Two cups with the same nominal diameter can behave very differently. Lip profile, internal support, bellows count, cup depth, material, and mounting determine how the cup contacts the part, how quickly it evacuates, how it resists lateral load, and whether it leaves a mark. Geometry should be chosen from the workpiece outward.
Describe the surface before choosing a cup
Record whether the contact area is flat, convex, concave, narrow, textured, porous, oily, dusty, hot, cold, flexible, or easily marked. Check variation across normal production, not only the clean sample used during design. Surface contamination and mold texture can matter as much as nominal shape.
Identify holes, seams, labels, embossed features, edges, and regions that cannot be touched. The usable contact area may be much smaller than the part drawing suggests. If formats change, overlay the cup layout on every format and check open cells and load distribution.
Flat cups for speed and stability
Flat cups have a small internal volume and can evacuate quickly. They are a strong starting point for smooth sheet, panels, glass, rigid packaging, and other surfaces that present a stable sealing plane. Internal supports can limit part deformation and help the cup resist collapse at deeper vacuum.
A flat cup has limited ability to absorb height error. Tooling alignment, individual compliance, or level compensation may be needed when the part or fixture varies. A lip that is too stiff may not seal; one that is too soft may roll under lateral load or fast acceleration.
Bellows cups for compliance
Bellows allow the cup body to compress and change angle as contact is made. They are useful on curved parts, uneven pickup planes, flexible packaging, and applications that need a short lifting motion after sealing. More folds generally add compliance and internal volume.
That flexibility has tradeoffs. A tall bellows can be less stable under lateral acceleration, may require longer evacuation time, and can introduce more movement into precise placement. Check the compressed and extended height, return behavior, spring force, and interference through the full cycle.
Oval and narrow-format cups
Oval cups provide area where a round cup would cross an edge or exceed the available width. They suit profiles, tubes, narrow cartons, elongated sheet regions, and parts with long uninterrupted sealing zones. Orientation matters: align the long axis with the usable surface and review lateral loads in both directions.
Foam and area sealing
Foam seals conform to rough, uneven, or structured surfaces. They are often paired with area tooling or high-flow generation because the seal admits more air than a molded lip on smooth material. Foam density, thickness, cell structure, compression, wear, and contamination all affect leakage.
Do not solve a severe leak only by increasing generator size. Improve contact, shorten the flow path, zone unused areas, reduce open cells, and choose an appropriate sealing element first. Then size flow for the remaining leakage.
Material is part of geometry
Compound hardness and elasticity change how the same geometry seals and carries shear. Temperature, oil, cleaning agents, abrasion, food-contact requirements, static control, and marking restrictions may eliminate an otherwise suitable cup. Verify the exact compound rather than assuming a color identifies material.
A useful comparison test
Compare candidate cups at the same working vacuum, tooling layout, motion profile, and surface condition. Measure evacuation time, stable vacuum, leakage, displacement, pickup reliability, lateral stability, release time, marking, and wear. Include worst-case part tolerance and contamination. The best geometry is the one that maintains margin across the allowed process, not the one that looks strongest on a clean static sample.
Use these principles for initial sizing and system review. Confirm final product specifications, interfaces, settings, and safety behavior for the actual workpiece and machine.