Keywords: trimming, splitting, 3D solid finite element meshes, virtual manufacturing, multi-step processes.

Automotive manufacturers suffer today, perhaps more then ever, increased pressures in a global and tremendously competitive industry. Especially in the triad markets - Europe, USA and Japan - constructors face the reality of saturated markets, with extremely demanded consumers. To overcome these difficulties, the key strategy has been the diversification of product range, followed by a reduction in both lead-time and investment costs in new car design, which allows a more flexible and fast reply to the market demands.

Since sheet metal forming has a relevant impact in the total design costs of a new car, this area assisted in the last decade to an enormous effort in order to diminishing, as far as possible, the old fashion and costly trial-error method for tool production. In replacement, the numerical simulation of the deep-drawing process, based on the finite element method, have been intensively developed. Apart some problems that remain to be solve, the entirely modelling and design of a car panel isn't far most of being totally developed recurring to virtually manufacturing, from the initial blank sheet to the final part ready to assembly, passing through several stages at tool machineries.

As for other steps, like deep-drawn or springback, trimming constitutes one or mores passes in usual fabrication of a panel. In this work this last aspect is addressed with the development of a program, DD3TRIM, that allows trimming 3D solid finite element meshes. This code arises in a development sequence, towards a complete multi-stage simulation of the deep-drawing process, of the home code family DD3. This group of codes has started with the 3D deep-drawing implicit finite element code, DD3IMP. The family increase latter with the implicit one-step springback module, DD3OSS. More recently DD3 family received two new members: the material parameters identification module DD3MAT and a toolbox for learning and teaching sheet metal forming technologies. DD3LT.

The implemented strategy of DD3TRIM consists firstly, to evaluate the elements that are to be eliminate/keep with the trimming and then adjust the remaining affected elements of the boundary to the desired trim geometry. This adjustment is done by node stretching technique for two different projection schemes with optimization of the final element shape at the boundary. Additionally, a splitting option is also introduced which allows, for instance, to open rings or other closed meshes. The implemented solutions were tested in the simulation of a multi-step deep-drawing benchmark test that consists on cutting a ring specimen from a drawn cup and then splitting it longitudinally along a radial plan. The process consists in a sequence of drawn, spring-back, trimming, splitting and final springback. All this steps were simulated with the DD3 family codes (DD3IMP, DD3OSS and DD3TRIM). In this example application problem, both algorithms (trimming and splitting) have show good reliability to treat the meshes during the multi-stage processes.

The influence of the different correction algorithms implemented in the overall results of the simulation of a multi-stage processes, is under evaluation and will be published elsewhere. Also, further work is under development to complement and develop the DD3TRIM code, namely: the implementation of a general trimming surface based in NURBS surfaces description.

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