Guide To Metal 3D Printing

Metal 3D printing has been present in various guises since the 1980s. A slow burner at first, it was only used for specific industry roles. In recent years, however, a need for different and diverse components has stimulated a search for new manufacturing methods, prompting a dedicated re-investigation of metal 3D production methods.

Since then, many more uses and applications have been discovered, and metal 3D printing is now one of the most researched and improved fields within metal manufacturing.

These days, a range of options now exist for a very high level of consistency and quality of work within 3D metal printing.

What is 3D Metal Printing Technology?

Metal 3D printing is an ideal option for the manufacture of complex components that are difficult to machine. At lower volumes particularly, it can be a cost-effective alternative.

Harder metals such as stainless steel and titanium are harder to work and require better tools, more costly machines and generally greater costs. Thus, 3D printing is the preferred option depending on the job at hand and volume requirements.

One of the primary advantages with metal 3d printing is its capacity for use with an ever-growing list of alloys, metals and metallic composites, allowing for continual expansion and improvement of processes and ideas.

Additionally, there are other substantial benefits of producing metal parts with 3D printing instead of the usual techniques and technologies. These include:


Reduced lead times

One significant, well-known advantage of this type of ‘additive manufacturing’ is its faster turn-around time, from rudimentary design state to final part production.

This is a consequence of its design method - ordinarily, no specific tools or machining devices are needed for processing after the part has been printed.

No milling or turning is required for shape adjustment as with traditional techniques, it is only necessary to remove elements, such as any support structures, created during the process.

This reduction in steps allows for a significant decrease in post-processing times.


Cost advantages through reduced material waste

Another great advantage is a reduction in material waste. In the case of metal 3D printing, the raw materials are added and created in a layer by layer formation, instead of being subtracted or cut out of an original solid bulk.

In this way, the material is used only where needed and the cost outlay of the material used to produce one component is largely reduced.

Recent advancements such as Electron Beam Melting (EBM) and Selective Laser Melting (SLM) have allowed the introduction of powdered metal as a manufacturing option, and this has proven to be a giant leap forward in the industry.

3D Metal Samples

[Above: 3D Metal Samples]

3D Printing Metal Powder

Metal powders are metals that have been ground into fine particles and are the preliminary base element for most 3D printing processes that create metallic parts.

3D printing, or ‘additive manufacturing’ is the building of parts and components layer by layer.

The properties of the metal powder and the type of the 3D printing method determine the characteristics of the end product.

Metal powders are produced using several techniques, such as solid-state reduction, chemical processing, electrolysis, milling, and atomisation.

The most abundant of these methods is atomisation, as it produces the most geometrically usable powders for 3D printing.

Atomisation is usually created by one of three different techniques:

  • water atomisation
  • plasma atomisation
  • gas atomisation.

In the case of 3D Printing, however, water atomisation is usually not used as it can produce irregularities not suitable for this style of manufacturing.


Plasma Atomisation

In this instance, the feedstock is introduced into the atomisation chamber in two possible forms, powder or wire.

In the chamber, a combination of co-axial plasma torches and gas jets melt and atomise the material, creating finitely round powder particles with a relatively finer size distribution.

Titanium is commonly produced this way.

There is a more specialised method called plasma rotating electrode process (PREP) and this utilises a rotating bar instead of a wire as the feed method.

In PREP, the bar extremity is melted at the entry point of the atomisation chamber by plasma torches, and the residual discharged melt becomes solid before reaching the housing walls.

This process creates powders of high purity, extreme roundness, and very fine particle sizes.


Gas Atomisation

In gas atomisation, a feedstock alloy is used, usually in ingot form, and melted in a furnace.

Ordinarily, a vacuum induced melting (VIM) furnace to monitor interstitial elements is used.

The furnace is aligned above the atomisation chamber to discharge material directly into the atomiser.

As this ‘melt’ channels through the chamber, high-pressure gas jets are utilised to atomise the material, which becomes solid spherical powder particles, and is then collected at the bottom.

Usually, this employs an inert gas, such as argon or nitrogen, to lessen oxidation and the possibility of contamination, but air can also be used.

The distribution of particle size can be modulated by adjusting the ratio of gas to melt flow rate.

Some powder materials producible by gas atomisation are cobalt, nickel, iron and aluminium.

Powder Atomisation

[Above: The Powder Atomisation Process]

Types of 3D Printing with Metal Powders

Metal powders are the backbone of metal 3D printing. Though they can be difficult and often hazardous to handle in their raw state, their stand-out qualities still make them the preferred stock for today’s 3D metal printing.

Various printing methods can be employed, including:

Powder Bed Fusion

Powder bed melting is today’s most common type of 3D metal printing.

This specialist machine distributes a fine layer of powder over a designated build plate and melts a cross-section of the desired component into the powder layer.

There are two very distinct types of powder bed melting techniques, Selective Laser Melting (SLM) and Electron Beam Melting (EBM):

Selective Laser Melting

Selective Laser Melting (SLM) is known under many guises, including Laser Powder Bed Fusion (LPBF), Direct Metal Printing (DMP), Direct Metal Laser Sintering (DMLS), and Selective Laser Sintering (SLS).

Most Powder Bed Fusion machines on the current market are SLM based.

The process of SLM uses high-powered lasers that are used to fuse metal layers into parts. Once the print is complete, the part is removed from the powder bed, the required material is cut away from the build plate where it is then post-processed.

SLM is considered the most established form of 3D Printing when using metal and produces geometric complexity unavailable to other types of printing.

The exact precision achieved is determined by the specific settings of laser beam width and layer height.

Encompassing many industries and being able to cater to small or large volume projects, SLM is an extremely versatile printing method.

While an incredible breakthrough in 3D printing, SLM machines do have some significant drawbacks for industrial applications:

  • They require highly trained users to operate them, and settings and tweaks are required throughout the process to get the desired end result, even after printing most products will require exhaustive post-processing and heat treatments.
  • The metal powders used are extremely dangerous to handle, and the machines themselves are excessively costly to run, as well as requiring a dedicated and experienced technician.

[Above: The SLM Process]

Electron Beam Melting

EBM machines use an electron beam as opposed to a laser for their fabrication.

Electron beams produce a less precise result, but are considered faster for larger parts that don’t require exact specifications.

The same handling dangers and costs still exist, however, and due to this combination of variables this processing method is often only found in the aerospace and medical industries.

3D Printing With Metal Powders

These days, there is a substantial range of powder materials that can be employed in 3D printing, the ideal powder though, depends on the desired characteristics of the end product and the printing method employed.

Many of the more common metal powders used include alloys of titanium, nickel, cobalt and steel, cobalt.

The list below illustrates some common metal powder materials with their 3D printing processing methods and application areas:

Steel Powder Metals

Steel is currently the most used material for 3D printing. It is easily converted to powder, yet retains strength and is easier to manage in post-processing.

Cost-wise it is also a more economical choice than many others so is the preferred choice for many applications.

Metal

Alloy

Application

Steel

H13

Hot work casting dies; hot forging and stamping dies; hot shear blades; plastic injection moulds

Steel

H11

Aircraft landing gear; hot forging and extrusion dies; helicopter blades; die casting moulds

Steel

17-4PH

Aerospace; chemical processing; nuclear and oil and petrochemical refining; surgical components


Righton Blackburns Powder Metals

Righton Blackburns is the exclusive UK distributor of Liberty Powder Metals – producers of premium metal powders, for the fast moving manufacturing arena of Additive Manufacturing, PM-HIP & MIM.

Establishing our own Powder Metals division, we now stock an extensive range of powder metals from steels and stainless steel, through nickel superalloys and cobalt chrome to aluminium and titanium alloys in a variety of particle size distributions. We also stock custom powders.

The information contained herein is based on our present knowledge and experience and is given in good faith. However, no liability will be accepted by the Company in respect of and action taken by any third party in reliance thereon.


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