A Robot Integration Case Study

Six-Axis Robot Integration Increases Accuracy and Safety

Nucor Steel is a successful company with a rich history as one of the nation’s largest producers of steel products. And yet demand for its products outpaced its ability to accurately inventory the billets used in its manufacturing process.

The Problem: Material Tagging

Steel mills tag steel billets as they come off the caster in order to have information about the steel’s characteristics when it is later used to make specific products. In typical manual tagging processes, the chance of human error in affixing the tags to the proper billets adds potentially serious quality control problems. Additionally, the area where tagging took place at Nucor was a dangerous spot, with workers exposed to hot steel, overhead crane traffic and repetitive-stress tasks.

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.

The Solution: Robot Integration

The robot system we developed for Nucor – BilletID – integrates a 3D laser scanner, a six-axis robot, an SQL database and other components. It is designed to operate mostly unattended, reliably and accurately welding a tag to each billet of steel – and verify that it was done correctly.

Scanner plus robot plus database

The robot integration we performed 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 Results

The new process improved safety and increased productivity. It also improved quality control by removing the risk of human error in accurately tracing the origin of each billet. Additionally, the project was designed so that it can later be integrated into a broader plant-wide track-and-trace system. Return on investment was 24 months.

Billet ID

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.

A foundation for other improvements

The gains seen from this robot integration 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.

Project Details