Although there are many methods of marking forged aluminum parts with lasers, none offers the same benefits. Laser marking is a skill that requires some knowledge, but it can be a great option if you require marking versatility, quick cycle times, and the ability to read part markings years later than they were made.
Forging applications of all types, particularly those that involve safety-critical components for automotive and aerospace markets, are becoming more complex. Individual part traceability is essential. Most people are familiar with part markings that include raised identification in the forging die, or stamp/cold press to identify the part number and alloy.
Customer logo, etc. However, components are now required to have unique identification for every part produced. These requirements are becoming more important in the development and production process.
There are many commercially available marking technologies, each with its own pros and cons. Many factors can play into the choice of the right technology to mark forgings when they are coming out of the press/forging die. These variables include: short cycle times, non-planar parts surfaces, elevated temperatures, surface lubricant, and particulate residue; the need to readability years after application; minimal fixturing and precise positioning; and marks that can be read even after intensive post-marking (such as shot blasting or painting, anodizing etc.). These include financial/commercial concerns.
It is important to have a fast cycle time. Complexity of the process and capital and operating costs must be reduced. Ideal would be a noncontact marking system that can work flawlessly, repeatedly, and without tolerance variations at any distance. Laser marking may be the only viable technology in these conditions, but laser marking requires experience.
Methods of marking
There are many different marking technologies that can be used to mark individual parts. They are not suitable for most forgings as they do not meet the above requirements.
Nameplates and labels
They have been used for many years to identify parts. The printed substrate is adhered to the part. These labels are not suitable for aluminum as they can easily be ripped off during the next process steps or when the parts are being used.
Znakowanie laserowe aluminium This involves using a gun and an nozzle to mark the part’s surface. Mark durability depends on the quality of ink and other factors.
Acid is used to create relief on the surface of a component. This process can create complex designs and logos, but the cycle times can often be too long for most forging applications.
Combination of CAD and CNC Machining. This is not suitable for most forging applications due to the long cycle time.
Pin stamping and micro-percussion (dot-peen) marking
These are often used to mark forgeries
Parts. These methods can make identifications more durable because they are etched into the material. These processes are mechanical and can take a while. They also may increase the scrap rate if they are not repeated enough.
It is an extremely reliable, fast, and non-contact alternative to the other solutions. The cost of consumables is reduced to zero while contrast and readability can be maximized. The surface modification creates contrast. For a laser marking on an aluminum forging, see Figure 1. Laser markers can be used to mark aluminum forgings with high precision and accuracy, even at high temperatures.
The high energy of an infrared pulsed fiber laser is used to mark metal parts. It absorbs the part’s surface and modifies it in order to reflect ambient light. This results in a high-contrast marking. Computer-controlled lasers make marking any feature, such as serial numbers, 1-D barcodes, 2-D barcodes, logos, and other features, easy.
Laser technology meets all criteria for forged-part identification. This ensures reliable traceability. All surfaces, including those with rough or uneven contours, can be marked reliably. Before the actual marking is done, surfaces can be etched, cleaned, and slightly smoothened by the laser. To improve readability, you can easily and quickly whiten the background or blacken the text and bar code.
The laser does not apply any ink. Instead, the laser modifies the surface texture of the part. After marking the part, some light is scattered at the microscopic level to make it appear white. Or, it is trapped between peaks or valleys, creating “black”. This effect can be achieved by introducing only 0.1mm of surface roughness.
Laser marking and surface treatments
Extensive research has been done on the effects of heat treatment and chromate coating on laser-marked parts. These treatments have little effect on the readability of laser-marked parts if used with care (Figure 2).
The most difficult post-processing step for any marking is shot blasting. This is an abrasive process that alters the surface’s roughness. Deep marking is a technique that allows a mark to survive the shot.  Cell size must be chosen according to the shot-blast medium.
Part markings can be difficult to read due to E-coating or painting. It is important to adjust the marking parameters and cell size. Figures 3a-3b show a 2-D code with and without a background. Figure 3c shows another angle of the same barcode. It is also very contrasty. However, the background is black and the barcode is white (inverted colors). This does not affect the readability of code.
To study the effects of blasting, E-coated samples were applied to marked samples. The appearance and readability were affected by the paint. The contrast was even more apparent after the E-coat paint was applied to the samples.
Implementation of a safe laser-marking system into a forging cell
The 1.06um fiber laser wavelength falls within the 0.4-1.4um wavelength range. This is the “danger zone”, which is the area that is most dangerous for the human retina. It is highly recommended that the laser-marking system be integrated within a Class 1 laser machine to ensure that all affected personnel are adequately protected. ANSI 1040.10 applies to the United States, and IEC 60825-1 is applicable for Canada or Europe.
Figure 4 shows the open-air safety enclosure. The enclosure actually consists of two separate enclosures, an outer (labeled 1) as well as an inner (labeled 2) In some cases, a human-access barrier may be required to restrict access to the enclosure. These three enclosures/barriers are required to ensure laser safety and comply with the ANSI 1040.1 standard.
The enclosed enclosure has a rotating loading table that allows the operator or robot to load and unload forgings while marking parts with lasers. This enclosure design is illustrated in Figure 4b. First, the part is loaded onto a fixture that was specifically designed for it. The part is then placed on a fixture that was specifically designed for it. The robot can still work on other tasks while this part is being marked (e.g., placing the part on an exit conveyor or grabbing the next one and verifying that the mark is correct).