1. Casting Processes Example Parts Requirements Terminology
Cooling Curves
Solidification Time
Fluidity
Design Considerations
Defects
Processes

2. Pouring Molten Metals
Non-ferrous application: probably zinc

3. Example of a large casting
Note all the subsequent
machining operations

6. Cast Products links http://www.texasmetalcasting.com/
Video link: stainless steel casting

7. Requirements Mold Cavity: single or multiple use Melting Process
Pouring Technique
Solidification Process
Mold removal
Clean, Finish, Inspection

8. Terminology Weir Core Print Draft Core Box Chills Insulation Dross
Better surfaces on bottom of casting
Trap

9. Cooling Curve
Pure
Eutectic
Material

10. Metal Properties
Metals are a crystalline structure that have a primary bond: metallic bond.
Rate of cooling determines the size of the crystal.
Size and shape of the crystal determines the mechanical properties.

11. Crystal Shapes Alloyed Pure Metal
Alloys tend to segregate to the center of the casting during cooling
Small, somewhat uniform crystals form the skin sections
Larger, directional, columnar crystals “grow” towards the center

12. Prediction of Solidification Time
Important for strength properties
Cast part should solidify before the risers
Most efficient design of risers minimizes surface area with required volume.

13. Prediction of Solidification Time
Chvorinov’s rule: V = volume A = surface area n = 1.5 to 2 B = constant for metal cast, mold material and casting conditions

14. Sprue, Runner and Riser Design
The art is progressively becoming
a science with the aid of
computer simulation

15. Fluidity Characteristics of the molten metal
Viscosity: temperature sensitive
Surface Tension: Oxide Films
Inclusions
Solidification patterns of the alloy

16. Fluidity Casting Parameters Mold design: sprue, riser, etc.
Surface characteristics of mold materials: heating mold means more fluidity, but slower cool, and less strength
Degree of superheat
Rate of pouring: slower = lower fluidity

17. Design Considerations
Parting Line Location
Section Thickness
Flat Areas
Shrinkage
Draft
Machine Allowances

18. Parting Plane Affects:
Number of cores required
Effective and economical gating
Methods used to support cores
Final dimensional accuracy
Ease of Molding

19. Section Thickness
Hot Spots
Angles

20. Flat Areas
Warping, surface finish, temperature gradients. Solution: break up with ribs, serration
Minimums:
steel: 3/16”
Gray Cast:: 1/8”
Aluminum: 1/8” alloys: 0.050”
Zinc Alloys: ”

21. Shrinkage Problems
Cavities
Allowances

22. Machine Allowances Draft: Bosses and Spot Faces
0.5 to 2 degrees
1/16”/foot to 3/16”/foot are typical
Bosses and Spot Faces
Tolerances: 1/32” for small castings, 1/4” for large

23. Defects Metallic Projections: flash, swells
Cavities, blowholes, and pinholes
Discontinuities: cracks, tears, cold shuts (knit lines), incomplete runs
Defective surfaces: sand layers, oxides
Inclusions: form stress risers: slag etc.

24. Processes Single Use Molds Sand Casting Plaster Mold Ceramic Mold
Investment Casting
Lost Foam
Multiple Use Molds
Permanent Molds
Die casting
Centrifugal casting
Continuous casting