High Pressure Die Casting (Process Level 2)

Description

THE PROCESS

Most small aluminum, zinc or magnesium components with a complex shape—camera bodies, housings, the chassis of video recorders—are made by DIE CASTING. It is to metals what injection molding is to polymers, and the two compete directly. In the process, molten metal is injected under high pressure into a metal die through a system of sprues and runners. The pressure is maintained until the component is solid, when the die is opened and the component ejected. The dies are precision-machined from heat-resistant steel and are water cooled to increase life.

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
0.01
-
50
kg
Range of section thickness
0.5
-
12
mm
Tolerance
0.15
-
0.5
mm
Roughness
0.8
-
1.6
µm
Surface roughness (A=v. smooth)
A
     
 
PROCESS CHARACTERISTICS

Primary shaping processes

True

Discrete

True

 
ECONOMIC ATTRIBUTES

Relative tooling cost

high

 

 

 

Relative equipment cost

high

 

 

 

Labor intensity

low

Economic batch size (units)

1e4

1e6

 

 
COST MODELLING

Relative cost index (per unit)

*28.5

111

 

Parameters: Material Cost = 6.21GBP/kg, Component Mass = 1kg, Batch Size = 1000, Overhead Rate = 68.3GBP/hr, Capital Write-off Time = 5yrs, Load Factor = 0.5
cost graph 

Capital cost

*1.02e5

5.092e5

GBP

Material utilization fraction

*0.75

0.8

 

Production rate (units)

*2

200

/hr

Tooling cost

*4.59e3

6.62e4

GBP

Tool life (units)

*2e4

-
1e6

 

 

SUPPORTING INFORMATION

Design guidelines

Pressure die casting allows thin walled shapes and excellent surface detail. The integrity of the material properties is less good: turbulent filling of the mold and fast cycle time can lead to shrinkage and porosity. The process can make complex shapes, but elaborate movable cores increase the tooling costs.

 
Technical notes

Two types of die casting equipment are commonly used: cold or hot. In the 'cold' process, the hot metal is held in a separate container and passed to the pressure chamber only for casting. In the 'hot' process the reservoir of hot metal is held in the pressure chamber, the prolonged contact times restrict this process to magnesium and zinc alloys.

 

Typical uses

Record player and video player chassis, pulleys and drives, motor frames and cases, switch-gear housings, housings for small appliances and power tools, carburetor and distributor housings, housings for gearboxes and clutches.

 

The economics

High tooling costs mean that pressure die casting becomes economic only for large batch sizes, but the process is one of the few that allows thin-walled castings. Aluminum has a small solubility for iron, limiting die life to about 100,000 parts. Magnesium has none, giving almost unlimited die-life. Gravity die casting has lower equipment costs but is usually less economic because the molten metal has to be more fluid—and thus hotter—to fill the mold well, this reduces the production rates.

 

The environment

Aluminum, zinc and magnesium scrap can all be recycled. The process poses no particular environmental problems.

 
Links

Reference

MaterialUniverse

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