Laser Hardening of Unimax Stainless Steel

Abstract

Nowdays, laser hardening of materials brings a comparative advantage over the conventional hardening technique. Fast cooling rate due to the heat distribution through its own bulk material, self-quenching property (rapid cooling without external water or oil), environmentally friendly characteristics since the procedure does not exhaust smoke, the localized heat input due to adjustable laser spot size to avoid distortion and minimum time to finish the operation are some of the advantages to mention. NIKO is a company specialized in making electrical products like socket outlets and switches by using injection molding techniques. Unimax is a kind of stainless steel used by the company to prepare some parts of the injection molding components like a Nozzle. This time, the company is using more and more fiber-reinforced polymers throughout their product line. These composites are far stronger than the polymer, but on the downside, the fibers are quite abrasive. The objective of this research was to harden the Unimax stainless steel using Nd:YAG (neodymium-doped yttrium aluminum garnet) laser technique. First, the laser transverse speed and spot size were identified as the primary process parameters. Then, the traverse speed of 100, 150 and 400 mm/min and spot size of 2164, 2169, 2288 and 2412 um were assigned with 3 replications. Afterwards, thermal simulation was done using COMSOL Multiphysics© followed by the real test on the metal bar. Therefore, the highest hardness of 650 HV was obtained at a speed of 150 mm/min and a spot size of 2169 um diameters. Finally, the corresponding depth of hardness and roughness values of 200 um below the surface and unmelt samples respectively were obtained.

HIGHLIGHTS

• Laser hardening of materials brings a comparative advantage over the conventional hardening technique
• The laser transverse speed and spot size were identified as the primary process parameters. Afterwards, thermal simulation was done using COMSOL Multiphysics© followed by the real test on the stainless steel bar
• The depth of hardening and Vickers hardness (HV) increased with the smaller spot size and slow traverse speed of the ND:YAG laser, but this resulted in a melt on the surface of the hardened metal
• One of the problems of making products using injection molding techniques using fiber-reinforced polymers is the abrasive nature of the fibers which widen the injection nozzle

GRAPHICAL ABSTRACT