Handling sheet metal and metal plates on a production line is not a lifting task that can be solved according to load weight alone. The material, thickness, surface condition, perforations, geometry, center of gravity and required movements directly affect gripper selection.
A flat and clean sheet may be gripped safely with vacuum, while the same method may be unsuitable for a perforated, oily, rough or formed sheet. A ferromagnetic steel plate may be handled with a magnetic gripper, but aluminum and many grades of stainless steel are not suitable for standard magnetic gripping.
Some applications require a mechanical gripper that holds the product by its edge, hole or geometric form. Operations involving rotation, precise placement or multiple product variants may also require a custom gripper that combines two gripping methods.
The sheet metal handling manipulator and its gripper must therefore be selected by evaluating the actual product characteristics and the complete operation together.
Can the Same Gripper Be Used for Every Sheet Metal Part?
No. Two sheet metal parts with the same weight and external dimensions may require completely different gripping solutions because of differences in their surfaces and geometries.
The main information affecting gripper selection includes:
- Material and grade
- Minimum and maximum weight
- Thickness and flexibility
- Flat, curved or formed geometry
- Position of holes and openings
- Oil, dust, scale, rust or coating on the surface
- Painted, galvanized or sensitive surfaces
- Product temperature
- Sharp or burred edges
- Center of gravity
- Single-sheet pick-up requirement
- Horizontal or vertical handling
- Rotation and turning requirements
- Positioning accuracy at the machine or fixture
A gripper is not merely an attachment that lifts the product. It is the system component that must hold the product safely, securely and in balance throughout the entire movement from the pick-up point to the release point.
When Can a Vacuum Gripper Be Used?
Vacuum grippers may be considered for sheet metal and metal plates with flat surfaces that allow the vacuum pads to establish sufficient and airtight contact.
A vacuum system generates holding force by creating a pressure differential between the pad and the product surface. The theoretical holding force can be expressed in simplified form as:
Vacuum holding force = Pressure differential × Effective contact area
Actual handling capacity cannot be determined from this theoretical force alone. The following factors must also be considered:
- Surface leakage
- Vacuum pad type, diameter and material
- Distribution of the pads across the product
- Sheet flexibility
- Lifting and handling direction
- Acceleration and deceleration forces
- Rotation movements
- Position of the center of gravity relative to the pads
- Required safety factor
- System behavior during vacuum loss
Vacuum grippers can provide fast and controlled gripping for flat, clean, airtight sheets with sufficient contact area. They may also allow painted or visually sensitive surfaces to be handled without mechanical clamping.
However, the possibility of pad marks, coating damage or surface slipping must be checked on the actual product. Vacuum generation, pad selection, monitoring and safety functions must be evaluated according to the real application conditions.
For more information, see Vacuum Handling Manipulator Systems.
Can Perforated Sheet Metal Be Handled with Vacuum?
The suitability of perforated sheet metal for vacuum handling depends on whether sufficient uninterrupted surface area is available for the pads.
If a vacuum pad overlaps a hole, continuous air leakage may occur. This may prevent the required vacuum level from being reached or reduce the available holding force during handling.
The following options may be evaluated for perforated sheets:
- Positioning pads on non-perforated areas
- Using smaller-diameter pads
- Designing a product-specific pad arrangement
- Creating independent vacuum zones
- Selecting a vacuum generation method suitable for leakage
- Combining vacuum gripping with mechanical support
- Changing to a magnetic or mechanical gripper
If the perforation pattern varies between products, a single pad arrangement should not be assumed to suit the entire product family. The available contact points must be checked separately for every product variant.
Can Vacuum Be Used on Oily Sheet Metal?
Oil on the sheet surface may affect vacuum sealing, pad material and the tendency of the product to slide across the pads.
A sufficient vacuum level may still be achieved on some oily surfaces, but the sheet may slip under lateral forces or during rotation. Oil can also affect pad service life and maintenance intervals.
The following conditions should be checked:
- Oil type and viscosity
- Amount of oil on the surface
- Compatibility between the pad material and the oil
- Handling and rotation direction
- Lateral forces generated during movement
- Pad cleaning and maintenance intervals
- Product slipping behavior on the pads
Vacuum gripping on oily sheet metal must be tested under actual product and process conditions. Mechanical support that limits slipping or a different gripping method may be required.
What Risks Are Associated with Thin Sheet Metal?
Thin sheets may bend, ripple or develop local deformation around the vacuum pad contact areas during lifting.
Using too few pads or placing them too far apart may cause the sheet to bend under its own weight. Excessive localized vacuum force may also leave marks or deform thin, sensitive surfaces.
The following points must be checked:
- Number and distribution of vacuum pads
- Unsupported span of the sheet
- Amount of deflection during lifting
- Pad diameter and contact pressure
- Handling speed and rotation movement
- Risk of picking up more than one sheet
If oil or process residue is present between stacked sheets, the sheet beneath the top one may also be lifted. Depending on the application, sheet separators, double-sheet sensors, thickness monitoring or product-presence detection may be required.
When Can a Magnetic Gripper Be Used?
Magnetic grippers may be considered for ferromagnetic products with suitable surface and contact conditions.
The fact that a product is made of metal does not automatically make it suitable for magnetic gripping. Magnetic holding performance is affected by:
- Magnetic properties of the material
- Sheet thickness
- Available contact area
- Surface curvature
- Paint, coating, scale, rust or contamination
- Air gap between the gripper and the product
- Holes and channels
- Handling and rotation direction
- Risk of picking up multiple sheets
The nominal magnetic force stated in a catalogue is generally based on ideal contact conditions. Coatings, air gaps, surface contamination, insufficient sheet thickness and material differences may significantly reduce the actual holding force.
How Should Power Loss Be Evaluated in Magnetic Systems?
Behavior during power loss depends on the magnetic technology being used:
- Electromagnets depend on continuous electrical power to maintain their holding force. A battery, uninterruptible power supply, mechanical safety device or another application-specific safety solution may be required to protect the load during power loss.
- Permanent magnets do not depend on continuous electrical power to maintain their holding force. However, activation, deactivation and controlled release must be verified according to the operating mechanism.
- Electropermanent magnets use an electrical pulse to change their magnetic state and may not require continuous power while holding the load. The magnetic state, controlled release and control-system failure scenarios must still be monitored and evaluated.
These technologies must not be treated as if they have the same behavior during power loss. The technical characteristics, control system and safety functions of the selected equipment must be verified through the application risk assessment.
Can Stainless Steel and Aluminum Be Handled with a Magnetic Gripper?
Not every grade of stainless steel is magnetic. Its magnetic behavior depends on alloy composition and manufacturing processes. Aluminum is not ferromagnetic and cannot be gripped with a standard magnetic gripper.
The following solutions may be considered for non-magnetic stainless steel and aluminum sheets:
- Vacuum gripping
- Mechanical edge gripping
- Gripping through a hole or geometric feature
- Bottom support
- Combined vacuum and mechanical support
- A product-specific combination gripper
A magnetic gripper should not be selected solely because a product is described as “metal” or “stainless steel.” The actual material grade and magnetic suitability must first be verified.
How Can Multiple-Sheet Pick-Up Be Prevented?
When thin sheets are stacked, a magnetic field, vacuum effect or oil between the sheets may cause more than one sheet to be lifted.
This can:
- Increase the total handled load
- Disrupt the machine-feeding process
- Cause an incorrect part to be placed in the fixture
- Allow sheets to separate during movement
- Create quality and cycle-time problems
Depending on the application, sheet separators, double-sheet sensors, thickness monitoring, controlled magnetic force or product-presence detection may be used. The requirement to pick up a single sheet must be defined clearly at the beginning of the project.
When Should a Mechanical Gripper Be Used?
A mechanical gripper may be used when vacuum or magnetic gripping cannot provide sufficient reliability.
Common mechanical gripping methods include:
- Edge clamping
- Gripping through a hole
- Holding a channel or geometric feature
- Pin centering
- Bottom support
- Hook gripping
- Jaw clamping
- Positive, form-based gripping
Mechanical grippers can provide advantages for perforated, oily, rough, non-magnetic or formed sheet metal parts. They can also create a controlled solution for products that must be rotated or held in an accurate position.
The gripping force must be determined carefully. Excessive force may crush a thin sheet or leave marks on its surface, while insufficient force may create slipping or dropping risks.
Grippers that depend entirely on friction require particular attention on oily surfaces. Where possible, positive gripping that uses the product geometry or a bottom-support solution may be preferable.
For more information about product-specific gripping methods, see Why Is Custom Gripper Design Important When Choosing a Manipulator?
How Should Formed and Pressed Sheet Metal Parts Be Gripped?
Pressed or three-dimensionally formed sheet metal parts may not provide sufficient flat area for vacuum pads.
The following product characteristics should be evaluated:
- Changing surface angles and curves
- Ribs, holes and channels
- Sharp edges
- Unbalanced center of gravity
- Manufacturing tolerances and springback
- Actual product position in the container or on the conveyor
- Nested part geometry
A gripper should not be designed only according to nominal CAD geometry. Actual production tolerances, surface condition and product position at the pick-up point must also be considered.
Depending on the application, a mechanical, vacuum, magnetic or combination gripper may be used. The final solution must be verified through gripping and movement tests using the actual product sample.
When Is a Combination Gripper Required?
A single gripping method may not be sufficient for every sheet metal application.
For example, vacuum may lift the product while mechanical support limits sliding during rotation. Magnetic gripping may also be combined with mechanical stops that maintain product position.
A combination gripper may be considered when the application requires:
- Additional support against vacuum loss
- Limited sliding during rotation
- Control of an unbalanced center of gravity
- Handling multiple product variants
- Precise machine or fixture loading
- Support for thin sheets at multiple points
- Horizontal-to-vertical rotation
The weight of the combination gripper must be included in the manipulator capacity calculation. The total weight and moment effects of the product, gripper, rotation mechanism and all moving equipment must be calculated together.
How Do Handling and Rotation Direction Affect Selection?
When a sheet is handled horizontally, the gripping elements generally work against the product weight. During vertical handling, sliding and lateral forces may become more critical.
During horizontal-to-vertical or vertical-to-horizontal rotation, the load direction changes continuously. Vacuum pads, magnetic contact surfaces and mechanical supports must be checked for the most critical position throughout the complete rotation.
The following movement information should be provided at the beginning of the project:
- Initial and final product orientation
- Rotation angle and axis
- Manual or pneumatic rotation requirement
- Need to stop at an intermediate position
- Required positioning accuracy
- Side from which the operator will control the product
- Potential collision zones during movement
A gripper selected only according to the product’s initial position may become insufficient during rotation.
Loading Sheet Metal into Machines and Press Lines
Sheet metal and formed metal parts may be loaded into laser-cutting machines, presses, CNC machines, welding cells, bending machines, assembly stations or quality-control fixtures.
In a machine-feeding application, the manipulator must do more than lift the part. It must hold the product in the correct orientation, approach the machine in a controlled way and place the part at the required position and accuracy.
The following site information is required:
- Machine access opening
- Pick-up and release heights
- Minimum approach distance
- Final position of the product inside the machine
- Fixture and placement tolerances
- Operator’s field of view
- Machine doors and moving components
- Collision zones
- Required cycle time
- Return movement of the empty gripper
The gripper dimensions and manipulator working envelope must be checked together with the machine layout in three dimensions.
For detailed machine-loading criteria, see How to Choose a Manipulator for Machine Feeding and Loading?
How Is Safety Ensured in Sheet Metal Handling Systems?
Safety functions must be selected according to the gripper technology and the actual operational risks.
Functions that may be considered for vacuum grippers include:
- Preventing lifting until sufficient vacuum is achieved
- Monitoring vacuum level and product presence
- Protecting the load during vacuum loss
- Independent vacuum zones
- Controlled release
- Audible or visual warnings
Functions that may be considered for magnetic grippers include:
- Confirmation of magnet status
- Detection of insufficient contact
- Single-sheet or double-sheet monitoring
- Controlled release
- Technology-specific safe behavior during power loss
Functions that may be considered for mechanical grippers include:
- Open and closed position monitoring
- Confirmation of gripping status
- Mechanical locking
- Preventing release before the product reaches a safe release position
- Protection of pinch and trapping areas
Normal operation, product changes, power loss, sensor failure, maintenance and foreseeable misuse must all be considered in the project risk assessment.
How Should Operator Ergonomics Be Evaluated?
Wide sheet metal parts may be difficult for an operator to control even when their weight is relatively low. Holding the product away from the body, controlling sharp edges and aligning it with a machine can increase strain on the back, shoulders, arms and wrists.
With a correctly designed manipulator and gripper system, the operator should:
- Apply no physical effort to lift the product
- Avoid direct intervention around sharp edges
- Control the gripper with a natural hand position
- Maintain clear visibility of the release point
- Avoid excessive effort during rotation
- Remain outside hazardous positions between the product and machine
- Guide the balanced load instead of physically carrying it
If the operator must stop the sheet from swinging by hand or continuously correct an unbalanced gripper, the system is not sufficiently ergonomic.
How Is the Correct Gripper Determined?
The following preliminary matching guide may be used during the first engineering evaluation:
- Flat, clean and airtight surface: Vacuum gripper
- Ferromagnetic steel sheet with sufficient contact area: Magnetic gripper
- Perforated or heavily formed sheet: Mechanical or custom gripper
- Non-magnetic metal sheet: Vacuum or mechanical gripper
- Oily surface: Vacuum, magnetic or mechanical solution verified through sample testing
- Thin and flexible sheet: Distributed support and sheet-separation control
- Sensitive or painted surface: Non-marking contact elements
- Part requiring rotation or accurate placement: Rigidly controlled or combination gripper
- Variable product family: Adjustable or interchangeable gripper
This guide is intended only for preliminary selection. The final decision must be verified through product data, site layout, engineering calculations and tests using actual product samples.
For a general assessment of large panels and sheet products, see How to Choose a Panel Handling Manipulator?
The PM Manipulators Approach
At PM Manipulators, sheet metal and metal plate handling applications are not evaluated according to product weight alone.
The product material, thickness, surface condition, perforations, geometry, center of gravity, gripping points, handling direction, rotation requirement, working area and machine layout are analyzed together.
Panelful may be considered for large, panel-shaped products, while Magnetful may be considered for ferromagnetic sheet metal and metal parts. The final manipulator model and gripper structure are determined according to the actual application conditions.
After the vacuum, magnetic, mechanical or combination gripper has been selected, its safety functions, control position, installation type and manipulator arm structure are designed as parts of the same handling system.
The objective is not simply to lift the sheet. The objective is to create a system that grips the product safely, reduces the risk of surface damage, lowers physical strain on the operator and positions the sheet accurately at the target point.
Share the sheet metal drawing, material information, weight, thickness, surface condition, pick-up and release points and an operation video so that we can evaluate the appropriate gripper and manipulator configuration together.
Conclusion
A sheet metal handling gripper cannot be selected solely according to product weight or the fact that the material is metallic.
A vacuum gripper may be considered for flat and airtight surfaces. A magnetic gripper may be suitable for ferromagnetic steel with sufficient contact area. Mechanical or combination grippers may be required for perforated, formed or difficult-to-grip products.
The final selection must consider the material, surface condition, geometry, sheet thickness, center of gravity, handling direction, single-sheet pick-up requirement, safety functions, machine layout and operator ergonomics together.