Compact manufacturing cells, efficient automation and fast set-up processes: With their large platens and free access to the mould area, tie-bar-less injection moulding machines fulfil the need for high efficiency and cost-effectiveness in production in the best possible way. 25 years ago, ENGEL became the first injection moulding machine manufacturer worldwide to present a tie-bar-less machine.
ENGEL
'The clamping unit of an injection moulding machine has four tie-bars.' Since the first single-screw injection moulding machine was developed in 1956, this design principle was regarded as inviolable. But when ENGEL unveiled a tie-bar-less machine at the world's biggest plastics trade show, K 1989 in Düsseldorf, the innovation by the Upper Austrian company was not appreciated by everyone. It was greeted with astonishment by some and ridicule by others and there were plenty of arguments against it. Twenty-five years on, tie-bar-less machines are among ENGEL's biggest revenue sources. More than 60,000 tie-bar-less machines have so far been delivered worldwide, which underlines the outstanding success of this design principle.
Better clamping force distribution compared to machines with tie bars
The idea for the new solution came from ENGEL's customers. Especially when using large moulds the tie bars would curb the creative freedom of mould manufacturers. The mould mount and dismount through the four tie bars is rather complicated. Already back in the 1980s, these restraints could not be reconciled with the demand for more efficiency in manufacturing.
In 1985, the ENGEL development department first came up with a new idea. They discussed the possibility of applying the clamping forces, which act on the mould mounting platens, via a C-shaped frame instead of tie bars. The challenge was to maintain the platen parallelism, because this is a deciding factor for the injection high quality of moulded parts and a high degree of mould protection. At the time, ENGEL already built vertical machines with a C-shaped frame construction, but simply applying this construction to horizontal machines was not an option.
The breakthrough happened in 1988, when the slanted position of the stationary mould mounting platen could be compensated for by attaching a joint to the moving platen. The pilot experiment was conducted by integrating a block with a lever behind the moving platen of a C-shaped rack, which solved the problem of asymmetrical force induction. In addition, the platen guidance received one degree of freedom upwards, which excludes any possible tension in the mould. This way, an even better clamping force distribution was achieved than with traditional machines with tie bars.
The success of the first experiments after the K show 1989 quickly convinced even those who had initially been sceptical. The interest on the market was so great that the tie-bar-less machine soon became the predominant construction design at ENGEL's headquarters in Schwertberg. In the subsequent years, the tie-bar-less machine turned into a full machine series which was dubbed ENGEL victory because of its victorious triumph.
More productivity per square metre of production space
The market soon realised that the barrier-free clamping unit did not only offer advantages in terms of setting up, but also facilitated very compact manufacturing cells with relatively low investment and operating costs. Since the mould mounting platens can be used to the hilt, relatively small injection moulding machines can be fitted with large or bulky moulds. In many cases a smaller machine can be used for the same mould size than compared to a machine with tie bars. Thus the purchasing cost is lower and the machine requires less energy and production space. As a consequence the productivity per square metre production space increases.
The efficiency potential is particularly large in manufacturing complex components, the use of multi-cavity moulds as well as multi-component processes. What these applications have in common is that they require large moulds, but the projected part areas and thus the required clamping force are often rather low.
Patent protection ensures uniqueness
With the tie-bar-less technology, ENGEL has a unique selling proposition until today. To date, there are a total of 45 patent families regarding tie-bar-less technology. Twelve of them are still in force today. Important milestones in the development concern mainly the Flexlink joint at the moving platen, which is employed in its fourth generation under the name force divider.
In a tie-bar-less clamping unit an expansion of the clamping frame and a minimal deflection of the clamping cylinder and the stationary mould mounting platen occur under clamping force. The central elastic element force divider, however, ensures that the moving platen exactly follows the mould while the clamping force builds up. To achieve this, the platen lifts itself from the guide shoes, automatically adjusts itself to the mould position and evenly distributes the clamping force throughout the entire cross section of the mould. The occurrence of transverse forces is thus avoided and the mould's service life prolonged.
As opposed to other machine designs, the stationary mould mounting platen of the tie-bar-less machine is not connected with the frame at the bottom end, but on the backside. This way it absorbs the machine's vibrations in a symmetric manner and remains parallel to the moving platen even during acceleration and deceleration.
On ENGEL's tie-bar-less machines, the parallelism of mould mounting platens can be adjusted very precisely, whereas the tolerances are significantly lower than according to the Euromap standard. Thanks to preloading of the patented force divider the platen parallelism remains constant even when the mould is mounted. Furthermore, the force divider ensures that the clamping force is evenly distributed throughout the platens. Also cavities located in the peripheral area of the mould are kept shut at the parting line with the same surface pressure.
Tie-bar-less and energy efficient
The tie-bar-less ENGEL machines continually adjust to the changing requirements of users. For example, also regarding the question of energy efficiency, the main topic of the 21st century, ENGEL has a tie-bar-less response. This response comprises the servo-hydraulic system ENGEL ecodrive, the machine series ENGEL e-victory with electrical injection units and the new all-electric ENGEL e-motion TL machine series, which combines tie-bar-less technology with an all-electric drive technology.
