OTHER DRAWING OPERATIONS
1. Ironing
Ironing is a method of redrawing a shell to reduce the wall thickness and to improve the surface finish. The process is also used to correct the natural thickening of the wall.
The clearance between the punch and die is less than the thickness of the shell wall. During drawing the metal is thinned and the length of the
shell is increased. In between the ironing process the shells are to be annealed.
The strain caused by ironing is expressed by the ratio of the wall thickness before and after ironing.
For ductile material ratio is 2 : 1
For ductile and fully annealed alloy the ratio is 2.5 : 1
2. Reverse drawing:-
In reverse drawing a pre drawn shell is drawn in the reverse direction of that of the previous draw. Reverse drawings are employed for redraws of shells or to produce reverse type flanges on drawn cups.
The advantage of reverse drawing method over the regular drawing method is that a greater amount of reduction in the diameter is obtained.
In some cases it will be economical to make a two stage draw component in a single tool with one straight draw and one reverse draw other than making two separate tools.
Comparison Design for Regular and Reverse drawing die
3. Eyelet Drawing
Eyelet drawing is the process of producing small diameter cups by drawing progressively. The main feature of eyelet drawing is that the depth of the shell is more compared to its diameter. Hence the overall draw ratio is very high. This indicates that these shell cannot be drawn in one stage and manufacturing number of tools to produce these components are
uneconomical.
In this method number of stages required are stacked with a single die set, so that the operation can be made in the progressive style.
The tool is similar to progressive tool. Pieces are drawn from the stock strip in single or multiple rows. However, it is observed from the practices the single row method is easier because enough material can be drawn from all sides.
Materials for Eyelet Drawing:-
All materials which comes under the group of ductile materials can be eyelet drawn. Ductile materials includes both ferrous and non- ferrous.
Some of the important ferrous ductile materials that are used for eyelet drawing process are
a) Steel
b) Steel, deep drawing quality
c) Steel, Stainless
d) Deep Draw Steel
e) Extra Deep Draw Steel
Some of the important non-ferrous ductile materials that are used for eyelet drawing process are
a) Aluminum, Soft
b) Aluminum, deep drawing quality
c) Brass,
d) Copper
e) Zinc
f) Tin
Capabilities in eyelet drawing
Rounds, Tapers, Ovals, Squares Other Irregular Shapes. Secondary Operations which can be incorporated into primary tooling including:
Threading, Beading, Bottom Piercing, Reverse Drawing, Step, Drawing, Bumping, Fluting, Curling, Necking, Side Lettering, Bottom Flanging, Bulging, Side Piercing, Knurling
Comparison between Deep Drawing and Eyelet Drawing:-
Sl No
|
Deep Drawing
|
Eyelet Drawing
|
01
|
Deep drawing is a stage tool process
|
Eyelet drawing is progressive tool process
|
02
|
Separate tools are involved to have separate stage operations.
|
Only one progressive tool is involved to have all the operations.
|
03
|
Designed for only large components
|
Specially designed for small capsule shaped components.
|
04
|
Cost is more
|
Cost is less
|
05
|
Hydraulic press technology is adopted
|
Transfer press technology is adopted
|
06
|
Bigger features necessitate thick tooling subjected to less cyclic shocks, less degradation and less breakage of tools
|
Small or thin features necessitate very thin tooling, which is subject to intense, cyclic shocks that can lead to tool degradation and breakage.Tool set up time
|
07
|
Tool set up time is more to get the final component
|
Tool set up time is less to get the final component
|
08
|
Necessary finishing operations
(grinding, polishing etc) of thicker tooling are not so delicate |
Necessary finishing operations (grinding, polishing etc) of thinner tooling are more delicate
|
09
|
Removes the material from the material strip at the first operation
|
Removes the finished part from the material strip immediately before ejection from the press
|
10
|
Takes more time to complete the full process of component
|
Takes less time to complete one full process of component
|
11
|
Producing big features requires less careful press set up
|
Producing small features requires more careful press
set up |
12
|
No material feeding is required, but the blank material is kept blindly
|
Manual or Automatic feeding for transfer of component is required
|
Strip layout for Eyelet drawing:-
COMMENTS