Large pulsed electron beam surface treatment of translucent PMMA

A large pulsed electron beam (LPEB) was used to modify the surface properties of a poly(methyl methacrylate) (PMMA) sample. Translucent PMMA samples were fabricated using a conventional milling process. Then, the surface was irradiated with an energy density of 2 to 4 J/cm2 by a large electron beam, 60 mm in size. Surface property characterization of the irradiated PMMA samples was performed using an ultraviolet-visible-near infrared (UV-vis-NIR) spectrophotometer, atomic force microscopy, a form tracer, and drop-shape analysis and compared with the non-irradiated surface. It was observed that the visible light transmission of the prepared PMMA sample was enhanced by 40%. The surface roughness of the PMMA sample after irradiation was also reduced by 30%, compared with the baseline case with no irradiation. Additionally, the water contact angle increased as the number of LPEB shots increased.close0

Finite Element Modeling of Three-Dimensional Milling Process of Ti-6Al-4V

Titanium and its alloys are widely used in aerospace and medical implants due to their excellent mechanical and chemical properties. Titanium is light, strong, corrosion resistant, and biocompatible; however, it has poor machinability. The low thermal conductivity and high strength result in large cutting forces and elevated temperatures during machining, as well as a reduced tool life and a poor machined surface. The current work is based on a 3D finite element method (FEM) modeling of dry milling processes on a Ti-6Al-4V workpiece. The FEM solver Abaqus Explicit (R) was used with the Johnson-Cook plasticity model to describe the deformation of the workpiece. Experimental work was carried out to validate the simulated cutting forces and chip morphology; the error in the predicted cutting forces in feed and normal to feed direction was in the range of 1-34%, which was mostly within the experimental variation. The measured chip morphology showed good agreement with the simulated data in terms of the chip size and shape. A parametric study of the effect of the machining parameters on the cutting forces was carried out, where the cutting speed, depth of cut, and feed rate were varied, and the radial, tangential, and axial cutting forces were measured. An increase in the feed rate from 50 mu m/tooth/rev to 200 mu m/tooth/rev resulted in an increase in the tangential and axial forces of 143% and 239%, respectively. An increase in the depth of cut from 50 mu m to 200 mu m resulted in an increase in the tangential and axial forces of 237% and 100%, respectively. We found that increasing the feed rate was preferable to increasing the depth of cut, as it led to a smaller tangential force.close

Tool life improvement in cryogenic cooled milling of the preheated Ti-6Al-4V

Cryogenic-based machining has been drawing attention for machining hard metals and super alloys such as the titanium alloys due to environmental concerns and growing regulations over pollution. In this study, cryogenic-assisted milling of Ti-6Al-4V has been performed with the preheated workpiece methods to avoid the cryogenic hardening by liquid nitrogen (LN2). Preliminary experiments show an increase in the cutting force due to cooling of the workpiece; therefore, workpiece preheating was adopted to increase the workpiece temperature. Three cutting speeds and three machining environments (dry, cryogenic, and cryogenic plus preheated) were considered in the analysis of tool wear, cutting forces, tool wear morphology, and chip morphology. Soft (Si coating) and hard (CrTiAlN)-coated tools were used in this study. It was observed that the tool life was increased by 50 to 90 % for Si-coated tools and 50 to 55 % for CrTiAlN-coated tools. The tool wear morphology showed that rubbing and chipping were the primary tool wear mechanisms. It is expected that the present work will be useful for improving tool life and reducing the cost of hard metal products. It may also be useful for reducing the ecological problems by conventional cutting fluids.close0