Why use sheet metal design?

Ever thought why use sheet metal design?

Sheet metal design bears a very important place in manufacturing industries that you may have noticed that from home appliances to industrial machines, most of them are enclosed in sheet metal.  Have you thought why is it so?

The following are some of the reasons that have convinced designers to use sheet metal for making enclosures.

  • Manufacturing with sheet metal is reasonably cheaper and easier, it is mostly associated with forming processes.
  • Manufacturing can be carried out on small scale, there isn’t any requirement of high-end machining centres. For forming a product out of sheet metal mostly a hydraulic press is employed with different tools to perform a variety of operations.
  • CNC plasma cutting technology has added to the applications of sheet metal due to its high precision and automated cutting of any shape.
  • Sheet metal working saves time due to simpler processes for example in case of solid you need to drill a hole but for sheet metal, you have to punch a hole. For making a slot in a solid, milling is required but in case of sheet metal, CNC plasma cutting, or a simple punch can do the job.
  • The weight of a sheet metal designed product is significantly less, that is why mostly enclosures are made of sheet metal and mostly aluminium sheets are used, due to a higher strength to weight ratio.

Applications of sheet metal are not limited to enclosures they have numerous other high-end applications such as making the aerodynamic profiles of vehicles and planes. Sheet metal is also used in structural applications such as making frames and roofs. Containers are also one of the numerous applications of sheet metal. HVAC systems are also one of the major applications of sheet metal, ducts made of sheet metal are used to supply air into the target space.

After having discussed the advantages of sheet metal manufacturing you might think about the challenges associated with sheet metal design? Sheet metal design requires special consideration because due to the smaller thickness of the sheet, the area to resist shearing is very small which makes the holes in sheet metal very vulnerable to shearing. So, the holes are always designed at a safe distance from the edge of the sheet. Sheet metal designing is mostly associated with bending and forming. When a bend is to be formed near the edge, provision for bend relief is made so that material may not tear near the bend.

Figure 1 Bend Relief
https://dfmpro.geometricglobal.com/files/2018/07/Benefits-of-Bend-relief.png

Figure 1 Bend Relief

https://dfmpro.geometricglobal.com/files/2018/07/Benefits-of-Bend-relief.png

The extent to which a sheet can bend is material dependent, so sheet metal designing is material specific because the bend radius is dependent on both material and sheet thickness. As the spring back effect is material dependent the bend angle is also material dependent it may be greater or less than the desired angle if you change the sheet material. How to overcome this limitation of material specific design?

To account for the difficulty of variation of parameters from design while manufacturing, k-factor is employed in sheet metal design, to determine the bend allowance and bend deductions because it is based on the position of neutral axis on the bend profile, which estimates the amount of stretching and compression occurring due to the bend it may be noticed that neutral axis is shifted towards the inner radius of the bend as the bend radius is decreased.

Figure 2 Parameters affecting k-factor.
http://sheetmetal.me/formulas-and-functions/k-factor/

K-factor is employed in most CAD software to account for allowance of material and thickness of the sheet. Due to abundant use of sheet metal in manufacturing industries almost all the reputed CAD software packages have a separate module to model for sheet metal design. In sheet metal module there are different options for modelling such as to fold or unfold a sheet, bending, creating a base flange, swept flange, edge flange, different types of hems, using the forming tool etc. Modelling in sheet metal module uses an entirely different approach for example if you create a base flange of a sketch containing two perpendicular lines and a sharp corner at joint, software will automatically specify the bend radius and no sharp corner will be seen. So, a parametric model employing k-factor can serve to generalize the sheet metal design. With the parametric model you just have to change the k-factor for new material and leave the rest on software, it changes the associated design parameters.

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