3-D Modeling of Stamping Dies

Fig. 1 Fig. 1 -- Conventional 2-D die plan view.

Competing in today's manufacturing environment requires having the technical competence to deliver a quality product at a fair price. However with the pressures to reduce time to market and just-in-time manufacturing methods, shorter lead times are becoming equally important. Every opportunity to save time must be considered.

To take advantage of the time savings 3-D solid modeling can contribute to a project schedule, Summit Tool Design of Rockford, IL, has been using Intergraph EMS PowerPak software for five years to electronically model sheet metal stamping dies. The Intergraph software is a comprehensive package that is capable of creating 2-D/3-D wireframe, 3-D surface/solids, free form surfacing and complete detail drawings in either an associative or non-associative mode. Associativity maintains the designer specified relationship of graphic elements, such as parallel lines, perpendicularity, tangency, concentricity, etc., as design modifications are made. This enables the designer to make a change and not have to adjust every related element individually, as the system will do it automatically.

More Useful Information

While complete 3-D modeling of a tool takes about the same amount of time as a conventional 2-D CAD design, Fig. 1, the information produced is more useful. With the power of electronic data in today's computerized tool shops, the more quality information that can be provided to the shop floor the more efficiently a tool can be built.

One of the most frequently heard comments from someone who has built a die using a 3-D design, Fig. 2, is how easy it is to visualize and interpret an object when a Isometric view is provided. Additional aids for interpretation that can be easily created from a 3-D data base are exploded assembly views, Fig. 3, auxiliary views and other views from any perspective to help visualize the design. When time is critical, the less time a diemaker has to spend interpreting a drawing the more time is available for building the tool.

A fully defined part model enables moving a step closer to a paperless system. The designer is responsible for creating a precise master 3-D solid model of each die component so that the NC programmer does not have to spend time interpreting 2-D graphics, CAD files or plotted drawings to generate the geometry required for programming. A model can be passed to NC manufacturing without a detailed paper drawing as all features of size, shape, depth of pockets, counterbores, draft angles, etc. have a complete mathematical definition.

Lee Bandini from Brenner Tool & Die in Croydon, PA, states that "typical large die components, die sections, strippers, etc., that normally would take the NC programmer 1 to 11Ú2 days to create the geometry and NC program can be completed in a half day when the 3-D geometry has already been created." With a large progressive die having 20 or more parts that fit this category, 80 to 160 hours can be saved on a project. In addition to shortening the lead time, this reduces errors and helps to maintain the original intent of the designer.

Fig. 2 Fig. 2 -- While complete 3-D modeling of a tool takes about the same amount of time as a conventional 2-D CAD design, the information produced is more useful.

Design Benefits

While 3-D designs have many benefits in the manufacturing phase of a tool there also are many benefits to be gained during the design phase. Frequently, piece part CAD data is created in 3-D, and every effort should be made to take full advantage of this data to begin the tool design. A flat blank for a part can be manually or automatically unfolded from a 3-D piece part model. In the case of a part with complex surfacing that does not lend itself to the conventional formulas for blank development, the automatic cross sectioning capabilities of the software can be used to cut a series of cross sections at a specified increment.

The length of the cross section then can be plotted from a known reference point and digitized to accurately estimate the blank profile. Fig. 4 compares the results of a blank estimated by cross sections to the final blank development. As the illustration shows, the estimate was not perfect. However, it did rapidly create a legitimate estimate sufficient for laying out the tool with confidence and provide a first hit development sample. For drawn shells it is easy to create a surface representing the center line of material thickness and measure the total surface area of the elements to arrive at the estimated blank size.

Because a 3-D model is easier to visualize, analysis and optimization of the design can be done early in the design phase of a project. As each part is modeled not only is the plan view -- "X" and "Y" axis -- of the part laid out, but also the elevation or "Z" axis of the part determined. This aids the designer in determining the proper proportions of the part, and any additional reinforcements that may be required for sufficiently stable mounting. With the "Z" axis defined the geometry for side, isometric, auxiliary and section views also is readily available for producing detail drawings.

Each part being assembled in true location in 3-D space allows for interference checking to be done between tool components as well as the work material. Conflicts can be checked for prior to material forming, after forming is complete or anywhere in between, as well as checking for material feeding or part ejection obstructions. The software is capable of defining where the interference is, and proper clearance then can be defined. This is more cost efficient then having to make changes and revisions later to completed hardened tool steel parts.

Fig. 3 Fig. 3 -- This partially exploded 3-D die plan view is easily created from a 3-D data base. Auxiliary views and other views from any perspective can be used to help visualize the design.

For detailing the design, the appropriate drawing views (orthogonal, isometric, section and auxiliary) that the designer specifies are placed. The system then processes the drawing views creating the correct line symbology required to display visible and hidden edges for a detailed drawing. This frees the designer to concentrate on the design and be confident that the information is correctly displayed.

Macro Libraries

Another powerful tool to reduce the time required to complete a design is the use of macro libraries to create standard parts. The macro enables creation of a 3-D part or feature by defining the dimensions of the part. The system automatically places the part.

Typical parts or features for a macro library are perforators, nitrogen cylinders, die sets, screw slots, "D" holes and other items that are common in many tools but vary in size in each application. For standard hardware items that are fixed in size, cell libraries can be created. Items for a cell library include fasteners, ball lock retainers, spring guards and die set bushings. With the use of a cell or macro library, complete 3-D parts can be placed in a matter of seconds or minutes, versus 10 minutes to an hour or more to create them from scratch each time.

Fig. 4 -- A flat blank for a part can be unfolded manually or automatically from a 3-D piece part model. In the case of a part with complex surfacing that does not lend itself to the conventional formulas for blank development, the automatic cross-sectioning capabilities of the software can be used to cut a series of cross sections at a specified increment. The length of the cross section can then be plotted from a known reference point and digitized to accurately estimate the blank profile.

The 3-D CAD data is available in several file types for downstream applications including 2-D or 3-D wireframe, 3-D solids or surfaces as well as a plotted drawing.

Summit Tool Design has provided designs for a broad spectrum of products in the automotive, hardware, furniture, electrical, electronics, power tool and steel toy industries. Piece parts have ranged from simple flat work to very complex free-formed surfaced parts to micro-miniature electronic connectors.

The advantages of 3-D modeling for stamping dies include, improved productivity, NC ready surfaces, fewer errors and ease of design interpretation. With the demands for quality and value of time always increasing, these essential advantages can not be ignored. The more complex the part geometry, the more a complete 3-D tool design will prove beneficial. MF