Linear motion technology supports precise 3D printing

Linear motion technology supports precise 3D printing
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How 3D printing works

How 3D printing works

A print head moves precisely via Cartesian axes along a predefined path above a box filled with sand or plastic particles. It sprays an inorganic binding agent in precisely defined contours onto the loose material from more than 10,000 nozzles. Then the bottom of the sandbox is lowered by 100 to 300 microns and a newly applied layer of sand fills the box. The particles stick together along the binding agent contours, at all other points it remains loose sand. This process repeats itself until the component is completed.

Content

March 2016

 

3D printers from voxeljet meet the highest accuracy standards thanks to durable linear motion technology from Rexroth.

3D printing is revolutionizing the manufacturing sector. In the automotive industry, in the manufacturing of designer furniture and architectural applications or sand cores for foundries, it is no longer a vision of the future. “With this additive process, our machines produce complex geometries with indentations from sand and plastics fully automatically and with high precision”, says Bastian Heymel, Manager for Systems Design at voxeljet AG in Friedberg, Bavaria. “Although we work without tools, when it comes to the components of our machines, as far as durability and accuracy are concerned, we strive to keep things to machine tool standards. This is especially true for linear motion technology.” voxeljet AG was founded in 1999 as a start-up at the TU Munich. Today, the company has a complete range of 3D printers in a variety of sizes.

voxeljet designed the VX1000 to be a powerful machine for universal use. These allow users make sand cores for light metal castings, automotive parts or individual architectural objects. A gantry axis moves the print head of the VX1000 with two Rexroth linear modules with belt drive along the Y-axis. They enable movement speeds of up to five meters per second and thus shorten the non-productive time between the printing of the individual layers. A further linear module with ball screw drive positions the print head with a repeatability of 0.005 millimeters along the X-axis. It moves a 20-kilogram print head on two tables precisely and uniformly, both are important prerequisites for attaining high accuracy in 3D printing. “The VX1000 achieves a printing resolution of 600 dpi, equivalent to 42 microns, which requires positioning the print head with a precision of less than five micrometers”, says Heymel of the precision at which the machines from voxeljet operate. Another gantry axis with linear modules moves the sandbox carrier in the Y-direction.

Well protected against sand and particles

“A key requirement is the resistance to sand, and other particles in some process solvents”, explains Heymel. Especially important for voxeljet, therefore, is the cover strip that closes the linear module on the carriage side facing outwards. Additional protection for the linear modules is provided by lateral seals and the front cover. This makes them encapsulated so that nothing enters and they attain a long life time in spite of the adverse operating conditions. Depending on size, the cover strip is made of PU high-performance plastic or stainless steel. Thanks to the high-precision BSHP ball runner blocks, that have been built into the linear systems since 2014, their service life also increases.

For the sandbox floor, voxeljet uses Rexroth roller rail systems in the Z-axis. “At the start of the process there is no load on the axis, but at the end, the sandbox of the VX1000 is filled with about 400 kg of sand and binding agents”, according to Heymel. Given the extremely small movements of less than 350 micrometers per cycle and the heavy load, only backlash-free roller rail systems meet the requirements consistently. Unlike the linear modules, the roller rail system is not fully enclosed. Nevertheless, they achieve a high service life thanks to the Rexroth sealing concept. “We have been using it in a variety of applications for twelve years and we aren’t aware of any breakdown in this axis”, says Heymel. At the end of the process, the sandbox is driven out over ball rollers from Rexroth onto the machine base and a replacement box is inserted.

On the global market

voxeljet has long been active on the world stage. In 2014, the company established a subsidiary in the USA. “We have already sold machines to the United States, South America and Asia”, says Heymel. “Precisely because the machines are constantly in operation at the customer’s site, it is important for us that Bosch Rexroth has a global presence and can quickly supply spare parts if needed.”