Examining the Mechanical Properties of 3D Printed Metals

A wide variety of metals are available in powder form for use in 3D printing. This includes stainless steel, titanium, aluminum, nickel and cobalt-chrome alloys, tool steels, tungsten and precious metal alloys.Metal additive manufacturing is gaining traction for applications from nuclear safety to aerospace. But scientists have yet to fully understand what happens within the printed material.

Tensile Strength

Using 3D printing, metal components can be produced to a high standard. The process is far more environmentally friendly than traditional manufacturing, and it reduces the amount of material wasted. It is no wonder that companies in the aerospace industry and other fields are increasingly turning to this method of production.

One question that remains is, how strong are these printed metals? The answer may surprise you. A team of researchers from Michigan Technological University has investigated the tensile strength of materials printed with open source hardware. They printed two different materials, acrylonitrile butadiene styrene (ABS) and polylactic acid (PLA). They also examined various infill patterns for these specimens to determine their mechanical properties.

The tensile test measures how much the printed material can be stretched before it breaks. It is important to know this value because it gives you an idea of how well the printed material will perform in its intended use. To measure this, the researchers used a universal testing machine equipped with a load cell capable of measuring up to 30 kN. They tested four specimens of each material at varying printing angles to obtain the values for elongation at yield, tensile strength, and elastic modulus.

Flexural Strength

Unlike the compressive strength which applies force inward to crush, flexural strength applies side force in order to bend a part. Depending on the material used and its application, flexural strength can vary from very low to extremely high.

From engine components utilised by aerospace manufacturers to custom-made prosthetic devices for patients suffering from scoliosis, it is clear that this technology is able to provide high-strength metal parts with much more ease and accuracy than traditional manufacturing methods.

Compressive Strength

Metal 3D printing has become a powerful, flexible production method for producing a range of complex metal components. The computerized, layer-by-layer building process can produce a variety of materials and create solid metal parts that rival traditional manufactured components in strength and durability.

A new study reveals that 3D-printed metals are capable of achieving very high compressive strengths — up to 1.4 gigapascals. This is a significant figure that exceeds the tensile strength of carbon steel alloys commonly used to make automotive parts and sharp professional cutlery.

The research, published in the journal Acta Materialia, focuses on a particular type of metallic alloy, called maraging steel. This alloy combines high tensile strength with good fatigue properties. To achieve these results, researchers analyzed how the cooling rates of the alloy during 3D printing affect its crystal structure. They studied the behavior of the alloy using powerful X-rays generated by cyclic particle accelerators, known as synchrotrons, at two separate facilities, Argonne National Laboratory’s Advanced Photon Source and Paul Scherrer Institute’s Swiss Light Source.

They found that varying the laser power and printing movement settings significantly influenced the cooling rate of the printed metal, impacting its crystal structure. Also, they used the same X-ray technique to examine the effects of different infill shapes and volume percentages on the mechanical performance of the printed parts. They discovered that strut diameter and length, along with infill inclination angle and the slenderness ratio of the printed struts significantly influenced their compression performance.

Impact Strength

The strength of 3D printed metals varies depending on the printing parameters and material used. The crystal structure of the material, along with its microstructure and surface finish, all affect the impact strength of 3D-printed metals.

These materials have good corrosion resistance, tensile and compressive strength. Other common metals that are suitable for metal 3D printing services include titanium and aluminium alloys, both of which have high tensile and compressive strengths as well as a high strength-to-weight ratio.

While the benefits of using 3D printing to produce metal parts are clear, some researchers have struggled to get the best performance from these processes. They’ve struggled to understand how to steer the metal toward particular kinds of crystals, which could result in better mechanical properties and a reduced need for support structures that would add weight to the final part. They’ve also struggled to optimize the topology of parts, which helps create lightweight components and minimize the need for waste material.

Some studies have shown that the print orientation of the material can significantly affect its Izod impact strength. They found that the samples with a 45-degree print orientation absorbed more energy before breaking, while the ones with a horizontal orientation exhibited less energy absorption.

Other studies have shown that the addition of a certain type of filler or a change in printing technique can increase the impact strength of 3D-printed metals. For instance, Cisneros et al. printed PLA-based biocomposite samples with unidirectional, cross-lay and quasi-isotropic layer structures. They found that the resulting materials had higher impact strengths than injection-molded plastics, but the impact strength of the samples deteriorated with increasing rice husk content.

Corrosion Resistance

Several methods are used for printing metals, but two are particularly promising for making parts that will work well in hostile environments: laser-based direct metal deposition (DMD) and friction stir deposition. Both print multiple layers at once and use heat-generating gasses to melt and solidify the powders. Unlike the powder bed fusion methods that have become dominant, they don’t require support structures, which can reduce the overall cost of the part and make it more likely to retain its shape.

LMD and friction-stir deposition can build parts much faster than a conventional machine, and they work at lower temperatures, which limits the energy they use. They also allow for the printing of a wide variety of metals and alloys, including many that aren’t possible to fabricate using traditional manufacturing techniques.

Beyond these post-processing measures, researchers are working on optimizing the material itself to boost performance. For example, Argonne National Laboratory scientists recently used X-ray crystallography to track how the structure of their printed stainless steel changed during the printing process.

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