Laser direct joining between stainless steel and polyethylene terephthalate plastic and reliability evaluation of joints

Abstract

Metals and plastics have been widely used in industrial applications, and joining of a metal to a plastic is necessary and important from a manufacturing viewpoint. Therefore, we have developed laser-assisted metal and plastic (LAMP) joining as an innovative rapid laser direct joining without adhesives or glues. In this research, the joining between a Type 304 stainless steel plate of 3 mm thickness and a polyethylene terephthalate (PET) plastic sheet of 2 mm thickness was exploited at several travelling speeds with a diode laser beam of line profile at 170 W power. The joints of 30 mm in width possessed extremely strong tensile shear loads of approximately 3000 N at the maximum. Transmission electron microscope photographs of the joints demonstrated that Type 304 and PET were bonded together on the atomic or molecular level through a Cr oxide film of stainless steel. X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry analysis indicated the possibility of chemical bonding between hydrocarbon and metal through oxygen. Concerning reliability evaluation for the LAMP joints, some joints could have high shear tensile loads of approximately 3000 N even after heat cycle test and show superior air-tightness in helium leak test. Consequently, it was confirmed that the LAMP joining of SUS304 and PET plates could produce a sound joint of high strength, nanostructural binding through the oxide film and fundamental reliability for practical use.