Thinking "outside of the box" has enabled General Motors to realize "weeks to hours" reduction in line change and transmission-build dynamics at its Toledo Powertrain plant. GM Toledo has invested $872 million in transmission production for its six-speed rear-wheel drive and front-wheel drive transmissions at the 2-million ft² (185,806-m²) plant, which employs 1400, mostly members of UAW Local 14.
Both six-speed transmissions, the rear-wheel drive Hydramatic 6L80 and the GF6 front-wheel drive, are being produced on the new line under the FACS (Flexible Assembly Configuration System) control solution control/communication technology from Siemens Industry Inc. (Elk Grove Village, IL). FACS supports flexible manufacturing while driving standard processes.
Production of the GF6 front-wheel drive transmission line for smaller fuel-efficient vehicles like the Chevy Malibu and new Chevy Cruze is currently ramping up to its initial target of 2200 units per day. There’s 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 and secondary operations, and assemble the finished transmissions.
GM engineering worked with its long-time controls suppliers to investigate ways of significantly reducing the workflow through the line, as well as enabling faster changeover, reducing reprogramming, and preventing situations where one out-of-spec machine could cause complete shutdown. Another key objective in the development of the GF6 line was the need to minimize maintenance time by installing PLCs, drives, and component pallet-recognition devices outside of the conventional cabinetry (the box) found on traditional assembly lines. In addition, controllers were distributed throughout the system, which allowed removal of typical zone controllers, increasing system flexibility.
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 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."
The major obstacle in process development was changeover and the need for a more flexible, yet highly automated system of transmission builds. In consultation with Siemens Automotive Center of Competence (Troy, MI) and Elite Engineering (Rochester Hills, MI), a deterministic study was undertaken, resulting in the line now in production. Siemens was the controls provider on the existing six-speed, rear wheel drive line, and Elite Engineering, the third-party supplier of the FACS software.
GM’s Jewell notes that Siemens responded to the challenges "with a plug-and-play technology approach" that allowed the run-time component in the system to function without the full configuration system being online, further complementing a decentralized architecture.
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’s FACS solution was used by Siemens to create its SIFACS solution, fully integrating all the control elements for every assembly operation and test station. 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.
Both the FACS configuration and monitoring system and Siemens’ automation run-time system are needed to run in sync to provide GM with configurable options, when changes in production or manufacturing enhancements are needed.
All operational, visualization, and diagnostic functions are streamlined in a consistent control scheme and coordinated under the Siemens Transline HMI Lite CE package. The Transline package provides a uniform user interface for operational and diagnostic functions on the majority of the machine tools, transfer lines, robotics, assembly machines, sensing devices, and vision systems throughout the entire facility. For safety communications, GM is currently reviewing another Siemens option for open safety communications technology on distributed automation systems.
As a workpiece proceeds through the line, 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 cycle time or takt time [the maximum time needed 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." In dynamic operation, RFID information at subsequent line stations can be read "on the fly" without any line stoppage. All data are read as the tag passes by the antenna.
Two interface protocols are supported, the ISO 15693 (open standard), and a proprietary Siemens-developed standard, Simatic RF300, to ensure signal quality over time and number of reads. 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 (64 KB) are handled in faster cycle times, while the overall RFID solution is applied in a high-speed, nonstop environment. Despite this level of sophistication in the RFID hardware, the system easily communicates over the existing Profinet, Profibus, and other common protocols.
Rather than product life-cycle management, Jewell sees FACS as more of a production line life-cycle management tool. Its inherent adaptability means common hardware can be made to do diverse tasks, at varying rates and with on-the-fly changeover, in far less time than previously possible.
On one automated Hanwha assembly station, various subassemblies of the transmission are produced, as other lines produce the components that go into the subassemblies. Adding a station, as Greg Nazareth, GM controls engineer, explains, requires simply adding a PLC with the standard SIFACS logic and desired process devices, and downloading an eFACS configuration. 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, 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.
Throughout the metalcutting process here, mostly in the gear and spline-forming, hobbing, grinding, and finishing operations, 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.
Similarly, in machining 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 operations, other motion-control devices and software solutions provided by Siemens execute, monitor, and control the assembly process, through the SIFACS solution set.
Through a decentralized and cabinet-less design, GM has achieved 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, all with no special hardware required, a further cost savings for GM. Safety features are numerous here, resulting in a complete failsafe system across all Siemens Simatic PLC, I/O devices and safety-integrated drives.
Drives, starters, and machine safety are integrated into the multifunctional machine-mount I/O system, Simatic ET 200pro, reducing overall engineering complexity. Panel design and wiring architecture are simplified, and project hardware is seamlessly integrated with software, resulting in a 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 control the total cost of the project.
Currently, GM uses the FACS at various plants in Mexico, China, India, Thailand, Korea, and the US—and soon will use it 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. ME
For more information from Siemens Industry Inc., go to www.siemens.com/automotive, or phone 847-640-1595.
Fluid Switch Promotes
Taking a risk is always challenging. For Brian Bradley, stamping operations supervisor at Unistrut International Corp.’s Wayne, MI facility, questioning current metalworking practices and introducing a process change have resulted in dramatic improvements and cost savings for the Tyco International division. Important improvements in worker environment and safety, and real cost savings have been realized, according to Bradley. "By eliminating the use of a straight oil in favor of a water-dilutable product, we have saved money as well as furthered Unistrut’s commitment to greener, safer, and more environmentally responsible operations."
Today, Unistrut is the global leader in metal-framing and pipe-support systems. Since 1924, customers have relied on Unistrut to provide a product representing the latest technologies in product design, quality, and performance. The initial Unistrut concept—a simple spring nut and bolt connecting a fitting to a continuous slotted-steel channel—has evolved into comprehensive engineered building and support systems. The company's success depends on precision components to assure a successful assembly for their customers.
Unistrut’s Wayne, MI facility has three nut-tapping lines and eight automatic press lines. The nut-tapping lines tap holes in cold-rolled steel nuts. Hole diameters range from ¼ to ½" (6.35–12.7 mm), using a titanium nitride-coated tap. There are a total of eleven tapping heads. Each tapper processes between 16 and 20 nuts/min. There are eight automatic press lines consisting of a coil straightener, feeder, and press. There are six 150-ton presses and one each at 75 and 250 tons. The smaller press does a simple cut-off and forming of a bracket. The other presses do cut-off and hole punching. The substrates are cold-rolled steel and 304 or 316 stainless. Thickness range of the substrates is 0.060–0.25" (1.52–6.35 mm). Hole diameters range from ¼ to 9/16" (6.35–14.28 mm). The most demanding operation is punching a 9/16" (14.28-mm) diam hole in the stainless substrate. The easy-forming operation runs at 140 strokes/min, and the hole-punching operations run at 60 strokes/min.
A straight-oil lubricant was used in both the nut-tapping and press lines, because of the lubricity requirements of these difficult metalworking operations. Bradley says, "The use of the straight-oil lubricants provided the lube needed to do these jobs, but there were some negative side effects like oil mist in the machining areas, slip hazards, skin irritations, and cleaning and pickling problems down the line."
Working closely with Bradley, Chemetall NAFTA (New Providence, NJ) proposed the use of a water-dilutable, semisynthetic metalworking fluid to replace the straight oil currently in use. Tech Cool 35045, a heavy-duty, semisynthetic metalworking fluid containing an extreme-pressure (EP) additive was chosen to be tested on one nut-tapping head. Concentration was set at a 25% by volume dilution with water. The one-month trial proved to be successful. The tapping process was not only smooth and efficient, but a tooling life improvement of 30% was documented. The Tech Cool 35045 was expanded to all 11 tapping heads in the three nut-tapping lines with equal success.
Similar success was realized on the press lines using a 25% by volume solution of Tech Cool 35045. The punches on these lines remained significantly cooler, and so did the workpieces, allowing for much easier handling. In the long run, keeping the punches cooler will dramatically extend their life. Cleanliness of both machines and work area is much improved.
"This product change has been very, very successful. I have a laundry list of improvements and savings that I have documented and I'm really pleased with the results," Bradley says. For tooling, documented benefits include 30% longer tap life. Punches on the press line remain cool as opposed to getting hot when using the straight oil.
On the chemical side of the process, annual coolant cost savings of 40% are realized. Ease of cleaning will reduce the usage of cleaner and pickling acids downstream dramatically (projected to be 50%), and less frequent dumping of clean/pickle lines results in less waste-treatment chemicals used.
Waste minimization results from significantly reduced amounts of oil containing water needing to be treated. Substantial reduction in the amount of chips/shavings produced reduces recycling costs and tool failure due to chip build-up. Chips are also significantly less contaminated with oil. In addition, there are a reduced number of oil soaked floor absorbent pads.
Important safety, health, and environmental benefits have resulted from 85% reduction of oil usage in all operations. There is a significant reduction in greenhouse gas emissions and a reduced carbon footprint. Oil mist is completely eliminated as are slip hazards resulting from to oil drag-out. Machine tools and work areas are cleaner. There is less wastewater discharge, and shop odors are virtually eliminated. Equally important operator discomfort resulting from skin irritation has been eliminated. ME
For more information on Chemetall, go to www.chemetallamericas.com, or phone: 800-526-4473.
Robotic System Cuts
and Finishes Paper Rolls
Founded in 1968, Norkol Converting Corp. (Northlake, IL) is one of the nation’s leading independently owned converters and distributors of commercial printing papers. The company’s HQ facility has full production capabilities and state-of-the-art machinery for winding, trimming, and sheeting. In the past, traditional slitter rewind equipment had been used to unwind, slit, and then rewind paper to new dimensions, though at an inefficient slow pace. "Rewinders have been used for years in the paper-converting industry," says Mike Maloy, Norkol Converting president. "Although they do the job, we are constantly researching and adopting the newest technologies to help us remain competitive. Our original rewinders take between 30 to 40 min to process one roll, so we were very excited when we were introduced to new technology that processes four to six rolls per hour without the need to unwind and rewind."
For a solution that would speed up the process, the company turned to system integrator Mapleroc Industries (Portland, ME) and their automation partners ABB Robotics (Cary, NC), a leading robotics manufacturer, and ATI Industrial Automation (Apex, NC), an engineering-based robotic accessory developer. Together the partners developed and implemented a new fully automated cutting and finishing system using Mapleroc’s RollRazor cutting technology, which features a highly engineered cutting blade capable of cutting as much as 300% more paper in one hour than traditional rewinders.
RollRazor cutting technology has significantly speeded up Norkol’s converting process and reduced their costs. The company estimates that with the new equipment they can produce one press-ready roll in 6 min where it originally would take approximately 30 min to process. For the company, this translates to increased production which, in turn, lowers their cost per ton and cost of labor. The new equipment increases plant flexibility, maintains original mill roll quality, guarantees original sheet orientation and web tension, and can also convert wet or damaged rolls.
There is a difference, however. Traditional slitter rewinding equipment makes a clean cut, producing new rolls that do not require any additional finishing. The RollRazor blade cuts through the entire roll with a circular saw blade. Because not all rolls are wound the same, not all cuts come out the same. To remove the "witness lines" that are left over from the cutting process and produce a consistent-looking roll, these edges then require sanding to meet the customer’s requirements.
To complete the robotic cutting application, Mapleroc, ABB, and ATI developed a roll-finishing solution to automatically sand and smooth roll edges. The robotic roll-finishing system features an ABB IRB 6620 class robot equipped with a force-controlled machining package with ATI Force/Torque Sensors to create a fully automated, high-precision, force-controlled roll-finishing system.
The IRB 6620 is a flexible and agile six-axis robot with a reach of 2.2 m that is able to handle payloads up to 150 kg. "The IRB 6620 robot is equipped with an end-of-arm roll-finishing tool and an integrated dust-collection system," notes Adrian Kiss, engineering manager of ABB Robotics. "As the robot sands the rolls, an integrated dust-collection system removes the excess paper using a vacuum system."
The system uses ABB’s force-control package featuring force/torque sensors integrated on to the robot wrist. Signals from the force/torque sensor are interpreted directly into the motion control of the robot. The package includes ABB’s RobotWare Force Control machining software with a user friendly machining GUI, an axis computer, a data acquisition board for the sensor, cabling between the sensor and controller, and ATI’s force and torque sensor.
With the cut roll moved into place, the robot equipped with the sanding head smooths the edges using the ATI Force/Torque sensor technology to provide force feedback. This enables the robot to feel and have a sense of touch just as a human would. This sense of touch allows the robot to make quick adjustments in real-time to maintain a constant contact force, all the while maintaining an average finishing temperature of 85°F (32°C). Together, the robot and sensor make this finishing task possible.
The key to smoothly sanding the paper rolls to meet the high standards Norkol’s customers require is the system’s sensor technology. The multiaxis force/torque sensor measures all six components of force and torque. It consists of a transducer, shielded high-flex cable, and an interface card specially designed to work in the ABB robot.
When a load is applied to the transducer, microscopic strains develop on its internal beams. Silicon strain gages placed on these beams react to the strains and electronics measure this reaction. Software analyzes the measurements and is able to report and transmit information about the amount of load being applied. In application, the transducer bends microscopically and measures that bending, and the software determines and transmits that information to the robot. Simply put, the sensors are giving the robot force feedback, indicating that the unit is pushing too hard or moving to the left or right.
"Robots integrated with these sensors make it possible to automate many different difficult assembly, machining, and finishing tasks without the need for skilled personnel or complex assembly machines, allowing manufacturers to cut costs and improve employee safety," explains Dwayne Perry, PE chief sensor technologist for ATI Industrial Automation.
The RollRazor uses a finely honed and engineered blade to cut parent rolls of paper in their rolled state in one pass, cutting them to press-ready roll sizes in 3 min without the need to unwind and rewind the paper. It’s said to be the fastest paper-roll converting machine currently available. The system can handle all grades of paper including tissue, napkin, cigarette, Bible, coated, uncoated, cardboard, and kraft papers.
"In addition to increasing cutting speed the RollRazor’s circular blade generates virtually no heat, cutting seamlessly in one pass through the roll, and thereby maintaining the paper quality of the mill-wound roll," says Todd Morrison, Mapleroc president. "This avoids possible errors inherent in the unwinding and rewinding process such as wrinkling and tension problems." Pressrooms today cannot afford upsets on press due to inconsistent roll quality. RollRazor ensures consistent mill-wound rolls with all the original manufactured specs still built-into the press-ready rolls".
Mapleroc estimates that mills or paper convertors can triple production output, improve efficiency by 2.7x, and reduce operating costs by as much as 72% using this new system.
The robotic roll-finishing system with its force/ torque sensing capability eliminates safety risks for employees and offers manufacturers a quick and efficient method of finishing the roll to the standards required by the customer. The system allows the robots to address all roll sizes and unfinished surfaces automatically, eliminating the need for manual setup. With this new system, all the machine intelligence is embedded in the robot control, thereby eliminating the need for an expensive PLC, which typically would be used to regulate pressure and prevent the paper from burning or melting.
"We have been very pleased with the new cutting and finishing system, as it is faster and eliminates problems for most applications. We are currently evaluating our results and considering replacing additional rewinders with this more efficient system," says Norkol’s Mike Maloy. ME
For more information on ABB Robotics, go to www.abb.com, or phone: 919-856-2360; on ATI Industrial Automation, go to www.ati-ia.com, or phone: 919-772-0115; on Mapleroc, go to
www.rollrazor.com, or phone: 207-878-3210; on Norkol, go to www.norkol.com,
or phone: 708-531-1000.
Getting Hip to Replacement Quality
There are over 300,000 hip-replacement surgeries each year in the US. These operations are performed to alleviate pain and improve the function of hips damaged by disease or fracture. Replacement hips are commonly made from high-strength, lightweight materials like titanium alloys. Modular hip prosthesis systems afford doctors the flexibility to choose properly sized components and treat a wide spectrum of patients, but are composed of several pieces that require precise dimensional and surface-finish control to work together perfectly.
These prosthetics can be prone to fretting along the tapered connections between subcomponents, resulting in surface microcracks that form and cause a reduction in the prosthesis’ fatigue strength and functional life. Depending on the size and activity level of the patient, it isn’t uncommon for additional hip repair surgery to be required within 10 years.
Exactech Inc. (Gainesville, FL), an orthopedic implant manufacturer, began examining different surface-enhancement processes that would mitigate fretting-initiated fatigue. Adding a layer of residual compression to a part has been shown to retard fatigue crack initiation and growth. Traditional methods, such as deep rolling, provided a smooth, shiny finish, but the compression imparted did not significantly improve fatigue and lacked the process control required for manufacturing.
In Low Plasticity Burnishing (LPB) from Lambda Technologies (Cincinnati), Exactech found a process that could be easily integrated into their machining operations and that provided the necessary combination of depth of compression to mitigate fretting fatigue, dimensional control, and required surface finish.
Lambda Technologies developed LPB to impart controlled residual compressive stresses in metal components, extending service life and performance. The surface treatment had been successful on aerospace components, many of which were made from materials similar to those used in hip replacements. LPB uses a single pass of a smooth, free-rolling ball under controlled force to create a deep, stable layer of beneficial, compressive residual stress in the component’s surface. This compressive stress makes the piece resistant to a variety of damage mechanisms, such as foreign object damage (FOD), stress corrosion cracking (SCC), high cycle fatigue (HCF), pitting, and fretting fatigue. LPB strengthens components without altering their material or design. Because treated components are more durable, designers gain the benefit of added strength without needing to use a more expensive material or one that is harder to machine.
"At our first meeting, it became apparent that Lambda’s approach was innovative," remembers Edmund Loftus, Exactech’s development engineer for the project. "Their focus was on understanding our application and then demonstrating how the LPB process could substantially improve fatigue performance."
Using finite-element modeling of the applied stresses and Lambda’s patented fatigue design protocol, a custom residual stress field was created for the application of LPB to the hip implants. Real-life conditions were simulated on a model to obtain the loads applied in service and determine the required depth of compression. Several factors needed to be taken into account: reallocation of residual tensile stresses, component distortion, and the cost of processing. Exactech had to be sure that the surface enhancement treatment chosen would not simply move the location of maximum stress, weakening another section. LPB prevents this by evenly dispersing the equilibrating tensile stresses during the design phase. Development and processing in the same lathes used for machining the prosthesis gave Exactech a way to answer fatigue issues and deliver a better product, without passing on major cost increases to patients.
LPB-processed prosthetics achieve compression deeper and higher in magnitude than either the untreated or roller-burnished specimens. Overall fatigue strength was increased almost 40%, extending the fatigue life by orders of magnitude. The depth of the LPB treatment was sufficient to eliminate fatigue initiation from fretting-induced microcracking, providing a fatigue strength superior to unfretted material, all without changing the material or prosthesis design.
Because medical implants are government-regulated devices, rigorous testing was performed by Exactech to ensure that LPB treated prosthetics met FDA standards. Results showed that the enhancement in no way affected the safe use of a modular hip replacement, and the process has been fully approved by the FDA for production. Ann Kelly, senior quality engineer for Exactech during the LPB development process, explains: "One of the most critical aspects of implementing LPB in our manufacturing operation was the need to ensure that the equipment and processes were properly qualified. Lambda’s ability to extract manufacturing performance data in real time helped to expedite the qualification process. We are certain, within a very tight tolerance, that when a part has been LPB-processed the compressive residual stress distribution is precisely what was specified by the engineer."
After verifying that LPB was the right surface treatment for their prosthetics, Exactech began implementing it into their manufacturing process. LPB operates using basic CNC code, and is said to be easy to install on existing machinery, such as lathes, mills, and robots. Processing can be done on either a dedicated unit, or by switching tools on the same machine used for manufacturing. Exactech determined that it would be simplest to have a designated surface-treatment lathe. The total footprint of the average LPB system is approximately 8 ft2 (0.74 m2), and system hardware can be packaged to relocate from one machine to another, if necessary.
Lambda provided a complete turnkey LPB machining process for the Exactech manufacturing facility, including the required CNC tool control code and pressure files that define the burnishing force. Once the LPB tool is installed, the machinist starts the operation and begins preparing the next piece. The use of a CNC-controlled toolpath delivers repeatability. LPB processing time for the hip implants is approximately 1 min.
During processing, LPB undergoes continuous, closed-loop monitoring. The computer-operated servocontrol makes pressure adjustments in real time, ensuring that each part is treated with the amount of force required. The system provides automatic pass/fail notification for each treated component, and QA personnel are informed immediately if there is a system malfunction or part rejection. SPC information is collected constantly, and each piece is tracked individually by serial number.
LPB offered Exactech several advantages over other surface-treatment options. Processing costs are significantly lower due to LPB’s rapid processing. The procedure requires no special coatings, uses only a single cycle for treatment, and implants don’t need to be moved from one machine to another or taken off site for remote processing. Since LPB tooling is designed to fit on existing CNC machinery, there is no costly requirement to teach machinists to run entirely unfamiliar equipment. Because of the low cold working of the surface, LPB produces a layer of compression that is thermally and mechanically stable. ME
For more information from Lambda Technologies, go to www.lambdatechs.com, or phone: 800-883-0851.
This article was first published in the February 2011 edition of Manufacturing Engineering magazine. Click here for PDF.