When a complex 17-piece steel weldment that was difficult to fixture began experiencing warpage and corrosion issues, it was time to change. The truck manufacturer OEM looked into converting the front bracket extension structure into a cast part. Working with foundry engineers at Monarch Industries Ltd. (Winnipeg, Manitoba, Canada), the OEM redesigned the bracket extension into a one-piece ductile iron casting, which provided multi-functionality, improved the lead time, reduced costs by 43%, eliminated the fabrication space and bottleneck, and gave better dimensional stability, tolerances, and aesthetics.

Simple parting line and core design accommodates multiple attachment points.

• The bracket has a single web design with a lightening pocket. Placing the parting plane through the web eliminated the core and offset parting. Just two cores were required.
• Attachment points were included in the design to facilitate being bolted on to various sub-assemblies, including the front frame crossmember, steering system, front engine crossmember, front suspension, cool pack, hood, and bumper. 

The engineering decision to have cored or machined hole features depends on the hole dimensions and location of features.

• Engineers consider the hole diameter and thickness, and how close to or far from the parting plane the hole is when deciding how to manufacture the part.
• The smaller holes in the front bracket were drilled because of their relative size and location from the parting plane being short.
• The larger openings were self-cored because of their size and location being coplanar to the parting plane. 

Adding strengthening ribs with corner radii and fillets provides better stiffness and fatigue life.

• Fillets and corner radii—typical features of castings—add to the aesthetics while also structurally reducing the stress concentration and providing smooth transitions at X, Y, L, T junctions and better fatigue performance than weldments, which typically have sharp corners.
• The bracket’s ribs provided extra stiffness and torsional strength—better than the weldment. They were designed such that they can be drafted normal to the parting pane.

Click here to see this story as it appears in the September/October 2019 issue of MCDP.