“Servo-Speed” from Coil to Sheet – SMEs develop innovative, servo-driven cut-to-length line for Steel Service Centre
“To be a cut above the others” – this was the aim, both literally and figuratively, of a group of medium-sized enterprises commissioned by a steel service centre to implement their special wishes in an automatic cut-to-length line for steel sheet. The “extras” on this facility include a long-stroke eccentric shear unit which is exceptionally flexible and dynamic thanks to its two servo drive motors. The “backbone” of the line incorporates control and drive technology from a single source.
Anyone purchasing ready-made engineering solutions has to take what is on offer and make do with off-the-shelf functionality. Hagener Feinblech Service GmbH (HFS) wanted more, opting instead to develop a cut-to-length line tailored to their specific needs and wishes, and made up of components from several different manufacturers. The finished cut-to-length line has since been put into operation following this successful joint project.
The HFS steel service centre is an independent, medium-sized enterprise that supplies customers all over Europe with precision-cut steel sheets in a wide range of grades and formats. The company is an “A” supplier to leading organisations, e.g. in the automotive, electro-technical and construction industries as well as in industrial applications, warehouse technology and mechanical engineering. Wherever it is appropriate for subsequent processing, coils can be cut into triangular, rhombic and trapezoidal shapes, thus minimising scrap. “Our main strength is the JIT provision of small and medium-sized lots of accurately dimensioned flat sheets in practically any steel grade”, says Andreas Ducke, technical director at HFS. “This diversity and flexibility is what our customers have come to expect from us; and to maintain our reputation in the long term, we make consistent investments in our machine park”. In 2007, for instance, when the company decided that it should additionally process high- and ultrahigh-strength sheet grades – types that are increasingly in demand, especially in the automotive industry. The objective was to develop and install production facilities that were technically fit for the future and would ensure reliable processing, as well as ranking well from an economical perspective.
Focus on flexibility, quality and productivity
When cutting sheets in various widths, lengths and thicknesses precisely and with utmost repetitive accuracy, while at the same time allowing for constantly changing dimensions, it is absolutely vital to have shears that are adaptable and fast. The concept provided for the shears to be fed with flat material from the coil by way of an in-line high-performance straightening machine with a dynamic forward feed mechanism. At the other end, the cut sheets had to be stacked quickly and accurately, made ready for shipment and disposed of promptly so that no bottlenecks would occur. Ideally, this was to take place fully automatically, and a change of format realized at the push of a button.
Several SMEs from the region around Hagen worked together with the sheet metal experts on the development of this new installation. The only exception was Huttenlocher & Schäfer GmbH (HSK) from Kirchheim/Teck in Swabia, whose shearing technology has been highly reputed for many years and was to be relied on in this project – combined with control and drive technology made by Siemens. To equip all the individual parts of the new line with this technology and coordinate them in a continuous line, HFS took on board the system integrator Elektroanlagen Gundermann from Nachrodt-Wiblingwerde.
Speedier cutting process with servo-technology
The throughput speed is determined by a high-capacity straightening machine (HiCap 70 Plus from Arku) which functions as the master and pacemaker of the new line. A high output is also conditional on how fast and how accurately the sheet can be positioned under the cutter bar, where it is stopped, cut and then removed. This in turn depends on the length of the individual sheet, which can range from 150 mm to 9,000 mm, with widths of between 400 mm and 2,050 mm, and sheet thicknesses of 0.3 mm to 4 mm. The performance specification defines length tolerances of just tenths of a millimeter and a squareness of less than 0.5 mm across the whole cutting width. “Servo drive motors that can be precisely controlled were evidently the most promising solution for achieving the required flexibility of this cut-to-length line”, says Dr. Timo Schäfer, engineer and managing director of the shear manufacturer, HSK. “For this reason, we set about developing a new generation of eccentric shears with servo drives in close consultation and with the active support of HFS, Gundermann and Siemens.”
The servo principle is already well established in the technically comparable field of press construction and was thus obviously predestined for this application as well. The decisive advantage of the servo drive: the motion sequence of the cutting blade can be configured extremely variably by adjusting the speed of the eccentric shaft; and the relation between the initial cutting time and the transfer time can be individually adapted to the product to be cut. As a result, it is possible to achieve a high output of relatively short sheets in continuous operations, whilst on the other hand assuring the cost-effective production of sheets of up to 9,000 mm in length. This is accomplished simply by adapting the continuously variable drive speed, using high speeds in the initial cutting range itself and lower speeds for the remainder of the stroke. The extra scope for faster feed rates (for larger sheets) allows for a longer stroke, for which the blade range and pressure angle are configured accordingly.
To ensure that sheets in soft and ductile grades could also be cut, HSK positioned a high-power synchronous servo motor (1FT6) from Siemens on either side of the cutter bar. In combination with torque and speed controls based on bevel gearing (Flender), these servo motors drive the eccentric shaft.
Innovative control and drive technology…
The linked motion sequences of the drives and shears are computed and controlled by a Simatic Microbox 420-T, an embedded automation system with special technology firmware and the functional attributes of a Simatic technology CPU S7-317T-2 DP by Siemens. The exceptionally compact and robust embedded PC has neither a hard disk nor a fan and communicates via its integrated profibus DP interface with the subordinate drive assemblies of the latest generation of Sinamics S120 from Siemens. More precisely, it is synchronized with the respective control units in the modular drive assemblies which ultimately feed the servomotors via separate power sections, known as motor modules of uniaxial and biaxial design. Moreover, they also feed the energy generated when the motors brake back to two intermediate circuits, which has a positive effect on the energy consumption of the system. A touch panel, type Simatic TP177A is connected to the microbox 420-T for visualizing the shear unit.
The new mechanical structure and the innovative control / drive concept of this bi-servo shears reduces the contact and/or stoppage time for cutting. The initial results were so convincing that HFS decided, during the commissioning phase, to implement the second discharge conveyor immediately instead of later, as originally planned, to reliably exclude the possibility of pile-ups and/or bottlenecks of finished sheets on the run-out side.
A further advantage of the new servo system for the shears is the straightforward mechanical structure as a result of which the time and effort needed for maintenance work during operation is greatly reduced – and consequently the costs as well. Smooth movements cause less strain on the mechanical components as well as having a positive effect on blade downtimes. The sensitive, automatic setting and adjustment of the cutting clearance also contributes to this factor. The entire cut-to-length line is, in fact, convenient and simple to set and adjust. The operator only needs to enter the length, width and thickness of the coil material, and around 50 drives, type Micromaster by Siemens, automatically bring the relevant parts of the system to the required starting position – and that rapidly and dependably. This process eliminates input errors and minimizes unproductive set-up times.
… from one source, all along the line
For cost- and space-saving reasons, the run-in section and the stacking facilities are controlled by real-time-compliant Siemens embedded controllers, type Simatic Microbox PC 427B. Apart from this, the Simatic WinCC flexible RT (run-time) visualising system for the line operates on the Microbox on the stacker. The straightening machine and stacker run-out – like all controllers – are integrated into the overall system by way of conventional, profinet-capable Simatic control systems and an industrial ethernet switch. The result is a perfectly coordinated, compatible system without any interface problems and with clearly assigned accountability.
Initial training in the systems, some of which were new, was uncomplicated and presented no problems, according to the system integrator, Günter Gundermann, who with his team has already automated similar installations for other manufacturers. In his experience, “Such a flexible, productive cut-to-length line is hard to find”.
Replacement parts and technical support are speedily on-site, whenever necessary. And in cases when that is not fast enough, a communication processor and WinCC flexible/SmartAccess option enable full access – even to the drive level of the line. Technical director Andreas Ducke is very satisfied, both with the intensive degree of collaboration between all those involved and also with the results achieved in such a comparatively short time. The new cut-to-length line has been running in 2- and 3-shift operations since mid-2008.
Shear manufacturers Huttenlocher & Schäfer have added this innovative variant of Siemens control and servo-drive technology to their portfolio and will consequently be in a position to fulfil their customers‘ wishes even more individually in future.