June 2007 Edition

CNC

20 Percent Productivity Gain Built In

It pays to take a second look at processes. A Swiss company knew it was doing well, but sought to do better.

Better is the enemy of good. With this in mind, Mikron Machining Technologies improved its multistep concept of a linear CNC transfer machining system for use in precision manufacturing. The modular system achieves up to 20 percent higher productivity than before. Mikron used a control and drive package with the IndraMotion MTX high-speed control system from Bosch Rexroth Corp., Hoffman Estates, IL.

 “The movements are faster and follow each other in a more fluid progression than before,” Rolf Held, design manager of Mikron GmbH, Rottweil, Germany, said of the increased speed of the Multistep XS.

 Saving Fractions of Seconds
 “Although it’s always only a matter of a few fractions of a second, overall we are managing more workpieces per unit of time. According to initial experiences, productivity is up to 20 percent higher than with the previous model.”

 The Multistep systems – there are more than 150 of them – were harbingers of these fast systems, which, due to their modular construction, combine the productivity of a transfer line with the flexibility of a machining center.

 Within the Multistep concept, Mikron combines extendable, individual modules that are fi rmly linked to one another in a linear mode. At the same time, the user can, depending on the production task, combine one to three standard machining modules, with a five-axis and side machining facility for each.

 From the first module, the machine is fully operational and features all CNC functionalities. The control is designed to handle up to three standard modules, one special module for special machining operations, as well as the automatic load and unload station.

 “Fully extended, the CNC can operate up to 30 axes simultaneously in closed-loop control,” Held said. Linear extension, by means of further modules, boosts productivity because complex machining operations for workpieces up to 10cm × 10cm ×10cm capacity can be processed in parallel.

 “This is suitable for series launches or series run-outs because, as a result of the modular construction, the user has just the right amount of machine he needs for the quantity required,” Held said.

 In the redesign, the development personnel from Mikron opted for the high-speed, CNC Rexroth IndraMotion MTX.

 One Control Handles 64 Axes
It is possible to operate up to 64 axes with one control, with 12 mutually-independent CNC channels. Connecting the integrated IEC 61131-3 PLC Indra-Logic with multitasking capability offers a close link between the CNC and the programmable logic controller – PLC – and, at the same time, makes performance data possible. For example, the PLC processes 1,000 instructions in 60 ms and the CNC offers, where eight axes are controlled, an interpolation cycle time of 1 ms at a maximum.

 There are time savings when it comes to the machining complex parts in standard Multistep XS mode. CNC programs do not have to be fully loaded into the main memory at first; instead, they are processed continuously following activation by means of “CNC-Streaming.”

 The machining process commences while the code is still being generated or loaded in the background. Part programs are organized in a file system with main memory or mass storage unit allocation flexibility. This means that there are no restrictions on program size.

 The dynamic preliminary processing of NC subprograms, as well as jerk-limited speed management, increase the machining speed while ensuring improved machining quality. Mikron also makes use of special functionalities in order to increase productivity.

“With the Indra-Motion MTX, we can precisely specify automatic clamping adjustments down to 0.1°,” Held said. In practical terms, long-winded maneuvers to adjust gripping tools are not required.

No Retooling
  The system transports the workpieces from one module to the next without retooling. The circulation concept developed by Mikron minimizes the number of encodable work carriers.

 By means of alternate transfers by pairs between neighboring modules, the system provides a constant fl ow of production. Furthermore, the line features forward- as well as backward-flow operation. The workpiece change time is about 5.5 second, the chip-to-chip time in the modules is about one second.

 Contributing to higher productivity are the intelligent Rexroth IndraDrive servo-drives, with an extensive range of rotary motors and direct-drive technology. The IndraDrive servo-drives feature integrated safety functions for safe stopping and safe movements, in accordance with the EN 954-1, Category 3, standard.

 “Overall we have reduced nonproductive time by almost 40 percent,” Held said.

 For control communication, Mikron has, in the case of the Multistep XS, opted for Profibus, by way of field bus and Sercos interface, for real-time communication with the drives. The universally-open IndraMotion MTX supports current field bus systems and can be connected via Ethernet to ranked company software.

 “We initially took to the IndraMotion MTX due to its universally-open interfaces,” Held said. “But, due to the high speed, we are now also able to offer a considerably more productive solution.”

 Bosch Rexroth Corp. www.rsleads.com/706mn-201

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