photo chemical benki

8/6/2019 Photo Chemical BENKI

1/18

Photochemical Machining:

(manufacturings best kept secret)

Benkim B A

Suvin P S

Manufacturing Technology


2/18

Introduction

y Photochemical machining (PCM), also known as

photochemical milling or photo etching, is the process

of fabricating sheet metal components using a photo

resist and etchants to corrosively machine away

selected areas.

y Photo etching can produce highly complex parts with

very fine detail accurately and economically.

y PCM can be used on virtually any commercially

available metal or alloy, of any hardness which includealuminium, brass, copper, inconel, manganese, nickel,

silver, steel, stainless steel, zinc and titanium.


3/18

Principle

y The method of material removal in PCM is based on the redox

reaction effecting metal oxidation resulting in material dissolution

with the formation of soluble by products that diffuse away from

the reaction site.

y Eg: M nFe2+ + Mn+

yphotochemical reaction chemical reaction caused by

absorption of light (including visible, ultraviolet, and infrared).

The light excites atoms and molecules.


4/18

The PCM process.


5/18

PCM process

The process sequence can be out lined as follows.

y A photo resistant coating is applied to make the sheet

metal sensitive to light.

y A photo mask is placed over the sensitized sheet metal.

y The sheet is exposed to ultraviolet light.

y The photo resist is developed into the masked pattern.

y The sheet is etched to remove exposed metal areas

leaving the final part.

y The part is then cleaned.


6/18

Etch profile development.


7/18

Etch factor

y The ratio of the depth to the undercut is termed theetch factor and it limits the minimum hole diameter

( min) that can be etched through a metal sheet of

thickness T.

y such that in general min

>T.

y The main limitation of PCM is to be found in the

characteristics of isotropic etching whereby the etchant

will attack not only downwards into the metal but also

sideways beneath the resist stencil layer.


8/18

Contd

y Etch factor = Depth of etch (D) / Undercut whereundercut = (B-A).


9/18

Photo resist

Photo resists are UV sensitive polymer layers that may

be applied to adhere on the sheet metal surface by hot

roller lamination.

They may be.

y positive- or negative-working.

y natural product- or synthetic polymer-based.

y applied as a liquid or dry film.

y organic solvent- or aqueous-based formulations.


10/18

Positive and negative photo resists.


11/18

Applications

y Thin gauge under 1.3 mm parts in a broad range of

alloys are candidates for photo etching.

y Industrial applications include fine screens and meshes,

apertures and masks, battery grids, fuel cell

components, sensors, springs, pressure membranes,heat sinks, flexible heating elements, RF and microwave

circuits and components, semiconductor lead frames,

motor and transformer laminations, metal gaskets and

seals, shields and retainers, electrical contacts,encoders and light choppers, EMI/RFI shields, jewelry

and washers.


12/18

components

Chemically engraved Cartier watch

movements

60 mm wide integrated circuit lead frames


13/18

An x-ray calibration chip (top right) comprising

a 5 m thick copper and 3 m gold pattern on 50 mKapton

Etched mobile telephone gasket Silver jewellery etched and filled with enamels


14/18

ECONOMIC ASPECTS

y The cost of fabricating etched parts is almost directly

proportional to the area that can be coated with photo

resist, imaged and etched in one series of operations.


15/18

Advantage of PCM over stamping

y Low art work and tooling cost.

y Economical edge for complex part and small to medium

quantity.

y Can modify easily the photo tool within a short period

of time.

y Components are burr free, so no need of finishing

operations.

y Does not affect the physical and chemical properties

inherent in the sheet metal.

y No residual stress.


16/18

Conclusion

y The PCM process is not much popular though it

has got a wide range of applications in the field

of sheet metal industry.

y They provide a cheaper and better machiningprocess in this industry.


17/18

References

y D.M.Allen, Photochemical Machining: from

manufacturings best kept secret to a $6 billion

per annum, rapid manufacturing process,

School ofIndustrial and Manufacturing ScienceCranfield University.

y Photochemical Machining (PCM),IC Professional

training Series

y www.wikipedia .com, /modernmcing/Photochemical_machining.htm


18/18

THANK YOU

photo chemical benki

Documents