|PHB Inc. used MagmaSoft casting-simulation software (www.magmasoft.com) to optimize fill and cooling paths for the Segway HT chassis. Prototype tooling confirmed the results of the MagmaSoft simulation and verified material shrink rates. Fluoroscope and X-ray tests confirmed the structural integrity of the chassis.|
The chassis for the two-wheeled, self-balancing, Segway Human Transporter (HT) from Segway LLC, Manchester, N.H. (www.segway.com), is a single die-cast part. It serves not only as structural foundation for the transporter but also as a motor housing, heat sink, and EMI shield.
Casting house PHB Inc., Fairview, Pa., (www.phbcorp.com), was sworn to secrecy when it worked for the project. Engineers there used Design for Manufacturability input that optimized chassis cost and performance. To provide "productionlike" samples and pilot parts within an aggressive time frame, it built a P-20 prototype die and produced parts in just 10 weeks.
The casting from aluminum 380 alloy is about the size of a laptop computer (360 3 360 3 90 mm). It weighs just 8.2 lb and eliminates eight to 10-plus fasteners in the original prototype parts.Other key design criteria included withstanding 14,000 lb of load from structural forces of the drivetrain, controls, and operator. Heat sinking had to dissipate heat generated by motors, battery pack, and power electronics.
Tooling called for positional location holes held to closer tolerances than allowed by North American Die Casting Association's (www.diecasting.org) Precision Guidelines. This meant most holes required machining. Some location holes have a span of almost 19 in. The NADCA Precision Guidelines require a true position tolerance of 0.056-in. diameter. Process monitoring and capability studies helped PHB designers halve the tolerances so the cover and ejector half-holes could be cast, keeping costs down.
-- Jean M. Hoffman