CHEMICAL MACHINING(CHM)CHEMICAL MACHINING(CHM)

Presented by:Presented by:

NAGESH N.M.NAGESH N.M.

CONTENTSCONTENTS

IntroductionIntroduction Principle Principle StepsSteps Processes Processes Design considerationsDesign considerations CharacteristicsCharacteristics Materials Materials Advantages and Dis-advantagesAdvantages and Dis-advantages ApplicationsApplications ConclusionConclusion ReferencesReferences

INTRODUCTIONINTRODUCTION

Chemical machining(CHM) Was developed based on the observation that Chemical machining(CHM) Was developed based on the observation that chemicals attack metals and etch them by using chemical dissolutions.chemicals attack metals and etch them by using chemical dissolutions.

CHM is the removal of metal by chemical attack by a corrosive liquid.CHM is the removal of metal by chemical attack by a corrosive liquid.

The areas of the work piece which are not to be machined are masked. The areas of the work piece which are not to be machined are masked.

The work piece is either immersed in or exposed to a spray of chemical The work piece is either immersed in or exposed to a spray of chemical reagent. reagent.

CHM was basically developed for aerospace industry to maintain strength CHM was basically developed for aerospace industry to maintain strength of part at reduced weight.of part at reduced weight.

PRINCIPLE OF CHMPRINCIPLE OF CHM

An etchant resistant mask, made typically of rubber or plastic is used to An etchant resistant mask, made typically of rubber or plastic is used to protect those parts of the component from which no material is to be protect those parts of the component from which no material is to be removed. removed.

Part to be machined is defined by any one of the procedures: scribing & Part to be machined is defined by any one of the procedures: scribing & removing the coating, exposing to light & dissolving unexposed region, or removing the coating, exposing to light & dissolving unexposed region, or silk screen printing.silk screen printing.

Strong acid or alkaline solution is used to dissolve materials selectively.Strong acid or alkaline solution is used to dissolve materials selectively.

Chemically resistant coating is applied to protect surfaces not to be Chemically resistant coating is applied to protect surfaces not to be machined.machined.

PrinciplePrinciple

Figure : (a) Schematic of chemical machining process (b) Stages in producing a profiled cavity by chemical machining

STEPS IN CHEMICAL MACHININGSTEPS IN CHEMICAL MACHINING

The 5 steps in chemical machining are as followsThe 5 steps in chemical machining are as follows::

Part preparation: cleaning.Part preparation: cleaning. Masking: application of chemically resistant materialMasking: application of chemically resistant material Etching: dip or spray exposure to etchantsEtching: dip or spray exposure to etchants Mask removal: stripping the maskant and cleaning the part.Mask removal: stripping the maskant and cleaning the part. Finishing: inspection and other processingFinishing: inspection and other processing

Types of masks used in CHMTypes of masks used in CHM

Cut and peel masks.Cut and peel masks. Screen resist masks.Screen resist masks.

Photo resist masksPhoto resist masks..

Cut and peel maskantsCut and peel maskants

Film of chemically resistant material is applied to the work piece by dipping, spraying or Film of chemically resistant material is applied to the work piece by dipping, spraying or flow coating.flow coating.

Vinyl, styrene and buta diene are used.Vinyl, styrene and buta diene are used. Rubbery film is then cut & peeled away selectively.Rubbery film is then cut & peeled away selectively. Manual scribing of mask material usually achieves an accuracy of ±0.13 mm to ±0.75 mm.Manual scribing of mask material usually achieves an accuracy of ±0.13 mm to ±0.75 mm.

Screen resist maskantsScreen resist maskants

Mask material is applied to the work piece surface by printing, using stencils and a Mask material is applied to the work piece surface by printing, using stencils and a fine polyester or stainless steel mesh screen.fine polyester or stainless steel mesh screen.

Relatively thin coatings with tolerances held to ±0.05 to ±0.18 mm are obtained by Relatively thin coatings with tolerances held to ±0.05 to ±0.18 mm are obtained by screen printing.screen printing.

Etching depths are restricted to about 1.5 mm because of thinness of the coating.Etching depths are restricted to about 1.5 mm because of thinness of the coating.

Photo resist maskantsPhoto resist maskants Photo resist mask is quite widely used & is often referred to as photochemical Photo resist mask is quite widely used & is often referred to as photochemical

machining.machining. Produces intricate & finely detailed shapes using a light activated resist materials.Produces intricate & finely detailed shapes using a light activated resist materials. WP coated with photo resist material & a master transparency is held against the WP coated with photo resist material & a master transparency is held against the

WP, while exposure to UV rays takes place.WP, while exposure to UV rays takes place. Light activates the photo resist material in those areas corresponding to opaque Light activates the photo resist material in those areas corresponding to opaque

parts.parts. Tolerances of ±0.025 to 0.005 mm can be produced.Tolerances of ±0.025 to 0.005 mm can be produced.

CHEMICAL MACHINING PROCESSESCHEMICAL MACHINING PROCESSES

   Chemical millingChemical milling Chemical blankingChemical blanking Chemical engravingChemical engraving Photochemical machiningPhotochemical machining

Chemical millingChemical milling

1.1. In chemical milling, shallow cavities are produced In chemical milling, shallow cavities are produced on plates, sheets, forgings and extrusions. on plates, sheets, forgings and extrusions.

2.2. The two key materials used in chemical milling The two key materials used in chemical milling process are etchant and maskant. process are etchant and maskant.

3.3. Etchants are acid or alkaline solutions maintained Etchants are acid or alkaline solutions maintained within controlled ranges of chemical composition within controlled ranges of chemical composition and temperature. and temperature.

4.4. Maskants are specially designed elastomeric Maskants are specially designed elastomeric products that are hand strippable and chemically products that are hand strippable and chemically resistant to the harsh etchants.resistant to the harsh etchants.

5.5. Chemical milling is used in the aerospace industry to Chemical milling is used in the aerospace industry to remove shallow layers of material from large aircraft remove shallow layers of material from large aircraft components missile skin panels extruded parts for components missile skin panels extruded parts for airframes.airframes.

Figure : Missile skin-panel section contoured by

chemical milling to improve the stiffness- to-

weight ratio of the part

Chemical milling is used in the aerospace industry to remove shallow layers of material from large aircraft components missile skin panels (Figure 7), extruded parts for airframes.

Chemical blankingChemical blanking

Chemical blanking is used to etch entirely through a metal part.Chemical blanking is used to etch entirely through a metal part.

In chemical blanking, holes and slots that penetrate entirely through the In chemical blanking, holes and slots that penetrate entirely through the material are produced, usually in thin sheet materials.material are produced, usually in thin sheet materials.

Used to produce fine screens, flat springs, etc…Used to produce fine screens, flat springs, etc…

Very cheap but efficient.Very cheap but efficient.

Figure : parts profiled by chemical blanking processFigure : parts profiled by chemical blanking process

Chemical EngravingChemical Engraving

Chemical Engraving is the practice of incising a design on to a hard, Chemical Engraving is the practice of incising a design on to a hard, usually flat surface, by cutting grooves into it. The result may be a usually flat surface, by cutting grooves into it. The result may be a decorated object in itself, as when decorated object in itself, as when silver, , gold, , steel, or , or glass are engraved, are engraved, or may provide an printing plate, of or may provide an printing plate, of copper or another metal, for printing or another metal, for printing images on paper as prints or illustrations; these images.images on paper as prints or illustrations; these images.

Types of engravingTypes of engraving

• Wood EngravingWood Engraving• Copper and Steel EngravingsCopper and Steel Engravings•   Laser engravingLaser engraving

Photo Chemical Machining (PCM)Photo Chemical Machining (PCM)

Photochemical machining (PCM), Photochemical machining (PCM), also known as photochemical also known as photochemical milling or photo etching, is the milling or photo etching, is the process of fabricating sheet metal process of fabricating sheet metal components using a components using a photo resist and and etchants to corrosively machine etchants to corrosively machine away selected areas.away selected areas.

PCM can be used on virtually any PCM can be used on virtually any commercially available metal or commercially available metal or alloy, of any hardness. It is limited alloy, of any hardness. It is limited materials 0.0005 to 0.080 in (0.013 materials 0.0005 to 0.080 in (0.013 to 2.0 mm) thick. Metals include to 2.0 mm) thick. Metals include aluminium, , brass, , copper, , inconel, , manganese, , nickel, , silver, steel, , steel, stainless steel, zinc and titaniumstainless steel, zinc and titanium

Process steps for photochemical machining

DESIGN CONSIDERATIONSDESIGN CONSIDERATIONS

Designs involving sharp corners, deep & narrow cavities, severe tapers or Designs involving sharp corners, deep & narrow cavities, severe tapers or porous work piece should be avoided.porous work piece should be avoided.

Undercuts may be developed because etchant attacks both in horizontal Undercuts may be developed because etchant attacks both in horizontal and vertical direction.and vertical direction.

To improve production rate the bulk of the work piece should be shaped by To improve production rate the bulk of the work piece should be shaped by other machining process priorly.other machining process priorly.

Dimensional variations can occur ,this can be minimized by proper Dimensional variations can occur ,this can be minimized by proper selection of artwork media by controlling the environment.selection of artwork media by controlling the environment.

Many product designs are now made with computer aided design.Many product designs are now made with computer aided design.

CHARACTERISTICS OF CHEMICAL MACHININGCHARACTERISTICS OF CHEMICAL MACHINING

Shallow removal of material (up to 12mm)Shallow removal of material (up to 12mm) Blanking of thin sheets.Blanking of thin sheets. Low tooling and equipment cost.Low tooling and equipment cost. Suitable for low production runs.Suitable for low production runs. Material removal rate(0.1mm/min)Material removal rate(0.1mm/min)

MATERIALSMATERIALS

Aluminum Aluminum ChromiumChromium Copper (oxygen free, rolled…)Copper (oxygen free, rolled…) NickelNickel Steel (carbon, stainless…)Steel (carbon, stainless…) LeadLead ZincZinc

ADVANTAGESADVANTAGES

1. Easy weight reduction 2. No effect of work piece materials properties such as hardness3. Simultaneous material removal operation4. No burr formation5. No stress introduction to the work piece6. Low capital cost of equipment7. Easy and quick design changes8. Requirement of less skilled worker9. Low tooling costs10. The good surface quality11. Using decorative part production12. Low scrap rates (3%)

DIS-ADVANTAGESDIS-ADVANTAGES

1. Difficult to get sharp corner2. Difficult to chemically machine thick material (limit is depended on work piece material, but the thickness should be around maximum 10 mm)3. Scribing accuracy is very limited, causes less dimensional accuracy4. Etchants are very dangerous for workers5. Etchant disposals are very expensive

APPLICATIONSAPPLICATIONS

High Precision PartsHigh Precision Parts

and Decorative Itemsand Decorative Items GasketsGaskets Washers Washers Sensors Sensors NameplatesNameplates Jewelry Jewelry Microprocessor ChipsMicroprocessor Chips

CONCLUSIONCONCLUSION

• Chemical machining is widely used to produce complex machine parts for various application as well as decorative parts.

• The machining operation should be carried out carefully to produce a desired geometry.

• Environmental laws have important effects when chemical machining is used.

REFERENCESREFERENCES

Modern machining process by P C Pandey.Modern machining process by P C Pandey.

www.ieee.orgwww.ieee.org

www.chemicalmachining.orgwww.chemicalmachining.org

www.photochemicalmachining.comwww.photochemicalmachining.com

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