Chemical Machining (CM)
Chemical machining (CM) was developed from the observation that chemicals attack and etch most metals, stones and some ceramics, thereby removing small
amounts of surface material. The CM process is carried out by chemical dissolution using reagents or conditioners, such as acids and alkaline solutions.
Chemical machining is the oldest of the advanced machining processes and has been used in engraving hard metals and stones, in deburring, and in the production of printed circuit boards and microelectronic devices.
Introduction
Chemical machining (CM) is the controlled dissolution of part material (etching) by means of a strong chemical reagent (etching). In CM, material is removed from selected areas of the part by immersion in chemical reagents or conditioners; such as acids and alkaline solutions. The material is removed by the microscopic action of the electrochemical cell, as occurs in the corrosion or chemical dissolution of a metal. This controlled chemical dissolution will simultaneously attack all exposed surfaces, even though material removal penetration rates may only be 0.0025–0.1 mm/min. The basic process takes many forms: chemistry
pocket milling, contouring, general metal removal, chemical blanking for engraving on thin sheets; photochemical machining (pcm) for chemical attack using photosensitive resistors in microelectronics; chemical or electrochemical polishing where weak chemical reagents are used (sometimes with remote electrical assistance) for polishing or deburring and chemical jet machining where a single chemically active jet is used. A schematic of the chemical machining process is shown in
Chemical grinding
In chemical milling, shallow cavities are produced in plates, sheets, forgings and extrusions. The two main materials used in the chemical milling process are paint stripper and masker. Paint strippers are acidic or alkaline solutions maintained within controlled ranges of chemical composition and temperature. Maskers are specially designed elastomeric products that are manually strippable and chemically resistant to aggressive strippers.
chemical machining Chemical grinding steps
· Residual stress relief: If the part to be machined has residual stresses from previous processing, these stresses must first be relieved to avoid warping after chemical milling.
· Preparing: Surfaces are degreased and cleaned carefully to ensure good adhesion of the masking material and uniform removal of the material.
· Masking: Masking material is applied (coating or protecting areas that should not be attacked).
· Etching: Exposed surfaces are chemically machined with etching agents.
· Unmasking: After machining, the parts must be thoroughly washed to avoid future reactions or exposure to any acid residues. Then the rest
the masking material is removed and the part is cleaned and inspected.
Chemical grinding application:
Chemical grinding is used in the aerospace industry to remove surface layers of material from large aircraft components, missile panels and
extruded parts for fuselages. The capacities of the reagent tanks reach 3.7 >< 15 m. The process is also used to manufacture microelectronic devices and is often called wet etching for these products (see Section 28.8.1). The surface finish and tolerance ranges obtained by chemical machining and other machining
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Some surface damage may result from chemical milling due to preferential etching and intergmnular etching, which adversely affect surface properties. O
Chemical milling of welded and brazed structures can result in uneven material removal. Chemical milling of castings can result in uneven surfaces caused by
porosity and non-uniformity of the material.
