Review Article

J. Manuf. Sci. Eng. 2016;139(1):010801-010801-10. doi:10.1115/1.4033758.

Additive manufacturing (AM) for mechanical devices and electronic components has been actively researched recently. While manufacturing of those mechanical and electronic devices has their own merits, combining them into a single form is expected to grow by creating new applications in the future. The so-called all-printed electromechanical devices have potential applications in mechanical, electrical, and biomedical engineering. In this paper, the recent advancement in all-printed electromechanical devices is reviewed. A brief introduction to various AM techniques is presented first. Then, various examples of sensors, electronics, and electromechanical devices created by AM are reviewed.

Commentary by Dr. Valentin Fuster

Research Papers

J. Manuf. Sci. Eng. 2016;139(1):011001-011001-10. doi:10.1115/1.4034136.

Fixturing of components during laser cladding can incur significant conductive thermal losses. However, due to the surface roughness at contact, interfacial conduction is impeded. The effective contact conductivity, known as gap conductance, is much lower than the contacting material conductivities. This work investigates modeling conduction losses to fixturing bodies during laser cladding. Two laser cladding experiments are performed using contrasting fixturing schemes: one cantilevered substrate with a minimal substrate-fixture contact area and one with a substrate bolted to a work bench, with a significant substrate-fixture contact area. Using calibrated gap conductance values, error for the cantilevered fixture model decreases from 20.5% to 6.49% in the contact region, while the bench fixtured model error decreases from a range of 60–102% to 11–45%. The improvement in accuracy shows the necessity of accounting for conduction losses in the thermal modeling of laser cladding, particularly for fixturing setups with large areas of contact.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2016;139(1):011002-011002-10. doi:10.1115/1.4034283.

Stress corrosion cracking is a phenomenon that can lead to sudden failure of metallic components. Here, we use laser shock peening (LSP) as a surface treatment for mitigation of stress corrosion cracking (SCC), and explore how the material differences of 304 stainless steel, 4140 high strength steel, and 260 brass affect their mitigation. Cathodic charging of the samples in 1 M sulfuric acid was performed to accelerate hydrogen uptake. Nontreated stainless steel samples underwent hardness increases of 28%, but LSP treated samples only increased in the range of 0–8%, indicative that LSP keeps hydrogen from permeating into the metal. Similarly for the high strength steel, LSP treating limited the hardness changes from hydrogen to less than 5%. Mechanical U-bends subjected to Mattsson's solution, NaCl, and MgCl2 environments are analyzed, to determine changes in fracture morphology. LSP treating increased the time to failure by 65% for the stainless steel, and by 40% for the high strength steel. LSP treating of the brass showed no improvement in U-bend tests. Surface chemical effects are addressed via Kelvin Probe Force Microscopy, and a finite element model comparing induced stresses is developed. Detection of any deformation induced martensite phases, which may be detrimental, is performed using X-ray diffraction. We find LSP to be beneficial for stainless and high strength steels but does not improve brass's SCC resistance. With our analysis methods, we provide a description accounting for differences between the materials, and subsequently highlight important processing considerations for implementation of the process.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2016;139(1):011003-011003-11. doi:10.1115/1.4034138.

Numerical and experimental analyses of milling bifurcations, or instabilities, are detailed. The time-delay equations of motions that describe milling behavior are solved numerically and once-per-tooth period sampling is used to generate Poincaré maps. These maps are subsequently used to study the stability behavior, including period-n bifurcations. Once-per-tooth period sampling is also used to generate bifurcation diagrams and stability maps. The numerical studies are combined with experiments, where milling vibration amplitudes are measured for both stable and unstable conditions. The vibration signals are sampled once-per-tooth period to construct experimental Poincaré maps and bifurcation diagrams. The results are compared to numerical stability predictions. The sensitivity of milling bifurcations to changes in natural frequency and damping is also predicted and observed.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2016;139(1):011004-011004-12. doi:10.1115/1.4033904.

Both electrically assisted tension (EAT) and thermally assisted tension (TAT) tests were performed on SS304 and pure copper to decouple the influence of elevated temperature from electric current on flow stress and ductility. It is found that the reduction on flow stress and ductility of SS304 are more dependent on the elevated temperature than electric current, but electric current has a stronger effect by 10% on reducing flow stress and ductility of pure copper than the elevated temperature does. As the flow stress and ductility of two metals are related to the dislocation evolution, a constitutive model considering both storage and annihilation process of dislocation was established to describe the effect of electric current and temperature on dislocation movement. It is found that electric current accelerated the annihilation process of dislocation in pure copper up to 20% in EAT compared with that in TAT, but such phenomenon was rarely observed in SS304. Furthermore, attempts have also been made to distinguish the influence of elevated temperature with that of electric current on microstructure evolution and it is also found that the formation of [111] crystals in pure copper is nearly 10% less in EAT than that in TAT.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2016;139(1):011005-011005-10. doi:10.1115/1.4032768.

Drop-on-demand (DOD) microdroplet jetting technology has diverse applications ranging from additive manufacturing (AM) and the integrated circuit (IC) industry to cell printing. An engineering model of droplet formation can provide insights for optimizing the process and ensuring its controllability and reproducibility. This paper reports a development of an engineering model on the fluid outflow and microdroplet formation based on alternating viscous-inertial force jetting (AVIFJ). The model provides a fundamental understanding on the mechanism of droplet formation driven by the alternating viscous force and inetial force. Furthermore, the model studies the fluid acceleration, velocity, and displacement under the conditions of a uniform cylindrical nozzle and a nonuniform cylindrical nozzle. In conjunction with an energy-based criterion for droplet formation, the model is applied to predict the formability of single microdroplets and the volume and velocity of formed microdroplets. A series of experiments was conducted to validate the developed model. The results show that the model predictions agree well with the experimental results. Specifically, comparing the model prediction and experimental results, the maximum difference of drop diameter is 4 μm, and the maximum difference of drop velocity is 0.3 m/s. These results suggest that the developed theoretical model will provide guidance to the subsequent cell printing applications.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2016;139(1):011006-011006-13. doi:10.1115/1.4034140.

This paper presents a novel trajectory generation technique, which has the capability to avoid excitation of inertial vibrations in precision manufacturing equipment. A major source of vibrations in fast moving precision manufacturing equipment is the inertial vibrations that are excited due to frequency content of reference motion commands (trajectory). In general practice, those inertial vibrations are avoided within the controller architecture through notch filtering. Or, input-shaping methods are utilized to attenuate critical frequency components of the reference trajectory so that lightly damped vibration modes of the structure are not excited. Instead of employing those postfiltering techniques that add unwanted delay to the coordinated motion, this paper introduces a direct trajectory generation technique with a shaped frequency content to suppress inertial vibrations. The time-stamped acceleration profile of the feed profile is defined as a ninth-order polynomial. Polynomial coefficients are solved through an optimization procedure where the objective function penalizes total frequency energy in a desired frequency band. As a result, generated reference acceleration commands do not contain any excitation near the vibration modes of the system and hence excitation of inertial vibrations is avoided. The proposed frequency optimal feed profiling (FOFP) system can be utilized to generate high-speed accurate point-to-point (P2P) trajectories as well as to interpolate continuous multi-axis coordinated motion. Effectiveness of the proposed FOFP scheme is evaluated through rigorous comparison against the well-known minimum jerk feed profiles (MJFP) technique through simulations and experiments. Experimental validation is performed on an in-house controlled machine tool with flexible structure.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2016;139(1):011007-011007-12. doi:10.1115/1.4033926.

This study examines the possibility of applying lasers for the formation of laser-affected bands in hardenable steel sheets, with a specific focus on how the formation of these hardened bands can improve the accuracy of the single point incremental forming process (SPIF). For this purpose, the process parameters for the hardening process have been chosen using finite-element (FE) modeling. The results of the modeling have been validated by temperature field measurements obtained from IR camera observations. The microstructural analysis of the laser-affected zones has been performed using optical microscopy (OM) and scanning electron microscopy (SEM). These investigations confirm a phase transformation to a martensitic structure during laser scanning, and microhardness (HV0·1) results show a hardness increase by a factor of about three in the laser-affected region in comparison to that of the base metal (BM). Finally, using a laser assisted single point incremental forming (LASPIF) setup, hardened bands have been generated for preprocessing and intermediate processing during the different phases of a SPIF procedure. Geometric accuracy studies show that appropriate use of hard martensitic bands can increase the process accuracy through significantly reduction of an unwanted sheet deformation, and has the potential to eliminate the need for a backing plate.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2016;139(1):011008-011008-13. doi:10.1115/1.4033692.

Ultrasonic metal welding has been used to join multiple layers of battery tabs with the bus bar in lithium-ion battery assembly operations. This paper describes joint performance models for ultrasonic metal welds of multiple layers of dissimilar battery tab materials, i.e., aluminum and copper. Finite element (FE) models are developed to predict the mechanical performance of the ultrasonically welded joints. The models predict peak shear load, energy absorption capability, and failure modes, which are necessary for modeling product performance and defining process requirements for the welds. The models can be adjusted to represent different quality of welds created in conditions of underweld (UW), normal-weld (NW), or overweld (OW) using physical attributes observed through microscopic analysis. The models are validated through lap shear tests, which demonstrate excellent agreement for the maximum force in the NW condition and good agreement for the UW and OW conditions. The models provide in-depth understanding of the relationship among welding process parameters, physical weld attributes, and the weld performance. The models also provide significant insight for further development of ultrasonic welding process for battery tabs and help optimize welding process for more than four-layered joints.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2016;139(1):011009-011009-11. doi:10.1115/1.4034137.

Cobalt chromium is widely used to make medical implants and wind turbine, engine and aircraft components because of its high wear and corrosion resistance. The ability to process geometrically complex components is an area of intense interest to enable shifting from traditional manufacturing techniques to additive manufacturing (AM). The major reason for using AM is to ease design modification and optimization since AM machines can directly apply the changes from an updated STL file to print a geometrically complex object. Quality assurance for AM fabricated parts is recognized as a critical limitation of AM processes. In selective laser melting (SLM), layer by layer melting and remelting can lead to porosity defects caused by lack of fusion, balling, and keyhole collapse. Machine process parameter optimization becomes a very important task and is usually accomplished by producing a large amount of experimental coupons with different combinations of process parameters such as laser power, speed, hatch spacing, and powder layer thickness. In order to save the cost and time of these experimental trial and error methods, many researchers have attempted to simulate defect formation in SLM. Many physics-based assumptions must be made to model these processes, and thus, all the models are limited in some aspects. In the present work, we investigated single bead melt pool shapes for SLM of CoCr to tune the physics assumptions and then, applied to the model to predict bulk lack of fusion porosity within the finished parts. The simulation results were compared and validated against experimental results and show a high degree of correlation.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2016;139(1):011010-011010-8. doi:10.1115/1.4034007.

Ultrasonic welding was investigated as a method of joining 0.076 in. (1.93 mm) thick aluminum 6061 flat sheet material. Joints were produced with ultrasonic additive manufacturing (UAM) equipment in a modified application of the ultrasonic welding process. Through joint design development, successful welds were achieved with a scarf joint configuration. Using a design of experiments (DOE) approach, weld parameters including weld amplitude, scarf angle, and weld speed were optimized for mechanical strength. Lower angles and higher amplitudes were found to provide the highest strengths within the levels tested. Finite-element studies indicate that 5 deg and 10 deg angles produce an increased relative motion of the workpieces as compared to 15 deg, 20 deg, and 25 deg angles, likely leading to increased strength. Successful joints showed no indication of voids under optical microscopy. As-welded joints produce tensile strengths of 221 MPa, while heat treated joints produce tensile strengths of 310 MPa, comparable to heat treated bulk material. High-temperature tensile testing was conducted at 210 °C, with samples exhibiting strengths of 184.1 MPa, similar to bulk material. Room temperature fatigue testing resulted in cyclic failures at approximately 190,000 cycles on average, approaching that of bulk material.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2016;139(1):011011-011011-12. doi:10.1115/1.4033905.

Polycrystalline diamond compact (PDC) cutters, as a major cutting tool, have been widely applied in oil and gas drilling processes. The understanding of the complex interactions at the rock and cutter interfaces is essential for the advancement of future drilling technologies; yet, these interactions are still not fully understood. Linear cutting of rock, among all the testing methods, avoids the geometric and process complexities and offers the most straightforward way to reveal the intrinsic mechanisms of rock cutting. Therefore, this paper presents an experimental study of the cutter’s cutting performance and the rock’s failure behaviors on a newly developed linear rock cutting facility. A series of rock cutting tests were designed and performed. The acquired experimental data was analyzed to investigate the influences of process parameters and the rock’s mechanical properties on chip formation and force responses.

Topics: Cutting , Rocks
Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2016;139(1):011012-011012-9. doi:10.1115/1.4033933.

Feedrate optimization for computer numerically controlled (CNC) machine tools is a challenging task that is growing in importance as manufacturing industry demands faster machine tools. The majority of research in this area focusses on optimizing feedrate using modeled process constraints. Some researchers have suggested using measured process parameters instead. The former approach suffers from uncertainties in the modeled process data that is the starting point of the optimization. The latter approach has difficulties achieving high levels of optimality. This study proposes the combination of both modeled and measured process data. To this end, a control architecture is described that allows combining measured and modeled process constraints. Within this architecture, a new algorithm to determine time optimum feedrates using modeled velocity and acceleration constraints is proposed. The new control structure including the novel feedrate optimization algorithm is verified experimentally on a high speed biaxial table.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2016;139(1):011013-011013-8. doi:10.1115/1.4034719.

Delamination as the main defect created during drilling of composite laminate is principally a crack nucleation and propagation phenomenon. The fracture-based investigation is performed to identify the significance of different modes involving in this process. The sensitivity analysis is implemented to evaluate magnitude and importance of each mode. As a result, mode I is a dominant mode while drill point removes the material; however, the crack continues to propagate under pure mode III for a while after drilling due to contact of flutes with spalls. This paper investigates the crack formation process for wide variety of drilling conditions and tool geometries. It is demonstrated that although mode III contributes, its minor effect might be neglected if comparing with fracture mode I. Therefore, it may be vanished as a tool design strategy. It is indicated that chisel edge plays a great role in crack propagation under major mode I; therefore, any further design approach which limits or eliminates opening action of chisel edge decreases delamination significantly. Material removal starting from hole perimeter as well as implementing small predrilled holes (such as action of primary cutting lips in step drill) are examined as solutions based on this approach.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2016;139(1):011014-011014-11. doi:10.1115/1.4034592.

The shapes of machined surfaces play a critical role affecting powertrain performance, and therefore, it is necessary to characterize the shapes with high resolution. State-of-the-art approaches for surface shape characterization are mostly data-driven by interpolating and extrapolating the spatial data but its precision is limited by the density of measurements. This paper explores the new opportunity of improving surface shape prediction through considering the similarity of multiple similar manufacturing processes. It is a common scenario when the process of interest lacks sufficient data whereas rich data could be available from other similar-but-not-identical processes. It is reasonable to transfer the insights gained from other relevant processes into the surface shape prediction. This paper develops an engineering-guided multitask learning (EG-MTL) surface model by fusing surface cutting physics in engineering processes and the spatial data from a number of similar-but-not-identical processes. An iterative multitask Gaussian process learning algorithm is developed to learn the model parameters. Compared with the conventional multitask learning, the proposed method has the advantages in incorporating the insights on cutting force variation during machining and is potentially able to improve the prediction performance given limited measurement data. The methodology is demonstrated based on the data from real-world machining processes in an engine plant.

Commentary by Dr. Valentin Fuster

Technical Brief

J. Manuf. Sci. Eng. 2016;139(1):014501-014501-7. doi:10.1115/1.4033929.

A new electromechanical modulation system designed with piezoelectric stacks for both linear actuation and force sensing functions is described. The system can be adapted for modulation-assisted machining (MAM) drilling processes where a low-frequency (<1000 Hz) sinusoidal oscillation is superimposed directly onto the drilling process, such that the feedrate is modulated. A series of drilling experiments were conducted in Ti6Al4V, 17-4 steel, and Al6061 with the system installed on a CNC machine. The drill displacement, thrust force, and chip morphology were characterized across a range of conventional and MAM drilling conditions. The mechanical response (stiffness) of the system agrees with the design specifications. The system offers new capabilities to control the modulation frequency and amplitude in MAM drilling, while simultaneously measuring the drilling thrust force in real time. The force sensing function enables detection of the intermittent separations between the drill tip and the workpiece surface (occurrence of discrete cutting), providing a method to prescribe and control the modulation conditions necessary for effective MAM drilling. Opportunities for force feedback control and process monitoring in MAM drilling processes are discussed. While the system described emphasizes MAM drilling, the capabilities can be extended to other machining processes.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2016;139(1):014502-014502-5. doi:10.1115/1.4034275.

A time-indexed integer programing approach is developed to optimize the manufacturing schedule of a factory for minimal energy cost under real-time pricing (RTP) of electricity. The approach is demonstrated using a flow shop operating during different time periods (i.e., day shift, swing shift, and night shift) in a microgrid, which also serves residential and commercial users. Results show that electricity cost can be reduced by 6.2%, 12.3%, and 21.5% for the three time periods considered, respectively. Additionally, a 6.3% cost reduction can be achieved by the residential and commercial buildings through adopting energy-conscious control strategies in this specific case study example.

Commentary by Dr. Valentin Fuster

Design Innovation Paper

J. Manuf. Sci. Eng. 2016;139(1):015001-015001-8. doi:10.1115/1.4034716.

The paper describes process development for producing sound, strong, and ductile Nb pipe–316L stainless steel (SS) flange brazed joint suitable for application in superconducting radiofrequency (SRF) cavities. The developed transition joints, made with BVAg-8 braze filler metal (BFM), were free of brittle intermetallic compounds, in contrast to the existing global brazing practice of using oxygen-free electronic copper as BFM which results in the formation of a continuous layer of Fe–Nb brittle intermetallic compound at Nb–braze interface. In view of the large difference in the mean thermal expansion coefficients between niobium and 316L stainless steel, a new design for manufacturing and assembly (DFMA) has been developed to ensure achievement of desired joint thickness with uniformity in circumferential and longitudinal directions. An environment-friendly prebraze cleaning procedure has been qualified and implemented. DFMA has resulted in (i) significant reduction of the out-of-roundness errors (≤10 μm) while machining of the niobium pipe, (ii) simplified clearance fit prebraze assembly at room temperature (RT), and (iii) uniformity of joint thickness. A process flow chart has been developed to ensure repeatability of joint characteristics. The brazed joint, of niobium pipe and 100CF knife edge 316L SS flange made by standardized practice, displayed helium leak tightness better than 5 × 10−10 mbar l/s at RT and at liquid helium temperature (LHT). The braze-joint sustained 873 K/10 h postbraze hydrogen degassing treatment and thermal cycling between RT and LHT without any loss in hermeticity.

Commentary by Dr. Valentin Fuster

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