Case studies of additive manufacturing with metals

Additive Manufacturing: comparison between studio system desktop metal, conventional filament and binder jetting printers

At Ecrimesa Group we have carried out in recent years an extensive benchmarking work on solutions and suppliers of 3D printers to implement this technology both in the manufacture of prototypes prior to the manufacture of the mold and to accelerate the MIM process through the study of prototypes of the final parts. Also, short series of parts with complex geometry are produced with Additive Manufacturing.
In this study process, case studies have been carried out with Desktop metal’s Studio System printer and Binder Jetting.
These are our conclusions.

STUDIO SYSTEM DESKTOP METAL PRINTER  

For a more precise evaluation of the quality that can be obtained with Desktop Metal’s Studio System printer, prototypes are printed in 17-4PH material with 3 different qualities and processed up to sintering to elaborate the analysis on metal parts.

PROTOTYPE	NOZZLE	LAYER HEIGHT
A	250 μm	0,05 mm
B	400 μm	0,15 mm
C	400 μm	0,3 mm

Prototype A marks the most optimal surface quality that can be obtained with the machine, with 250µm nozzle and 0.05mm layer height, while prototype C reflects the least optimal quality of the machine, printed with standard 400µm nozzle and 0.3mm layer height. Prototype B reflects an intermediate quality between A and C. It is the most optimal quality that the standard 400µm nozzle can print.

The properties obtained after debanding and sintering are shown in the table below. The higher the surface quality (smaller nozzle diameter and layer height) the better density and structure we obtain. The larger the nozzle and layer height, the greater the printing defects resulting in low densities after sintering.

PROTOTYPE	NOZZLE	LAYER HEIGHT	DENSITY	% C	HARDNESS
A	250 μm	0,05 mm	7,64 g/cc	0,03	288 HV10
B	400 μm	0,15 mm	7,60 g/cc	0,03	291 HV10
C	400 μm	0,3 mm	7,46 g/cc	0,04	192 HV10

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If the deformation of the prototypes is evaluated, we obtain the opposite effect. The deformation increases the smaller the nozzle and the layer height, obtaining prototypes that require subsequent straightening processes to achieveacceptable tolerances.

PROTOTYPE	NOZZLE	LAYER HEIGHT	DEFORMATION/OVAL
A	250 μm	0,05 mm	0,17 mm
B	400 μm	0,15 mm	0,05 mm
C	400 μm	0,3 mm	0,01 mm

It is important to find a balance between the surface quality obtained and the deformation of the sintered prototype.

Finally, a relationship is established between surface quality, printing time and price for each prototype studied.   

 

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PROTOTYPE	NOZZLE	LAYER HEIGHT	DEFORMATION / OVAL	COST
A	250 μm	0,05 mm	0,17 mm	10,17 €
B	400 μm	0,15 mm	0,05 mm	9,83 €
C	400 μm	0,3 mm	0,01 mm	9,60 €

CONVENTIONAL FILAMENT PRINTER

Ecrimesa Group has acquired in its facilities a conventional filament printer that, like Desktop Metal’s Studio System, uses FDM printing technology but differs in that the raw material is given in the form of filament instead of bars. The manufacturing technology is also defined in this case as FFF (Fused Filament Fabrication). The advantage of this printer over the Studio System is that it is a printer with open material, i.e., it is capable of printing filaments from different suppliers, including filaments developed for specific applications and uses. For this reason, Mimecrisa has been committed to the development of filaments in collaboration with the CDTI and a technology center (stainless steels, low alloy carbon steels, superalloys, etc), for more than two years for printing prototypes and processing within its facilities, in addition to being able to use commercial filaments that already exist in the market.

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BINDER JETTING AT ECRIMESA GROUP 

According to the evaluation carried out in Ecrimesa Group on the prototypes printed by Binder Jetting technology, it can be concluded that the final properties of the parts printed by this technology are the most similar to the MIM technology, if we compare the Additive Manufacturing techniques based on sintering. However, the investment required for the implementation of Binder Jetting technology is much higher than in the case of FDM technology. This is why we contemplate the subcontracting of Binder Jetting work whenever the project requires it, waiting for the technology to mature and settle before incorporating the purchase of the machinery to the group.

The following point lists some design recommendations to take into account before printing parts using Binder Jetting technology (source: www.digitalmetal.tech):

• Maximum length: preferably <50 mm in the longest side, but permissible up to the dimensions of the print box to scale. Tamaño mínimo: 1 x 1 x 3 mm.
• Minimum size: 1 x 1 x 3 mm.   
• Corner R: 35 µm.  
• Chamfer: 35 µm steps in Z direction.  
• Resolution: 35 µm. 
• Wall thickness: Preferably > 300 µm, up to 150 µm depending on area and design.  
• Holes: > 200 µm.  
• Surface quality: Ra 6 µm (without secondary operations).

CASE STUDIES BINDER JETTING PROTOTYPES  

The sintering process is one of the most critical fundamental stages of the Binder Jetting technology. The sintering cycle must be optimized for each material to obtain metal parts with the right density, carbon and deformation. Sintering in unsuitable sintering cycles can result in problems of defects, deformations, wrong shrinkage factors, incorrect properties, etc. In this sense, Ecrimesa Group has a Know-How in the sintering process consolidated during years of experience. So much so that all the sintering tests of Binder Jetting prototypes carried out in Ecrimesa Group have better results of density, carbon and deformation than the prototypes received already sintered by the suppliers of printing machines.

	MATERIAL: 316L	MATERIAL: 316L	MATERIAL: 316L
	DENSITY	% C	OVAL
PROVIDER	7,72-77 g/cc	0,011	0,01 mm
MIMECRISA	7,72-77 g/cc	0,003	0,01 mm

	MATERIAL: 316L	MATERIAL: 316L	MATERIAL: 316L
	DENSITY	% C	OVAL
PROVIDER	7,90-92 g/cc	0,011	0,20 mm
MIMECRISA	7,87-89 g/cc	0,007	0,14 mm

	MATERIAL: 17-4PH	MATERIAL: 17-4PH	MATERIAL: 17-4PH
	DENSITY	% C	OVAL
PROVEEDOR	7,63-65 g/cc	0,010	0,15 mm

	MATERIAL: 316L	MATERIAL: 316L	MATERIAL: 316L
	DENSITY	% C	OVAL
MIMECRISA	7,85 g/cc	0,004	0,01 mm

At Ecrimesa Group we use Additive Manufacturing for:  

• Manufacture of prototypes prior mold manufacturing with properties as close as possible to those obtained with MIM technology.   
• Possibility of offering the customer design studies with prototypes prior to mold manufacturing.   
• Acceleration of the MIM process by means of studies on prototypes (sintering positioning, sintering supports, study of deformations, defects, etc).   
• Manufacture of short series of parts with complex geometry, whose investment in MIM molds is not appropriate due to geometric limitations or its cost.