February 2024 Volume 6

AUTOMATION

Types of Gripping Most of the time we use a parallel gripper to pick a work piece. It is straight forward to program the robot using parallel grippers. When you engage the part, it should not “jump” sideways. IF it does, your point is not quite right. Adjust the robot point to prevent this. Another approach is to use an angular gripper. Angular grippers are a bit trickier to teach than a parallel gripper. Angular grippers are readily available and can be set up with options like mentioned above for parallel actuators. Another type of gripper is a push rod tool. This type of gripper is custom designed and has a fixed finger(s) and the other finger(s) are moved with a push rod that is typically powered by an air cylinder. The beauty of a push rod tool is the tool frame can be long to allow the gripping point to reach inside furnaces. Also, the actuator can be mounted away from the heat. Sensors proving open/closed/part in hand can be mounted away from the hot area.

Flexibility All of these grippers have a fixed stroke. It is good practice to keep a bit of stroke available for billet diameter tolerance and finger wear. Therefore, you should never plan on using all of the stated strokes. We suggest you leave at least 3mm of stroke at a minimum when gripping a part. The bigger the stroke the more expensive and massive the gripper. Bigger grippers require a bigger robot to sling them around. So, a large diameter range for billets might require a finger change. Don’t use blind holes for bolted connections as it will be difficult to extract a broken bolt. Try to use through holes so any broken bolts can be driven out easily. We recommend using counterbored socket head cap screws in forge tooling. Avoiding anything that projects outside the fingers will avoid nuisance crashes caused by catching an edge. Due to scale and die spray build up, consider using socket head cap screws. Try to use one size only for a one wrench changeover. You might have to dig scale out of the sockets unless you plug them with putty after swapping fingers. It is imperative the tool center point is repeatable so use ring dowels or pull dowels to key the gripper components together. Make sure any changeover details have poke yoke features to prevent incorrect assembly. This can be handled with simple mechanical design details. If your gripper has sufficient capacity, you can design your fingers to use multiple grip points. For example, if the robot will handle the billet and the work piece after the bust hit, use a smaller set of jaws closer to the gripper body to pick out of the heater, and use the outside set of jaws to handle the larger diameter work piece.

Billet handling push rod tool Programming for a push rod tool requires a bit more attention as the robot has to approach the part with the fixed finger away from the work piece. The robot is then programmed to have the fixed finger “kiss” the work piece then extend the moving finger to clamp up. Releasing the part is the reverse process where you place the workpiece, open the moving fingers, then shift the fixed finger away from the part. Another tool used for forged part handling is the “shark bite” tool. We use these tools to pick on the flash around a part. The idea is the part has to be ejected so we can get a fixed finger under the flash. Then using an angular motion, we rotate the clamping finger(s) into contact with the flash. The lower finger is designed to come in contact with the wall of the forging to present it from “sagging” during motion to the next station.

Dual jaws on the same fingers Sometimes the billet undergoes a large geometry change after the bust station. In this case we use two finger sets on the same gripper. We stacked two complete sets of arms and fingers in a high/low configuration, both powered by the same actuator. Finger set #1 handles the billet to the bust station. Set #2 handles the work piece after the first hit by rotating the wrist 180 degrees. Check how much “daylight” you have in the press carefully.

FIA MAGAZINE | FEBRUARY 2024 33