detailset DESIGN
Design Makes Dentist Chairs More Comfortable
JITEN SHAH, PRODUCT DEVELOPMENT & ANALYSIS, NAPERVILLE, ILLINOIS CASTING PROFILE
Cast Component: Rigid link casting.
Process: Semi-permanent mold. Material: Aluminum. Weight: 0.66 lbs. Dimensions: 9 x 3 x 3 in.
O
ne of the largest dental furniture manufacturers in the world part- nered with L A Aluminum Casting Co., Hayden, Idaho, to make a rigid articulated arm for its dental chairs that was lightweight, strong and attractive to better meet its clients’ needs. Originally a bent tube/weldment combination, the arm also had to conceal
cumbersome tubes and wires, have a wide range of motion and be ergonomic. Permanent mold was chosen as the casting method because of its cost eff ective- ness at high volumes, good surface fi nish, superior strength and the ability to cast hollow spaces with shell cores. T e design is the furniture company’s most popular arm today.
Using fi lling and solidifi cation simulation tools makes it pos- sible to predict the cooling rates and mechanical properties for high strength structural parts demanding high integrity. • Imagine a 300-lb person leaning on top of the articulating arm and the amount of loading the rigid attachment link experiences.
• Finite element analysis allows design engineers to predict the stresses and therefore assist in selecting the right cast alloy and process, which need to be validated for the actual casting confi guration with gating system design and process parameters using casting fi lling and solidifi cation simulations during the design and development stage.
The key requirements of the part should appropri- ately match the capabilities of the process. • Semi-permanent mold provides superior strength when com- pared to sand and investment casting processes and superior surface fi nish when compared to sand casting.
• T e high stress of the application is met with aluminum permanent mold casting due to higher cooling rates and lower DAS (dendritic arm spacing) compared to sand casting, ulti- mately providing higher mechanical properties.
• Complex interior cored hollow features required for electrical wiring and tubes are made using shell sand cores, which also provide superior surface fi nish over conventional sand cores.
16 | METAL CASTING DESIGN & PURCHASING | May/Jun 2016
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