Chemical Machining Process | Electro Chemical Machining Process

CHEMICAL MACHINING

In chemical machining, some chemicals are used to remove material from the required portions of the workpiece. This process is also called chemical milling. Chemical milling is done in the following steps.

01 - CHEMICAL MACHINING PROCESS - UNCONVENTIONAL MACHINING PROCESS

Cleaning

The workpiece surface is carefully cleaned.

Masking

The portions of the workpiece which do not require machiningis covered with masking sheets. The sheet is cut and taken from the area where machining is required. Templates are used for this purpose. If the entire area of the workpiece is to be machined, masking is not necessary. Usually vinyl, neoprene and rubber based materials are used as mask sheets.

Etching

After masking, the workpiece is submerged in a hot chemical solution. This solution is called the etchant. For Aluminium Caustic soda is used as etchant. Acids are used for steel, magnesium and titanium alloys. The etchant removes the metal from workpiece by chemical action. The rate of metal removal is about 0.025mm per minute. The rate of metal removal depends upon the concentration and the temperature of the etchant. For higher concentration and higher temperature, the rate of metal removal is more. The amount of metal removal also depends upon the time duration for which the workpiece is immersed in the etchant.

Demasking

After etching, the workpiece is taken out from the etchant. The workpiece is cleaned with the help of water. Then the masking is removed.

ELECTRO CHEMICAL MACHINING (ECM)

Electro chemical machining process is the reverse of electro plating process. The workpiece becomes anode) and the tool becomes cathode. Therefore the workpiece looses metal. Normally, the metal will flow through the electrolyte and get deposited on the cathode. Here the tool is the cathode. Therefore the metal gets deposited on the cathode. The dissolved metal is forced away with the electrolyte.

01 - ELECTRO CHEMICAL MACHINING PROCESS - UNCONVENTIONAL MACHINING PROCESS.

The workpiece is held in a suitable fixture inside a tank. The workpiece is connected to the +ve terminal (anode) of a 20 V D.C. supply. The tool is held in position over the workpiece. The tool is hollow one. It is connected to the –ve terminal (cathode) of the supply.

The shape of the tool depends on the shape to be produced on the workpiece. A small gap of about 0.2mm is maintained between the workpiece and the tool. The sides of the tool are insulated. So the sides of the tool will not machine the workpiece, this avoids taper in the hole machined.

An electrolyte, usually sodium chloride, sodium nitrate or sodium chlorate is passed through the hollow tool.

When the D.C. supply is given, the current flows through the circuit. Electrons are removed from the surface of the workpiece (anode). These ions will attempt to reach the cutting tool (cathode). But these ions are carried away by the fast flowing electrolyte. The tool is fed towards the workpiece the workpiece automatically to maintain the gap between the workpiece and tool surface. The machining rate and surface finish are directly proportional to the current. The electrolyte is filtered and recirculated using a pump. The temperature of the electrolyte is maintained between 25 to 60°C.

Shearing Operations | Process Done in a Pressing Machine

Punching

Punching is a piercing operation. It is the operation of producing a circular hole in a sheet metal using a punch and die.

01 - PUNCHING OPERATION - SHEARING OPERATION

The material pushed out through the die is the scrap. The punch size will be exactly the same as the size of the hole to be pierced. The die opening is made slightly larger to get the clearance. The sheet metal is introduced between the punch and die through the stripper. The punch pierces the hole in the metal when it moves down. The pierced out metal drops down through the die opening. After piercing, the punch moves up. The sheet metal on the die may stick with the punch surface. The stripper strips off the sheet metal from the punch.

Blanking

01 - BLANKING OPERATION - SHEARING OPERATION

Blanking is the operation of cutting off a flat sheet of required shape. The metal blanked out through the die is the required product. The sheet metal left on the die is the scrap. The blank is further processed-bending or drawing is done on the blank. The size of the blank depends on the size of the die. So the size of the die opening is equal to the blank size. Clearance is given to the punch.

Cutting off

01 - CUTTING OFF OPERATION - SHEARING OPERATION

Cutting off is the operation of cutting piece from a sheet metal. The cut is made along a straight line or a curve. The lower blade is fixed to the machine frame. The upper blade is connected to the ram. It slides vertically. The workpiece is placed between the two blades. When the upper blade moves down, it cuts off the sheet metal. A slight clearance is given between the cutting edges of the blades. The clearance depends upon the thickness of the workpiece. In cutting off, there is no scrap.

Parting

01 - PARTING OFF PROCESS - SHEARING OPERTION

Parting is the operation of cutting the sheet metal into two pieces. There are two lower blades fixed to the machine frame. A gap is provided between the cutting edges of the lower blades. This gap depends upon the thickness of sheet metal. The gap can be adjusted. The upper blade is connected to the ram. The workpiece is placed between the upper and lower blades. The upper blade moves down cuts the sheet metal. Some scarp is removed in this operation.

Notching

01 - NOTCHING OPERATION - SHEARING OPERATION

It is the operation of cutting small notches at the edge of the sheet metal. A notching die and punch are used.

Slitting

01 - SLITTING PROCESS - SHEARING PROCESS

It is the operation of cutting a sheet metal in straight line. The cut takes place along the length of the sheet metal.

Lancing

Lancing is the operation of cutting a sheet metal through a small length and then bending the cut portion.

Trimming

During drawing operations, the blank is held over the die by a holder. Impressions are formed on the area gripped by the pressure pad or holder. Impressions are formed on the area gripped by the pressure pad or holder. This unwanted metal surface should be cut off. Cutting off of the excess metal edge is called trimming. Dies and punches similar to blanking dies are used for trimming operation.

Shaving

The edges of components produced in sheet metal operations may not be smooth. They may have burrs and irregularities. These edges are finished by a shearing operation. This operation is called shaving. The component to be finished is located over a die. A shearing punch is used to shear off the burrs.