Altair's Student Guides - Instructor's Manual - CAE for Simulation of Sheet Metal Forming

August 31, 2017 | Author: KFourMetrics | Category: Simulation, Finite Element Method, Sensitivity Analysis, Friction, Computer Aided Design
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Short Description

Designed for use by Engineering Students, this book provides 4 industry-derived projects for use with Altair's Hyper...

Description

Student Project Summaries

CAE for Simulation of Metal Forming Contents

Introduction.............................................................................................2 Installation Instructions: .......................................................................2 Simulation of Springback in Aluminum.......................................................3 Description of the Problem ....................................................................3 Data Organization .................................................................................4 Building the Tool...................................................................................4 Process Parameters...............................................................................5 The Nonlinear Solution ..........................................................................6 Results and Design Modifications ...........................................................6 Further Work ........................................................................................7 Summary .............................................................................................8 Blank Size Optimization for an A-Pillar .......................................................9 Description of the Problem ....................................................................9 Data Organization ............................................................................... 10 Building the Tool................................................................................. 10 Process Parameters............................................................................. 11 The Nonlinear Solution ........................................................................ 12 Results and Design Modifications ......................................................... 12 Further Work ...................................................................................... 13 Summary ........................................................................................... 13 Optimization of Blankholding Force for a Seat Riser.................................. 15 Description of the Problem .................................................................. 15 Data Organization ............................................................................... 16 Building the Tool................................................................................. 16 Process Parameters............................................................................. 17 The Nonlinear Solution ........................................................................ 18 Results and Design Modifications ......................................................... 18 Further Work ...................................................................................... 19 Summary ........................................................................................... 19 Multi-stage Forming of a Suspension Cover.............................................. 21 Description of the Problem .................................................................. 21 Data Organization ............................................................................... 22 Building the Tool................................................................................. 22 Process Parameters............................................................................. 23 The Nonlinear Solution ........................................................................ 24 Results and Design Modifications ......................................................... 24 Further Work ...................................................................................... 25 Summary ........................................................................................... 26

1

Student Project Summaries

CAE for Simulation of Metal Forming

Introduction This material is best used after reading the book Managing The CAE Process. Access to HyperWorks software is not essential for you, the instructor. Of course, if you choose to solve the problems yourself before working with your students, you will need HyperForm, Radioss, HyperView and HyperGraph. This book describes 4 assignment problems that highlight different applications of HyperWorks. Each problem is independent, and is complete in itself. Students may choose to do more than one, depending on their interest. To make best use of this material you will need a computer with a soundcard and speakers. Your computer should have a media-player program (such as Windows Media Player) and an Internet Browser that supports JavaScript. The material can be copied to a server and accessed by clients. You can customize the HTML files to suit your requirements. After opening the file, doubleclick on any text to edit it. Use the save changes link on the left of your Browser window when you are finished.

Installation Instructions: 1. Copy the folders to your computer or to your server. If you are working on a server, it is a good idea to set the folders to “read only” to prevent inadvertent modifications. 2. The videos are best played in full-screen at a resolution of 1024 x 768. You may need to install the CamStudio Codec to view video on your computer. To do this, right-click on the file camcodec.inf and choose Install from the popup menu. You may need administrator privileges to do this. 3. Ensure that JavaScript is enabled on your browser. 4. Each folder contains one HTML file. Double-click on it to open the instructions. 5. Data files are provided as relevant – IGES files, HM files, etc. 6. In case you need support, contact your distributor or email [email protected]

2

Student Project Summaries

CAE for Simulation of Metal Forming

Simulation of Springback in Aluminum Areas covered:

• • • •

Software used:

• • • •

Data import and geometry cleanup Layout and organization of components of the press-tool Specification of process parameters Controlling the incremental solver for explicit forming analysis and implicit springback analysis HyperForm Radioss HyperView HyperGraph

Description of the Problem Aerospace components often use aluminum for the weight advantage it provides over steel. Unfortunately, aluminum has two disadvantages from a forming perspective. First, its behavior is more sensitive to the strain-rate than ordinary steels. Second, it is more prone to springback recovery of elastic strains after forming. The component that has been supplied to a die designer is geometrically simple, but the press shop has no experience in working with Aluminum. The range of forces to be used, for both the blank holder and the ram, are to be verified. Further, the die designer has to confirm whether the component will pass dimensional checks after forming, or whether springback must be compensated for - either by forming the component a little too much or by using a subsequent operation. So the analyst must cover two distinct steps. The first is to check for the effect of springback. The task is complicated by the fact that the press shop has not supplied material data for Aluminum. Aerospace manufacturers tend to be very specific 3

Student Project Summaries

CAE for Simulation of Metal Forming

in the grade of alloys that are permitted, so the die designer wants to supply, along with the design, the effects of changes in the material properties of some common Aluminum alloys on the performance of the process. Next, the analyst must establish the process parameters - forces, lubricant, etc. – and, if springback is significant, suggest how the press shop can deal with the problem.

Data Organization The initial data is available as an IGES file. This includes both the die-surfaces and the blank. Simulation of forming does not call for every part of the press tool to be modeled! Only those components that directly contact the blank are needed. Further, analysis assumes that all components but the blank are rigid. For the single-action press that this problem uses, this means the analyst needs surface-data defining the die face, the blank, the binder and the punch. Specifying and locating each component can be tedious: it is here that the automated options in HyperForm shine. If the data is organized according to the recommended convention (orientation, names, etc.) this step can be extremely easy. Understanding the convention and organizing the data according to this is all that is required.

Building the Tool Theory tells us that the binder is an important part of the tool design: in practice, however, it is customary for the die designer to leave it to the machinist to "derive" the binder and punch from the die face by applying an offset. Since this is the case for this project, the first step is to check that the IGES geometry is 4

Student Project Summaries

CAE for Simulation of Metal Forming

correct – for instance, to check for gaps in the surfaces, which is a common occurrence given the finite precision of many CAD modelers. Gaps can either be repaired manually or automatically. Then the Tool Build macro is used to generate the FE models for the binder and punch. This component has a "flat" parting plane, so binder wrap is not an issue. Even though the geometry is simple, the IGES data has several gaps, so the various methods to "repair" the data - some automatic and some manual – are reviewed. Note that the FE model of the tool is made up entirely of shell elements. The punch, binder and die are rigid (that is, we neglect any deformation in them) so the "Finite Element" characteristics of shell elements apply only to the blank.

Process Parameters The automatic-process definition options make it very easy to define all the process parameters, but it is important to take care to make sure all the correct options have been specified! For instance, the setup requires a single-action press. This section covers how to • • • • • •

specify the kind of press apply draw beads specify the material for the blank using library data define the die movement by specifying the velocity vs. distance curve apply a blank holder gap, so that the blank holding force can be calculated review data such as the friction coefficient and level of adaptive-meshing

It's important to remember that the shell elements represent the mid-plane of the blank. 5

Student Project Summaries

CAE for Simulation of Metal Forming

Since the blank thickness is given, the die-traveldistances should be modified accordingly. Also, it is customary to use velocities that are much higher than those actually used in the press. This higher velocity reduces the computational time significantly, without hurting the fidelity of results significantly. However, forming simulation for Aluminum needs more care since Aluminum has a higher strainrate sensitivity. Further, one of the vexing problems in most dieanalysis is to characterize the coefficient of friction: what is the impact of a lubricant on the flow of material? The initial analysis deals with this by using a representative value (0.125) in the model. The Further Work section addresses ways to carry this approach to its logical conclusion.

The Nonlinear Solution The most time consuming step of any forming simulation is the solution time: the solver must step forward in time, checking whether the time step must be changed, whether the elements must be refined, and so on. From a user-interaction perspective, of course, there's little of interest in this step. The steps to note are that the data is organized in folders, and that the solver creates several different files - the data "deck", the animation files, the result files and the time history.

Results and Design Modifications One of the problems with non-linear analysis is that verification of results is not always easy - it's often hard to decide whether the simulation's predictions are accurate, since even non-intuitive results may be correct.

6

Student Project Summaries

CAE for Simulation of Metal Forming

If your students have a good grasp on the mathematics of the finite element method, they should use the on-line documentation to check for output measures that help judge the quality of the solution. Your students should appreciate that in a production scenario, simulation is intended to reduce tryouts, not eliminate them entirely. The usual practice is to verify that the simulation has adequately captured the behavior of one tryout then to perform what-if simulations using this model as a reliable estimator. HyperView and HyperGraph are used to • • • •

load the results and animate the deformation of the blank plot thickness contours to check for the tendency to wrinkle or tear generate a Forming Limit Diagram (using the "theoretical" Forming Limit Curve in the absence of experimental results) plot the contact forces to estimate the required tonnage

This section also covers how to • •

perform the "implicit" springback calculations for Aluminum verify the changes in the component shape after it has been permitted to relax

Further Work There are several aspects that can make the project more complete. You may choose to assign these to your students based on their level of proficiency, the time available, etc. Some of the areas for further work include • • • •

coming up with an alternate die design or forming process to compensate for springback optimizing the blank holding force running the simulations with an increased level of adaptivity to ensure that the numerical computations are accurate enough interfacing with HyperStudy to use mathematical methods to optimize the die for the first stage and process parameters (for a robust process design)

You could also suggest to your students that they investigate the effects of friction. If the die manufacturer can verify the model against an analysis, the model can be fine-tuned to mimic real-life behavior, then used for what-if analyses. Since your students are unlikely to have access to a press, they 7

Student Project Summaries

CAE for Simulation of Metal Forming

can generate curves showing the variation of process-behavior with the coefficient of friction.

Summary By the end of this assignment, the student will know how to • • • • • • • • • • • • • • • • • • • • •

8

import IGES files perform manual and automatic geometry cleanup create filler surfaces equivalence edges search for duplicate faces use different parameter files for automatic cleanup rename components in accordance with the auto-process requirements derive the binder and punch surfaces from the die face create draw beads choose material models and data from a library specify die velocity and range of movement apply blankholder forces specify the memory used by the solver edit the time-of-simulation specify the coefficient of friction read the simulation “list” files for information on the simulation view the animated, large-deformation, plastic deformation of the blank generate thickness contours predict tearing and wrinkling generate a Forming Limit Curve and the Forming Limit Diagram calculate blankholder forces and press tonnage

Student Project Summaries

CAE for Simulation of Metal Forming

Blank Size Optimization for an A-Pillar Areas covered:

Software used:

• • • •

Data import and geometry cleanup Layout and organization of components of the press-tool Specification of process parameters Use of HyperNest for blank-yield calculations

• • • •

HyperForm Radioss HyperView HyperGraph

Description of the Problem A press-shop is quoting for the manufacture of a part of an "A Pillar" of a car. The component has a nominal thickness of 1 mm and is made of CRDQ (Cold Rolled Die Quality steel). The product data has been supplied, based on which the press-shop has arrived at a preliminary die design. The die designer has created the dieface, using the CAD model of the component as the base. There are three problems the press shop wants to address. The first problem is to estimate several process parameters. Principally, the analysis must indicate whether or not draw beads will be required, and whether a lubricant must be used or not. The component specifications call for the thickness to be within 12% of the nominal thickness. Next, the size of press that will be needed must be estimated. That is, the press tonnage must be calculated. Finally, since the press shop will have to manufacture the components if it wins the order, it would be to its advantage if it can optimize the blank shape. Even though the component is a little large, the press-shop wants to check if a 9

Student Project Summaries

CAE for Simulation of Metal Forming

"trimless" blank can be specified. This allows the press shop to save on the post-forming trimming operation. If not, can wastage be reduced? A preliminary blank has been given, but this is only indicative: the press shop wants to know the best blank shape.

Data Organization The initial data is available as an IGES file. This includes both the die-surfaces and the blank. Simulation of forming does not call for every part of the press tool to be modeled! Only those components that directly contact the blank are needed. Further, analysis assumes that all components but the blank are rigid. For the singleaction press that this problem uses, this means the analyst needs surface-data defining the die face, the blank, the binder and the punch. Specifying and locating each component can be tedious: it is here that the automated options in HyperForm shine. If the data is organized according to the recommended convention (orientation, names, etc.) this step can be extremely easy. Understanding the convention and organizing the data according to this is all that is required.

Building the Tool Theory tells us that the binder is an important part of the tool design: in practice, however, it is customary for the die designer to leave it to the machinist to "derive" the binder and punch from the die face by applying an offset. Since this is the case for this project, the first step is to check that the IGES geometry is correct – for instance, to check for gaps in the surfaces, which is a common occurrence given the finite precision of many CAD modelers.

10

Student Project Summaries

CAE for Simulation of Metal Forming

Gaps can either be repaired manually or automatically. Then the Tool Build macro is used to generate the FE models for the binder and punch. This component has a "flat" parting plane, so binder wrap is not an issue. Even though the geometry is simple, the IGES data has several gaps, so the various methods to "repair" the data some automatic and some manual – are reviewed. Note that the FE model of the tool is made up entirely of shell elements. The punch, binder and die are rigid (that is, we neglect any deformation in them) so the "Finite Element" characteristics of shell elements apply only to the blank.

Process Parameters The automatic-process definition options make it very easy to define all the process parameters, but it is important to take care to make sure all the correct options have been specified! For instance, the setup requires a single-action press. This section covers how to • • • • • •

specify the kind of press apply draw beads specify the material for the blank using library data define the die movement by specifying the velocity vs. distance curve apply a blank holder gap, so that the blank holding force can be calculated review data such as the friction coefficient and level of adaptive-meshing

It's important to remember that the shell elements represent the mid-plane of the blank. Since the blank thickness is given, the die-travel-distances should be modified accordingly. Also, it is customary to use velocities that are much higher than those actually used in the press. 11

Student Project Summaries

CAE for Simulation of Metal Forming

This higher velocity reduces the computational time significantly, without hurting the fidelity of results significantly. Further, one of the vexing problems in most dieanalysis is to characterize the coefficient of friction: what is the impact of a lubricant on the flow of material? The initial analysis deals with this by using a representative value (0.125) in the model. The Further Work section addresses ways to carry this approach to its logical conclusion.

The Nonlinear Solution The most time consuming step of any forming simulation is the solution time: the solver must step forward in time, checking whether the time step must be changed, whether the elements must be refined, and so on. From a user-interaction perspective, of course, there's little of interest in this step. The steps to note are that the data is organized in folders, and that the solver creates several different files - the data "deck", the animation files, the result files and the time history.

Results and Design Modifications One of the problems with non-linear analysis is that verification of results is not always easy - it's often hard to decide whether the simulation's predictions are accurate, since even non-intuitive results may be correct. If your students have a good grasp on the mathematics of the finite element method, they should use the on-line documentation to check for output measures that help judge the quality of the solution. Your students should appreciate that in a production scenario, simulation is intended to reduce tryouts, not eliminate them entirely. The usual practice is to verify that the simulation has 12

Student Project Summaries

CAE for Simulation of Metal Forming

adequately captured the behavior of one tryout then to perform what-if simulations using this model as a reliable estimator. HyperView and HyperGraph are used to • • • •

load the results and animate the deformation of the blank plot thickness contours to check for the tendency to wrinkle or tear generate a Forming Limit Diagram (using the "theoretical" Forming Limit Curve in the absence of experimental results) plot the contact forces to estimate the required tonnage

This section also covers see how to • • •

use the One-Step solver to estimate the blank size export this "custom" blank shape for subsequent analysis use HyperNest to compare the yield for this shape over the initial blank shape, under various nesting-configurations

Further Work There are several aspects that can make the project more complete. You may choose to assign these to your students based on their level of proficiency, the time available, etc. Some of the areas for further work include • • •

optimizing the blank holding force running the simulations with an increased level of adaptivity to ensure that the numerical computations are accurate enough interfacing with HyperStudy to use mathematical methods to optimize the die for the first stage and process parameters (for a robust process design)

You could also suggest to your students that they investigate the effects of friction. If the die manufacturer can verify the model against an analysis, the model can be fine-tuned to mimic real-life behavior, then used for what-if analyses. Since your students are unlikely to have access to a press, they can generate curves showing the variation of process-behavior with the coefficient of friction.

Summary By the end of this assignment, the student will know how to •

import IGES files 13

Student Project Summaries • • • • • • • • • • • • • • • • • • • •

14

CAE for Simulation of Metal Forming

perform manual and automatic geometry cleanup create filler surfaces equivalence edges search for duplicate faces use different parameter files for automatic cleanup rename components in accordance with the auto-process requirements derive the binder and punch surfaces from the die face create draw beads choose material models and data from a library specify die velocity and range of movement apply blankholder forces specify the memory used by the solver edit the time-of-simulation specify the coefficient of friction read the simulation “list” files for information on the simulation view the animated, large-deformation, plastic deformation of the blank generate thickness contours predict tearing and wrinkling generate a Forming Limit Curve and the Forming Limit Diagram calculate blankholder forces and press tonnage

Student Project Summaries

CAE for Simulation of Metal Forming

Optimization of Blankholding Force for a Seat Riser Areas covered:

• • • •

Software used:

• • • •

Data import and geometry cleanup Layout and organization of components of the press-tool Specification of process parameters Impact of drawbeads and blankholding force on wrinkles HyperForm Radioss HyperView HyperGraph

Description of the Problem A die manufacturer has been asked to design and manufacture the die for a car seat riser - a sheet metal component that has a nominal thickness = 0.7mm and is made of CRDQ. Since the geometry is complex, the CAD data has been supplied to the die designer, who has to design, manufacture, verify and supply the die to the component manufacturer. The die designer has created the die-face, using the CAD model of the component as the base. The problem now is to freeze several process parameters. The first information that the component manufacturer needs is the size of press that will be needed. That is, the press tonnage must be confirmed. The die designer also wants to know if any draw beads will be required, so that the manufacturing process can be planned while the design activity proceeds. The component specifications call for the thickness to be within 10% of the nominal thickness. 15

Student Project Summaries

CAE for Simulation of Metal Forming

Data Organization The initial data is available as an IGES file. This includes both the die-surfaces and the blank. Simulation of forming does not call for every part of the press tool to be modeled! Only those components that directly contact the blank are needed. Further, analysis assumes that all components but the blank are rigid. For the single-action press that this problem uses, this means the analyst needs surface-data defining the die face, the blank, the binder and the punch. Specifying and locating each component can be tedious: it is here that the automated options in HyperForm shine. If the data is organized according to the recommended convention (orientation, names, etc.) this step can be extremely easy. Understanding the convention and organizing the data according to this is all that is required.

Building the Tool Theory tells us that the binder is an important part of the tool design: in practice, however, it is customary for the die designer to leave it to the machinist to "derive" the binder and punch from the die face by applying an offset. Since this is the case for this project, the first step is to check that the IGES geometry is correct – for instance, to check for gaps in the surfaces, which is a common occurrence given the finite precision of many CAD modelers. Gaps can either be repaired manually or automatically. Then the Tool Build macro is used to generate the FE models for the binder and punch. This component has a "curved" parting plane, so the binder itself is curved. This means the analyst has to move the punch to avoid binder-wrap. That 16

Student Project Summaries

CAE for Simulation of Metal Forming

is, the position of the punch must be adjusted so that the blank is held firmly between the die and the binder before it touches the punch. This is essential, to preserve the principal purpose of the binder - to grip the blank. Remember that the FE model of the tool is made up entirely of shell elements. The punch, binder and die are rigid (that is, we neglect any deformation in them) so the "Finite Element" characteristics of shell elements apply only to the blank.

Process Parameters The automatic-process definition options make it very easy to define all the process parameters, but it is important to take care to make sure all the correct options have been specified! For instance, the setup requires a single-action press. This section covers how to • • • • • •

specify the kind of press apply draw beads specify the material for the blank using library data define the die movement by specifying the velocity vs. distance curve apply a blank holder gap, so that the blank holding force can be calculated review data such as the friction coefficient and level of adaptivemeshing

It's important to remember that the shell elements represent the mid-plane of the blank. Since the blank thickness is given, the dietravel-distances should be modified accordingly. Also, it is customary to use velocities that are much higher than those actually used in the 17

Student Project Summaries

CAE for Simulation of Metal Forming

press. This higher velocity reduces the computational time significantly, without hurting the fidelity of results significantly. Further, one of the vexing problems in most dieanalysis is to characterize the coefficient of friction: what is the impact of a lubricant on the flow of material? The initial analysis deals with this by using a representative value (0.125) in the model. The Further Work section addresses ways to carry this approach to its logical conclusion.

The Nonlinear Solution The most time consuming step of any forming simulation is the solution time: the solver must step forward in time, checking whether the time step must be changed, whether the elements must be refined, and so on. From a user-interaction perspective, of course, there's little of interest in this step. The steps to note are that the data is organized in folders, and that the solver creates several different files - the data "deck", the animation files, the result files and the time history.

Results and Design Modifications One of the problems with non-linear analysis is that verification of results is not always easy - it's often hard to decide whether the simulation's predictions are accurate, since even non-intuitive results may be correct. If your students have a good grasp on the mathematics of the finite element method, they should use the on-line documentation to check for output measures that help judge the quality of the solution. Your students should appreciate that in a production scenario, simulation is intended to reduce tryouts, not eliminate them entirely. The usual practice is to verify that the simulation has 18

Student Project Summaries

CAE for Simulation of Metal Forming

adequately captured the behavior of one tryout then to perform what-if simulations using this model as a reliable estimator. HyperView and HyperGraph are used to • • • •

load the results and animate the deformation of the blank plot thickness contours to check for the tendency to wrinkle or tear generate a Forming Limit Diagram (using the "theoretical" Forming Limit Curve in the absence of experimental results) plot the contact forces to estimate the required tonnage

Further Work There are several aspects that can make the project more complete. You may choose to assign these to your students based on their level of proficiency, the time available, etc. Some of the areas for further work include • • •

optimizing the blank holding force using HyperStudy running the simulations with an increased level of adaptivity to ensure that the numerical computations are accurate enough interfacing with HyperStudy to use mathematical methods to optimize the die for the first stage and process parameters (for a robust process design)

You could also suggest to your students that they investigate the effects of friction. If the die manufacturer can verify the model against an analysis, the model can be fine-tuned to mimic real-life behavior, then used for what-if analyses. Since your students are unlikely to have access to a press, they can generate curves showing the variation of process-behavior with the coefficient of friction.

Summary By the end of this assignment, the student will know how to • • • • • • •

import IGES files perform manual and automatic geometry cleanup create filler surfaces equivalence edges search for duplicate faces use different parameter files for automatic cleanup rename components in accordance with the auto-process requirements 19

Student Project Summaries • • • • • • • • • • • • • •

20

CAE for Simulation of Metal Forming

derive the binder and punch surfaces from the die face create draw beads choose material models and data from a library specify die velocity and range of movement apply blankholder forces specify the memory used by the solver edit the time-of-simulation specify the coefficient of friction read the simulation “list” files for information on the simulation view the animated, large-deformation, plastic deformation of the blank generate thickness contours predict tearing and wrinkling generate a Forming Limit Curve and the Forming Limit Diagram calculate blankholder forces and press tonnage

Student Project Summaries

CAE for Simulation of Metal Forming

Multi-stage Forming of a Suspension Cover Areas covered:

Software used:

• • • •

Data import and geometry cleanup Layout and organization of components of the press-tool Specification of process parameters Die design for multi-stage forming

• • • •

HyperForm Radioss HyperView HyperGraph

Description of the Problem The die design for a cover used in the suspension of a truck has been supplied. The component is 2 mm thick, and the designers want to form the component in a single stage. This is a little ambitious, since the previous tool for a similar component used two stages. Given the advantages that a reduction-in-stages has, the die designers want to know whether the current design will work. The component is made of CRDQ (Cold Rolled Die Quality steel), and is permitted a 15% variation in thickness over the nominal thickness (2 mm). The product data has been supplied, based on which the press-shop has arrived at a preliminary die design. The die designer has created the dieface, using the CAD model of the component as the base. There are two problems the designers want to address. The first is to estimate several process parameters. Principally, the analysis must indicate whether or not draw beads will be required, and whether a lubricant must be used or not.

21

Student Project Summaries

CAE for Simulation of Metal Forming

Then, depending on whether two stages are needed or one is adequate, the size of press that will be needed must be estimated. That is, the press tonnage must be calculated.

Data Organization The initial data is available as an IGES file. This includes both the die-surfaces and the blank. Simulation of forming does not call for every part of the press tool to be modeled! Only those components that directly contact the blank are needed. Further, analysis assumes that all components but the blank are rigid. For the single-action press that this problem uses, this means the analyst needs surface-data defining the die face, the blank, the binder and the punch. Specifying and locating each component can be tedious: it is here that the automated options in HyperForm shine. If the data is organized according to the recommended convention (orientation, names, etc.) this step can be extremely easy. Understanding the convention and organizing the data according to this is all that is required.

Building the Tool Theory tells us that the binder is an important part of the tool design: in practice, however, it is customary for the die designer to leave it to the machinist to "derive" the binder and punch from the die face by applying an offset. Since this is the case for this project, the first step is to check that the IGES geometry is correct – for instance, to check for gaps in the surfaces, which is a common occurrence given the finite precision of many CAD modelers. Gaps can either be repaired manually or automatically. Then the Tool Build macro is used to generate the FE models for the binder and punch.

22

Student Project Summaries

CAE for Simulation of Metal Forming

This component has a "curved" parting plane, so the binder itself is curved. This means the analyst has to move the punch to avoid binder-wrap. That is, the position of the punch must be adjusted so that the blank is held firmly between the die and the binder before it touches the punch. This is essential, to preserve the principal purpose of the binder - to grip the blank. Remember that the FE model of the tool is made up entirely of shell elements. The punch, binder and die are rigid (that is, we neglect any deformation in them) so the "Finite Element" characteristics of shell elements apply only to the blank.

Process Parameters The automatic-process definition options make it very easy to define all the process parameters, but it is important to take care to make sure all the correct options have been specified! For instance, the setup requires a single-action press. This section covers how to • • • • • •

specify the kind of press apply draw beads specify the material for the blank using library data define the die movement by specifying the velocity vs. distance curve apply a blank holder gap, so that the blank holding force can be calculated review data such as the friction coefficient and level of adaptive-meshing

It's important to remember that the shell elements represent the mid-plane of the blank. Since the blank thickness is given, the die-travel-distances should be modified accordingly.

23

Student Project Summaries

CAE for Simulation of Metal Forming

Also, it is customary to use velocities that are much higher than those actually used in the press. This higher velocity reduces the computational time significantly, without hurting the fidelity of results significantly. Further, one of the vexing problems in most die-analysis is to characterize the coefficient of friction: what is the impact of a lubricant on the flow of material? The initial analysis deals with this by using a representative value (0.125) in the model. The Further Work section addresses ways to carry this approach to its logical conclusion.

The Nonlinear Solution The most time consuming step of any forming simulation is the solution time: the solver must step forward in time, checking whether the time step must be changed, whether the elements must be refined, and so on. From a user-interaction perspective, of course, there's little of interest in this step. The steps to note are that the data is organized in folders, and that the solver creates several different files - the data "deck", the animation files, the result files and the time history.

Results and Design Modifications One of the problems with non-linear analysis is that verification of results is not always easy - it's often hard to decide whether the simulation's predictions are accurate, since even non-intuitive results may be correct. If your students have a good grasp on the mathematics of the finite element method, they should use the on-line documentation to check for output measures that help judge the quality of the solution.

24

Student Project Summaries

CAE for Simulation of Metal Forming

Your students should appreciate that in a production scenario, simulation is intended to reduce tryouts, not eliminate them entirely. The usual practice is to verify that the simulation has adequately captured the behavior of one tryout then to perform what-if simulations using this model as a reliable estimator. HyperView and HyperGraph are used to • • • •

load the results and animate the deformation of the blank plot thickness contours to check for the tendency to wrinkle or tear generate a Forming Limit Diagram (using the "theoretical" Forming Limit Curve in the absence of experimental results) plot the contact forces to estimate the required tonnage

This section also covers see how to • • •

use the results of the first analysis to estimate the die for the first stage of forming redo the analysis with this "new" design, after making sure the the "state" file is saved by the previous stage use the blank from the first stage as the starting point of the second stage, by reading the state file

Further Work There are several aspects that can make the project more complete. You may choose to assign these to your students based on their level of proficiency, the time available, etc. Some of the areas for further work include • • •

optimizing the blank holding force running the simulations with an increased level of adaptivity to ensure that the numerical computations are accurate enough interfacing with HyperStudy to use mathematical methods to optimize the die for the first stage and process parameters (for a robust process design)

You could also suggest to your students that they investigate the effects of friction. If the die manufacturer can verify the model against an analysis, the model can be fine-tuned to mimic real-life behavior, then used for what-if analyses. Since your students are unlikely to have access to a press, they can generate curves showing the variation of process-behavior with the coefficient of friction.

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Student Project Summaries

CAE for Simulation of Metal Forming

Summary By the end of this assignment, the student will know how to • • • • • • • • • • • • • • • • • • • • •

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import IGES files perform manual and automatic geometry cleanup create filler surfaces equivalence edges search for duplicate faces use different parameter files for automatic cleanup rename components in accordance with the auto-process requirements derive the binder and punch surfaces from the die face create draw beads choose material models and data from a library specify die velocity and range of movement apply blankholder forces specify the memory used by the solver edit the time-of-simulation specify the coefficient of friction read the simulation “list” files for information on the simulation view the animated, large-deformation, plastic deformation of the blank generate thickness contours predict tearing and wrinkling generate a Forming Limit Curve and the Forming Limit Diagram calculate blankholder forces and press tonnage

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