Sheet metal bending deduction, also known as the bend allowance, is a parameter setting in Solidworks. It is an algorithm used in sheet metal fabrication workshops for calculating the bending coefficient. Let's first take a look at the calculation formula in Solidworks.
Lt = A + B - BD
Where:
Lt is the total flat length.
A and B are as shown in the diagram.
BD is the bending deduction value.
In Solidworks, the bending deduction is only used for calculating 90-degree sheet metal bends. However, it can also be used for non-90-degree sheet metal flat pattern calculations, but the bending deduction value for non-90-degree bends needs to be determined using a bending coefficient table. Each manufacturer may have a different bending coefficient table, and there can be variations in accuracy. Non-90-degree bends are not commonly used in some sheet metal fabrication shops.
Today, I will mainly share the calculation methods I am familiar with for the 90-degree bending deduction.
There are approximately four algorithms for calculating the bending deduction:
1. 1.7 times the material thickness
Sheet metal fabrication shops generally use 1.7 times the material thickness as the bending deduction. This method is the simplest calculation method for sheet metal flat pattern development but is not very accurate. It can be used directly if precision requirements are not high in sheet metal fabrication. Different materials may have different factors; for example, aluminum sheets can be calculated using 1.6 times the material thickness, and stainless steel sheets can use 1.8 times the material thickness.
2. Bending deduction = 2 times the material thickness + 1/3 of the material thickness
This bending deduction calculation formula is a rough method developed through long-term experience in sheet metal fabrication. It is also a rough calculation method. The theoretical explanation for this formula is that the flat pattern of the sheet metal is calculated as the sum of the A length, B length, 2 times the material thickness, and 1/3 of the material thickness as an extension factor. The first part calculates the shortest straight-line length, and then the extension factor is added, assuming that the sheet metal will elongate during the bending process.
3. Bending deduction = 2 times the material thickness - (0.72t - 0.075V - 0.01)
This formula is derived from a calculation method mentioned in an online magazine article. Its characteristic is that it considers the influence of the width of the bending lower die on the bending deduction. The experimental data was obtained from carbon steel plate tests, and the accuracy for other materials is not clear. I have used it for calculating the flat pattern of aluminum sheets bent with a lower die width of 4 times the material thickness, and the values obtained were quite accurate. It is very accurate for calculating the flat pattern of carbon steel plates.
Explanation:
t is the actual thickness of the sheet metal, not the nominal thickness. The first two methods mentioned above are rough calculations and do not have strict thickness requirements. This formula requires the actual thickness measured with a caliper.
V is the width of the lower die slot. Generally, a width of 6-8 times the material thickness is used for the slot width. Use the actual width for calculation, for example, for a width of 1.5, use a lower die with a width of 10 for bending.
4. There are many other calculation methods for the bending deduction, including formulas based on the neutral layer theory. However, these formulas are not practical for actual sheet metal fabrication, so they are not discussed here. The three methods mentioned above are the most practical and simplest for sheet metal bending deduction or flat pattern calculations in sheet metal fabrication shops.
