover, the mold surface strain profile could indicate the part weight or thickness and the critical time when the part surface lost contact with the cavity surface in a large area. The monitoring of the mold surface strain could serve as an interesting alternative to the direct monitoring of the cavity pressure with respect to process and part quality control for ICM.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2013;135(2):021004-021004-13. doi:10.1115/1.4023364.

Manufacturing of lithium-ion battery packs for electric or hybrid electric vehicles requires a significant amount of joining, such as welding, to meet the desired power and capacity needs. However, conventional fusion welding processes, such as resistance spot welding and laser welding, face difficulties in joining multiple sheets of highly conductive, dissimilar materials to create large weld areas. Ultrasonic metal welding overcomes these difficulties by using its inherent advantages derived from its solid-state process characteristics. Although ultrasonic metal welding is well-qualified for battery manufacturing, there is a lack of scientific quality guidelines for implementing ultrasonic welding in volume production. In order to establish such quality guidelines, this paper first identifies a number of critical weld attributes that determine the quality of welds by experimentally characterizing the weld formation over time using copper-to-copper welding as an example. Samples of different weld quality were cross-sectioned and characterized with optical microscopy, scanning electronic microscopy (SEM), and hardness measurements in order to identify the relationship between physical weld attributes and weld performance. A novel microstructural classification method for the weld region of an ultrasonic metal weld is introduced to complete the weld quality characterization. The methodology provided in this paper links process parameters to weld performance through physical weld attributes.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2013;135(2):021005-021005-12. doi:10.1115/1.4023377.

Increasing demands and concerns for reliable supply of liquid transportation fuels make it important to find alternatives to petroleum-based fuels. One such alternative is ethanol made from cellulosic biomass. Considerable investigations have been conducted to evaluate the viability of cellulosic ethanol production in several aspects (including cost competitiveness). Cost estimates of cellulosic ethanol production have been reported by many researchers in order to evaluate the economic viability of cellulosic ethanol production. However, the reported cost estimates in the literature have a large variation. The current literature contains limited reviews on the cost estimates of cellulosic ethanol production and mostly focused on some individual processes. This paper presents a literature review on the cost estimates of entire cellulosic ethanol production. It reviews the estimated costs for both the entire cycle (from planting to conversion) and individual processes for cellulosic ethanol production. It also covers factors that lead to variations among reported cost estimates.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2013;135(2):021006-021006-5. doi:10.1115/1.4023378.

Increasing demands and concerns for reliable supply of liquid transportation fuels make it important to find alternative sources to petroleum-based fuels. Cellulosic biofuels provide one such alternative in the short to medium term. Size reduction is the first step for converting biomass into biofuels. In the literature, there are inconsistent reports about the effects of particle size and biomass crystallinity on sugar yield (proportional to biofuel yield). An important reason for this inconsistence is that particle formation in current size reduction methods is not well controlled, causing the effects of these two variables confounded. One paper investigating the confounding effects of particle size and biomass crystallinity using a metal-cutting (milling) process was previously published in this journal. This paper presents a follow-up study. In this study, a lathe was used to produce poplar wood particles with the same crystallinity but different sizes, making it possible to study the effects of particle size on biofuel yield independently without being confounded by the effects of biomass crystallinity. Results showed that, for the three levels of particle size used in this study, sugar yield increased as particle size became smaller. This study also revealed future research opportunities to understand the effects of size reduction and biomass crystallinity in cellulosic biofuel manufacturing.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2013;135(2):021007-021007-9. doi:10.1115/1.4023711.

Melting, vaporization, and resolidification in a gold thin film subject to multiple femtosecond laser pulses are numerically studied in the framework of the two-temperature model. The solid-liquid phase change is modeled using a kinetics controlled model that allows the interfacial temperature to deviate from the melting point. The kinetics controlled model also allows superheating in the solid phase during melting and undercooling in the liquid phase during resolidification. Superheating of the liquid phase caused by nonequilibrium evaporation of the liquid phase is modeled by adopting the wave hypothesis, instead of the Clausius–Clapeyron equation. The melting depth, ablation depth, and maximum temperature in both the liquid and solid are investigated and the result is compared with that from the Clausius–Clapeyron equation based vaporization model. The vaporization wave model predicts a much higher vaporization speed, which leads to a deeper ablation depth. The relationship between laser processing parameters, including pulse separation time and pulse number, and the phase change effect are also studied. It is found that a longer separation time and larger pulse number will cause lower maximum temperature within the gold film and lower depths of melting and ablation.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2013;135(2):021008-021008-11. doi:10.1115/1.4023453.

Dynamic response of a machine tool structure varies along the tool path depending on the changes in its structural configurations. The productivity of the machine tool varies as a function of its frequency response function (FRF) which determines its chatter stability and productivity. This paper presents a computationally efficient reduced order model to obtain the FRF at the tool center point of a machine tool at any desired position within its work volume. The machine tool is represented by its position invariant substructures. These substructures are assembled at the contacting interfaces by using novel adaptations of constraint formulations. As the tool moves to a new position, these constraint equations are updated to predict the FRFs efficiently without having to use computationally costly full order finite element or modal models. To facilitate dynamic substructuring, an improved variant of standard component mode synthesis method is developed which automates reduced order determination by retaining only the important modes of the subsystems. Position-dependent dynamic behavior and chatter stability charts are successfully simulated for a virtual three axis milling machine, using the substructurally synthesized reduced order model. Stability lobes obtained using the reduced order model agree well with the corresponding full-order system.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2013;135(2):021009-021009-12. doi:10.1115/1.4023714.

The effects of the uncertainties of various parameters, including the laser fluence, diameter of metal powder particles, laser pulse width, and the initial temperature of metal particles on solid-liquid-vapor phase change processes of metal particles under nanosecond laser heating are investigated in this paper. A systematic approach of simulating the phase change with uncertain parameters is presented and a sample-based stochastic model is established in order to investigate the influence of different uncertain parameters on the maximum surface temperature of metal particles, the maximum solid-liquid interface location, maximum liquid-vapor interface location, maximum saturation temperature, and maximum recoil pressure and the time needed to reach the maximum solid-liquid interface location. The results show that the mean value and standard deviation of the laser fluence have dominant effects on all output parameters.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2013;135(2):021010-021010-11. doi:10.1115/1.4023269.

Understanding and modeling of the human welder's response to three-dimensional (3D) weld pool surface may help develop next generation intelligent welding machines and train welders faster. In this paper, human welder's adjustment on the welding current as a response to the 3D weld pool surface characterized by its width, length, and convexity is studied. An innovative vision system is used to real-time measure the specular 3D weld pool surface under strong arc in gas tungsten arc welding (GTAW). Experiments are designed to produce random changes in the welding speed resulting in fluctuations in the weld pool surface. Adaptive neuro-fuzzy inference system (ANFIS) is proposed to correlate the human welder's response to the 3D weld pool surface using three inputs including the weld pool width, length and convexity. The human welder's behavior is not only related to the 3D weld pool geometry but also relies on the welder's previous adjustment. In this sense, a four input ANFIS model adding the previous human welder's response as a model input is developed and compared with the fitted linear model. It is found that the proposed ANFIS model can derive a more accurate correlation between the human welder's responses and the weld pool geometry and help understand the nonlinear response of the human welder to 3D weld pool surfaces.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2013;135(2):021011-021011-11. doi:10.1115/1.4023366.

For the current practice of improving fuel efficiency and reducing emissions in the automotive sector, it is becoming more common to use low density/high strength materials instead of costly engine/drivetrain technologies. With these materials there are normally many manufacturing difficulties that arise during their incorporation to the vehicle. As a result, new processes which improve the manufacturability of these materials are necessary. This work examines the manufacturing technique of electrically-assisted forming (EAF) where an electrical current is applied to the workpiece during deformation to modify the material's formability. In this work, the thermal response of sheet metal for stationary (i.e., no deformation) and deformation tests using this process are explored and modeled. The results of the model show good agreement for the stationary tests while for the deformation tests, the model predicts that all of the applied electrical current does not generate Joule heating. Thus, this work suggests from the observed response that a portion of the applied current may be directly aiding in deformation (i.e., the electroplastic effect). Additionally, the stress/strain response of Mg AZ31 under tensile forming using EAF is presented and compared to prior experimental work for this material.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2013;135(2):021012-021012-10. doi:10.1115/1.4023367.

One of the major challenges in spot welding of ultra-thin gage steel (e.g., <0.6 mm) is the short cap life. Because of the elevated temperature developed at the electrode/sheet interface, the electrodes often require dressing or replacement within a fraction of the time when welding more traditional automotive gage steel (>0.75 mm). In this study, the method of inserting flexible strips between the electrode and workpiece in resistance spot welding of 0.4 mm thick galvanized SAE1004 steel sheet has been adopted in order to reduce electrode tip temperature and improve weld quality. The effect of the inserted strips on the Joule heat generation and temperature distribution has been analyzed analytically. Then, because of the difficulties in measuring the experimental electrode tip temperature, a finite element model has been employed to estimate temperature distributions within the weld zone. The effects of the process variables (i.e., strip material and thickness) on the cap temperature and weld quality were modeled. Experiments were also conducted to validate the modeling results. Test data and modeling results showed that the presence of the strip significantly facilitated weld initiation and growth and decreased the rate of electrode degradation. Of the materials investigated, the desirable strip for resistance spot welding 0.4 mm thick galvanized SAE1004 steel was determined to be 0.12 mm thick Cu55Ni45 alloy.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2013;135(2):021013-021013-15. doi:10.1115/1.4023454.

Optimization in turning means determination of the optimal set of the machining parameters to satisfy the objectives within the operational constraints. These objectives may be the minimum tool wear, the maximum metal removal rate (MRR), or any weighted combination of both. The main machining parameters which are considered as variables of the optimization are the cutting speed, feed rate, depth of cut, and nose radius. The optimum set of these four input parameters is determined for a particular job-tool combination of 7075Al alloy-15 wt. % SiC (20–40 μm) composite and tungsten carbide tool during a single-pass turning which minimizes the tool wear and maximizes the metal removal rate. The regression models, developed for the minimum tool wear and the maximum MRR were used for finding the multiresponse optimization solutions. To obtain a trade-off between the tool wear and MRR the, a method for simultaneous optimization of the multiple responses based on an overall desirability function was used. The research deals with the optimization of multiple surface roughness parameters along with MRR in search of an optimal parametric combination (favorable process environment) capable of producing desired surface quality of the turned product in a relatively lesser time (enhancement in productivity). The multi-objective optimization resulted in a cutting speed of 210 m/min, a feed of 0.16 mm/rev, a depth of cut of 0.42 mm, and a nose radius of 0.40 mm. These machining conditions are expected to respond with the minimum tool wear and maximum the MRR, which correspond to a satisfactory overall desirability.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2013;135(2):021014-021014-7. doi:10.1115/1.4023455.

Current sheet metal hydroforming processes require special equipment such as a hydroforming press with an external high pressure generator. This holds the barriers for entering the market high, especially for small and medium companies that cannot invest such an amount of money. In this article, a method and tool design is presented that allows setting up a sheet metal hydroforming process on single action presses without using special hydroforming equipment. The inner pressure for forming the part is generated by tool integrated pistons and results from the difference between ram and cushion force in relation to the part's projected surface. To explore the limits of the process, a tryout tool was manufactured for producing test samples of medical parts in DX54D and AlMg3 0.6 mm. After the experiments, the parts were measured and analyzed to investigate the accuracy of the process, in comparison with the simulation done beforehand. This work will enable small and medium enterprises (SMEs) to produce small series hydroformed parts in a cost efficient way on their conventional presses.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2013;135(2):021015-021015-10. doi:10.1115/1.4023706.

Steadily improving performance of inertial sensors necessitates significant enhancement of the methods and equipment used for their evaluation. As the nonlinearity of sensors decreases and gets close to that of the exciters, new challenges arise. One of them, addressed in this research, is a superposition of errors caused by the nonlinearity of tested devices with nonlinear distortions of excitation employed for experimental evaluation. This can lead to a cancellation, at least partial, of the effects of both imperfections and underestimation of the actual distortions of the evaluated sensors. We implement and analyze several system architectures and evaluate components of applicable motion generation systems from the viewpoint of satisfying the relevant, often conflicting requirements posed by the evaluation of high performance inertial sensors. Robust mechanical integration of the guidance, actuation, and measurement functions emerges as a key factor for achieving the needed quality of generated test patterns. We find precision air bearing stages, such as ABL1500 series (Aerotech) most suitable for implementing the needed experimental setup. We propose an architecture with two reciprocating stages, implement and evaluate its core components, and illustrate its performance with experimental results.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2013;135(2):025001-025001-12. doi:10.1115/1.4023707.

A new servo drive for electro discharge machining industrial applications is presented in this paper. The development processes of the servo feed drive have passed through three main stages. The first stage focused on design and development of a linear piezoelectric ultrasonic motor. The second one concentrated on development of an electronic driver and its embedded software. The integration, testing, and validation in electro discharge machining system, was the last stage of the development lifecycle. The linear piezoelectric ultrasonic motor consists of three main parts, the stator, rotor, and sliding element. The motor design process, basic configuration, principles of motion, finite element analysis, and experimental examination of the main characteristics are discussed in this paper. The electronic driver of the ultrasonic motor consists of two main stages, the booster and piezoelectric amplifier. The piezo amplifier consists of four output transistors, a push-pull and bridge, connected in order to achieve the necessary electrical parameters to drive and control the motor servo feed drive traveling speed. The essential experimental arrangement to implement and examine the developed ultrasonic servo feed drive in an electro discharge machining system was carried out. The initial results showed that the servo drive is able to provide: a reversible directional of motion, no-load traveling speed equal to 28 mm per s, maximum load of 0.78 N, a resolution <50 μm, and a dynamic time response <10 ms. The electron microscopic micro examination into the machined samples showed that: ultrasonic servo drive showed a clear improvement in the surface profile finish, a notable reduction in the stability, processing time, material removal rate, arcing, and short-circuiting teething phenomena. This was verified by assessing the electrode movements, the variations of the inter electrode gap voltage, current, and feedback control signals.

Commentary by Dr. Valentin Fuster

Technical Briefs

J. Manuf. Sci. Eng. 2013;135(2):024501-024501-6. doi:10.1115/1.4023375.

This article investigates the feasibility of using supercritical carbon dioxide based metalworking fluids (scCO2 metalworking fluids (MWFs)) to improve micromachinability of metals. Specifically, sets of channels were fabricated using micromilling on 304 stainless steel and 101 copper under varying machining conditions with and without scCO2 MWF. Burr formation, average specific cutting energy, surface roughness, and tool wear were analyzed and compared. Compared to dry machining, use of scCO2 MWF reduced burr formation in both materials, reduced surface roughness by up to 69% in 304 stainless steel and up to 33% in 101 copper, tool wear by up to 20% in 101 copper, and specific cutting energy by up to 87% in 304 stainless steel and up to 40% in 101 copper. The results demonstrate an improvement in micromachinability of the materials under consideration and motivate future investigations of scCO2 MWF-assisted micromachining to reveal underlying mechanisms of functionality, as well as to directly compare the performance of scCO2 MWF with alternative MWFs appropriate for micromachining.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2013;135(2):024502-024502-4. doi:10.1115/1.4023713.

This investigation concerns the effect of the process parameters on surface roughening during plastic deformation. The modeling is based on the assumption that surface roughness is proportional to the maximum shear stress on the surface layer. Therefore, an equation is developed in order to describe the relationship between the surface roughness and such process parameters as the initial roughness, grain size, effective strain, and maximum shear strain ratio on the surface layer. In a tensile test, the surface roughness increases nonlinearly with a normal anisotropic value and linearly with the effective strain or grain size. The surface roughness also increases nonlinearly with the effective stress and the strain hardening exponent under some fixed conditions. The normal anisotropic value must be considered in order to evaluate surface roughening during deformation. The experimental results support the proposed model. The proposed model improves our understanding of the mechanism of surface roughening in sheet metal forming.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2013;135(2):024503-024503-5. doi:10.1115/1.4023715.

This paper focuses on the grid cathode design in electrochemical machining (ECM) in order to develop a new cathode design method for realizing a breakthrough: one cathode can produce different workpieces with different profiles. Three types of square cells, 2.5 mm × 2.5 mm, 3 mm × 3 mm, and 4 mm × 4 mm in size and three types of circular cells, with diameters of 1.5, 2.0, and 2.5 mm are utilized to construct the plane, slant, and blade grid cathode. The material of the cathode and anode is CrNi18Ti9 and the ingredients of the electrolyte are 15% NaCl and 15% NaNO3. A large number of experiments are conducted by using different grid cathodes to analyze the effects of the shape and size of the grid cell on the machining process. In addition, we compare the workpiece quality and machining error between using the grid cathode and the unitary cathode and discuss the reasons for the errors in order to obtain a better surface quality of the workpiece. Our research supports the conclusions that the grid cathode can be used to manufacture workpieces with complex shapes, the workpiece quality is better if the square cell is smaller and, for the same equivalent area, the circular grid cathode produces a better quality workpiece than the square grid cathode.

Commentary by Dr. Valentin Fuster

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