Laser Assisted Cold Bending of High Strength Steels

This paper presents the feasibility of an innovative application of laser-assisted bending process. The high strength steel sheets bending, carried out after a laser heat treatment, is studied. Several strategies aimed at obtaining a ductile structure along the bending line, suitable for cold forming, are investigated. The influence of laser processing parameters on the microstructure, hardness and strength of the sheets are discussed and analyzed. In order to predict the temperature and ensure the repeatability and reliability of the process, a model for heat treatment simulation is developed. The study of the experimental data and the integration with the simulation of the heating phase lead to the definition of specific process parameters suitable for achieving a crack-free cold bending of high strength steels.

Modeling and Simulation of Flexible Needle Insertion Into Soft Tissue Using Modified Local Constraint Method

This paper presents a new simulation model for flexible needle insertion into soft tissue using modified local constraint method. In this work, we assume deformation of the needle is relatively small, therefore, the soft tissue deformation in the radial direction is far less than it is in the axial direction. Under the assumptions above, the spring model in the radial direction of the needle is established and applied in the puncture procedure to obtain the equilibrium position of the needle-tissue system. The FEM model for the simulation includes three iterative steps: 1. Distribute the axial force on the needle into tissue nodes, and add radial constraint on tissue nodes that are connected with needle’s shaft, then calculate the whole displacement of the tissue nodes; 2. Based on the whole displacement of all nodal points and the effective stiffness matrix, we get the radial force on the tissue, then we use the spring model in the radial direction to get the equilibrium position; 3. Compound the radial and axial force on the tissue nodal points to obtain the actual displacement. Simulation results are presented and discussed.

Investigation and Optimization of Disk-Laser Welding of 1 MM Thick Ti-6Al-4V Titanium Alloy Sheets

Welded Ti-6Al-4V joints are employed in nuclear engineering, civil industries, military and space vehicles. Laser beam welding has been used for welding thanks to its advantages in terms of increase in penetration depth and reduction of possible defects; moreover a smaller grain size in the fused zone is benefited in comparison to either TIG and plasma arc welding, thus providing an increase in the tensile strength of the welded structures. The aim of this work is to develop and test the regression model for a number of crucial responses. The study has been carried out on 1 mm thick Ti-6Al-4V plates; a square butt welding configuration was considered employing a disk-laser source. A three level Box-Behnken experimental design is considered. An optimum condition has been suggested via numerical optimization of the desirability function with proper weights and importance of constraints. Vickers micro hardness testing was conducted to discuss structural changes in fused and heat affected zone.

Fabrication of Tapered Micro Pillars on Titanium Using Electric Discharge Micromachining

Materials are made harder, tougher, heat resistant and more corrosion resistant which make them difficult-to-machine by traditional machining methods. Titanium and its alloys are in the group of these difficult-to-machine materials, and these alloys have applications in aerospace, power generation, surgical instruments, automobile, chemical plants etc. Ti-6Al-4V is amongst the commonly used titanium alloy, and the current research is focused on its efficient machining. Electro discharge micromachining can be used for producing features in micro range on electrically conductive materials. Straight micro electrodes have been produced using EDMM process. The main objective of the current research is to achieve array of tapered micro pillars on Ti-6Al-4V Work piece material using EDMM process. The effect of process parameters such as gap voltage, discharge current, pulse on-time and duty cycle on the response parameters such as taper angle, material removal rate (MRR) and tool wear rate (TWR) are studied. The experiments are designed using statistical technique. After studying the results of the experiments, the array of micro tapered pillars of different taper angles is produced to see the feasibility of fabrication of tapered pillars on titanium alloy using EDMM process.

Microstructural and Dynamic Mechanical Characterization of Biodegradable Magnesium-Calcium Alloy for Orthopedic Implants

Magnesium-Calcium (Mg-Ca) alloy is an emerging metallic biomaterial for manufacturing biodegradable orthopedic implants. However, very few studies have been conducted on mechanical properties of the bi-phase Mg-Ca alloy, especially at the high strain rates often encountered in manufacturing processes. The mechanical properties are critical to design and manufacturing of Mg-Ca implants. The objective of this study is to study the microstructural and mechanical properties of Mg-Ca0.8 (wt %) alloy. Both elastic and plastic behaviors of the Mg-Ca0.8 alloy were characterized at different strains and strain rates in quasi-static tension and compression testing as well as dynamic split-Hopkinson pressure bar (SHPB) testing. It has been shown that Young’s modulus of Mg-Ca0.8 alloy in quasi-static compression is much higher than those at high strain rates. Yield strength and ultimate strength of the material are very sensitive to strain rates and increase with strain rate in compression. Strain softening also occurs at large strains in dynamic compression. Furthermore, quasi-static mechanical behavior of the material in tension is very different from that in compression. The stress-strain data was repeatable with reasonable accuracy in both deformation modes. In addition, a set of material constants for the internal state variable plasticity model has been obtained to model the dynamical mechanical behavior of the novel metallic biomaterial.

Processing of Porous Zirconium Tungstate and Their Thermomechanical Properties

This paper explores a new processing method to fabricate porous zirconium tungstate (ZrW2O8 or ZT) with the porosity content up to 40% in volume. The method uses spherical graphite powders that are mechanically stable, allowing us to compact with ceramic powders in dry condition. Thus, the ceramic powders mixed with spherical graphite powders can be compacted and sintered to a near full density. During sintering, the graphite powders burn out without damaging the powder compact due to their inherent near-zero thermal expansion. The processing route discussed in this paper is applicable to all oxide ceramics where the sintering can take place in air and above 700°C to dissociate the graphite. In this paper, we have applied this processing technique to fabricate porous ZrW2O8. Many porous ZrW2O8 with a range of porosity levels were fabricated and tested for their theromomechanical properties including elastic modulus (E) and coefficient of thermal expansion (CTE). The experimentally determined properties were compared with the predictions based on the micromechanical Mori-Tanaka scheme.

Single Point Diamond Turning of Silicon by Using Micro-Laser Assisted Machining Technique

In this study, single point diamond turning (SPDT) is coupled with the micro-laser assisted machining (μ-LAM) technique. The μ-LAM system is used to preferentially heat and thermally soften the work piece material in contact with a diamond cutting tool. In μ-LAM the laser and cutting tool are integrated into a single package, i.e. the laser energy is delivered by a single mode fiber laser to and through a diamond cutting tool. This hybrid method can potentially increase the critical depth of cut (DoC), i.e., a larger ductile-to-brittle transition (DBT) depth, in ductile regime machining, resulting in a higher material removal rate (MRR). An IR continuous wave (CW) fiber laser, wavelength of 1064nm and max power of 100W with a beam diameter of 10μm, is used in this investigation. In the current study SPDT tests were employed on single crystal silicon (Si) wafer which is very brittle and hard to machine by conventional methods. Different outputs such as surface roughness and depth of cut for different set of experiments were analyzed. Results show that an unpolished surface of a Si wafer can be machined in one pass to get a very good surface finish. The Ra was brought down from 1.2μm to 275nm only in one pass which is a very promising result for machining the Si wafer.

Experimental Validation of Active Fixture Design Methodology

A design methodology for active and fully-active fixtures has been established previously. In this work the results of a part of the validation for the design are presented, namely the differences between two different layouts and the difference between application of an passive and active clamp. The test-bed consist of a reconfigurable fixturing system with an active clamp holding a thin-walled plate. For three cases passive and actively controlled clamping forces were exerted during a series of milling operations. These are (1) passive clamping at a suboptimal and (2) at the optimal position and (3) clamping with an actively controlled clamping force at the optimal clamping location. The previously proposed design procedure has been qualitatively validated since its predictions regarding optimal layout and adaptive clamping forces hold true, when comparing the surface finishes, which improve from case to case.

Surface Integrity Studies in Ball End Milling of Thin Shaped Cantilever Inconel 718

The paper presents the surface integrity analysis in ball end milling of thin shaped cantilever plate of Inconel 718. It is noticed that the workpiece deflection has significantly contributed to machined surface integrity in terms of surface topography and subsurface microhardness. The ball end milling performed with 15° workpiece inclination with horizontal tool path produced higher surface integrity which varies with the location of machined surface region. In general, the mid portion of the machined plate shows lower surface roughness and microhardness with less surface defects.

A Mixed Toolpath Strategy for Improved Geometric Accuracy and Higher Throughput in Double-Sided Incremental Forming

Incremental sheet forming has attracted considerable attention in the recent past due to advantages that include high process flexibility and higher formability as compared to conventional forming processes. However, attaining required geometric accuracy of the formed part is one of the major issues plaguing this process. The Double-Sided Incremental Forming process has emerged as a potential process variant which can preserve the process flexibility while maintaining required geometric accuracy. This paper investigates a mixed toolpath for Double-Sided Incremental Forming which is able to simultaneously achieve good geometric accuracy and higher throughput than is currently possible. The geometries of parts formed using the mixed toolpath strategy are compared to the desired geometry. Furthermore, an examination of the forming forces is used to uncover the reasons for experimentally observed trends. Future work in this area is also discussed.