Manufacturing processes

Question 1

Sheet bending:

Explain air bending

Answer 1

> Metal only touches the machine at 3 points
- Punch
- Twice at the die edges
> few tool changes required 
> Not very precise

Question 2

Sheet bending:

Explain coining

Answer 2

> There is a mould for the sheet metal to be formed into
A punch forces the metal into the mould
Requires more force
More controlled angle
Very little spring back

Question 3

Sheet bending:

Explain whiping

Answer 3

Metal is bent around the edge of a surface using a shear force

Question 4

Sheet bending:

What are 3 design considerations?

Answer 4

> Minimum bend angle
Springback
Bending force

Question 5

Sheet bending:

Why is there a minimum bend radius and how is it noted?

Answer 5

> The minimum radius is because if you bend it too much then it will cause the metal to fracture
Expressed as a multiple of sheet thickness

Question 6

Sheet bending:

Why does springback occur?

Answer 6

Because at the centre of the metal, the material does not deform plastically and instead deforms elastically which causes it to return to its original position causing spring back

Question 7

Sheet bending:

How can you prevent springback?

Answer 7

By overbending

Question 8

Sheet bending:

What is the equation for bending force?

Answer 8

FB = k × (σy × W × t^2) / R
k = Constant (depending on the process)
σy = yield stress
W = Sheet width
t = Sheet thickness
R = Radius

Question 9

Sheet bending:

What is spinning?

Answer 9

A blank is spun around a mandrel and a tool is pressed against the blank to slowly form it to the shape of the mandrel

Question 10

Sheet bending:

What sort of shapes can be made using spinning?

Answer 10

An asymmetrical shape

Question 11

Sheet bending:

What is deep drawing?

Answer 11

> Essentially punching but instead of cutting it forms the sheet into a shape
The process is repeated with multiple operations so that the metal is slowly drawn out into the correct shape

Question 12

Sheet bending:

Where is lubricants applied for deep drawing?

Answer 12

> On the edge of the die and the top bit that holds the metal down a bit.
Lubricants are not applied to the punch because you want high friction

Question 13

Shearing:

Define shearing

Answer 13

Using blades to cut material without forming it into chips

Question 14

Shearing:

What is the punching/blanking process? What is the piece that is removed?

Answer 14

> A punch cuts a hole in a piece of sheet metal

> A slug is produced

Question 15

Shearing:

What is punching and blanking? What is the difference?

Answer 15

> Punching is when you discard the slug

> Blanking is when you keep the slug

Question 16

Shearing:

What are 4 shearing operations?

Answer 16

> Perforating
> Slicing
> Notching
> Lancing
> Parting

Question 17

Shearing:

What is happens if the clearance between the die and the punch is too large / too small / perfect?

Answer 17

> Too large = Excessive distortion, does not actually shear
Too small = Ragged edges, excessive tool wear
The recommended clearance is 10-15% of the sheet thickness

Question 18

Shearing:

What is fine blanking?

Answer 18

This is the same a blanking but using a grip to hold the sheet down

Question 19

Shearing:

What is the equation for the punching force?

Answer 19

Fs = k × Lp × t ×τ
k = Factor to account for frictional deviation
Lp = Perimeter length
t = Thickness
τ = Ultimate sheer strength