Saturday, December 5, 2015

Sheet Metal Basics | Sheet metal Interview Questions for freshers | Sheet metal Design

How is sheet metal components formed?

Sheet metal components are generally metal formed through various forming processes majorly involving Bending, deep drawing, Roll forming, Stamping, Punching, Piercing etc. The sheet metals are initially received as Rolls and cut into plain blankets and then formed into desired shape using above mentioned processes mainly bending and stamping.

What are precision sheet metal components?

Sheet metal components that are made using high precision dies with sheet of close tolerance in machines with high stability are generally called as precision sheet metal components. The precision of the component has to be decided based on the purpose that the components is going to serve,

What is the standard bending radius followed during sheet metal fabrication?

Sheet metal enclosures are usually fabricated by 'cold forming' technique, where the metal is clamped and bent in machines called 'press brakes'. Because of this, metal typically cannot be formed into a true 90 degree corner. Instead, the corners are curved or filleted in practical which is technically denoted as bend radius,

Different degrees of curvature can be achieved and Note that bend radius is specified as the radius of the INSIDE surface of the bend

What common methods of Welding, would be associated with sheet metal fabrication?

Depending on your sheet metal design, you may desire spot-welded enclosures or fully seam-welded enclosures. With many enclosure designs, such as our standard U-shape (clam shell), no welding is required. One section of the enclosure contains small flanges with self-clinching nuts and the other section of the enclosure is fastened using mechanical fasteners such as machine screws or sheet metal screws.

Spot welding would be used in cases where disassembly is not required. Fully seam welded edges may also be a requirement, especially if the application requires a more tightly sealed enclosure.

What is meant by Bending allowance in sheet metal fabrication ? How to calculation bending allowance?

Bend allowance comes from the fact that when sheet metal is bent, the inside surface of the bend is compressed and the outer surface of the bend is stretched (elongated)//.

So, when we want a 90 degree bend in which one panel side has a length of A, and the other panel side has a length of B, the total length of the flat piece will NOT be A+B, but rather equals A+B plus a bend allowance or A+B minus a bend deduction(depending on how we measure A and B).

So bend allowance is a term which describes how much material is needed between two panels to accommodate a given bend. Determining bend allowance is commonly referred to as “bend development” or simply “development”.

What is K-factor in sheet metal fabrication?

As explained in bend allowance, when sheet metal is bent, the inside surface of the bend is compressed and the outer surface is stretched, but somewhere within the thickness of the metal lies its Neutral Axis, which is a line in the metal that is neither compressed nor stretched.

The location of the neutral line varies depending on
  •  the material itself, 
  • the radius of the bend,
  • the ambient temperature, 
  • direction of the material grain, 
  • and the method by which it is being bent, etc. 
The location of this neutral line is referred to as the K-factor.

Many CAD programs also work out bend allowances automatically by using K-factor calculations.

K-factor is a ratio that represents the location of the neutral line with respect to the thickness of the sheet metal.

What are all the surface finish processes used for sheet metal fabrication?

Powder coating is a commonly used surface finishing technique. It is a type of coating that is applied as a free-flowing, dry powder.

What is the necessity of surface treatment process in Sheet metal components ?

Surface treatment is necessary for sheet metal parts in-order to prevent corrosion , protect the part form mechanical damage, protect the component due to temperature changes, to provide additional strength, durability, to improve aesthetic appearance, to protect against rust.
Zinc plating, Nickel plating, Anodizing, Tinning, Dip coating and powder coating are some of the familiar surface treatment processes followed for sheet metal components.

Mention few surface coating process form sheet metal brackets

  • Phosphate coating ZP12,,
  • CED Black Coating ,
  • CATION type electro deposition coating after Phosphating

What are some common parameters , to be considered while material selection for sheet metal fabrication?

  • Good corrosion resistance
  • Formability
  • Weldability

What are all the reinforcement techniques followed to improve the strength of the sheet metal component?

  • Changing the geometry : Including beads, flanges, notches in weaker cross section. The weaker cross sections of the sheet metal component can be identified using Hand calculations considering the loads acting on the component and evaluating the stress, displacement and vibration throughout the component.
  • Changing the material : Introducing higher grade or different material than the existing one may sometimes results in improved strength of the component. The cost of the material should have been considered while proposing for an alternative.
  • Reducing the load acting on the component.