Analysis of Fiber Optic Sensor to Measure Velocities During High Deformation Rate Material Forming Processes

Abstract: Previous methods of measuring high velocities, e.g., during electromagnetic forming (EMF) and magnetic pulse welding processes where the workpiece is deforming, include photon Doppler velocimetry (PDV), laser micrometers, and high speed photography. In this paper, an alternative method is presented, implementing a fiber optic, reflectance dependent sensor. The sensor is shown to be an attractive, low purchase cost solution to measure high velocities. Data are shown with respect to sensor characterization including various surface reflectivity values, curvatures, and misalignments; implementation in two EMF/welding processes; and verification with high velocity PDV measurements. The sensor system is one twentieth the purchase cost of a PDV system, and yet measures velocities accurately (using PDV measurements as the reference) to at least 150 m/s provided that local curvature is not extreme and the displacement is less than approximately 27 mm. Sensor performance is also enhanced by the use of retroreflective tape, which is shown to increase the displacement range by 9×, decrease sensitivity to misalignment, and increase repeatability and ease of implementation.

Thibaudeau, E., Turner, B., Gross, T., Kinsey, B. L., 2015, “Analysis of Fiber Optic Sensor to Measure Velocities During High Deformation Rate Material Forming Processes”. Journal of Manufacturing Science and Engineering 137(3). https://doi.org/10.1115/1.4029650

Analytical Design and Experimental Validation of Uniform Pressure Actuator for Electromagnetic Forming and Welding

Abstract: In this paper, an analytical model is used to design a coil, called a Uniform Pressure Actuator (UPA), for use during electromagnetic forming (EMF) and magnetic pulsed welding (MPW) by combining and extending past efforts by other researchers. The UPA offers increased forming efficiency and repeatability, as well as a robust design. Magnetic pressure applied to the workpiece and workpiece velocity are predicted to ensure impact conditions are sufficient for MPW. The UPA is constructed and tested experimentally to validate the accuracy of the analytical model, as well as verify assumptions made during modeling. The coupling coefficient introduced in the magnetic analysis is experimentally determined and compared to previous researchers’ values. Workpiece velocities for various energy levels, workpiece thicknesses, and materials with various conductivities and densities are compared to analytical predictions and show good agreement for the initial acceleration in the process. Workpiece velocity measurements were obtained using a Photon Doppler Velocimetry (PDV) system, which provides a robust method for measuring velocities with submicron displacement and temporal resolution in the nanosecond range. Uniformity of the workpiece deformation is also examined, which is an advantage of the UPA.

Thibaudeau, E., Kinsey, B. L., 2014, “Analytical Design and Experimental Validation of Uniform Pressure Actuator for Electromagnetic Forming and Welding”.  Journal of Materials Processing Technology 215, pp. 251-263. https://doi.org/10.1016/j.jmatprotec.2014.08.019

Effect of specimen planar area on electromagnetic flanging

Abstract: The specimen parameter that is often mentioned with respect to the ability to achieve electromagnetic forming (EMF) is the specimen thickness. If the skin depth is small compared to this parameter, efficient forming will be achieved. However, another parameter that may affect the ability to achieve efficient forming is the specimen’s planar area, i.e., the length and width of the specimen. This would particularly become an important factor if EMF is used to fabricate meso/microscale components. In this research, a flat spiral coil was used to flange 0.508mm thickness, CuZn30 specimens of varying widths (i.e., 10, 14, 18, 22, 35, and 47mm). These widths were varied in order to modify the projected area of the coil over the specimen. Results showed that a decrease in the specimen width was generally associated with a decrease in forming (i.e., lower flanging angle) due to edge effects in induced eddy currents. Since the magnetic field distribution from the flat spiral coil is asymmetric, material was overhung on both sides of the die. This yielded an extra half turn on the left side of the specimen, and increased forming. The die was also translated to assess differences in flanging generated. In order to achieve meso/microforming with EMF, attention to the interaction between coil design and specimen dimensions is required.

VanBenthysen, R., Thibaudeau, E., Kinsey, B. L., 2013, “Effect of specimen planar area on electromagnetic flanging”.  Journal of Manufacturing Processes. 15(2), pp. 194-200. https://doi.org/10.1016/j.jmapro.2013.01.005

Analytical Design and Implementation of a Uniform Pressure Actuator for Electromagnetic Forming and Welding

Abstract: Lightweight sheet metal components and assemblies formed and welded electromagnetically can be implemented in various industries such as automotive, aerospace, and electronics. Past applications and modeling of Electromagnetic Forming (EMF) and Magnetic Pulse Welding (MPW) have typically focused on crimping and expansion of tubular workpieces. While some Finite Element Analysis (FEA) packages exist that are capable of modeling these processes, there is a lack of simplified analytical modeling efforts, especially for sheet metal workpieces. Analytical modeling is attractive for its simplicity and cost in effectively determining e.g., an optimal coil design. In this paper a coil design and analysis procedure developed at The Ohio State University is modified and extended through an analytical model and FEA. The coil, named a Uniform Pressure Actuator (UPA), offers increased forming efficiency and repeatability, as well as a robust design. Coil design parameters such as the number of turns and conductor cross section are determined for a given workpiece. Magnetic pressure applied to the workpiece and workpiece velocity are predicted to ensure impact velocities are sufficient for MPW. A coil was constructed based on the analyses, and experimental results are compared to the analytical predictions for both electrical characteristics and workpiece velocity.

Thibaudeau, E., Kinsey, B. L., 2013, “Analytical Design and Implementation of a Uniform Pressure Actuator for Electromagnetic Forming and Welding”. ASME 2013 International Manufacturing Science and Engineering Conference.
https://doi.org/10.1115/MSEC2013-1238