Page 34 - MetalForming-Dec-2018-issue

Fabrication: Automation
the air lines remain free of moisture and debris as any airborne contami- nants can clog the venturi and cause it to malfunction.
Cup Depends on Material Characteristics
Material types generally fall into one of two categories: porous or non- porous. Porous materials include card- board, wood and Styrofoam, all of which generally require higher vacuum flow, but don’t necessarily require high- level vacuum generation in order to be lifted. Nonporous materials such as steel, aluminum and hard plastic can be lifted via a lower vacuum flow.
Surface types also fall into two cat- egories: dry or oily. Most objects to be lifted are dry, but some materials may feature a fine oil on the surface. Sheet- metal treated with rust inhibitors prior to stamping can leave an oily sheen.
As for contour, cup selection depends on whether the material is flat, or has curves or rounded edges. In some cases, where an object con- tains too many curves or undulations, a vacuum cup will not work. Also, objects with too many closely spaced holes are not compatible with vacuum cups.
Designed for Differing Uses
Users traditionally have chosen from two vacuum-cup shapes: round or oval. Round vacuum cups represent the default style, but should an operation require grabbing of a thin rail around a car-door window, for example, a long, oval vacuum cup may be needed. How- ever, bell-shaped vacuum cups have grown in popularity. The main design advantage here: The bell-shaped vac- uum cup’s body adheres easily to con- vex or concave surfaces through a refined internal friction, or tread, pat- tern built to withstand high shear forces.
Vacuum-cup families include two general design types: flat or bellows- style. A bellows-style vacuum cup resembles an accordion, making it more flexible and allowing for grasping of items without consistent shapes, or
A variety of of cup shapes, materials and hardness levels serve a variety of applications.
not well-aligned with the cup. In these instances, though, a higher vacuum flow is needed to remove the larger volume of air inside the vacuum cup. Flat vacuum cups require a lower volume of air to be evacuated, but these are not as pliable as their bellows-style cousins.
Cup Hardness Signifies Possible Applications
A durometer measures
the hardness of a material
—typically polymers, elas-
tomers and rubbers. Most vacuum-cup suppliers test for this by using the Shore A hardness scale, which measures the hardness of flexible molded rubbers. These rubbers range in hardness from very soft and flexible, to medium and somewhat flexible, to hard with almost no flexibility. Higher numbers indicate harder materials. Here are some cup scale numbers and what they mean:
• 30—soft, ideal for use with con- toured panels. A cup with this measure, however, exhibit a shorter lifecycle than a harder cup.
• 45—a medium-hard rubber that effectively seals and adapt to most con- tours, making it ideal for all-around usage. Such a cup generally has a longer operational life than a 30-durometer cup.
• 60—the hardest durometer meas- ure, and a cup with this measure is effective for extremely oily, flat surfaces. It features a longer service life than a 45-durometer cup.
32 MetalForming/December 2018
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Cups with certain characteristics perform more ably when tasked with gripping contoured surfaces.
Some vacuum-cup suppliers color- code their products by durometer for simple identification, maintenance and replacement.
When choosing a durometer for the application, remember that contoured parts, or those with sharp corners or edges, need a softer durometer so that the vacuum cups can easily grip the contours. Flat surfaces are ideal for harder durometers because the vacuum cup has stronger holding properties.
Like the manufacturers of vehicle tires, all vacuum-cup suppliers have created their own unique tread pattern. The design of the tread pattern deter- mines the holding power or grip of the vacuum cup on the surface of a part or sheet. What works in one application may not work in another, especially if a material surface is dry or oily. Some vacuum cups combine their unique treads with a range of durometers to help increase grip strength.