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

2 SR No.TITLEPAGE 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 CENTRIFUGAL CASTING SQUEEZE CASTING PRECISION CASTING FABRICATION OF PLASTICS DESIGN CONSIDERATIONS 16

3 Fundamentals of Casting Casting, one of the oldest manufacturing processes, dates back to 4000 B.C. when copper arrowheads were made. 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. 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).

4 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.

5 Sand Casting Terminology

6 Green Sand Casting Process

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

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

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

10 Casting Defects and Design Consideration

11 Centrifugal Casting True centrifugal casting Centrifuging

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

13 Precision Casting Plaster Molding Ceramic Molding  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.  The process produces fine detail with good dimensional accuracy and surface finish. Used to cast aluminum, zinc and copper-based alloys (low-melting temperature.)  Similar to plaster molding, except it uses ceramic as a mold which is suitable for high temperature applications. Mixture of zircon (ZrSiO 4 ), aluminum oxide (Al 2 O 3 ), silica (SiO 2 ) and other bounding agents.

14 Fabrication of Plastics Injection Molding

15 Fabrication of Plastics Hot-Compression Molding Vacuum Forming

16 Design Considerations  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.  Round interior and exterior corners to in radius (min.), prevents an edge from chipping.