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In a sheet-metal design, specifying hole sizes, locations, and their alignment is critical. You need to plan hole positioning correctly the first time. Understanding hole positioning in sheet metal fabrication can save you time and money and help your manufacturer deliver the results you're after

What Happens When a Hole Is Designed Improperly?

Holes are designed to attach the part to another component using a rivet or other fastener. 

Wrongly designed hole causes surrounding metal to tear or crack, compromising the structural integrity of the product. This effect worsens as more force is applied. Depending on the application, this cracking can decrease the part's lifespan or even make it unusable.

Hole Diameters

Hole diameters should be greater than the thickness of the sheet metal. This ensures efficient punching and smooth edges. 

Hole diameters less than the sheet thickness result in higher punch loading, longer burnish in the holes, and excessive burr. 

Hole Spacing

Spacing between holes or between a hole and a boundary should be at least twice the sheet thickness. Distance between holes ensures strength of the metal and prevents holes from deforming during the bending or forming processes. 

Without adequate clearance between the holes, the holes or sheet deforms.

Hole When Bending

If the hole is near a bend, make sure the hole is outside of the bend radius. Spaces between pierced holes and bends should accommodate the bend radius (H) and be far enough from the bend. The preferred distance between holes and a bend is 1.5 times the sheet thickness plus the bend radius (1.5T+H).

When a hole is placed too close to a future bend in the metal, it can become warped during bending.

Bending in Sheet Metal Fabrication 

Bending is also known as press braking, flanging, die bending, folding and edging. This method is used to form a material to an angular shape and is done through the application of force on a workpiece. 

Bend Relief

Bend relief refers to an indentation that designers should make on sheet metal designs so that the bending process is simple during manufacturing.

The bend relief’s depth should be equal to or greater than the inside radius of the bend.

If bending relief is not provided the sheet could go under cracking and tearing.

Bending Radius

Minimum bend radii requirements can vary depending on applications and material. For aerospace and space applications, the values may be higher. 

It is recommended that minimum inner bend radius should be at least 1 times material thickness.

When the radius is less than recommended, this can cause material flow problems in soft material and fracturing in hard material. Localized necking or fracture may also occur in such cases.

Ninad Kashid

Nov 9, 2022


Design Guidelines for Sheet Metal Fabrication

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