Open-pore cast aluminum

In contrast to foamed metals ( metal foam ), open- pore aluminum chill casting belongs to the melt- metallurgical casting processes with lost placeholders. The morphological, mechanical, thermal, decorative and other properties of the open-pore aluminum casting differ in many aspects from known foamed metal melts or sintered metals and open up new application possibilities.

Manufacturing

Production: a) NaCl salt granulate, b) molten metal, c) machining, d) removal of NaCl, e) finished component

The manufacturing process consists of the following steps:

• Filling the mold up to a defined volume with NaCl - salt granules
• further filling the mold with molten aluminum
• conventional mechanical processing of the molded part
• Rinsing the salt out of the pores

The result is a finished molded part with an open pore structure.

The functional properties of the open-pore aluminum casting can be predetermined by a large number of parameters:

• the size of the grain of salt: from a few micrometers to a few centimeters;
• the shape of the grain of salt: chunks of natural stone, round ground salt, shaped salt, etc. a .;
• any salt mixes;
• the fill level of the mold with partial salt filling ensures a partially porous component;
• Use of application-specific mold shapes;
• Use of inserts made of metals, ceramics, glass, etc. a .;
• Variability in some parameters of a casting process;
• conventional machining and surface treatment of the porous component.

properties

In contrast to the undefined foamed light metals, the structure of the open-pore aluminum chill casting can be determined according to the laws of soil mechanics (distribution of the salt granulate in the chill). This allows a plausible computer simulation during product development. The production in the permanent mold casting process offers several advantages:

• Production of complex and precise components with the option of casting inserts;
• increased density of the alloy, a fine-grained structure of the casting and high values ​​of mechanical properties;
• Small and large series production.

The material properties of the open-pore cast aluminum allow the use of various fastening elements, e.g. B. rivet nuts.

Another advantage of open-pore cast aluminum is its flexibility with regard to possible joining processes:

• Assembling (inserting, hanging, sliding into one another);
• Filling cavities with materials (plastic injection molding);
• Press fitting and pressing (screwing, nailing, press fit);
• Forming (flanging, bending, riveting);
• Primary molding (casting);
• Soldering;
• Glue;
• Hybrid joining (combination of several joining processes).

Material example with specifically mixed pore sizes. Large pores (D) are defined by the NaCl placeholders. Small connecting pores (d) arise in the casting process. The right image shows a 2D section through a CT image in the small-pore area of ​​the component.

Current series processes allow the production of very different property profiles.

NaCl salt grain size, μm	100-200	140-315	200-400	315-630	630-1,000	1,000-1,600	1,600-3,000
material	Aluminum and aluminum casting alloys
Density, g / cm 3	1.35 - 1.22
Thermal conductivity, W / mK	30-50
Average pore size "D" (depending on the NaCl placeholder), mm	0.15	0.23	0.3	0.47	0.66	1.12	2.3
Filter fineness "d", μm (depending on the NaCl placeholder and casting process)	5	10-15	25-35	40-60	80-100	120-150	200-250
Specific surface area, m 2 / m 3	18,300	12,500	9,700	6,300	4,600	2,800	1,400
Max. Compressive strength, MPa	118	105	59	58	49	37	32
Max. Tensile strength, MPa	33	29	16	16.5	14th	12	8th

application

Filters and silencers made of open-pore cast aluminum have application-specific material-locking connections between porous and solid areas.

The main areas of application for open-cell cast aluminum are currently silencers, protective sensor housings and filters for fluids and gases with which aluminum does not react. Many other applications, such as B. vacuum tables, tools for thermoforming or decorative products for indoor and outdoor use are gradually being developed.

A molded tool part made of open-pore cast aluminum and the thermoformed plastic film

Aluminum is the most widely used material for tools used in thermoforming or in the processing of foam particles ( EPS , EPP , EPE ) into molded foam parts . Incorrectly placed or missing vent holes in such tools lead u. a. for the formation of air pockets and dents in the finished component. Molded parts made of open-pore cast aluminum do not require any ventilation holes. In addition, they are 50% lighter and more efficient in terms of cooling, heating and air permeability than molded parts made of solid aluminum with ventilation holes.

Open-pored cast aluminum opens up new application possibilities thanks to its special properties:

• adjustable, reproducible mechanical properties;
• Production of any constructions by CNC-precise shaping;
• new possibilities for function integration, such as B. Thread;
• plausible FEM simulation;
• better heat conduction than with foamed metals due to the larger proportion of material in the structure;
• definable power transmission when used in material hybrids.

This applies both to the open-pore cast aluminum as an independent material class, as well as to material-hybrid functional structures. Even in the standard version, the new material offers great potential for new applications in the following areas:

• function-integrated lightweight construction;
• multifunctional material hybrids;
• highly integrated crash elements;
• integrated heat exchanger;
• Energy and heat storage;
• Homogenization and distribution of air, fuel, etc. a .;
• Energy and vibration absorption;
• optimally tempered tools for thermoforming and plastic injection molding.

Individual evidence

1. ↑ Gesamtverband der Aluminumindustrie eV: Aluminum foams. Manufacturing, application, recycling. Ed .: General Association of the Aluminum Industry eV Merkblatt W17. Düsseldorf 2017, ISBN 3-937171-10-X .
2. ↑ Eugen Pfeifer: Open-pore aluminum chill casting opens up new fields of application . In: Federal Association of the German Foundry Industry (Ed.): GIESSEREI trade journal . Edition 3/2019. DVS Media GmbH, Düsseldorf 2019.
3. ↑ Peter Schwarzmann: Thermoforming in practice . Ed .: Illig Maschinenbau GmbH. Carl Hanser Verlag, Munich 2016, ISBN 978-3-446-44403-4 , pp. 503 .
4. ↑ Andreas Burkert: Open-pored cast aluminum for economical lightweight construction. Springer Professional, December 7, 2017, accessed March 13, 2019 .