Thinking Outside of the Box
GM realizes "weeks to hours" reduction in line change and transmission build dynamics at Toledo Production Plant.
The tried and true saying, “thinking outside of the box” usually refers to a pattern of thought or action that results in rapid innovation, enhanced relationships being developed from established concepts as well as new ones, plus a genuine willingness to forego past practices in favor of a better way.
For General Motors Powertrain in Toledo, Ohio, however, that saying refers to the facility’s new GF6 six-speed, front wheel transmission line for smaller, more fuel-efficient vehicles such as the popular Chevy Malibu and new Chevy Cruze. Nothing new about such an event, until a closer look reveals how it came about.
Several years ago, during the development of this line, GM engineering contacted its longtime controls suppliers to investigate ways to reduce the workflow through the line, enable faster changeover, reduce reprogramming and prevent situations where one out-of-spec machine caused complete shutdown. Another key driver was the need to minimize maintenance time by installing PLCs, drives and component pallet recognition devices outside the conventional cabinetry found on traditional assembly lines. In addition, controllers were distributed throughout the system, which allowed for removal of typical zone controllers and, in turn, substantially increased system flexibility.
Following considerable investigation into the process for the new line, the major obstacle remained changeover and the need for a more flexible yet highly automated system of transmission builds. In consultation with the controls provider, Siemens Automotive Center of Competence and third party software package provider, Elite Engineering, undertook a deterministic study, which resulted in the line now in production.
Siemens provided the PLC, CNC, HMI, RFID and its high-level Ethernet protocol, Profinet, to run on the GM network. Overlaying this hardware and communications topology, Elite Engineering delivered its Flexible Assembly Configuration System (FACS), complemented by Siemens to create its SIFACS solution, wherein all the control elements for every assembly operation and test stations would be fully integrated. SIFACS largely focuses on the integration of the core PLC software blocks and functionalities of the individual stations with the RFID tags on each of the workpiece pallets.
AN INTEGRATED APPROACH
Within any flexible automated assembly system, the keyword is flexible. By creating a decentralized control network that was nonetheless in complete harmony with the overall workflow of the plant, GM and Siemens devised the optimum modular yet flexible architecture for the entire system. This integrated automation approach not only addressed multiple families of hardware involved, it also coordinated all code development, safety and communications functions into an interdependent yet highly flexible and adaptive control scheme.
This integration is nowhere more visible than in the modular and open controller and I/O rack assemblies located throughout the facility. A Siemens Simatic S7 CPU, the Siemens Safety Integrated drives platform and all I/O, including RF antennas for RFID tag reading, are configured and reside here. Diagnostics in the system are similarly integrated, according to Matthew Thornton and Jeremy Bryant, who consulted from Siemens.
“As our starting point, we devised pre-made templates and blocks important to the powertrain build process,” said Thornton, who further noted the importance of placing the critical performance data on all the HMI panels in the system for easy operator access. “With all motion and safety functions integrated into the drives, there was no need to build a separate troubleshooting architecture for what would be a more traditional safety network of relay cabinetry.”
“Only a few components talk on the Profibus system,” Bryant added. “All other I/O and automation components communicate over Profinet.”
Reinhold Niesing of the Siemens Automotive Center of Competence further explained the contact process between his group and the provider of the FACS. “They provided the configuration and monitoring system, while we [Siemens] provided the automation run-time system. Both systems needed to run in sync to provide GM with configurable options, when changes in production or manufacturing enhancements were needed.”
The result of this collaboration, coordinated under the Siemens Transline solution, was the Transline HMI Lite CE package, in which all operational, visualization and diagnostic functions are streamlined in a consistent control scheme. This package provides a uniform user interface for operational and diagnostic functions on the majority of the various machine tools, transfer lines, robotics, assembly machines, sensing devices and vision systems throughout the facility.
RFID GETS THINGS STARTED
As a workpiece proceeds through the line, each pallet is equipped with an RFID tag. “The key here is the data throughput in the system, as it directly impacts the cycle time or ‘takt time’ (maximum allowable time to produce one finished part or product) of the line,” explained Niesing, engineering manager on the project for Siemens. “The tags must be able to function in static mode, whereby the data on the part must be read before the process begins. Model number, serial number and build status information are all contained in the tag. The faster we read the information, the faster the process begins.”
Niesing also detailed the dynamic mode of operation for this RFID system, in which the information at subsequent line stations must be read “on the fly” without any line stoppage. In this case, all data are read as the tag passes by the antenna.
Often, in less sophisticated applications, the signal can degrade over time and number of reads. For the new GM line, however, two interface protocols are supported, namely the open standard ISO 15693 and a proprietary Siemens-developed standard, Simatic RF300. The latter uses a state-of-the-art chip paired with highly optimized communications to achieve the faster data read/write rates. Relatively large amounts of data (64kB) are handled in faster cycle times, while the overall RFID solution is applied in a high-speed, non-stop environment. One of the key drivers in the system is the fact that each RFID tag has both EEPROM and FRAM. The 20-byte EEPROM is designed to be a one-time programmable memory chip (OTP), a security feature that was deemed most desirable by GM for this application. Meanwhile, the FRAM can be written and rewritten many times for optimum utilization of the hardware, over time.
LOGIC BLOCKS ALL AROUND
The overall thrust of the line development, according to George Jewell, the GM engineer responsible for the implementation of the FACS online at the Toledo plant, was to have consistent, even identical logic blocks at every station. This would allow, as is seminal to the FACS architecture, immediate successive modifications to be made in the machine or assembly operations performed, throughout all stages of the line. When rebalancing was needed, an upturn/downturn in current production was required or an entirely new model came onto the line, the changeover needed to happen in hours, rather than in weeks, as was the industry norm.
By standardizing on the hardware, software and communication protocols used, engineering costs could be contained. As a collateral but vital side effect, maintenance on the system could be made more efficient with much of the system hardware exposed on the line, rather than enclosed in electrical cabinets. Flexible modules would allow more rapid reconfiguration and product changes, as the new GF6 transmission ramped up to incremental target levels of production.
Jewell noted that Siemens responded to the challenges, “…with a plug-and-play technology approach, coupled with an understanding of the processes we utilize.” From the utility perspective, he also noted that the run-time component in the system would function without the full configuration system being online, further complementing a decentralized architecture.
“The Siemens commitment to provide this value added functionality geared towards flexibility within our manufacturing principles has substantially supported GM Powertrain’s efforts to standardize processes, controls and continuously improve,” commented Bob Raven, GM controls manager.
Currently, GM uses the FACS at various plants in Mexico, China, India, Thailand, Korea and the U.S. FACS will soon be used in Canada and Eastern Europe, for the production of transmissions, engines and even the generator on the new Chevy Volt. These products, it should be noted, can be manufactured, assembled and tested, all within the same flexible control architecture, while supporting standardized GM processes.
Rather than textbook product life cycle management, Jewell sees FACS as more of a production line life cycle management tool, as its inherent adaptability means common hardware can be made to do diverse tasks, at varying rates, with on-the-fly changeover, in far less time than previously possible.
Safety features are numerous within the facility, resulting in a complete failsafe system across all Siemens Simatic PLC, I/O devices and safety-integrated drives. All safety devices are networked over Profisafe protocol, a certified safety network, eliminating time-consuming and difficult to maintain traditional hardwired safety connections. All safe I/O, failsafe drives are part of the Siemens Totally Integrated Automation (TIA) protocol. Since it is fully integrated, this protocol provides comprehensive system diagnostics, which can help guide maintenance staff to exact fault location and mitigate downtime.
Since the drives, starters and machine safety are integrated into the multi-functional machine mount I/O system, Simatic ET 200pro, the overall engineering complexity is reduced because of simplicity in panel design, wiring architecture and seamless integration to the project level hardware configuration, which is reduced due to the totally integrated automation design. For service requirements in the event of a fault, hot swapping of an I/O module is possible during operation, without switching off the entire station. There is nonetheless a very high degree of integral protection, to IP65/67 standards. The fact that an enclosure is not required also helped save on the total cost of the project for GM.
Between the two lines, GM Toledo has invested $872 million on its six-speed, rear- and front-wheel drive transmission production at this 2 million square-foot facility, which currently employs 1400 employees, most members of UAW Local 14.
The highly fuel-efficient rear-wheel drive Hydra-matic 6L80 transmission is now joined by the GF6 front-wheel drive, six-speed units being produced on this new line under the FACS control solution that supports flexible manufacturing while driving standard processes.
“From our first installation in Ramos Arizpe (Mexico) to this Toledo plant, we’ve seen great results, with activities that took months reduced to weeks and what took weeks reduced to hours,” said George Jewell, the GM engineer who spearheaded the implementation of FACS. “There’s less ramp-up time, plus the changeover and line balancing upsides are already proving this was a beneficial investment.”