What metal additive manufacturing technologies exist?

There are three main technologies for producing metal parts using additive manufacturing:

  • Selective Laser Melting (SLM or Selective Laser Fusion). This technology is also sometimes called Powder Bed Fusion (PBF) or Direct Metal Laser Sintering (DMLS).
  • Metal Binder Jetting (MBJ) o Inyección de Aglutinante (sobre polvo de metal).
  • Bound Metal Deposition or Bound Metal Deposotion

Selective Laser Melting or SLM (/PBF/DMLS)

Introduction

SLM technology is one of several names for this technology. It was developed in 1995 at the Fraunhofer Institute ILT in Aachen, Germany. After patenting this technology, at the beginning of the 21st century, Doctor Dieter Schwarze started a business project that today is known as SLM Solutions. Doctor Schwarze continues, to this day, working at SLM Solutions and leading the most important advances in SLM technology (reactive materials, multi-laser, closed-loop dust management, etc.).

How it works?

This technology is based on spreading a thin layer of metal powder on a metal plate. Using a high-power laser, we apply energy to said metal powder, fusing its particles together. In this simple way, we can produce the first "slice" of our metal part. Next, we extend another equal layer on top of the previous one and apply the laser on its surface again. On this occasion, the dust particles are going to merge with each other and with those immediately below, previously merged.

We repeat this process, layer by layer, until our part is, made up of fused powder particles, inside the printing vat, surrounded by loose powder.

Then we just have to extract the loose powder and sift it to use it again in the next impression, clean our piece and remove the supports that join it to the build plate.

Strengths

  • This is the technology that obtains parts with greater capacities and mechanical performance..
  • Given the longevity of the technology (we are at the beginning of its third decade) we have a wide range of materials with which we can work.
  • In addition, and for the same reason, it is a very proven technology, widely used in sectors such as moulds, the automotive industry, aeronautics or prosthetics, among others. Nowadays, it is easy to know what we can obtain from this technology for a specific project.
  • We can also make parts of a certain size, within certain limits, without significantly affecting issues such as precision or mechanical properties of the finished part.
  • Finished part tolerances are the highest found in metal additive manufacturing, though still far from what is achieved in machining.

Weaknesses

  • It is not a fast technology. Despite great advances in this aspect, such as the use of twelve lasers simultaneously in a single print, it is a technology more suitable for the field of tooling, prototyping or pre-series, than for mass production and very long series.
  • The increase in speed requires a greater number of lasers, which in turn multiplies the initial investment cost.
  • The metal powder used has certain requirements at the level of development and quality control that lead to relatively high production costs.
  • The pieces must be separated from the construction plate by cutting and eliminating the supports that join them to it. Such work requires a metalworking shop.

References

Metal Binder Jetting de metal o MBJ

Introduction

La tecnología Binder Jetting fue desarrollada por el MIT en 1993 y consiste en «imprimir» con un cabezal de inyección de forma similar a una impresora de chorro de tinta, excepto que lo hace sobre una capa de polvo en lugar de sobre papel. El equipo que desarrolló esta tecnología fue el que registró el término «Three Dimensional Printing» y su abreviatura «3DP».

An exclusive license for this technology was granted to the company ExOne (today owned by Desktop Metal) in 1996. Since then, many companies have developed new technologies and additive manufacturing processes based on this technology, especially where the manufacturing speed has been considered the most important goal (eg Desktop Metal or HP).

How it works?

This technology is also based on spreading a thin layer of metal powder on a plate. Then, using a binder injector, we bond the metal powder particles together. And then, when repeating in the next layer, we join them again but also with those of the previous layer.

What we are building are not finished metal parts, but "green" parts made of metal powder held together with a binder. These parts are not finished and do not have the properties or strength of a metal part.

Next, we just have to extract the loose powder and sift it to use it again in the next impression, clean our parts and place them in a sintering oven.

Strengths

  • Without a doubt, the fastest additive manufacturing technology that exists is binder jetting. If we talk about metal, the technology is undoubtedly metal binder jetting.
  • The technology is not complex, so the investment are medium, the reliability of the technology is high and the maintenance and operation of the printers is simple.
  • The requirements of the metal powder to be used are not as demanding, so the costs are than using other technologies.
  • There is no need for a metal shop to remove supports since parts are supported in loose powder during printing. This significantly reduces the cost and time of post-processing.

Weaknesses

  • Since the final processing is carried out in a sintering oven, similar to the classic MIM technology, there is a contraction in the piece that makes it difficult to obtain really small precisions.
  • The process is multi-phase. This means that, although the technology is extraordinarily productive, the normal time to first piece is around three days.
  • It is a much more suitable technology for the manufacture of a large number of small and medium sized parts than for large or very solid parts.

References

Bound Metal Deposition o BMD

Introduction

Bound Metal Deposition technology was developed by Desktop Metal in 2017 and, although not yet widely known, it incorporates a number of unique benefits that make it stand out from other more productive or higher performance solutions.

Fundamentally, that this technology is the only one that can be used in an office environment for the manufacture of real parts from different types of metal.

How it works?

Similar to how an FDM printer makes a plastic part, extruding a fine thread of molten material, the BMD printer extrudes a thread of bonded metal powder. With this thread we obtain the "green" piece, that is, a piece that has the correct shape but without the properties of the final metal piece.

Immediately after printing said piece, or a certain number of pieces printed in parallel on several printers, we place them inside a sintering oven.

In this oven, the binder will melt and disappear while the metal powder will fuse to form the final piece, now with all the properties of the corresponding metal.

Strengths

  • The initial investment is low cost since the printer itself is very similar to an FDM printer and therefore cheap.
  • The production strategy is very scalable since we can incorporate additional printers, even far from each other, and sinter the production of all of them in a centralized oven. Since printers are the economic element of the solution, expanding capabilities in the future is very easy and inexpensive.
  • The material is quite cheap, which means that it allows parts to be produced at very low costs.
  • This printer can be used in an office environment, just like any FDM printer.
  • Switching between materials is a breeze compared to any other metal additive manufacturing technology, making it the most versatile solution in the industry.
  • Although this printer use supports to make the green part, it deposits a ceramic material as an interface between the part and the support. After the sintering process, it is possible to separate the finished part from its supports using nothing more than the hands, without the need for tools, workshop or long times.

Weaknesses

  • Since the final processing is carried out in a sintering oven, similar to the classic MIM technology, there is a contraction in the piece that makes it difficult to obtain really small precisions.
  • The process is multi-phase. This means that the normal time to first piece is around three days. Also, the printer itself is slow, so we can't expect high volumes of production either.

References

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