What is Metal 3D Printing?

Metal 3D Printing is an advanced manufacturing method that builds metal parts from a CAD file using a layer-by-layer technique known as additive manufacturing.

Introduction to Metal 3D Printing

To understand metal 3D Printing, we first must understand the difference between “what it’s made of” (the material) and “how to make it” (the technique). Metal refers to the category of materials that we use and 3D Printing – also known as Additive Manufacturing (AM) – refers to the category of material processing techniques that consolidate the metal materials, one layer at a time, from the bottom up. Software is used to slice a solid three-dimensional (3D) computer generated model into a set of layers for the 3D printer hardware. The first layer attaches directly to a dedicated build plate, the second layer fuses with the first layer, and so on. In metal 3D Printing, production builds can consist of thousands or tens of thousands of layers and can take days, weeks, or even months to complete.


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Finished metal 3D printed part still on the build plate.
Finished metal 3D printed part still on the build plate.

In the world of metal 3D Printing, the end that we have in mind is a 3D metal part that matches the exact size and shape of our 3D CAD model. This one-to-one equivalence is sometimes difficult to achieve with metal materials. The bottom of each build for most metal 3D Printing processes is a large piece of metal called a build plate. The build plate must be flat within the 3D printer prior to starting any metal 3D Printing process.
The first step in the process is to attach the initial layer of metal to the build plate successfully. Subsequent layers are added one-at-a-time, until the 3D geometry is realized.

The particulars of exactly how the metal is attached to the build plate, and subsequently to previous layers of the build, is where things get interesting and processes differ from one another. Methods of realizing metal 3D geometries differ primarily in two dimensions: 1) by the feedstock delivery system used (the way new material is fed into the system), and 2) by the consolidation mechanism leveraged (the physics of how the new material is fused to the build plate and to previous layers).

Metal 3D Printing Processes

As the metal 3D Printing industry continues to grow in scale and complexity, especially in the automotive, maritime, medical, aerospace, and space industries, more and more R&D-grade and production-level solutions continue to be developed. This proliferation of technology is a potential boon for advanced manufacturers across the globe; however, not all metal 3D Printing processes are created equally. As mentioned, each process comes down to 1) how new material feeds into the 3D printer, and 2) how that material is consolidated into a 3D geometry. At the time of writing, there are several popular industrial solutions on the market, listed here in order of perceived popularity.

  • Powder Bed Fusion (PBF)
    • Feedstock: Metal Powder
    • Consolidation Mechanism: High Temperature Laser or Electron Beam Melting
  • Binder Jetting (BJ)
    • Feedstock: Metal Powder and Chemical Binder
    • Consolidation Mechanism: Chemical Binding and Heat Treating
  • Direct Energy Deposition (DED)
    • Feedstock: Metal Powder or Wire/Filament
    • Consolidation Mechanism: High Temperature Laser or Electron Beam Melting
  • Bound Powder Extrusion (BPE)
    • Feedstock: Metal Powder encapsulated in Polymer
    • Consolidation: Low Temperature Conduction Melting, Polymer Removal, and Sintering
Powder Bed Fusion (PBF) using a laser to fuse a layer of metal material.
Powder Bed Fusion (PBF) using a laser to fuse a layer of metal material.

There are several industry-leading manufacturers that use each technology, and more competitors are entering these spaces all the time as the global metal 3D Printing ecosystem evolves and grows. We will dive further into the details of each process above in future articles in this series on Metal 3D Printing – stay tuned!

About the author:
Greg Loughnane is a university professor at the University of Dayton, Ohio. Greg completed his PhD in Computational Design & Optimization in 2015.
[email protected]

What is 3D Resin Printing?

Stereolithography (SLA), Digital Light Processing (DLP), and Liquid Crystal Display (LCD) are 3 different types of 3D Resin Printing processes. In these vat polymerization methods, light sources are used to cure liquid resin, layer-by-layer, to form a desired 3D model. Although SLA, DLP, and LCD all use a light source, a build platform, and a vat of resin, each process uses a different type of light source.


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3D Resin Printer
Bottom-up 3D resin printer showing build platform and resin vat.

SLA 3D Resin Printing

SLA, the original form of 3D Printing, was patented in 1986. In this technique, galvo mirrors focus an ultraviolet (UV) laser that solidifies the cross-section of each layer, point-by-point. In general, SLA 3D Printing may be top-down, as is used in some industrial applications, or bottom-up, as is used for desktop printers.

In top-down SLA 3D Printing, the laser source is positioned above the vat of resin. The build platform begins at a predetermined layer height under the top surface of the liquid resin. After solidifying a layer, the build platform drops by a specified layer height, typically between 25-100 microns, to solidify the next layer and merge it with the previous. This process repeats until the model is complete, at which point it rises from the vat. Unlike other 3D Printing methods, curing continues after completion. Extra exposure to UV light is generally needed to fully cure the resin and improve the model’s hardness and temperature resistance.

In bottom-up SLA 3D Printing, the light source is positioned under the vat and the model is formed upside down. The build platform begins at a predetermined layer height above the tank’s bottom surface, which is transparent to allow light to penetrate the liquid resin. After each layer is solidified, the build platform rises, removing the cured resin from the bottom of the tank in a process called “peeling.” Forces applied to the model during peeling are the main cause of print failures in bottom-up SLA 3D Printing.

SLA/DLP (Stereolithography / Direct Light Processing)
Dental SLA 3D printer with model on build plate.

DLP 3D Resin Printing

DLP is similar to bottom-up SLA 3D Printing in that the light source is positioned below the vat of resin. However, instead of a using a UV laser, DLP uses a projector screen to flash a pixelated 2D image of the layer onto the tank bottom. This allows for faster processing times. The disadvantage of DLP is the restriction of build accuracy, which is determined by pixel size.

LCD 3D Resin Printing

LCD is similar to DLP in that it also uses a pixelated 2D image. You may recognise the term LCD from computer monitors and other display devices. In LCD 3D Printing, an array of UV LCDs shine the entire layer image directly onto the tank bottom to cure the liquid resin. As no mirrors are used to project each layer image, there is no distortion of the light. This means that the quality of LCD 3D Printing is determined by the LCD density. LCD generally uses cheaper components than both SLA and DLP, which is often a good introduction to Resin 3D Printing for the first-time owner.

SLA, DLP, LCD Printed Chess Pieces
High detail 3D printed chess rook from resin plastic.

With 3D Resin Printing, high levels of accuracy can be achieved with smooth surfaces. As the UV curing method tends to leave models brittle, most 3D Resin Printing is better suited for non-functional parts and visual models. But, as material science continues to develop, functional resin printed parts are now becoming a reality. Visit the 3D Printing comparison page for more information about the ideal 3D Printing method for your next project.

About the author:
Chris Brennan is a Manufacturing Engineer and the founder/owner of Thirteen Design Consultancy based out of County Louth, Ireland.
[email protected]
Instagram: @thirteendesignconsultancy
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Fused Deposition Modeling (FDM), sometimes referred to as Fused Filament Fabrication (FFF), is one of the most popular types of extrusion 3D Printing. The FDM process creates plastic 3D models by superimposing multiple layers of melted thermoplastic polymer material into a predefined area via a computer controlled printing nozzle. While FDM may not be the strongest, fastest, or most advanced example of 3D Printing technology, it is one of the most affordable and is ideal for producing concepts and prototypes.

A direct drive or Bowden type extruder is used for FDM, depending on the 3D printer type and setup. Thermoplastic polymer materials in the form of a continuous filament are fed from the extruder cold end to the hot end. The hot end contains an interchangeable nozzle that can be sized according to the specifications of the printed object. To control the movement and placement of the nozzle, the printer is equipped with a gantry system, generally powered by individual stepper motors. These motors make sure the extruded filament is laid down in the correct position for each printed layer. With every pass, the nozzle lays the filament down on top of the previous layer, gradually building up the required shape of the object.

With FDM technology, the quality of the 3D printed object depends on various parameters such as layer height, nozzle diameter, and the use of support materials. Because of the layered build process, support structures must be printed under high degree overhangs and large unsupported bridges to stop the extruded filament from sagging. Although printed supports can increase post-processing time, they are often necessary to produce high quality prints. Because FDM uses one single-point nozzle to extrude a single layer of material at a time, the finished object contains layer lines that are often visible on the exterior surfaces. These layer lines can be removed with various post-processing methods.

FDM offers a wide variety of materials to print with, including flexible thermoplastics; objects can be either rigid or flexible. FDM printing uses a wide variety of high-performance, engineering, and basic filaments that allow for the practical application and use of each printed object to be uniquely different. Available filaments include ABS, PLA, PETG, Nylon, and PEEK, to name but a few, and most come in a wide variety of colors. Then there are TPU plastics, which tend to be the most flexible and may require specific types of extruders and hot ends to print properly. The mechanical properties of FDM objects are anisotropic because of the layered build process.

The benefits of FDM include the cost-effectiveness for producing prototypes and functional objects, the ability to create complex new designs that are not possible with traditional manufacturing technologies, and the wide selection of build materials – for applications ranging from basic to high-performance. Along with these great benefits, however, FDM does have its limitations, namely its anisotropic mechanical behaviour, the visible layer lines that may require extra post-processing time to remove, and lower dimensional accuracy and resolution when compared with other 3D Printing technologies.

About the author:
Chris Dudek
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Instagram: @chris_dudek

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Introduction

Selective Laser Sintering (SLS) is an Additive Manufacturing (AM) process that uses laser power to sinter powdered material, typically plastics, into a solid 3D model. Sintering—using atomic diffusion to create objects from powdered material—has been around for thousands of years. However, it was first developed as an AM technique in the 1980s at the University of Texas at Austin and has been used as a foundation to develop similar processes for metals, glass, ceramics, and some composites. Although desktop and hobby 3D printers are widely available, there are very few SLS versions due to the complexity of the process.

The main benefit of SLS over other AM processes (such as Stereolithography (SLA), Fused Deposition Modelling (FDM), or Fused Filament Fabrication (FFF)) is the unfused powder acting as a self- supporting material, eliminating the need for including support structures in the model. In addition to reduced print times, this results in the creation of intricate and complex geometries, including interlocking parts, moving parts, and complex lattice structures that maximize the part’s strength in desired locations, while also minimizing weight. SLS is a popular technique in the aerospace and medical device industries due to its ability to quickly produce low quantities at mass production accuracy levels, as well as the variety of materials that can be utilized.

The theory behind SLS is similar to other AM processes, in that source material is heated and built up layer by layer to complete a 3D structure imported as a STL file from Computer-Aided Design (CAD) software. The laser pulses on to the build platform, mapping a cross-section of the model on the loose powder, heating the powder to slightly below the melting point which fuses the particles together. While the layer height is dependent on the machine and the required accuracy, it is generally in the region of 100 microns. Once all the layers have been constructed, the object is left to cool before being removed for post-processing.

In addition to minimizing material wastage, post-processing can be less involved than other AM processes due to the absence of solid support structures. Unlike many other AM processes generally used for prototyping, SLS parts can be used in production, which would be the reason for the majority of post-processing. Due to the nature of the process, SLS parts have a grainy surface finish. Polishing can be included in post-processing for a smoother surface finish, including a coating with a watertight material to counteract the porosity of the finished part. Depending on the intended use of the part, metal plating can also be added. In comparison to other AM techniques, the grainy surface finish and internal porosity would be considered as negative aspects, but the main downside to SLS printing is its susceptibility to warping, which affects the accuracy of large flat surfaces and small holes.

Selective Laser Sintering is a relatively new technique that has allowed the manufacturing world the opportunity to reconsider the design process, design opportunity costs, and how parts and assemblies are produced, even within the sphere of AM.

About the author:
Chris Brennan is a Manufacturing Engineer and the founder/owner of Thirteen Design Consultancy based out of County Louth, Ireland.
[email protected]
Instagram: @thirteendesignconsultancy
Facebook: @thirteendesignconsultancy
Twitter: @13DesignIreland
Prototype Hubs Profile: Thirteen Design Consultancy