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On-demand riveting process 

To riveting processes in one machine, supplemented by task oriented automation components, facilitate plant configurations ranging from manual feed to an automated riveting cell

The functional and process reliability of today's various cold riveting processes are so advanced that secure and tight joints can be fabricated with rivets for many industries, even on safety relevant components. A variety of processes are available to fabricate these positive fit connections. The various advantages of these can now be ideally used with a new CNC riveting machine by swapping out riveting heads or anvils.  Various transport and add-on facilities are also available to upgrade these from manual plants to automatically operating riveting cells.


Various forms of riveting joints and automation levels are one of the performance characteristics of S. Dunkes GmbH machinery factory. When manufacturing safety relevant, function-specific, fixed, mobile, or visually appealing joints, the know-how and the machinery and process product line make the machinery builders from Kircheim/Teck to a highly sought after supplier for users world-wide. The new CNC riveting machines, which can be used for wobble and radial riveting by swapping riveting heads, yet again demonstrate the company's innovation capabilities. Wobble riveting is used when a part requires short cycle times in combination with high forming forces at clearly defined flow directions. Radial riveting is used when the primary objective is to rivet insertion hardened or coated components. The user's process selection decision is now simplified, since the new product technology allows him to select the most efficient joining technology, depending on the application, workpiece load, desired riveting quality, part geometry, and series unit volume.


From pivot tables to cells

Dunkes provides a variety of automation and add-on facilities for different series unit volumes and riveting patterns. In addition to the process selection, the user can select from additional modules to solve their requirements cost-effectively and with a minimum of effort. The available facilities range from pivot tables to multi-station rotating index tables, as well as task-oriented automation elements for component feeding and retrieval. These base concepts can be further upgraded and automated with add-on facilities such as rivet feeds, measurement and control facilities, as well as various controls, including the documentation of all properties for 100% quality inspection, etc.


For instance, the pivot table is used for simple, strictly manual feeding of the riveting machine. In the 2-station configuration, the part is placed into the workpiece-specific receiver and cycled by 180° into the machine. During the riveting process, a completed part can be retrieved from the first station while a new part is inserted. When other processing units need to be integrated, we recommend using a rotary index table with 4, 6 or more stations. Depending on the processing task, these multi-station solutions can be equipped with user-defined workpiece receivers, and upgraded with rotating and retrieval stations, or equipped with additional functions by adding assembly, screw placement, or marking facilities. They can also be controlled by appropriate control and monitoring systems to a degree that various riveting patterns and shapes can be manufactured in automatic processes. Workpiece carrier transportation systems provide additional alternatives for workpiece feeding and retrieval, in which case the CNC riveting machine is integrated into the overall material flow.


Cell with swappable rivet head

Of the basic concept of an indexing table configuration involves a mechanically actuated 4 station table that receives the parts to be riveted, and cycles these through the loading station, the riveting machine, and to the retrieval position. When required, the orientation of the part, the presence of a rivet, and the rivet height can be inspected at the second station. This station can be adapted to the desired automation level and the quality requirements with additional add-on facilities.


The riveting pattern of the workpiece is positioned in X and Y directions by an NC coordinate table secured into a receiver of the indexing table. Its motions are defined relative to the home position of the workpiece, and not relative to the home position of machine. This avoids conversion errors for chain dimensions and significantly reduces the programming effort. The z-axis stroke is performed by the riveting machine. When required, a spring-loaded holddown secures the parts to be joined, therefore preventing a misalignment of the hole patterns during the and anvil impact. The rivet head for the wobble or radial process can be swapped with a quick-swap facility. One process can be converted to the other in the shortest possible time, and can also be accomplished manually, similar to a tool change in a machining centre. When rivet shapes change frequently, the respectively required anvil can also be inserted with the automatic swap facility. The programmable Z-axis allows the stroke to be conveniently adjusted to the various rivet heights for multiple rivets.


Any parts identified as defective are automatically sorted out and deposited outside of the machine. In accordance with safety regulations, the riveting cell is surrounded by a safety fence on three sides. Access from the front is secured by a light curtain that also releases the processing cycles of the indexing table. This also significantly reduces the cycle time when the single or two cycle trigger process is used during manual insertion. All machine configurations correspond to the CE regulations.


Controlling and monitoring

The control has a particularly user-friendly design. The operator enters important parameters, such as the riveting force, riveting stroke and the X/Y travels via the monitor. Originating from the upper lip of the indexing table, the home location of the Z-axis is selected such that the rivet height and the feed motion are determined and programmed with the greatest possible ease. When automatic processes are involved, the rivet height can also be detected before the riveting process. The user-friendly screen can also visualize the respective status, and also display faults and provide troubleshooting recommendations. Riveting forces can also be programmed with a min. / max. envelope stored in the control and displayed as a force-distance diagramme. When the measured riveting force is within the specified tolerance range, the part is cycled to the next station; when the riveting forces are outside of the range, the part is  identified as a defect and is removed manually, or, in the case of an automatic configuration, conveyed from the workspace by a handling device.


The additionally available rivet force detection also allows target and actual riveting values to be forwarded for documentation analysis to an external computer using a serial RS-232 interface, or to a printer via a Centronics interface. 32 selectable target value sets with 8 force-travel envelopes each are available for this purpose. This solution provides significantly more representational formats than a commercially available PC. Analysing the travel, time, or force dependent measurement results is therefore possible on-demand, regardless of the respective rivet pattern.


Consolidated process benefits

The new CNC riveting machine facilitates the use of pneumatically as well as hydraulically driven riveting units with forces from 5 to 120 kN. This permits riveting of shaft diameters from 2 to 30 mm. Special riveting heads are available for smaller diameters, which are characterized by extremely low bearing friction and a fixed anvil. The process benefits of radial riveting also permit processing of high quality, galvanised, as well as insertion-hardened rivets or components. But also visually less demanding joints can be fabricated cost-effectively in the riveting cells. For instance, in this case, the use of the also Dunkes supplied press riveting technology with its high bearing stress provides an additional alternative to fabricate riveting joints for high loads.


Many applications in the automobile, electrical, EBM and hardware industry, in mechanical engineering and other industries, frequently require additional processing steps during component manufacturing, such as part marking processes involving  coining, engraving, or colour additions, as well as torque inspection, assembly work, etc. Proven components and automation elements are available from Dunkes for these tasks, which can be integrated into the production process flow surrounding the riveting units. Starting with competent process consulting, the user is assured that they will be supplied with properly matched components for an economically and reliably working riveting plant from a single source.

Basic configuration of a riveting cell with 4-station rotary index table
Operator and control elements of the riveting cell with a rivet force recording facility
The CNC riveting machine is programmed at the monitor