MIND OF METAL: ALUMINUM

Aluminum. Common! But NOT boring. We’ll intro this blog post with some of the basics about this amazing metal and its alloys, and then move on to what we suspect will really grab you — its utility in 3D printing and design considerations you should have in mind when using it.

This article is divided into 4 sections, and each one is relevant to 3D printing:


THE VIRTUES OF ALUMINUM

The Fuller Moto 2029 Majestic features 3D printed aluminum parts on a retro frame based on the French classic 1929 Majestic.
Possible replica of the aluminum cutlery used by Napoleon III.


Did you know that Aluminum is the most abundant metal in the Earth’s crust? So perhaps it isn’t surprising that humanity has found so many uses for it. Aluminum is the most widely used metal in the world. In fact, no other metal compares when it comes to the sheer span of its applications. 

Aluminum is so useful and so popular because it is:

  • Lightweight
  • Strong
  • Corrosion resistant
  • Durable
  • Ductile
  • Malleable
  • Conductive
  • Odorless

For a metal, Aluminum has a low melting point (660°C /1220°). This is higher than PEEK, so in a sense, aluminum is a midpoint between plastics and more robust metals like stainless.

Did you know that Aluminum is also an environmentally conscious choice? The Aluminum Association estimates that 75% of the aluminum ever produced is still in use today!

It is 100% recyclable and recycling it requires only 5% of the energy required in new aluminum production. Importantly, recycling Aluminum does not compromise its natural properties.

Interesting fact about aluminum…

Despite the fact that it is so common, it wasn’t extracted into useable metal form until the 1800’s. That’s because raw aluminum doesn’t exist naturally. It has to be extracted (most popularly today from bauxite). At the time, aluminum was considered even more valuable than gold. Napoleon III served his guests with aluminum (not gold) cutlery not unlike the set shown in the picture in the margin.


THE VAST SPECTRUM OF ALUMINUM ALLOYS

Made in Canada Quad-Antennae produced jointly by Burloak, MDA and the NRC.

Even though you can find aluminum everywhere – from muffin tins to your iPhone — it is most commonly used in alloy form.

Why? Because while aluminum is common and useful, it is not the ‘best-in-class’ when it comes to different features. For example, while aluminum’s thermal conductivity (237) is comparatively high, it is only about 60% of copper. Creating alloys that blend aluminum and copper (series 2xxx) enhances thermal conductivity.

Each standard aluminum alloy designation was designed and optimized for certain uses. Alloy 6061, for instance, is suited to structural applications, and alloy 7075 for aerospace. Companies even develop custom aluminum alloys to better suit their needs (E.g. Alferium, Magnox, and Titanal).

Aluminum is broadly categorized into 3 groups: Commercially pure, heat treatable, and non-heat treatable alloys. Aluminum series include:

  • 1xxx: Commercially pure (99%) aluminum, most commonly used in transmission (power) lines and food packaging
  • 2xxx: Heat treatable alloy,. Copper is used as the principle alloying element and can be strengthened significantly through solution heat-treating.  These alloys possess a good combination of high strength and toughness, but do not have the same degree of atmospheric corrosion resistance as many other aluminum alloys. 
  • 3xxx: Manganese is the major alloying element in this series, often with smaller amounts of magnesium added.  However, only a limited percentage of manganese can be effectively added to aluminum.
  • 4xxx: 4xxx series alloys are combined with silicon, which can be added in sufficient quantities to lower the melting point of aluminum, without resulting in brittleness.
  • 5xxx: Magnesium is the primary alloying agent in the 5xxx series and is one of the most effective and widely used alloying elements for aluminum.  Alloys in this series possess moderate to high strength characteristics, as well as good weldablility and resistance to corrosion in the marine environment. 
  • 6xxx: Heat treatable alloy. The 6xxx series are versatile, heat treatable, highly formable, weldable and have moderately high strength coupled with excellent corrosion resistance.  Alloys in this series contain silicon and magnesium in order to form magnesium silicide within the alloy. Extrusion products from the 6xxx series are the first choice for architectural and structural applications.
  • 7xxx: Zinc is the primary alloying agent for this series, and when magnesium is added in a smaller amount, the result is a heat-treatable, very high strength alloy. 
  • 8xxx: This series for wrought aluminum is a bit of a catch all for aluminum alloys containing elements not mentioned above, or a more diverse variety of elements (like alloy 8006)


THE IMPORTANCE OF ALUMINUM POWDER

Why
You may already realize that certain metal printing technologies (such as SLM, DMLS and DED) require aluminum powder even when the component being manufactured is of a different metal.

If you would like a quick overview of metal additive processes, please click here.

How
While there are a number of ways to create metal powder (gas atomization, granulization, electrolysis, chemical), the best aluminum alloy powders are manufactured by inert gas atomization, a process that shoots an intense blast of inert gas at droplets of liquefied metal (blast a shot of air at running water and you’ll get the basic idea). Proper quality controls are designed to ensure uniform powder morphology, which is critical in ensuring optimal material printed density.

Types
The powders shown in the accompanying pictures are of the AlSi10Mg alloy by Osprey Saandvik, and show a near uniform size and shape. The AlSi10Mg powder is similar in composition to alloy 6061, and is well suited to thin walled and complex geometries, and lightweight aerospace and transportation applications.

The AlSi10Mg was designed for powder bed fusion 3D printing, and when used with SLM printers like the EPlus3D line of SLM printers can achieve densities of 99.9%.

Other aluminum powders include AlSi7Mg from Osprey Saandvik, and a series of alloys by Rusal that include 2xxx series AlCu RS-230, and higher strength AlSiCu RS-320.

Quality
The aluminum powder is melted and fused together with a laser to produce metal parts of equal quality to machined models. 3D-printed aluminum doesn’t look like traditional shiny milled aluminum. Instead, it has a matte gray finish with a slightly rougher and less defined surface. The subtle sparkle you’ll notice is caused by the silicon in the alloy.

Please contact us for more information about the EPlus3D EPM line of SLM printers, and Osprey Saandvik and Rusal powders.


3D PRINTED ALUMINUM PARTS

3D printed pistons tested in the Porche 911 GT2 RS could add 30HP
Heat exchanger by Eplus3D and the Harbin Institute of Technology
Complex structural supports like this one designed by Eplus3D application engineers adds structural rigidity without increasing the net weight.

One of the biggest advantages of metal 3D design and printing is the accommodation of complexity. That complexity take the form of nesting – creating parts with internal channels and features that aren’t possible to manufacture any other way – and lightweighting.

Both of these features have tremendous practical applications. You can print a multi-part assembly as one unit, drastically cutting down in manufacturing and assembly time, and developing a more economical and efficient parts overall.

Here are a just a few areas where 3D printed aluminum is blazing a path forward.

Engine components
Aluminum’s light weight and high thermal conductivity makes it an ideal choice for engine blocks and components. The prime enemy of any engine (other than neglect or accidents) is heat, so thermal conductivity is important to minimize wear due to excessive heat. The majority of engine’s currently in production are made of aluminum, as opposed to cast iron.

Additive’s strengths have allowed for a rethink of a great number of engine components, including the design of pistons to enhance performance and cooling, connecting rods, intake manifolds, and so forth. Ford designed a high performance manifold was uniquely suited to 3D printing. The manifold allows for the greater air intake required by an all-aluminum 3.5 litre 914 horsepower V-6. 3D printing it also reduced waste and cut back on prototyping time and cost.

Other Auto Components
Still related to automotive use, 3D printed aluminum has found growing use in other automotive applications. For example, Eplus3D designed a mono-form heat exchanger in collaboration with Harbin Institute of Technology. This heat exchanger was designed for an award winning electric race race, and is created as a solid unit, reducing the potential for ruptures or leaks due to seams.

Drone/UAV Components
Lightweight aluminum components in drone production increase the drone’s durability and allow greater versatility for attachments (such as cameras). While cost conscious producer of personal use drones still rely heavily on polymer components, the use of aluminum enhances the drones robustness and re-usability for commercial application.

For example Cobra Aero, on contract for the American military, is 3D printing a new engine casing for its UAV product.

Robotics
Robotics is very broad field that ranges from from articulated industrial robotics used for fabrication, to the the creation of endo-skeletal structures for more classically humanoid robots, or exoskeletal assists, the use of 3D printed aluminum components is almost a no brainer. Here again additive design grants broad benefits when it comes to enhancing strength and lightweighting.

Prosthetics
The variability of the human body generates a high requirement for custom components when considering the production of prosthetics. Metal 3D printing makes use of lightweight, durable aluminum components more accessible than ever before.


DESIGN CONSIDERATIONS FOR ALUMINUM PRINTING

You will want to account for each of these in your product or part design. While many of the considerations apply to metals generally, work by Eplus3d application engineers have found that aluminum is a comparatively more accommodating material to work with, so additional comments have been included to distinguish aluminum.

This cut-away of monoform conduit box by Eplus3D illustrates shell thickness.
  • THICKNESS
    As a rule of thumb, minimum wall thickness of any aluminum part should be 1mm. However, where post-processing is needed, wall thickness may need to be increased. (E.g. A part that will be milled or blasted before use.)

  • DETAIL
    Aluminum lends well to printing very fine detail.

    While not the only application, this is a great benefit if the printed components need to be identified with a serial number. Fine detailing like engraved or embossed text will print very nicely if you outline the letters with a line thickness of 40µm and use a minimum height of 40µm (and/or a minimum depth of 15µm).

    Some SLM printers like the Eplus3D’s EPM line can actually print in detail as small as 25µm.

  • GEOMETRY
    Always an important consideration when 3D printing. Apart from aesthetics, part geometry can govern part strength, surface adhesion, support use and the amount of post-processing. Generally speaking, it is better to use steep angles (greater than 35°) as this makes it easier to achieve a quality smooth surface.

    A note about supports…
    The use of supports is a subset of part geometry but is important enough to warrant further consideration. As useful as supports can be, ideally the designer wants to minimize if not completely remove the need for supports. Supports are useful to keep the model rigid while building and prevent internal stress and deformations, but….

    They need to be removed. And support structure removal can require a lot of work, which is compounded by the number of supports. With DMLS technology, a high-powered laser sinters Aluminum powder to form the print. However, support structures are required, (and in fact, are automatically generated and 3D printed. They keep the model rigid during printing and prevent internal stress and deformations, but post print, manual removal of supports may require grinding, sanding and sandblasting for smooth finish.

    Interestingly, Eplus3D application engineers have noted that printing aluminum using the EPM series SLM printers have been more accommodating of flatter angles (to almost 15°, versus the normal angle of 45°). This benefits the designer by support reduction, and further facilitation of design complexity such as larger circles or holes.

    For more information on post-processing, please review our article: Mind of Metal: Post-Processing.

  • ESCAPE HOLES
    It is usually advisable to plan for lower overhang angles and bigger holes than when 3D printing steel.

If that wasn’t more than you wanted to know about Aluminum 3D printing, we’d love to the chance to answer your questions! Contact us.

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