CHEMICAL MACHINING PROCESSES (CHM)

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‍Chemical machining is one of the non-conventional machining processes where material is removed by bringing it in contact of a strong chemical enchant.There are different chemical machining methods base on this like chemical milling, chemical blanking, photo chemical machining, etc.

Working Principle of CHM: The main working principle of chemical machining is chemical etching. The part of the work piece whose material is to be removed, is brought into the contact of chemical called etchant. The metal is removed by the chemical attack of enchant. The method of making contact of metal with the enchant is masking. The portion ofwork piece where no material is to be removed, is mashed before chemical etching.

Process Details of CHM: Following steps are normally followed in the process of CHM:

Cleaning: The first step of the process is a cleaning of work piece. This is required to ensure that material will be removed uniformly from the surfaces to be processed.

Masking: Masking is similar to masking action in any machining operation. This is the action of selecting material that is to be removed and another that is not to be removed. The material which is not to be removed is applied with a protective coating called mask ant. This is made of a materials like neoprene, polyvinyl chloride, polyethylene or any other polymer. Thickness of mask ant is maintained up to 0.125 mm. The portion of work piece having no application of mask ant is etched during the process of etching.

Etching: In this step, the material is finally removed. The work piece is immersed in the enchant where the material of work piece having no protective coating is removed by the chemical action of enchant. Enchant is selected depending on the work piece material and rate of material removal; and surface finish required. There is a necessity to ensure that mask ant and enchant should be chemically in active. Common enchants are H₂SO₄,FeCL₃, HNO₃. Selection of enchant also affects MRR. As in CHM process, MRR is indicated as penetration rates (mm/min).

Damasking: After the process is completed, damasking is done. Damasking is an act of removing mask ant after machining.

Various applications of CHM are discussed below:

Chemical Milling: It is widely used in aircraft industry. It is the preparation of complicated geometry on the work piece using CHM process.

Chemical Blanking: In this application,cutting is done on sheet metal work pieces. Metal blanks can be cut from very thin sheet metal, this cutting may not be possible by conventional methods. Photo chemical Machining: It is used in metal working when close (tight)tolerances and intricate patterns are to be made. This is used to produce intricate circuit designs on semiconductor wafers.

‍Advantages of CHM:

(a) Low tooling cost.

(b) Multiple machining can be done on a work piece simultaneously i.e. at the same time.

(c) No application of force so on risk of damage to delicate or low strength work piece.

(d) Complicated shapes/patterns can be machined.

(e) Machining of hard and brittle material is possible.

Disadvantages and Limitations of CHM:

(a) Slower process, very low MRR, so high cost of operation.

(b) Small thickness of metal can be removed.

(c) Sharp corners cannot be prepared.

(d) Requires skilled operators

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