What is in this article?:
- Robotic Core Setting for Permanent Mold Casting
- Enhancing the Sequence
- Start with good cores
- Defining the EOAT
- Fixtures of quality
- Step by step
Adding to the difficulty of the arrangement, gripping the core was a very specific challenge. The end-of-arm tool (EOAT) or end effector uses a rubber “squash” ring to expand inside a hole in the core, and a parallel gripper to contain the tail section of the core without actually gripping it. The core was specially designed with a hole to allow the tool to grip it.
Robotic sand core setting into a mold has the potential to increase molding productivity and reduce casting scrap.
With the evolution of casting designs, driven by requirements for lower-weight parts and (in automotive applications) a desire to minimize assemblies, there follow designs with thinner walls and smaller openings/cavities. These structures need cores to create those thin wall sections, and in some examples these walls are as thin as 4 mm. In addition, small cores are used to create small openings and cavities.
But, small cores are fragile and prone to crack, and when they do crack the result is a scrap casting. Usually, that scrap is not detected until the finishing stage, or under X-ray analysis, and sometimes it’s not discovered at all.
Scrap reduces profitability, and so for foundries that produce thin-wall castings to achieve competitiveness, the core handling and setting process must be gentle and repeatable.
Obviously, good cores are the starting point. Proper resin levels, adequate definning, and accurate assembly are the foundation of that effort. Transporting these cores and core assemblies to the molding machine without breaking them is the next critical step. The final step is setting the core into the mold.
Setting the core in the mold -- specifically into a permanent mold -- can be a delicate procedure. Done manually, there is potential to cause damage to the core and leave loose sand inside the mold. Further, the machine operator is at risk of burns, crush injuries, back strains, and carpal tunnel syndrome in the wrist thanks to the strain of repetitive awkward motions required to place the core properly. Automating this core setting operation with a six-axis, foundry-hardened robot (which will replicate the movements of an operator), addresses the issues of core damage during setting and sand inclusion, as well as removes the operator from the hazards mentioned above.
Design in Progress
Rimrock Corp. was tasked with setting cores for a high-volume casting involving a horizontally parted permanent mold. The cores were cold-box products and had some thin, 12-mm round sections. The mold had two cavities and was mounted in a tilt-casting machine. There were eight machines on the turntable, which indexed every 40 seconds.
Adding to the difficulty of this arrangement, gripping the core was a very specific challenge. The EOAT — end-of-arm tool, or end effector, which is a device distinct from the robot and selected with specific application to the automation task — was mounted on an ABB IRB 4600 Foundry Plus robot. The tool utilized a rubber “squash” ring to expand inside a hole in the core and a parallel gripper to contain the long tail section of the core without actually gripping it. For this automation effort, the core had been specially designed with a hole to accommodate the EOAT’s grip.
Core setting into permanent mold machines that are mounted on a turntable is especially difficult because the turntable does not always stop in the same location in front of the robot. Depending on the machine’s location with respect to the “ideal” location on the turntable, the location of the each mold in relation to the robot may be different.
The location delta from “perfect” to actual will change whenever a machine is removed and replaced on the turntable, or whenever the mold is removed and replaced in the machine.