Acoustic Properties of Aluminium foam

Fraunhofer-Institut für Fertigungstechnik und Angewandte

Materialforschung, Bremen

Metal Foams

Acoustic Properties - Overview Airborne Sound Structure borne Sound

Sound absorption coefficient [%]

• concrete

• glass

• Al foam

• sound absorbing

materials (PE fibres)

1

3

10

50

Loss factor [-]

• conventional Al (solid)

• Al foam

• plastics

10-4

10-3

10-2

Metal Foams

Acoustic Properties - air borne sound Sound absorption coefficient as function of excitation frequency measured for

Al foam produced according to the IFAM process

(foam density approx. 0.5 g/cm3, surface cut off)

Metal Foams

Acoustic Properties - air borne sound Sound absorption coefficient as function of excitation frequency measured for

ALPORAS foam (foam density approx. 0.37 g/cm3,

surface cut off)

Metal Foams

Vergleich der Dämpfung über die Frequenz

bei gleichem Gewicht

0

0,2

0,4

0,6

0,8

1

1,2

1,4

1,6

0 100 200 300 400 500 600

Däm

pfu

ng

[%

]

AFSDichte 0.9 g/cm^3

spez. Biegesteifigkeit 41.5 [10e4 N mm^3/kg]

Höhe=10,7 mm

StahlDichte 7.85 g/cm^3

spez. Biegesteifigkeit 0.21 [10e4 N mm^3/kg]

Höhe 1,2 mm

AluminiumDichte 2.7 g/cm^3

spez. Biegesteifigkeit 2.5 [10e4 N mm^3/kg]

Vergleich der Dämpfung über die Frequenz

bei gleichem Gewicht

0

0,2

0,4

0,6

0,8

1

1,2

1,4

1,6

0 100 200 300 400 500 600

Frequenz [Hz]

Däm

pfu

ng

[%

]

AFSDichte 0.9 g/cm^3

spez. Biegesteifigkeit 41.5 [10e4 N mm^3/kg]

Höhe=10,7 mm

StahlDichte 7.85 g/cm^3

spez. Biegesteifigkeit 0.21 [10e4 N mm^3/kg]

Höhe 1,2 mm

AluminiumDichte 2.7 g/cm^3

spez. Biegesteifigkeit 2.5 [10e4 N mm^3/kg]

Materialeigenschaften, Dämpfung

source: Karmann

Aluminium foam sandwich AFS

Metal Foams

0,5 1,0 1,5 2,0 2,50

5

10

15

20

25

30

35.( 10-4)

unfoamed

materialLoss factor

density (g/cm3)

Damping properties (structure borne sound) of p/m Aluminium foam

Metal Foams

example: arm of a textile machine

Textile machine arm with an Alporas

foam core : 1590mm x 280mm x

160mm, 60% reduced amplitude of

resonance frequency, production:

appr.1000/a source: von der Au Metallgießerei

Metal Foams

Example: sound reduction of a gear wheel

Metal Foams

gear wheel: manufacturing steps

m=4625 g m=3030 g m=3156 g (-32 %)

Metal Foams

gear wheel: 2nd generation

Metal Foams

Sound pressure level vs. rotational speed (torque = 50 Nm) Comparision: Al foam <-> CFK (carbon fibre reinforced plastic)

sound pressure

level of Al foam is

below that of CFK

for all rpm

(exception: 800

1/min).

reduction of the

sound pressure

level up to 10 dB

peak values and

general niveau are

reduced

Metal Foams

Sound pressure level vs. torque (rotational speed= 700 1/min) Comparision: Al foam <-> CFK (carbon fibre reinforced plastic)

sound pressure

level of Al foam is

below that of CFK

for all rpm values

reduction of the

sound pressure

level up to 8 dB

peak values and

general niveau are

reduced

Metal Foams

Damping of APM Aluminium hybride foam

ram of a 5-axis milling centre

aim: improvement of tracking accuracy and material removal rate

Metal Foams

tracking deviations reduced by 50%

material removal rate increased by 100%

Damping of APM Aluminium hybride foam

ram of a 5-axis milling centre

Metal Foams

Damping properties of syntactic metal foam

loss factor of syntactic INVAR foams (FeNi36)

Metal Foams

Sound velocities of syntactic metal foams

Material Density [g/cm3] Sound velocity

(longitudinal)

[m/s]

Sound velocity

(transversal)

[m/s]

AlSi9Cu3 2.70 6320 3130

AlSi9Cu3-

S60HS foam

1.26 4510 2570

Zinc alloy 410 7.14 4170 2410

Zinc alloy 410

- S60HS foam

2.24 3330 1935

reduced sound velocities

suitable as impedance matching material