PRODUCTION TECHNOLOGY

Angular Velocity:  

            The angular velocity of a rotating body is the distance covered per second by a point lying at a distance of one meter from the axis of rotation, along the periphery of circle of 1 meter radius and having its centre along the axis of rotation.

ω = 2πN / 60 rad / sec
V = rω

Work holding devices:

Magnetic chuck:

            There are two types.  They are electromagnetic chuck and permanent magnetic chuck.  The magnetic power of the electromagnetic chuck can be carried according to the size of the work.  But not so in the case of a permanent magnet chuck.  Thus type of work holding device is suited for ferrous work pieces.

De-magnetizer:

            It is a special device used to remove the magnetic power from an object.  In grinding whenever a job is ground by holding in a magnetic chuck, the job will also get some magnetic power.  A demagnetizer is therefore required to remove this.

Vice: 

            Vices are used to hold jobs with narrow surface or non-ferrous work pieces ( which cannot be conveniently held in magnetic chucks ).  A vice may be placed directly on the grinder table or on a magnetic chuck.  There are three types.  They are 

• Plain vice,
• Tilting type vice and
• Universal vice.

Angle plate: 

            Are used to hold the work piece while grinding one surface perpendicular to another surface or while grinding one surface at an angle to another surface.

'V' block:

            Are used to hold the round work piece while grinding a flat on the work piece.  These are used for holding tube or bar work pieces for grinding flat surfaces on the exterior.  Magnetic vee blocks may be used in combination with other mounting devices, such as angle plates which themselves can be clamped to the work table or held in position on a magnetic chuck.

Clamps: 

            are used to hold any work piece or a work holding device.  Alternatively they may be held on a magnetic chuck.

Basics of Machine tools:

            Machine tools produce the required shape by performing some metal removing operation on the raw material.  For this the machine tools

• Hold / support / guide the work piece/ tools.

• Regulate the cutting speed and feed between tool and work piece.

Parts of a Machine Tool:

1. Machine Bed frame and Structure : This houses and supports other parts.  Some are in motion and others are fixed.  this provides stability.

2. Slide ways and Slide : They are attached to the top of bed and guide the slides.  The movement of slides should be accurate.  The different types are flat, vee, dovetail, cylindrical and combined.

3. Spindles and Bearings : Spindles are provided to ensure that the position of axis or rotation is within line.  Members that rotate the work piece and cutters are called spindles.  These spindles are shaft mounted on bearings.  The spindles must be rigid and must have rotational accuracy.

4. Machine tool drives : electric motor is the power unit and the power from motor reaches the work piece or cutter through belts, gears, chains and pulley.

            In machine tools there are two types of motion.  They are

• Primary Motion : This is higher that other speeds.

• Feed motion : This is less than primary motion.

Metal Sawing: This machine is used to produce work piece of desired length.  Following are the different sawing machines.

1. Reciprocating Saw ( manual and power operated )

2. Band saw ( Band filing, Vertical, Horizontal and friction )

3. Circular saw ( Cold saw, Steel friction disk and Abrasive disk )

Lathe: Following are the important parts in a lathe.

1. Head stock,

2. Tail stock,

3. live centre,

4. dead centre,

5. apron,

6. cross slide

7. top slide and

8. Tool post.

            A lathe is specified by

• Length of bed,

• width of bed,

• No of spindle speeds and

• Maximum distance between centers.

            Following are the different types of lathes.

• Speed lathe,

• Engine lathe,

• Special lathe

• Automatic lathe,

• Bench lathe,

• Tool room lathe and

• Turret lathe.

Machining time:

• L - Length of cut.

• f - feed in mm / rev

• S - cutting speed in m / min

• N - Spindle speed and

• D -  Diameter of work piece.

            Machining time = L / f x N            Where N = 1000 S / πD.

Shaping operations:

            There are three shaper diving mechanisms.  They are

1. slotted link quick return mechanism,

2. Whitworth quick return mechanism and

3. Hydraulic mechanism.

            Shaping operations can be used to cut splines and gears.        

Cutting speed : On a shaper may be defined as the average speed of tool during the cutting stroke and primarily depends on number of strokes / min and length of stroke.

            L - length of stroke
            N - Number of strokes / min.
            Distance moved per minute = LN.
            Machining is done during cutting stroke and return stroke is a idle stroke.
            Cutting stroke / Return stroke = 3 / 2
            Cutting time / Total time = 3 / 5.

            Thus actual time to cut LN metres is 3 / 5 min and not 1 minute.  Hence in one minute the tool cuts 5 / 3 LN metres.

Slotting Machines:

            These can be considered as a vertical shaper.  The difference between a shaper and slotter is the direction of cutting action.  They are used to create splines, key ways, Internal and External gears.

Planners:  

            These are similar to shaping machines, but the tool is stationary and the work piece slides back and forth.  The following are the different types of planers.

• Double housing planner.

• Open side planer,

• Pit type planner and

• Divided table planner.

            Following are the differences between shaper and planner.

Drilling Machines:

            Following are the different types of drilling machines.

1. Portable Drilling Machine.
2. Bench type Drilling Machine
3. Sensitive Drilling Machine
4. Multiple Drilling Machine
5. Deep hole Drilling Machine and
6. Automatic Drilling Machine.

Different types of drilling operations:

Drilling:  

            Is used to make circular holes.  Drilling involves the creation of holes that are right circular cylinders. This is accomplished most typically by using a twist drill, something most readers will have seen before. The figure below illustrates a cross section of a hole being cut by a common twist drill.  The chips must exit through the flutes to the outside of the tool. As can be seen in the figure, the cutting front is embedded within the work piece, making cooling difficult. The cutting area can be flooded, coolant spray mist can be applied, or coolant can be delivered through the drill bit shaft.

The characteristics of drilling that set it apart from other powered metal cutting operations are:

• The chips must exit out of the hole created by the cutting.
• Chip exit can cause problems when chips are large and/or continuous.
• The drill can wander upon entrance and for deep holes.
• For deep holes in large work pieces, coolant may need to be delivered through the drill shaft to the cutting front.
• Of the powered metal cutting processes, drilling on a drill press is the most likely to be performed by someone who is not a machinist.

Reaming :  

            This uses a multipoint cutting tool.  Cannot produce holes but produces accurate size and good finish.  Reaming is a process which slightly enlarges a pre-existing hole to a tightly toleranced diameter. A reamer is similar to a mill bit in that it has several cutting edges arranged around a central shaft, as shown below. Because of the delicate nature of the operation and since little material is removed, reaming can be done by hand. Reaming is most accurate for axially symmetric parts produced and reamed on a lathe.

Reamed holes should not intersect with drilled holes, so the configuration below should NOT be implemented

Boring : This operation, enlarges a existing hole and finishes it.  Used when a drill of a particular size is not available.  Adjustable boring head eliminate the need for a complete inventory of expensive large size drills.

Counter boring :  Where as boring enlarges for a entire length of hole, counter boring does not.

Counter sinking : Bevels the mouth of hole with a tool called counter sink.

Tapping : Used to cut threads in drilled holes.

Trepanning : is used when a large hole has to be created on a thin metal sheet.

Types of Work holding devices:

• Machine vice,
• V- Block,
• T bolts,
• Strap clamps,
• Step blocks and
• Angle plate.

Broaching:

• This operation uses a tool called as broach.
• A tapered tool, where there is a teeth of desired contour.  It passes through the work piece and produces the contour in a single pass.
• Used for mass production.
• Can machine both internal and external surfaces
• A broach has 3 types of teeth.  They are Roughing teeth, finishing teeth and semi-finishing teeth.

            It is very similar to shaper but uses a multipoint cutting tool, as it has many teeth.  Each successive tooth has a greater cutting edge.  Each tooth removes a predetermined quantity of material.

Surface Finish Process:

• Honing : It is well cutting process which removes metal by means of a revolving honing tool.  This tool moves up and down inside the work piece.
• Lapping and
• Super finishing.

Welding:

            It is the process of joining different metals.  Various welding and allied process are classified below.

1. Gas Welding

• Air acetylene
• Oxy acetylene
• Oxy hydrogen
• Pressure gas welding.

2. Arc welding 

• Carbon arc welding and
• Shielded metal arc welding.

Oxy-Acetylene Welding:

            In this acetylene is mixed with oxygen in proper proportions.  Produces a temperature of 3200 C.  There are three types of flames produced.  They are

1. Neutral flame : Produces no chemical change on molten metal.  Hence no cambering or oxidizing.
2. Oxidizing flame : Produces a loud roar.  High temperature is reached.  The ratio of oxygen to acetylene is 1.5 : 1.
3. Carburizing flame.

Metal Arc welding:

            It is a arc welding process done by heating the work piece by striking a arc between the electrode and work piece.  The arc melts the electrode and job and molten metal is transferred from electrode to work piece.  The flux coating melts and forms a gaseous shield and slag to prevent atmospheric contamination of molten metal.

Submerged Arc Welding:

            In this instead of a flux coated electrode, granular flux and base electrode is used.  The job remain submerged under the flux.  The flux serves a shield and protects the molten metals from contamination.

Tungsten Inert Gas Welding:

            It is a arc welding process done by heating the job within a electric arc struck between tungsten electrode and job.  A gas shield namely helium or Argon is used to avoid atmospheric contamination of welding pool.

Metal Arc Welding:

            It is done by striking a arc between a continuously fed metal electrode and the job.  No flux is used by t he act and molten metal is protected by helium or Argon.

Plasma Arc Welding:

            In this arc is circulated between tungsten electrode and water cooled nozzle.  Two inert gases are used.  One of them produces the plasma arc and the second acts as a shield.  In this there are two types.

1. Non-transfer arc process:  In this arc is produced between nozzle and tungsten electrode.  Work piece does not form part of electrical circuit.
2. Transfer arc process : This is a arc between tungsten electrode and work piece.

Resistance Welding:

            In this the joint is produced by using the resistance of the work piece for the flow of current and by application of pressure.  No filler metal is required.

Spot welding:

            It is a type of resistance welding process, in which two overlapping sheets of metal are joined by local fusion at one or more spots by the heat produced by resistance to the flow of current, that are held together by the forces or electrodes.

Cold Welding:

            It is a solid state welding carried out at room temperature and no heat is produced.  The condition is that one of the material must be ductile.  Only mechanical pressure is applied.

Ultrasonic Welding:

            In this a high frequency vibratory energy is applied on work piece.  The work piece is held in a interface.  The combine effect of pressure and vibration causes movement of metal molecules and this creates a sound bonding.  This completed in 0.5 - 1.5 seconds.

Friction and Inertial Welding:

            The work piece are rotated and suddenly pressure is applied and both pieces get welded,  Because of the high heat generated.

Atomic-Hydrogen Welding:

            In this the joint is produced by an arc between 2 electrodes in a atmosphere of hydrogen, which acts as shielding gas.  Job does not become a part of electrical circuit.

Electron Beam welding:

            In this joint is produced by heat obtained by concentrated electron beam which contains high speed electrons.

Brazing:

            In this joint is produced by heating to a suitable temperature and by using a filler material having liquidus below the solidus of base metal.  Used for non ferrous metals.

Soldering:

            The melting point of the filler material is below 427^o C.  The melting point of filler material used in brazing is above 427^o C.