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1. Manufacturing Technology II
(ME-202)
Overview of
Manufacturing
Processes
Dr. Chaitanya Sharma
PhD. IIT Roorkee

2. Title of slide
Lesson Objectives
In this chapter we shall discuss the following:
Learning Activities
1. Look up
Keywords
2. View Slides;
3. Read Notes,
4. Listen to
lecture
Keywords:

3. ©2007 John Wiley &
Sons, Inc. M P
Additional Steps After
Solidification
• Trimming
• Removing the core
• Surface cleaning
• Inspection
• Repair, if required
• Heat treatment

4. ©2007 John Wiley &
Sons, Inc. M P
Trimming
Removal of sprues, runners, risers,
parting-line flash, fins, chaplets, and any
other excess metal from the cast part
• For brittle casting alloys and when cross
sections are relatively small, appendages
can be broken off
• Otherwise, hammering, shearing,
hack-sawing, band-sawing, abrasive
wheel cutting, or various torch cutting
methods are used

5. ©2007 John Wiley &
Sons, Inc. M P
Removing the Core
If cores have been used, they must be
removed
• Most cores are bonded, and they often
fall out of casting as the binder
deteriorates
• In some cases, they are removed by
shaking casting, either manually or
mechanically
• In rare cases, cores are removed by
chemically dissolving bonding agent

6. ©2007 John Wiley &
Sons, Inc. M P
Surface Cleaning
Removal of sand from casting surface and
otherwise enhancing appearance of
surface
• Cleaning methods: tumbling, air-blasting
with coarse sand grit or metal shot, wire
brushing, buffing, and chemical pickling
• Surface cleaning is most important for
sand casting
– In many permanent mold processes, this step can
be avoided

7. ©2007 John Wiley &
Sons, Inc. M P
Heat Treatment
• Castings are often heat treated to
enhance properties
• Reasons for heat treating a casting:
– For subsequent processing operations such as
machining
– To bring out the desired properties for the
application of the part in service

8. ©2007 John Wiley &
Sons, Inc. M P
Casting Quality
• There are numerous opportunities for
things to go wrong in a casting operation,
resulting in quality defects in the
product
• The defects can be classified as follows:
– General defects common to all casting processes
– Defects related to sand casting process

9. Casting Cleaning :
•The casting is separated from the mold
and transported to the cleaning
department.
•Burned-on sand and scale are removed.
•Excess metal is removed (Fins, wires,
parting line fins, and gates).
•Subsequently the casting can be
upgraded using welding or other such as
procedures.
•Final testing and inspection to check for
any defects
Advantages:
•Improves the surface appearance and finish of casting
•Improves overall quality and functionality by removing impurities,
such as sand, scale and excess metal
Finally the sand from the mold is separated and processed through a
reclamation system for further use.

10. • Defects may occur due to one or more of the following
reasons: Fault in design of casting pattern
• Fault in design on mold and core
• Fault in design of gating system and riser
• Improper choice of molding sand
• Improper metal composition
• Inadequate melting temperature and rate of pouring

11. • Classification of Casting Defects
• Surface Defects Blow, Scar, Blister, Drop,
Scab, Penetration, Buckle
• Internal Defects Blow holes, Porosity, Pin
holes, Inclusions, Dross
• Visible Defects Wash, Rat tail, Swell, Mis run,
Cold shut, Hot tear, Shrinkage/Shift

12. • Discontinuities in
castings that exhibit a
size, shape,
orientation, or location
that makes them
detrimental to the
useful service life of
the casting
• Some casting defects
are remedied by minor
repair or refurbishing
techniques, such as
welding
• Other casting defects
are cause for rejection
of the casting
Casting Defects

13. • Metallic Projections: fins (flash), swells,
and scabs
– Fins are excessive amounts of metal created by
solidification into the parting line of the mold
Fins are removed by grinding or sandblasting
– Swells are excessive amounts of metal in the
vicinity of gates or beneath the sprue
– Scabs are surface slivers caused by splashing and
rapid solidification of the metal when it is first
poured and strikes the mold wall
Casting Defects — Metallic Projections

14. • Blowholes, pinholes, shrinkage cavities, & porosity
– Blowholes and pinholes are holes formed by gas
entrapped during solidification
– Shrinkage cavities are cavities that have a rougher
shape and sometimes penetrate deep into the casting
Shrinkage cavities are caused by lack of proper
feeding or non-progressive solidification
– Porosity is pockets of gas inside the metal caused by
micro-shrinkage, e.g. dendritic shrinkage during
solidification.
Casting Defects — Cavities

15. • Cracks in casting and are caused by hot tearing, hot
cracking, and lack of fusion (cold shut)
– A hot tear is a fracture formed during solidification
because of hindered contraction
– A hot crack is a crack formed during cooling after
solidification because of internal stresses developed in
the casting
– Lack of fusion is a discontinuity caused when two streams
of liquid in the solidifying casting meet but fail to unite
Rounded edges indicate poor contact between various
metal streams during filling of the mold
Casting Defects — Discontinuities

16. • Casting surface irregularities that are
caused by incipient freezing from too
low a casting temperature
• Wrinkles, depressions and adhering
sand particles
Casting Defects — Defective Surfaces

17. • Particles of foreign material in the
metal matrix
• The particles are usually nonmetallic
compounds but may be any substance
that is not soluble in the matrix
– Slag, dross, and flux inclusions arise from
melting slags, products of metal treatment, or
fluxes
They are often deep within the casting
– Mold or core inclusions come from sand or mold
dressings and are usually found close to the
surface
Casting Defects — Inclusions

18. ©2007 John Wiley &
Sons, Inc. M P
A casting that has solidified
before completely filling mold
cavity
Figure 11.22 Some common defects in castings: (a) misrun
General Defects: Misrun

19. ©2007 John Wiley &
Sons, Inc. M P
Two portions of metal flow
together but there is a lack of
fusion due to premature
freezing
Figure 11.22 Some common defects in castings: (b) cold shut
General Defects: Cold Shut

20. ©2007 John Wiley &
Sons, Inc. M P
Metal splatters during pouring and
solid globules form and become
entrapped in casting
Figure 11.22 Some common defects in castings: (c) cold shot
General Defects: Cold Shot

21. ©2007 John Wiley &
Sons, Inc. M P
Depression in surface or internal void
caused by solidification shrinkage
that restricts amount of molten
metal available in last region to
freeze
Figure 11.22 Some common defects in castings: (d) shrinkage cavity
General Defects: Shrinkage Cavity

22. ©2007 John Wiley &
Sons, Inc. M P
Balloon-shaped gas cavity caused
by release of mold gases during
pouring
Figure 11.23 Common defects in sand castings: (a) sand blow
Sand Casting Defects: Sand Blow

23. ©2007 John Wiley &
Sons, Inc. M P
Formation of many small gas
cavities at or slightly below
surface of casting
Figure 11.23 Common defects in sand castings: (b) pin holes
Sand Casting Defects: Pin Holes

24. ©2007 John Wiley &
Sons, Inc. M P
When fluidity of liquid metal is high,
it may penetrate into sand mold or
core, causing casting surface to
consist of a mixture of sand grains
and metal
Figure 11.23 Common defects in sand castings: (e) penetration
Sand Casting Defects: Penetration

25. ©2007 John Wiley &
Sons, Inc. M P
A step in cast product at parting
line caused by sidewise relative
displacement of cope and drag
Figure 11.23 Common defects in sand castings: (f) mold shift
Sand Casting Defects: Mold Shift

29. ©2007 John Wiley &
Sons, Inc. M P
Foundry Inspection
Methods
• Visual inspection to detect obvious
defects such as misruns, cold shuts, and
severe surface flaws
• Dimensional measurements to insure
that tolerances have been met
• Metallurgical, chemical, physical, and
other tests concerned with quality of
cast metal

30. Shell molding
• Advantages
•
• Better surface finish
• Better dimensional tolerances.
• Reduced Machining.
• Less foundry space required.
• Semi skilled operators can handle the process.
• The process can be mechanized.
Disadvantages
The raw materials are relatively expensive.
•The process generates noxious fumes which must
be removed.
•The size and weight range of castings is limited.

31. CHILLS

32. Manufacturing,
Engineering &
Hot Tears in Castings
Figure 10.12 Examples of hot tears in castings. These defects occur because the casting
cannot shrink freely during cooling, owing to constraints in various portions of the molds
and cores. Exothermic (heat-producing) compounds may be used (as exothermic padding)
to control cooling at critical sections to avoid hot tearing

33. Manufacturing,
Engineering &
Common Casting Defects
Figure 10.13 Examples of common defects in castings. These defects can be minimized or
eliminated by proper design and preparation of molds and control of pouring procedures.
Source: After J. Datsko.