In order to bring new products to market in increasingly shorter times, companies must continually improve their products and their development processes. Process innovation can be achieved from new tools and methods, but also from new methods of work organization. At Audi AG the tool and die designers have created a comprehensive 3D software-based process to develop press tools. They have also introduced simultaneous engineering procedures that incorporate their production technology expertise into the conceptual phase of chassis development.
To support these processes, Audi has implemented the ICEM Surf surface modeling, analysis, and visualization software suite as a tool for the virtual formation of drawn parts and as a medium for exchanging design information.
The Tool Design division within Audi AG has around 1,100 employees located at Ingolstadt and Neckarsulm in Germany and offers its services to subsidiaries in the VW group, as well as to outside customers. In fact, some 30% of the division''s workload is for external customers. Each year, some 60 tool and die sets -- each consisting of up to six individual tools and dies -- are produced. Depending on the requirements, Audi subcontracts the production of less technically demanding components but keeps the development of complex deep-drawing systems exclusively in-house.
The role that Audi''s Tool Design division plays has expanded significantly from a tool and die supplier to that of a system partner with the stamping plant and the body-in-white (BIW) group. Today, the tool and die design group is responsible for the entire process sequence from method planning, to tool and die design, to the production and implementation of tools.
In its role as the "Center of Excellence" within the VW group, the tool and die design group has a great deal of influence on the future configuration of the tool and die development process. Continued development of important key technologies, such as calculation methods and CAD systems, are significant issues in this regard.
To allow for the comprehensive use of CAD data throughout the entire process sequence and to ensure clarity, the decision was made a few years ago to adopt a computer-aided direct 3D modeling approach in both method planning and tool and die design. This decision meant a fairly radical break with the past. While drawing systems in the past had been milled using CAD data from method planning, the drawing system models were generally initially modified manually and then digitized so that the altered geometry could then be used for setting up the milling program.
Now, the deep-drawing systems and the tools and dies for subsequent operations are created completely as 3D models. The aim was to develop production methods with safe processes, as well as tools and dies, directly on the CAD system and to thereby minimize the need for manual rework.
Method Planning
The use of 3D CAD systems in method planning at Audi is the basis for a unified process sequence in tool and die design. Method planners are responsible for ensuring feasibility in the technical manufacture of sheet metal parts. They determine the sequence of operations and the geometry for the individual operations, such as production position, tool separation, binder and addenda device surfaces, as well as the direction of strike. They have to ensure foolproof process forming and the desired part quality with regard to dimensional accuracy and surface quality, that the operations are adjusted to the machines, and that the material usage and material costs are kept to a minimum.
Since the manufacturability of a component as well as its costs are highly dependent on the geometry of the component, method planners at Audi are involved very early in the development process. They consult with the stylists during the early concept models creation phase and then support the designers in Technical Development -- where responsibility for the production release of aesthetic, or Class A surfaces, lies -- with the detail part design, from the outset.
At Audi, simultaneous engineering (SE) is viewed as a strategic measure to transfer production technology expertise to the development area and thus contribute long-term to the creation of components appropriate for production and demand. For this reason, tool and die design is embedded in the project-related SE organizational structure. Each project team is divided into different SE specialty groups which, in turn, are subdivided into individual SE work groups comprising various disciplines, such as detail part design and tool and die method planning.
ICEM Surf In Tool Design
It was through close contact with the designers in Technical Development that the tool and die designers found out about ICEM Surf. The software had been used in Technical Development at Audi for some time for vehicle body and interiors surface model development and production surface layout.
As a spokesman for Audi''s Tool Design division points out, since the people in method planning are responsible for achieving quality in tools and dies, it seemed obvious to them that it would make sense to process the component geometry further using the same system as Technical Development uses. In the process of evaluating the suitability of ICEM Surf for this task, it was determined that the software''s direct modeling facilities offered clear advantages over the classic surface setup using curves and guide lines.
The definition of the tool surfaces in method planning posed specific demands on the surface modeling functionality of the software. On the one hand, the existing surface geometry of the components must be as easy to modify or as flexible as possible in order to compensate for effects such as sheet resiliency, or spring-back, during the forming process. This ensures that in the end the finished sheet metal part actually corresponds to the desired shape. On the other hand, the system must support expansion of the part surfaces with new geometry -- for example, the addition of drawing beads and addenda surfaces.
After an extensive testing phase, the Tool Design division decided to integrate the ICEM Surf surface modeling system into the process sequence. By using functions in ICEM Surf for global surface manipulations, the method planners are now able to develop tool and die surfaces directly on the component surface model to compensate for sheet metal spring-back effects. Surface forces are simply drawn to a specific point in the plane. In the process, changes to the light curves, which can be analyzed and visualized using ICEM Surf, provide information on selecting the correct grip point.
The actual simulation of the deep-drawing process is done in another software package, called Autoform. Parameters such as material strength, friction coefficients, press pressure, and blank size are taken into consideration in the simulation. The ICEM Surf data is read into the finite element system and then meshed and analyzed. On average, each tool or die needs five to six iteration loops from the surface generation to go from simulation to modification. Originally, this could take up to four days depending on the intensity of the simulation. For complex parts for which there are no reference parts, the number of loops could quickly increase.
In the early days of their use of ICEM Surf, the tool and die designers therefore thought it would be useful to be able to play the data from the simulation system back again so that the geometry could be modified faster and more precisely based on the simulation results. In conjunction with Audi''s tool and die designers, ICEM therefore developed an interface that allows for bidirectional exchange of data. This enabled method planners to work with the CAD and simulation systems at the same time, which reduced waiting times and avoided time-consuming data conversion processes.
Thanks to close integration between ICEM Surf and the simulation systems, the tool and die designers at Audi have been able to speed up the development of tools and dies and to provide greater reliability in the ''virtual workshop.'' Before, parts cracked regularly during the forming so that the tools and dies subsequently had to be changed. Now that everything that happens on the milling machine is simulated in advance, this problem has been largely overcome.
More importantly, production parts are now of a higher quality than they were in previous years.
According to their own estimates, the completion rate in method planning and tool and die design at Audi has increased by some 15% since a comprehensive 3D surface modeling process was implemented using ICEM Surf.
But aside from meeting the highest quality demands, one of the most important goals was to shorten development times. As an Audi representative points out, if 10% can be cut off a process that takes eight weeks, then this is only four days. But measured by the Audi Tool Design division''s capacity, this means that each year an additional three to four tool and die sets can be processed. And this represents a significant increase in productivity.