details DESIGN
Stiff Requirements Guide Casting Conversion
JITEN SHAH, PRODUCT DEVELOPMENT & ANALYSIS, NAPERVILLE, ILLINOIS CASTING PROFILE
Cast Component: Front truck cab support bracket. Casting Process: Green sand.
Material: 80-55-06 ductile iron. Weight: 35.3 lbs. Dimensions: 18 x 16 x 9 in.
Iron Works, Lethbridge, Canada, represented a consolida tion of three castings, seven welded assemblies and 16 parts into two castings, zero welded assemblies and four low-level parts. Changing the material from 65-45-12 to 80-55-06 ductile iron increased both ultimate tensile and yield strength by about 23%. With wall thicknesses of 0.25 in., the new com ponent is 7 lbs. lighter than its 42-lb. predecessor. Intricate coring and robotic grinding provided the customer the near- net-shape part without machining. T e total cost reduction was 35%.
D
aimler Trucks, Portland, Ore., wanted to consolidate the front bracket for its mid-size and large trucks into a one-size-fi ts-all design. To do so, it needed to be 10 times stiff er than the multiple- piece welded tube structure used on the Western Star platforms. T e fi nal part design delivered by casting supplier Lethbridge
Generous radii and fi llets provide smooth transitions at intersecting junctions and web corners.
• Stresses in most structural components, especially those loaded dur- ing bending, are highest on the surface. Smooth transitions at inter- secting junctions and web corners help reduce the stress concentra- tions to make the casting more durable during fatigue loading.
• In good casting design, fi llets and radii are driven by the minimum thickness of the two adjoining sections, typically 0.125 to 0.25 in.
Cross-ribs stiffen the structure.
• To eliminate tooling complexity, cross-ribs are located perpendicular to the parting plane of the pattern and corebox so they can be drawn from the mold without creating back draft, which would require a core or loose piece.
• Cross-ribs should be thinner than the base casting section so they can be fed completely by the liquid metal.
22 | METAL CASTING DESIGN & PURCHASING | Mar/Apr 2012
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68