1. Casting process

3. Casting process

4. Classification of solidification processes
Polymer modified cement
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e

5. Casting Principle of the process Configuration / Structure
Process modeling
Defects
Design For Manufacturing (DFM)
Process variation
Module 4a

6. Principle of the Casting Process
Module 4a

7. Casting – Principle of the process
Casting is a process in which the molten metal flows by gravity or other force into a mold and solidifies in the shape of the mold cavity.
Physics: 1. Fluid flow and interaction with solid
2. Thermal dynamics
Any material can be cast, as any material undergoes the liquid state and solid state.
Module 4a

8. Basic casting steps (very simplified):
Melt metal
Pour it into mold
Let it freeze
Furnace
Casting system

9. Casting Principle of the process Configuration / Structure
Process modeling
Defects
Design For Manufacturing (DFM)
Process variation
Module 4a

10. Casting system
Module 4a

11. Casting System – (Generic) structure
Basic components and their connections
Make a cavity
Module 4a

12. Animation
Module 4a

13. Casting Principle of the process Configuration / Structure
Process modeling
Defects
Design For Manufacturing (DFM)
Process variation
Module 4a

14. Process modeling Heat up metal to a certain temperature
Pour molten metal into mold cavity
Solidify molten metal
Module 4a

15. Heat up metal Heat metal above the melting point
Pour it into the mold cavity
Heat energy required for
heat for raising the temperature to the melting point,
heat of fusion to convert the solid to the liquid,
heat for raising the molten metal to the metal at the desired temperature ready to pour it into a cavity.
Module 4a

16. Heat up metal 3.1 Heating Period Thermal Analysis
(2) heat of fusion to convert
the solid to the liquid
3.1 Heating Period Thermal Analysis
(3) heat for raising the molten metal to
the metal at the desired temperature ready
to pour it into a cavity.
heat for raising the temperature
to the melting point
Given T0, determine the total energy H, and then set up the furnace property
Module 4a

17. Pour molten metal into mold cavity
Flow rate at the base of a sprue (energy balance:
Module 4a

18. Pour molten metal into mold cavity
Mass balance
Mass in = mass out
Q=v1 A1 = V2 A2
v2>v1, so A2<A1, so the sprue must be designed as tapered
Assumption: Fluid is incompressible.
Module 4a

19. Pour molten metal into mold cavity
Time to fully fill the mold cavity
Assumption: not consider the transient process of molten metal in the cavity.
MFT is shorter than the actual time needed to fill up the mold cavity because of the assumption
Module 4a

20. Process modeling Heat up metal to a certain temperature
Pour molten metal into mold cavity
Solidify molten metal
Module 4a

21. Solidify molten metal
Chvorinov’s rule: the time needed for the molten metal to completely solidify in the mold cavity
TST: total solidification time, min
V: volume of the casting, in.3 (cm3)
A: surface area of the casting, in.2 (cm2)
n: exponent, 2
Cm: mold constant, min.in.2 (min/cm2)
Module 4a

22. thermal properties of the cast metal
Cm is a function of
mold material
thermal properties of the cast metal
pouring temperature relative to the melting point of the metal.
Determination of Cm can be done through experiment.
The principle of such an experiment is to have a scenario that is the same as the casting and a known cavity geometry, to operate the process, and to record the Time TST.
Module 4a

23. Implication of Chvorinov’s Rule:
A casting with a higher volume-to-surface area ratio will cool and solidify more slowly than one with a lower ratio.
Module 4a

24. Casting Principle of the process Configuration / Structure
Process modeling
Defects/quality control
Design For Manufacturing (DFM)
Process variation
Module 4a

25. Defects Defect 1: incomplete filling of cavity
Defect 2: gaps in casting
Incomplete filling is caused by too fast solidification and flow blockage. Solutions: multiple pouring cups, riser, etc.
Gaps in casting is caused by a phenomenon called shrinkage. Solutions: riser, pattern allowance, etc.
Module 4a

26. The source of problems in any process involving the heat transfer
Shrinkage:
The source of problems in any process involving the heat transfer
Module 4a

27. Shrinkage  gaps and voids
Liquid
Contraction
0.5%
Further Contraction
Lack of molten metal
Different metal thermal expansion coefficients
Shrinkage  gaps and voids

28. Riser: overcoming the two defects
Casting
Cup and Sprue to pour the molten metal
Riser = Reservoir
Module 4a

29. Casting can be applied to any material
Summary of discussions so far
Principle of casting process (liquid fills up cavity, and then cool down to solid)
Casting can be applied to any material
Three processes: heat up, pour, solidify
Defects (incomplete filling, gap)
Module 4a