Laser Forming

---

Forming traditionally has been the manufacturing process by which the size or shape of a part is changed by the application of forces that produce stresses on the part that are greater than the yield strength and less than the fracture strength of the material. It requires the use of dies that determine the final shape of the part.

Simple examples of parts produced by this method are beverage containers, angle brackets, or connecting rods. Thermo-mechanical forming, however, enables parts (sheet metal, rod, pipe, or shell) to be formed without external forces and does not require the use of dies.

Laser forming is a type of thermo-mechanical forming and may be used to form an angle bracket, for example, without using dies. More complex parts, such as connecting rods to involve bulk forming, can only be made by traditional forming methods. However, where laser forming can be used, it also serves as a useful tool for rapid prototyping.

Introduction to Laser Forming

Laser forming (LF) is a highly flexible rapid prototyping and low-volume manufacturing process, which uses laser-induced thermal distortion to shape sheet metal parts without hard tooling or external forces. A schematic of the laser forming process is shown in Figure 1. After laser forming, the shape of the sheet material will be changed, as shown in Figure 2a-c.

Figure 1: Schematic of Laser forming process

Compared with traditional metal forming technologies, laser forming has many advantages:

• No tooling. The cost of the forming process is greatly reduced because no tools or external forces are involved in the process. The technique is good for small batches and a variety of sheet metal components. With the flexibility in the laser beam’s delivering and power regulating systems, it is easy to incorporate laser forming into an automatic flexible manufacturing system.
• No contact. Because this process is a non-contact forming process, precise deformation can be produced in inaccessible areas.
• Easy to control. The size and power of the laser beam can be precisely manipulated, enabling accurate control of the forming process and improving reproducibility.
• Energy efficient. Laser forming uses localized heating to induce controlled deformation instead of tradition entire work piece heated. Therefore it has the advantage of energy efficiency.
• Variety of applications. Laser forming offers more applications than conventional mechanical forming, such as adjusting and aligning sheet metal components.
• Forming hard-to-formed materials. Laser forming is suitable for materials that are difficult to form by mechanical approaches. Because in typical laser forming processes metal degradation is limited to a very thin layer of the irradiated surface due to short interaction time, laser forming is suitable for materials that are sensitive to high temperature. The microstructure of the heat-affected zone of laser formed parts can be improved when proper process parameters are used.

Therefore, laser forming has potential applications in aerospace, shipbuilding, microelectronics, automotive industries, etc. The rapid, flexible and low-cost metal forming can improve the competitiveness of these industries. Examples of Laser formed parts are given in Figure 2 a-c.

Figure 2 a-c: Examples of Laser formed parts

The Principles of Laser Forming

The technique for laser forming is very similar to that for laser surface heat treatment and involves scanning a defocused beam over the surface of the sheet metal to be formed. Moving the laser beam along a straight line without interruption causes the sheet to bend along the line of motion (Figure 3).

The components of laser forming system include:

• The laser source with beam delivery system
• Motion table unit on which the workpiece is mounted, or robot for holding a fiber-optic system
• Cooling system where necessary
• Temperature monitoring system
• Shape monitoring system
• Computer control system.

Figure 3: Schematic of the laser beam bending process

Figure 4: Photos of three sheet metals bent using a laser

The typical bend angle that is achieved in single step is about 2°, but may be as high as 10°. The total bend angle can be as high as 90° and higher by repetition of the process. The bend angle obtained after the first scan is greater than the bend angle obtained for each of subsequent scans. However, after the first scan, the bend angle increases almost in proportion to the number of the scans.

More complex shapes can be obtained by offsetting each track by a small amount. In this case, the radius of the part produced depends, among other processing parameters, on the amount of offset of each track. The smaller the offset, the smaller the radius.

The bend angle that is achieved for each step increases with a decrease in sheet thickness due to a resulting decrease in bending restraint. The bend angle per step, however, decreases with a decrease in plate width. This is because with decreasing plate width, the volume of material that acts as a heat sink reduces and as a result, the temperature gradient associated with the process decreases, resulting in a reduced compressive strain and thus bend angle. On the contrary, for high width-to-thickness ratios greater than 10, the bend angle is almost independent of the plate width.