Common problems with 3D metal printing - and how you can solve them

Metal 3D printing has made impressive progress in recent years. Companies are increasingly investing in technologies for highly complex industrial applications. However, in addition to the benefits of producing lightweight and sophisticated metal parts, the metal 3D printing process also has some challenges to overcome. Today's tutorial examines the main problems with metal 3D printing and how to solve them.

Metal 3D printing - an overview

There are various printing processes for 3D metal printing. These can be roughly divided into three groups:

Powder bed fusion processes (SLM, EBM)
Direct energy deposition (DED)
Metal bonding machines

Powder bed fusion is the most common method of producing metal parts using AM and involves the use of a laser beam (SLM) or electron beam (EBM) to selectively melt a layer of powder material uniformly on the build platform.

Direct energy deposition covers a range of technologies and typically involves a process in which the material is melted by a laser or electron beam before being deposited on a build platform. The object is then formed layer by layer. While polymers and ceramics can be used with this process, DED is typically used with metals in powder or wire form.

Metal binder jetting uses a print head to apply a liquid binder to layers of powder, fusing the powder particles together layer by layer. The bonded powder can then optionally be infiltrated with another metal (usually bronze) to achieve a higher density.

Each of the processes has its strengths and limitations, but common challenges are generally encountered when 3D printing metals. These challenges must be overcome in order to achieve the best possible mechanical properties for your 3D printed metal parts.

5 common problems you should watch out for

1. porosity

3D printed metal parts are often plagued with high porosity, which occurs during the printing process when small holes and voids are formed within the part. These tiny, usually microscopic pores can cause low density - the more pores there are, the lower the density of your part. They can also directly affect the mechanical properties of a part, making it prone to cracking or other damage, especially when subjected to high loads.

There are usually two main reasons for highly porous 3D printed metal parts: Either this is due to a problem with the powder manufacturing technique or the 3D printing process. For example, the use of gas atomization can sometimes cause pores to form in the powder material. However, the more common source of such tiny holes is the printing process, when the energy of the holes is insufficient and therefore the metal cannot melt properly. The opposite can also be true: Excessive laser energy can cause the droplets of molten material to splatter, resulting in pores.

How to reduce the porosity of your metal parts

Fortunately, there are several ways to eliminate porosity in your 3D printed metal parts and achieve stronger, more durable parts: as material quality can sometimes be the source of high porosity, be sure to buy raw materials from a trusted supplier.

• The porosity caused during the printing process can be eliminated by adjusting the printer parameters.
• The correct density can be achieved with post-processing methods, such as hot isostatic pressing. This eliminates possible cavities and at the same time improves the mechanical properties of a 3D-printed metal part.
• Infiltration is another post-processing option for powder-bed fusion parts. This method is used to fill the remaining cavities in the metal part.

2. density

Industrial applications of 3D metal parts often require high mechanical properties, which is why the density of a part is extremely important. When a part is working under cyclic stresses, its density determines whether or not the part will fail under load. In other words, the lower the density of a part, the more likely it is to crack under pressure. Powder bed technologies (SLM, EBM) can produce parts with densities of 98% and more, which are critical for stressful applications.

Improve the density of your parts

To ensure that a part has consistent quality and density, the specific parameters of the material such as particle size, shape, distribution and flowability must be optimized. Particles with a spherical shape, for example, can result in a higher density as they can reach the maximum relative density compared to other shapes.

However, as there are a number of variables that can affect the density of a part, the rule of thumb is to first consider the quality of your metal powder and adjust the parameters of the process accordingly.

3. component under voltage

Heating and subsequent cooling are common features of metallic AM processes. However, if a component is exposed to such extreme thermal changes, this can lead to residual stresses. The residual stress has an unfavorable effect on the integrity of a manufactured part and leads to various deformations. The highest residual stress concentration is found at the contact surface between the bottom of a printed part and a print bed.

Reduce residual stress

As residual stresses can make the difference between a successful metal print and a structural failure, this issue should be properly addressed. There are several ways to do this:

• Through predictive modeling and the use of generative design, the appropriate parameters such as heat input and layer thickness can be estimated in order to build components with low residual stress.
• By implementing support structures and optimizing the component orientation, the occurrence of residual stresses can also be minimized.
• Preheating the print bed and build material before the printing process begins reduces temperature gradients that often cause residual stress. However, as EBM works at lower temperatures, this technique is more successful with EBM than with SLM or DED.
• In powder bed fusion processes, the "island" scanning strategy can help to reduce the build-up of residual stresses. With this strategy, the exposure area is divided into smaller sections, known as "islands", and the length of the scan vectors is shortened.

4. cracks and distortions

Residual stresses can be very destructive, leading to a number of structural problems in a part, with cracking and deformation being the most common. Such problems typically occur when the molten metal cools after printing. Cooling causes contraction, causing edges of a part to curl and deform. In extreme cases, stresses can exceed the strength of the part, which can cause the part to crack (cracking can also occur if the powder material has not been properly melted).

Prevent cracking and warping

There are two main methods to prevent cracking and warping of your metal part. One way is to preheat the print bed, another is to improve the adhesion of a part to the print bed and place the required amount of support structures. Thermal post-processing can also help to repair minor cracks, while determining the right amount of support structures from your side is essentially to avoid warping.

5. finishing and surface roughness

Typically, metal parts are not ready for their final applications when they are first printed and need to undergo post-processing, such as powder and support removal, heat treatment and surface treatment. However, you will often encounter some challenges in the post-processing steps.

For example, you may have difficulty removing the support structures on your parts. This can be the case, for example, if your metal part has supports in small holes and tubes. These can be difficult to remove without damaging the part and subsequent machining is required.

Surface roughness is another issue. Additively manufactured components for demanding applications require an average surface roughness. However, 3D printed parts are often produced with rough surfaces and require additional post-processing such as machining, grinding or polishing to achieve a better finish. Since surface roughness is directly related to layer thickness, it can be reduced by printing with thinner layers. However, producing a part with finer layers can significantly increase build time.

Rough surfaces can also be caused by incorrect powder fusion. This happens when not enough energy has been applied to melt the metal completely. In this case, the surface roughness can be reduced by increasing the power of your laser.

Summary

There are a number of potential challenges when using AM to manufacture metal parts. However, understanding these challenges is the first step to producing high quality and reliable components. With the continued growth of metal 3D printing, we will certainly see an increase in the use of additively manufactured metal components for industrial applications.