http://www.ruger.com/casti
ng/PDF/PineTreeCastings.pdf
Motivation
• Advantages:
– complex shapes
– good surface finishes
– close tolerances
– good for materials/shapes that are difficult to
machine since as-cast parts deliver good
dimensional control
• Disadvantages:
– expensive / slow
Economics
• Lead Time: weeks
• Production Rate: 11-1000 parts per hour
• Tooling cost: low to moderate
• Equipment Cost: low to moderate
• Direct Labor Cost: high
• Finishing Cost: not bad
Geometry
• Complex shapes, undercuts
• Wall Thickness 1mm-75 mm (40 thou to 3 inch)
• Surface Finish 125 micro inch
• Tolerances +.008
• Common in aircraft engines and firearms.
– Both are looking for good quality near net shape parts
at low to medium volume.
• Also common in Jewelry and Dentistry.
– cost is less important than unique geometry.
Design Considerations
• include draft to facilitate removal of the pattern (Bralla 5.54, fig
5.3.8)
• Make gradual changes in wall thickness
• Join walls and place ribs to avoid shrinkage locations (maintain
constant wall thickness
• Design corners for flow and wall thickness. Fillet radii > or= wall
thickness
• Follow rules for space between bosses, boss diameter, and boss
height
• Aspect ratio of passage length to wall thickness is important. 3:1
for closed passages, and 6:1 on through passages for good filling of
material.
• Internal walls should be thinner than external (so they cool first)