| CASTING
PROCESS |
DESCRIPTION |
METALS |
SIZE
RANGE |
TOLERANCES |
TOOLING
COST |
RELATIVE
COST IN
QUANTITY |
RELATIVE
COST FOR
SMALL QTY. |
SURFACE
FINISH |
MIN.
DRAFT
REQ. |
NORMAL
MIN.
SECTION
THICKNESS |
EASE
OF
CASTING
COMPLEX
DESIGN |
EASE
OF
CHANGING
DESIGN IN
PROD. |
STATUS |
| INVESTMENT
CASTING |
Metal
mold makes wax or plastic relica. These are sprued, then surrounded
with investment material and baked out. Metal is poured in resultant
cavity. |
Most
all Castable Metals |
Fraction
of an ounce to 100 pounds |
+/-.005"
up to 3" +/- .002" there after |
$25.00 |
$500
- $20,000 |
Highest |
Medium |
60-120
RMS |
None |
Aluminum
Alloy: 0.30" Beryllium Copper: .030"
Ductile Iron: .060"
Carbon Steel: 0.090" |
Best |
Fair |
Used
for precision castings, particularly in gas turbine engines. A specialized
process usually performed in foundrys not used for other processes. |
| DIE
CASTING |
Molten
metal is injected under pressure into hardened steel dies. |
Aluminum,
Zinc, Magnesium, and limited Copper Base |
Not
normally over 3 feet sq. Some foundrys capable of larger sizes. |
.0015"/in.
Not less than .002" on any one dimension. Additional .010"
on dimensions affected by parting line. |
$25,000 |
$5,000
- $150,000 |
Lowest |
Highest |
20-90
RMS |
Aluminum:
1 to 3 degrees Zinc & Mag: 1/2 to 2 degrees |
Aluminum:
.050" Small parts .080" Med parts Zinc & Mag.: .025"
Small |
Good |
Poorest |
Very
widely used for high production of aluminum and zinc castings. An
inexpensive way of obtaining precision parts. |
| PERMANENT
MOLD |
Molten
metal is gravity poured into cast iron molds, coated with ceramic
mold wash. Cores can be metal, sand, shell or other. |
Primarily
Aluminum with some Copper Base and Cast Iron. |
Limitation
mainly foundry capabilities. Aluminum: Usually 1/2 lb. To 100 lbs. |
Aluminum
+/- .015 to 1" $8,000 add .002" for ea. additional inch.
If across parting line add +/- .010" (Small Casting) to +/-
.030" (Large Casting) |
$8,000 |
$1,500
- $75,000 |
Low |
High |
Aluminum:
125-200 RMS Iron: 200-420 RMS Copper Base: 175-225 RMS |
Aluminum:
2 to 4 deg. Iron: 3 to 5 Copper Base: 3 to 5 |
Aluminum:
.100" to .150" Iron: .187" to .250" Copper Base:
.100" to .150" |
Fair |
Poor |
Used
for moderate quantities of semi-precision castings. Is normally
less expensive than sand casting for 100's part or a few 1000 parts.
Limited applicability for ferrous metals. |
| V
PROCESS |
Cope
and Drag Method. Softened plastic is drawn to pattern. Sand is backfilled. |
Most
all Castable Metals |
All
sizes |
+/-
.020" up to 6" than +.002" per inch. Add .020"
per inch across parting line. |
$5,000 |
$3,000
- $20,000 |
Medium |
High |
125-150
RMS |
None |
0.090"
to 0.125" |
Good |
Fair |
Unlimited
pattern life. Used for medium to med high volumes. |
| SHELL
MOLD |
Resin
coated sand is poured onto hot metal patterns, curing into bonded
sand mold halves. These are removed from pattern, assembled with
or without cores, and metal is poured into the resultant cavities. |
Most
all Castable Metals |
Normal
maximum 550 sq. in. usable mold area |
Ferrous:
+/- .008" per in. 5000 up to 3" Add .003" per in.
over 3" Non-Ferrous: under 1" = +/-.004" 1"-3"
= +/-.010" 3"-6" = +/-.013" 6"-12"
= +/-.016" 12"-20" = +/-.020" Add .005"-.010"
across parting lines |
5000 |
$1500
- $25,000 |
Medium |
Medium |
Iron:
200-350 RMS Copper Base: 150-200 RMS Aluminum: 75-125 |
Outside:
0 to 1-1/2 deg Inside: 0 to 2 deg |
Non-Ferrous:
.100" Ferrous: .125" |
Good |
Fair |
Used
for production of fairly small parts for which closer tolerances
are required than are obtainable from sand castings. Widely used
for cores. |
| SAND
CASTINGS |
Cope
and Drag Method - Tempered sand is packed onto wood or metal pattern
halves; removed from pattern, assembled with or without cores and
metal is poured into resultant cavities. Various materials can be
used. |
Most
Castable Metals |
Limitation
mainly foundry capabilities. All sizes. |
0-3"
= 1/32" 3"-6" = 3/64" +6" = +1/18"
Across parting line add .020" to small castings .090"
to large castings |
$2,000 |
$50
- $15,000 |
Low |
Lowest |
Aluminum:
175-350 RMS
Copper Base: 300-560
Ferrous: 420-900 RMS |
1
to 5 |
Non-Ferrous:
.125" - .250" Ferrous: 250"-.375" |
Fair
to Good |
Best |
Most
widely used process for ferrous metals for both small and large
production runs. Various binder systems available. |
