Page 33 - MetalForming-Dec-2018-issue

FABRICATION
Choosing the Right
Vacuum Cups
Here’s what they can do in automated pick-and- place operations, and what to consider when selecting them.
BY ROB PITERA
Manufacturing efficiency and reliability reached a higher level when many tasks involved in assembly and workholding processes began to be automated. This refinement has continued to a level where, today, most manufacturers rely on highly technical computer-con- trolled and -monitored systems that utilize robots to perform tasks once completed by human hands.
Many of these computer-controlled and robot-reliant systems would be nothing more than inanimate erector sets if not for what appears at the end of computerized arms: the humble vac- uum cup. Often an afterthought during design of automated workholding sys- tems, vacuum cups play a significant role as the components that actually make contact with the sheet or part to be grasped and passed along.
Rob Pitera is global product develop- ment director of manual clamps and end effectors for Destaco, Auburn Hills, MI; www.destaco.com.
Nonporous materials such as steel, aluminum and hard plastic can be lifted via a lower vacuum flow, but surface conditions such as the presence of rust-inhibitor prior to stamping require research into proper vacuum-cup selection.
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Here we’ll highlight the importance of vacuum cups in manufacturing automation systems, and illustrate the unique operational characteristics and parameters to be considered and sat- isfied in order to choose the ideal cup for a specific task.
Not Suction Cups
That’s right...vacuum cups are not suction cups. Suction cups operate through the use of downward pressure onto an object, which creates a seal as the air under the cup is expelled. Admittedly, this action does create a vacuum that allows the suction cup to stick to an object. But, what differen- tiates the vacuum cup from the suction cup is the vacuum cup’s use of a pneu- matic vacuum generator with a venturi,
which creates compressed air that pro- duces the vacuum.
The vacuum generator draws the air out of the cup, which lowers the air pressure inside of the cup below that of the surrounding atmosphere. The greater atmospheric pressure pushes the object onto the vacuum cup and allows it to be lifted. The lower the pressure inside of the cup (i.e., the higher the vacuum), the greater the lifting force of the vacuum cup. When the object reaches its new position, the air supply to the venturi is cut off and vacuum generation ceases, which allows an object’s release.
Typical vacuum generators allow delivery of about 60 psi of compressed air to the venturi via flexible, polyurethane air lines. Operators must ensure that