SolidWorks 2011 Parts Bible - Matt Lombard [277]
bend type:
unit:
material thickness:
radius
k-factor
bend angle
The first three items listed must have colons, and the last three items must not have colons or you will get an error saying that the first improperly formatted item is invalid. It works this way in SolidWorks 2011 SP 0, and because this looks like a bug, it may change in later releases.
The available options for Bend Type are Bend Allowance, Bend Deduction, K-Factor, and Bend Calculation.
The available options for Unit are Inch, Millimeter, Meter, and Centimeter (although it looks like plurals are also allowed, such as inches, but abbreviations such as in are not).
The material thickness can be any variable letter you choose. The radius can also be any variable letter you choose.
The F-Factor can be an equation or a specific value. In the SolidWorks Web Help, the equation shown as a sample is k = 0.65+.5*lg(r/t). The lg in this case is assumed to mean logarithm. After some research, the DIN 6935 standard says that the formula for the k-factor is k = (0.65+log(r/t)/2)/2, which differs from the SolidWorks-provided equation by a /2 term. K is sometimes approximated as 0.447*T. You should note that K-Factors are usually determined experimentally, and it is a good idea for designers not intimately familiar with the process details to work with a manufacturing expert to learn the ropes of calculating sheet-metal flat patterns.
Caution
The equation given in the SolidWorks Web Help for 2011 SP 0 for the K-Factor in the Bend Calculation Table example may be incorrect. It is different from what is referenced by a DIN standard. You should verify all equations independently before using them to create manufacturing data.
The headers shown in Row 8 of the Excel spreadsheet in Figure 21.7 must be spelled as shown without embellishment.
The equations in cells B9 to B11 can use the variables for thickness and radius from the parameters specified in the declarations at the top of the table. It may seem odd, but the equations are just entered as text into the cells of the spreadsheets. These are not active Excel equations. They must be read into SolidWorks and evaluated there, not in Excel. I have not verified these equations for accuracy. As demonstrated with the K-Factor equation, it is best for you to verify the equations yourself or with help before depending on them for production data.
The variable v used on the left side of the equations represents the length of the flattened (developed) bend area. The Web Help (which is the most complete source of information available for this feature as of this writing) refers to a β (beta) variable, which in the equations appears to be replaced with the letter b.
So you have to assume that b stands for bend angle, and the equation for bend angle (180 – a) includes the variable a, which is shown in the Help diagrams as a linear dimension, but which you have to assume is the angle through which the sheet metal must bend. So when a is 45, b is 135, which corresponds to bending the sheet metal 45 degrees, but the bend angle is 135 degrees. Figure 21.8 shows how these variables relate to actual geometry.
FIGURE 21.8
Assigning variables to geometry in Bend Calculation Tables
Notice that the tangent length option can only apply when the bend angle is 90 degrees or less. For more than 90 degrees, you have to use the virtual sharp method.
Also, just be aware that the angles here are measured in degrees. In design tables, you have the option to use degrees or radians.
Auto Relief
When a bend does not go all the way across a part, some sort of feature is needed at the end of the bend. In real manufacturing processes, the metal may just transition smoothly from the bent area to the flat area, but in SolidWorks, the software cannot create that smooth transition, or it could, but it would add significantly to sheet metal rebuild times. For this reason, all bends in SolidWorks sheet metal must terminate cleanly, with some sort of a cut, or as they are called here, a