Chemical Methods of Material Removal

1
Chemical Methods of Material Removal

• Chapter 6

2
Overview

• History
• Types of Chemical Milling
• Photo-Chemical Machining
• Immersion Machining
• Electro-Chemical Machining
• Advantages and Disadvantages

3
History

• Organic acids first used for corrosive purposes
  in 400 B.C.
• 15th Century Salt, charcoal, Vinegar etchants,
  linseed oil paints as maskant
• Used extensively in armor
• 18th 19th century discoveries propelled
  chemical milling

4
Chemical MachiningComponents

• A dissolving process.
• Terms
• Stock
• Material to be machined
• Mask
• Used to protect area not to be machined
• Chemical
• Acidic solution to etch stock

• Anode () charged material
• Cathode (-) charged material
• Electrolytic solution (medium for process)

5
Photo-Chemical Machining (PCM)

• Mainly used for sheets or plates
• Computer-generated picture used to produce
  phototool
• Part covered with photoresist and tool, exposed
  to UV light
• Part exposed to etchant chemical
• Photoresist removed

6
Photo-Chemical Machining (PCM)
7
Photo-Chemical Machining (PCM)

• Advantages
• Precise removal of material
• Removal of material too small or fragile to
  machine
• Used on a variety of materials
• No burrs created
• No residual stress introduced

• Disadvantages
• Uses hazardous chemicals
• Surfaces can be rougher than honed ones
• May be relatively slow process
• Very expensive on a per-pound basis

8
Electro-Chemical Machining (ECM)

• Terms
• Electrolyte
• Anode
• Cathode
• Ions
• Coating on anode controls amount of metal to be
  removed.

9
Electro-Chemical Machining (ECM)

• Uses electrolysis
• Work piece positively charged, tool (inverse of
  desired shape) negatively charged
• Current passed between the two
• Surface metal ionizes, removed by solution

10
Electro-Chemical Machining (ECM)

• Advantages
• Current and metal removal rate can be controlled
• Can create elaborate shapes and contours
• Tool lasts indefinitely once created
• No burrs created
• No residual stress introduced

• Disadvantages
• Expensive equipment and tools
• Electrolytic solution is hazardous to environment
  as well as equipment

11
Immersion Machining

• Similar to PCM
• Maskant attached to areas not desired to be
  machined
• Entire part immersed in etchant chemical
• Can be repeated until correct part created

12
Materials

• Virtually any material can be used as long as an
  etchant and maskant are available
• Aluminum
• Titanium
• Steel
• Brass
• Copper
• Lead
• Silver
• Nickel
• Zinc

13
Conclusion

• Chemical machining began as early as 400 B.C.
• PCM, Immersion Machining, and ECM are a few
  examples
• Reduces tooling and cost
• Can make eccentric shapes
• Eliminates burrs and secondary finishing
• Chemicals can be hazardous to the environment