Product Development Support for Suppliers of Forgings

E. Doege ( I ) , M. Muckelbauer, M. Michael Institute for Metal Forming and Metal Morming Machine Tools (IFUM), University of Hanover, Hanover, Germany

Received on January 7,1999

Abstract This paper describes software tools which were developed at the Institute for Metal Forming and Metal For- ming Machine Tools at the University of Hanover, Germany (IFUM) as add-ons for the CAD system ProlENGINEER. The software tools support the entire forging design process from the rough design to the finished part. It is now possible to use information on the functionality of the product for forging design instead of technical drawings or conventional CAD models. The described approach supports the migration of the product development from the customer to the supplier. The use of FEM for the load simulation and the PRINZ simulation tool (also developed by IFUM), which calculates and visualizes the material flow during the forming process, are also described. Keywords: Hot forming, Product development. CAD

1 INTRODUCTION Close cooperation between product designer and manufacturer is imponant to be able to get the best compromise between the functionality of forged parts and the cost of production. The adaptation andlor custom development of CAD systems allows existing design know-how to be used in additional product development processes and can also provide built-in support for standards and guidelines [l]. Modern CAD systems can generally be adapted by the user to meet particular requirements. For example, design guidelines for the production of forgings can be supported by add-on functions which are integrated within the user interface of the CAD system. The integration of software design tools throughout the entire design process - from the specification of product requirements through to the design and the quality assurance stage - can lead to a reduction of design errors and data redundancy. Furthermore, a CAD system which is customized for the design requirements can save development time and reduce production costs and generally leads to higher quality products.

2 PRODUCT DEVELOPMENT BY SUPPLIERS OF

Forging companies are becoming more and more involved in their customers' product development processes. Nowadays, product requirements detailed in the customer specifications include information on placement space, mechanical loads and other fixed parameters. In addition, the customer specifications can even include a sketch of the part, as shown in Figure 1 [2]. With a complex geometry. it is necessary to have access to the CAD data of the assembly in order to ensure that the part fits into the available space. The customer specifications are the basis for a function model which is initially designed without considering the production method. One or more production methods are then chosen according to the cost of production and ecological factors. Based on that choice, the part is then

FORGINGS

designed for production under consideration of design standards and guidelines. The design work can be simplified by adapting the CAD system to the requirements of the design process [3] [4]. In addition, the use of simulation tools to improve the preforms is becoming more widespread. Such systems, which are usually based on FEM, can be applied to both product design and choice of manufacturing sequence PI.

Kinematics Mechanical properties Weight

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Figure 1 : Schematic of customer specifications [S].

3 DESIGN SUPPORT WITH FUNKO It is advantageous to develop a rough design in the first modeling step because this reduces the modeling effort and makes it easier to carry out design modifications. Various approaches. such as the methods of functional surfaces and form features, can be used for this purpose m PI. A suite of software tools have been developed at IFUM to support the functional-surface and form-feature oriented design of forgings. For example, the FUNKO software

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(‘Function-Oriented Design’) was developed by IFUM as an add-on for ProlENGINEER, a widely-used commercial CAD system. The two methods can be used independently or in combination. One advantage of ’Design using functional surfaces‘ is the fast rough design, which is often called the function model. Surfaces, or quilts as they are called in the CAD system, can be copied from the assembly and thus do not need to be redesigned - a major benefit particularly in the case of complex functional surfaces. However, with this method it is then necessary to design the forging and the finished part manually. The method ‘Design using form features’ supports the design of the forged part by accessing specific information integrated in the features. With the latter method, the design is done by choosing form features from a feature library. The part is modeled by choosing form features and by specifying the dimen- sions. These features are stored in such a way that only a few parameters need to be entered to specify the model. The data structure of the functionality information also contains two other models: the forging model and the finishedpart model (Figure 2). All required values such as machining allowances, draft angles and corner radii are calculated by FUNKO automatically. FUNKO contains a database for this purpose which includes information on the DIN 7523 standard (Design of Steel Forging Parts) and other guidelines. The database supports and accelerates the process-oriented design of the forging.

‘copy surfaces I

Figure 2: Model content of the features.

Copy datum

Q IFUM

The geometry of the finished part is equivalent to the forging after the finishing process, for example the milling or drilling. This is determined by the function model data. Both methods - ‘Design using functional surfaces’ and ‘Design using form features’ - can be easily combined. For example, the basic geometry can be modeled first using the features and then modified in functional areas using the function model data. The placement of the part into the assembly can be carried out automatically with both methods. This allows an analysis of the assembly for collision of parts to be performed by the user. The FUNKO application was developed by IFUM with the program interface PromOOLKlT and is integrated in the user interface of ProlENGINEER. Figure 3 shows the FUNKO menu in Assembly mode. The copying of datums (reference data) and functional surfaces is advantageous because it avoids the difficult and time-consuming input of parameters. In addition it provides a logical connection between the functional geometry of the assembly and the part. For example, a modification of the distance between two shafts automatically extends the pa ts web. All further operations take place in the Part mode of ProENGINEER by opening the new component in a new window, whereby the copied surfaces and datums taken

from the assembly can be used for the placement of the form features or for the method of functional surfaces.

[Create surfaces I /Create component I Assembly

P -

L P C ?

Figure 3: Menu items in Assembly mode.

The basic structure of the Part mode menu is shown in Figure 4. The two methods are implemented in the menu items Form feature and Surface, respectively. The Model item allows you to choose the active model (function model, forged part or finished part model). Rough design allows you to choose a set of features for an initial design of the part without the integrated automatic forging design. The form features are grouped according to their symmetry and other geometric properties. The library can be extended by the user to allow adaptation to specific needs.

I Initiation I

...... .. : -. . ..... .

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Figure 4: Menu items in Part mode.

The choice of model depends on the phase of the design process. The Function model is used to create or change the rough design of the part. A lot of modifications have to be made in this phase and thus it is necessary to minimize the complexity. Especially for parts that need to be checked with simulation tools, the reduction of the number of design elements can accelerate the simulation process. Furthermore, it may be necessary to carry out the placement of some of the design features manually, particularly if the geometly is complex. The Forged part model is used for the design of the pre- forms and the forming tools. Wherever possible, computer-aided design and simulation tools should be used throughout the entire design process to achieve

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lower production costs and times and to ensure higher quality products (91. The Finished pad model is used for final simulation stages and assembly analysis.

4 EXAMPLE OF PRODUCT DEVELOPMENT A real-life vehicle component was selected to test the use of computer-aided design and simulation tools for product development. The chosen part, a pedestal for a car gearbox (Figure 5), is currently being produced by the Carl Dan. Peddinghaus GmbH & Co. KG (COP) in Ennepetal. It's purpose is to absorb the forces resulting from acceleration and braking. The customer speci- fications detailed both the geometry of the assembly (frame and gearbox) and an initial design of a gearbox pedestal made from welded sheet metal. The sheet metal version proved to be unsuitable for economic and structural reasons, and a decision was made to replace it with a forging.

Figure 5: Photo of forged gearbox pedestal.

As a result of the data transfer process, the CAD model, which was originally designed as a volume, only contained the surfaces of the part. The CAD model was first 'cleaned of unnecessary elements to give a better overall view, whereby all surfaces not needed for the design of the part were suppressed. After that, a new component was created into the assembly and the relevant functional surfaces and datums where copied into it. The first design for the part was generated with the help of the copied items by using the form feature library (Figure 6).

Figure 6: Rough design of the gearbox pedestal using form features.

Direct placement of the features into the part and thus into the assembly allowed collision control to be performed immediately. Each feature can be examined and modified if necessary. The defining parameters of the features are very useful since they make it easy to modify the geometry. However, it should be noted that the CAD system cannot modify all geometries without limitation. Some elements such as radii have to specified manually following the placement of the features. After completing the rough design (i.e. the function model), FEM analysis was camed out to simulate the mechanical stresses (Figure 7). The FEM method allows critical areas to be detected and resolved very early in the design process without needing costly forging tests.

Figure 7: Simulation of loads with FEM. The forged part was designed after finishing the rough design. First of all, the geometry of the function model was used to define the parting plane. The machining allowances, draft angles and radii were then modeled. Areas such as holes that could not be manufactured by forging have to be suppressed or filled with material. The suppressed elements can be retrieved later when designing the finished part model.

5 FORGING TOOL DESIGN WITH RUSCHKO AND

Two further software applications - RUSCHKO ('Com- puter Aided Design of Forging Tools') and PRINZ ('Rapid Simulation of Material Flow in the Forging Process') - were developed at IFUM in Hanover to support the design of forgings and forging tools. In the case of complex parts, FUNKO is generally used for the rough design only. The geometry then needs to be modified for the chosen manufacturing process. RUSCHKO helps to design the forging sequence and the forging tools. Parameters such as machining allowances and draft angles can be specified easily with this program. As with FUNKO, the required parameters are calculated from a standard database. The tools supported in RUSCHKO are the blocker, clipping tools and preforms manufactured by rolling. RUSCHKO is also integrated within the user-interface of ProlENGINEER. Preform design with RUSCHKO starts with a calculation of the mass distribution of the forging. Following a leading curve through the modeled part, the program places equidistant planes into the geometry to perform cuts in a radial direction. The areas of the cuts along the leading curve correspond to the distribution of the part's mass. The distance between the planes and the number of planes determine the accuracy of the calculation. After carrying out the calculation, the results can be displayed in a simple diagram or as a modeled surface above the part showing the calculated mass distribution

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(Figure 8). The modeled surface is then used to design the preform by smoothing the results and calculating the additional material required for the flash.

6 SUMMARY Modern computer-aided technologies such as CAD, CAM, FEM, etc. can be used to optimize the design and development process for forgings. Such optimization leads to lower production costs and manufacturing times and results in higher quality products. This article describes custom software tools which support the design of optimized forging sequences. Starting with a rough design of the part, the software tools described automate the design and the optimization of the forging and the preforms. The PRINZ Rapid Simulation System ensures a complete filling of the form without voids and an economic use of material. The design of products with reduced weight and costs are essential for companies in the forging sector to remain competitive in the future.

7 REFERENCES

Figure 8: Display of the calculated mass distribution.

The preform can then be checked with PRINZ (Figure 9). PRINZ, which was also developed at IFUM, is a rapid material flow simulation tool for bulk forming processes [lo] [ll]. The calculation model was optimized for short computing times and low cost for model generation. The high simulation speed allows interactive simulation of the forming process. Export functions which have been written by IFUM for ProIENGINEER and for the popular STL interface standard can then be used to generate the necessary simulation models [12].

Figure 9: User-interface of PRINZ.

Depending on the development objectives, the simulation with PRINZ can take place during the design and development work which is done with RUSCHKO. PRINZ allows conclusions to be made about optimized preforms by calculating the material flow during the whole forming process, the contact state in each calculation step, the displacement development and the aggregation of material. The displacement and aggregation can then be used to estimate the generalized strain equivalent of the forming process. After using both RUSCHKO and PRINZ, the user is then able to optimize the manufacturing sequence to meet customer requirements concerning the weight and the cost of the product.

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