1. Hot chamber process and
2. Cold chamber process.

Hot Chamber Die Casting Process

In this process. the holding furnace for the molten metal is integrated within the die casting machine. Hot chamber die casting is mainly used for low melting point temperature materials.

Construction

1. Goose neck which is used to pump the molten metal into the cavity is made of grey, alloy or ductile iron ore of cast steel and is submerged into the holding furnace in which molten metal is stored.
2. One end of the goose neck is connected with a nozzle, this is connected with the sprue of stationary die of the machine.
3. Other end has a plunger made of alloy C.I.
4. Plunger is hydraulically operated and is responsible for the entry of the liquid metal into the casting cavity by developing the required pressure for the metal.

Operation

1. Initially, the die is closed.
2. Goose neck is filled with the liquid metal.
3. With the help of the plunger, the liquid metal is forced into the cavity and is allowed to solidify by holding it at the same pressure.
4. Die is opened and the cores are retracted if any.
5. Unused metal is returned back by moving the plunger.
6. Eject the casting and uncover the entry part by plunger. so that the liquid metal enters the goose neck.
7. Process is repeated for next casting.

Cold Chamber Die Casting Process

This process consists of pouring of molten metal into a shot chamber with the help of ladle for each casting cycle. It is commonly used for casting the materials with high melting point such as aluminium, brass. magnesium etc.

Construction

1. Cold chamber die casting machine consists of cylindrical chamber called as shot chamber with hydraulically operated piston or ram.
2. One end of the chamber is connected to the die of the machine.
3. A separate furnace is provided to melt the metal.
4. A small ladle is used to transfer the metal into the shot chamber.

Operation

1. Initially the die is closed after applying die lubricants over the walls of die cavity.
2. Metal in furnace is brought to molten state.
3. Then, molten metal is poured into the shot chamber by using auto ladle or manually operated ladle at the previously fixed instant of time in the casting cycle.
4. Hydraulic ram is operated so that the molten metal is forced into the die cavity with a pressure around 150 MPa. The same pressure is maintained until solidification is completed.
5. Die is then opened and the casting is taken out with the help of ejector pins.
6. Now the plunger moves back to its initial position. Same process is repeated for next casting.

Applications

1. It is used for casting high melting point alloys of aluminium, brass, copper and aluminium—zinc in manufacturing industry.
2. Industrial equipment’s like motor switches, rotor fan, electrical sockets, etc.

Advantages

1. The castings produced by this method are of dense structure and have more dimensional accuracy.
2. Die components experiences less thermal stresses due to low temperature of molten metal.
3. Efficiency and life of the casting is more.

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Among all the machine tools, the jig boring machine is most accurate (accuracy ranges from 0.0025 mm) and precise. These machines are mainly used to manufacture components which need a greater degree of accuracy like jigs. fixtures, tools, etc. A typical diagram of jig boring machine is shown in the figure.

Parts of Jig Boring Machine

Bed:

It is a box type and rigid construction. It acts as main supporting member. It supports a vertical colunm at the back and saddle at the front.

Table and Saddle:

The saddle is mounted on the base. It gives cross-feed to the work. The table is mounted over the saddle and it can be adjusted cross-wise. The table and saddle is provided with measurement reading and clamping mechanisms. A separate motor supplies power for the movement of table and saddle.

Spindle Head:

It slides in front of the column. It houses drive gear box, quill and feed gear box for the spindle. An indicator device is provided on spindle head, to measure the boring depth accurately. The driving mechanism provided to it is capable of giving speeds ranging from 300-1500 revolutions per minute. The quill is attached to it. which slides in the housing.

Column:

It is a hollow vertical structure. The colunm is provided with vertical guideways and it supports spindle head. The spindle head slides on the vertical guideways of the column. It houses the counter weights, to balance the spindle head.

These machines are characterized by,

1. Provision of highest accuracy through rigidity.

2. Locating and spacing holes by accurate measuring of distance.

3. Low thermal expansion.

A jig boring machine is visually similar to the vertical milling machine but not in case of operation and accuracy. To avoid deflections and vibrations, the spindle and other components of the machine are made extremely rigid. Antifriction bearings are used to run the spindle and housings of the spindle are made of invar to avoid its expansion during working at various temperatures. These machines are operated at temperature controlled rooms to avoid inaccuracy in the machine and work.

Types of Jig Boring Machine

The jig boring machines are classified into two types. They are,

Vertical Milling Machine Type:

This machine is visually similar to vertical milling machine it consists of a spindle, column, bed, work table. The spindle is arranged in the vertical axis and the work table is mounted on the bed in front of the column. The table can be moved in parallel, perpendicular and combined directions with respect to column face.

Planer Type:

This machine is designed in such a way that it consists of vertical columns on both sides of the work table which is mounted on the base. The table can be moved to and fro for adjusting the work. A cross rail is arranged on two vertical columns in the form of a bridge and the spindle is mounted on it. In this machine, the movements of the table (longitudinal) and spindle along with cross rail (cross) are used to locate the hole.

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Radial drilling machines are most suitable for drilling on large and heavy workpieces and can drill holes up to 50 mm in diameter. The radial and vertical motion of the arm. horizontal motion of drill head over radial arm makes the machine more versatile.

Parts of Radial Drilling Machine

The main parts of a radial dulling machine are as follows,

Base:

It is a heavy rectangular structure made of graded steel whose upper surface is accurately finished and provided with T slots to clamp work holding devices or to mount heavy works directly. On one end of the base has a vertical column is supported and on another end is mounted with a work table. The base is designed in such a way that it can tolerate heavy vibrations produced while drilling.

Column:

It is a vertical cylindrical structure mounted on the base and is equipped with the motor on top of the column and an elevating screw to provide vertical motion to radial arm in either direction.

Radial Arm:

It is a horizontal extension mounted on the vertical column and can slide vertically on the guideways provided on the column and also can swing around the column tip to 180° or more. Guideways are provided oui front vertical face upon which drill head is slid.

Drill Head:

It is a heavy rigid casting mounted on the guideways of the radial arm and can slide along the guideways to alter the position of the spindle according to the workpiece. It acts as a housing for all the mechanisms of speed and feed.

Spindle Speed and Drive Mechanism:

In most of the cases, a constant speed motor is directly mounted on top of the drill head and spindle obtains multiple speeds and feeds through motor via gear trains. In some cases, the motor is mounted on another side of the radial arm to partially balance the weight of the drill head. And is connected to spindle through bevel gears.

Advantages of Radial Drilling Machine

1. The arrangement is simple and any improvements or modifications can be done easily.
2. More than two holes can be drilled at a time with the help of proper jigs.
3. The various operations such as tapping. reaming. boring, counter-boring, trepanning, spot facing, counter-sinking, etc.. can also be done on this machine.
4. It does not requires highly skilled operator.
5. The cost of operation is less and is a quick process.
6. The work table and base of machine has capacity to accommodate different sizes and various types of jobs.

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Grinding is defined as the process of removing metal in small quantities, by using an abrasive wheel called grinding wheel. In order to bring the workpiece to required size and shape, to obtain quality of work surface and dimensional accuracy grinding process is used. The metal removal is carried out in small quantities, which bring the machining process to desired accuracy. The microscopic examination of removed chips are similar to that of machined metal chips. The unique surface finish and accuracy in size is obtained by the grinding process.

This process, also removes material in a small area where machining is impossible. It is an efficient method of removing material from the machine parts, which are hardened. Due to high hardness of abrasives, complex profiles can be produced with extremely low pressure. Extremely smooth finish at bearing surface can be produced only by this process.

Elements of Grinding

The basic elements of a grinding process include (see Figure 1),

1. Workpiece Material :

Workpiece being ground is firmly held against the rotating grinding wheel, to remove the unwanted metal.

Various parameters of workpiece such as shape, size, stiffness, hardness, chemical and thermal properties have impact on the quality of grinding.

2. Grinding Wheel :

It is the cutting tool, made up of abrasive materials, which should be harder than the workpiece material. The grinding wheel should possess the following properties for better accuracy and surface finish,

1. High hardness and stiffness
2. Low heat sensitivity
3. High wear resistance
4. Better grain size
5. Good structure of bond
6. Highly resistant to thermal and chemical effects.

3. Grinding Machine :

The machine structure provides the static and dynamic constraints between the tool and the workpiece. Type of machines to be selected depends upon the type of operations to be performed.

A perfectly designed grinding machine should experience less vibrations and provide high accuracy movements. Thus, the specification, design and manufacturing of the grinding machine, influence its performance.

4. Kinematics :

Kinematics of grinding process includes the geometry and motions governing the movement or engagement between the workpiece and grinding wheel.

5. Dressing Conditions :

The factors which affect the dressing conditions are type of tool, cooling medium, lubrication, speed and feed, maintenance, etc.

6. Grinding Fluid (Coolant) :

Grinding fluid is used to reduce the wheel wear, cool the workpiece and flush away the swarf (fine chips and abrasive particles). Flow rate, velocity, pressure, physical, chemical and thermal properties of grinding fluid affects its effectiveness.

Advantages of Grinding

1. It can be employed for materials, which are too hard to machine by other processes.
2. Better surface finish and smooth surfaces can be obtained.
3. The pressure required during grinding process is less.
4. Complex profiles can be produced accurately.
5. The grinding wheels have self sharpening property.
6. High cutting speeds can be employed.
7. High material removal rate.
8. The abrasives can sustain at high temperatures.
9. High dimensional accuracy up to ± 0.02 mm can be obtained.

Disadvantages of Grinding

1. High cost of tool, power and labour is required.
2. The value of the operation lies in the quality of finish obtained and accuracy of the product, but not in the amount of material removed.
3. The time taken in removing a certain quantity of stock through grinding operation is more.
4. The grinding wheels wear out more quickly than other types of cutting tools.
5. Incorrect grinding leads to glazing and clogging.

Applications of Grinding

1. It is used for sharpening the cutting tools.
2. It is used for grinding threads.
3. It is used for machining hard surface, which are difficult to machine by HSS and carbide tools.
4. It is used for rapid stock removal from the workpiece.

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Fig. 1: Vacuum forming.

Vacuum forming is also known as Thermoforming. Vacuum forming consists of heating a thermoplastic sheet (0.125 mm to 3.2 mm) to its processing temperature (55°C to 90°C) and forcing it against the counters of the mould. The material is moved pneumatically with difference in pressure created by vacuum. Following figure 1 shows the typical vacuum forming setup.

The mould is closed with hot plastic sheet, creating a mechanical seal between the mould and the sheet. A vacuum is then used to rapidly remove the air between them. Thus, atmospheric pressure forces the hot sheet into the mould and hold it there until it cools and hardens. The sheet can be wrapped over male or female mould as shown in Fig. 2.

Fig. 2: Use of male mould in vacuum forming.

High continuous vacuum after the part has been formed ensures faster cooling, better dimensional tolerances and sharp detail. Male moulds are cheaper to make as compared to female moulds. All thermoplastic materials have a shrinkage factor. The various types of sheet shrink from 0.25

Fig. 3: Use of female mould in vacuum forming

Advantages of Vacuum Forming

1. Low cost for machining and tooling.
2. Low internal stresses and good physical properties in finished parts.
3. The capacity of forming light, thin and strong parts for packing and other use.

Disadvantages of Vacuum Forming

1. Higher cost of using sheet or film instead of plastic pellets.
2. The necessity of trimming the finished parts.

Applications of Vacuum Forming

A wide variety of products may be made from thin sheet plastic using thermoforming. These products include small jelly containers used in restaurants, refrigerator inner part, containers for packing etc.

Products of Vacuum Forming

1. Packaging for cosmetics, chocolates, and biscuits.
2. Yogurt container.
3. Disposable cups.

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Working Principle of Planer Machine

Fig. 1: Principle of operation of a planer.

Planers are rarely used for production work as they are less efficient than other machining processes like milling, grinding etc. In case of planer, the work table slides in the guideways of machine bed. The work table is provided with T-slots for mounting the workpiece (see Figure 1).

The cutting tools are held in tool head and can slide horizontally on cross rail (in a direction perpendicular to the direction of movement of work table). The cutting tool can also be adjusted vertically with the up and down movement of crossrail. Cross rail can slide on vertical guideways of column. Cross rail may move up and down by elevating screws accommodated with in column. Cutting is achieved by movement of work table in guideways (motion X) and feeding the tool at right angle to the movement (Y). Like the shaper, tool post is mounted on the clapper box to avoid interference between the cutting tool and table during idle stroke.

Parts of Planer Machine

Fig. 2: Planer machine.

Main parts (see Figure 2) of a double housing planer are:

1. Bed
2. Worktable
3. Housing and columns
4. Cross rail
5. Tool head
6. Driving and feed mechanism

Bed:

Planer bed is strong and robust structure made of cast iron. The bed acts as foundation of machine and supports other parts of planer. The length of bed is slightly more than the length of stroke. For movement of work table on bed dovetail, flat or V guideways are provided on the top of the bed. For lubrication of guideways, pressure lubrication is adopted. The hollow space with in the box like structure of bed houses the driving mechanisms of work table.

Work table:

The work table holds and supports the workpiece. It slides on the guideways provided in the bed. The worktable is heavy rectangular shape and is made of cast iron. The top face of cast table is accurately finished to locate the workpiece. The T slots are provided on the table so that workpiece and work holding devices may be bolted upon it. Accurately machined holes are also there on top surface of worktable to support stop pins.

Housing and columns:

The columns are vertical members and are there on both sides of the bed in case of double housing planer and on one side in case of an open side planer. In the front of columns, accurately machined guideways are there along which cross rail may slide up and down. Columns enclose cross rail elevating screw, vertical and cross feed screws for vertical and horizontal movement of tool head. These screws may be operated either by hand or power. The column also encloses counter balancing weight for cross rail.

Cross rail:

Cross rail is heavy box like construction between two columns. The cross rail slides on vertical guideways of column. The movement of cross rail may be controlled by hand or by power operated screws. The purpose of cross rail is to carry tool head and to provide cross feed and vertical movements (up and down) to cutting tool. Up and down (vertical) movement to cutting tool or tool head is provided by means of an elevating screw accommodated with in column. The cross feed screw is used for the cross feed movement of tool head. It is very essential that cross rail must remain parallel to work table during cutting to achieve accurate machined surfaces of workpiece.

Tool head:

The tool head of planer is similar to that of shaper in construction. Important parts of tool head are tool slide, swivel base, clapper box, clapper block, tool post. The clapper box of tool head carries a tool post in which cutting tool is held. The tool post is hinged to tool head for the tool during backward (idle) stroke. The tool head slides in the horizontal guideways of cross rail.

Operations Performed on Planer Machine

Operations performed on planer machine are similar to that of shaper. The only difference is that planers are used for planing large workpieces which can not be accommodated by shaper (see Figure 3). The common operations performed on a planer are:

1. Planing flat horizontal surfaces.
2. Planing vertical surfaces.
3. Planing at an angle.
4. Planing slots and grooves.
5. Planing curved surfaces.

Fig. 3: Various surfaces machined by planer.

Work Holding Devices for Planer Machine

Since heavy cuts (as much as 25 mm) are taken at a speed of 20-30 m/minute on a planer, the workpiece must be properly fastened to the work table, various type of devices used for hold workpieces on planer worktable are:

1. Planer vice
2. V blocks
3. Angle plate
4. Paralleiships
5. Cramps
6. Holding with dogs
7. T bolt, nut, washer, wedges and packings etc.

Specifications of Planer Machine

Planers are made in different sizes and are specified by following dimensions:

1. Horizontal distance between vertical columns.
2. Vertical distance between top surface of table and cross rail, (when the cross rail is at the max. height).
3. Maximum length of stroke.

The above three dimensions are principal dimensions and provide the measure of maximum size of the job that can be machined on a particular planer. In addition to these other specifications are:

1. Length of bed.
2. Length of table.
3. Mechanism of driving table (geared or hydraulic)
4. Horsepower of motor.
5. Number of feeds available.
6. Floor space required.
7. Net weight of the machine.

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1. The constant demand for decreasing the lead time from design to production.
2. The cost of finishing operation is necessary to be taken nearly as 15
3. 

   Figure 1: Abrasive Flow Finishing.

Working Principle of Abrasive Flow Finishing

Thus, a manual finishing operation is needed instead of automated finishing operation. The working principle of abrasive flow finishing process is shown in the figure 1. It comprises of two cylinders placed vertically in the opposite direction to each other, and partially filled with media. And workpiece is positioned in between the cylinders. The viscosity of media is so high that it can hold between the fingers. The media deforms like a ball made of rubber when certain amount of pressure applied. The abrasive media is forced through the passages formed by workpiece or tooling in the forward and backward direction. If the restriction offered by the passage way is more then large amount of force is required. In Abrasive Flow Finishing, the velocity of media is controlled by the cross-sectional area of passages. Abrasive flow finishing process is also known as multi-point cutting process since, abrasive particles are used as cutting tools.

Advantages of Abrasive Flow Finishing

1. It is used for machining multiple components simultaneously to increase the productivity.
2. The same machine can be used for wide range of jobs by varying tools and machining parameters, media and abrasive due to high flexibility.
3. Abrasive flow finishing is applicable for both metals and non-metals.
4. It provides the better accuracy, high efficiency, economy and consistency.

Limitations of Abrasive Flow Finishing

1. The finishing rate is low when compared to other machining process.
2. The abrasive particles tends to get embedded in the ductile materials.
3. It is limited to closed environment.
4. The tool wear is relatively high

Applications of Abrasive Flow Finishing

1. Deburring of aircraft valve bodies.
2. Radiusing of cooling turbine blades.
3. Removing recast layer.
4. Producing compressive residual stresses.

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Figure 1: Friction Welding.

In friction welding, the heat is obtained by the friction between the surfaces of the two parts which are to be joined. These parts are held under pressure, where one part is stationary and other part is made to rotate at high speed. The welded joint is obtained hen a force on the stationary part is applied, after stopping the rotation of the part (see Figure 1).

High friction created due to rotation of the part is converted into heat, this heats the surfaces to high temperature below its melting point. The speed of rotation ranges from 1500 -3000 r.p.m. The weld is completed, when the relative motion between the two parts is stopped with the application of high pressure.

Friction welding is done for 2 to 30 seconds. This type of welding is used for circular parts like bars and pipes etc. The heat effected zone is very narrow and due to which the dissimilar metals can be easily joined.

Steps involved in Friction Welding

Step-1

The two parts to be welded should be held in axial alignment.

Step-2

One of the parts is rotated and accelerated to the required speed, by holding it in the chuck or spindle of a machine.

Step-3

The part held stationary in a movable clamp is now moved towards the rotating component, such that a pressure contact is maintained between them.

Step-4

Pressure is maintained continuously till the high temperature at the contact surface makes the metals plastic for welding. The metal is extruded from the weld region to form an upset.

Step-5

After sufficient heating at the interface, the rotation is stopped by applying the brakes and axial force is further increased to forge the two components.

Advantages of Friction Welding

1. High quality of weld can be obtained.
2. Annealing of weld zone is not required.
3. Power required is less.
4. Process is simple and requires less skilled person.
5. Initial cost is less.
6. It is a clean process.
7. Dissimilar metals can be easily joined.

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Figure 1: Plasma Arc Machining (PAM).

Working Principle of Plasma Arc Machining (PAM)

The gas molecules at room temperature consists of two or more atoms. When the temperature of gas molecules is heated to 2000°C, the molecules dissociated out as atoms. If the temperature is further increased to about 3000°C, the atoms dissociate their electrons and the gas becomes ionized (ions and electrons). The gas in this condition or state is known as plasma. The plasma is commonly developed by direct current generation method as shown in figure 1. It consists of hot tungsten cathode and water-cooled copper anode. The gas is allowed to pass around the cathode and it is made to flow out through the anode. The temperature of plasma depends on the orifice diameter of cathode. The smaller the orifice diameter, the greater is the temperature i.e., 28000°C. Thus, the plasma arc with such high temperature impinges on the workpiece, due to which the material undergoes melting and vaporization. As a result, the material is removed by the stream of ionized gas. The materials which have high thermal conductivity, good oxidation resistance and large heat capacity properties can be cut easily by Plasma Arc Machining (PAM).

The Plasma Arc Machining system use DC power source under following medium.

Dual Gas System

This system requires two types of gases i.e., plasma gas and secondary gas. Generally nitrogen is used as plasma gas. The gases such as argon-hydrogen, carbondioxide, oxygen, etc., are used as secondary gas for shielding of machining zone and they are selected based on material to be cut. The sharp corners on the top portion of the cut edges can be retained by using secondary gas system.

Water Injected Torch

In this system nitrogen is used as plasma gas at pressure more than 1 MPa. Water is used as secondary gas and it is injected through a ceramic nozzle normally at pressure of 1.2 MPa, either radially or swirling vertically about 10 percent of this injected water gets evaporated and forms thin layer of vapour. The nozzle is insulated and plasma is constricted by the steam layer. By using this system less smoke is generated, nozzle life is increased and reduces generation of oxides on the machined edge of the work component. Also, one of the cut edge is obtained exactly straight when water is injected swirling vertically.

Water Muffler

It is a hollow shell which is positioned around the plasma torch. The gap between the shell and plasma torch provides passage for water. Smoke and noise generation is controlled by using water muffler.

Metal removal mechanism of Plasma Arc Machining

Figure 2: Mechanism of Plasma Arc Machining.

The main reason behind the removal of metal in PAM is due to the production of high temperature. The workpiece gets heated by direct electron bombardment and also due to the convection heating from the high temperature plasma. The heat that is produced has the capacity to raise the temperature of the workpiece above its melting point. The molten metal is blown away by the high velocity gas stream. It is possible to remove the metal if 45

Applications of Plasma Arc Machining

The applications of plasma arc machining are as follows,

1. It consists of multiple torch system hence can be used to cut a variety of shapes from single plate at a time.
2. PAM is most commonly used to prepare ends of a pipe section before the welding has been done.
3. CNC types PAM systems are used for performing operations such as punching and shape cutting. Shape cutting operations are performed on light duty plates which are complicated to machine by oxy-fuel system.
4. Suitable for machining materials such as stainless steel, aluminium and copper.
5. The operations which are complicated to turn or cut the material is done by using PAM method.

Limitations of Plasma Arc Machining

1. Surfaces contain metallurgical alterations.
2. It requires secondary machining on the surfaces.
3. Operator requires eye shielding and noise protection.
4. High initial cost of the equipment
5. Shielding may be needed, as the oxidation and scale formation takes place.

Safety Precautions are taken in performing Plasma Arc Machining

The safety precautions that are to be taken while performing plasma arc machining are as follows,

1. It is essential to protect the eyes from the ultraviolet and infrared radiations. These radiations are generated from the plasma flame and if observed in large quantity, it will be harmful to the eye. Hence, more care must be taken while working with plasma.
2. The over-exposing of ultraviolet and infrared radiation causes the reddening of eyes and due to loss of sleep a gritty feeling will be observed by an operator
3. And overexposing of ultraviolet rays may lead to painful skin bums and cancer in most of the cases.
4. Therefore, it is very essential that before going near to the torch. the worker should wear proper glasses and dresses
5. The worker should cover the most of his body and quality of glasses must be good, so that it can protect from ultraviolet and infrared rays.
6. The torches are required to be operated in an airy room so that toxic gases such as No₂, O₂, etc., can be synthesized in the atmosphere.
7. While operating the torch; it may be noticed that the noise levels are very high. Hence, ear plugs should be used to protect the ears.
8. While operating the hand torches, the worker should wear asbestos gloves having leather as inner layer.
9. Every operator seek a consultation by a health physician depending upon the hours limit in operating the plasma torch.

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Figure 1: Chemical Machining.

Working Principle of Chemical Machining

Chemical machining is a process used for removing the material by dipping it into a chemical solution which dissolves all the material of the workpiece. Depending upon the requirement the material is removed from the workpiece portions which are uncovered with the masks.

Steps involved in Chemical Machining

The various steps involved in chemical machining process are as follows.

1. Initially, clean the workpiece thoroughly, such that the masking material can stick easily to the workpiece. This reduces the chances of stray etching on the workpiece, that occurs due to maskant de-bonding.
2. Then, apply the chemical resistant mask on the workpiece surfaces.
3. Dip the workpiece in a chemical solution called etchant for sufficient time period.
4. Maintenance is required to strengthen the chemical solution as it becomes weak with the time by the absorption of workpiece material.
5. Finally, remove the mask and clean the workpiece.

Various Maskants used in Chemical Machining

Maskants are the resistant materials used for covering the parts of the workpiece that are not to be machined. These substances are acidic or alkaline in nature and acts as resistance to etchant, so that etchant does not get penetrated into workpiece material. Based on the method of application, the maskants are classified as cut and peel, screen printing and photochemical. The characteristics of various maskants are,

Cut and Peel Maskants

1. It gives high chemical resistance.
2. Depth of etchant is restricted to 13 mm.
3. It is not suitable for obtaining critical dimensional tolerances.
4. Re-scribing of maskant is possible.
5. It is used in batch size production.

Screen Printing Maskants

1. It is limited to parts with area not more than 1 m × 1 m.
2. Accuracy obtained is low i.e., ( ≤  ± 0.2 mm).
3. It is suitable for flat surfaces or simple contours.
4. It is used for high volume production.

Photochemical Maskants

1. It is suitable for thin materials (upto 0.8 mm thickness).
2. Accuracy obtained is very high compared to other maskants.
3. It is used for complicated and accurate shapes or surfaces.
4. Machining with these maskants gives repeatability of about 0.0005 mm.

The different types of maskants used in chemical machining are neoprene, butyl and vinyl based materials such as vinyl polymer, neoprene polymers, polyethylene, etc.

Advantages of Chemical Machining Process

1. It is a versatile process based on the design aspect.
2. It is possible to machine both the surfaces of the workpiece together.
3. The hard and brittle materials can be easily machined by this process.
4. The complicated contours in chemical machining can be machined without any difficulty.
5. There is no presence of burrs on the workpieces.
6. Tools are available at lower costs.
7. The tooling time is considerably less compared to other processes.

Limitations of Chemical Machining Process

1. It is a time consuming process.
2. It requires maximum floor space.
3. An expertise operator is required for performing the operation.
4. It does not generate the sharpened corners.
5. The cost incurred for manufacturing is more.
6. It machines the minimal thickness of metal.

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