ROI: 24 months
Project duration: 6 months
Client: 3 engineers
Concept Systems: 3 engineers
Concept Systems’ time on site: 15 days
- Lack of traceability
- Increased quality through better traceability
- Increased productivity
- Reduced overall risk by improving safety
- Nachi MC50 6-axis robot
- Hermary Opto 3D laser scanner
- Cognex 2D code reader
- Keyence ML CO2 Laser Marker
- California Vibratory Bowl Feeder
- Pannier metal tags
- Southern Stud Capacitive Discharge stud welder
Safety risks and potential for human error
For many years, steel mills have tagged steel products as they come off the caster. The primary reason is traceability. For mills that run a variety of grades, it is essential to know the heat number that produced the steel when determining what end product it will be rolled or processed into.
If the steel is not going directly into the secondary forming process, but will stored temporarily, it’s essential that there is a way to identify the product type later. In a typical tagging process, an operator prints off several tags in a remote room and then carries those to the tagging location. There is a high chance of human error in affixing the tags to the proper billets. If a tag is dropped or left in a pocket, the tag order could be off by one for a considerable period of time.
Additionally, the area where hot steel tagging took place at Nucor was a dangerous location with exposure to high-temperature steel and as well as overhead crane traffic. And tagging was done with a hilti gun that had a significant kickback and repetitive-motion risks. Workers needed to tag 1,200 billets per shift.
This combination of the quality control, reliability and safety risks led Nucor Steel to look for ways to automate the process. Nucor approached Concept Systems because of our experience with integrating unique vision-guided robotic systems in challenging environments. Through work conducted in a variety of industries, we bring a unique perspective on technologies that are proven, but underutilized.
Scanner plus robot plus database
The system we developed for Nucor is designed to operate mostly unattended. Steel billets, blooms or blanks move across the cooling bed from the four-strand caster. Once the group of bars has indexed into position, the robotic system receives a discrete signal from the plant PLC to start the tagging process. Upon receipt of the signal, a heat shield barrier is lowered and a six-axis robot moves to perform a 3D laser scan for the bar positions. The system uses a 3D laser scanner in order to create a point cloud image to fully understand the position of the steel billets on the cooling bed for the purposes of welding position, and to determine if the bar already has a tag.
Concurrently, the system’s SQL database receives production information such as bar number, heat number, strand number and cut length from the mill’s Level 2 system. Once received by the SQL database, it is located a short time later and put into the tag printing queue. Typically, the SQL database is loaded prior to the group of bars being moved into position to allow the burning laser to start burning the tags.
Affixing the tag
Once the 3D scan is performed, the robot moves to a bowl feeder where it picks up a stud. Once the system has brought the stud to the verification station and the stud is verified, the robot then moves to the tag feeder machine where it picks up the tag printed with production information. The robot then takes the tag to the verification station to ensure it has properly been loaded. With the robot end-effector loaded with the stud and tag, it moves back to the steel billet where a weld tip controlled by a pneumatic cylinder extends to create contact with the stud and billet. The system uses a capacitive discharge welding technique to affix the metal tag to the billet end.
After the welding is complete, the robot uses a Cognex Dataman 2D code reader to ensure that the tag adhesion was successful and that the tag is readable. After a successful read, the SQL database is updated with the verification time and date for the tag, and the robot continues to repeat this cycle until all the billets within range have been tagged. When all the tags have been welded, the robot lowers into its home position, the heat wall drives up to protect it from radiant heat, and the PLC is notified that the robot has moved outside of the tagging zone.
The system, which we call BilletID, is made of a variety of off-the-shelf components. Concept Systems insists on using class-leading, off-the-shelf hardware in every project, making it easier for Nucor or any end user to source parts from local distributors that they are already using.
The new process improved safety and increased productivity. Nucor fully embraced the project methodology that we developed, creating a strong partnership focused on making the most reliable automated billet tagging system possible. This partnership between an end user and a system integrator – or any vendor, for that matter – is vital to the success of any project.
A foundation for other improvements
The gains seen from this project aren’t isolated to the tagging process. The project allows additional improvements elsewhere in the mill. For example, the end game of deploying a system to tag billets is to implement a robust track-and-trace system that provides mills with information that they can use to make better business decisions. The automated tagging system, along with a more automated material handling system, would allow mills to map inventory yards and create a snapshot of actual inventory, inventory control reports or other advanced reports.
Traceability of product is not limited to billets or slabs coming off the caster. There are many other areas in a steel mill where tagging product is taking place, such as tagging product for shipping, tagging coils or tagging plate product. Many of these areas could likely benefit from the same or similar proven vision-guided robotics and welding techniques.