Analysis of Hole Quality for Pre-Tempered Float Glass While Using Rotary Ultrasonic Machining

Abstract

In today’s industrialization era, the innovation in the field of hard and brittle material such as float glass is still under investigation, because of its continuous demand as an operational application. It’s fascinating features such as high thermal stability, strength, toughness, and high optical transmittance makes it a high-performance material. The major application of such materials is listed as optical lenses, automotive glass, thermal collector, solar concentrator, sensors, and solar panel etc. These materials are known as difficult to machine material, because of their brittleness. Analysis of a float glass during machining or drilling process is considered as a brainstorming research area. The drilled hole quality is characterized by the amount of chipping generated near hole edge corners on both sides of the hole as well as the surface roughness of the hole. Hence, the research endeavor of the present work is to pay attention and introduces their strategies to minimize the unwanted chipping near the entrance and exit periphery of the hole by deploying trending rotary ultrasonic machining technique. In the entire study, the hole entrance chipping is measured as average radial chip distance (RCD), hole exit chipping is quantified as the maximum chip radial distance (CRD) and the maximum chip thickness (tc) in horizontal and vertical direction, respectively. In the first case study, multi-shaped tools are used to create blind holes by rotary ultrasonic machining and conventional drilling. The intention is to select the best tool among all to get the negligible RCD along with least tool wear. It is noticed that according to the tool shapes, each tool has paying should be own path of drilling and effective contact area which influences the chip formation and the quality of the hole. The multi tool study for blind holes shows that rotary ultrasonic drilling process attained smallest measurement of radial chip distance as compare to CD for all types of tools. The concave circular tool is found as the best tool particularly to get the least radial chip distance (entrance chipping) during drilling i.e. 0.1145 mm. In the second study, L 18 optimization technique is deployed to visualize the influence of various process parameters i.e. spindle rotation speed, feed rate and vibration amplitude during drilling of float glass specimen by rotary ultrasonic machining technique. After optimizing the process parameters, the least radial chip distance (RCD) is 0.425 mm at hole entrance, chip radial distance (CRD) is 0.70 mm at hole exit, chip thickness (tc) is 0.55 mm at hole exit and hole internal surface roughness is 1.09 μm. In the third case study, the comparison between the edge chipping (RCD) size; before and after iv tempering process has been investigated at optimized parametric condition during conventional drilling and rotary ultrasonic drilling. It is investigated that after tempering process, the chipping (RCD) size near machined corners of the float glass specimen has been propagate. It is revealed that during the float glass tempering process, the combined effect of elevated temperature and high pressure creates some breakage (such as chipping) due to change in physical characteristics of the float glass material. Hence, the chipping amount should be as little as possible on pretempered float glass. It is noticed that RCD size is smaller in case of rotary ultrasonic drilling process as compared to conventional drilling process i.e. 36.92 %. The mechanism behind the formation of chipping during float glass drilling by rotary ultrasonic machining and conventional drilling is also reported. It is revealed that during conventional drilling, abrasives loaded over the tool periphery are in continuous contact with the surface of the specimen to be drilled. It is one of the major reasons of chipping on the workpiece. During rotary ultrasonic drilling, the abrasive impregnated over the tool end face is travelled in definite sinusoidal paths along the axis of the workpiece with some specific tool revolution. In the present study, a FE analysis is developed to investigate the effect of stress generation on hole exit during rotary ultrasonic glass drilling and conventional drilling of float glass. The results showed that the present strategies would be appropriate and capable to overcome the challenges like severe chipping, poor surface finish, excessive tool wear and inappropriate machining parameter selection during float glass drilling. Therefore, rotary ultrasonic machining technique is suggested to get the better hole quality and tend to reduce heavy monetary loss expenditure in the form of machining cost and rejection cost.