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METAL ADDITIVE MANUFACTURING
From: Time:2020/9/30 16:47:39 Hits:759

Metal Additive Manufacturing offers the possibility to produce complex parts without the design constraints of traditional manufacturing routes. Components that would not have even been possible just a few years ago can now be made to high standards using a wide range of metal powders. No longer solely a prototyping technology, Additive Manufacturing is now being used for the production of series components for the most demanding applications. Additive Manufacturing, also referred to as 3D Printing, is a technology that produces three-dimensional parts layer by layer from a material, be it polymer or metal based. The method relies on a digital data file being transmitted to a machine that then builds the component. The following introduction to Additive Manufacturing outlines a number of the key technologies used to process metal parts and provides a look at the current state of the industry.

Metal Additive Manufacturing offers unrivalled design freedom with the ability to manufacture parts from a wide range of materials. This is a prototype of an optimised bracket for an Airbus A380 made from stainless steel powder, with conventional bracket behind (Courtesy EADS)

Background to Additive Manufacturing

Additive Manufacturing offers many advantages in the production of parts, presenting unrivalled design freedom with the ability to manufacture single or multiple components from a wide range of materials.

The method is considered as an additive process rather than a subtractive process that removes layers of material, such as milling. Other terms often used to describe the general process include 3D Printing, Additive Fabrication, Freeform Fabrication, Fabbing and Additive Layer Manufacture.

The early AM processes were established in the mid 1980s as a solution for faster product development. At this time the practices were called Rapid Prototyping, because the idea was really to produce three dimensional models or mock-ups in order to check form, fit and function.

In 1987 3D Systems began the commercialisation of the plastic processing technique known as Stereolithography (SL), offering completely new possibilities to designers and engineers and supporting the fast growing market of “short life” products. The process essentially solidifies thin layers of UV light sensitive liquid polymer using a laser and was the first commercially available AM system in the world.

In the early 1990s other polymer based AM technologies began commercialisation, including fused deposition (FDM) from Stratasys, Solid Ground Curing (SGC) from Cubital and Laminated Object Manufacturing (LOM) from Helisys. Selective Laser Sintering (SLS) from DTM was also introduced at this time, a process that fuses powder materials using a laser.

The latest metal AM machine from EOS was introduced in 2013. The EOSINT M400 uses a 1 kW laser (Courtesy EOS)

Metal based AM processes were developed in the 1990s and introduced to the market soon after. At this time several companies launched systems for laser sintering approaches which were able to produce metal parts directly, providing an alternative to direct multi stage processes.

In 1994 EOS demonstrated their prototype EOSINT M160 machine based on direct metal laser sintering technology. In 1995 the company’s EOSINT M250 was launched, enabling the rapid production of metal tools. These systems where able to manufacture metal parts by sintering the powder, but in many cases the mechanical characteristics of the materials were more comparable to composites than to metal alloys, due to the combination of a low melting material (e.g. a bronze-based matrix) with a high resistant material (e.g. stainless or tool steel).

In 1998 Optomec commercialised its Laser-Engineered Net Shaping (LENS) metal powder system based on technology developed at Sandia National Labs, USA. In 1999 Röders, a German company, began marketing its Controlled Metal Buildup (CMB) machine based on technology developed at the Fraunhofer Institute for Production Technology in Germany. Also in 1999, ExtrudeHone introduced its ProMetal Rapid Tooling System RTS-300, the commercial realisation of MIT’s process for manufacturing metal parts and tooling. Similar to the use of polymers and waxes in the preparation of feedstock for the Metal Injection Moulding (MIM) process, this system was able to print a binder on a powder bed, binding the metal particles and producing “green parts” which subsequently have to be debound, sintered and infiltrated to get completely dense material.

In 2002 Precision Optical Manufacturing began sales of its Direct Metal Deposition (DMD) laser-cladding systems, a process that produces and repairs parts using metal powder.

The continuing development of AM systems has enabled the fabrication of usable parts made in the desired material in a single-step process. It is now possible to manufacture almost 100% dense functional designs. Over time these systems have become more reliable and more efficient, with the range of suitable materials growing significantly.


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