Direct Part Marking: An Expert Overview

Chirag Sheth, Global Marketing Manager at Videojet, looks at the vital importance of direct part marking in the automotive industry.

Direct Part Marking - Picture by Videojet

Direct part marking (DPM) standards have been adopted in the automotive industry in order to allow individual parts and assemblies to be tracked throughout the manufacturing process and the supply chain. This allows parts to be located should they need to be recalled, for example, and can assist in other areas such as liability and warranty resolution. This is achieved through the application of machine readable codes, which can be created using a variety of techniques, from printers to lasers. Two-dimensional codes are becoming the standard, due to their ability to hold a large amount of information within a relatively small footprint.

The DPM process consisting of three main elements:

Encoding

One dimensional bar codes have been standard for many years within the automotive parts production industry, but this format is being replaced with 2D codes, primarily as they are able to contain far more information in a more confined space.

DataMatrix ECC 200 is the current standard, and requires parts to be marked with a 2D matrix bar code arranged in either a square or rectangular pattern. This pattern consists of black and white modules capable of storing large amounts of numeric or alphanumeric information – for example, the largest square symbol can encode up to 3,116 digits. Essentially, a string of data is rendered into a pattern of dark and light cells, which is then used by the marking device.

The DataMatrix codes are governed by Global Standards One (GS1), the international body responsible for bar coding application standards, who have symbology in multiple sizes in order to match a wide range of data content. Square format ranges from 10x10 modules up to 144x144, whereas the rectangular format can go from 8x18 to 16x48 modules.

The data itself is stored within the matrix by using a series of dots – either square or circular in shape – and must be positioned correctly within the grid in order to ensure code reliability. Dots that are misaligned, too big or too small may lead to readability issues, therefore an accurate printing solution is of the utmost importance.

Marking

Direct Part Marking - Printing technology and substrate suitability - Picture by Videojet

The method you choose to employ to mark your parts will depend largely on the substrate in question and your code requirements. Various polymers and alloys are used in automobile production, and the most commonly used methods for coding and marking are laser, continuous inkjet printing (CIJ), electrochemical etching and dot peening.

Laser printers make permanent marks by using light to change the surface color of the substrate, either by melting, foaming or removing the material surface. By varying the wavelength of the laser, different marking effects can be achieved – from ablation (removing the top layer of the substrate – normally paint – to create a mark), to engraving – which goes deeper into the material, generating a depression. Laser marking is a popular option given that the mark can survive chemical treatment further down the production process and harsh operating conditions, as found in engine and fuel systems.

CIJ is a popular method for printing DataMatrix codes as the drops of ink are distinctly formed in the process and ensure excellent readability. Capable of working at high speeds, CIJ printers can also be used to mark a wide variety of substrates depending on the ink used. Most inks printed in this way can also be removed if required by using an appropriate solvent. This may be necessary where manufacturing occurs within cells. A part will be manufactured in one cell and marked, for example, with mounting points. This part will then be taken to another cell, where the operator will utilize the marks to mount the product and remove them once the final product is assembled.

The final two common marking techniques are electrochemical etching and dot peening. The former removes layers of material via electrolysis – taking an image on a stencil and transferring it to the substrate by using electrolytes and electricity. The latter uses an indenting pin to create an indentation for each dot in a DataMatrix code. 

Verifying

Verification is a critical part of the DPM process, as it allows manufacturers to assess the effectiveness and performance of the DPM equipment in use and to be instantly alerted if a code does not meet the required standard. Verification systems are usually centered on a fixed camera, in conjunction with optics, lighting, part fixtures and verification software.

Every care should be taken when selecting a verification system to ensure your individual requirements are met. You will need to know exactly what the system is checking for and precisely how that data is being interpreted in order to comply with code specifications.

Quality and accuracy are of the essence and codes must meet certain criteria in order to pass evaluation. Standards such as ISO/IEC 16022, EN9132 and AIM DPM are used for 2D DataMatrix codes and check areas such as symbol contrast, dot center offset and cell size, for example, when verifying. The system should also be capable of logging, reporting and sharing results, as well as being able to track, record and score quality metrics for every part it identifies.

Conclusion

DPM is essential in the automotive industry. Not only does it enable parts to be tracked throughout the manufacturing process and supply chain for logistical purposes, it also greatly reduces the risk of counterfeit parts being used in production – which can have extremely detrimental effects if gone undetected. Which method you choose to employ will depend greatly on your product, and working with a recognized expert to ensure you get it right from the outset will certainly pay dividends. Whatever your application, there is a solution available that will not only produce clear, compliant codes but will also help you maximize uptime within a 24/7 production environment.