Automated production of small batch sizes

Machine tool automation

Lauffen/Neckar, (PresseBox) - Considerable success has been made in automated machine loading: even in the production of extremely small batches it is possible to significantly reduce setup-related downtimes and to achieve full machine utilization around the clock with minimal manpower. The well-considered choice of clamping devices and gripping systems is a decisive factor in this respect.

Modern concepts for automated machine tool loading account for three central factors: minimal cycle times, maximum system availability and the capability of versatile response to production modifications and changes in demand. Best practice examples confirm that any manufacturer with requirements for a high level of variance and maximum efficiency in the production of small batch sizes should first of all reduce the complexity of his processes. This requires stringent tool conventions as well as clear agreements on toolholding and workholding devices. It is just as important to minimize set-up times through relocation to the immediate vicinity of the particular machine and to smooth out production by means of parts storage units. It is especially important for enterprises to have a good overview of the entire system consisting of the machine, clamping device, tools, gripping technology and other loading components. Because the individual circumstances always dictate the optimum method of machine loading for small batch production: direct change of the clamping device or handling of the parts by means of a robot, gantry or a flexible production system. The world’s largest assortment of clamping technology and gripping systems from SCHUNK, with more than 11,000 standard components, offers the ideal basis for customized solutions.

Individual modular solutions

Standardized palletizing systems enable highly versatile and stable change of clamping devices. The workpieces and clamping devices are set up on clamping pallets, stored in a rack and transferred from the pallet rack successively to the machining center. The bottom sides of the pallets are equipped with a standardized interface to the quick-change pallet system. Comparable to an adapter, they connect the machine with different workpieces. Modern palletizing systems additionally feature a lateral interface for stable connection to a robot or gantry. An especially efficient solution is the SCHUNK VERO-S NSA plus palletizing module, which has an extremely flat design, leaving plenty of room for the workpiece and for axial movements in the machine room. Due to a patented fast and clamping stroke, it achieves pull-down forces of up to 15,000 N and holding forces of more than 100,000 N. All functional components such as the base bodies, slide assemblies and locking rings are made of hardened stainless steel and are therefore absolutely corrosion-proof. A forced airflow cleans the end faces and short taper during automated changing to ensure a flat work surface with no chips. Centering rings then ensure exact positioning with reference points. Clamping slides provide for form-fit, self-locking clamping. Monitoring of the back pressure makes it possible to reliably monitor all process steps. A lifting pin lifts the pallet slightly to facilitate workpiece change. As opposed to other clamping systems the SCHUNK VERO-S NSA plus requires no energy during machining. The pallets themselves remain securely clamped even if the pressure in the air system should suddenly drop. The integrated spring assembly ensures permanent and safe clamping. A pneumatic system pressure of 6 bar is sufficient for opening the modules.

Robot couplings for loads up to 1,000 kg

To provide a standardized interface to the robot or gantry and to ensure a stable process, SCHUNK developed the compact SCHUNK NSR lightweight coupling with optimized interfering contours. It can also be used in small spaces and allows palletizing extremely close to the machine table. This enables the design of particularly low clamping stations and pallets. Since the parts outside of the force flow are aluminum and the parts in the force flow are stainless steel, the coupling achieves an optimum combination of rigidity, robustness and weight. The locking mechanism is form-fitting and self-locking. Opening, closing and the presence of a pallet are monitored by inductive proximity switches to ensure reliable monitoring of the entire change process. To increase process stability, the robot coupling is completely sealed against chips and lubricants and has an integrated cleaning function as a standard feature. Steel inlays at the contact points make the robot couplings extremely resistant to wear. The modules are extremely lightweight at only 400 g (NSR mini 100) and 1,600 g (NSR 160). They are ideal for the reliable handling of pallets weighing up to 75 kg (at 200 x 200 mm) and 300 kg (at 400 x 400 mm). In addition, SCHUNK developed the NSR maxi 220 robot coupling particularly for handling heavy loads of up to 1,000 kg. The module transmits torques of up to 4,000 Nm. Locking and unlocking are monitored by a path measuring system and the pallet presence is monitored by inductive proximity switches.

Clamping device change without a pallet

As an alternative to automated pallet change, complete clamping devices can also be used for automated machine loading. The SCHUNK VERO-S quick-change pallet system is then likewise used as the interface to the machine. This makes it possible to transfer SCHUNK TANDEM plus clamping force blocks to the machine within seconds for direct loading of workpieces by means of robots and SCHUNK grippers. Quick-change jaws provide for additional versatility. Some users even go further: they set up spring-loaded SCHUNK TANDEM plus clamping force blocks with rough parts offline and then transfer them to the machine in clamped state by means of a robot. The quick-change pallet system reliably absorbs lateral forces with no change in the position of the workpiece and no vibrations at the cutting edge of the tool.

Quick-change solutions for clamping devices

Highly versatile solutions are also possible with the jaw quick-change system of the SCHUNK ROTA THW plus wedge bar power chuck. Instead of setting up entire clamping devices, the required versatility is achieved by means of quick jaw change. Without having to turn the chuck jaws, they can be changed within a maximum of two minutes at a repeat accuracy of 0.02 to 0.03 mm. The chuck is particularly designed for the high requirements for process speed, precision and versatility of modern multi-tasking machines. The compact design ensures that there is plenty of space in the machine. Even more: in combination with workpiece-specific SCHUNK hydraulic expansion toolholder solutions that can be directly transferred to the modified power chuck, it is also possible to automatically load parts that are sensitive to deformation. All that is necessary for activation of the clamping mechanism is that the machine cylinder is pressed bluntly against the hydraulic expansion piston. When the cylinder retracts, the hydraulic expansion toolholder automatically releases. SCHUNK hydraulic expansion arbors and toolholders are an effective solution for minimizing set-up times, automated centering of workpieces and clamping at a repeat accuracy of up to 0.003 mm. Instead of using a separate base chuck for each workpiece size, SCHUNK hydraulic expansion toolholder solutions require just one base chuck, such as the SCHUNK ROTA THW plus.

Fast set-up processes are also achieved with a system for a tool free jaw change without tools that was specially developed for the SCHUNK ROTA NCO power chuck. A nose and a spring-loaded pressure piece allow manual change of the chuck jaws within just a few seconds, without the use of a tool. The chuck jaw does not lock into place until it is correctly positioned. This system completely eliminates typical errors related to chucks with fine serration, such as incorrect positioning of the chuck jaw, incorrect serration position or incorrect torque. The SCHUNK quick-change system reduces the set-up time for a complete chuck to less than one minute. Afterwards, the high-precision power chuck can be loaded fully automatically. Individually configured special jaws enable use of the system with an extremely large range of parts variation.

A new capability for versatile automation of power-clamped jaw chucks is the recently developed SCHUNK PRONTO jaw quick-change system. It enables fully automated set-up and loading of power chucks for a new parts spectrum. The required clamping inserts are stored on SCHUNK VERO-S base plates, from which they are transferred by a robot to the power chuck. Locking and unlocking are achieved with a special Allen key, which is also operated by the robot.

Front end quick-change solutions

To enable diverse utilization of handling systems, SCHUNK also offers a broad spectrum of quick-change modules for the robot front end. Generally they consist of two parts: a quick-change head, which is mounted on the robot, and a quick-change adapter, which is connected to the respective tool or gripper. When the tool is changed, both parts are automatically coupled with each other to create a stable mechanical connection. Depending on the application, they also ensure the reliable feed-through of pneumatic and hydraulic lines, as well as a stable power supply and the feed-through of diverse electrical signals. The patented “no-touch locking system” also enables reliable changing when the head and adapter are at a distance of up to 2.5 mm from each other. In addition, the locking system features a patented self-locking mechanism, which ensures a stable connection between the quick-change head and the quick-change adapter at a repeat accuracy of 0.015 mm – a significant improvement over other modules on the market. Mechatronic gripping modules, such as the SCHUNK PEH long-stroke gripper, feature a freely controllable jaw stroke for versatile handling of different workpieces and also provide important information, for example on the presence of a tool or on dimensions.

Freely positionable linear axes for linking machine tools

In the course of flexibilization of the production processes for Industry 4.0, the freely variable interconnection of machine tools is gaining of importance. Therefore, linear motor driven axes of SCHUNK LDx series are ideal for applications requiring versatile and dynamic transport along one axis. As opposed to conventional servo axes, they eliminate the need for complicated reference runs during system start up and after emergency stops. In addition, neither end nor reference sensors are required, which reduces investment costs, programming requirements and the number of cables in the cable set. Since several freely programmable slides can be placed on one guide profile, SCHUNK LDx modules can be used to achieve particularly compact and cost-effective concepts. The SCHUNK linear module series Gamma are particularly designed for machine linking when it comes to high payloads. It has a closed and therefore particularly rigid basic profile, and combined with highly loadable profiled rail guides, it ensures for an enormously high load capacity even without additional support. Due to the modules modular design, they can be excellently adapted to the individual applications. On option, they can be equipped with rack and pinion drive for high loads or with toothed belt drive for high traverse speeds. Equipped with rack and pinion drive, two or several slides can be actuated independently of one another; and with a toothed belt drive, two slides are working independently from each other. The reason for this particularity is based on the closed design, which allows positioning of two belt drive systems next to each other. For vertical applications, an additional rail clamping element is available, which prevents an uncontrolled drop in the case of an emergency stop or power failure.

SCHUNK at the EMO 2017: hall 3, booth E55

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