Scott F. Miller

Experimental and Numerical Analysis of the Friction Drilling Process

Friction drilling is a nontraditional hole-making process. A rotating conical tool is applied to penetrate a hole and create a bushing in a single step without generating chips. Friction drilling relies on the heat generated from the frictional force between the tool and sheet metal workpiece to soften, penetrate, and deform the work-material into a bushing shape. The mechanical and thermal aspects of friction drilling are studied in this research. Under the constant tool feed rate, the experimentally measured thrust force and torque were analyzed. An infrared camera is applied to measure the temperature of the tool and workpiece. Two models are developed for friction drilling. One is the thermal finite element model to predict the distance of tool travel before the workpiece reaches the 250 C threshold temperature that is detectable by an infrared camera. Another is a force model to predict the thrust force and torque in friction drilling based on the measured temperature, material properties, and estimated area of contact. The results of this study are used to identify research needs and build the foundation for future friction drilling process optimization.

Microstructural alterations associated with friction drilling of steel, aluminum, and titanium

Friction drilling, also called thermal drilling, is a novel sheet metal hole-making process. The process involves forcing a rotating, pointed tool through a sheet metal workpiece. The frictional heating at the interface between the tool and workpiece enables the softening, deformation, and displacement of work-material and creates a bushing surrounding the hole without generating chip or waste material. The bushing can be threaded and provides the structural support for joining devices to the sheet metal. The research characterizes the microstructures and indentation hardness changes in the friction drilling of carbon steel, alloy steel, aluminum, and titanium. It is shown that materials with different compositions and thermal properties affect the selection of friction drilling process parameters, the surface morphology of the bore, and the development of a highly deformed layer adjacent to the bore surface.

Experimental study of joint performance in spot friction welding of 6111-T4 aluminium alloy

Abstract The effect of process parameters (cycle time, tool speed and axial force) on the specimen temperature measured 2 mm away from the weld in spot friction welding (SFW) of Al 6111-T4 is investigated. The temperatures were correlated to the lap shear load. Results revealed that, to achieve a good joint strength with the maximum lap shear load >2˙5 kN, temperatures should be greater than a threshold value, which is 350°C at a location close to the SFW joint in this study. By studying the specimen macrographs, two internal weld geometric features based on the cross-section area were identified and correlated to the shear and mixed failure modes of the lap shear tested specimens. A model was developed and validated using experimental data of the cross section area of SFW joint with either shear or mixed mode fracture. The model predicts that the SFW joint strength is maximised at the transition region between the shear and mixed mode fracture.

Thermo-Mechanical Finite Element Modeling of the Friction Drilling Process

Friction drilling uses a rotating conical tool to penetrate the workpiece and create a bushing in a single step without generating chips. This research investigates the three-dimensional (3D) finite element modeling (FEM) of large plastic strain and high-temperature work-material deformation in friction drilling. The explicit FEM code with temperature-dependent mechanical and thermal properties, as well as the adaptive meshing, element deletion, and mass scaling three FEM techniques necessary to enable the convergence of solution, is applied. An inverse method to match the measured and modeling thrust force determines a coefficient of friction of 0.7 in this study. The model is validated by comparing the thrust force, torque, and temperature to experimental measurements with reasonable accuracy. The FEM results show that the peak temperature of the workpiece approaches the work-material solidus temperature. Distributions of plastic strain, temperature, stress, and deformation demonstrate the thermomechanical behavior of the workpiece and advantages of 3D FEM to study of work-material deformation in friction drilling.

Thermal-Electric Finite Element Analysis and Experimental Validation of Bipolar Electrosurgical Cautery

Cautery is a process to coagulate tissues and seal blood vessels using heat. In this study, finite element modeling (FEM) was performed to analyze temperature distribution in biological tissue subject to a bipolar electrosurgical technique. FEM can provide detailed insight into the tissue heat transfer to reduce the collateral thermal damage and improve the safety of cautery surgical procedures. A coupled thermal-electric FEM module was applied with temperature-dependent electrical and thermal properties for the tissue. Tissue temperature was measured using microthermistors at different locations during the electrosurgical experiments and compared to FEM results with good agreement. The temperature- and compression-dependent electrical conductivity has a significant effect on temperature profiles. In comparison, the temperature-dependent thermal conductivity does not impact heat transfer as much as the temperature-dependent electrical conductivity. Detailed results of temperature distribution were obtained from the model. The FEM results show that the temperature distribution can be changed with different electrode geometries. A flat electrode was modeled that focuses the current density at the midline of the instrument profile resulting in higher peak temperature than that of the grooved electrode (105 versus 96°C). DOI: 10.1115/1.2902858

Fuzzy Logic Control of Microhole Electrical Discharge Machining

A microhole electrical discharge machining (EDM) system with adaptive fuzzy logic control and precision piezoelectric stage is developed in this study. A high-speed EDM monitoring system is implemented to measure the gap voltage, current, and ignition delay time, which are used to derive three input parameters—the average gap voltage, deviation in spark ratio, and change in the deviation in spark ratio—for the fuzzy logic control. Servo displacement and speed of the piezoelectric stage during each sampling duration are synthesized in real time by the adaptive fuzzy logic controller. Effects of the single and multiple input parameters, ignition delay threshold value, and maximum servo displacement and speed on the EDM drilling process are experimentally studied. Experimental results show that the fuzzy logic EDM control system yields a much more stable and efficient microhole EDM drilling process.

A pulsatile blood vessel system for a femoral arterial access clinical simulation model

The model-based, rapid-prototyping-enabled design and manufacture of a pulsatile blood vessel (PBV) for high-fidelity mannequin-based clinical simulations is presented. The PBV presented here is a pressurized, flexible tube with alternating fluid pressure created by a pump to mimic the behavior of a human vessel in response to pulsatile pressure. The use of PBVs is important for the fidelity of a clinical simulator that requires residents to palpate and/or access the vessel. In this study, a PBV is presented which features the integration of 3D modeling using patient-specific computed tomography (CT) data, mold fabrication using rapid-prototyping, and finite element method for estimating the required pumping pressure to generate the same level of force (about 1.5 N) experienced by the user through palpation. The relationship between this palpation force and the vessel pressure is studied using two strategies: finite element analysis (FEA) and experiments in a femoral arterial access simulator with a pump, artificial vessel, and surrounding phantom tissue. The experimental results show a discrepancy of 8.7% from the FEA-predicted value. Qualitative validation is done by exposing and surveying 19 interventional cardiology residents at four major educational institutions to the simulator for accuracy of its feel. The overall survey results are positive.

Formation and Structure of Work Material in the Friction Stir Forming Process

There has been significant work on the application of ultrahigh strength steels and aluminum alloys for automotive body mass reduction. Integration of these materials into the automotive structure is non-trivial and advanced methods are required to effectively join the dissimilar materials with the properties required for automotive applications. Friction stir forming is a new environmentally benign manufacturing process for joining dissimilar materials. Fundamentally this process is based on frictional heating and mechanically stirring a plasticized material into a mechanical interlocking joint with a second material. In this research, the significant process parameters were identified and their optimized settings for the current experimental conditions defined using a design of experiments methodology. The overall joint structure and grain microstructure were mapped along different stages of the friction stir forming process. Then, friction stir forming of aluminum work material into different cavity geometries was mapped to study geometrical effects. Two layers were found to form within the aluminum, the thermo-mechanical affected zone that had been deformed due to the contact pressure and angular momentum of the tool, and the heat affected deformation zone that deformed into the interlocking cavity. The geometrical study produced interesting results about the direction and magnitude of material forming under different areas of the tool.

Effect of Localized Metal Matrix Composite Formation on Spot Friction Welding Joint Strength

In this study, metal particles were added during the spot friction welding (SFW) process, a solid state sheet metal joining process, to create a localized metal matrix composite (MMC)for the improvement of lap shear strength in AISI6111-T4 aluminum alloy sheets. The Ancorsteel ® 1000 particles were compressed between the upper and lower sheets and distributed concentrically around the tool axis perpendicular to the plate surface, which formed a localized MMC and were effective as the reinforcement particles in aluminum 6111 -T4 alloy sheets. Results revealed that the MMC reinforcement improved the lap shear strength of SFW joints by about 25%. An aluminum-ferrous solid solution was formed around the steel particles along the aluminum matrix interface. The load-deflection curve shows that the steel particle MMC increased both the strength and ductility of SFW joint. This is attributed to two phenomena observed on the failed lap shear tensile specimens with SFW MMC. One is the longer and more torturous crack path, and the other is the secondary crack on steel particle MMC reinforced SFW joints.

Friction Drilling: A Chipless Hole-Making Process

This paper summarizes the research on friction drilling, a chipless hole making process using the rotating conical tool. Extensive research in experiment, modeling, tool wear, and metallurgical analysis of friction drilling tool and workpiece has been carried out to demonstrate the feasibility of this technology for hole-making in thin metals. The experimentally measured thrust force and torque were analyzed and compared with analytical and finite element modeling results for validation. The microstructures and indentation hardness were characterized on the cross-section of friction drilled holes for different work-materials. For brittle cast metals, effects of workpiece temperature, spindle speed, and feed rate were analyzed. The wear of a tool, which is made of hard carbide material, for friction drilling of carbon steel workpiece, was also studied to demonstrate the capability of a durable tool in the production environment.Copyright