TITLE OF PROJECT

“Optimization of process parameters in
Photochemical Machining of Phosphor Bronze with spray etching.”

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RELEVANCE

Ø  Photo chemical machining is an engineering production
technique for the manufacture of burr free and stress free flat metal
components by selective chemical etching through a photographically produced
mask.

Ø 
For complex parts

Ø  Characteristics
of metal material not altered

Ø 
Variable edge profile

Ø  Multi
level depth etching

Ø  Low
cost tooling

Ø  Lead-times
in hours/days not weeks/months

Ø  Any
material temper

Ø  Virtually
every metal type

Ø  Stress
and burr free manufacture

Ø  No
additional costs for complex shapes

Ø  Interfaces
easily with other manufacturing techniques

Ø 
Economic manufacturing
cost

 

 

 

 

PRESENT
THEORY & PRACTICES

                The development of knowledge of
acid attack upon metals is not new; its origins lie in antiquity. Legend tells
that the ancient Greeks had discovered a fluid, which is referred to as liquid
fire that attacked both inorganic and organic materials. However as this was
the Bronze age it is unlikely that they possessed the technology to manufacture
such an acidic chemical. The ancient Egyptians etched copper jewellery with citric
acid as long ago as 2500BC. The earliest reference to this process describes an
etchant made from common salt, vinegar and charcoal acting through a hand
scribed mask of linseed oil paint. These techniques were adapted and improved by
etchers operating in close co-operation with armourers until, by the
seventeenth century.

                The
sixteenth century saw the use of etching techniques to produce printing plates
of a superior quality to those previously engraved. The main advantage being
the lack of burrs. By 1925 the huge daily newspaper industry made large-scale
use of printing plates etched in nitric acid solution. By 1927 the use of
chemical milling through a rubberised paint mask, which was hand cut around a
template, was being used as an engineering production tool.

                John Snellman may have been the
first to produce flat metal components by photo chemical machining of shim
stock that was too hard for punching. He innovated the use of cutting lines, or
outlines, in the photoresist mask. This ensured even simultaneous etching of
every component detail and also his use of tabs secured the parts into the
parent metal sheet. He patented the process in 1944 where after it was increasingly
used to manufacture shims, springs, stencils, screens and virtually any complex
shape which for technical reasons could not be punched.

               The technique is relatively
modern and became established as a manufacturing process about fifty five years
ago. The processing technology has been kept a closely guarded secret within a
small number of industrial companies but despite this, the sales of parts made
by pcm at the end of the twentieth century was approximately US $ 6
billion.  

 

 

PROPOSED
WORK

Ø 
PLAN
OF PROJECT

 Year 2011-2012

Activity         
Month                                      

July

Aug

Sept

Oct

Nov

Dec

Jan

Feb

Mar

Statement of problem

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Literature survey

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Purchase of material

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

D.O.E.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Experimentation set up

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Preliminary Test

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

D.O.E. Test

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Analysis &Con.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Report writing

 

 

 

 

 

 

 

 

 

 

Ø  Selection
of material

§  Type:
Phosphor bronze

§  Dimensions:
flat rectangular sheet thickness 0.013mm to 2mm

§  Properties:
Alloy of copper with 3.5% to 10% of tin and phosphor content 1%.

These alloys are notable for their roughness,
strength, low                    coefficient of friction and fine grain.

 

Ø  Selection
of chemicals

§  Dip
coating: photoresist (1020),Photo resist developer, photoresist dye, lith film

§   Etchant: Ferric chloride solution.

 

Ø  Equipments
used

§  Dip
coater

§  Air
dryer

§  UV
exposer

§  Spray
etching setup

 

Ø  Experimental
design

             In dip etching process some removed material
particles during chemical reactions deposited on workpiece which affect the
further material removal rate (MRR). In spray etching process this problem is
over come by carried away the deposited burrs by pressurized etchant to achieve
MRR.

       Design
a spray model with titanium heating element inside the cpvc pipe to achieve
desire temperature for effective etching. In which pump is used to pressurize
the etchant. The nozzles are used to spray the hot etchant on

workpiece.

EXPERIMENTAL VARIABLES

Ø 
Control
parameters

§ 
Temperature
(oC)

§ 
Time
(Min)

§ 
Concentration
of etchant.

 

Ø 
Fixed
parameters

There are other factors, which can be
expected to have an effect on the measures of performance. In order to minimize
their effects, other factors were held constant. The other fixed parameters are

§ 
Etchant
– Ferric chloride

§ 
Work
piece material

§ 
Work
piece thickness

§ 
Work
piece area

§ 
Work
piece size

DESIGN OF EXPERIMENT

A well planned set of experiments, in which all
parameters of interest are varied over a specified range, is a much better
approach to obtain systematic data. Mathematically speaking, such a complete
set of experiment ought to give desired results. Usually the no of experiments
and resource (Materials, time and money) required are prohibitively large.
Often the experimenter decides to perform a subset of the complete set of
experiments to save time and money. However, it does not easily lend itself to
understanding of science behind the phenomena. The analysis is not easy.
(Though it may be easy for the mathematician / statistician) and thus, effect
of various parameters on the observed data are not readily apparent.

 In many case, particularly those in which some
optimization is required, the method does not point out the best setting of
parameter. Any experiment that has flexibility to make desired changes in the
input variables of process to observe output response is known as experimental
design. Good experiment must be efficient. It is not an isolated test but well
planned investigation that point the way towards understanding the process.
Experimental design is a systematic manipulation of set of variables in which
the effect of these manipulation is determined, conclusions are made and the
result are implemented. 

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