Effect of Electrical Pulsing on Various Heat Treatments of 5XXX Series Aluminum Alloys

Previous studies have shown that the presence of a pulsed electrical current, applied during the deformation process of an aluminum specimen, can significantly improve the formability of the aluminum without heating the metal above its maximum operating temperature range. The research herein extends these findings by examining the effect of electrical pulsing on 5052 and 5083 Aluminum Alloys. Two different parameter sets were used while pulsing three different heat treatments (As Is, 398°C, and 510°C) for each of the two aluminum alloys. For this research, the electrical pulsing is applied to the aluminum while the specimens are deformed, without halting the deformation process. The analysis focuses on establishing the effect the electrical pulsing has on the aluminum alloy’s various heat treatments by examining the displacement of the material throughout the testing region of dogbone shaped specimens. The results from this research show that pulsing significantly increases the maximum achievable elongation of the aluminum (when compared to baseline tests conducted without electrical pulsing). Significantly reducing the engineering flow stress within the material is another beneficial effect produced by electric pulsing. The electrical pulses also cause the aluminum to deform non-uniformly, such that the material exhibits a diffuse neck where the minimum deformation occurs near the ends of the specimen (near the clamps) and the maximum deformation occurs near the center of the specimen (where fracture ultimately occurs). This diffuse necking effect is similar to what can be experienced during superplastic deformation. However, when comparing the presence of a diffuse neck in this research, electrical pulsing does not create as significant of a diffuse neck as superplastic deformation. Electrical pulsing has the potential to be more efficient than traditional methods of incremental forming since the deformation process is never interrupted. Overall, with the greater elongation and lower stress, the aluminum can be deformed quicker, easier, and to a greater extent than is currently possible.

Modeling Machining at High Speeds as a Fluid Mechanics Problem

Even though many models for machining exist, most of them are for low-speed machining, where momentum is negligible and material behavior is well approximated by quasi-static plastic constitutive laws. In machining at high speeds, momentum can be important and the strain rate can be exceedingly high. For these reasons, a fluid mechanics approach to understanding high-speed, very high-speed, and ultra-high-speed machining is attempted here. Namely, a potential flow solution is used to model the behavior of the material around a sharp tool tip during machining at high speeds. It is carefully argued that the potential flow solution is relevant and can be used as a first approximation to model the behavior of a metal during high-speed, very high-speed, or ultra-high-speed machining events; and at a minimum, the potential flow solution is qualitatively useful in understanding mechanics of machining at high speeds and above. Interestingly, the flow solution predicts that there is a stagnation point on the rake face, not at the tool tip as is usually assumed. Because the stagnation point is not at the tool tip, the flow solution predicts a significant amount of deformation in the workpiece resulting in large residual strains that may lead to a temperature rise on the finished surface.

Mathematical Modelling and Finite Element Simulation of Pre-Bending Stage of Three-Roller Plate Bending Process

Continuous three roller bending process is widely used in practice to bend the plates into cylinders. Bending load for plate material under bending is affected by plate thickness, width and shell diameter combinations. Maximum top roller load is encountered during the edge pre-bending stage as top roller is set at an offset distance from its mid position. Shell diameter, thickness and material for cylindrical structural element to be produced are fixed by design. Width of the plate for roller bending decides number of cylindrical segments required to achieve the designed shell length. Maximum pre-bending width depends on maximum top roller load imparting capacity. Looking to the above considerations, maximum width which can be pre-bend at limiting top roller load (for designed shell diameter, thickness and material combinations) specifies the capacity. Presented work aims at developing the mathematical model of top roller load for pre-bending. Top roller offset for pre-bending were calculated based on practical top roller pre-bending load data, for different grades of C-Mn steel plates (as per ASME sec II part-A). Based on these top roller offsets, finite element analysis (FEA) of pre-bending stage were performed using Hyperform LS-DYNA. Effect of co-efficient of friction at roller plate interfaces was analyzed. FE simulation of pre-bending of cladded plate (54 mm thick C-Mn steel plate of material grade SA-387Gr11Cl2 having 3 mm thick layer of stain less steel material grade SS-308) was performed. FEA load results were found in good agreement with the practical load results and can be used for capacity assessment and analysis of roller bending machines.

A Comparative Study on Hydraulic Bulge Testing and Analysis Methods

Hydraulic bulge testing is a material characterization method used as an alternative to tensile testing with the premise of accurately representing the material behavior to higher strain levels (∼70% as appeared to ∼30% in tensile test) in a biaxial stress mode. However, there are some major assumptions (such as continuous hemispherical bulge shape, thinnest point at apex) in hydraulic bulge analyses that lead to uncertainties in the resulting flow stress curves. In this paper, the effect of these assumptions on the accuracy and reliability of flow stress curves is investigated. The goal of this study is to determine the most accurate method for analyzing the data obtained from the bulge testing when continuous and in-line thickness measurement techniques are not available. Specifically, in this study the stress-strain relationships of two different materials (SS201 and Al5754) are obtained based on hydraulic bulge test data using various analysis methods for bulge radius and thickness predictions (e.g., Hill’s, Chakrabarty’s, Panknin’s theories, etc.). The flow stress curves are calculated using pressure and dome height measurements and compared to the actual 3-D strain measurement from a stereo optical and non-contact measurement system ARAMIS. In addition, the flow stress curves obtained from stepwise experiments are compared with the ones from above methods. Our findings indicate that Enikeev’s approach for thickness prediction and Panknin’s approach for bulge radius calculation result in the best agreement with both stepwise experiment results and 3D optical measurement results.

Analytical Modeling of Metal Transfer for GMAW in the Globular Mode

A lumped parameter dynamical model is developed to describe the metal transfer for gas metal arc welding (GMAW) 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.

Manipulating Shape and Size of Nanoparticles With Plasma Field

Tuning the plasma field in reactive ion etching generates different etching profile of nanoparticles. For nanoparticles in an isotropic plasma field, there will be uniform shrinkage of the particle sizes due to the isotropic etching, with the curvature of the particles unchanged after the etching. An anisotropic etching, on the other hand, provides rich opportunities to modify the shape of the particles with reduced dimensions. For a monolayer of silica nanoparticles on a flat substrate in a unidirectional plasma field, the reactive ion etching changed the shape of silica nanoparticles from spherical to spheroid-like geometry. The mathematical description of the final spheroid-like geometry was discussed and matched well with the experimental results. The surface curvature of the particles after etching remained the same for both the top and the bottom surfaces, while the overall shape transformed to spheroid-like geometry. Varying the etching time resulted in particles with different height to width ratios. The unique geometry of these non-spherical particles will impact fundament properties of such particles, such as packing and assembly. In the case of spheroid-like particles, packing of such particles into ordered structures will involve an orientational order, which is different from spherical nanoparticles that have no orientational order.

Definition of Cutting Conditions for Thin-to-Thin Milling of Aerospace Low Rigidity Parts

The main drawback of the high speed milling of monolithic parts for the aerospace industry is the high buy-to-fly ratio that leads to a huge material waste. This problem is caused by the need to stiffen the part during the machining in order to avoid chatter, excessive vibration and residual stresses. The present work proposes a methodology for the milling of compliant parts based on the selection of cutting conditions free of chatter. First, the modal parameters of the part in the most problematic stages of the machining are calculated by means of the finite elements method. Secondly, a three-dimensional stability model is used in each stage to calculate a three-dimensional stability lobes diagram dependent on the tool position along the whole tool path. Given the fact that the depth of cut is defined by the bulk of material, the three-dimensional stability diagram can be reduced to a two-dimensional one, which relates tool position during the machining and spindle speed, and indicates how to change the spindle speed in order to avoid the unstable areas. What is more, the proposed methodology can also be used to dimension the bulk of material, select the proper tool or improve the fixturing of the part. Finally, the methodology is validated experimentally on a test part.

Experimental Study on a New Method of Double Side Incremental Forming

This paper presents a new configuration for sheet metal incremental forming using DSIF (Double Sided Incremental Forming) to overcome the limitation of single point incremental forming (SPIF). The new process can produce geometrical features on either side of the initial plane of the sheet without changing setup. A component having such challenging features is selected to demonstrate the capabilities of the proposed method and a contour tool path is generated using UniGraphics (UG) surface machining module and formed by mounting the new setup on a CNC milling machine. The final formed shape was scanned and compared to the designed profile. In addition, two more components having cylindrical and spherical geometries are formed to study the effect of geometry on the accuracy of the component that can be produced by using the proposed method. A simple analysis model has been developed to explain the effect of squeezing and stretching to the part elongation during the DSIF process.

Effect of Bias Voltage on Fatigue Behavior of CrN Film Deposited on Ti-6Al-4V Alloy

PVD technique incorporating CrN coating was applied to the titanium alloy (Ti-6Al-4V) and its effects on the fatigue life and fatigue strength were studied in this paper to explore the fatigue behavior of Ti-6Al-4V specimens. A CrN film deposited by arc ion plating (AIP) improved the mechanical properties; specially hardness and fatigue life of Ti-6Al-4V specimens. The properties were studied using XRD, hardness and fatigue testers. The fatigue life of CrN-coated Ti-6Al-4V specimens was improved significantly compared to those of uncoated specimens. The enhanced fatigue life can be attributed to the improved hardness of CrN film due to change of bias voltage during the film deposition. The initiation of fatigue cracks is likely to be retarded by the presence of hard and strong layers on the substrate surface. It has been determined that the fatigue fracture of the substrate-coating composite is dominated by the fracture of the CrN film since fatigue cracks have been observed to form first at the surface of the film and subsequently to propagate towards the substrate. It has also been concluded that the increase in fatigue properties of the coated substrate is associated mainly with the changing of bias voltage during the coating observed in most of the maximum alternating stress range explored in this work.

A Comparability Study of a Wireless Electret Accelerometer to a Traditional Piezoelectric Accelerometer

Traditional piezoelectric accelerometers used for machine condition monitoring are expensive and represent a capital risk when placed in the harsh environment of a cutting process. Additionally, these components require signal conditioning hardware and are sampled on a PC via an independent data acquisition interface (DAQ card). The goal of the research discussed herein is to test an industrial-friendly electret-based accelerometer that can perform tasks similar to a traditional piezoelectric accelerometer. The sensor will be adapted to utilize Bluetooth wireless data capabilities, further enhancing the sensors industrial practicality. The output of this electret-based sensor will be compared to the output of a traditional piezoelectric accelerometer and accompanying DAQ. More specifically, the study will focus on the effects of elevated temperature on the sensor. To achieve this, a comparison of both the electret and piezoelectric accelerometer response spectra will be observed over a range of 21°C to 77°C. To further validate the sensor, turning data is collected wirelessly from the sensor and compared to the output of the traditional piezoelectric sensor. Finally, the performance of the sensor for monitoring a tool’s condition during turning is evaluated and presented. The generated trend is contrasted to the comparable trend developed from the piezoelectric-based accelerometer.