THINKING OUTSIDE OF THE BOX - LITERALLY
GM realizes “weeks to hours” reduction in line change and transmission build dynamics at Toledo Powertrain, resulting from Flexible Assembly Configuration System (FACS) and Siemens control/communication
A tried and true euphemism nowadays, “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. Enter the GF6 six-speed, front wheel transmission line at General Motors Powertrain on Alexis Road in Toledo, Ohio.
Here, a new front wheel drive transmission line for smaller, more fuel efficient vehicles such as the popular Chevy Malibu and new Chevy Cruze is currently ramping up to its initial goal of 2200 units per day. Nothing new about such an event, until a closer look reveals the method used to program this line, implement changeover, stage the workpiece flow, perform all machining, secondary operations and assemble the finished transmissions.
During the development of this line, several years ago, GM engineering contacted its longtime controls suppliers to investigate ways of significantly reducing the workflow through the line, as well as enable faster changeover, reduce reprogramming and prevent the curse of all automated manufacturing lines, situations where one out-of-spec machine caused complete shutdown. Another key driver in the development of the GF6 line 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 on the existing six-speed, rear wheel drive line, Siemens Automotive Center of Competence (Troy, Michigan), as well as third party software package provider, Elite Engineering (Rochester Hills, Michigan), a deterministic study was undertaken and the result was 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, according Jim Remski, manager of powertrain activities for Siemens.
AN INTEGRATED APPROACH
Within any flexible automated assembly system, the keyword is flexible. All hardware and related software must be designed with a deterministic functionality that is both valuable to the customer’s build strategy and cost-competitive, as well. Working with technical specialists in safety integrated systems and industrial communications alike was the key to the success of this project at GM Toledo. 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 totally integrated automation approach not only addressed multiple families of hardware involved, it also coordinates all code development, safety and communications functions into a seamless and 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. “We devised pre-made templates and blocks important to the powertrain build process, as our starting point,” commented 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.”
Bryant continued, “Only a few components talk on the Profibus system, 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, whereby all operational, visualization and diagnostic functions are streamlined in a consistent control scheme, was the Transline HMI Lite CE package. This package provides uniform user interface for operational and diagnostic functions on the vast majority of the various machine tools, transfer lines, robotics, assembly machines, sensing devices and vision systems throughout the entire facility. As Michael Grass, project manager for Siemens, explains, “The best part is that the package can be customized to meet specific user needs and preferences. It provides our SIFACS (see sidebar) system of configurable assembly automation very useful information, as the two systems complement each other quite well.” In the safety communications area, he also noted that GM is currently reviewing another Siemens option for open safety communications technology on distributed automation systems.
RFID GETS THINGS STARTED
As a workpiece proceeds through the line, having been delivered by an AGV in most cases, each pallet is equipped with an RFID tag. Reinhold Niesing, engineering manager on the project for Siemens, explains, “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. 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, as is often seen in conventional packaging, shipping or other line applications for RFID. 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. Here, according to the Siemens technical specialists, two interface protocols are supported, namely, ISO 15693 (open standard) 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. 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 actually 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.
Despite this level of sophistication in the RFID hardware, the system easily communicates over the existing Profinet, Profibus and other common protocols.
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, when an upturn/downturn in current production was required or when 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 and, as a collateral but vital side effect, maintenance on the system could be made much more efficient with much of the system hardware exposed on the line, rather than enclosed in electrical cabinets, again the norm for the industry in the past. Flexible modules would allow more rapid reconfiguration, product changes and a genuine synergy with the ongoing GM commitment to continuous improvement in the line, 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. Bob Raven, GM controls manager, further commented, “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.”
Currently, GM uses the FACS at various plants in Mexico, China, India, Thailand, Korea and the U.S. — and soon 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.
TYPICAL STATION DYNAMICS
On one automated assembly station, Hanwha produces the various sub-assemblies of the transmission, as other lines produce the components that go into the sub-assemblies. Adding a station, as Greg Nazareth, GM controls engineer, explained, requires simply adding a PLC with the standard SIFACS logic, desired process devices and downloading an eFACS configuration. In contrast to the traditional zone control, this reconfiguration is not a building block concept; rather, the instructions being given impact the entire line. Nazareth worked with the full GM controls team, headed by Ron Goeckerman, to implement FACS with the host server.
By contrast, all manual workstations on this line have the same download received to a PLC, provided by Siemens in its Simatic lines. While not reliant on the server network in a deterministic mode, the manual stations nonetheless utilize the same software to execute quick tooling changes, machine sequence variations, line balancing and report tracking. Operators received training from both Siemens and Elite Engineering personnel for these tasks.
All part build histories, troubleshooting and machine debugging are recorded for further analysis.
CONTROLS CALL THE BALL AT EVERY STEP
Throughout the metalcutting process here, mostly in the gear and spline forming, hobbing, grinding and finishing, CNC technology is onboard dozens of machine tools. Most of the machines here are controlled by Sinumerik® 840D, the highest-level CNC offered by Siemens. The control not only processes the particular part dimensions in the cutting theater of the machine, it also coordinates all motion control and movements into and out of the machine. Working in tandem with the other hardware and communication network software in the line, for example, ring gears cut on a Wera Profilator machine are indexed from one station to the next, in timed sequences, to coordinate with predetermined production requirements. This operation occurs in a fully automated mode, requiring no operator intervention, except for maintenance and planned inspections.
Likewise, in the machining of valve bodies and transmission cases, each step of the process is controlled by the Siemens CNC to produce the required components in the proper sequence for subsequent assembly and testing operations. During those subsequent operations, other motion control devices and software solutions provided by Siemens execute, monitor and control the assembly process, through the SIFACS solution set.
PROFINET TALKS THE TALK
Through a decentralized and cabinet-less design, GM achieves highly integrated RFID control with easy access and true out-of-the-box solutions for the control architecture installed on this line. A Profinet solution provides GM with a high-performance, reliable network with minimum bandwidth impact or additional network load achieved at this plant, all with no special hardware required, a further cost savings for GM.
SAFETY FIRST — AND LAST
Safety features are numerous here, 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.
MAJOR INVESTMENT PAYING OFF
Between the two lines here, 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.
As George Jewell, the GM engineer who spearheaded the implementation of FACS, stated, “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. There’s less ramp-up time, plus the changeover and line balancing upsides are already proving this was a beneficial investment.”