Surface inspection
During surface inspection or surface testing , the visible shell of an object is checked. Properties and defects in the interior of the object are not subject to the surface inspection.
Why do you do surface inspections?
Customers demand absolutely flawless goods from the manufacturer. A well-functioning quality management system is therefore urgently required for the producers . Methods such as Six Sigma or the zero-defect strategy help to improve production processes. Quality is becoming increasingly measurable, and automatic test systems provide the information.
Functionality and aesthetics are essential quality features , and here in particular the surface of the product plays a decisive role. Defects in the surface can lead to the function of the device being restricted or not given at all. In addition, visible surface defects in particular often lead to expensive complaints , even if the function of the product is not restricted as a result.
Tactile surface inspection
With tactile surface inspection , the workpiece is traversed using the stylus method. Today, this method is mostly only used for very precise roughness measurements in the micro or nano range .
Optical surface inspection
The optical surface inspection is a non-contact and non-destructive test method. There are two types of this test method, on the one hand human testing and on the other hand automated optical surface testing .
Human testing
This test method is probably the first and easiest form of quality assurance . The workpiece goes through its production process and at the end of this chain there is a person who takes a closer look at the part. He takes the part to be checked in his hand, turns it in all directions and, given the appropriate framework conditions (lighting, room climate, cleanliness, ...) can identify most errors relatively quickly.
However, serious errors often go undetected during human testing. The reasons for this are, for example, a lack of concentration, personal constitution, breaks, etc. Only well-trained staff ensures that these mistakes do not happen. Although humans are much more flexible than a test system, they are never as constant and objective as an automatic test system.
Automated optical surface inspection
The inspection is carried out with the help of cameras. Here are line scan cameras and area scan cameras available. The images made are processed with the help of image processing . There are two fundamentally different approaches to troubleshooting:
- In the simpler variant, the image is compared with a target image; any deviations lead to exclusion.
- With the much more sophisticated approach, the software detects the error based on a description of the error, and highly complex algorithms are used here.
Thanks to the steadily growing computer power and the continuously improving cameras, it is possible in most cases to carry out an automated in-line surface inspection. With very short cycle times , the particular challenge is to program suitable software . In most cases, the quality of the evaluation software decides whether the system meets the requirements (i.e. the very fast test times) or whether the specifications cannot be met.
Motivation for automatic testing
Serious errors often go undetected during human testing. This human factor is excluded in the automated test. A recorded 100% check is carried out. This is extremely important, especially in today's world, in which safety-critical components, such as vehicle brakes or turbine blades, are subject to more stringent test criteria.
economics
In global competition, we in Germany cannot escape the automation race. Forward-looking companies are therefore not only automating production, but increasingly also quality testing. Automatic inspection systems guarantee cost-efficient and error-free production.
Quality improvement
Complaints or recourse are always costly - not to mention the internal processing effort. If the quality is right, there is no need to re-sort in quick action on site. Basically: If you don't want to be dependent on the daily form of the test staff, you cannot avoid an automatic test with objective and verifiable criteria.
Production optimization
Industrial image processing creates higher throughputs than manual inspection with staff - with significantly lower staff costs and better workplace conditions. In addition, the incorruptible statistical feedback from the machine allows the production process to be optimized in a timely manner. Because a 1% reduction in rejects through immediately available quality data always brings more than any rationalization measure.
Areas of application
The automated optical surface inspection is mostly used for the in-line inspection of safety-critical components after individual process steps. The aim is a reproducible, objective test with very high cycle rates and 100% defect detection.
Take brake discs, for example : in the most safety-critical assembly of every automobile, zero defects are an absolute must. The laser triangulation method is used to check the surface quality precisely, reliably and efficiently . A system of this category is in the foundry of Daimler AG in Esslingen-Mettingen. The system of automation W + R GmbH checked daily 32,000 blanks in three shifts.
The surface inspection is also of great importance in areas where it is not primarily about safety, but about the appearance of the components. An example of this would be fittings in the sanitary area or checking the surface of rawhide prior to further processing