Bend Tables

Bend table allow you to specify the bend allowance or bend deduction values for a sheet metal part.

Fig. 1. (Solidworks Window)

Types of Bend Tables

The bend table also contains values for bend radius, bend angle and part thickness. There are two types of bend table you can use:

1. Text files.
2. Microsoft Excel spreadsheet.

Solidworks recommend you use the Microsoft Excel spreadsheet unless you have legacy Bend tables from Solidworks 2000 or earlier. It is important to note that if you create a bend table as a text file, you will need to provide that bent table text file when you share the sheet metal part file. Whereas if you create an excel spreadsheet, it is embedded into a solid worksheet metal part file while you can create a new bend table by going to insert sheet metal, then table, then new. It is recommended that you rename and edit an existing bend table provided by Solidworks.

                                                                        Fig. 2.

 To find these bend tables, you need to go to the C drive, program files, Solidworks file/ Solidworks Corp (corporation), language, English and then sheet metal bend tables. Inside of the sheet metal bend table folder, we have two subfolders: bend allowance and bend deduction and five sample tables.

                                                                        Fig. 3.

The last one is a text file. Even though it’s a BTL extension which is renamed by Solidworks, this is still a text file. Open it, double click on a sample text file and notice that this is nothing more than a regular text files that you can go through, edit and change the values as needed.

                                                                        Fig. 4.

Tip: anytime you modify these files, first make a copy of the original file. That way you keep the original sample files intact.   

Take a look at one of the four Microsoft Excel spreadsheets. Open a metric base bend table. After opening the file, you will see the values are not filled in. this is for you to complete.

                                                                        Fig. 5.

 If you want to see a filled table, go into the bend allowance folder and notice there are four more sample tables which are completed. Fig. 6. Open the bend allowance you will see the values are taken from the Machinery’s hand book, 26^th Edition. Fig.7

                                                                        Fig. 6.

                                                                        Fig. 7.

Application of Bend Table in Sheet Metal Part

Now we will see how to apply and modify bend table for our sheet metal part. Go over to your “feature” manager tree, expand the sheet metal feature, right mouse click on sheet metal one and go to edit feature. You will notice the bend allowance is grayed out. This is because in case you have a multi body sheet metal part and you want to make changes in a single body sheet. But this is not the case we have here because we do not have a multi body part. Simply go up to the sheet metal feature, click on the edit feature and there you have the bend allowance which is not grayed out.

                                                                        Fig. 8.

Click on the drag down list and select bend table, select browse button. Scroll down and expand the sheet metal bend table select bend allowance and click okay. Come back to the drag down list and select table1-bend allowance. You see the bend table which is just selected is now applied to the sheet metal part. Go back and edit the sheet metal feature and look at the other type of bend allowances.

                                                                        Fig. 9.

K-Factor

K-factor is a ratio that represents the location of the neutral sheet with respect to the thickness of the sheet metal part. When you select k-factor as the bend allowance, you can specify a k-factor bend table.

Solidworks also comes with the k-factor bend table in a Microsoft Excel format in the same directory you were just in and you can see a K-factor bend table as a Microsoft Excel spread sheet.

                                                                        Fig. 10.

The next two bend allowance options are bend allowance and bend deduction. Both of these allow you to input your own values to determine the flat length of a sheet metal part to give you the desired dimensions of the bend part. These two options are generally used by individuals experienced in sheet metal design. The last option is bend calculation where you calculate and develop length of the sheet metal part using bend calculation tables which define different angular ranges. Assign equations to those angular ranges and calculate the developed part. This is another option that is used by individuals experienced in sheet metal design.

Unless you are well-versed in a sheet metal bend allowances, you will find that you use bend table or K-factor over the other three options. If you like to learn more about these bend allowances, keep in mind that Solidworks has a great help feature and there is a lot of information regarding bend allowances.

Difference between K-factor, Bend Allowance and Bend Deduction

A question is asked about the difference between K-factor, bend allowance and bend deduction. When sheet metal is put through the process of bending, some of the material is bent and some of the material is compressed.

                                                                        Fig. 11.

If you have a look in this bend region, we can see that the red material is compressed while the blue material is stretched which inherently means that when you bend part, it actually gets longer because more part is stretched. Inside this bend region, you will see the arc. This arc is neither compressed nor stretched. It retains the same length. It was also placed on what we call the mutual axis that runs through the entire part. Now the location and length of this arc can be calculated by Solidworks by using k-factor, bend allowance or bent deduction. These are the different approaches depending on your experience machine that you can use inside your part.

 K-factor represents the location of this mutual axis from the inside of the spin with respect to the thickness of the overall part. Now the only true way of knowing the distance R from the inside bend to the neutral axis is to take a piece of material, bend it and then measure the bent material. Now in Solidworks, it actually calculates the distance of where this mutual axis should be while still retaining the leg links of your part by using the constant k-factor value that you give. Now the value must be greater than or equal to zero and it should be less than or equal to 1.

K-factor = dist/Thickness

Bend allowance is defined as the material that you add to the bend region. It will increase the overall flat pattern length and there is no limit to what you can do with actual allowance. There is a formula you can use to create a chart. You will need to know the angle, bend radius, k-factor and thickness. The chart can be implemented into Solidworks so that the calculations can be done.

                                                                        Fig. 12.

Max Bend Allowance = User Discretion            

BA = pi/180 * (bend radius + K-factor * Thickness)

Flat pattern length = BA1 + BA2 = BA

Bend deduction is defined as the material that you remove from the bend region in order to avoid the flat pattern. The formula when working with bend deduction is:

 Max Bend Deduction < 2* outside setback

Flat pattern length = BD1+BD2-BD

                                                                        Fig. 13.

Conclusion

After reading this article, I hope you have understood the difference between text file and Microsoft Excel spreadsheet, where to find the files and how to modify them, the application of bend table in our sheet metal part, role of K-factor, bend allowance and bend deduction. This will conclude our lesson on bend tables.