Jutras Die Casting hired me to help integrate 3 GMF S-420-F robots into die casting workcells. These were high-pressure injection aluminum die-casting machines. The two halves of the die are closed together using a high-pressure linkage, and then molten aluminum is forced into the die at about 2,000 psi in a fraction of a second. Some time after the robotic workcells went into production, the quality control (QC) manager told me the robot was bending the parts.
My reply was that robots don’t bend parts. The robot grips the biscuit, part of the waste aluminum, dunks it into a water tank to cool it, and moves the part to a trim press, where the gates and sprues are sheared off. So I asked the QC manager to show me the bent parts, and he said the robot had stopped bending the parts. My next comment was to alert me as soon as he noticed the problem again.
After each production run, the die halves go to the tool room to be cleaned, and repaired if necessary. When the next production run began, I again was told the robot was bending the parts. I went to the machine operator and asked him to interrupt the automatic cycle, and manually remove a casting for me. I then quenched the casting, and used a band saw to trim the gates and sprues. By using the band saw I was also taking the trim press out of the sequence, in case that was the problem. I then gauged the part, and found the part was undersize. I explained to the QC manager that the robot had not touched these parts.
The reason I called the part undersize is because the die halves get dirty. During production, die lubricant and debris build up on the mating faces. The casting “grows” because the die halves are slightly spaced apart. When the die halves don’t mate properly, the molten aluminum escapes during the injection, and, with enough force, it can hit a ceiling 10 feet above the machine. That is why visitors to die-casting shops are told to never stand opposite the parting line where the two die halves meet.
I explained to the QC manager that the parts would pass inspection after the die had become dirty enough to make the parts thicker. And the next time the die was in the tool room for cleaning, to get the die reworked to make that area deeper to compensate for the changes from heat stresses.
This entry was submitted by Glenn Aitchison and edited by Rob Spiegel.
Glenn Aitchison’s first field service job was in 1987. Since then he has worked in robotics, automotive, as well as industrial automation and machinery. He received his Certificates of Qualification as an Industrial Electrician and as an Industrial Mechanic (Millwright).
Tell us your experience in solving a knotty engineering problem. Send stories to Rob Spiegel for Sherlock Ohms.