Hybrid Machining using Direct Laser Assistance and Micro Texturing
Creators: name: Wei, Yuan
Publisher: name: Graduate Studies
Year: 2018
Subjects: subject: Machining
subject: Laser Assistance
subject: Micro Texturing
subject: Cutting Forces
subject: Engineering--Mechanical

description: Hard-to-cut materials, such as structural ceramics, metallic glasses, and fibre reinforced polymers, are widely used in aerospace engineering, medical appliances, and other fields. However, due to the materials’ high strength and hardness, the machining costs for these materials are high. Consequently, improving the machining process of hard-to-cut materials is necessary. Laser assisted machining is often used to improve the machining process of hard-to-cut materials. However, the current laser assisted machining method normally uses high power lasers due to low heating efficiency; overheating and surface phase changes cannot be avoided, especially for metallic glasses and resin-based composites. In this study, a novel laser assisted machining method, direct laser assisted machining (DLAM), is proposed and developed to improve the machining of hard-to-cut materials. In the conventional laser assisted machining process, a workpiece is pre-heated by a laser prior to the removal of the material to soften the workpiece material and improve the machinability. Whereas DLAM passes the laser beam through a cutting tool, and then directly heats the location (at the tool tip) where the material is to be removed. Energy consumption is reduced and overheating the workpiece can be avoided. In the DLAM process, the cutting tool is made from sapphire because sapphire is very hard and has perfect optical transparency so that laser can pass through. The sapphire tool not only works as a cutting tool but also delivers the laser beam to its rake face. Effects of micro tool surface texture on the rake face in DLAM are also investigated. Tool surface texturing can reduce the cutting forces and tool wear by minimizing friction and reducing the contact area. A new tool texturing, micro-abrasive blasting method is used to fabricate the micro texture on a sapphire tool rake face. The texture effects in the tribological test and the cutting process are investigated. The numerical modeling of the DLAM cutting process was performed using a commercial finite-element analysis software. Cutting model coupling with laser heating effect and tool surface texture were built and carried out. The simulation results were used as a reference for the cutting test design, and they were compared with the cutting tests data. A series of cutting tests were performed on metallic glass, CFRP, and aluminum alloy under different cutting conditions. The cutting forces were measured and analyzed. The machined surface and chips were examined and compared to the simulations. For all materials, the cutting forces were reduced when optimal laser power is applied. For the bulk metallic glass, DLAM significantly reduced the cutting forces at a low output power of 2.8 W. However, a high laser output power (7.9 W) did not decrease the cutting forces; in certain cases, it led to higher cutting forces due to a phase change of material. The surface roughness was improved when the laser power was 2.8 W. When the laser output power was 7.9 W, the surface roughness changed slightly compared to 2.8 W. The shear band formation was affected using the laser. Less chip segmentation was identified when the laser was applied, implying an enhanced ductility of the bulk metallic glass (BMG) material. In addition, the combined application of DLAM and a tool surface micro texture reduced the cutting forces even further. DLAM combined with tool surface texture provides a possible laser assisted solution for machining temperature-sensitive materials without unwanted material phase change. This study also provides an understanding of chip formation on BMGs when additional heat is applied during the cutting process. Finite-element model of the process provides a fundamental understanding of the DLAM working mechanism, and it can be used to predict cutting forces and cutting temperature.