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e UN CFC – India – Zinc Die Casting

Joe Annetts

International Zinc Association

Die Design – Feed System and Thermal

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e Feed System and Thermal Design

• Feed system design along with thermal design

are elements of die design.

• Both are critical elements of the die casting

process.

• They play a major role in defining casting

quality and cost

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e Feed System Design

Casting Defects

Porosity and flow marks make up around 80% of casting defects

• Poor feed system design is the major cause of porosity.

• Poor feed system and poor thermal design and control, are the

major cause of flow marks.

Porosity Flow Marks

Macro

Micro

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e Feed System Design

• The so called “tapered runner” method – optimises feed system

design

• Developed by IZA in 1970’s.

• Accepted around the world, but penetration of the method still

limited

• “Tapered runner” refers to the continuous and smooth reduction in

cross section area from nozzle to gate.

• But there is much more to it

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DEFINE THE CAVITY FILL

PATTERN WANTED

SELECT GATE LENGTH,

POSITION TO ACHIEVE FILL

PATTERN

DESIGN RUNNERS FROM

NOZZLE TO GATE TO

ACHIEVE DESIRED FILL

PATTERN

DEFINE FILL CONDITIONS

AND CALCULATE GATE

AREA TO ACHIEVE THIS.

CALCULATE GATE

THICKNESSES

DESIGN VENTS

DIECASTING

MACHINE INJECTION

CAPACITY

PRESSURE/FLOW

LOSSES -

DISCHARGE

COEFFICIENT

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Air pushed out through vents

Gate

Good filling

pattern - air

pushed

ahead of

uniform

metal flow

Poor filling pattern

resulting in flow

around the outside

of the cavity and

air entrapment

Gate

Vents blocked off before cavity fills

Cavity Filling Pattern

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Design Runners from Gate to Nozzle

A B

C

E

F

D Nozzle

Outlet

A B

D C

G

A

T

E

Cross

Section

Area

Gate

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Flow Angle

1) Flow component

along the runner

2) Flow

component

due to metal

pressure at

the gate

Resultant metal

flow direction

FlowAngle

Runner

A Gate = length X thickness

Ain

0 1.0 2.0

Ain / Ag

Flow

Angle

(degrees)

10

30

50

70

45

For example:

1. If the ratio is

1:1 the flow angle

will be 45 deg

2. If the ratio is

2.0 the flow angle

will be 27 deg

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Calculating gate area -& defining cavity fill conditions

MACHINE

INJECTION

ENERGY

PRESSURE

LOSSES IN

FLOW

SYSTEM

ENERGY AT

GATE DEFINES

GATE SPEED

AND FILL TIME

The recommended filling conditions are:

* Plating quality castings - Gate Velocity 40 to 50 metres/ second

Cavity Fill Time 0.01 to 0.02 seconds

* Other casting - Gate Velocity 40 to 50 metres / second

Cavity Fill Time 0.01 to 0.04 seconds

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Calculation of the Optimum Gate Area - When P - Q squared data not

available

Casting Volume ( cubic mm) = Casting Weight (gms)

0.00612 gms/ cubic mm

(Density of molten zinc alloy #3 = 0.00612 gms/ cubic mm)

Select a desired combination of gate speed and cavity fill time from the above

data and then calculate the gate area by substituting in the following equation:

Gate Area ( square mm) = Casting Volume (cubic mm)

Cavity fill time (seconds) X Gate speed (mm/second)

Calculating gate area

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Design Runners from Gate to Nozzle – design features

Sprue runners Sprue cone wall

0.0 - 0.3mm thick

Cross section through a cast sprue cone

2 – 4 mm

Sprue Design

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Design Runners from Gate to Nozzle – design features

Rule 1 - Gated “Y” junction : Ain = 110% x ( Aout1 + Aout2 )

Aout1 = Aout3 +Ag1 & Aout2 = Aout4 +Ag2

Rule 2 - The runner is not gated across the whole “Y” junction, the centre part is un gated

as shown in the diagram

Ain

Aout3 Aout4 Ag1 Ag2

Ain

Aout1 Aout2

Rule - Splitting an ungated “Y” junction: Ain = 110% (Aout1 + Aout2) - this type of “Y”

junction is commonly used to split a single runner into two runners to feed two cavities

Aout1

Aout2

‘Y’ Junction

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Design Runners from Gate to Nozzle – design features

2a

a

a

10 degrees

2a 45 degrees

Runner cross section - ungated Runner cross section - gated

Gate

Recommended runner cross sections

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Design Vents

GATE = 100mm X 0.3mm = 30 sq mm

Vent Area = 10 to 20% of gate area

At 10% of gate area, vent area = 3 sq mm

At 0.05mm gate thickness, vent length = 60 mm

20mm 20mm 20mm

VENT VENT VENT 0.05 – 0.15mm GATE

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Overflow at

point of last

fill Main

runner

Gated bends

“tangential”

runners

Sprue

using

“sprue

runner”

Shock absorber

Example of a “tapered runner” shot

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Example of a short shot

Use of long, thin

gate to achieve

optimum fill

pattern

An example of a Y junction

This

area not

gated

“Short

Shot”

shows

flow

pattern

as

predicted

from flow

angle

consider

ation

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Findings from Project:

• Short Shots

• Casting Yield

• Defects linked to feed system design

• Design work done and outcomes

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Short Shots 1

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Short Shots 2

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Short Shots 3

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Casting yield = weight of casting / total shot weight X100%

Casting Runners Sprue

Overflows Casting

Total Shot Weight = 200 grams Casting Weight = 75 gms

Casting yield = 75/200 X100 = 37.5%

Casting Yield

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e Casting Yield Measurements

Factory Shots measured

Minimum %

Maximum %

Average %

1 13 46 85 57

2 6 30 49 37

3 5 30 83 48

Good Yield = 60% +

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e Feed System Design

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