The pick that works perfectly on a demo box fails in production for predictable reasons: the real product is porous, the surface is textured, or no two parts sit the same way. This guide covers the vacuum side of that problem, from flat suction cups and vacuum pad grippers to bellows cups and foam faced area grippers, and shows how to match the gripping face to flat, porous, and irregular parts.
Why Standard Suction Cups Fail on Difficult Parts
A suction cup only works while its lip seals against the product, and three things break that seal. Porosity lets air flow straight through the product, so cardboard, fabric, and open bags leak faster than a small ejector can evacuate. Texture and curvature leave gaps under a flat lip, so embossed panels and contoured parts never seal in the first place. Flexibility lets the product peel away from the lip under acceleration, which is why thin films and pouches drop mid transfer. None of these are vacuum problems, they are gripping face problems, and each has a dedicated solution.
When Flat Suction Cups Work, and Where They Stop
Flat suction cups are the right answer more often than not: on smooth, rigid, non porous surfaces such as glass, sheet metal, plastic panels, and sealed cartons they grip hard, center the part, and resist shear during fast moves. Their thin profile also keeps the part from deforming, which matters on thin sheet. They stop working exactly where the surface stops cooperating: heavy texture, curvature, or porosity all defeat the flat lip, and adding vacuum level does not bring a broken seal back. The physics behind that limit is covered in our vacuum gripper guide.
Bellows Cups and Vacuum Pads for Uneven Surfaces
When the surface is curved or the pick height varies, bellows cups add compliance: the folded body compresses on contact, follows the contour, and gives the lip a chance to seal before the robot lifts. Single bellows designs stay stable under shear, while multi bellows versions absorb bigger height differences at the cost of some stiffness. A vacuum pad gripper extends the same idea to larger contact areas, spreading grip force across a wide pad so delicate or flexible products are held without local stress. Oval cups cover narrow parts such as profiles and tubes where a round lip would overhang the edge.
Foam Faced Area Grippers for Porous Products
Porous products flip the sizing logic: the winning combination is a sealing face that tolerates leakage plus a vacuum source with high flow. A foam faced area gripper presses a continuous foam mat with many small vacuum openings against the product, so the foam conforms to texture and gaps while the flow keeps pulling despite the leaks. This is how cardboard, sacks, shrink wrapped trays, and mixed size layers get picked reliably. Our Area Surface Gripper (ASG) line covers this category, including the Spider Gripper (SPI) for full layer picking, and the rest of the lineup lives on our EOAT grippers hub.
Managing Leakage in the Vacuum Circuit
Leakage management decides whether a difficult pick is stable or marginal. Size the vacuum ejector for the real leak rate of the product, not the sealed surface ideal. Zone the gripping face with check valves or flow restrictors so openings that miss the product do not drain the grip from the openings that hit it, which is what makes one tool handle mixed sizes. Keep the vacuum generation at the tool to shorten evacuation paths, and route the air through printed internal channels instead of hose bundles so there is less volume to evacuate on every cycle.
Matching the Gripping Face to the Part
| Part | Gripping Face | Why |
|---|---|---|
| Flat, rigid, smooth (glass, sheet, panels) | Flat suction cups | Hard grip, shear resistance, no deformation |
| Curved or height varying rigid parts | Bellows cups | Compliance lets the lip seal on contour |
| Delicate or flexible products | Vacuum pad gripper | Grip force spread over a wide, gentle area |
| Porous or mixed products (cardboard, bags, layers) | Foam faced area gripper | Conforming seal plus high flow tolerance |
| Contoured or oddly arranged parts | Custom printed sealing face | Face shaped to the exact product geometry |
The last row is where we spend most of our time: printing the sealing face, internal air channels, and structure as one part on our SLS systems means the gripping face matches the product exactly instead of approximating it with catalog cups. If the choice is between gripping technologies rather than vacuum faces, our vacuum vs mechanical vs magnetic comparison covers that decision.
Difficult Part Questions
What are flat suction cups used for?
Flat suction cups grip smooth, rigid, non porous surfaces such as glass, sheet metal, plastic panels, and sealed cartons. Their thin profile grips hard, resists shear during fast robot moves, and avoids deforming thin parts.
Why do suction cups fail on cardboard?
Cardboard is porous, so air leaks through the product faster than a standard ejector evacuates it, and the seal never forms. The fix is a foam faced area gripper combined with a high flow vacuum source rather than a deeper vacuum level.
What is a vacuum pad gripper?
A vacuum pad gripper holds the product with a large, compliant pad instead of individual cups, spreading grip force across a wide area. It suits delicate, flexible, or lightly textured products that concentrated cup lips would mark or drop.
How do you pick irregular shaped parts with vacuum?
Either add compliance with bellows cups so the lips follow the contour, or shape the sealing face to the part itself. 3D printed grippers take the second route, printing a contoured face with internal vacuum channels that matches the exact product geometry.
Fighting a Part That Will Not Seal?
Send us the product, the surface, and the cycle time, our team will match the gripping face, size the vacuum flow, and design the tooling around your part.
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