High pressure die casting (Process Level 3)

General

DESIGNATION

Casting: die casting

THE PROCESS

In PRESSURE DIE CASTING, molten metal is injected under high pressure into a metal die through a system of sprues and runners and pressure is maintained during solidification. Afterwards, the die halves are opened and the casting is ejected. Because of the high pressures involved, the two die halves are held together by a high force and locked with toggle clamps. The dies are precision machined from heat resistant steel and are water-cooled. They often include several movable parts and are therefore complex and expensive.

Two types of die casting machines are used. In the 'hot chamber' or gooseneck process, the molten metal is held in a furnace in which a gooseneck chamber is submerged. Upon each cycle, the gooseneck is filled with metal which is then forced into the die. Because of the prolonged contact between the metal and the injection system, this process is restricted to zinc-base alloys. In the 'cold chamber' process (see figure above), metal is melted in a separate furnace and then transported to the die casting machine. The cold chamber process can be used for a variety of alloys. Because of internal porosity, die castings cannot be heat-treated. The process is very competitive for producing large quantities of thin-walled castings.

PROCESS SCHEMATIC

die casting schematic
Pressure die casting
 

SHAPE

Circular prismatic

True

Non-circular prismatic

True

Solid 3-D

True

Hollow 3-D

True

 
PHYSICAL ATTRIBUTES
Mass range
0.05
-
15
kg
Range of section thickness
1
-
8
mm
Tolerance
0.15
-
0.5
mm
Roughness
0.8
-
1.6
µm
Adjacent section ratio
1
-
2
Aspect ratio
1
-
30
 
PROCESS CHARACTERISTICS

Primary shaping processes

True

Machining processes
False

Prototyping

False

Discrete

True

Continuous

False

Tertiary 

False

 
ECONOMIC ATTRIBUTES

Economic batch size (units)

5e3

1e6

 

Labor intensity

low

 

 

 

 
COST MODELLING

Relative cost index (per unit)

14.4

87.2

GBP

Parameters: Material Cost = 4.97GBP/kg, Component Mass = 1kg, Batch Size = 1000, Overhead Rate = 62.95GBP/hr, Capital Write-off Time = 5yrs, Load Factor = 0.5
cost graph 

Capital cost

1.17e5

5.86e5

GBP

Material utilization fraction

0.75

0.85

 

Production rate (units)

2e4

1e6

/hr

Tool life (units)

2e4

-

1e6

 

Tooling cost

5.27e3

-

7.61e4

GBP

 

SUPPORTING INFORMATION

Design guidelines

Shape complexity can be high, but elaborate movable cores increase tooling cost.

 

Technical notes

Usually restricted to lower melting point alloys (Tm<1200K); most usually aluminum and zinc alloys. High melting point alloys can be processed with a variant called the Ferro Di process

Wall thicknesses should be as uniform as possible. Excellent surface detail. Die castings are not renowned for their metallurgical integrity. Turbulent filling and fast cycles mean that castings exhibit gas and shrinkage porosity.
 

Typical uses

Automotive applications: carburetor and distributor bodies, clutch and gearbox housings; electrical applications: motor frames and cases, switchgear housings; general applications: pulleys, rotating parts, record player parts, etc.

 

The economics

Tooling cost range covers small, simple to large, complex dies. Production rate depends on complexity of component and number of cavities.

 

Links

MaterialUniverse

Reference

Shape

No warranty is given for the accuracy of this data.  Values marked * are estimates.


January 13, 2016