BENGHAZI UNIVERSITY

Industrial &Manufacturing Systems Engineering Department

Nontraditional Machining Process:IM527(selected Topic)

lecture 1:Chemical machining

Instructor : Omar Elmabrouk Engineer : Rania.A. Elrifai

2011/2012 spring

Chemical machining

What is Chemical machining (CHM)?• Chemical machining that removes metal from a workpiece by

immersing it into a chemical solution.• Chemical machining (also known as photo chemical machining or

PCM, photofabrication, or photo chemical milling) is a process through which decorative metal items and precision metal parts are formed.

• Chemical machining is a well known nontraditional machining Photofabrication Engineering, Inc. (PEI) has perfected the Chemical Machining process, starting with the creation of phototools from a fully-dimensional drawing or CAD file supplied by the customer.

Cont…….(CHM)

• process is the controlled chemical dissolution of the machined workpiece material by contact with a strong acidic or alkaline chemical reagent .

• the machining method is widely used to produce micro-components for various industrial applications such as micro electromechanical systems(MEMS) and semiconductor industries.

History of the chemical machining processs. • machining method which is used to shape copper

with citric acid in the Ancient Egypt in 2300 BC .• Until the 19th century this process was widely

used for decorative etching. The development of photography provided a new dimension to chemical machining .

• William Fox Talbot (1852) patented a process for etching copper with ferric chloride, using a photoresist .

• John Baynes, in1888, described a process for etching material on two sides using aphotoresist which was patented in the USA (US Patent No: 378423).

• The main industrial application of chemical machining developed after the war.

Steps of chemical machining

Chemical machining process has several steps for producingmachine parts. These are given below:1- Workpiece preparation: The workpiece material has to be cleaned in the beginning of chemical

machining process.• The cleaning operation is carried out to remove the oil, grease, dust, rust or

any substance from the surface of material.• A good cleaning process produces a good adhesion of the masking material.• There are two cleaning methods: mechanical and chemical methods , the most widely used cleaning process is

chemical method due to less damages occurred comparing to mechanical one. Ultrasonic cleaning machine is applied with using special cleaning solution

and heating is beneficial during the cleaning process.

2. Coating with masking material: • The next step is the coating cleaned

workpiece material with masking material.

• The selected masking material should be readily strippable mask,

• which is chemically impregnable and adherent enough to stand chemical abrasion during etching.

3. Scribing of the mask: This step is guided by templates to expose the areas that receive

chemical machining process.The selection of mask depends on the size of the workpiecematerial, the number of parts to be produced, and the desireddetail geometry. Silk-screen masks are preferred for shallowcuts requiring close dimensional tolerances.

Etching (micro fabrication)

4. Etching: • This step is the most important stage to

produce the required component from the sheet material.

• This stage is carried out by immerse type etching machine.

• The workpiece material is immersed into selected etchant and the

uncovered areas were machined. • This process is generally carried out in

elevated temperatures which are depended on the etched material. Then the etched workpiece is rinsed to clean etchant from machined surface.

5. Demasking- Cleaning masking material( the maskant is removed from the part):

• Final step is to remove masking material from etched part. The inspections of the dimensions and surface quality are completed before packaging the finished part.

• Masking material which is called maskant is used to protect workpiece surface from chemical etchant.

• Polymer or rubber based materials are generally used for masking procedure.

The selected maskant material should have following properties .

1. Tough enough to withstand handling2. Well adhering to the workpiece surface3. Easy scribing4. Inert to the chemical reagent used5. Able to withstand the heat used during

chemical machining6. Easy removal after chemical machining

etching

Types of masks used in CHM

• Cut and peel masks.• Screen resist masks.• Photo resist masks.

Cut and peel maskants

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

• Vinyl, styrene and buta diene are used.• 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.

Screen resist maskants

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

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

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

Photo resist maskants

• Photo resist mask is quite widely used & is often referred to as photochemical machining.

• 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, while exposure to UV rays takes place.

• Light activates the photo resist material in those areas corresponding to opaque parts.

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

Chemical Machining Processes 

• Chemical milling• Chemical blanking• Chemical engraving• Photochemical machining

Chemical milling1. In chemical milling, shallow cavities are

produced on plates, sheets, forgings and extrusions.

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

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

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

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

Chemical blanking

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

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

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

• Very cheap but efficient.

Figure 2 : parts profiled by chemical blanking process

Chemical Engraving

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 decorated object in itself, as when silver, gold, steel or glass are engraved, or may provide an printing plate, of copper or another metal, for printing images on paper as prints or illustrations; these images.

Types of engraving

• Wood Engraving• Copper and Steel Engravings•  Laser engraving

Photo Chemical Machining (PCM)Process steps for photochemical

machining• 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.

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

Applications

• Thin gauge (under 0.050 in (1.3 mm)) parts in a broad range of alloys are candidates for photo etching.

• Industrial applications include fine screens and meshes.• Battery grids•  fuelcell components•  sensors,• springs• pressure membranes• RF and microwave circuits and components, semiconductor • leadframes

Characteristics Of Chemical Machining

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

The Benefits of Chemical Machining

• No effect on the metal properties

• Burr free metal parts

• Low cost tooling

• Quick turnaround & Affordable short runs

Conclusion

• 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.

Video shows (PCM)

_#x202a_D?ip Tank - Finishing Line - Chemical Milling - Product Coating System_#x202c__rlm_ - YouTube.FLV

Important parameters in (CHM)(a) MRR= C×A

,(mm³/min)(b)C: penetration

rate( mm/min).(c) Time of etch (Tm)

=d/c , (hr)(d)Fe(factor etch)=d/u,

d: depth (mm), under cut(mm)

Solve the problems about (GHM)• What is a photoresist in chemical machining? Photoresist is the masking material that is sensitive to light . When exposed , it chemically

transforms and can be removed from the surface of the work, leaving the desired surface • chemical milling is used in which of the following applications .(a) drilling holes with high depth – to- diameter ratio (b) Making intricate patterns in the sheet metal© removing material to make shallow pocket in metal(d) removing material from aircraft wing panels(e) Cutting of plastic.26.15: A= 200×400-4(15x15- ¼ π(15)²= 79806.5mm²(a) MRR= C×A= 0.024X79806.5= 1915.4mm³/min(b) Time of etch (Tm) = 12/0.024= 500 min(c) Fe(factor etch) =1.75,Fe=d/u → u=d/Fe =12/1.75=6.86mmMaskant opening length = 400- 2(6.68)=386.28mm Maskant opening width = 200-2(6.68)= 186.28mm, radius corner 15-2(6.68)= 8.14mm

• 26.16: area of ellipse A= π×a xb =3.14×9×6=1696.5.in², d=0.4in,pentration rate=0.001inlmin

• (a) MRR= 0.001X1696.5=1.6965 in³/min=101.179in³/hr• (b) Tm= 0.4/0.001=400 min=6.67hr• © Fe= 2, undercut (u)= d/Fe= 0.4/2= 0.2 in, • maskant opening a = a-2u= 9-2(0.2)= 8.6 in• maskant opening b = b- 2u= 6- 2(0.2)= 5.6 in• 26..17: because the Tolerances of ±0.025 to 0.005 mm can be

produced so, it should have been used in the case.• 26.18: Fe= 1.75 , in chemical blanking, etching will occur on two

sides hol4ndepth on each side = 0.015/2= 0.0075 In , undercut u= 0.0075/1.752= 0.0043 in

• Diameter opening =0.001- 2(0.0043)= 0.0914 in