Michigan Prototype Firm Helps Vehicle Engineers Beat the Clock
This technical information has been contributed by
3-Dimensional Services Group
Quick production of a functional rear axle housing prototype and a hand tool used to insert sensor terminals into a pre-production engine assembly help customers meet crucial deadlines.
Automakers are today faced with a combination of circumstances that include fluctuations (mostly spiraling upward) in gas prices, emerging evidence of global warming, and risks associated with the rapid depletion of oil supplies. At the same time, government has intervened to increase mileage standards. It’s a situation that has many in the auto industry scrambling to embolden their product fleets with vehicles that yield higher gas mileage ratings and lower emissions, yet still provide the performance that drivers have come to expect—especially the tough, rugged, and powerful pickup truck sector.
As a result, most domestic and global automakers have begun dynamic review, research, and development programs to find the right combination of engine, drivetrain, powertrain, and driveline components that will deliver optimum driving performance and mileage ratings. For one automaker, that combination includes, among other component concepts, a new high-strength, lightweight “banjo” rear axle concept for use in both its 2-wheel and 4-wheel drive vehicle truck models. The rear axle is designed to be a viable solution to the problem of balancing driving performance and reliability with weight savings and fuel economy.
Construction of a “banjo” axle typically involves the welding together of stamped, high-strength components to form an axle housing that can greatly reduce the mass of the part and, therefore, vehicle weight (as is usually the case with cast “Salisbury” type axles). In this case, the powertrain engineers for the automaker were faced with time constraints and were looking to avoid potential interruptions to existing production cycles. They sought the assistance of the 3-Dimensional Services Group, a Rochester Hills, Michigan-based firm that specializes in the design, engineering and analysis, in-house tool construction, and complete build of first-off parts and low- to medium-volume production runs. In addition to the rapid prototyping firm 3-Dimensional Services (Rochester Hills, Michigan), the 3-Dimensional Services Group also includes two other companies—Urgent Plastic Services (also in Rochester Hills, Michigan), and Urgent Design & Manufacturing (Lapeer, Michigan).
In the more than 16 years since its founding, 3-Dimensional Services has put its own stamp on prototyping by providing an expanded array of technologies used to manufacture complete, production-like prototype parts in a rapid time frame. Together, the three companies provide rapid prototype services for numerous process disciplines, including laser cutting and welding, machining, stamping, hydroforming and tube bending, injection molding, vibration welding, castings, RIM tooling, rapid modeling, high definition stamping of exotic alloys, and assembly.
Cognizant of the automaker’s need to receive parts and components for crucial testing deadlines and final review decisions, 3-Dimensional Services began its work on the rear axle housing. The housing consisted of nearly 30 individual stampings, many structural components fabricated from high strength sheet steel at 4.5mm (3/16-inch) thick, others from 1008-1010 carbon steel. Because the vehicle company’s engineers were looking for as many as 55 axle housing units within a 10-week delivery timeframe, work started fast at 3-Dimensional, with only the part design provided.
For Scott Duffie, project engineer at 3-Dimensional, the axle project quickly became an all-out effort, challenging the capabilities of the staff and the capacity of the firm’s technologies. “We immediately began work on the dies for producing the various stampings,” said Duffie, “including the two axle halves—the upper and lower U-formed housing pieces—that measure nearly 5-½ feet in length with a nearly 7-inch depth radius draw for the differential section. As the die design and machining progressed, we turned our attention to the fixturing—the weld fixtures required to secure and accurately locate the 28 or so different pieces during the assembly process.
“The design of these fixtures, in particular, was very demanding for our welding experts,” Duffie continued. “The workholding tools needed to be precise, yet highly adaptive; that is, with adjustability to fine-tune holding points and pressures, to compensate for or prevent any distortion that could occur during the welding stages. Considering the die work and fixturing construction required for this project, a lot of time was spent in preparation. And with intense assembly steps to follow, 10 weeks seemed doubtful. Fortunately, we made it.”
A number of factors, including the high number of parts, the quality checks, and the processes involved in completing the axles, left open the real possibility for multiple delays. In addition to the axle halves, other stamped pieces included baffles, front and rear backing plates, rear cover, front mounting ring, strengthening gussets, numerous brake cable guides and hose brackets, harness brackets, spring seats and reinforcements, shock brackets, drain plug insert, and pipe brackets. The large upper and lower halves of the axle were formed in 3-Dimensional Services’ 1,600-ton press, one of 44 presses the firm employs. The stamping operations were sped along by the use of both Kirksite and aluminum alloys for die materials.
“We’ve tested various aluminum alloys and have found a particular one we call E-Z Cut holds up well for stamping prototype runs,” Duffie remarks. “The speeds at which the aluminum can be cut, however, helps to reduce machining times by 50% or more as compared to some tool steels. Coupled with today’s high-speed CNC machining centers, the aluminum tooling allows us to turn out tools, and stamped parts, faster than ever before.”
After the stampings were completed, some of the components, and in particular, the upper and lower housing halves, were laser trimmed using the range of 3-Dimensional Services’ thirteen 5-axis laser processing systems. The laser trimming provided the accurate height of each half’s axle wall, which, when assembled, results in the correct I.D. for the axle shafts and differential gearing and carrier.
With the forming and laser trimming accomplished, the main section halves were welded together using the company’s robotic welding stations. Each end of the housing was then machined (bored) using one of the company’s large, bridge-style Awea 3-axis machining centers. The machining center provides a 120-inch x 63-inch travel envelope and supplemental 2-axis rotary fixture to accommodate the press fit of the wheel hub forgings that were furnished by the automaker’s forging supplier. The next process was to assemble the hub forgings and weld them in place, then weld the miscellaneous brackets to the housing.
“A critical step in the welding, and a required process by the client, was to verify production intent by completing the wheel flange welding process in a single, continuous weld,” notes Duffie. “To minimize tooling and equipment costs, we were able to accomplish this by using two robotic arms in unison—one generating the weld, while the second controlled the rotation of the part. With this weld, in fact with all the welds, we recorded all parameters of the individual welding processes—heat, cycle, et cetera—to provide the car company with this data for production runs. At the same time, we had to conduct certified weld inspections in upwards of 50 locations on the assembly, with cutting, etching, and measuring weld penetrations to correlate with the process data. We have on staff five certified inspectors, along with a specific software program that helps identify and measure penetration depths, so these critical inspections could be completed quickly in-house.”
Following the welding certification inspection, each assembly and weld integrity were further tested for leaks. In these tests, the ends were plugged and pressurized air was injected into the pieces under water. Quality control then inspected the assembly by conducting a CMM dimensional inspection of approximately 320 points.
With quality approval of these still in-process axles, the assemblies were sent out for E-coat (one of the few processes not done in-house), then brought back to the Awea machine for final machining of the forged flange hubs, including hub diameters, bushing seal surfaces, and ABS sensor mountings. After machining, a final CMM inspection was completed, again with 320 points of measurement. In the two inspections of the assembly, CMM inspection was conducted on a total of 640 points of measurement, in addition to inspections of all the individual components during fabrication.
“We were able to complete and ship the first pieces to the vehicle’s prototype assembly and test center in the 10-week time period, and now are in the process of completing a second run of 17 to 20 pieces, incorporating some modifications and engineering changes,” Duffie points out. “We expect to ship this lot in just seven weeks. Importantly, these prototypes included full verification of their manufacturing intent and process standards, so that, if this axle design is selected for future truck models, the automaker and its future high-volume suppliers will have a dynamic head start to implementing a viable manufacturing process and a successful, timely production launch. What’s more, the automaker now has the production-like quality and integrity with which to gauge the functioning of these axles and to help determine their effect on overall vehicle performance.”
Engine Builder Gets Quick Grip on Pre-Production Assembly Tooling
For nearly 70 years, Detroit Diesel Corp. (Detroit, Michigan), now a subsidiary of DaimlerChrysler AG and part of the Freightliner group of companies, has been one of the world’s leading producers of power train components. The company is also a supplier to premier builders of commercial trucks, motor coaches, and RV motor homes, as well as buses and emergency vehicles, around the globe. Over this time period, the company has continuously developed cutting-edge technologies for its product lines of diesel and alternative fuel engines, transmissions, and axles.
These technologies have helped establish performance specifications for reliability, durability, and power. In addition to helping to improve mileage ratings and reduce fuel costs, they’ve helped deliver the torque to haul loads more efficiently and the technologies to be in compliance with the many different air quality standards from nations all over the world. To keep up with these wide-ranging specifications and performance standards may not require a whole new engine concept, but it may require numerous enhancements of engines, incorporating design modifications and the latest innovations in components. The process frequently requires prototype parts and, of course, comprehensive testing.
As a recent example illustrates, assistance is sometimes required to complete the assembly procedures of modified engines. Ken Zalucki, sales engineer for 3-Dimensional Services, described the situation.
“Detroit Diesel had developed the sixth generation of its electronic engine control system, called the DDEC VI,” says Zalucki. “This advanced system uses a more powerful microprocessor, more memory, and better diagnostics capabilities than previous versions, and is capable of monitoring and managing all engine functions—including the critical ‘after-treatment’ systems required for 2007 emissions standards. Major components of the DDEC VI are a series of sensors installed at each of the six fuel injectors on the top of the engine head and under the valve cover that provide operational monitoring and control. Placing the new sensor terminals into the engine during the pre-production build stages, that is, completing engines for various testing and trials while also coordinating the necessary assembly procedures, turned out to be somewhat of a challenge.”
The terminal, Zalucki explains, required a male wiring plug be inserted into its female counterpart at the injector location, a position too close to the engine wall and between two valve springs that limited access for assembly by hand.
“Positioning the plug in the socket was about the only thing assembly technicians could do,” Zalucki continues. “The process proved very difficult, if not impossible, to put enough pressure on the plug while securing the retaining clips to successfully engage the parts. For those few times when the plug was forced in, connector blades were frequently bent or misaligned, requiring repair or replacement. It was, as one Detroit Diesel engineer put it, an ergonomic nightmare. And, since this was only the pre-production builds, completion of most tools and assists planned for production schedules were still up to 12 weeks down the road. That’s when Detroit Diesel asked for any assistance that we at 3-Dimensional could provide. They also asked three to four other firms for ideas as well.”
For 3-Dimensional Services, it was a somewhat unique task. According to Zalucki, the firm had provided approximately 12 prototype parts for this latest engine variant, and has worked with Detroit Diesel on numerous projects over the years. Typical prototype parts constructed included stamped support brackets and injected-molded plastic brackets and harnesses for routing and securing wiring.
“In the past, we’ve worked with various part configurations, and virtually all types of manufacturing disciplines,” Zalucki remarks, “so coming up with a tool design was somewhat different. I presented the application specifics to our engineering team and, within three days, we presented to Detroit Diesel a working sample. It was gratifying to hear that our competitors in this effort were only able to provide a CAD drawing of their proposal in this same time frame.”
As Mr. Zalucki relates, this first attempt by 3-Dimensional consisted of a pliers-like design with thin jaws, similar to needle nose pliers. Each side had multiple step surfaces to properly locate and grasp the plug, and to depress the locking flanges. A stop pin was incorporated into the design to prevent the tool from being pressed too hard and exerting excessive pressure on the parts that could crush the terminal, plug, or contact blades.
“Once Detroit Diesel verified the operation of this initial tool and provided feedback, we began the process of fine-tuning and finalizing the design,” notes Zalucki. “Some of the modifications included making sure the tool met all of their ergonomic criteria. Examples of these are the curve of the handle, the distance between handles (to fit comfortably in the greatest percentile of hand sizes), and the force/tension required to operate the spring-loaded handle grips. The first finished tool, now measuring nearly 10 inches long and meeting all specifications, plus with a cushioning rubber coating on the handles to improve comfort, was delivered approximately seven days after the original prototype tool. Three additional tools were completed within another week, and more may be ordered for service centers to complete warranty work in the future.”
To complete the tools, 3-Dimensional Services relied upon a sampling of its production process resources, including its laser cutting capabilities, with 17 laser processing systems on hand, to cut and trim the handles from ?-inch-thick durable steel, and to cut and shape the work holding jaws. The jaws were also machined to final size and form utilizing CNC machining centers, and then each jaw tip was welded to the handles. To assemble with the included spring action, the handles were drilled, tapped, and fastened. Where necessary, surfaces were hardened, ground, and polished to provide a finished appearance, and the tools were given an acid bath resulting in an attractive and rust-resistant gunmetal gray color. The final process was the rubber dip to complete the handles.
Its ability to complete the tool manufacture within the same time frame that others needed just to develop a drawing model is something that 3-Dimensional Services takes in stride. The company’s use of advanced process methods and manufacturing technologies is said to enable it to typically provide prototype parts up to 70% faster than conventional prototype shops.
“When it came to completing the terminal insertion tools, the steps...the design, the fabrication, the working with the client...were no different than our typical prototype part procedures” says Zalucki. “We had a customer in need of assistance, and our staff answered the call. Three-day response may seem fast to most, impossible to others. It is, however, our way of doing business.”
For more on Detroit Diesel, visit www.detroitdiesel.com.
For more on 3-Dimensional Services, visit www.3dimensional.com.
This technical information has been contributed by
3-Dimensional Services Group
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