Sheet metal design guidelines are followed to design quality sheet metal enclosures. This helps in delivering the product at low cost and faster timelines. All sheet metal design guidelines are very difficult to follow in complex sheet metal parts.
Therefore exceptions can be there for complex sheet metal parts. But testing these exceptions before design release is always a good practice. In this article we will discuss sheet metal design guidelines for manufacturing sheet metal parts using a press bending machine.
Table of Contents
- Sheet Metal Design Guidelines
- Sheet Metal Material Selection
- Minimum inside bend Radius for Sheet Metal Parts
- Minimum Sheet Metal Bend Length Recommendations
- Minimum Hole Diameter Guidelines
- Hole/Slot Distance from Bend Edge
- Center to Center Distance Between two Holes
- Effect of Grain Direction in Sheet Metal Bending
- Bend Relief in Sheet Metal Bend
- Extrude Hole Size and Position Guidelines
- Round Emboss Design Guidelines
- Dimple Feature Design in Sheet Metal Parts
- Louver Feature Design in Sheet Metal
- Round Knockout Design Recommendation
Sheet Metal Design Guidelines
Following points should be considered during the design of sheet metal parts for press bending.
Sheet Metal Material Selection
Sheetmetal are available in standard thickness. Manufacturer provide sheets thickness in gauge. But designers design sheet metal parts considering sheet thickness in mm. Material selection is a very important part of product design. It has impact on sheet metal part design as well. Sheet thickness and material selection can be done in the following ways.
- Simulation Studies
- Past Experience
- Reverse Engineer existing products
- Experimental Studies
Minimum inside bend Radius for Sheet Metal Parts
Recommended inside bend radius for sheet metal parts should be equal to material thickness. But for harder materials ( e.g. CRCA), inside bend radius equal to 0.65 times of sheet thickness is also enough.
Sharp inside bend radius in sheetmetal parts can cause material flow problems in soft material and fracturing in hard material. Which results in localized necking or fracture. Therefore sharp bend radius is not recommended in sheet metal parts.
Bend radius throughout the sheet metal part is kept constant to take the advantage of using the same tool during manufacturing.
Minimum Sheet Metal Bend Length Recommendations
The minimum sheet metal flange bend length is required to avoid cracks in the bending area. It shall be equal to three times of sheet thickness plus bend radius.
Minimum Sheet Metal Flange Bend Length = 3 x Sheet Thickness + Bend Radius
Minimum Hole Diameter Guidelines
Small sized punches are more prone to failure during sheetmetal punching operation. Therefore for softer materials, the recommended minimum hole diameter is equal to sheet thickness. Whereas for harder materials recommended minimum hole diameter is equal to two times of sheet thickness.
Hole/Slot Distance from Bend Edge
Minimum distance between hole/slot edge to bend edge is recommended to avoid metal distortion, deformation and fracturing. Recommended minimum distance between hole /slot edge to bend in sheet metal parts is three times the sheet thickness plus bend radius.
Center to Center Distance Between two Holes
Minimum center to center distance between two holes in sheet metal parts is required to avoid metal distortion, deformation and fracturing.
Recommended Minimum distance between two hole centers in sheet metal design should be equal to sum of hole radius plus two times the sheet thickness.
Recommended Distance = Radius of Hole1 + Radius of Hole2 + Sheet Thickness
Effect of Grain Direction in Sheet Metal Bending
During sheet metal processing ( rolling operation), material grains are arranged in the direction of rolling. When Sheetmetal is bend perpendicular to rolling direction grain rearranges. That has negligible impact on part strength. Whereas bending parallel to rolling direction can lead to cracks because of destruction in grain structure.
Bend Relief in Sheet Metal Bend
Bend relief is provided at the end of the bending edge in sheet metal design to avoid any crack tearing in the corner. Relief height is generally kept greater than two times of sheet thickness plus bend radius.
Extrude Hole Size and Position Guidelines
Creating an extruded hole using a punching process requires extreme pressure/Force. Extruded holes very close to the part edge can lead to sheet metal deformation or tearing. Therefore the minimum distance between the extruded hole to edge if maintained.
Extruded hole to part edge (B) = 3T + D/2
Center of extruded Holes (A) = (5 + Hole Dia + 2T)
Extruded Hole and bend edge (C) = 3T + R + D/2
Round Emboss Design Guidelines
Creating Emboss feature using sheet metal punching requires extreme pressure. Very close emboss to the part edge, can lead to deformation in the sheet metal part.
A – Distance From Emboss To part Edge = 3T + D/2
B- Distance Between Two Emboss = (5 + D)
C- Distance between Emboss and Sheet Metal bend = 3T + R + D/2
Dimple Feature Design in Sheet Metal Parts
Louver Feature Design in Sheet Metal
Minimum distance between louver feature and bending edge is maintained to avoid metal deformation.
(P1) Distance Between Two lowers on Shorter Edge = 5 mm
(P2) Distance Between Two lowers on Longer Edge = 8 mm
Round Knockout Design Recommendation
Minimum distance between knockout feature and bending edge is maintained to avoid metal deformation.
(P1) Distance Between Two knockout = (5 + D) mm
To sum up, sheet metal design guidelines are followed to ensure good quality, reduced cost and robust design. All design guidelines can not be followed in one part. Therefore exceptions can be there for complex features design. We suggest you read this article on electronics enclosure design. This will give you an overview of the complete enclosure design process.
We will keep adding more information on sheet metal design guidelines. Please write to us if you need any support in sheet metal part design.