Pre-competitive standardization as a building block in success
As part of the work of the VDA materials committee, its working groups, ten of which are currently allocated, and more than 30 project groups, a large number of VDA recommendations are produced every year for pre-competitive standardization. The goal of these VDA recommendations is to standardize specifications, test procedures, data formats, material and component properties or material compatibilities by means of voluntary standardizations. The “Colorimetry” VDA project group has been drawing up recommendations for color measurement on all kinds of surfaces in the vehicle for more than ten years now. The eighth part of VDA recommendation 280 has now been completed, and is available from the VDA.
VDA 280 part 8 deals with visual color sampling and color assessment, sampling devices for the interior of vehicles as well as illumination for sampling bodies or body parts featuring effect paints. The use of colorimetry equipment for measuring color differences in vehicle paints both inside and outside of vehicles became established in the automotive industry about 15 years ago. The Colorimetry VDA project group has followed the process of instrumental color quality control with numerous VDA recommendations, thus making a contribution to achieving comparable measurement results in correlation with the visual impression. In doing so, the VDA project group was able to rely on the expertise of highly qualified specialists in the area of colorimetry.
The description of color effects on exterior paint, which are becoming more and more varied, has led to ever-more complicated measurement geometries, predominantly developed in the ASTM (American Society for Testing Materials). It has been revealed that the visual sampling practices established previously only correlated with the results of the color measurement if analogous measurement geometries were maintained during the visual color sampling under constant ambient conditions. It also became apparent that there was an urgent requirement for uniform terminology to be used when describing color differences, as well as defining the sampling conditions. In light studios, color differences can be assessed reproducibly under defined conditions with artificial daylight at any time of day. The necessary reproducibility of sampling results imposed certain requirements on the configuration of these light studios and on the procedure for visual sampling itself. This also includes monitoring mechanisms, especially for the lights used.
Preferably, visual assessment takes place under artificial daylight with the normal light type D65 in a neutrally colored environment, with an observation geometry corresponding to the measurement geometry (illumination angle 45°, different observation angles). Other light types such as A or F11 are possible, and can be used for assessing other effects.
These developments made it necessary for the “Colorimetry” VDA project group to address requirements on visual color evaluations and color sampling procedures from 2009 onwards. In 2014, VDA recommendation 280 part 8 was approved, and consists of three parts (each in a German and English version). This VDA recommendation exclusively refers to visual assessment of all decorative, visible surfaces inside and outside the vehicle.
VDA 280 part 8 A indicates the target and purpose, as well as the scope of application of this recommendation. A definition is given of all terms used in the visual assessment. The procedure for performing the visual assessment itself and the requirements on it are described, as well as the limits on accuracy of the assessment results and documentation of the necessary data.
VDA 280 part 8 B provides specific information about sampling conditions for decorative, visible surfaces inside the vehicle. It gives information about lighting with regard to the light type and illumination, especially with regard to using different materials inside the vehicle. Both diffuse and partially diffuse illumination is required due to the particular reflection conditions. The customer‘s perspective must be reconstructed during the assessment. Information is provided regarding how and under what conditions surfaces fitted in the vehicle are to be assessed, as well as separate individual components and test samples. It is stated that the usual practice of “sample tilting” results in a change of all angular geometries (illumination and observation angles), and no longer corresponds to the measurement geometries of the color measurement. The requirements on the lights are indicated.
VDA 280 part 8 C provides specific details on the requirements for and conditions of visual sampling of vehicle surfaces coated with effect paints. The various observation angles and the relationship to the measurement angle are clearly described in order to avoid possible misunderstandings in the use of language. The requirements on the light with regard to the light type, method and mode of radiation, as well as examination of the light and the requirements for samples and the test environment are indicated. Preferably, the visual color sampling takes place at a fixed lighting angle of 45° and different observation angles. However, the method involving a constant observation angle and varying the lighting angles is also possible. In doing this, however, the relationship between the angles should always be maintained. It is essential to avoid varying both the lighting and the observation angles simultaneously.
For reasons of reproducibility, comparability and independence from natural daylight, visual color sampling procedures should be carried out in light cabins with artificial daylight D65 under standardized conditions. Various light cabins are presented, which are adapted to the size of the sample, e.g., sample panel, add-on part or complete vehicle. The method for evaluating the sparkle effect is described. The criteria for evaluation, evaluation scale and information to be documented are listed. The appendix contains information about various designs of light cabins and equipment for visual evaluation.
Irrespective of the configuration variant that is selected for visual evaluation of the color and effects of vehicle surfaces with effect paint, analogous sampling geometries should be used in order to achieve comparability between the results of the visual color sampling and the color measurement. Sampling in light cabins under standardized conditions with artificial daylight is to be preferred over sampling under natural sunlight.
Both visual color sampling and color measurement by instruments are necessary for complex assessment of the decorative visible surfaces of a vehicle. The choice of assessment method is determined by the requirements on the surface to be assessed, and should take account of the benefits of the particular method. In order to achieve comparability between the results of both methods, it is necessary to standardize and agree the sampling conditions as exactly as possible, especially the sampling geometries (lighting and observation angles / measuring angles). VDA 280 part 8 is a guideline that, for the first time, standardizes the requirements, conditions and procedure for visual sampling of decorative, visible surfaces on and in the vehicle. Different or even contradictory evaluations due to different evaluation methods can thus be avoided. Practical experience has shown that when using complex measuring geometries, it is only possible to achieve a correlation between the measured values and the visual impression if the sampling conditions defined in this VDA recommendation are complied with.
VDA 280 8 part A Visual sampling and color assessment, general part
Assessment of color differences and color effects on all decorative, visible surfaces in and on the vehicle
- Nonmetallic/effect paints
- Structured/textured surfaces
VDA 280 8 part B Sampling conditions for the interior
Assessment of color differences on
- Moldings in which the surface appearance ranges from high-gloss through to gloss silk and matt
- Moldings with a structured and/or textile surface
- Nonmetallic paints (for effect paints, see section C)
Observation geometry for colors that vary according to angle.
VDA 280 8 part C Sampling of bodies or body parts with effect paints
Examples for standardized and uniform language use for describing color deviations. The criteria for color assessment have been taken from colorimetry. The following criteria are to be used for each angle:
Brighter: The sample is brighter than the reference.
Darker: The sample is darker than the reference.
More colorful: The sample is more colorful than the reference.
Less colorful: The sample is less colorful than the reference.
- Color tendency
Red: The sample is redder than the reference.
Green: The sample is greener than the reference.
Blue: The sample is bluer than the reference.
Yellow: The sample is yellower than the reference.
More glossy: The sample is more glossy than the reference.
More matt: The sample is more matt than the reference.
- Graining/structure of the surface
More grainy: The graining/structure of the sample is coarser than the reference
Finer: The graining/structure of the sample is finer than the reference.
Location-dependent effect characteristics are to be described as follows.
The assessment must be carried out both in relation to the surface and the intensity.
- Sparkle intensity
More: The sample sparkles more intensively than the reference.
Less: The sample sparkles less intensively than the reference.
- Sparkle surface
More: The sample sparkles more than the reference.
Less: The sample sparkles less than the reference.
Coarser: The graininess of the sample is coarser and denser than the reference.
Finer: The graininess of the sample is finer than the reference.