PC-based control enables additive manufacturing of large plastic parts
3D printing processes have become a linchpin for innovation in the development, prototype construction and small-series production of plastic parts. Only precision, speed and object size appeared to be the limiting factors – or so it seemed. Polish machine builder ATMAT has now pushed back the limits of what’s possible in a major way through the use of control and drive technology from Beckhoff.
Until around 10 years ago, 3D printing was used mainly in rapid prototyping. Nowadays, however, the procedure has increasingly become a part of serial production. Krakow-based machine builder ATMAT recognized the great potential of 3D printing early on and, along with traditional mechanical engineering, has specialized in the manufacture of industrial 3D printers as a second mainstay. With Saturn and Jupiter, its current large-series printers, the company has raised the scale of the workspace to a new level – without any sacrifices to precision, printing speed and operating convenience. The developers have implemented this on the basis of PC-based control, i.e. with TwinCAT 3 software, an Economy CP6700 built-in Panel PC as well as EtherCAT I/O terminals and servo drive technology from Beckhoff.
There is no shortage of interesting application areas for the large-format 3D printer, including both the automotive and the aviation industries. One exceptional project is, for example, the restoration of a French Caudrin CR.714 model old-time airplane from the days before the Second World War. Not only was the fuselage damaged during the war, but the plane was also missing the propeller blades, hub, propeller cover and motor housing. This meant that a reconstruction of the plane using traditional methods would have required a great deal of time and expense. It was therefore decided to produce these parts using 3D printing with the support of ATMAT. "The most important aspect of the project, and at the same time its greatest challenge, consisted of reproducing the form of the fuselage and its real dimensions as precisely as possible," explained Robert Grolik, Head of the Automation Department at ATMAT. "Given that we were dealing with a museum piece, we also had to make provisions for fastening the printed parts in such a way that the historic elements would not be damaged at the time of assembly."
Precise printing of filigree components up to 1.2 m³ in size
Prerequisites for this type of restoration are precise 3D printers with sufficiently large workspaces for the production of large-format airplane parts along with their often complex geometries. All parts were printed using FFF/FDM (melt deposition technology). With this process, a strand-shaped filament is heated with an extruder until it melts, fed into the print head and applied precisely on the worktable – layer by layer until the component is finished. In so doing, the worktable functions as the Z axis and the timing belt-driven portal axes act as the X and Y-axes. A Saturn-type 3D printer was used for the reconstruction of the airplane parts. With a workspace of 1200 x 1000 x 1000 mm, it represents the second 3D printer manufactured by ATMAT in XXL format after the Jupiter. "From the beginning, we concentrated in parallel fashion on both the customer-specific projects and on 3D printers. It is only due to the know-how we acquired with respect to compact 3D printers that we were able to develop an efficient, large-format 3D printing technology such as is used in the Jupiter and Saturn models," emphasizes Robert Grolik.
It is not only for the creation of functional prototypes that Jupiter and Saturn are eminently suitable. The systems are designed to be integrated directly into production lines, which enables optimized mass production of individual 3D components. "International corporations, particularly those of the automotive industry, are happy to take advantage of this," explains Robert Grolik. The reason: The individualization of vehicles, in addition to the many equipment options available, is becoming ever more important. "Additive technology enables the production of these personalized equipment options – in a short time, in simple fashion and with low financial overhead." It is not only such simple components as rim caps or steering wheel elements which can be printed; nowadays, larger and quite complex structures can be implemented, ranging up to dashboards and lighting elements.
Furthermore, vehicle manufacturers are taking seriously the possibility of using 3D printing for the production of entire automobiles – not only for limited vehicle series, but also for functional prototypes ─ in order to be able to present the real appearance of a new model in 1:1 size even before the start of series production. This trend is visible not only in the automotive industry: "We are seeing this in the increasing share of unusual orders and small product series," notes Robert Grolik. This is because 3D printing not only enables the testing of innovative solutions prior to production; 3D printing also simplifies the organization of small-series production by companies. One no longer needs to order and store components in advance; they are printed in accordance with requirements.
The Saturn large-format printer is a prime example of these benefits. Specially developed for sophisticated (i.e. highly precise) applications, the machine combines a massive granite workbench with a portal axis with two printing units (main and auxiliary heads) for a high printing speed. The main head is comprised of two extruders with either one or two printing nozzles. This accelerates the printing considerably, even with complex geometries, explains Robert Grolik. The correct temperature of the working platform is ensured by a four-zone heating system built into the massive table. Its independent temperature controls reduce not only energy consumption, but also enable a more rapid achievement of the set working temperature. To keep the temperature constant, the enormous printing area is installed in an insulated heating chamber.
Compact drive technology for precise motion control
ATMAT has furnished the large-format printers with the compact AM8121 Servomotors from Beckhoff. Together with the massive construction, they ensure a positioning accuracy of 50 µm (X/Y axes) and 10 µm for the Z axis. For ATMAT, the positive experiences from previous work with the Jupiter series was decisive for the selection of the drive components. "An advantage of the AM8121 servomotors is that they can be actuated by the EL72xx servomotor terminals," says Krzysztof Pulut, Regional Sales Manager at Beckhoff. "With their compact dimensions in the standard EtherCAT Terminal format, they enable considerable space savings in the control cabinet in comparison with conventional servo drives." Furthermore, the One Cable Technology (OCT) considerably reduces the cabling effort for the printer, as power and feedback are combined in a single line. "Besides that, OCT lessens the risk of incorrect cabling and reduces the number of system components the machine builder needs to keep on hand," adds Krzysztof Pulut. The movement of the Z axis is executed with a stepper motor that is actuated by the EL7031 EtherCAT Terminal.
Beckhoff also supplied all of the I/O modules, including the safety technology. The safety requirements are implemented with the EL6900, EL1904 and EL2904 TwinSAFE Terminals. The special sensors, which monitor the temperature of the extruder heads, the table and the chamber (among others), use corresponding EtherCAT Terminals. "Temperature regulation is decisive for melt layering with FDM printers as it ensures the quality of the printed part," says Robert Grolik to explain the importance of the terminals for the printing process. Also essential for good printing results is an additional interesting solution which has occurred to the automation specialists at ATMAT: They use a laser sensor to measure the distance between the print head and table, which improves print quality, particularly in the first material layers.
Intuitive operation with TwinCAT HMI
The 3D printer is automated and controlled via TwinCAT 3 and the CP6700 built-in Panel PC from an Economy series. "The Intel Atom® processor (dual core) and 4 GB RAM are completely sufficient, even for our complex 3D printing orders," emphasizes Robert Grolik. With respect to system integrity, the experts rely on 30 GB of flash memory as an external medium and on a Beckhoff UPS with 1 s backup. It was primarily the capacity to withstand the occasionally rough production conditions and the integrated TwinCAT HMI visualization software that were decisive for the selection of the control hardware. "The latter offers a multitude of layouts and short response times, remote access and the support of QR code scanners," says Robert Grolik.
"The thing that convinced us about working with Beckhoff is the company’s openness for innovation. Beckhoff continuously develops and implements solutions which are rare among other manufacturers. From our point of view, the most important things were OCT, an advanced development environment for the HMI, and the Panel PC with Windows 10 as its operating system, which facilitated the integration of our 3D printers in higher-level systems," concludes Robert Grolik.