Simulation of a plastic dashboard being thermoformed. The results show that the part experienced a defect in the form of excessive thinning. (Image courtesy of ESI Group.)
But material and mechanical engineers know that not every composite is designed to offer structural support in worst-case scenarios.
However, these non-structural materials still have performance parameters that must be taken into consideration by engineers who need to avoid cosmetic defects and improve noise, vibration and harshness (NVH) performance.
To achieve these optimal parameters, engineers use computer-aided engineering (CAE) tools to design custom materials that fit specific non-structural roles. The result is a car interior, for example, that is more affordable, lighter and meets customer satisfaction.
“PAM-COMPOSITES allows the simulation of the [manufacturing] process up-front in the product development process, and a long time before the design freeze,” said Mathilde Chabin, composites product marketing manager at ESI Group. “It is then possible [for engineers] to predict what defects will be induced by manufacturing, and how to fix them by modifying process parameters or through a review of the design.”
By bringing these as-manufactured defects to light early in the development cycle, engineers will be able to reduce development times and the risk of expensive, last-minute design changes.
“The differences between parts as-designed and parts as-manufactured can be important,” noted Chabin. “To be able to predict these thicknesses from a thermoforming simulation, engineers must perform multiple iterations to alter the process parameters to be as close as possible to the target.”
Simulate Composites to Improve NVH and Quality
Composite automotive carpet (right) compared to a simulated carpet post thermoform (left). (Image courtesy of Kotobukiya Fronte.)
Composites are engineered materials made by combining two or more materials that have different physical and chemical properties. The resultant material gains properties that are different than its constituents.
For instance, take the carpet used in cars. Chabin explains that engineers have been able to create synthetic material options that have considerable advantages over their natural counterparts.
“The industry went from rubber carpet to synthetic fiber material carpet,” said Chabin. “Thanks to that revolution, we went from sound insulation carpets to sound absorption carpets. Composites, if properly exploited, allow the integration of several functions at a light weight.”
When engineers design materials, both structural and non-structural, they can use CAE software such as ESI PAM-COMPOSITES to simulate their production process and predict a composite’s as-manufactured properties. This will help the engineers assess the composite’s internal strains and ensure that parts are made fast, affordable and within tolerances.
“There are two types of challenges to overcome when dealing with non-structural composites components: cosmetic defects and NVH performance,” noted Chabin. “Cosmetic defects include excessive stretching or compression during the thermoforming process, resulting in tearing, zones with poor aspect, or wrinkling.”
“As for NVH performance,” continued Chabin, “during the thermoforming the material can become more compressed in some areas. This means the final thickness distribution of the part is not uniform. These thicknesses are defined by design engineers to meet desired NVH performances.”
If the quality isn’t up to snuff, or there are too many cosmetic defects, then the engineer can tweak the production parameters in the simulation, or the part geometry, to digitally optimize the product.
With respect to thermoforming, engineers will have control over parameters that determine the tool velocity, temperature and pressure cycle, clamping conditions, laminate sequence, ply orientation and the overall tool design from the grippers to the mold geometry.
“Simulation will also allow an optimization of the thermoforming process to minimize the production cycle and increase product quality,” said Chabin. “Thanks to thermoforming simulation, you can not only determine what the right process parameters leading to a good product should be, but you can also look for the best combination of process parameters.”
However, things get a little more complicated if the engineering is unable to determine a parameter mix that will create the designed outcome for the composite. In this case, it’s back to the drawing board to redesign the part. The benefit to simulation is that you will hit this wall early in a part’s development, instead of late in the development cycle when there are no easy or inexpensive solutions.
“With the introduction of simulation, testing of process variations can be quickly evaluated without additional cost,” explained Chabin. “Indeed, each iteration of simulation takes a couple of hours, while each physical testing takes several days and is very expensive.”
Some of the features and defects that PAM-COMPOSITES can predict include:
- Fiber orientation
- Thickness distribution
- Optimal initial flat pattern
- Stress and strain Bridging and wrinkling
How to Simulate the Thermoforming of Composites
As- manufactured simulation of a composite fabric armset has local stretching, according to ESI PAM-COMPOSITES. (Image courtesy of ESI Group.)
This is because optimized thermoforming processes can meet this industry’s high demands for tolerance, reproducibility and mass production.
To simulate the thermoforming of your custom trim composite, you first need a list of all the material data.
In other words, engineers will need to collect stress-strain curves at various temperatures and velocities from their suppliers. If this information is unavailable then the engineers will need to perform the tensile testing themselves.
Next, the engineer needs to import their computer-aided design (CAD) geometry into PAM-COMPOSITES’ thermoforming module, PAM-FORM.
“The following steps in the modeling process are: meshing of the female and male tools that form the part, the creation of the initial flat layup, the initial positioning of the material between the tools, definition of the kinematics of the tools and of the gripping system,” listed Chabin. “Once the modeling is done, computations can be launched.”
This manufacturing data of the simulated composite can then be passed onto other CAE tools, such as ESI VA One to assess how this as-manufactured part would perform in the real world with respect to its noise propagation.
“By transferring thickness distribution predicted by PAM-COMPOSITES thermoforming simulation to NVH simulation software, engineers can expect more accuracy,” said Chabin. “The result is that NVH analysis and margins applied on design can be reduced. By reducing these margins, we decrease the overall weight. PAM-COMPOSITES results can be transferred to any acoustic, vibration or structural software in HDF5 format.”
It should be noted that PAM-COMPOSITES includes additional modules which can simulate other composite production methods. These modules cover:
- The curing processes of thermoset composites
- Draping and thermoforming of dry textiles and prepreg materials
- Liquid composite molding for infusions and resin transfer molding (RTM)
Additionally, the software also has modules that can transfer data between ESI tools and CATIA CPD and assist in the calculation of residual stresses and part distortions.
These modules are also able to transfer data between each other to ensure that each stage of the process has up-to-date as-manufactured information.
The goal engineers should have when using PAM-COMPOSITES is to reduce design margins and optimize parts based on their weight and performance. This is done by digitally optimizing the production parameters to improve the quality of the final product and avoid cosmetic defects before the product gets to its initial physical run. The simulations can then be used later in the lifecycle to further optimize production of the physical product or study how it performs in NVH software.
“ESI PAM-COMPOSITES is equipped with the features and parameters necessary for carpet analysis,” said Takumi Fujino, of the Acoustic & Simulation Group of Kotobukiya Fronte, a Japanese automotive supplier. “The accuracy and the usability are excellent. The graphical display of analysis results is also easy to understand, which is why we rate it highly.”
Fujino added that ESI has also been very forthcoming then it comes to helping Kotobukiya Fronte reduce calculation time and optimize the modeling process. These consultations from vendors are priceless when learning and implementing a new CAE tool.
To learn more about PAM-COMPOSITES, watch this webinar.
ESI Group has sponsored ENGINEERING.com to write this article. All opinions are mine, except where quoted or stated otherwise. —Shawn Wasserman