ppt 4 Flashcards
Functions of Patterns
-molding the gating system
-establishing the parting line
-making core provisions
-establish locating points
-minimize casting defects attributable to the pattern
-economy in molding
Types of Patterns
-single/ loose pattern/ solid
-gated pattern
-match plate pattern
- cope and drag pattern
-special patterns and designs
are single copies of the casting but incorporating
the allowances and core prints necessary to
producing the casting.
-single/ loose pattern/ solid
Gating systems are hand-cut in the sand.
-single/ loose pattern/ solid
The gating system is actually a
part of the pattern and eliminates
hand cutting of the gates
-gated patterns
an improvement on ungated loose
patterns.
-gated patterns
Large quantity production of small castings
requires this type of pattern or more specialized
types of pattern equipment.
-match plate pattern
The cope and drag portions of the pattern are
mounted on opposite sides of a wood or metal
plate conforming to the parting line.
-match plate pattern
___________ are also integrally cast, in which
case pattern and plate are cast as one piece in
sand or plaster molds
-match plate
Consist of the cope and drag parts of the pattern
mounted on separate plates.
-cope and drag pattern
The halves of the mold may be made separately by
workers on different molding machines
-cope and drag pattern
Separate pattern plates require accurate alignment of
the two mold halves by means of guide and locating
pins and bushings
-cope and drag pattern
The shape, finished sizes, and other details
pertaining to a certain casting are usually obtained
from a _______
drawing
Methods or procedure are planned in arranging
and constructing the pattern so that ________
may be obtained at a ___________.
good castings; minimum costs
Considerations in Making a Pattern
Corners, angles, and section thickness
Shrinkage/ compaction
Flat surfaces
Parting line
Draft
Tolerance
Machining allowance
[Considerations in Making a Pattern] Corners, angles, and section thickness
Sharp corners, angles and fillets should be
avoided as they cause cracking and tearing
during solidification.
Fillet should be selected to reduce stress
concentration and to ensure proper liquid
metal flow
_______ are concave connecting pieces
used at the intersection of two surfaces
that form an internal angle or corner
fillets
Three Stages of Volume Change between pouring the
molten metal and retrieving the casting from the mould:
- Liquid changes which take place during the fall in
temperature from pouring to freezing or solidification. - Shrinkage during freezing (solidification)
- Solid shrinkage, or contraction, on the solidified
casting as it cools to atmospheric temperature.
[Considerations in Making a Pattern] Shrinkage/contraction
Allowance for shrinkage during solidification and
cooling to room temperature to achieve desired
casting dimension.
[Considerations in Making a Pattern] Flat Surfaces
Large flat areas should be avoided, as they warp
because of temperature gradients during cooling or
develop poor surface finish because of uneven flow
of metal
[Considerations in Making a Pattern] Parting Line
▪ It is desirable for the parting line to be along a flat plane.
▪ The location of the parting line influences mold design,
ease of molding, number and shape of cores, method of
support and the gating system
[Considerations in Making a Pattern] Draft
▪ A small draft (taper) is provided in the
sand mold pattern for easy withdrawal of
the pattern without damaging the mold.
▪ Draft angle ranges from 0.5 to 2
[Considerations in Making a Pattern] Tolerance
▪ The permissible variations in the dimensions of a part
▪ Depend on the particular casting process, size of the
casting and type of pattern used
▪ Should be as wide as possible but within the limits of
good part performance
[Considerations in Making a Pattern] Machining Allowance
▪ For castings that require additional
finishing operation such as machining,
allowance should be made.
▪ Allowances usually range from 2 mm to 5
mm for small casting, to more than 25
mm for large casting
