With 3D printers from Voxeljet, it is possible to create sand cores for cast metal components, custom movie sets, functional plastic components, or architectural models. This is supported by an integrated automation and control solution by B&R.
"IN ADDITION TO OUR PRIMARY CUSTOMERS in the automotive industry, we are increasingly seeing new customers in a wide range of industries discover the potential of 3D printing. This is particularly true when it comes to producing proto-types, small production runs, and models quickly and without special tools," explains Björn Matthes, responsible for electrical planning at Voxeljet. "In recent years we have drastically expanded our range of printing services, and at the same time we have also developed a full spectrum of devices to handle workpieces of virtually any size."
The printing technique used by Voxeljet (Germany) is quite similar to that used by traditional ink-jet printers. The difference is that the company's specially developed print head uses a liquid binder instead of ink. Layer by layer, the binder is applied on top of a coating of particles on the printer's platform in the shape of the workpiece to be created. This is how the VX4000 – the largest 3D printer in the world according to the company – creates components measuring up to 4 m length, 2 m width and 1 m hight out of plastic, sand, or other particle-based materials.
First produced by Voxeljet in 2009, the VX4000 prints each layer in just 75 seconds with a resolution of 600 dpi and a thickness of 150 µm to 300 µm. The spacious platform allows the VX4000 to produce large individual components or several smaller parts. By using the CAD data directly, it provides precision and accuracy. The printer's software places the 3D CAD model in a virtual workspace and then breaks it down into print layers. In order to process the large volumes of data involved, the system uses an industry-grade PC featuring an SSD system disk and an additional hard disk with at least 1 TB of storage.
"On all the 3D printers we built prior to the VX4000, the PC was also responsible for controlling the entire system via a CAN connection," says Matthes. In developing the VX4000, the company introduced an additional level of abstraction in order to further simplify the control architecture and relieve the PC of some of its burden. They also needed to develop a gantry system to drive the two portal systems on which the print head and particle recoater are mounted.
In the automation solution for the VX4000, which uses B&R technology for everything except the PC, a CPU module from B&R's (Germany) X20 series functions as the motion controller. Movement commands generated by the PC are transmitted via Ethernet to the CPU module, which converts them into the corresponding motor movements. The VX4000 uses four servo motors controlling the Z axis of the two portals of the gantry system. All motors are powered by B&R’s Acopos Multi. The drives are also used to coordinate the sequence of lower level functions that regulate tasks directly related to printing, such as the moving the print head and filling the recoater.
The automation solution now incorporates the Safe Torque Off (STO) and Safely Limited Speed (SLS) safety functions. Both functions were implemented by Voxeljet developers using B&R’s inverter modules. "Even with the large dimensions of the printer, which measures 20 m long and 7 m wide, servicing and commissioning are much easier because personnel can safely move around inside the printer and monitor the processes without having to hold down an enable switch," says Matthes.
The system was designed with the I/O modules split into two strands. While the safety I/O channels are connected directly to the CPU, the I/O channels with no implications on safety are isolated via Powerlink. Originally, this separation didn't exist. "By separating the channels it is now easier to expand the system. Another bonus is being able to disconnect the power supply for the standard slices without affecting the safety-related areas," continues Matthes.
In addition to the integrated safety functions, Voxeljet has since also incorporated the concept of virtual axes into the system's architecture. Now all master axes are implemented as virtual axes. This means when developing the control software, it doesn't matter which drive will later be connected to a particular axis or how the axes should work together. "This allows us to simulate the drive hardware and test the automation solution even before the system is completed," explains Matthes. "What's more, using virtual axes makes it much easier to reuse the automation architecture for other systems."
Voxeljet already has its sights set on its next innovation. "We use an eccentric shaft in the recoater. This puts extreme pressure on the bearings," explains Matthes. "Since a print job can only be interrupted briefly, stoppages caused by worn out bearings can result in an entire workpiece being lost." This is particularly frustrating if it happens just as you are finishing a large item, where the printing process can take several hours. With this in mind, the company investigated the possibilities of condition monitoring and the corresponding X20 module from B&R for detecting bearing damage before it becomes critical.
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