Quality Assurance Traceability of Die Castings through Laser Engraving
In critical components, quality assurance and traceability go hand in hand. If a part fails, manufacturers must be able to track it back to its origins. Since the average vehicle on the road today can contain as many as 600 pounds worth of castings, traceability is of vital importance in the automotive sector.
Today, the increased production of hybrid and electric vehicles (EVs) have two key requirements that impact the die casting industry: lighter weight parts to extend the range of EVs and complete traceability of high-value die casted parts.
In addition to conventional high pressure die casting, there is also increased use of structural die casting to produce large body components. Tesla recently announced plans to use a giant die casting machine to combine processes and produce a single die cast part instead of casting 70 individual parts. This would create almost the entire rear section as a single piece and reduce production costs.
Regardless of how many parts are used or how components are manufactured, automotive OEMs will continue to demand complete traceability for high-value castings such as EV drive units, battery trays, body and frame components, and shock towers.
Meeting OEM Compliance
Die casters will need to comply with new requirements if they want to supply castings to EV manufacturers. EV manufacturers require that no defective codes make it to the end-user and that 100 % of die casted parts are traceable to the exact origin of defects to avoid having to do large-scale and expensive recalls. Laser etching at the die casting cell is the most effective way to accomplish single piece traceability.
As you know, traceability isn’t a simple process. For example, as structural die castings are heat treated to improve ductility and strength, the heat treatment can compromise traceability by making codes unreadable. Castings such as EV drives are often shotblasted to improve surface finish. This can also cause problems with code readability.
The solution? Laser engraving codes directly into the casting that will remain readable during the heat treatment or shotblasting process.
Laser Engraving: The Solution to Complete Traceability
By deep engraving markings directly onto the casting, they can be both shotblast and heat treatment resistant.
This process provides complete traceability through every step of the shotblasting and heat treatment process and produces markings that are readable.
How Shotblast Resistant Laser Engraving Works
When castings like EV drive units are treated with shotblasted post treatment, codes and alphanumerical characters are typically erased. A unique shotblast resistant laser marking process resolves this issue with codes that remain readable after shotblasting.
An important thing is to have the right cell size: too small and the cells are clogged by the shot; too big and the shot goes in and erases the contrast. The key is to make each cell separate from one another by keeping a wall in between them.The laser process for engraving can easily be adapted to accommodate the size of the blast media.
How Heat-treatment Resistant Laser Marking Works
EV manufacturers often require that those parts be heat treated to meet strength and ductility requirements, so the codes need to maintain traceability throughout the heat treatment. When a part has been treated with heat, it undergoes thermal expansion before returning to its normal form and dimensions. As a result, identifiers located on the part surface will typically lose their legibility. Laser marking can counter this effect by increasing the cell and code size of the identifier.
How to Integrate Laser Technology in the Die Cast Cell
Integrating a laser directly into a die cast cell can be a complex technical challenge. You need to:
- Minimize impact on the cycle time
- Minimize maintenance
- Monitor quality
- Ensure work safety
Minimizing the Impact on Cycle Time
Cycle times will vary greatly depending on the size of the casting. The larger a casting is, the more time that is available for the laser marking operation. Using a high-speed laser will reduce the amount of time it takes to engrave markings in components, but there are also other ways to reduce cycle time during integration. For example, laser technology integrates well with the type of robots that are typically installed in die cast cells.
Integration might include:
- If there is ample robot idle time, the robot can simply hold the part during laser marking.
- If the robot’s idle time is short, it can drop the part into a two-position rotary table. This allows the laser marking to be completed in hidden time. In this case, the part would be marked while the robot is loading the next part.
- The robot could drop the part into a machine to complete the laser marking while it goes on to perform other tasks or cast the next part.
The right laser technology equipment will keep maintenance to a minimum. This allows the die caster to maximize uptime and minimize downtime in the die cast cell.
Air Knife (Blower)
Dust can cause all sorts of problems in the marking process. Dust accumulates on the lens during the laser process and needs to be removed regularly. If not, it can block the line of sight that the laser needs to complete the job. Since this requires manual intervention, you’re looking at downtime for maintenance. An air knife, also known as a blower, blows dust off the lens and will keep your operation running more smoothly.
Since the laser head must be positioned in the die cast cell to mark components, it is exposed to harsh environments. To ensure it is sealed against dust and liquids it may encounter during the process, it should have a minimum IP67 rating.
Using an electrical cabinet will enclose most of the laser equipment except for the head. This protects the inner working from harsh environments. Since the cabinet can be located outside of the die cast cell, it is not exposed to the same harsh environment as the laser head, so an IP54 rating is sufficient for protection.
In most cases, the laser system must be equipped with an autofocus system because the castings are not always placed precisely. An autofocus system can detect the casting’s position using cameras and adjust the laser process or the laser head’s position accordingly. This way, part positioning variations are managed automatically by the laser without intervention.
A barcode reader to check the laser engraving is an excellent way to monitor quality. If for some reason the quality of the markings drops, this signals that something isn’t working properly during the marking process. For example, the air knife might have stopped working which allows dust to accumulate on the lens. Barcode checks can also help you know when equipment maintenance is needed.
Ensuring Worker Safety
American physicist Gordon Gould first used the acronym laser to describe “light amplification by stimulated emission of radiation.” While low-level lasers are safe, the higher the laser class, the more potential there is for safety concerns.
A Class-1 laser enclosure provides the assurance that the laser beam is properly enclosed and that no harm can come to your workers or to your work environment. To ensure that you follow international standards for Class-1 lasers, a Class-1 enclosure should be used. This allows employees to work near the laser marking machine without needing Personal Protective Equipment (PPE).
Produce Consistent and Complete Traceability
Shotblasting is a highly abrasive treatment that compromises traceability. Heat treatments naturally result in thermal expansion which can make markings hard to read. Laser marking technology has now evolved so that it can meet complete traceability requirements with shotblast resistant engravings, and it can also be integrated without impacting die cast cell operations. This provides a solid solution for die casters who need to comply with a complete traceability requirement before they can apply to automotive OEM programs.