Product data management (PDM) has helped engineers shrink the time needed to develop a new cross-country motor coach called Renaissance. Engineers used virtual prototypes to confirm that movable parts in the motor coach would fit properly and to identify interferences before physical prototypes were built. The Renaissance uses some highly innovative technology. It is the only cross-country motor coach built in North America to feature six-wheel anti-lock disc brakes for speedy stops and a steering tag axle that greatly improves manoeuvrability. Motor Coach management believes that the use of computer design eliminated some of the costs associated with building and rebuilding portions of the prototype. It also reduced the cycle time considerably. The entire project, from concept to customer deliveries, took 39 months. The PDM system helped engineers by allowing them to see the association of their files with their designs. Solid modeling and PDM helped engineers slash the Renaissance's parts count by 60 percent, reduce suppliers from 53 to 48, and cut build hours by 45 percent.
When engineers at Motor Coach Industries International embarked on the development of a new luxury tour coach, to be called the Renaissance, they decided to create the design digitally, relying heavily on computer-aided design and solid-modeling tools to design the vehicle. Although it was the first time they had attempted to execute a virtual product-development process, the massively complex files that resulted proved to be easily manageable with the use of a product-data-management (PDM) system. As a result, it was possible for engineers to meet the goals they had established for the project-reducing the number of parts, parts suppliers, and assembly stations needed to produce the new coach-and to bring the Renaissance from concept to production in record time.
The Renaissance is intended to make traveling long distances between cities as comfortable as first class air travel-but with a better view. It is easy to board, thanks to an entrance door that is wide enough for two adults and a six-step spiral staircase that facilitates passenger boarding. The vehicle also has wide aisles, a 34-speaker digital sound system, and large windows for viewing the scenery. And, of course, there are comfortable seats.
The Renaissance also uses some highly innovative technology. It is the only cross-country motor coach built in North America to feature six-wheel anti-lock disc brakes for speedy stops and a steering tag axle that greatly improves maneuverability. In fact, Winnipeg, Manitoba-based Motor Coach holds six patents on the various component subsystems of the coach.
New Design Approach
Before they started designing and building the Renaissance, Motor Coach engineers completely re-engineered their product-realization processes. They wanted to start from scratch on this project so they could produce a new, simpler coach platform that would have fewer parts and be easier to assemble.
To accomplish these goals, 100 people were hired from different areas of the company and outside-everyone who wanted to work on the project had to apply for a position. They were organized into 10 teams that examined every facet of the design and manufacturing process. In addition to curb appeal and customer excitement, the teams also focused on cutting out unnecessary parts and processes. As a result of their work, before building began on the first actual prototype coach, the teams had streamlined some of the manufacturing practices, simplified the bill of materials, and reduced the number of suppliers that would be used to produce parts for the coach.
As part of this process re- engineering, it was decided to design the Renaissance entirely in the Unigraphics solid-modeling system from. Unigraphics Solutions in Maryland Heights, Mo. Motor Coach has used Unigraphics since 1987, but this was the first time the company had designed a coach completely in the CAD system using solid models. Every component of the Renaissance was modeled as a solid. Previously, Motor Coach designers had used mostly 2-D drawings and wireframe models, so even parts that were picked up from earlier designs for use in the new coach were recreated in Unigraphics Solids.
Solids were the basis of the virtual-product-development approach to the new coach design. By modeling all the components of the coach in mathematically accurate solids, it was possible to virtually build the coach inside the computer. Designers could see how each part and assembly fit, and they analyzed and simulated the performance of some of the components in the computer. For example, they used the mechanism design features of Unigraphics software to confirm that the movable parts in the coach, such as the doors, operated properly.
Using solid models to prototype the Renaissance in the computer allowed engineers to produce an accurate physical mock-up of the coach early in the design process. A prototype is necessary to verify that every part and assembly works properly together. Making a physical prototype, however, is costly and time-consuming. By doing most of the mock-up in the computer, it was possible to use physical models primarily as verification of the computer model. Motor Coach management believes that the use of computer design eliminated some of the costs associated with building and rebuilding portions of the prototype. It also reduced the cycle time considerably. The entire project, from concept to customer deliveries, took 39 months.
Motor Coach would not have accomplished its goals for the Renaissance without some way to manage the large CAD files developed as a part of the project. This is where PDM came into the picture. This was the first time Motor Coach had used a PDM system, and the company selected the IMAN Information Manager from Unigraphics Solutions. The software ran on two servers, an Oracle database server to handle the metadata that describe the location of files, and a separate file server. (When an engineer selects a file in the PDM system, he is actually searching for metadata about the file. The Oracle server then makes a call to the file server to download the file.) The Oracle server operates on a Hewlett-Packard 9000 K-class computer, which is a midrange machine. It is tuned to perform database transactions quickly.
One of the reasons [MAN was selected as the PDM system was that it understands all the relationships between parts and assemblies in a solid model. These relationships are complex and not easily tracked, because three-dimensional models are never stored as a single entity. A 3-D assembly model is really a reference file containing a set of pointers to all the parts files that make up the assembly. When an engineer calls up a model, the computer uses the references to select the correct parts for display. Tracking all part and assembly data is especially difficult if there are different versions of the parts or assemblies involved.
Of course, the CAD program understands all the geometry and its relationships. But human beings using a solid model do not know how all its component parts are stored. One advantage of ’Using IMAN and Unigraphics on the Renaissance was that both programs together presented the assembly structure to the engineers, so they could see and manage component-assembly relationships. By allowing them to view and manipulate the assembly structure, IMAN gave them control over the data and’ helped keep the revision process under control.
The PDM system also helped engineers by allowing them to see the association of their files with their designs. In IMAN, the different items associated with a version, such as a model, drawing, or specification, are called objects. An object describes the type of fuel that is stored, and each object is represented by a different icon. An engineer on the project would open up his IMAN workspace, which is a graphical desktop that displays all the information related to a product, and see a list of folders. Inside the folders would be objects representing parts, assemblies, and specifications. A folder contains all the information related to a specific model. A folder of an assembly containing four different parts might contain the 3-D models for the parts, 2- D drawings, the specifications related to each part, and the bill of materials defining the assembly structure. Each of these items would be available to the engineer, who could click on an item on the screen and view the file associated with it.
Before computers, Motor Coach’s design process was always controlled through the print room. Blueprints were kept in a separate room and were checked in and out of the room by engineers. If the blueprint was checked out, it was not available to other engineers who might want it.
Ensuring Master File Integrity
Now that all design work was being done on computers, there was another problem to deal with. Engineers working on the Renaissance could have copied files and made changes to them without any control, resulting in multiple conflicting copies of the same file in a variety of directories, without anyone knowing which one was the most up-to-date version. It was necessary to make sure that there was only a single master file for each assembly, especially considering the complexity of the solid models involved. PDM helped control access to the master file. One important function of a PDM system is to lock a file when it is in use. The [MAN system was set up to prevent more than one person at a time from making changes in a file. Once a file was checked into the PDM, it could not be checked out by anyone without permission to do so.
In a sense, IMAN brought to the Renaissance project the control that formerly came from using a print room. The system was set up so that all assemblies and parts were controlled by the groups and individuals who were responsible for them. For instance, only people in the powertrain group could make changes to components within the engine or transmission systems of the coach.
Often, however, several engineers needed access to the same file to look at information or to suggest changes. They were accommodated by setting up the PDM system so that read-only files could be checked out. Thus, if one engineer had a file checked out, others could examine a read-only copy of it. Any changes indicated were added once the master was checked back into the PDM system.
The product structure for the new coach assemblies was tracked through bills of materials (BOMS) developed in the IMAN Product Structure Editor. The information in the BOMs reflected the as-engineered configuration of the coach. There was only one BOM for the Renaissance as a whole. In a change from the practice employed with other Motor Coach models, product definition resided in the engineering database (IMAN), not in the manufacturing-resources-planning (MRP) system. Only those parts that required scheduling were entered manually into the MRP system. The MKP system was not linked to [MAN at that time, although that is planned for the future. There are also plans to allow service, parts, and purchasing staff to view the IMAN bill of materials to source parts used in Motor Coach products. This will allow purchasing agents direct access to the most current engineering specifications for a product, making it less likely that they will order the wrong part.
All in all, the use of solid modeling and PDM in the Renaissance project helped decrease the number of parts in the coach by 60 percent, compared to previous models. The number of suppliers used was reduced from 53 to 48, while the assembly stations needed to produce a coach were slashed by 69 percent. The build hours necessary to put together a motor coach were cut by 45 percent.
The Renaissance has proved successful in the market. Before its introductory tour was even complete, Motor Coach had two months’ worth of back orders, and the coach is now in full-scale production, with up to 10 vehicles rolling off the assembly line each week. The Renaissance is also the coach platform of the future for Motor Coach. As the company creates new coaches based on this design, the benefits from allowing engineers to find their files easily with PDM should be even greater than those on this first project.