3D printing – Made to measure
Using 3D printers from voxeljet it is possible to create complex sand cores for cast metal components, custom movie sets, functional plastic components as well as highly accurate architectural models in just a couple of hours. Beyond the high levels of precision and unprecedented levels of design complexity that can be achieved with 3D printers, what users really appreciate is the tremendous time savings to be gained when producing small production runs, prototypes and models. All of this is supported by a versatile, integrated automation and control solution based on high-performance B&R technology, which ensures that even large print jobs can be handled reliably, precisely and accurately.
"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 prototypes, 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."
Largest 3D printing system in the world
The printing technique used by voxeljet 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 – creates components measuring up to 4 meters long, 2 meters wide and 1 meter high 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 150-300 µm. The spacious platform allows the VX4000 to produce large individual components or several smaller parts simultaneously. By using the CAD data directly, it ensures high levels of 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 voxeljet system uses an industry-grade PC featuring an SSD system disk and an additional hard disk with at least 1 TB of storage.
A seamless product portfolio without rival
"On all the 3D printers we built prior to the VX4000, the PC was also responsible for controlling the entire system via a CAN bus connection," says Matthes. In developing the VX4000, voxeljet introduced an additional level of abstraction in order to further simplify the control architecture and relieve some of the burden from the PC. They also needed to develop a gantry system to drive the two portal systems on which the print head and particle recoater are mounted.
"We've learned from experience that if different suppliers are involved in producing the drive system, problems can arise due to tension and unclear responsibilities," explains Matthes. "That's why we were looking for an partner who could handle the entire automation system, from the gears right through to the control system and HMI."
Matthes notes that voxeljet quickly concluded its selection process with a clear favorite. "B&R's seamless product range, which includes integrated safety and a universal development and configuration tool, really convinced us that we had found the right partner. The B&R system gives us everything we need as well as plenty of scope for future innovations."
The decision was sealed in a meeting with application engineers from B&R, where voxeljet was able to see firsthand just how easy it is to build a gantry system using B&R technology.
In the automation solution for the VX4000, which uses B&R technology for everything except the PC, a CPU module from B&R's X20 series functions as the motion controller. Movement commands generated by the PC are transmitted via standard Ethernet to the CPU module, which converts them into the corresponding motor movements. In addition to the four servo motors controlling the Z axis of the two portals of the gantry system, the VX4000 uses up to an other another eight LSA and JSA servo motors which are partially synchronized (2 x X1 and 2 x X2). voxeljet uses exclusively servo motors in order to keep the architecture flexible, respond quickly to future requirements and optimize inventory. All motors are powered by ACOPOSmulti drives which communicate with the controller via POWERLINK. The drives are used for more than just motion control. They 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 (Y) and filling the recoater.
"The prototype VX4000 which was built using this architecture is still working efficiently and reliably at our service center," says Matthes. "Of course, we have continued to develop and improve the architecture since then."
Simple commissioning with openSAFETY
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 ACOPOSmulti inverter modules with integrated SafeMC safety technology and Safe I/O modules from the X20 system. "Even with the large dimensions of the printer, which measures 20 meters long and 7 meters 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 equipment and time needed to integrate the safety functions was minimal thanks to the openSAFETY communication protocol."
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.
Virtual master axes simplify reuse
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. For voxeljet this means that, 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."
Matthes is speaking from experience, because voxeljet has already reapplied the B&R-based automation solution to its recently launched VX2000 with only minimal modification.
Automation Studio offers a number of clear benefits for voxeljet. It provides a single tool that unifies the entire range of B&R automation components, including control software, HMI and safety functions. The comprehensive diagnostic functions make analyzing software and troubleshooting errors much easier. Of particular value is the clear structuring of the engineering environment and the ability to synchronize hardware configurations thanks to the integrated EPLAN interface. All new automation projects from voxeljet are created using Automation Studio 4.
Bearing wear at a glance with condition monitoring
voxeljet already has its sights set on its next big 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, voxeljet investigated the possibilities of condition monitoring and the corresponding X20 module for detecting bearing damage before it becomes critical.
The developers at voxeljet received great support from B&R when introducing this and other technologies. As Matthes explains, "from the very first training session it was clear that B&R really thinks ideas through from start to finish to ensure that they are implemented right. The level of support at B&R is outstanding and it has helped us many times in the past to quickly answer questions and develop our engineering skills."