Injection molding of magnesium permitted a new design for a revolutionary miniature bar code scanner and provided additional benefits in protecting sensitive internal electronic components from water and other potential environmental problems.
The MS3 scanner from Microscan Systems “may not be smallest scanner available, but it is the best combination of size and performance,” says Malinda Elien, staff mechanical engineer for Microscan, Renton, WA. “This is the most compact, high-performance mechanical design around.” The chassis had to hold tolerances of ±0.002” in very thin wall sections (0.027”). Molten magnesium can travel longer distances prior to solidification than is possible with conventional die casting. The high pressure of injection molding and careful tool design made the difference. The density of the magnesium molding process (called thixomolding) was also a critical difference. “We were able to achieve thinner wall sections without having to worry about water leaking through random pores in the metal,” said Elien, who had the final call on whether to try thixomolding or stay with die casting. “Initially we were trying to decide between Phillips Plastics and our traditional die-casting vendor,” Elien said. “We never had the question in our mind if Phillips was telling us the truth or if they were telling us what we wanted to hear...Every day I am happy that I made the decision that I did.”