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Sand casting
Sand casting is defined as pouring of molten metal into a sand mold (molds are generally
provided with a cavity of the shape to be made) and allowing it to solidify inside the mould.
Various patterns are used to create cavity in the molds wherein, pattern can be said as the
replica of the final object to be made with some modifications. Depending on production
quantities, different pattern materials namely wood, aluminum, ferrous metals are used in
practice. These materials are used for low, moderate and high production quantities
respectively. Figure M2.1.1 shows a typical mould arrangement for a sand mold casting.
Pouring cup
Cope
Down sprue
Riser
Cast metal in
cavity
Core
Drag
Figure M2.1.1: Typical mould arrangement for a sand mold casting
The composition of “sand” refractory is usually a mixture of high purity silica sand, bentonite
clay, organic additives, and water. The cavity is formed by packing the moulding sand around
a pattern by ramming and squeezing. Holes and internal cavities in the casting are produced
by placing an accurate strong component called cores. After the refractory has compacted or
chemically hardened, the mould is opened at the parting line and pattern is removed. The two
halves of the mould are placed together by using a pin called dowel pins. Metal is poured in
to the mould cavity through a previously prepared opening called pouring cup.
Table M2.1.1: Metal commonly used in sand casting (Source: Design for Manufacturability
Handbook by James G Bralla, 2nd Ed)
Common metals and alloys
Cast iron G1800
Tensile
strength,
MPa
124
Remarks
Cast iron G2500
172
Ductile iron (60-40-18)
410
Magnesium AZ63A
200
Copper alloys (Leaded semi
red)
235
Leaded red brass
255
Good general-purpose casting alloy; used
forfire-equipment fittings, small gears,
small pumpparts;
Aluminum (C355.0)
248
Crankcases, gear housings air compressors,
fittings
Stainless steel (CF-8M)
550
Similar to wrought 316; used for aircraft
parts,chemical processing, electronics,
nuclear equipment, food processing,
mining, fertilizer equipment, missiles
Nickel CZ-100 alloy
345
Standard grade nickel casting alloy with
excellent castability; used for pressure tight
components, pumps, valves, equipment for
processing caustics at elevated temperatures
Used where high strength is not a
requirement; best machinability, damping
properties, and resistance to thermal stress
Used for small cylinder blocks, pistons,
gear boxes, clutch plates, and light-duty
brake drums
Used for auto crankshafts, hubs, parts
requiring shock resistance
Good castability; general casting alloy
having good strength, ductility, and
toughness
For low-pressure valves and fittings,
hardware parts, brass plumbing fixtures;
Typical characteristics of a sand cast part

Complex castings can be produced by the use of sand moulds. For example: Intricate
shapes (under cuts, complex contours), both internal and external can be made in the
above method which is generally difficult to machine for achieving such shape.

The metals those can be melted can be used for casting in this method. Table M2.1.1
shows the list of metal commonly casted in the sand molding process.

Further, casting of any size and weight even as high as 200 Tons can be made in the
above method.

Cast components are usually stable, rigid and strong as compared to products which
are produced in other manufacturing process.

Generally sand mold casted products are somewhat irregular and grainy surfaces and
hence machining is required to get a better surface finish product.

Sand casting processes are used in cylinder blocks, machine tool beds, pistons, water
supply pipes, bells etc.
Design considerations and recommendations
The following important recommendations are need to be considered while designing the
sand casted products.

Shrinkage: As the molten metal cools and solidifies in the mould, the natural shrinkage
occurs. The dimension of the casted product gets reduced as compared with the mold
cavity. The amount of shrinkage depends upon the type of metal. In order to compensate
the shrinkage allowance for outer dimension, the size of the pattern is made over size
and for inner dimension like hole; the pattern is made under size. It has been observed
that shrinkage happens towards the material side. Table M2.1.2 shows shrinkage of
various metals commonly cast in sand mould.
Table M2.1.2: Shrinkage Allowance for Metals used in Sand Moulds (Source: Design
for Manufacturability Handbook by James G Bralla, 2nd Ed)
Metal
Gray cast iron
White cast iron
Ductile cast iron
Malleable cast iron
Aluminum alloys
Yellow brass
Gunmetal bronze
Phosphor bronze
Aluminum bronze
Manganese bronze
Allowance (%)
0.83-1.3
2.1
0.83-1.0
0.78-1.0
1.3
1.3-1.6
1.0-1.6
1.0-1.6
2.1
2.1

Parting line: The parting line is a continuous line around a part that separates two
halves of the mould. Straight parting lines are more economical than the stepped parting
lines as shown in the Figure M2.1.2.
Not recommended
Straight parting line
Recommended
Figure M2.1.2: Recommended straight parting line

Draft: For easy removal of pattern from the moulding sand, some degree of taper or
drafts are provided. With the provision of little or no draft, there are chances that the
pattern may damage the mould rather than slipping out smoothly. Various factors
responsible for selecting the proper drafts are: method of moulding and drawing of the
pattern, pattern material, surface smoothness and degree of precision. Table M2.1.3
summarizes the recommended draft angles for outside surface of the sand moulded
casting. Often risers are provided to compensate the shrinkage. Figure M2.1.3
Pattern
Taper surface
Pattern
Figure M2.1.3: (a) Pattern withdrawal problem for no draft (b) smooth withdrawal of pattern
from Mould
Table: M2.1.3 Draft angle for outside surface for sand molded casting (Source:
Design for Manufacturability Handbook by James G Bralla, 2nd Ed)
Pattern material
Wood
Aluminum
Ferrous
Pattern-quality level
Ramming method Normal High Normal High Normal High
Hand
Squeezer
Automatic
Shell molding
Cold cure

5°
3°
-
3°
2°
-
4°
3°
2°
3°
2°
1°
3°
2°
2°
1°
1½°
1°
-
½°
¼°
-
Placement of risers: Risers are generally attached to the heaviest section. Heavier
sections are closer to the riser and the thinnest sections are farthest from the risers due to
faster solidification in thinner section. This minimizes the chances of getting voids.
(Refer Figure M2.1.4.)
Not this
Risers
Not this
This
Risers
This
Figure M2.1.4: Incorrect and correct designs of castings and riser location

Ribs and webs: In case of heavier sections, rib intersection with the casting wall can
cause hot spot shrinks. The number of intersecting ribs should be minimized to avoid
hot spot shrinks. Whenever it is necessary to bring all the ribs to a single point, a cored
hole would help in faster solidification, thereby avoiding hot spot shrinks. (Figure
M2.1.5. to M2.1.7.)
This
Not this
Figure M2.1.5: Incorrect and correct casting-rib design.
Poor
Much Improved
Much Improved
Figure M2.1.6: Reduce the number of reinforcing ribs that intersect at one point
Poor
Better
Best
Figure M2.1.7: Design alternatives to prevent hot-spot voids at rib and casting wall
intersections.
• Corners and angles: Hot spot are most common defect in corners and angles of
casting design. Use rounded corners having same radius for both internal and external
corner. Again too much rounding promote shrink defect in the corner. In particular, in
case of T sections, larger inside radius can be used to minimize stress concentration and
hot spots. Use of dished contours one on each side of the center legs are also affective.
Further, intersection of two walls of the casting should be at right angles to each other if
possible to minimize heat concentration. This feature is clearly shown in Figure M2.1.8
& Figure M2.1.9.
Figure M2.1.8: Sharp corners cause uneven cooling
Sharp
Corner
Void
Cold spot
Severe hot spot
Not this
This
Figure M2.1.9: Avoid sharp-corner and acute angles that cause areas of uneven cooling

Wall thickness: If the metal is flowing for a longer distance in the mould, then the
section should be heavier. But heavier sections also cause problem with voids and
porosity. Keep the wall thickness as uniform as possible (Figure M2.1.10).
Internal porous area
Preferred Design
Original Design
Figure M2.1.10: Keeping wall thicknesses uniform promotes sounder castings
Table M2.1.4: Recommended wall thickness. (Source: Design for Manufacturability
Handbook by James G Bralla, 2nd Ed)
Section length
To 300 mm To 1.2 m To 3.6 m
Aluminum
3-5 mm
8 mm
16 mm
Ductile iron
5 mm
13 mm
19 mm
Gray iron, low strength
3 mm
Gray iron, 138-Mpa
4 mm
10 mm
Gray iron, 207-Mpa
5 mm
10 mm
19 mm
Gray iron, 276-Mpa
tensile strength
6 mm
13 mm
25 mm
Gray iron, 345-Mpa
tensile strength
10 mm
16 mm
25 mm
Magnesium alloys
4 mm
8 mm
16 mm
Malleable iron
3 mm
6 mm
Steel
8 mm
13 mm
25 mm
White iron
3 mm
13 mm
19 mm

Section changes: Abrupt changes in the section must be avoided. The relative thickness
of the adjoining section should be less than 2:1. If heavy section is unavoidable then a
taper of 4:1 is advisable.(Figure M2.1.11)
Bad
Good
t
>2t
t
<2t
Bad
Good
T
L= 4 (T-t)
t
>2t
If heavy section is unavoidable use 4:1 taper
Figure M2.1.11: Design rules for areas where section thickness must change

Interior wall and sections: These members should be 20% thinner than the outside
members, since they cool more slowly. ( Refer Figure M2.1.12)
Not this
This
Figure M2.1.12: Design for interior walls (20 % thinner than exterior walls)

Lightener holes: To reduce the weight in low stressed area, lightener holes can be
added.

Holes and pockets: The draft on the inside of a pocket must be twice as on the
surrounding outside surface. The depth of hole or pocket should not be more than 1.5
times its narrowest dimension if it is in the drag half of the mould and this depth should
be no more than the narrowest dimension if the hole or pocket is in the cope half of the
mould.(Figure M2.1.13 to M2.1.14)
Figure M2.1.13: Recommended hole drilling after casting (diameter less than 19 mm)
Figure M2.1.14: Extra material around the hole as reinforcement in a highly stressed section.
 Bosses and pads Bosses: pads and lugs should be minimized as it creates voids and
hot spots.(Figure M2.1.15)
Figure M2.1.15: Design suggestions for minimizing material thickness at bosses
 Cores: It is recommended to avoid the use of cores as it is expensive to make and
handle. Often use of cores are unavoidable and are used to make holes. In such case,
the core diameter should have at least equal to the surrounding wall thickness and
preferable twice the wall thickness or more. If possible, side bosses and undercuts
should be avoided. In case internal cores are used, addition of venting holes are
required for removing the gases that are generated while the core comes in contact
with the molten metal.(Figure M2.1.16 to Figure M2.1.18)
Figure M2.1.16: Minimize the need for cores as much as possible by eliminating
undercuts.
Figure M2.1.18: Avoid small cored hole
Incorrect
Correct
Figure M2.1.19: Internal pockets in castings to facilitate cleaning after casting.
 Gears, pulleys, and wheels: To minimize the stress proper balance between the section sizes
of the rim, spokes and hub must be attempted. It is recommended to have odd number of
spokes with curved in shape. Excessive surface variation is to be avoided.(Figure M2.1.20
to M2.1.21)
Figure M2.1.20: Incorrect and correct proportions of elements of pulleys and gear blanks.
Figure M2.1.21: An odd number of curved wheel spokes to dissipate cast-in stresses.

Lettering and other data: Any lettering should be parallel to the parting plane. These
data need to be placed in such a way that these will not interfere with the machining.
These can be either sunken or raised above the surface.

Weight reduction: Casting weight is minimized by removing the metal from low
stress region and adding to high stress area by the use of simple inexpensive pattern
change.(Figure M2.1.21)

Insert of different metals: It is sometime desirable in casting to incorporate a section
of different material either harder or softer than the base metal depending on the
purpose and is proves to be economical.(Figure M2.1.22)
Aluminum casting
Cast iron insert
Figure M2.1.22: A cast-iron wear-surface insert in an aluminium aircraft-brake casting.

Design to facilitate machining: Sharp corners and edges are avoided by making
sufficiently rounding edges and corners.

Machining allowance: After casting, machining is required to achieve better surface
finish. Table M2.1.5 provides the guidelines about the machining allowance.
Table M2.1.5: Guidelines for machining allowance (Source: Design for Manufacturability
Handbook by James G Bralla, 2nd Ed)
Allowance(mm)
Casting size (overall casting length),
mm
Up to 150
150-300
300-600
600-900
900-1500
1500-2100
2100-3000
Drag and sides
Cope surface
2.3
3
5
6
8
10
11
3
4
6
8
10
13
16
Cast steel
Up to 150
150-300
300-600
600-900
900-1500
1500-2100
2100-3000
3
5
6
8
10
11
13
6
6
8
10
13
14
19
Ductile iron
Up to 150
150-300
300-600
600-900
900-1500
1500-2100
2100-3000
2.3
3
5
6
8
10
11
6
10
19
19
25
28
32
Nonferrous
metals
Up to 150
150-300
300-600
600-900
1.6
2.3
3
4
2.3
3
4
5
Gray iron

Dimensional factors and tolerance recommendation: Different factors which
influence the variation of dimension of cast pieces are: use of different methods,
pattern inaccuracies and difference in mould hardness, internal stress and many more.
Table M2.1.6 provides the guidelines about various tolerances.
Table M2.1.6: Recommended tolerances are provided in under average condition. (Source:
Design for Manufacturability Handbook by James G Bralla, 2nd Ed)
Location
One side of parting line
Dimension
Tolerance
0-25 mm
25-75 mm
75-150 mm
150-230 mm
230-300 mm
300-400 mm
400-500 mm
500-600 mm
600-760 mm
760-900 mm
± 0.6 mm
± 0.8 mm
± 1.2 mm
± 1.5 mm
± 2.3 mm
± 2.6 mm
± 2.9 mm
± 3.2 mm
± 3.5 mm
± 3.8 mm
6-65 cm²
65-320 cm²
320-650 cm²
650-1600 cm²
1600-4000 cm²
4000-6500 cm²
± 0.5 mm
± 0.9 mm
± 1.0 mm
± 1.3 mm
± 1.5 mm
± 2.0 mm
0-75 mm
75-150 mm
150-230 mm
230-600 mm
600-1500 mm
Over 1500 mm
± 0.8 mm
± 1.5 mm
± 2.3 mm
± 3.0 mm
± 4.5 mm
± 6.3 mm
Area at parting line
Additional tolerance for
dimensions across
parting line
(tolerance to be
added to that above)
Dimension
Between two cores
Cores: shell, hot-box,
cold-cure, etc. (one side
of core box)
0-25 mm
25-50 mm
50-75 mm
75-150 mm
150-230 mm
230-300 mm
Over 300 mm (over 12 in)
± 0.15 mm
± 0.30 mm
± 0.45 mm
± 0.75 mm
± 1.0 mm
± 1.3 mm
± 1.3 mm plus 0.2%
Shift, mold or core; largest
casting dimension A
greater than smallest B
0-200 mm
200-450 mm
450-900 mm
900-1500 mm
± 2 mm
± 3 mm
± 5 mm
± 6 mm