The characteristics of additive manufacturing and how to use it in the fabrication of metal pieces

What is additive manufacturing? 

Additive manufacturing, also known as 3D printing or rapid prototyping, is the fabrication of metal parts by using a 3D model and applying several layers of material to it. 

Fabricating metal parts through additive manufacturing has become one of the most interesting technologies of the sector throughout the last decade – one the one hand, because it offers the possibility of prototyping for process and case studies, on the other hand through the option of fabricating complex geometric pieces directly. Additive manufacturing is the speerhead of an industrial revolution in different sectors, especially in aviation, heavy industries and the health sector, but also in automotion and the energy economy.  

There are two groups of fabrication technologies for metal parts in additive manufacturing : fusion-based technologies, where the final part is produced by directly melting the primary material, and technologies that rely on sintering, where a green part is produced first, while the final product is obtained through de-binding and sintering. The following image shows the classification of additive manufacturing technologies according to ISO / ASTM 52900.  

Depending on the pre-defined objectives, either FDM (Fused Deposition Modeling) or Binder Jetting technologies are selected to implement additive manufacturing.  

Definition of FDM and Binder Jetting technologies 

FDM and Binder Jetting are forms of additive manufacturing the most resemble the MIM process in terms of the specifics of the process and the final products.  

When fabricating metal parts through FDM, powdered materials (metal and polymeres) are applied layer by layer through a jet. This technology can use filaments, pellets, or bars as primary material.  After creating obtaining the green shape, de-binding and sintering are necessary to obtain the final product.   

In Binder Jetting, layers of metal powder are applied to a printing model and mixed with polymeric materials which are applied through a jet. These polymeric glues have to dry and harden after each layer. After finishing the printing, a so-called “de-powder” process is necessary to remove the excess material and obtain the green part. Then, de-binding and sintering are necessary to obtain the final product. The de-binding process is less critical than usual in the Binder Jetting process as very little gluing material has to be applied between the layers. This makes it easier to remove the binders, but in turn also amkes the green shape more fragile and complicated to handle.  

The heightened economic interest in additive manufacturing has resulted in the development of a very competitive market for 3D printers. At Ecrimesa Group, we have conducted an extensive benchmarking process over the last few years in order to evaluate providers of 3D printers and implement the technology in our facilities. After the comparative study based on characteristics such as the resilience of the green shape, surface quality, porosity, deformation and the costs of the printer, we selected the Studio System printer by Desktop Metal in order to implement additive manufacturing in the company. This enables us to explore new markets and create more added value for our customers.  

STUDIO SYSTEM PRINTER BY DESKTOP METAL 

Flowchart foe the fabrication of prototypes with the printer Desktop Metal:  

How to use additive manufacturing in the fabrication of metal parts   

The design of the pieces has to be adapted to the technology used for their fabrication. As with traditional technologies, additive manufacturing too has certain limits that have to be respected when designing the piece. This is why Desktop Metal has developed a set of ground rules for the design that have to be applied when developing the metal parts. These rules are recommendations – if the limits shown in the following table are not respected, problems might arise in different steps of production. 

The Studio System printer is equipped with two printing heads for different printing qualities: a standard jet with a diameter of 400µm and a high definition jet with a diameter of 250µm. The design recommentations in the following table are sorted per jet.   

		Standard jet 400µm	High definition jet 250µm
	Maximum size of the parts	X 240mm Y 150mm Z 155mm	X 60mm Y 60mm Z 60mm
	Minimum  size	X 6mm Y 6mm Z 6mm	X 3mm Y 3mm Z 3mm
	Minimum wall thickness	1mm	0.6mm
	Maximum wall thickness	10mm	10mm
	Infill density	1.5-3.2mm	1.75mm
	Minimum drill size	1.5mm	0.75mm
	Minimum pin diameter	3mm	1.5mm
	Minimum overhang angle	40º	40º
	Aspect ratio	8:1	8:1
	Thickness of layers	0.15-0.3 mm	0.05-0.15 mm
	Minimum elevation	X/Y W 0.45mm H 0.50mm  Z W 0.25mm  H 0.50mm	X/Y     W 0.30mm  H 0.30mm  Z         W 0.15mm  H 0.30mm
	Min engraving size	X/Y W 0.45mm H 0.50mm  Z   W 0.25mm  H 0.50mm	X/Y W 0.30mm H 0.30mm Z W 0.15mm H 0.30mm
	Empty space between components	0.3mm	0.2mm

In terms of the dimensional tolerances that can be reached with the printer, Desktop Metal guarantees the following values for the standard printing profile. The characterisation of the other printing profiles has yet to be determined. 

The obtained tolerances depend directly on the printing, de-binding and sintering processes. Dimensions of less than 65mm result in dimensional tolerances of ±0.5mm, bigger dimensions result in dimensional tolerances of ±0.8% of the measured height. These tolerances can be guaranteed when sticking to the design rules described here. 

The surface finish is one of the most important aspects of additive manufacturing. As it is one of the main limits of the technology, further processes are necessary in many cases to obtain the desired surface quality. The roughness of the printed objects depends on the size of the jet as well as the thickness of the printed layers.  

Business development strategy for additive manufacturing  

These are the main goals of Ecrimesa Group in the implementation of additive manufacturing:  

• Manufacturing of prototypes prior to the production of the mould with characteristics as close as possible to MIM-fabricated pieces 

• Possibility of design studies with the client prior to the production of the mould 
• Increase the speed of the MIM process through studies on prototypes (positioning during sintering, deformation studies, defects, etc.) 
• Production of short series of metal parts with complex geometry that would be too costly to fabricate by MIM or whose form is too complex to produce by MIM