This blog post introduces a new series of articles coming out of the French AutoForm world. Below you’ll see real results for the simulation of hotforming of aluminum alloys .
Today’s featured metal forming company is Constellium, a leading supplier in design and fabrication of innovative aluminum products. While forming of such parts is a hot topic in automotive stamping today, it poses a number of challenges for many manufacturers, which we address with this inside story.
Presently the Constellium group runs twenty-two production sites throughout Europe, North America and China. Its research center located in Voreppe, France, has become a cradle of advanced aluminum solutions in the packaging, aerospace and automotive industries.
For the automotive industry, Constellium has developed a complete range of products for body in white hang-on parts, helping car manufacturers and suppliers to design lighter vehicles. Their particular support is geared towards improving fuel consumption and reducing the carbon footprint.
In addition to their already existing solutions adapted to structural parts, such as Strongalex© and Securalex©, Constellium develops new high strength alloys (series 6xxx) and ultra-high strength alloys (series 7xxx): Ultralex©.
In order to form parts made from Ultralex®, Constellium performs internal as well as external experimental phases – with the help of suppliers or manufacturing partners – on the hot forming technology using a sheet treatment ranging from 400 to 500°C.
Thus, the hot forming process of a B-pillar at Constellium starts with the heating of the blank over several minutes to a temperature that is close to that needed for the process.
After the metal sheet is transferred into the press, it is stamped using room temperature tools (“cold”) then quenched with those tools still closed.
Under these lab conditions at Constellium, the complete forming cycle lasts less than 20 seconds while the whole heating process requires 8 minutes per batch.
The Constellium Research Center in Voreppe has been equipped with AutoForm stamping simulation software since 2011. It More specifically Constellium uses the hot forming simulation software AutoForm-ThermoSolver®plus to get the job done, while validating the relevance of the simulation correlating with press try-outs.
Here, they fully utilize simulation software in order to bring added value to their customers by demonstrating the hot forming simulation of their innovative alloys for real-life stamped parts.
The minimal set of data items required to carry out a simulation with AutoForm are:
- Flow stress curves obtained at different temperatures,
- Thermal material parameters (thermal capacity, conductivity, etc.),
- Thermal exchange parameters.
Beyond this, there are far more options given to customize models describing the forming behavior of any kind of aluminum alloys. These options involve the description of the yield loci, FLDs or even temperature dependent r-values in order to specify the material. For a thorough understanding of the process conditions we highly recommend to review one of our recently published posts addressing the warm- and hotforming of Aluminum-alloys. In principle all tools and the various steps are taken into account during the process definition.
After the simulation of the hot forming process, AutoForm-ThermoSolver®plus provides numerous result variables and allows for the display, for example, of the temperature history in the stamping throughout the manufacturing process (see image below).
Constellium observes a good correlation between calculation results and experimentally measured values, as seen here-below for instance: a comparison of the thickness distribution between real measurements and simulation results (results in red and measurements in white). With AutoForm-ThermoSolver®plus, Constellium can therefore adopt a specific course for the marketing of its innovative products. Indeed, the work of the Voreppe Research Center confirms the advantages and the added value in using the digital technology for the group’s customers, assuring them the possibility to simulate their hot forming processes using Constellium’s innovative aluminum alloys.
According to Constellium, by using AutoForm-ThermoSolver®plus, they can now adopt a specific course for the marketing of their innovative products.
Read our earlier post on aluminum warm and hotforming HERE.
This is an informative website and I quite enjoy the content about Aluminum Industry. The articles are very important.
Thank You For Your Useful Information
It is an excellent software for sheet metal forming industry! For the development of hot forming of aluminum alloys, especially 7XXX, I think AF is a good tool to analyse it. However, I have come up some questions about the application of AF in hot forming of Al alloys. As we all know, the stress-strain behavior of Al alloy in high temperature is decreasing, so how to describe it in AF? which does not allow the data to decrease due to the calculate method of Yield function.
Thank you very much, we highly appreciate your comments and remarks! You are right, there is still a limitation regarding the implementation of decreasing flow stress curves. But, this could only theoretically become an issue dealing with real AL hotforming processes. From what we have experienced so far this has practically no relevance as long as customer’s input data for the flow stress curves were measured appropriately und fulfil some basic requirements. First of all it should be a tensile test, applied in order the do measurements. Many customers also consolidate data taken from uniaxial tensile tests and bulge tests for higher strains beyond necking. This approach is rather difficult to apply for higher temperatures since the bulge test has its limitations. What’s important is, apart from taking care of the most comparable stress state and amount of hydrostatic pressure generated in the test, the strain rate regime. Actually, during the tensile tests the cross head’s speed of the testing device has to be increased in order to keep the strain rate constant. This strongly influences diffusion driven effects such as recovery and recrystallization which leads to more or less pronounced increase of the flow stresses over strain. Since AL is a high stacking fault energy material, for many it becomes rather unlikely to obtain sections of decreasing stresses in the relevant strain range up to – let’s say – ϕ=0.4. Nevertheless, there is a lot of data published which unfortunately has to be considered as kind of outdated with respect to the way they have been measured. So, please make a contact with your local AutoForm-representatives and specialists. They will assess your specific case. And yes, if there is a proved need for implementing changes we will not hesitate to consider this in one of the upcoming releases of our software.
Kr,
Michael
Thanks for your reply! I have check the experiment data that obtained from Gleeble device. It’s true that the curve of high temperature will not decrease sharply but just keep horizontal.
Another question is, the function of keeping pressure in part when cooling. I have tried that in R7 ‘Process’ module, the ‘D-20 Thermal’ the quenching force can be set when i use a ‘Quenchable’ type, i.e. ’22MnB5.mtb’. But all the icons become gray when using a ‘Thermal’ type material card.
This can result in a problem when simulating the hot forming of Aluminium sheet, the free springback happen in the cooling period for none constraints. I think it’s the problem of quenching force. How can I use it when i use the ‘Thermal’ type material card? In other word, realize the pressing state when cooling, to calculate the springback correctly.
For this problem, I know the amount of springback (elastic) will not change whether the press is used, but this may cause problem when writing a report because springback happens after the cooling in real production process.
Thank you again!
Sincerely,
Jason Chen
Hi Jason, it`s a pleasure to answer your questions since it reminds me on former times when I personally was conducting such tests. Since Aluminium is a material which does not undergo any pronounced phase transformation processes, I would recommend the book ‘Recrystallization an Related Annealing Phenomena’ from Humphreys and Hatherly. How the steady-state in the flow-stress-curves forms is described comprehensively and in detail. The answer to your question was also reflected with one of our specialist – to whom you also have access via a support request as long as you are a regular user of AutoForm-software. Assuming that there is no phase transformation, there is also no dilatometric effect observed. Thus, it is valid to say that quenching force and quenching time will not influence the accuracy of the prediction of springback. Therefore, we distinguish between quenchable and non-quenchable materials. So, Aluminum materials are handled in form of thermal, but non-quenchable material cards. As discussed before: In case that there is clear evidence that this does not apply to your specific case, don’t hesitate to discuss this topic with our application engineers on duty in our support offices.
Kr, Michael’