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details DESIGN


Strengthening Thin Walls Bolsters Magnesium Bracket


JITEN SHAH, PRODUCT DEVELOPMENT & ANALYSIS (NAPERVILLE, ILLINOIS) CASTING PROFILE


Cast Component: Tilt and steering column bracket. Process: Investment casting. Material: AZ91E-T6. Weight: 2.2 lbs.


A


n automotive parts manufacturer was developing a redesign of a two-piece steering column to eliminate the need for post machine assembly and contacted Aristo-Cast Inc. (Almont, Michigan) for help in delivering 10-20 brackets, fully heat treated, x-ray inspected and machined, in a few weeks. Aristo-Cast worked with the cus-


tomer to enhance the bracket design by eliminating machine stock and casting certain features to eliminate machining. Aristo-Cast then added the gating system and shrink factors to the design and incorporated tie bars to keep the casting from distortion during solidifi cation. A successful casting was produced in fi ve days, and after it came back from x-ray inspection as approved, the remainder of the 15 parts were produced, helping the customer stick to its aggressive schedule for develop- ment for production.


The key driver for this design was to consolidate parts by incorporating two machined diecast subcomponents and features into a one-piece casting, which was near-net shaped and lighter. • In conventional sand and permanent mold casting processes, feature placements and locations are constrained by the orientation with respect to the parting plane of the mold. In investment casting, multiple random parting plane orienta- tions are allowed, so any complex features can be cast along with the main shape.


• T e complex shapes are broken down into individual wax shapes, which can be drawn from the wax dies and then assembled together, so the fi nal assembly is an exact replica of the fi nished casting. T e process allows fl exibility of the placement of features away from the parting plane in the desired orientation from the form, fi t and functionality.


Generous fi llets and radii are essential to prevent hot tearing or cracking. • From a structural engineering standpoint, smooth transitions provide much less stress concentration, resulting in better fatigue life.


• Generous fi llets and radii also provide smoother entry of the liquid metal into the investment shell mold.


18 | METAL CASTING DESIGN & PURCHASING | Sept/Oct 2017


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