The difference between a crash and draw form

To many die and toolmakers this may seem a simple question, however, for those new in the industry or without much experience, it is worth explaining in more detail. A crash form means that a male punch and a female die are closed together without any springs, cushions or otherwise to hold the blank as the forming process takes place. The punch and die simply "crash" together. The method is successful on simple, shallow parts with basic shapes. Basically, the flow of material cannot be controlled in this method, and that is why wrinkling results in deep parts.

Parts can be "crashed" from a square blank and then trimmed OR a blank can be trimmed first and then crashed. The latter is the cheapest tooling method.

A draw form is usually designed to control the stretch of the material to prevent wrinkles and stretch the material evenly. This is done by a blank holder OR binder. The binder is often a flat surface that is mounted on high-force gas springs. Usually, it surrounds the punch. This means as the die closes, the blank is held around the edges very tightly first, then stretched over the punch. The flow of material can be controlled by the binder shape, the holding force and the placement of draw beads (to further stop material flowing, as might be required to stop wrinkles). This almost always means that the blank is square and larger than that required in a crash form. Furthermore, the drawn panel almost always needs to be trimmed after drawing and possibly formed again into the final shape.

Because of the cost implications, whenever possible, toolmakers and sheet metal stampers like to use a crash form. However, it is often difficult to know if a crash form process will produce a panel free from wrinkles and splits.

With forming simulation, a crash form simulation result will quickly tell you whether or not a crash form process is feasible for your part. This is the most common request for forming simulation I receive.

We will leave you with the words of one of our customers who asked us to simulate a crash form on his part and discovered that a draw process was instead required: "I am convinced you saved my customer thousands of dollars. Thanks again."

About StampingSimulation.com

StampingSimulation.com is a world wide team of specialist forming simulation and sheet metal forming engineers. With resources across three continents (North America, Europe and Australasia) we are uniquely placed to offer fast turn around times on all structural simulation, hydro forming simulations, ANSYS simulations and sheet metal forming simulations.

About AutoForm

AutoForm offers software solutions for the die-making and sheet metal forming industries, and is recognized by the Top 20 automobile producers and their customers, as the number one provider of software for product formability, die face design and virtual tryouts to the global automotive industry. The use of AutoForm software improves reliability in planning, reduces the number of die tryouts and tryout time, and results in higher quality part and tool designs that can be produced with maximum confidence. In addition, press downtime and reject rates in production are substantially reduced.

The Basic Steps of Die Design

When using a tool like AutoForm to design die faces, with the intent of simulating the design for verification, there is a basic path or set of steps that are used to end up with a die face design.

We will now briefly out line such steps. As we have mentioned in many of our blogs, a complete CAD model is needed that as radii. The first and foremost step is always a blank shape estimate, but this is not really part of a die face design, rather it is an indication of material usage for budgeting purposes and later use in simulation. So actually, the first step in a die face design is to inspect the geometry of the part and perform an undercut check.

If it is possible to form all of the part’s shape in a single form stage (be it crash form or a draw) then an attempt is always made to do so. This is done by tipping the part’s geometry into the most favorable pressing angle, then extending and adding additional geometry (where needed) to ensure that the blank will be “captured” by the tooling surfaces and formed correctly

From this point, the die face design starts to differ from the final part’s geometry. Pre-draw geometry must be created that carefully considers the problems encountered in the single stage forming simulation. For example, a deep drawn cup shape may need an over drawn bowl shape to start with. This is where the software does not magically come up with a die face design and the skill and experience of the die face designer is required to produce suitable geometry.

Of course, the huge advantage is that many different variations can be tried and tested in the virtual environment to get the pre-draw shape just right, before a tool is manufactured. Furthermore, if either of the form stages require draw beads to help control material flow (to prevent problems like wrinkling) then draw beads can be simulated too.

Again, the software is not magical and placement, length, shape and size of draw beads needs to be considered by the die face designer. The determination of such parameters for draw beads is again based on the results seen in the single stage form OR the results seen in a draw stage WITHOUT draw beads. The great thing about using forming simulation is that experiments with different types, lengths and placements of draw beads can be performed for little expense and the best result can be chosen for use in an actual tool build.

Once all die faces of each forming stage (including draw beads, if required) have been designed and tried in the virtual environment, the final virtual part can be subjected to a springback check. If the amount of springback is un-acceptable in the final part, then a further die face design revision can be made in any of the form stages, to countermeasure the predicted springback.

Finally, once satisfaction with all the simulation results is achieved, all die faces that were used in the simulation are converted to CAD and exported for use in an actual tool build.

About StampingSimulation.com

StampingSimulation.com is a world wide team of specialist forming simulation and sheet metal forming engineers. With resources across three continents (North America, Europe and Australasia) we are uniquely placed to offer fast turn around times on all structural simulation, hydro forming simulation, ANSYS simulations and sheet metal forming simulations.

About AutoForm
AutoForm offers software solutions for the die-making and sheet metal forming industries, and is recognized by the Top 20 automobile producers and their customers, as the number one provider of software for product formability, die face design and virtual tryouts to the global automotive industry.

The use of AutoForm software improves reliability in planning, reduces the number of die tryouts and tryout time, and results in higher quality part and tool designs that can be produced with maximum confidence. In addition, press downtime and reject rates in production are substantially reduced.

How to reduce the risk of splits in a sheet metal part

The best way to answer this question is via the Forming Limit Diagram (FLD). The colors and predictions of splits/compression, etc., are all based on the the FLD.

It was established a few decades ago that metal forming limits can be predicted by using the FLD and there are TWO key parameters that set the position of the limit curve. One of these is MATERIAL THICKNESS.

As material thickness INCREASES, the limit curves moves UP the Y axis and therefore, the limits of the material are greater. That is, a thicker material will accept (tolerate) more strain before failure occurs. This has been proven many times in simulation and the real world.

To remove any risk of splits, one possibility is to increase the material thickness. HOWEVER, this is usually undesirable because this also increases material costs which can often be as much as 70% of a part's cost! Another point to be aware of, is that the YELLOW (risk of splits) is a safety margin before splits are definitely predicted.

It is possible to REMOVE this criterion in which case, the yellow areas would simply turn green (SAFE) but this leaves absolutely no room for production variation.

About StampingSimulation.com

StampingSimulation.com is a world wide team of specialist forming simulation and sheet metal forming engineers. With resources across three continents (North America, Europe and Australasia) we are uniquely placed to offer fast turn around times on all structural simulation, hydro forming simulations, ANSYS simulations and sheet metal forming simulations.

About AutoForm

AutoForm offers software solutions for the die-making and sheet metal forming industries, and is recognized by the Top 20 automobile producers and their customers, as the number one provider of software for product formability, die face design and virtual tryouts to the global automotive industry. The use of AutoForm software improves reliability in planning, reduces the number of die tryouts and tryout time, and results in higher quality part and tool designs that can be produced with maximum confidence. In addition, press downtime and reject rates in production are substantially reduced.

Hydro Forming Simulation

AutoForm Incremental simulation technology includes the ability to design, develop and simulate both sheet hydroforming and tube hydroforming problems, including tube bending and forming (crushing).

The SME market has experienced the power of AutoForm simulation technology via StampingSimulation.com since April 2007 for traditional sheet metal parts pressed in a mechanical process. Smaller and medium size companies can now also access the same benefits for their tube and hydroforming processes, that simulation technology brings.

Tube Bending Simulations

Tube bending problems are designed, developed and simulated based on a final design of a tube product. The entire bending process is designed and simulated and all tooling components (mandrels, beads, etc) are developed as part of the simulation and provided as outputs of a SimulateComplete job. Tube bending is often the first step of a complete HydroForming process.

Tube Forming Simulations

A tube forming problem may be an end form where the tube is crushed by external tooling, to form a desired feature. Simulation outputs include the usual formability, thinning and force results, in addition to a full incremental simulation of the forming process. Tube forming is usually the second step of a complete HydroForming process.

Tube Hydro Forming Simulations

After tube bending and forming takes place, the hydro forming process is usually the last process, although any process can be simulated individually. After the tube is formed between two female dies, hydro pressure is applied from both ends of the open tube. The resulting metal deformation is simulated and captures the usual outputs showing
formability and thinning, predicting splits, thin spots and wrinkles.

Sheet Hydro Forming Simulations Sheet hydro forming is not similar to the above mentioned tube forming simulations, but is a closer match to the traditional mechanical press process. However, it differs in that ONE of the solid tools is replaced by hydro-mechanical pressure, usually the female die cavity. The hydro pressure is commonly contained within a flexible bladder into which a solid punch travels, with the sheet metal blank in between. The punch is surrounded by a solid ring, to act as a binder surface while the sheet is drawn into the hydro filled bladder. This process is simulated and the usual outputs are available.

About StampingSimulation.com

StampingSimulation.com is a world wide team of specialist forming simulation and sheet metal forming engineers. With resources across three continents (North America, Europe and Australasia) we are uniquely placed to offer fast turn around times on all structural simulation, hydro forming simulations, ANSYS simulations and sheet metal forming simulations.

About AutoForm

AutoForm offers software solutions for the die-making and sheet metal forming industries, and is recognized by the Top 20 automobile producers and their customers, as the number one provider of software for product formability, die face design and virtual tryouts to the global automotive industry.

The use of AutoForm software improves reliability in planning, reduces the number of die tryouts and tryout time, and results in higher quality part and tool designs that can be produced with maximum confidence. In addition, press downtime and reject rates in production are substantially reduced.

Metal Stamping Simulation and Efficiency

Sheet metal forming simulation has proven to be accurate time after time. Why then, does the industry hesitate to simulate upfront and save time and money on the shop floor at the end of the project? Those who do reap the rewards.

This example shows the output of a metal stamping simulation job where a crash form process was proposed.

The stamping simulation clearly predicts a large folded wrinkle as the major problem with this process. The consequences of tooling this process could not have been confidently predicted up front, without sheet metal forming simulation technology.

In this case, StampingSimulation.com was able to engineer a solution which involved drawing metal with a binder, instead of crash forming.

Thankfully, the actual result you see was not a result of a bad process being tooled, but rather, this is a scaled down soft tool which was created to demonstrate how accurately this problem was predicted.

About StampingSimulation.com

StampingSimulation.com is a world wide team of specialist forming simulation and sheet metal forming engineers. With resources across three continents (North America, Europe and Australasia) we are uniquely placed to offer fast turn around times on all structural simulation, hydro forming simulations, ANSYS simulations and sheet metal forming simulations.

About AutoForm

AutoForm offers software solutions for the die-making and sheet metal forming industries, and is recognized by the Top 20 automobile producers and their customers, as the number one provider of software for product formability, die face design and virtual tryouts to the global automotive industry.

The use of AutoForm software improves reliability in planning, reduces the number of die tryouts and tryout time, and results in higher quality part and tool designs that can be produced with maximum confidence. In addition, press downtime and reject rates in production are substantially reduced.

Sheet metal stamping simulation in the real world

Williams Tooling, Dorr MI, is a regular client who use StampingSimulation.com’s SimulateLite service to simulate their solid tool designs prior to commencing tooling fabrication.

The Virtual Tryout service means the metal forming process is previewed before any hard tooling is made, meaning problems such as wrinkles and splits can be found and counter measured before any steel is cut.

Jeremy Dutkiewicz, Tool designer comments, "since incorporating sheet metal forming simulation into our company, we have seen a significant reduction in time spent in tool tryouts, often avoiding time consuming changes by getting a good result at first tryout".

The predicted splits were countermeasured by adjusting the DRAW form shape in the localized problem area and allowing it to be re-struck in the 2nd Form. Using forming simulation, it was shown that this was a successful countermeasure.

Sheet metal Simulation technology is common in large OEM companies in the industry but now the same AutoForm technology can be accessed by even the smallest toolmaker via StampingSimulation.com’s online services, delivering the same engineering services found in Tier 1 and OEM suppliers. In this case study, SimulateLite was used to find and countermeasure a splitting problem that may have otherwise only appeared at first tryout, after which costly tooling changes would have been required to rectify the problem. In addition, stretch carrier shape and design was refined as part of the simulation service.

About Stamping Simulation.com

StampingSimulation.com is a world wide team of specialist stamping simulation and sheet metal stamping engineers. With resources across three continents (North America, Europe and Australisia) we are uniquely placed to offer fast turn around times on all structural simulation, hydro forming simulations, ANSYS simulations and sheet metal stamping simulations.

Using the power of the AutoForm suite of software the StampingSimulation.com team can help tool and die manufacturers and designers with spring back, forming forces and help develop blank shapes accurately.

About AutoForm

AutoForm offers software solutions for the die-making and sheet metal forming industries, and is recognized by the Top 20 automobile producers and their customers, as the number one provider of software for product form ability, die face design and virtual tryouts to the global automotive industry.

The use of AutoForm software improves reliability in planning, reduces the number of die tryouts and tryout time, and results in higher quality part and tool designs that can be produced with maximum confidence. In addition, press downtime and reject rates in production are substantially reduced.

The capabilities of sheet metal stamping simulation Part 3

We would like to explore the capabilities of forming simulation, as well as provide some descriptions of how the technology works. So here is a quick summary of a few typical applications of metal forming simulation technology. Being aware that metal forming simulation is actually a specific application of the Finite Element Method (FEM also known as FEA) may assist your understanding.
Splitting, thinning and wrinkling checks.

It goes without saying that the primary purpose of the forming simulation step is to check how the material behaves prior to machining of any tool steel.

The results produced in the forming simulation step illustrate very clearly the calculated areas of material yielding (splitting), amounts of necking (thinning or changes in thickness) and areas of material compression (wrinkles and folds). The Forming Limit Diagram (FLD) is key to analyzing this data as it plots each element’s strain (in major and minor axis) on a graph and compares it to the material’s limits to determine if any of these defects will be present. With this information in hand, countermeasures and adjustments are made to the die face design and then the forming
simulation is re-run, until each defect is removed or an acceptable result is achieved.
Multiple-stage forming.

If a part cannot be formed in a single stage then each subsequent stage can be simulated and checked too. It is simply a matter of taking the result from each previous stage and feeding it into the next. The previous stage results may include a draw, a trim, a hole pierce or any other operation, each of which gets carried over into the next stage’s simulation.

Pierce hole roundness checks.

You may have realized already that it is possible to simulate a forming process with a hole pierced in a blank. This gives an accurate simulation demonstrating whether a hole can be safely pierced in a blank stage, then drawn, without losing its roundness or desired position (usually determined by the quality specification of the final part). Conversely, such a simulation may show that an unimportant hole will go “egg shaped” after forming, but if acceptable, it can remain as a hole pierced in the blank, as opposed to piercing it last, when maybe a cam unit or something else would be required.

Spring back check.

A springback check can be performed after any stage, for example, after the first draw stage or after the final stage. The end result is not just a number on paper of the amount of springback, but a full 3D CAD model of the part in the sprung back state (that can be exported in any CAD format). This means it is very easy to use this data to counteract the spring back or decide if the amount of spring back is acceptable or not.