For more than two decades, the usage of LS-DYNA® in the simulation of sheet metal stamping has been steadily increasing with a reputation for prediction accuracy. During this period, state-of-the art constitutive models were added for simulating high strength steel and aluminum alloys now commonly used in the automotive industry. In addition, the much improved robustness, speed, and accuracy of the implicit solver has resulted in gravity loading, binder wrap, and springback calculations becoming routine. Die face compensation calculations in LS-DYNA® save money and time by eliminating the trial and error in die manufacturing. Many original and unique ideas are implemented for insuring reliable stamping simulations, which make LS-DYNA® an excellent choice for this manufacturing process.

Typical Applications:

• Sheet metal gravity loading, binder closing, deep-drawing

• Springback prediction, and springback compensation

• Trimming and lancing

• Flanging and hemming

• Hydro-forming

• Magnetic forming and thermal forming

• Superplastic forming

• Denting

• Scrap fall simulation

• One-Step simulation for woven carbon fiber composite

     (a) Incremental solution      (b) One-step result

            One step result vs. incremental result

Features:

• Mesh adaptivity

• Advanced material models for aluminum alloy and high strength steels

• Smooth contact to minimize contact noise

• One-step method in blanksize development

• Un-flanging method in trimming curve development

• Parametric input

• Mesh coarsening

• Formability Index gave more reliable forming limit prediction for non-linear strain path

• Predict fiber orientations in the final part

• Predict initial blank size corresponding certain fiber orientation

   (a) Before un-flanging    (b) After un-flanging

Accurate un-flanging simulation for trimming curve development

      (a) Before closing            (b) After closing

          Implicit binder closing for floor-pan

One-Step prediction of fiber orientation matches test data

(Courtesy of Dr. Danielle Zeng of Ford )

Gravity Loading

Due to gravity effect, the initial flat sheet fall on the die surface. This process is called gravity loading. In this process, blank has large displacement, but little or no plastic deformation. Accurate prediction of this process can have important effect on the following analysis, such as formability analysis, springback prediction, and surface quality. LS-DYNA® ‘s implicit approach can give a fast and accurate prediction of this process.  The most important control keyword is *CONTROL_IMPLICIT_FORMING.  Sometimes, it is necessary to prebend the blank, so as to achieve certain shape after gravity loading. *CONTROL_FORMING_PRE_BENDING provide necessary capabilities to pre-bend the blank.

Deep-Drawing

The main purpose of deep drawing simulation is to predict sheet metal formability and provide forming information for the following analysis, such as springback prediction.  To improve computation efficiency, large initial blank size is used, and the elements will be refined (mesh adaptivity) based on the curvature in the corresponding die surface. To have efficient prediction of this process, the parameter selection is very important. For feasibility analysis,  the requirement for prediction accuracy is not very high, and there is a set of parameters that can give an very efficient prediction. For springback analysis, we have to use another set of parameters so as to achieve high accuracy. In LS-PREPOST, there is suggested values for the parameter selection for each analysis.

Trimming

After the finish of forming analysis, the scrap needs to be trimmed. To satisfy different trimming operation, LS-DYNA® provides two choices:  the first one is that the trimming happens along one defined orientation, such as in z-direction. The second option is to trim the blank based on the nearest element normal. After trimming, the elements along the boundary might not be in good quality and affect the following simulation, then user can use *CONTROL_CHECK_SHELL to fix these elements.

Springback Prediction

After the forming, the upper tools are removed, the internal force inside the blank is no longer balanced , which will cause deformation for the blank, this is springback process. The initial implementation of implicit algorithm in  LS-DYNA® is mainly for springback prediction.  Accurate springback prediction is significantly affected by the forming analysis, in which the control parameter selection and material model are critical. From many benchmark analysis,  we have found a set of reliable parameter and make sure that user can obtain accurate springback prediction. In addition, LS-DYNA® provides around three hundred different material models so as to meet the requirement of different users. From benchmark studies and user feedback, LS-DYNA® has been superior to the other software in this application.

Springback Compensation

Accurate springback prediction is very important to take use of the springback prediction and automatically compensate the rigid tools can be more meaningful. It will significantly reduce the time and cost for die manufacturing. Springback Compensation is a non-linear process, usually, several compensations are needed to reduce the deviation within the tolerance. Accordingly, an iterative method in LS-DYNA® for springback compensation, for most of the part, two to three iterations are needed to reach target. After compensation, LS-DYNA® automatically modifies the mesh for the punch, die and binder. Due to its efficiency and reliability, this algorithm has long been used in die manufacturing.

One Step Method

Before die design, one step method can be used to give a rough guess of sheet

metal formability. In the same time, it can also be used to obtain guess for initial blank size. Due to its simplicity and efficiency, one step method becomes very popular in die design.  In LS-DYNA®, there are many options in one step method, and user has choice to define drawbead bead, binder force, etc.

Trimming Curve Development

In the manufacturing of trimming tools, the trimming curves design is very challenging. Curved boundary has to be un-wrapped to the smooth die surface. To meet this need, LS-DYNA® provide a function, called un-flanging. If the obtained trimming curves are not satisfactory, user can use iterative method to correct those curves by using *INTERFACE_BLANKSIZE_DEVELOPMENT.