“Five years ago, our fit and finish was below average,” said Dr. Raj Kawlra, director of dimensional strategy and management of Chrysler Group (Auburn Hills, MI). “To be the future world-leaders, we knew that we had to focus on all aspects of quality … vehicles that look good, feel good, sound good, and are reliable.”
As manufacturers have known since the dawn of the industrial revolution, the number-one enemy of quality in mass-produced goods is variation—from part to part, assembly to assembly, vehicle to vehicle. Understanding and managing variation on hundreds of thousands of dimensions on the thousands of parts that go into every vehicle is a challenge. This usually requires more than fancy new metrology equipment, or even new charts and procedures. It often requires commitment, education, and the scariest of all, a new way of doing things.
With support from his leadership after Fiat took control of Chrysler, Kawlra established a new metrology-oriented organization focused on improving the perceived quality of the new Chrysler Group products. To do this, Chrysler implemented standardized control plans derived from Engineering Build Objectives. His 180-member organization includes engineers who run the new Metrology Centers already established at most of Chrysler’s assembly plants. Before 2008, Kawlra said, “we were spinning our wheels because there was not a central organization responsible for developing and implementing standardized control plans and then efficiently leading all dimensional problem-solving during the new product launches.” The team for each vehicle program would develop their own, resulting in inconsistency from one vehicle control plan to the next—organizational variation.
A standard control plan for body-in-white (BIW) exterior and interior parts was created to guide both measurement and corrective actions on the critical characteristics that truly affect a vehicle’s performance, functionality, or perceived quality. “These are the parts the customer sees, like gaps and flush around door, feels such as closing effort, and hears like undesirable annoyances of squeaks and rattles that establishes perceived quality,” Kawlra said.
Chrysler followed three basic steps in developing its standard control plan, Kawlra said. Step 1 was to identify the ‘vital few’ characteristics required to establish a common template for all product lines. Step 2 was to establish the standard equipment and supporting tools as well as the off-line measurement programs to ensure a consistent way of monitoring process control organization-wide. Step 3 was to tailor the corporate standard for each specific vehicle model (such as the 2014 Jeep Cherokee). Ultimately, the team works to ensure the plant can build the desired number of vehicles a day with consistent quality before turning the program entirely over to plant management.
Chrysler developed this standard, corporate-level control plan using various tools, including Variation Simulation Analysis (VSA), to understand how tolerance stack-ups could be measured and controlled effectively for all vehicles. The resulting standard control plan identified hundreds of critical parts and vital few critical and special characteristics on each part that required to be measured and controlled. As part of the measurement strategy, Chrysler chose to use well-known concepts of statistical process control. These include process and capability indices such as Pp and Ppk, Cp and Cpk, which are calculated from raw measurement data and compared to tolerances.
To efficiently make measurements for effective root-cause analysis, Chrysler invested over $100 M to build Metrology Centers at its assembly plants. Each Metrology Center is housed in 12,000–15,000 ft2 of space. For example, the center at the Toledo Assembly Complex is 12,400 ft2 with one 18-m, quad-arm horizontal CMM, two 6-m horizontal dual-arm CMMs, two portable laser trackers with hand-held T-probe, a white light scanner, and laser gages. The Toledo Assembly Metrology Center is staffed with 11 metrology engineers and 19 UAW skilled tradesmen.
Program teams now spend up to an hour every week going over dimensional quality data in great detail with top management, according to James Cole, metrology manager for the Toledo Assembly Complex. They review the status of part quality, BIW geometry, and Engineering Build Objectives, such as gap, flush, and closing effort.
Radical improvement required a break from past practices. Starting at 12 months before the initial prototype builds to three months after Job One, dimensional validation engineers examine parts, processes, and tooling. By quantifying issues, understanding root causes, and incorporating a big-picture view, the team goes well beyond a mentality of simply measuring parts and rejecting those that are out-of-tolerance. Call it ‘dimensional systems engineering.’
The Chrysler team felt that the Parts Production Approval Process (PPAP) and Parts Submission Warrant (PSW), good as it might be, was no longer good enough. “Using that procedure, we would basically trust that what suppliers were sending us was meeting the specifications,” Cole said. “However [even if they met specifications], we would miss many key measurements for these parts. For example, we could have parts that are within tolerance, but slightly shifted from the absolute target or biased. When mated with another part that is slightly within tolerance and also biased, it can create a bad assembly.”
That is why the Chrysler team introduced its own Part Qualification Process (PQP). It requires suppliers to submit a few parts with data on all critical characteristics based on the control plan, which is far more comprehensive than what is called for in the PSW process. Chrysler uses these parts in their dimensional systems engineering.
To gain an understanding of assembly quality versus part quality, Chrysler Group now uses Meisterbocks and Quality Assurance Fixtures (QAF) as perfect models for BIW sheetmetal parts and interior/exterior trim parts respectively. Meisterbocks are precision hybrid fixtures that replicate the body shop’s part locating scheme [also referred to as assembly tooling Principle Locating Point (PLPs)] for a particular vehicle. “For the Jeep Cherokee program, we have about 30 different Meisterbocks,” Cole said. “What that represents is the entire body-shop assembly process, here inside the metrology center. This gives me the ability to fully simulate the assembly of what is being done out in the body shop—but do it here in a perfect world.”
Chrysler demonstrated a Meisterbock that replicates the tooling and process for putting sheet metal stampings into a completed door assembly. Meisterbocks combine the precision of gaging with the flexibility of PLP adjustments, if desired. This allows precision movement of Meisterbock PLPs and alignment points that can be useful in root-cause analysis and up-front validation of potential tool adjustment studies.
QAF is a perfect body for interior/exterior trim parts. These parts include door moldings, glass, fascia, or instrument panels. Chrylser creates the perfect body with monolithic CNC machined parts, in lieu of body stampings, fitted over a precision armature. Together, they provide a geometrically ‘perfect’ body shell. Chrysler Group engineers place fully marked up and measured interior or exterior parts submitted by suppliers on this perfect body to see how they fit. It is in a sense a step back to the pre-CAD days of package bucks used for interference checks, but with far more precision—and with more purpose. A laser tracker outfitted with a T-handle provides the metrology measurements, a tool that did not exist in those days.
“Now, we can fully understand the supplier parts,” Cole said. “We then understand how those parts progress through assembly and the deviations that may or may not occur during the assembly process. It gives us a really quick and easy way to identify issues before they get to the floor.”
With this detailed process—rather than simply examining parts in isolation—Chrysler can identify whether a quality issue is due to a part, the assembly or manufacturing process, or an issue that may require a CAD design change.
The laboratory setting provided by the Metrology Centers means isolating key parameters for deeper understanding of issues. “For example, we have weld guns and welding robots, and other robotic automated processes out on the floor that could directly influence the quality level of the part,” Cole said. “There are 900 robots on the shop floor, interacting with 284 [critical] body parts for the 2014 Jeep Cherokee.” If dimensionally correct parts are assembling well onto the QAF or the Meisterbock, by process of elimination, any issues must be coming from the shop floor.
While individual point measurements from CMMs are useful, they are still limited in range, even when 8000–10,000 points are measured on all the parts. This is where area scanning such as from “white light” scanners comes in handy, as demonstrated by Randy Wall, Chrysler Group’s dimensional validation manager. By scanning millions of points on individual stampings, and then scanning progressive assemblies of stampings as they became a door, Wall measures areas that could go in and out of tolerance during the process. He then uses individual scans of each part and digitally assembles them, which he termed it a ‘Digital Meisterbock.’ This helps to identify interferences between the parts not apparent either in CAD interference checks or with point measurement techniques.
Chrysler also has enhanced its launch process to include a series of quality gates, held roughly every month until Job One. Management reports, frequently updated, provide the basis for these quality reviews. “We feed a ‘stoplight’ report to upper management every week,” Wall said. The Cp and Cpk of a subset of critical characteristics (CCs) are computed from measurements. The stoplight term comes from the use of red (bad), yellow (on-notice), and green (good) measures attached to each CC, a common practice in automotive OEMs, using Cp and Cpk thresholds.
Another action tool the Metrology Center established was a way to track and monitor critical tooling points that affect the 447 CCs established in the control plan. At Toledo Assembly, for example, the plant contains 900 robots, of which over 131 stations alone are dedicated to geometry setting. Chrysler developed a tool they call the X-Matrix to map those 447 CCs to the specific station on the shop floor that controls their quality. “Then we take it to the next step and figure out which component inside that tool is actually controlling that [CC],” he said. Even with perfect parts that will ideally fit together perfectly, imperfection in these tools will introduce variation.
To eliminate this last potential source of variation, Chrysler introduced on-going maintenance in a disciplined fashion. “In the past, we would receive shipment of completed automated assembly tools for the body shop from the OEM tooling source, we would certify it one time and install it, and that would be it,” Cole said. Now Chrysler maintains the equipment proactively. “We do this instead of reacting to emergency breakdowns as they might occur,” Wall said. He likened it to continuous re-certification.
Is it working? Both internal and external measurements indicate that it is. Kawlra presented corporate data that showed some dramatic improvements in Cp and Cpk levels from 2011 to 2013. “Cp levels overall went from 20% red in 2011 to only 3% red in 2013,” explained Kawlra. “Cpk, which is a more difficult metric to achieve, went from 64% red in 2011 to only 15% red in 2013.”
For those not well versed in statistical process measures, J.D. Power’s Initial Quality Survey provides another assessment. It is a survey of new-vehicle owners and lessees after three months of ownership.
Since 2007, both the Chrysler and Jeep brands have shown improvements in problems reported per 100 vehicles (pp100). Chrysler’s pp100 dropped from a high of 151 in 2007 to 109 in 2013. The Jeep brand dropped from a high of 167 in 2008 to 118 in 2013.
Stay tuned as Chrysler launches the 2014 Jeep Cherokee, which is scheduled to be in dealer showrooms in the third quarter of 2013. ME
This article was first published in the September 2013 edition of Manufacturing Engineering magazine.
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