advanced material and designe
ENGT5253: Advanced Materials & Design
Background Information
Related to
Assignment 1
Sheet Metakworking
Processes
Assignment 1: Background Information
Sheet Metakworking
Feed stock: metal sheets 1- 6 mm thick
Commercial significance: autombile & truck bodies,
airplanes, raiway cars, locomotive, farm, electrical
& electronic appliance, construction …..
Carried out mostly under cold-forming condition
Tooling: Punch and die with a machine press
Cutting Operations
Accomplished by a shearing action between two
sharp cutting edges
Three steps involved
Punch
Die
Plastic
deformation
(2) Penetration
(1/3 thickness)
(3) Fracture
Plastic deform.
Penetration
Fracture
Assignment 1: Background Information
Cutting Operations
Characteristics of sheared edges
t
Rollover
Burnish
Fractured
zone
Burr
Plastic deformation
Penetration
Fracture of metal
Elongation before
final separation
Assignment 1: Background Information
Cutting Operations
The most important parameter: Clearance
Die
Punch
c
In order to cut, a clearance (c) is
required between the punch
and the die
The clearance (c) is 4-8%
of sheet thickness, depend
on material to be cut
c = a x t
Assignment 1: Background Information
Cutting Operations
The most important parameter: Clearance
The harder the metal sheet, the larger the a value,
i.e. the larger the clearance
The thicker the metal sheet, the larger the clearance
c = a x t
Assignment 1: Background Information
Example: You plan to cut a 10 mm sheet of 1100S
aluminium, then
c = 0.045 x 10 = 0.45 mm
If you have the same sheet of stainless steel, then larger
clearance is required:
c = 0.075 x 10 = 0.75 mm
What happen if the clearance is
too small: the fracture line tends to
pass each other, causing double
burrs and larger cutting force
too large: the metal becomes
pinched between cutting edges
and excessive burr results
Assignment 1: Background Information
Three Operations
Shearing:
Blanking:
Punching:
Used to cut large sheets into small ones
for subsequent operations
To cut a piece of metal with closed outline
from a metal sheet for use
To punch a hole in a metal sheet part
Blanking
Punching
Assignment 1: Background Information
How to determine die and punch size
for blanking and punching?
Note: die opening is always
larger than punch size
Die opening determines
blank size
Punch size determines
hole size
To produce a blank
of size Db:
Blank die size = Db
Punch size = Db – 2c
Hole punch size = Dh; Hole die size = Dh + 2c
(2) To produce a hole with size Dh:
A round disc of 75 mm diameter is to be
blanked from a cold rolled steel sheet of 4 mm thick,
then a hole of 10 mm diameter is to be punched at
the centre of the blanked disc. Determine the
appropriate die and punch sizes for these two
operations.
(1) Determine clearance, c
c = a x t = 0.075 x 4 = 0.3 mm
(2) Blanking die and punch
Die opening dia. = 75 mm
Punch dia. = 75 – 2c =74.4 mm
(3) Punching die and punch
Punch dia. = 10 mm
Die opening dia. = 10 + 2c =10.6 mm
Example:
Typical blanking dies: many blanks can be produced
by one die/punch set from the same metal sheet
Your Design Project
Material to be blanked: soft stainless steel sheet
Sheet thickness: t = 2 mm
Shape/Outline to be blanked: two letters from your name
Y
Die
Punch
30-50 mm
40-70mm
Any artistic style
Any size within the range
Y
Your task