CASTING DEFECTS Subject MPII Submitted by Jaymin Panchal

CASTING DEFECTS Subject : MP-II Submitted by, Jaymin Panchal Submitted to, A. R. Patel M. K. Patel 1

SR No. TITLE PAGE NO. 1. FUNDAMENTALS OF CASTING 3 2. CASTING PROCESS 4 3. SAND CASTING TERMINOLOGY 5 4. GREEN CASTING PROCESS 6 5. SOLIDIFICATION TIME 7 6. CASTING DEFECTS 8 7. CASTING DEFECTS AND DESIGN CONSIDERATION 10 8. CENTRIFUGAL CASTING 11 9. SQUEEZE CASTING 12 10. PRECISION CASTING 13 11. FABRICATION OF PLASTICS 14 12. DESIGN CONSIDERATIONS 16 2

Fundamentals of Casting • Casting processes basically involve the introduction of a molten metal into a mold cavity, where upon solidification, the metal takes on the shape of the mold cavity. • Casting, one of the oldest manufacturing processes, dates back to 4000 B. C. when copper arrowheads were made. • Simple and complicated shapes can be made from any metal that can be melted. • Example of cast parts: frames, structural parts, machine components, engine blocks, valves, pipes, statues, ornamental artifacts…. . • Casting sizes range form few mm (teeth of a zipper) to 10 m (propellers of ocean liners). 3

Casting Processes • Preparing a mold cavity of the desired shape with proper allowance for shrinkage. • Melting the metal with acceptable quality and temperature. • Pouring the metal into the cavity and providing means for the escape of air or gases. • Solidification process, must be properly designed and controlled to avoid defects. • Finishing, cleaning and inspection operations. • Mold removal. 4

Sand Casting Terminology 5

Green Sand Casting Process 6

Solidification Time Ø Where C is a constant that depends on mold material and thickness, metal characteristics and temperature. Ø Solidification time = C(volume/surface area)2 7

Casting Defects Hot tearing – hot tearing, cracking, occurs if casting is restrained from shrinking, during solidification. 8

Casting Defects Hot spots – thick sections cool slower than other sections causing abnormal shrinkage. Defects such as voids, cracks and porosity are created. 9

Casting Defects and Design Consideration 10

Centrifugal Casting Centrifuging True centrifugal casting 11

Squeeze Casting Ø Cast parts have good mechanical properties, good dimensional accuracy, fine microstructure, good surface finish. 12

Precision Casting Ceramic Molding Ø Similar to plaster molding, except it uses ceramic as a mold which is suitable for high temperature applications. Mixture of zircon (Zr. Si. O 4), aluminum oxide (Al 2 O 3), silica (Si. O 2) and other bounding agents. Plaster Molding Ø Plaster of Paris (gypsum) is used as the mold material, other components are added to improve the strength and reduce the setting time. The pattern is dried at 400 o. F and the two halves are assembled and molten metal is poured into the cavity. Ø The process produces fine detail with good dimensional accuracy and surface finish. Used to cast aluminum, zinc and copper-based alloys (low-melting temperature. ) 13

Fabrication of Plastics Injection Molding 14

Fabrication of Plastics Hot-Compression Molding Vacuum Forming 15

Design Considerations Ø Wall thickness should be kept uniform if possible. Non uniform wall thickness could lead to warpage and dimensional variations. Minimum recommended; . 025 in or. 65 mm, up to. 125 for large parts. Ø Round interior and exterior corners to. 01 -. 015 in radius (min. ), prevents an edge from chipping. 16