Production Engineering - 3

A shaper operates by moving a hardened cutting tool backwards and forwards across the workpiece. On the return stroke of the ram the tool is lifted clear of the workpiece, reducing the cutting action to one direction (forward stroke) only.

Pattern draft is the taper placed on the pattern surfaces that are parallel to the direction in which the pattern is withdrawn from the mould (that is perpendicular to the parting plane), to allow removal of the pattern without damaging the mould cavity.

Least count is said to be the smallest value that can be measured by a measuring instrument. A Vernier scale on calliper may have a least count of 0.02 mm while a micrometre may have a least count of 0.001 mm.

Gear Hobbing is a continuous generating process in which the tooth flanks of the constantly moving work piece are formed by equally spaced cutting edges of the hob. The main advantage of this process is its versatility to produce a variety of gears including Spur, Helical, Worm Wheels, Serrations, Splines, etc. The main advantage of the method is the higher productivity rate of the gears.

Gear Milling is one of the initial and best known and metal removal process for making gears. This method requires the usage of a milling machine. This method is right now used only for the manufacture of gears requiring very less dimensional accuracy.

Gear shaping is a generating process. The cutter used is virtually a gear provided with cutting edges. The tool is rotated at the required velocity ratio relative to the gear to be manufactured and any one manufactured gear tooth space is formed by one complete cutter tooth. This method can be used to produce cluster gears, internal gears, racks, etc with ease, which may not have the possibility to be manufactured in gear hobbing.

Gear forming: In gear form cutting, the cutting edge of the cutting tool has a shape identical with the shape of the space between the gear teeth. Two machining operations, milling and broaching can be employed to form cut gear teeth.

Simple dies are also known as single operation dies as a single operation is performed for each stroke of the die press.

Progressive dies which performed two or more operations at different stages every time the ram descends.

Compound dies differs from a progressive die in that it performs two or more cutting operations during one stroke of the press at one station only. These dies allow simultaneous cutting of internal as well as external part features in a single stroke in some cases.

Combination dies combines cutting operations with a non cutting operation. The cutting operations may include blanking, piercing, trimming, and cut off and are combined with non cutting operations which may include bending, extruding, embossing, and forming

Drop forging is a metal forming process that a billet is inserted into a die and then hammered until it has assumed the shape of the die. The lower die is a stationary part, while the upper part is a moving hammer droppedonto the workpiece in order to deform it.

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• This process is called sodium silicate moulding process because in this process, the refractory material is coated with a sodium-based binder.
• In this process CO₂ gas is passed through the core or mold. The CO₂ chemically reacts with the odium silicate to cure or harden the binder.

Boring: Boring is an operation to enlarging of an existing hole, which may have been made by a drill or may be the result of a core in a casting.

Drilling: Drilling is a cutting process that uses a drill bit to cut or enlarge a hole of circular cross-section in solid materials. The drill bit is a rotary cutting tool.

Reaming: Reaming is a sizing operation that removes a small amount of metal from a hole already drilled. It is done for two purposes : to bring holes to a more exact size and to improve the finish of an existing hole.

Internal turning: Turning is a form of machining, a material removal process, which is used to create rotational parts by cutting away unwanted material. This may be classified as external or internal. External operations (Turning, Facing, Grooving etc.) modify the outer diameter of the work piece, while internal operations (Drilling, Boring, Reaming, Taping) modify the inner diameter.

• Pure tungsten electrode offers shorter life than coated electrodes because of rapid wear and tear of pure tungsten electrode owing to thermal damage caused by their low current carrying capacity.
• Pure tungsten electrodes are frequently coated oxides of Th, Zr, La & Ce. These oxides are expected to perform two important function.

1. increasing arc stability

2. Increasing the current carrying capacity of the electrodes.

Plug Gauges are used for checking holes of many different shapes and sizes. There are plug gauges for straight cylindrical holes, tapered, threaded square and splined holes. At one end, it has a plug minimum limit size, the ‘go’ end and; at the other end a plug of maximum limit, the ‘no go’ end.

Snap gauges are used for checking external dimensions. Shafts are mainly checked by snap gauges.

Thread gauges are used to check the pitch diameter of the thread.

Positive rake – helps reduce cutting force and thus cutting power requirement.

Negative rake – to increase edge-strength and life of the tool

Zero rake – to simplify design and manufacture of the form tools

Negative back rake angle is preferable for carbide tool. Carbide tools are very brittle in nature, so deformation occurs if we provide positive back rake angle.

Positive back rake angle is used for machining low tensile strength and non-ferrous materials. Negative back rake angles are used for machining high tensile strength material, heavy feed and interrupted cuts.

Wrought iron is a very pure iron where the iron content is of the order of 99.5%. It is produced by re-melting pig iron and some small amount of silicon, sulphur, or phosphorus may be present. It is tough, malleable and ductile and can easily be forged or welded. It cannot however take sudden shock. Chains, crane hooks, railway couplings and such other components may be made of this iron.

Pig iron is an intermediate product of the iron industry. Pig iron has a very high carbon content, typically 3.8–4.7%, along with silica and other constituents of dross, which makes it very brittle, and not useful directly as a material except for limited applications.

Cast iron is an alloy of iron, carbon and silicon and it is hard and brittle. Carbon content in CI may be within 1.7% to 3% and carbon may be present as free carbon or iron carbide Fe₃C. In general, the types of cast iron are (a) grey cast iron and (b) white cast iron (c) malleable cast iron etc

Steel is basically an alloy of iron and carbon in which the carbon content can be less than 1.7% and carbon is present in the form of iron carbide to impart hardness and strength. Two main categories of steel are (a) Plain carbon steel and (b) alloy steel.

Thus, wrought iron is an iron alloy with a very low carbon (less than 0.08%) content in contrast to cast iron.

Sintering is done to increase the final strength.

Sintering is the process whereby the green compacts are heated in a controlled atmosphere which results in decrease in porosity and brittleness which in turn increases the final strength of the component.

Metal working operations may be separated into categories as given below:

a) Direct Compression

b) Indirect compression

c) tension type processes

d) Bending processes

e) shearing processes

• In rolling & forging operations, direct compression forces are used to move metal at right angles to the compression direction
• Indirect compression includes drawing & extrusion, where the metal flows under the action of combined stresses that include a high compressive stress.

The hermaphrodite caliper is a tool used to layout lines that are parallel with the edges of the work piece. It can also be used to locate the center of cylindrical shaped workplaces.

Standard work holding devices used in lathe operations are:

a) Chucks                                                                       b) Centres

c) Carriers (also known as driving dogs)                        d) Face plates                    

e) Mandrels

Chucks:

Four jaw chuck: A chuck with jaws that open & close independently. Independent chucks can be adjusted to accommodate irregularly shaped work pieces such as odd items square in shape.

Three jaw chuck: Used to hold round & hexagonal work.

Collect chuck: Most accurate chuck & is used for high precision work and small tools.

Magnetic chucks: are used to hold iron or steel parts that are too thin (or) that may be damaged in conventional chuck.

Faceplates: Used to hold work that is too large or such a such a shape that it can not be held in a chuck or between centres.

Abrasives are classified into two categories:

Natural Abrasives:

Garnet

Corundum

Emery (impure corundum)

Calcite (calcium carbonate)

Diamond dust

Novaculite

Pumice

Rouge

Sand

Sandstone

Tripoli

Powdered feldspar

Staurolite

Synthetic Abrasives:

Boron carbide

Borazon (cubic boron nitride or CBN)

Ceramic

Ceramic aluminium oxide

Ceramic iron oxide

Dry ice

Glass powder

Steel abrasive

Zirconia alumina

Slags

In EDM a fluid is used to act as a dielectric and to help carry away debris. Quite often kerosene based oil is used as dielectric in EDM. The dielectric fluid is circulated through the tool at a pressure of 0.35 N/m² or less to free it from eroded metal particles, it is circulated through a filter.

In AutoCAD, a block is a collection of objects that are combined into a single named object. Block represents a repeatable item used in drawing.

Advantages of Blocks:

1. It increases the speed of drawing creation
2. Using block greatly reduces the file size of saved drawing
3. Blocks help in keeping consistency in project drawing thus avoiding confusions