Andrew Brown Jr.
Most design and manufacturing firms are trying to find ways to shorten design cycles, improve product quality, and ultimately increase market share. But these goals seem mutually exclusive. For instance, improving quality demands more time in design cycles, not less.
To solve the conundrum, engineers at Delphi's Steering Systems Div., Saginaw, Mich., searched for a commercial solution that would link 3D design data to manufacturing. They found none. So company management asked its CAD/CAM team to find a better, software-vendor-neutral way to design parts that would speed up the entire production cycle.
The team came up with two processes: One for design departments and one for manufacturing operations. Both are CAD-neutral and require no additional investment in new software, hardware, or IT services. The design side works with Unigraphics, Catia, SolidWorks, and Pro/E, and the first three CAD systems on the manufacturing side as well. But before elaborating further, it's instructive to examine the current state of production frustration that led to the new processes.
Problems with tradition
Unfortunately, feature-based, solid-modeling software has not made it easier for designers to work closely with manufacturers. The problem is this: CAD vendors suggest making models by building features one on top of another in a vertical hierarchy, in so-called "parent-child" relationships. It's supposed to help make changes quickly but instead causes unanticipated and disruptive changes. Because of the parent-child dependencies, changes that look simple are usually complicated and often impossible. Designers can be forced to dismantle or completely recreate models to make changes. Many designers refer to the change method as "hack and whack" because creating additional features means hacking and whacking their way through the vertical part trees to modify geometry that can't be independently edited.
In addition, each designer has a preferred way of building models, so 10 designers will build the same model 10 different ways. There is no standardization in most design departments. And edits can be cumbersome when a model must be changed by someone who did not originally build it. The model could be scrapped and rebuilt from scratch, or hacked and whacked. Lastly, should a designer discover a better way to build models, it is lost because there is often no way to document the method or make it a standard operating procedure.
Manufacturers encounter different problems, but they stem from the same difficult-to-change design geometry. For instance, when most receive 3D models for production design, they turn to 2D CAD systems to create drawings for manufacturing operations. Furthermore, they manually create 2D views for each manufacturing operation -- one for castings, one for milling, and so on.
Another method creates separate solid models for each operation. If the model is to be cast, for instance, manufacturing designers add runners, vents, and sprues. Process drawings are then made from vertical, feature-based models, which means creating multiple, nearly redundant, nonassociated geometry for each operation.
All this requires duplication and rework, partially because designers have not uncovered all the useful features in their software, and because heavy workloads don't let those intimately involved with production pause to find better ways. Ironically, engineers and production people have known for years that improved cooperation between the two disciplines was always the key to developing better products.
Better ways to design
To get around the pitfalls, Delphi engineers developed the Horizontal Modeling (HM) method that eliminates the need to recreate CAD data to accommodate ECOs or manufacturing. HM is a detailed, disciplined, yet straightforward technique for using existing 3D CAD systems. It essentially flattens the traditional vertical feature tree making it horizontal, hence the name. HM is composed of several best practices that describe ways to build models that are more easily edited.
Most CAD vendors teach the vertical-modeling process. HM users are taught to make features that are placed and positioned on global references rather than features. Users create datum or reference planes relative to the model (not on the model) when placing features. So instead of placing a boss on a rib, they create a datum plane relative to the rib and place the boss on the plane and position it to the datum as well. So when the rib changes, the boss remains unmodified. HM allows design intent to remain flexible. Control of the model is maintained through values from parametric expressions, which can be manipulated as needed. This method avoids inflexible relationships inherent in the parent-child structures.
The emphasis in HM is on minimizing parent-child relationships because it is where problems begin. HM recognizes, however, that there are times when such relationships are unavoidable, such as in preferred methods for making blends and chamfers. These types of features require a direct dependency between an edge and surface of a model.
Another best practice deals with ways to treat legacy data that is built in the vertical structure. When legacy data is needed, there are simple ways to create a core set of datum planes that restructures the model feature by feature and replaces the parents for positioning in part trees. Most all CAD systems can handle the prescribed techniques and generate many downstream benefits.
Better ways to manufacture
Digital Process Design (DPD) is the companion to HM. DPD also is a software-neutral method for defining manufacturing operations and handling in-process design changes. When handed a model built in the horizontal design process, DPD users create separate associative 3D in-process models and 2D manufacturing-process documents with functions already in the software. Most CAD systems can associate drawings to models so that a change to the model updates all drawings. Before HM and DPD users did not create associative in-process models, so creating manufacturing process documentation has become a series of disconnected steps with manual intervention.
To illustrate a better way to create manufacturing in-process models, consider a cast hydraulic manifold designed with the HM method. The cast-manifold model, however, only has finished geometry on it -- smooth ports and all holes threaded. To define the manufacturing process of the casting being machined to the finished manifold, a manufacturing designer would use the production manifold file as a seed file and perform a save-as function, saving it as the manufacturing process documentation file. The manufacturing designer adds in-process features to the design model for the needed machining after casting. For example, finished holes, are produced by the manufacturing designer inserting three production steps before the hole (chamfer, finish, thread). This adds a chronology to the feature tree from casting to finished diameter.
In the Unigraphics CAD system, for instance, the commands for adding manufacturing steps are Extract, Body, and Time Stamp. The function varies in Catia, SolidWorks, and Pro/E, but the process is similar. The manufacturing in-process model captures 3D physical and associative representations of what it looks like at different moments in the production cycle.
The Extract function captures what has been done. Design and manufacturing models are separate but associated solids. The point here is that there is only one set of geometry while many would be made in a traditional production system. Machine features for all operations are captured in one master process model as the manufacturing designer adds necessary steps.
Another manufacturing best practice deals with purchased parts. If there is a model available for these items they are usually dumb solids -- no features and nothing parametric. Product design would treat it as a production part, but manufacturing personnel would put it into either a manufacturing or assembly file. In the UG environment, a function called a geometry linker connects the part to where it came from. In the Horizontal Manufacturing file, this becomes the master process model. The benefit is twofold: The manufacturing person does not need the product file to open his files, and better yet, when a revision of the dumb solid comes in, it's just unlinked from the old file and relinked to the new one. The CAD program propagates the updates downstream to the process models and process sheets with the new component. This described linking and unlinking function will ONLY work if the receiving model is created using HM.
These design ideas also allow more concurrent operations between product and process design because manufacturing people are not punished with regenerating their work each time a new design model surfaces. This leads to a shorter manufacturing cycle.
Delphi Technologies Inc.,
The Best training
CAD vendors, to their credit, have improved the reliability, capability, and ease of use of their software. In fact, it's so developed, many of the features and functions go unused.
Traditional training generally covers how to navigate the menu structure and use each command individually. Little or no information is generally available on how to design better products, or how to optimize the design process. For that, design departments are on their own. Consequently, the best training comes from classes that focus on teaching designers and engineers how to use the 15 best practices (at last count) of HM and DPD in concert.
The new design methods are more thoroughly conveyed in a formal classroom setting because they include learning to design a new way and an introduction to best practices for design and manufacturing. To support the new methods, Delphi Technologies has established the Delphi Center of CAD/CAM Excellence (DCCE) www.delphi.com/dti/dcce. The Center provides training and support to those interested in training and certification programs in the methods. Classes span three days and will soon be available online through Cadpo, Westminster, Colo. A course overview and syllabus are available at the DCCE.