Chemical Machining

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  • Topic: Machining, Etching, Chemistry
  • Pages : 9 (2239 words )
  • Download(s) : 81
  • Published : February 10, 2013
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CHEMICAL MACHINING

OBJECTIVES
← To be able to know and familiarize chemical machining ← To know what are the types and processes of Chemical machining ← To know what are the advantages and disadvantages of the process.

DISCUSSIONS

INTRODUCTION (history)

Nontraditional machining processes are extensively employed to produce geometrically complex and precision parts from engineering materials in industries as diverse as aerospace, electronics and automotive manufacturing. There are many multiple geometrically designed precision parts, such as deep internal cavities, miniaturized microelectronics and fine quality components may only be manufactured by nontraditional machining processes. Special coatings called maskants protect areas from which the metal is not to be removed. The process is used to produce pockets and contours and to remove materials from parts having a high strength-to-weight ratio. Moreover, the machining method is widely used to produce micro-components for various industrial applications such as micro-electromechanical systems (MEMS) and semiconductor industries.

Chemical machining method may be the oldest nontraditional 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 and in 1826 J.N. Niepce was the first to use a photo-resist made from bitumen of Judea asphalt for etching pewter (an alloy of 80-90% of tin and 10-20% of lead). William Fox Talbot (1852) patented a process for etching copper with ferric chloride, using a photo-resist made from bichromated gelatin (GB Patent No:565). John Baynes, in 1888, described a process for etching material on two sides using a photo-resist which was patented in the USA (US Patent No: 378423).

The main industrial application of chemical machining developed after the war. In 1953, North American Aviation Inc. (California USA) used the process to etch aluminium components or rockets. Manuel C. Sanz, an engineer with the North American Aviation Company, is credited with solving a critical weight problem on a missile casing by utilizing the process. The company named the process "chemical milling" and patented it (US Patent No: 2739047) in 1956. The machining method is called in different names such as etching, chemical etching, wet etching, etc.

There are several factors contributing to the popularity of chemical machining processes as follow:
a. Chemical machining process is mature and well established.
b. It is simple to implement.
c. There is no additional cleaning step needed.
d. Cheaper machining process.

CHEMICAL MACHINING (CHM)

Chemical machining is a well known nontraditional machining process; the controlled chemical dissolution of the machined workpiece material by contact with a strong acidic or alkaline chemical reagent. It is used to remove large amounts of metal to obtain parts that cannot be machined easily through traditional machining methods. Parts that require precision engineering, like miniaturized micro-components or those containing deep internal cavities are just some of the components produced with chemical milling. While it has numerous applications in automotive manufacturing and electronics, it is very extensively used in the aerospace industry.

The entire process is quite simple and involves cleaning and masking the parts that don't require etching. The metal is then submerged in large tanks of etching solution. The amount of material removed is controlled by the concentration of the chemical solution, the type of etchant used, the time spent in the tank, and the temperature. An ultrasonic thickness tester helps the operator to regularly assess the thickness of the part until it meets the thickness specified in the blueprint. The etched parts are cleaned and inspected for quality...
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