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3D Printing Ceramics

It is becoming more practical for potters and ceramic artists or entrepreneurs to take on projects never before possible because of the increasing accessibility of 3D printing of ceramic materials or of materials that can act as piece molds or block molds. Objects themselves can be printed directly by extruding layers of a ceramic paste from a nozzle and by fusing powder particles layer-by-layer. This is an additive process as opposed to subtractive where material is cut away from a block to create a 3D object. The latter is more practical for making molds of relief designs for pressing the faces of tiles or for ramp pressing plastic clay.

The practicality of additive processes and quality and shapes that can be made are still big limiting factors to the technology. However it is clear that refractories (like shelves, posts, supports and even entire kilns) can also be printed and the smoothness of finish is not nearly as important. By printing a honeycomb structure within the refractory they can be made very light and well insulating and can be made from much more expensive materials than would otherwise be possible. Even things like stainless steel can be printed, this enables making complex molds for use with plastic and dust pressing processes.

Many technologies must be understood and exploited to make this possible in an application. One of the most difficult to surmount is learning the software design and conversion tools. This can be very confusing since hundreds of products are available. However there are standards and printers expect to receive a specific file format: STL. 3D design software can be very expensive but there are open source solutions. A major enabler has been a policy change by AutoDesk, the maker of industry standard tools for many years. They are building their future of mechanical design around a new product named Fusion 360 and, as of 2015, are releasing it for free use by education and business earning less than 100,000 per year. This product has exceptional online resources and training and this development could be the most important single factor the puts 3D into prime-time ceramic production.

Another factor is the RepRap international movement to develop open source hardware and software platforms for 3D printing. Reprap printers use standard buy-at-a-hardware-store parts or ones that the printer itself can make. This means that anyone can buy and assemble a printer to learn many details of their mechanics and operation. Once understood a printer of any size could theoretically be constructed. In ceramics the focus is on the print head and how to deliver a thick paste to it, extrude it an a constant rate and be able to turn the flow on and off in an instant. The latter can be a real challenge and one solution is to pressure-feed the paste to a print head having a barrel and auger like a pugmill and control the auger using a stepper motor to feed the actual extruder nozzle.

There is a problem with scaling to a bigger size. The printhead must be able to move on three different axes, X, Y, Z. There must be a minimum of mass resisting movement in any of the three directions in order to have precise and quick movement of the print head. On most small RepRap printers the bed on which the item being printed sits moves as the y-axis but this is not possible on larger printers where the item being printed has too much mass. That means that the Delta printer design is more practical since the head itself can move on all three axes and the item being printed is stationary.

A major challenge is making it set fast enough so that the next layer applied over it will have a firm base. When plastics are extruded they simply cool and firm up, but a clay paste must set. Solutions may involve additions of polymers or other materials to set the clay paste and finding ways to pressure-deliver stiff pastes of low water content. When large objects, like an entire kiln are printed, fans and the extra time may be enough to enable a strong enough structure. In some types of 3D printing support structures are printing at the same time and these are later removed, this could be practical for ceramics also.

An exciting technology is laser fusing of powder, even metal powder. In this way stainless steel can be printed. This enables printing complex molds for dust pressing of tiles.

The computer board on a common RepRap 3D printer

The computer board on a common RepRap 3D printer

This controls all the stepper motors and the heating element and watches temperature and position sensors. It run open source software that knows how to interpret an STL file. As it reads that file steps the z-axis upward for each slice and then prints that layer by moving the printhead and movable bed for the x and y axes.

The movable printing bed on a common 3D RepRap printer

The movable printing bed on a common 3D RepRap printer

Objects are printed on a platform that moves along the y-axis. The bed is attached to bushings that run along stainless steel rods. Its position is controlled by a rubber belt that feeds around a pulley in the front and around a gear on a stepper motor at the back. It is heated to prevent printed layers from hardening too rapidly.

The printhead of a common RepRap printer

The printhead of a common RepRap printer

The assembly consists of stepper motor with its own cooling fan and a heated brass nozzle mounted in a small aluminum block (at the bottom). The nozzle has a heat sensor and its own cooling fan). A plastic filament feeds down through a hole in a laser-cut aluminum spring loaded part. It has an attached roller that forces the filament against a gear fastened to the motor shaft. When the motor steps it pulls in the filament and feeds it down into the heated print head below. The entire head assembly is screwed to a plate that is in turn screwed to bushings that are pulled along the x-axis by a belt controlled by another stepper motor. The computer can thus control the rate of filament feed, the temperature of the nozzle and the x-position of the entire head.

X and Z axis stepper motors on a RepRap printer

X and Z axis stepper motors on a RepRap printer

In this printer the printhead moves along two stainless steel rods (for the x-axis). Its position is controlled by the front top stepper motor (which has a gear through which runs a rubber belt attached to the printhead. The two lower stepper motors with worm gears attached to their shafts control the vertical z-axis position of the printhead assembly. Since the computer controls these motors it can move the head to any position on the x or z axis. Vertical z-movement is slower and more precise since it determines the thickness of each slice to be printed.

Out Bound Links

By Tony Hansen

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