Temperature Gradient-Based Laser Bending of Full Plates and Plates With Cutout

Temperature Gradient-Based Laser Bending of Full Plates and Plates With Cutout

Paramasivan Kalvettukaran, Sandip Das, Sundar Marimuthu, Dipten Misra
DOI: 10.4018/978-1-7998-1831-1.ch012
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The laser bending process, also called the laser forming process, consists of irradiating the surface of a sheet or a plate by means of a moving laser beam with a predefined scanning strategy to generate the desired shape through thermally induced residual stress. This chapter presents the mechanisms of a laser bending process and the technological aspects concerning laser v-bending of rectangular AISI 304 plates for full plates and plates with a central cutout at its middle to highlight the process fundamentals and how processing affects the final bending angle of the workpieces. Laser bending involving plates with a cutout will have numerous applications for car bodies, such as front and rear panels where bending is required to be performed on panels with cutout geometries. To investigate the effects of shape and size of the cutout on temperature distribution, stress distribution, and final bending angle, different shapes such as circular, ellipse, rectangular, and square, as well as different dimensions of cutouts have been chosen.
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In recent years, laser beam forming (LBF) has emerged as a new and promising technique in diverse industries, such as aerospace, automotive, microelectronics and shipbuilding. The reasons for the ever-increasing applications of laser forming over conventional techniques are some typical advantages of the process. Specifically, this method requires no mechanical contact and hence is noise free from noise, vibration and frequent repair and maintenance of the system. It offers a versatile and flexible manufacturing process by way of generating different complex shapes (Hennige, 2000; Gollo et al., 2015) (e.g., sinusoidal, dish-shape, saddle, pillow, etc.) and micro-bending for precise adjustment (Dirscherl et al., 2006; Hu et al., 2011), without using special tools and dies, with a controllable moving beam. In addition, laser forming has attracted considerable attention over flame bending since the former can produce a steep thermal gradient in thin materials with high reflectivity and high thermal conductivity. Moreover, material degradation, caused by laser forming, is less than that by flame heating, as the laser beam produces a smaller and narrower heat affected zone (HAZ).

In laser bending process, the laser beam is traversed across the sheet surface; the scanning path depends on the target shape. In the simplest case, the beam delivery may be at a single point. For V-bending, it may follow a straight line across the whole part as shown in Figure 1. For complex shapes, the scanning path may involve combination of radial, circular, archimedean or other trajectories (Venkadeshwaran et al., 2010; Safari et al., 2015). Moreover, during the scanning process, the beam power, the beam diameter and the scanning speed may need to be varied as per the process requirement. Multipass scanning following the same path may be used to achieve large bending (Kant & Joshi, 2015). The workpiece thickness is the most important parameter as it directly controls the temperature gradient along the thickness direction (Dixit et al., 2015). The increase in the thickness leads to the change in the bending mechanism from the one to another. The bending angle is approximately inversely proportional to the square of the workpiece thickness. Moreover, the microstructures of laser irradiated material varies depends on the plate thickness. The grain size is smaller for smaller strip thickness since the temperature of the top surface is higher which implies that thinner the strip, the harder becomes the laser irradiated surface (Fetene et al., 2017).

Figure 1.

Schematic diagram of laser forming process


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