Dimensional inspection of a product

Compliance with the dimensional specifications of mechanical parts is an important issue for their manufacturers. Dimensional inspection in industry relies on a variety of methods, each with its own advantages and limitations. By choosing the appropriate method based on part specifications and application requirements, manufacturers can guarantee the quality and conformity of their products, while optimizing their operational efficiency.

Why carry out dimensional checks on a product?

In the manufacturing industry, ensuring product quality is obviously a top priority. For many mechanical parts, which have to be fitted into complex assemblies, checking their dimensions is of key importance to ensure their performance, reliability and compliance with the required specifications.

Accurate dimensions are essential to ensure the right mechanical connection between these parts, with correct clearance or fit. This ensures optimum assembly functionality.

To meet these requirements, various dimensional measurement methods are used, each offering its own advantages, limitations and specific applications.

Dimensional inspection with the pneumatic method

The pneumatic method of dimensional measurement is based on the use of compressed air to measure the dimensions of parts. This method offers the advantage of simple, fast and reliable measurement. It can be applied in any workshop, and therefore does not need to be carried out in a metrology laboratory. It is particularly well suited to industrial environments where speed is crucial. Through a combination of several dimensional measurements, it enables certain geometric specifications to be checked, such as perpendicularity, parallelism, coaxiality, etc.

Although this pneumatic method is effective for measuring parts with simple shapes, it can prove limited when it comes to checking parts with very small dimensions or complex shapes. In such situations, the measuring tools used, such as air plugs or rings, may be more difficult to position accurately on the parts to be inspected.

Dimensional checks using touch probes

Dimensional measurement by tactile method is based on the use of LVDT (Linear Variable Differential Transformer) sensors to detect distances between various control points.

This method offers high precision and measurement reliability, making it an ideal choice for applications where dimensional accuracy is critical. It is widely used in high-precision industries such as aerospace and automotive . The tactile method can be limited by the need for physical contact with the part, which can potentially lead to surface defects if the necessary precautions are not taken.

Furthermore, measurement points on the surface of parts must be accessible to allow contact with the sensor, making the operation complicated for parts with complex shapes, or even inapplicable for measurements of internal dimensions.

Dimensional inspection using industrial machine vision

Machine vision is an inspection method that uses cameras and advanced software to capture, record and analyze digital images of parts.

While its applications tend to focus on the detection of assembly or surface defects, it is also a fast, non-invasive dimensional measurement solution, making it particularly suitable for complex, delicate parts. It offers good accuracy and can be automated for high-throughput applications, improving the efficiency of manufacturing processes.

However, machine vision can be limited by variable lighting conditions or visual obstructions, which can affect the quality of the images captured and therefore the accuracy of the measurements made.

Dimensional checks using optical micrometry

Optical micrometry is similar to machine vision, but is based on the analysis of the shadow projected by the part to be inspected.

This technique generates images whose high contrast facilitates processing by imaging algorithms. Like machine vision, it enables rapid, non-intrusive measurements, ideal for checking the size of parts without altering them. Often integrated into automated systems , it is ideally suited to high-throughput applications. However, it is limited to measuring the dimensions of the external contours of inspected parts.

Dimensions control using X-rays

Industrial radiography is an inspection method that uses X-rays to check parts through their material. The resulting images are recorded and processed by image analysis software.

This method enables internal defects and dimensions to be identified with great precision, without damaging the part. It is particularly suited to opaque or thick materials where other measurement methods may be limited. Industrial radiography requires strict safety precautions due to the use of ionizing radiation.

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