How to choose the right metal technology

Metal Technologies How to choose the right metal technology

How to choose the right metal technology

Typically more than one suitable technology for each application

Choosing the right technology can be tricky. Selecting the right process always depends on your application and its requirements. Before presenting an overview of typical characteristics of the different technologies covered in this online learning program, we will present 2 common selection criteria: part dimensions and productivity.

Additive Manufacturing Training Part Identification

What you will find in this section

Part dimensions

Part size is a simple first indication to narrow down possible technologies

One of the most common selection criteria for metal processes are part dimensions: 

  • Material Extrusion and Binder Jetting are mostly suitable for small components. Here the limitation results from  the fragility of the green body and shrinkage during sintering.
  • L-PBF and E-PBF can be used for small to medium-sized components. Standard industrial machines reach up to 400 mm in each dimensions, with few machines coming up reaching up to 1m in size.
  • DED technologies such as Powder and Wire Energy Deposition and can be used for medium and large components. Parts can reach dimensions up to several meters and are mainly limited by machine design.

In general, the lower limit of part dimensions is restricted by the process itself. Fine features in the range of a tenth of a millimeter can be manufactured by L-PBF, where the resolution is in the dimension of the diameter of the laser spot. In Binder Jetting, high resolution printing heads and small powder particle distribution facilitates building fine features. In general, powder-based technologies have higher resolution than rod or wire-based technologies.

Productivity versus accuracy

Higher productivity often comes at the expense of lower accuracy

Metal AM technologies differ greatly in their productivity and accuracy. An increase in productivity often results in decreasing accuracy and resolution of the process.

While the specific application as well as the processing parameters have a significant influence on build speed, a simplified comparison of the productivity can be performed considering the built-up rate of volume per time (cm³/h).

In L-PBF, the productivity is mainly driven by the volume of material a laser melts per time interval. Certain materials, such as titanium alloys, already exhibit physical limitations in their melting speed at today’s available laser power. Thus, a further scaling of the processing speed can only be achieved through adding further laser beam sources or increased layer thickness but not by increasing the power per laser. For layer heights of around 50 µm, a single laser melts at a rate of 10 to 20 cm³/h of titanium or stainless steel powder, and aluminum alloys at a rate of 20 to 30 cm³/h. An increase in layer height can improve these figures while reducing resolution and surface quality. The time for applying a new layer of powder, ie. recoating, or taking pictures for quality assurance measures is non-productive and can sum up to a significant and costly portion of the total process time of 25% or more.

The productivity of Binder Jetting is highly driven by the passing time of its coating and printing head over the complete powder layer. Announced BJ machines from companies DESKTOP METAL and HP will include single-pass coating and printing of the full width of the build envelope. If single pass coating and printing is achieved the productivity of the system is depending on the packing density of parts in the build chamber. A high packing density of parts in the build envelope results in high productivity while accuracy stays constant. The above mentioned companies claim green body printing of several thousand cm³/h, however, they currently lack independent sources for empirical confirmation of such high speeds. For Besides printing, times required for depowdering and sintering need to be taken into account. 

In ME the application rate of material is not only limited by the nozzle diameter, but for filament based systems also by the speed the metal filament can be mechanically handled. Conveying the brittle and fragile metal filament at high speeds can cause breakage and stop of the process. The material built-up rate is about 15 cm³/h.

For DED technologies the productivity is highly dependent on many different factors, such as system technology and part geometry as well as material and processing parameters. The duration for setup as well as necessary cooling phases during the build, which are highly dependent from part geometry, can range from neglectable duration up to 50 % or more of the total processing time. Such an increase has a subsequent negative impact on the productivity.

In Powder Laser Energy Deposition, the nozzle diameter impacts the resulting resolution of the process and the overall productivity. The material built-up rate ranges from about 50 to 500 cm³/h. Wire Electric or Plasma Arc processes typically exhibit built-up rates of about 100 to 800 cm³/h, however, with a decrease in accuracy compared to the powder feed process. For Wire Electric Arc Energy Deposition as well as Coldspray technology, the material built-up rate can exceed 1,000 cm³/h.

Technology comparison

How do the different metal technologies compare?

We therefore created an overview of the main metal technologies below that will help you choose the right technology for your needs. You can dive deeper into the different metal technologies at the bottom of this page. 

Keep in mind that the values given below should only provide you a general rule of thumb – within each technology the exact values will differ depending on machine and material.

ME

BJT

L-PBF

E-PBF

LMD

WAAM

Functional Principle

binder

Process Category

Extrusion

Binder Jetting

Powder Bed Fusion

Directed Energy Deposition

Typical Part size

15-150 mm

5-50 mm

15-300 mm

20-300 mm

100-1000 mm

0.2-2 m

Typical Productivity

5-50 cm³/h

10-1000 cm³/h

10-30 cm³/h (per laser)

15-50 cm³/h

50-500 cm³/h

 100 -1000 cm³/h

Supports

Needed to print, debind & sinter

Not needed, may improve sinter

Usually required for low angles

Usually required for low angles

Typically not needed

Typically not needed

Surface Roughness

Ra 5-20 µm

Ra 3-5 µm

Ra 5-10 µm

Ra 15-25 µm

Ra 20-175 µm

Waviness >1 mm

Typical layer thickness

0.1-1 mm

50-120 µm

25-90 µm

~50 µm

0.1-1.5 mm

~3 mm

Metal AM Process Overview

How to get started

Usually more than one process for your application

The above table should provide you a general guideline how to get started selecting the right process. Keep in mind that often there is more than one process for your application. There are different databases, such as the SENVOL Database of Industrial AM machines and materials or the ANIWAA AM marketplace. These databases will allow you to narrow down the list of possible machines or materials by applying filters such as your material category, part dimensions or required part properties. 

Once you have one or several technologies in mind, the next step is to reach out to an AM expert to discuss this in more detail. 

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Sinter-based AM technologies and process chain

Sinter-based AM - a technology overview

Many different printing technologies - one sintering process

The sinter-based AM (SBAM) technologies have, as the name suggests, the sintering process in common. In this process, the printed green part is consolidated into a dense part and receives its final properties. The green part can be printed in advance using different technologies.They all have in common that metal powder is bound to the desired shape by a binder. The best-known printing technologies include Binder Jetting and Filament Material Extrusion.

In this section, you learn everything about the sinter-based AM  process chain and get an overview of the different printing technologies.

Goal and structure of this course

This course is aimed at engineers, designers and other professionals that are working closely with sinter-based AM technologies. The goal is to cover the most important aspects that will enable engineers and designers to fully grasp the capabilities and technical limitations of the printing technologies and the sintering process to succeed in technology selection and part design. Besides going through the course from the beginning until the end, this course can also act as a constant source of knowledge while working on AM projects. 

The course is structured into the following sections.

This section will start with an overview of the sinter-based AM process chain and its printing technologies, followed by a technology deep dive into the most important aspects of the BJT technology, followed by a closer look at the debinding and sintering step also including sintering simulation .

The second section will provide an overview of the different materials that are available as well as part characteristics that can be achieved with the BJT process and typical methods for quality assurance. Finally, several common defects in the BJT process are presented. 

The last section will act as a guideline for designers. Besides generally describing the process when designing for Additive Manufacturing, actionable restrictions and guidelines for the BJT process are provided. The final section will present several design examples from different industries. 

What you will find in this section

Sinter-based AM process chain

From digital model to finished part

Data preparation

Simulation to compensate the deformation during the sintering step, nesting of parts and definition of printing parameters

Printing

Through various printing processes, different feedstocks such as metal powders, filaments, pellets or dispersions are processed into green parts

Unpacking

Unpacking of fragile green parts needs to be done carefully and is typically a manual process.

Debinding

Debinding describes the process of removing the binder which results in a brown part

Sintering

To reach the structural integrity of a metal part, a sinter process is required. The powder particles fuse together to a coherent, solid structure via a mass transport that occurs at the atomic scale driven via diffusional forces.

The brown part shrinks ~13-21 % in each direction.

The process chain of sinter-based technologies differs from other AM Technologies. Especially the post-printing processes (debinding and sintering) are crucial to achieve the intended mechanical properties.

Technology principle

How does Binder Jetting work?

Binder Jetting is a powder based Additive Manufacturing technology in which a liquid polymer binder is selectively deposited onto the powder bed binding the metal particles and forming a green body.

The metal powder is applied to a build platform in a typical layer thickness of 40 µm to 100 µm. Subsequently a modified 2D print head apply a binder selectively onto the powder bed. Depending on machine technology a hardening or curing process of the binder is performed in parallel for each layer and/or at the end of the whole build. During the in-situ curing process a heat source is used to solidify the binder and form a solid polymer – metal powder composite.

Working Principle of Binder Jetting

Afterwards the build platform moves downward by the amount of one layer thickness and a new layer of powder is applied. Again, the liquid binder is deposited and hardened in the required regions of the next layer to form the green body. This process is repeated until the complete part is printed. After the complete printing process is finished the parts have to be removed from the “powder cake” meaning the surrounding loose but densified powder. To improve the removal of the excess powder from the green body often brushes or a blasting gun with air pressure are used.

To create a dense metal part the 3D printed green body has to be post-processed in a debinding and sintering process. Similar to the metal injection molding process BJT parts are placed in a high temperature furnace, where the binder is burnt out and the remaining metal particles are sintered together. The sintering results in densification of the 3D printed green body to a metal part with high densities of 97 % to 99,5%, dependent of the material.

Printing Technologies

Metal Binder Jetting

Binder Jetting is a powder based Additive Manufacturing technology in which a liquid polymer binder is selectively deposited onto the powder bed binding the metal particles and forming a green body.

The metal powder is applied to a build platform in a typical layer thickness of 40 µm to 100 µm. Subsequently a modified 2D print head apply a binder selectively onto the powder bed. Depending on machine technology a hardening or curing process of the binder is performed in parallel for each layer and/or at the end of the whole build. During the in-situ curing process a heat source is used to solidify the binder and form a solid polymer – metal powder composite.

Working Principle of Binder Jetting

Material Extrusion

Binder Jetting is a powder based Additive Manufacturing technology in which a liquid polymer binder is selectively deposited onto the powder bed binding the metal particles and forming a green body.

The metal powder is applied to a build platform in a typical layer thickness of 40 µm to 100 µm. Subsequently a modified 2D print head apply a binder selectively onto the powder bed. Depending on machine technology a hardening or curing process of the binder is performed in parallel for each layer and/or at the end of the whole build. During the in-situ curing process a heat source is used to solidify the binder and form a solid polymer – metal powder composite.

Working Principle of Binder Jetting

Mold Slurry Deposition

Binder Jetting is a powder based Additive Manufacturing technology in which a liquid polymer binder is selectively deposited onto the powder bed binding the metal particles and forming a green body.

The metal powder is applied to a build platform in a typical layer thickness of 40 µm to 100 µm. Subsequently a modified 2D print head apply a binder selectively onto the powder bed. Depending on machine technology a hardening or curing process of the binder is performed in parallel for each layer and/or at the end of the whole build. During the in-situ curing process a heat source is used to solidify the binder and form a solid polymer – metal powder composite.

Working Principle of Binder Jetting

Metal Selective Laser Sintering

Binder Jetting is a powder based Additive Manufacturing technology in which a liquid polymer binder is selectively deposited onto the powder bed binding the metal particles and forming a green body.

The metal powder is applied to a build platform in a typical layer thickness of 40 µm to 100 µm. Subsequently a modified 2D print head apply a binder selectively onto the powder bed. Depending on machine technology a hardening or curing process of the binder is performed in parallel for each layer and/or at the end of the whole build. During the in-situ curing process a heat source is used to solidify the binder and form a solid polymer – metal powder composite.

Working Principle of Binder Jetting