Chemical Milling

Chemical milling is most commonly known as metal etching. The process has been known for a long time and used for creating depressed designs on metal plate. These metal etchings are required for many reasons including metal industrial parts that have many small grooves and holes or that require a decorative finish. The process is also used to create the metals of required weight. There are various techniques with which chemical milling or metal etching can be performed though the basic process remains same.

Photo etching is the most common and popular type as it has many advantages above other types of milling. It is a high precision milling with which almost all metals can be etched and the final product is free of burrs. The metal is not deformed and the thickness of etch can be easily varied. It is the most economical technique.

Process
The metal is first covered with a protective layer and the required image is cut into the layer using different techniques like photo imaging, stamping etc. The layer is then chemically treated and the metal beneath the cut lines i.e. the area without the protective coating dissolves. The protective coating is then removed and the final etched metal product is obtained. A lot many chemicals, acids or other techniques can be used for the etching.

Types
Abrasive Etching uses high-pressure compressed air to direct abrasives like sand or aluminum oxide at a material surface for etched effect.

Dry etching does not employ the use of chemicals.

Electro-Etching requires the use of chemicals along with direct electric current.

Laser etching removes specified pattern on a metal piece by laser.

Photochemical etching is the most common type requiring photo resist chemicals

Reactive Ion Etching (REI) also known as plasma etching is dry etching involving electrical circuits and high-energy gas having ionized particles of fluorine or chlorine.

Sputter etching is a type of REI etching but without the employment of ions.

Vapor phase etching is a dry etching technique using reactive gases.