3D printing is used to generate complex geometries which previously may not have been possible to produce. As long as a CAD file can be created it is no longer necessary to have tooling made, saving significant time and money on many projects. The creation of all ‘green’ bodies with 3D printing as with traditional process requires sintering and debinding of ceramic and metal parts.
To obtain a useful density (up to 99.5%) it necessary to extract the carrier material once the required geometry has been formed. Debinding; either by use of a chemical bath or furnace to apply heat, is the process to rid the part of this carrier. The time taken to do this depends on the geometry but can take up to 24-36 hours. Following the debind, the part will need to be sintered to make a fully dense part that has the fantastic material properties we all know and want from ceramic.
As with many traditional ceramic forming processes, and for that matter; 3D printing of materials like metal, as used on systems like Markforged Metal X, will require the use of a carrier. The 3DCeram and Nanoe materials, as supplied by 3D Matters in the UK, also require a carrier which contains ceramic particles and is necessary for the printing of ceramics.
- Debind and Sintering Process
As an example, we conducted the following cycle on some parts;
A furnace containing alumina parts are heated to 225°C with a heating rate of 2°C/min. Then a second phase where parts are heated to 550°C with a heating rate of 1°C/min and maintained for 2 h. Thirdly, the parts are heated to 1,300°C with a heating rate of 6°C/min and maintained for H minutes (H = 40, 65, 90, 120, 150, 180 min).
Finally, parts are cooled to 600°C with a heating rate of 6°C/min and subsequently cooled in a furnace. The samples were denoted as S(H), and H = 40, 65, 90, 120, 150, 180 min.
Debinding and sintering cycles will vary depending on the ceramic or metal material being used.
With most oxide ceramics it is not necessary to use gases like hydrogen and nitrogen, although there are occasional reasons to do so. Processing nitrides, carbides and metals will require sintering under gas to achieve fully dense parts.
Ramp ups and hold times are proven to influence the intergranular bonding of ceramic/metal particles with a geometry, irrespective of the process used to create the part, and it is more of a factor in 3D printing where parts are built layer by layer making it important to have control of these aspects. For example, it is known that pores decrease in size by approx. 25% with a doubling of a hold time from 30 mins to 60 mins so directly effecting the parts’ porosity.
The cycle time and temperatures can be run as defaults as supplied or altered to optimise the process for certain applications. This is a key feature for users of our technology in an Education or R&D environment so that parameters and their effects can be explored. This is in contrast to most systems, for example, the sintering process on the Metal X is a closed system designed to make it easier for users and as a result makes it a prescribed and controlled outcome, without the flexibility to alter the parameters.
- During debinding and sintering will my part change in size?
The removal of the carrier to obtain dense ceramic and/or metal parts is inevitable due to the removal of it in the debind and sintering process. Having parts formed layer by layer leads to a weaker binding force in the Z direction compared to the X and Y direction. It is for this reason that the shrinkage rates are different in the Z compared to the X and Y. The great thinking about knowing this is that the shrinkage can be managed so that accurate parts can be obtained. It is typical to expect a shrinkage of approximately 20% but is dependant on the material and cycle profiles. As a customer of 3D Matters we will provide the precise details, along with training so that accurately printed parts can be repeatably achieved.