Electrophoretic Deposition Coating (EDC) or short E-Coating has become a de-facto standard process in car manufacturing. It is commonly used for depositing a high-quality anti-corrosion coating on the metallic surfaces of the body-in-white. In general this is one of the first steps in the paint shop process pipeline.
Advantages of E-coating over other variants of coating such as powder coating include:
THESEUS‑FE E-Coating is a cost-efficient way for verifying high-quality coating across the whole body-in-white, especially for problematic areas such as columns or sills. Used in series development it reduces the need for complex and costly measurements of numerous prototype car bodies. It allows for rapid analysis of various car body variants, e.g. with varying sizes and locations of drill holes applied to improve coating in problematic areas. The E-Coating module is complemented by our Oven module where we predict temperatures in the paint-drying ovens that are used in the following production phases.
Cathodic Electrodeposition Coating was traditionally considered a highly opaque process. Basic questions concerning the coating of a body-in-white an engineer would ask include:
In the past, all these points had to be evaluated with cost-intensive and tedious measurements of physical prototypes.
Using THESEUS‑FE E-Coating makes simulating and analyzing the coating process a breeze. Coat layer thicknesses are quickly available for all car body parts. Walking through the cavities and identifying problematic areas is dead easy. Variants of the same car model with different placements of holes can be done within just a few hours.
Get in contact with us and hear more about THESEUS‑FE E-Coating and related engineering services we have to offer.
Our E-Coating module is built on top of the core THESEUS‑FE tools and benefits from
Specialized features mainly applicable for E-Coating include
Have a look at the general THESEUS‑FE product overview pages for detailed information about the THESEUS‑FE package.
Once the paint and process parameters are known and the finite element mesh prepared, setting up an E-Coating simulation is a matter of minutes. Full visual feedback for the model definitions and simulation results is available at any time.
The core numerical solver accepts the finished E-Coating model and produces a solution for the coupled electrostatic field problem and transient paint layer thickness evolution equation. The simulation itself runs on multicore workstations with full body geometries and mesh sizes typically in the range of 10 to 50 million elements in a matter of hours.
The simulation results that are of most concern are the local paint layer thickness and the total quantity of coated material on the body. These results are easily accessed from the graphical user interface. Transparency effects and selection of threshold values are useful techniques for rapidly identifying any critical areas where the coating remains too thin to provide adequate corrosion protection.
For a simulation of the paint layer thickness the user needs to supply several paint and process parameters, including
Since some of the process parameters, especially the solid paint layer conductivity, are not easily measured, our Optimizer module is regularly employed in practice to calibrate the model against measurements of paint thicknesses. The Optimizer module is included in the THESEUS‑FE E-Coating package and provides optimization methods for parameter calibration and sensitivity analyses. Both global optimization methods based on evolutionary algorithms and some local, derivative-free algorithms are available.
Please have a look at the general THESEUS‑FE product overview pages for detailed information about the THESEUS‑FE package and the Optimization package in particular.
15 to 18 kilogram of adhesives are used in modern car bodies. Experience has shown that using adhesives in addition to welding leads to significantly better performance in crash tests. Adhesive use has the potential of reducing car body weight while maintaining good crash safety. Another great advantage of adhesive technology is that it is less intrusive for the joined body parts. This means that adhesive connections lend themselves perfectly for customer-visible outer body parts such as doors, roof or the engine hood. Furthermore, adhesive seams are used as moisture seals in gaps as a typical corrosion protection strategy. Considering that modern car bodies are assembled using a mixture of materials, classical joining technology will no longer work and adhesive bonding gains even more importance.
Since the late 1990s, 1K adhesive systems based on epoxy resin have become standard in car body construction. These adhesives rapidly cure at temperatures above 150 °C. During the construction process heat is applied in special stages to cure the applied coating and adhesive material. For example, after the electrocoating paint bath the wet car bodies are run through a long hot-air paint drying oven and heated to temperature levels around 200 °C. The drying oven process can last approximately one hour. During the heatup the 1K adhesives change chemically and reach their final desired mechanical stability. To maximize the rigidity, structural adhesive material requires high values for Young's modulus and preferably thin layers.
Modern mixed design car bodies, e.g. combining aluminium, steel or carbon-fibre reinforced materials, are the current major challenge of car body construction. Using mixed materials several major OEMs have recently managed to reduce car body weight by up to 100 kg from one model generation to the next. However, mixing different materials implies mixing different thermal expansion coefficients. This leads to issues during the heatup and subsequent cooldown in the paint drying oven as thermal stresses cause deformation and unappealing dents on outer surfaces. In the worst case the stress causes failure of adhesive lines.
Simulations are used to predict the car body temperature distribution, adhesive curing and resulting deformations during the paint drying process. A paint process engineer can evaluate the results and choose proper adhesive materials or undertake possible pre-treatment process changes. The design goal is to minimize permanent deformation while guaranteeing complete adhesive curing and paint drying.
The prediction of car body temperatures during the passage through a paint drying oven is the task of the THESEUS‑FE Oven module. For the mechanical simulation we rely on the mechanical solver Abaqus from Dassault Systèmes to solve for deformations and stresses. The highly complex behaviour of adhesive materials can not be fully analyzed with Abaqus built-in material models. For that reason we have developed a material user subroutine (UMAT) for Abaqus in close cooperation with our industry partners. This user material employs sophisticated state-of-the art model equations for treating polymer materials. Using the temperature at each location on the car body the local curing level and viscoelastic properties of the adhesive material are determined. As long as the polymer is not cured, plastic deformations accumulate and are stored in the material model.
Adhesive materials used in car manufacturing are typically polymeric materials with highly complex thermo-mechanical properties.
To properly simulate their behaviour when they are used for car body bonding, several material properties have to be determine to adequately characterize them with mathematical models.
Material properties that are needed include:
Instruments that are typically used for determining the necessary material parameters are
Some of these instruments can be used interchangeably for determining certain material properties. With our in-house laboratory we also provide measuring and characterizing polymers as an engineering service. For more information about our measuring services simply contact us.
Adhesive Simulation and Measurements
[english, 2.2 MB]
S. Paulke
P+Z Engineering
January 15, 2019