Machining, Pattern and Moulding.pdf

Workshop/ Manufacturing Practices  What is Workshop? Workshop is a centre of practical learning about 1. engineering materials, 2. manufacturing practices, 3. tools and equipment and 4. safety precautions to be observed in manufacturing operations. Wh...

Workshop/ Manufacturing Practices  What is Workshop? Workshop is a centre of practical learning about 1. engineering materials, 2. manufacturing practices, 3. tools and equipment and 4. safety precautions to be observed in manufacturing operations. Why to study about Manufacturing Workshop? Manufacturing processes is a very fundamental subject since it is of interest not only to mechanical engineers but also to those from practically every discipline of engineering. It is so because engineering, as a whole, is meant for providing various materials for human consumption. For various products such as plant machinery required for chemical, civil, electrical, electronic, textile, etc., the manufacturing process forms a vital ingredient. A detailed understanding of the manufacturing processes is thus essential for all engineers. This helps them appreciate the capabilities, advantages, and also the limitations of the various manufacturing processes. This in turn helps in the proper design of any product required by them. Firstly, they would be able to assess the feasibility of manufacturing from their designs. They may also find out that there is more than one process available for manufacturing a particular product, and so they can make a proper choice of the process which would require the lowest manufacturing cost, and would deliver the product of desired quality. They may also modify their design slightly to suit the particular manufacturing process they choose. Laboratory Outcomes of Workshop Practices Upon completion of this laboratory course, students will be able to fabricate components with their own hands. They will also get practical knowledge of the dimensional accuracies and dimensional tolerances possible with different manufacturing processes.  By assembling different components, they will be able to produce small devices of their interest. In subsequent sections, we will study in detail about 1. engineering materials, 2. manufacturing practices, 3. tools and equipment and 4. safety precautions to be observed in manufacturing operations.  Engineering materials A product designer, tool designer and design engineer should always be familiar with various kinds of engineering materials, their properties and applications to meet the functional requirements of the design product. They must understand all the effects which the manufacturing processes and heat treatment have on the properties of the engineering materials. Classification of Engineering Materials The ferrous metals are those which have iron as their main constituents. The ferrous metals commonly used in engineering practice are cast iron, wrought iron, steel and alloy steels. The basic principal raw material for all ferrous metals is pig iron which is obtained by smelting iron ore, coke and limestone, in the blast furnace. The principal iron ores with their metallic contents: Pig Iron It is produced in a blast furnace and is the first product in the process of converting iron ore into useful ferrous metal. The iron ore on initial refining and heating in blast furnace becomes pig iron by sand casting into pigs which is a mass of iron roughly resembling a reclining pig. It is roughly of 20" × 9" × 4" in size. Pig iron acts as the raw material for production of all kinds of cast iron and steel products. It is obtained by smelting (chemical reduction) of iron ore in the blast furnace. It is partly refined in a cupola furnace that produces various grades of cast iron. By puddling processes, wrought iron is produced from pig iron. Steel is produced from pig iron by various steel making processes such as bessemer, open-hearth, oxygen, electric and spray steel making. Cast Iron Cast iron is basically an alloy of iron and carbon and is obtained by re-melting pig iron with coke, limestone and steel scrap in a furnace known as cupola. The carbon content in cast iron varies from 1.7% to 6.67%. It also contains small amounts of silicon, manganese, phosphorus and sulphur in form of impurities elements. Cast iron is very brittle and weak in tension and therefore it cannot be used for making bolts and machine parts which are liable to tension or shocks. It has low cost, good casting characteristics, high compressive strength, high wear resistance and excellent machinability. These properties make it a valuable material for engineering purposes. The compressive strength of cast iron is much greater than the tensile strength. The carbon in cast iron is present either of the following two forms: 1. Free carbon or graphite. 2. Combined carbon or cementite. Grey cast iron Grey cast iron is grey in color which is due to the carbon being principally in the form of graphite (C in free form in iron). When fractured it gives grey color. It possesses high vibration damping capacity. It has high resistance to wear. It possesses high fluidity and hence can be cast into complex shapes and thin sections. Applications o The grey iron castings are mainly used for machine tool bodies, Machine tool structures such as bed, frames, column etc. White cast iron The white color is due to the fact that the carbon is this iron is in combined form as iron carbide which is commonly specified as cementite. It is the hardest constituent of iron. Its name is due to the fact that its freshly broken surface shows a bright white fracture. It is very hard due to carbon chemically bonded with iron as iron carbide (Fe3C), which is brittle also. It possesses excellent abrasive wear resistance. Since it is extremely hard, therefore it is very difficult to machine. Wrought Iron Wrought iron is the assumed approximately as purest iron which possesses at least 99.5% iron. This iron is produced from pig iron by re-melting it in the puddling furnace or air furnace or reverberatory furnace. This iron contains practically no carbon and therefore cannot be hardened Properties The wrought iron can be easily shaped by hammering, pressing, forging, etc.  It is never cast and it can be easily bent when cold. Applications It is used for making chains, crane hooks, railway couplings, etc. Steels Steel is an alloy of iron and carbon with carbon content maximum up to 1.7%. The carbon occurs in the form of iron carbide, because of its ability to increase the hardness and strength of the steel. Other elements e.g. silicon, sulphur, phosphorus and manganese are also present to greater or lesser amount to import certain desired properties to it. Plain carbon steel Plain carbon steel is an alloy of iron and carbon. It has good machineability and malleability. It is different from cast iron as regards the percentage of carbon. It contains carbon from 0.06 to 1.5% whereas cast iron possesses carbon from 1.8 to 4.2%. Depending upon the carbon content, a plain carbon steels can divided to the following types: o Dead carbon steel — up to 0.15% carbon o Low carbon or mild steel — 0.15% to 0.45% carbon o Medium carbon steel — 0.45% to 0.8% carbon o High carbon steel — 0.8% to 1.5% carbon Low Carbon or Mild Steel Low carbon steel is sometimes known as mild steel also. It contains 0.20 to 0.30% C. It is tough, malleable, ductile and more elastic than wrought iron. It can be easily forged and welded. It can absorb shocks. It rusts easily. Its melting point is about 1410°C.  It is used for making angle, channels, case hardening steel, rods, tubes, valves, gears, crankshafts, connecting rods, railway axles, fish plates, small forgings, free cutting steel shaft and forged components etc. Medium Carbon Steels Medium carbon steel contains carbon from 0.30 to 0.8%. High Carbon Steels High carbon steels (HCS) contain carbon from 0.8 to 1.5%. Because of their high hardness, these are suitable for wear resistant parts. They may only be used in the manufacture of cutting tools operating at low cutting speeds. High speed steel (18:4:1) High speed steels (HSS) are most commonly used as material for manufacturing cutting tools which is operated at much higher speed i.e. twice or thrice of High Carbon steel. It is the most common kind of cutting tool material. It contains 18% tungsten, 4% chromium and 1 % vanadium, 0.8 carbon and remaining iron. It is considered to be one of the best of all-purpose tool steels. This brand of high speed steel is used for machining operations on steel and non-ferrous materials. This is generally used for lathe, planer and shaper tools, drills, millings cutters, punches etc. Stainless steel Stainless steel contains chromium together with nickel as alloy and rest is iron. It has been defined as that steel which when correctly heat treated and finished, resists oxidation and corrosive attack from most corrosive media. Stainless steel surface is responsible for corrosion resistance. Minimum chromium content of 12% is required for the film’s formation, and 18% is sufficient to resist the most severe atmospheric corrosive conditions. A steel containing 18% chromium and 8% nickel is widely used and is commonly referred to as 18/8 steel. Availability of steel in market Steel are available in market in various rolled forms like sheets, plates, strips, rods, beams, channels, angles, tees etc. as shown in fig. below.  Manufacturing Processes To understand different manufacturing processes please watch the video: Types of Manufacturing Process | Manufacturing Processes Production or manufacturing can be simply defined as value addition processes by which raw materials of low utility and value due to its inadequate material properties and poor or irregular size, shape and finish are converted into high utility and valued products with definite dimensions, forms and finish imparting some functional ability. A lump of mild steel of irregular shape, dimensions and surface, which had almost no use and value, has been converted into a useful and valuable product like bolt by a manufacturing process which imparted suitable features, dimensional accuracy and surface finish, required for fulfilling some functional requirements. Production Engineering covers two domains: (a) Production or Manufacturing Processes (b) Production Management Manufacturing Processes This refers to science and technology of manufacturing products Production Management This is also equally important and essential in the manufacturing world. It mainly refers to planning, coordination and control of the entire manufacturing in most profitable way with maximum satisfaction to the customers by best utilization of the available resources like man, machine, materials and money. In present subject, we will only concentrate on introduction to various manufacturing processes. There are a large number of processes available for manufacture to engineers. These processes can be broadly classified into four categories. 1. Casting processes 2. Forming processes 3. Fabrication processes 4. Material-removal processes 1. Casting Processes These are the only processes where liquid metal is used. Casting is also one of the oldest known manufacturing processes. It requires preparation of a cavity usually in a refractory material to resemble closely the final object to be made. Molten metal is poured into this refractory mould cavity and is allowed to solidify. The object after solidification is removed from the mould.  The solidified object is called casting. 2. Forming Processes These are solid-state manufacturing processes involving minimum amount of material wastage and faster production. In a forming process, metal may be heated to a temperature, which is slightly below the melting temperature and then a large force is applied such that the material flows and takes the desired shape. These are generally economical and, in many cases, improve the mechanical properties too. Some of the metal-forming processes are Rolling Forging Extrusion Wire and Tube drawing Sheet metal operations NOTE: Casting and Forming processes are treated as Primary manufacturing processes which convert raw material or scrap to a basic primary shaped and sized product. Secondary manufacturing processes further improve the properties, surface quality, dimensional accuracy, tolerance, etc. 3. Fabrication Processes These are secondary manufacturing processes where the starting raw materials are processed by any of the previous manufacturing processes described. It essentially involves joining pieces either permanently or temporarily, so that they would perform the necessary function. The joining can be achieved by either or both of heat and pressure and/ or a joining material. Some of the processes of interest in this category are Gas welding, Electric-arc welding, Electric-resistance welding, Thermit welding, Brazing, Soldering. 4. Material-removal Processes These are also the secondary manufacturing processes, where the additional unwanted material is removed in the form of chips from the blank material by a harder tool, so as to obtain the final desired shape. Material removal is normally the most expensive manufacturing process because more energy is consumed and also, a lot of waste material is generated in the process. Still this is widely used because it delivers very good dimensional accuracy and good surface finish. It also generates accurate contours. Material-removal processes are also called machining processes. Various processes in this category are Turning Drilling Shaping and planing Milling Grinding Broaching Sawing. Questions for Practice: 1. What do we learn in manufacturing workshop? 2. What is the necessity to study about Manufacturing workshop? 3. Name the shops available in workshop. 4. State the differences between steel and cast iron? 5. Classify the steels according to the percentage of carbon in it. 6. What is the effect of adding carbon in pure iron? 7. Which steel is commonly used as cutting tool material? State its composition. 8. How does different manufacturing processes improve the value of a material? 9. Name 4 common manufacturing processes. 10. Guess the manufacturing method among Casting, Forming, Welding, Machining: a. Liquid metal is used b. Improves mechanical properties c. Joins two different parts d. Results in very good dimensional accuracy and surface finish  Metal Cutting or Machining Metal cutting or traditional machining processes are also known as conventional machining processes. These processes are commonly carried out in machine shops or tool room for machining a cylindrical or flat job to a desired shape, size and finish on a rough block of job material with the help of a wedge-shaped tool. Rough metallic block Machining  Machining Products The cutting tool is constrained to move relative to the job in such a way that a layer of metal is removed in the form of a chip. Machining processes are performed on metal cutting machines, more commonly termed as machine tools using various types of cutting tools (single or multi-point). Machine Tools A machine tool is a power-driven metal cutting machine which assist in managing the needed relative motion between cutting tool and the job that changes the size and shape of the job material. In metal cutting (machining) process, working motion is imparted to the workpiece and cutting tool by the mechanisms of machine tool so that the work and tool travel relative to each other and machine the workpiece material in the form of shavings (or swarf) known as chips. The machine tools involve various kinds of machines tools commonly named as lathe, shaper, planer, slotter, drilling, milling and grinding machines etc. The machining jobs are mainly of two types namely cylindrical and flats or prismatic. Cylindrical jobs are generally machined using lathe, milling, drilling and cylindrical grinding whereas prismatic jobs are machined using shaper, planner, milling, drilling and surface grinding. Cutting Tool Cutting tools performs the main machining operation. They comprise of single point cutting tool or multipoint cutting tools. It is a body having teeth or cutting edges on it.  Single point cutting tool Multipoint cutting tool A single point cutting tool (such as a lathe, shaper and planner and boring tool) has only one cutting edge, whereas a multi-point cutting tool (such as milling cutter, milling cutter, drill, reamer and broach) has a number of teeth or cutting edges on its periphery. Commonly cutting tool are made from high speed steel. MECHANICS OF METAL CUTTING The work piece is securely clamped in a machine tool vice or clamps or chuck or collet. A wedge shape tool is set to a certain depth of cut and is forced to move in direction as shown in above figure. The tool will cut or shear off the metal, provided the tool is harder than the metal. Cutting Speed, Feed and Depth of Cut Cutting Speed It is defined as the rate at which its cutting edge passes over the surface of the workpiece in unit time. It is expressed in terms of meters per minute.  Selection of a proper cutting speed has to be made very judiciously. If it is too high, the tool gets overheated and its cutting edge may fail. If it is too low, too much time is consumed in machining and full capacity of the tool and machine are not utilized, which results in lowering of productivity and increasing the production cost. Feed Feed is the distance the tool travels towards the unmachined portion of workpiece after every pass of the tool. Feed rate is feed per unit time. Depth of Cut It is defined as the penetration of cutting edge of the tool into workpiece material in each pass. Measured perpendicular to the machined surface. It determines the thickness of metal layer removed by the cutting tool in one pass. Turning Operation Shaping  LATHE MACHINE Lathe is one of the most versatile and widely used machine tools all over the world. It is commonly known as the mother of all other machine tool. The main function of a lathe is to remove metal from a job to give it the required shape and size. The job is secure1y and rigid1y held in the chuck or in between centers on the lathe machine and then turn it against a single point cutting tool which wi1l remove meta1 from the job in the form of chips. Working principal of lathe machine Principal components of a centre lathe A simple lathe comprises of a bed made of grey cast iron on which headstock, tailstock, carriage and other components of lathe are mounted. The major parts of lathe machine are given as under: 1. Bed 2. Head stock 3. Tailstock 4. Carriage 5. Feed mechanism 6. Thread cutting mechanism Bed The bed of a lathe machine is the base on which all other parts of lathe are mounted. It is massive and rigid single piece casting made to support other active parts of lathe. On left end of the bed, headstock of lathe machine is located while on right side tailstock is located. The carriage of the machine rests over the bed and slides on it. Generally, cast iron alloyed with nickel and chromium material is used for manufacturing of the lathe bed. Head Stock The main function of headstock is to transmit power to the different parts of a lathe. It consists of gear train arrangement, main spindle, cone pulley, back gear arrangement. The main spindle possesses chuck to which the work piece can be attached. It supports the work and revolves with the work. The cone pulley is used to get various spindle speed through electric motor. The back gear arrangement is used for obtaining a wide range of slower speeds. Tail Stock Supports long circular job being turned on lathe. Holds drill bit for drilling on lathe. Carriage Carriage is mounted on the outer guide ways of lathe bed and it can move in a direction parallel to the spindle axis. Upper part is known as saddle with cross-slide. The lower part of the carriage is termed the apron in which there are gears to constitute apron mechanism for adjusting the direction of the feed using clutch mechanism and the split half nut for automatic feed.  The cross-slide is basically mounted on the carriage, which generally travels at right angles to the spindle axis. On the cross-slide, a saddle is mounted in which the compound rest is adjusted which can rotate and fix to any desired angle. The tool post holds the tool holder in place by the tool post screw. Chucks Chuck is one of the most important devices for holding and rotating a job in a lathe. It is basically attached to the headstock spindle of the lathe. Three jaws or universal Chuck Four jaw independent chuck All 3 jaws move simultaneously when chuck To move a particular jaw chuck key is rotated key is rotated in one of the key slots. in corresponding key slot. All 4 jaws are independent of each other. It can only hold a job of radially symmetrical It can hold a job of any cross section. cross section e.g., cylindrical Easy and fast to clamp the job in chuck. To clamp the job, centering is required. It Centering is not required. requires skill and time.  Eccentric turning is not possible Eccentric turning can be done Centering accuracy is lower Centering accuracy is better Less gripping power More gripping power Heavier workpieces can’t be held Meant for any kind of job. SPECIFICATION OF LATHE The size of a lathe is generally specified by the following means: Swing or maximum diameter that can be rotated over the bed ways Maximum length of the job that can be held between head stock and tail stock centres Bed length, which may include head stock length also Maximum diameter of the bar that can pass through spindle or chuck. Maximum swing or maximum diameter that can be rotated over carriage Height of centers over bed Number of spindle speeds Size of electrical motor LATHE OPERATIONS Straight Turning: Diameter of job is reduced by a fixed amount. Step Turning: Diameter is reduced in steps after a decided length of straight turning. Taper Turning: Gradual and continuous reduction in diameter for the entire length of turning. Facing: Length of the job is reduced, cross sectional face is machined. Chamfering: The extreme end of job is beveled by 45o. Reason of chamfering: i. To enable nut to pass freely on threaded work piece ii. To remove burrs and protect the sharp end of the work piece from being damaged iii. For better look.  SHAPER Shaper is a reciprocating type of machine tool in which the ram moves the cutting tool backwards and forwards in a straight line. It is intended primarily to produce flat surfaces. These surfaces may be horizontal, vertical, or inclined. A shaper is used to generate flat (plane) surfaces by means of a single point cutting tool Principal Parts of Shaper The main parts are given as under. Base  Column Table Ram Tool head Clapper box Base It is rigid and heavy cast iron body to resist vibration and takes up high compressive load. It supports all other parts of the machine, which are mounted over it. Column The column is a box shaped casting mounted upon the base. It houses the ram-driving mechanism. Two accurately machined guide ways are provided on the top of the column on which the ram reciprocates. Table The table is a box like casting having T -slots both on the top and sides for clamping the work. It provides crosswise and vertical movements to the work clamped in vice over it. Ram  It is the reciprocating part of the shaper, which reciprocates on the guideways provided above the column. Ram is connected to the reciprocating mechanism contained within the column. Tool head The tool head of a shaper performs the following functions- o It holds the tool rigidly, o It provides vertical and angular feed movement of the tool, and o It allows the tool to have an automatic relief during its return stroke using clapper box. Working Principle of Shaper A single point cutting tool is held in the tool holder, which is mounted on the ram. The workpiece is rigidly held in a vice or clamped directly on the table. The ram reciprocates and thus cutting tool held in tool holder moves forward and backward over the workpiece. In a standard shaper, cutting of material takes place during the forward stroke of the ram. The backward stroke remains idle and no cutting takes place during this stroke. Define speed, feed, depth of cut SPECIFICATION OF A SHAPER The size of a shaper is specified by the maximum length of stroke or cut it can make. Usually the size of shaper ranges from 175 to 900 mm. Type of drive (belt drive or individual motor drive), floor space required, weight of the machine, cutting to return stroke ratio, number of stroke power of the motor Crank and Slotted Lever Mechanism The time taken during the idle stroke is less as compared to forward cutting stroke and this is obtained by quick return mechanism. It converts rotary motion of motor into reciprocating motion of ram. The quiz return mechanism is demonstrated in the following video: https://www.youtube.com/watch?v=s3G3au-EyAQ  MILLING A milling machine is a machine tool that removes metal as the work is fed against a rotating multipoint cutter. The milling cutter rotates at high speed and it removes metal at a very fast rate with the help of multiple cutting edges. One or more number of cutters can be mounted simultaneously on the arbor of milling machine. This is the reason that a milling machine finds wide application in production work. Milling machine is used for machining flat surfaces, contoured surfaces, surfaces of revolution, external and internal threads, and helical surfaces of various cross-sections. PRINCIPLE OF MILLING In milling machine, the metal is cut by means of a rotating cutter having multiple cutting edges. For cutting operation, the workpiece is fed against the rotary cutter. PRINCIPAL PARTS OF MILLING MACHINE Base It is a foundation member for all the other parts, which rest upon it. It carries the column at its one end. Column The column is the main supporting member mounted vertically on the base. It is box shaped, heavily ribbed inside and houses all the driving mechanism for the spindle and table feed. The front vertical face of the column is accurately machined and is provided with dovetail guideway for supporting the knee. Knee The knee is a rigid grey iron casting which slides up and down on the vertical ways of the column face. An elevating screw mounted on the base is used to adjust the height of the knee and it also supports the knee. The knee houses the feed mechanism of the table, and different controls to operate it. Saddle The saddle is placed on the top of the knee and it slides on guideways set exactly at 90° to the column face. The top of the saddle provides guide-ways for the table. Table The table rests on ways on the saddle and travels longitudinally. A lead screw under the table engages a nut on the saddle to move the table horizontally by hand or power.  The top of the table is accurately finished and T -slots are provided for clamping the work on vice. Overhanging arm It is mounted on the top of the column, which extends beyond the column face and serves as a bearing support for the other end of the arbor. Spindle It is situated in the upper part of the column and receives power from the motor through belts, gears. and clutches and transmit it to the arbor. Arbor It is like an extension of the machine spindle on which milling cutters are securely mounted and rotated SIZE OF MILLING MACHINE The size of the column and knee type milling machine is specified by The dimensions of the working surface of the table, Its maximum length of longitudinal, cross and vertical travel of the table. number of spindle speeds, power available, floor space required and net weight of machine. Non-Traditional or Unconventional Machining Processes Non-traditional machining processes are also known as un-conventional metal machining or advance machining processes. The recent increase in the use of hard, high strength and temperature resistant materials in engineering has necessitated the development of newer machining techniques. With the exception of grinding, conventional methods of removing material from a workpiece are not readily applicable to these new materials. New materials such as hastalloy, nitralloy, waspalloy, nimonics, carbides etc., are difficult to machine and which possess tremendous applications in aircrafts, nuclear reactors, turbines, special cutting tools etc.  Conventional machining processes when applied to these harder materials have following difficulties which are given as under. o Conventional machining processes are uneconomical to these materials, o Produce poor degree of accuracy and surface finish, o Produce some stress in the metal being cut whereas newer machining techniques are essentially stress free. o These processes are slow and highly insufficient. Non-traditional or unconventional machining processes may be classified on the basis of the nature of energy employed in machining, Chemical o Chemical machining (CHM) Electro-chemical o Electro-chemical machining (ECM) o Electrolytic grinding (ECG) Electro-thermal o Electrical discharge machining (EDM) o Electron beam machining (EBM) o Plasma arc machining (PAM) o Laser beam machining (LBM) Mechanical o Ultrasonic machining (USM) o Abrasive jet machining (AJM) o Water jet machining (WJM) Questions for Practice: 1. Before operating a lathe machine, you should … a. remove all safety guards. b. oil the area surrounding the machine.  c. wear rings and jewelry. d. make sure you know the location of the ON and OFF switch. 2. Carbon steels are identified according to their carbon content percentage. Low-carbon steel contains less than …% carbon. a. 0.45 b. 0.3 c. 0.7 d. 1.5 3. The lathe operates on the principle of... a. the cutter revolving against the work piece. b. the cutting tool, that can be controlled, can be moved vertically across the work piece. c. the work piece rotating against the cutting tool, which can be controlled. d. both cutter and work piece rotating. 4. What is the difference between machine tools and cutting tools? 5. Identify the parts: 6. Write in brief the principle of metal cutting with a suitable diagram. 7. How are the cutting tools classified? Name a few tools of each type. 8. Explain the terms ‘Cutting speed’, ‘Feed’, and ‘Depth of cut’, as applicable to metal cutting. 9. Describe in brief the principal components of a lathe with a suitable diagram. 10. Explain the working principle of Lathe machine. 11. Differentiate between 3-Jaw and 4-Jaw chuck. 12. How is a lathe specified? 13. Explain following operations performed on lathe:  Step turning, Taper turning, Facing, chamfering. 14. Draw a neat sketch of shaper showing the following parts on it: Base, Column, Table, Ram, Vice, Clapper Box. 15. Explain the working principle of shaper. 16. Why is Quick return mechanism used in shaper? 17. Explain the working of Milling machine. 18. Differentiate among Lathe, Shaper and Milling machine. Carpentry The useful work on wood is being generally carried out in a most common shop known as carpentry shop. The work performed in carpentry shops comprises of cutting, shaping and fastening wood and other materials together to produce the products of woods. Therefore, carpentry shop deals with the timber, various types of tools and the art of joinery. Some More Information  Timber is a common name imparted to wood suitable for engineering, construction and building purposes. Timber is obtained from trees by cutting the main body of tree in the suitable sizes after the full growth of tree. The common types of well recognized timbers available in India are Shisham, Sal, Teak, Deodar, Mango, Mahogany, Kail, Chid, Babul, Fir wood, Walnut and Haldu,. Out of these, Deodar, Chid, Kail, Fir wood and Haldu fall in the categories of softwoods and Shisham, Sal, Teak, Kiker, Mango, Walnut fall in the categories of hardwoods. Some of the other foreign timbers commonly used in India are Ash, Burma, Hickory, Oak and Pine. Difference between Hard Wood and Soft Wood S.N Hard Wood Soft Wood o. 1 It is dark in color Its color is light 2 It is heavy in weight. It is light in weight 3 Hard woods are harder and denser. Soft woods are comparatively lighter 4 It has less resin content Few softwoods are resinous. 5 It does not split quickly It gets splitted quickly 6 It is difficult to work. It is easy to work. Its annual rings are well spaced and It’s annual rings are close and often 7 quit indistinct distinct 8 It is slow growing. It is fast growing. It has good tensile resistance but is It has good tensile and shear 9 weak resistance. across the fibers. 10 It does not catch fire very soon It catches fire very soon. FELLING, CONVERSION AND SEASONING OF WOOD Cutting of living or standing trees to obtain timber is called felling of trees. Trees are cut at appropriate time. The best time for sawing the tree is immediately after the tree has achieved its full growth or maturity age so that the maximum quantity and best quality of wood can be obtained. If an immature tree is cut, it will carry a lot of sapwood which may not be much useful for the carpentry work. Contrary to this, if the tree is allowed to stand for long after attaining the maturity the most valuable part of timber will be subjected to decay. Therefore enough care must be taken to see that felling is accomplished only at the appropriate time. Conversion means sawing of timber logs into different commercial sizes. Seasoning of wood is the reduction of the moisture or sap content of it to the point where, under normal conditions of use, no further drying out will take place. The main objective of seasoning is to reduce the unwanted amount of moisture from the timber. As the moisture contained in the cell walls evaporates, shrinkage of the timber takes place. Therefore for  these reasons green or unseasoned timber should not used for any work but for rough work. Once the timber is seasoned before use, it will not shrink, twist or swell during its further use. PLYWOOD For the last so many years, the use of the plywood and other manufactured boards has, in varying degrees have replaced the use of solid timber in the making of furniture, fittings, paneling and many forms of constructional work. Plywood is generally made of three or more sheets of veneer glued together, with the grain of successive plys laid cross-wise. Since the strength of timber lies along the grain, when plys of veneer are bonded in opposing grain direction, strength is distributed to both length and breadth of the piece. The plywood can be obtained in much larger sizes without shrinkage and warping in comparison to plain wood. The molded plywood boats, television and radio cabinets can be formed from plywood. The plywood can withstand easily against humid condition. Plywood is lighter in weight and stronger across the grain than even the toughest hardwoods. Screws and nails can be driven close to the edge of plywood without any danger of splitting. High class surface finish can be are easily obtained on plywood. COMMON TOOLS USED IN CARPENTRY SHOP Common hand tools used in carpentry shop can better be understood through the following video with the link: https://youtu.be/MSqlHwYr-ig Marking and Measuring Tools Marking in order to make wooden components of the required size or the marking of exact dimensions on the wooden piece is essential to produce quality jobs. Some of the important marking and measuring instruments namely Rules, Try Square, Bevel Gauge, Marking Gauge, Spirit Level and Compass are commonly used for this purpose. Rules Rules are straight edge of wood or steel engraved in millimeters- centimeters or in inches-foot or in both.  These are used to mark, measure the length, widths and thicknesses of work-piece. Try Square Try square is generally utilized for o measuring and checking of squareness, perpendicularity of dimensions o testing of finish of planned surfaces o drawing parallel and perpendicular lines. Marking Gauge The marking gauge is made of wood which is important tool utilized to make lines at a uniform distance from the edge of a board or piece of work and is used principally when preparing wooden components to size before jointing. Holding and Supporting Tools Work Bench Every carpenter generally needs a good solid bench or table of rigid construction of hard wood on which he can perform or carry out the carpentry operations. Work bench should be equipped with a vice for holding the work and with slots and holes for keeping the common hand tools. Carpenter Vice Carpenter vice is very important tool in wood working shops for holding wooden jobs Clamp Bar Clamp G or C Clamp Clamps are commonly used in pairs in gluing up operations at the final assembly of wood joinery work. These clamps can provide pressure required to hold joints together until they are secured due to the setting of glues. Cutting Tools Saws Saws are wood cutting tools having handle and a thin steel blade with small sharp teeth along the edge. The rip saw is used for cutting timber along the grains. The teeth of rip saw are chisel-shaped and are set alternately to the right and left. A 24" long point saw is a good for sawing work. Tenon Saw It is lighter and however possesses a thinner blade and finer teeth. The handle is round, to provide a delicate grip for fine cutting. This saw is used where absolutely finer and delicate cutting is required in wood work. Planes A plane is a special tool with a cutting blade for smoothing and removing wood as shavings. It is just like a chisel fixed in a wooden or steel body. Jack plane Jack plane is most commonly used plane. It is good for rough surfaces that require a heavier chip. It is ideal for obtaining a smooth and flat surface. Chisels https://www.youtube.com/watch?v=Nwtl44RUWVo A Chisel is a strong sharp edge cutting tool with a sharp bevel edge at one end. Its construction is composed of handle, tang, ferrule, shoulder, and blade. Chisels are generally made up of high carbon steel. They are used to shape and fit parts as required in joint making. Firmer Chisel Firmer chisel possesses a blade of rectangular section. Mortise Chisel Mortise chisel is designed for heavy work. A mortise chisel has a blade which is very nearly square in section and so may be used as a lever for removing chips and will withstand heavy blows from a mallet. Rasps and Files It is used after planning to obtain a smooth surface. It is also used for cleaning up work at its curved edges, concave section and other similar work. Striking tools Mallets and various types of hammers are generally used as striking tools in carpentry shop. A hammer delivers a sharp blow, its steel face being likely to damage the chisel handle whereas the softer striking surface such as mallet will give better result.  Mallet Claw Hammer The claw hammer is a striking tool. One of its end possesses curved claw which is used for extracting nails in order to provide the extra strength needed for this levering action. The other end is used for light striking work. A strong handle on claw hammer is always necessary for carrying out the task. COMMON WOOD JOINTS  Some extra tools https://www.youtube.com/watch?v=_glqvJZ6qLM https://www.youtube.com/watch?v=tKAPLN-2hOA https://www.youtube.com/watch?v=ea71-qIoTUs Questions for Practice: 1. Differentiate among following carpentry tools: a. Steel Rule and Try Square b. Hand saw and Tenon saw c. Firmer Chisel and Mortise Chisel d. Mallet and Hammer Casting There are a large number of processes available to engineers for manufacturing objects from raw materials. These processes can be broadly classified into four categories. 1. Casting processes (Molten metal is solidified to desired shape) 2. Forming processes (Metal is deformed into desired shape by applying pressure) 3. Fabrication processes (Different parts are joined together to get desired shape) 4. Material-removal processes (Extra metal is removed from blank to get desired shape). Casting Processes These are the only processes where liquid metal is used. Casting is also one of the oldest known manufacturing processes. It requires preparation of a cavity usually in a refractory material to resemble closely the final object to be made. Molten metal is poured into this refractory mould cavity and is allowed to solidify. The object after solidification is removed from the mould. The solidified object is called casting. What is Sand Casting? https://www.youtube.com/watch?v=pwaXCko_Tkw Casting an Iron Wheel in Factory https://www.youtube.com/watch?v=eTr8cscmx-M Advantages Any intricate shapes, internal or external, can be made. It is possible to cast practically any material, be it ferrous or nonferrous. The necessary tools required for casting moulds are very simple and inexpensive. As a result, for trial production or production of a small lot, it is an ideal method. It is possible in the casting process to place the amount of material where it is exactly required. As a result, weight reduction in design can be achieved. Casting of any size and weight, even up to 200 tons can be made. Limitations  The dimensional accuracy and surface finish achieved by the normal sandcasting process would not be adequate for final application in many cases. The sandcasting process is labour intensive to some extent. Some of the applications of the sandcasting process: 1. Cylinder blocks of IC engine 2. Machine-tool beds 3. Water-supply pipes 4. Bells. etc. Steps in Casting The metal casting process has been divided into the following five major operations: Obtaining the Casting Geometry: The process is referred as the study of the geometry of parts and plans, so as to improve the life and quality of casting. Pattern making: In pattern making, a physical model of casting, i.e. a pattern is used to make the mold. The mold is made by packing some readily formed aggregated materials, like molding sand, around the pattern. After the pattern is withdrawn, its imprint leaves the mold cavity that is ultimately filled with metal to become the casting. n case, the castings is required to be hollow, such as in the case of pipe fittings, additional patterns, known as cores, are used to develop these cavities. Coremaking & Molding: In core making, cores are formed, (usually of sand) that are placed into a mold cavity to form the interior surface of the casting. Thus, the annul space between the mold-cavity surface and the core is what finally becomes the casting. Molding is a process that consists of different operations essential to develop a mold for receiving molten metal. Alloy Melting and Pouring: Melting is a process of preparing the molten material for casting. It is generally done in a specifically designated part of foundry, and the molten metal is transported to the pouring area wherein the molds are filled. Casting Cleaning: Cleaning is a process that refers to the different activities performed for the removal of sand, scale, and excess metal from the casting. However, all the operations may not apply to each casting method but such processes play an important role to comply with environmental guidelines. Casting Terms A moulding flask is one which holds the sand mould intact. It is made up of wood for temporary applications or more generally of metal for long-term use. Drag: Lower-moulding flask. Cope: Upper-moulding flask. Cheek: Intermediate moulding flask used in three-piece moulding. Pattern: Pattern is a replica of the final object to be made with some modifications. Core: It is used for making hollow cavities in castings. Pouring Basin: A small funnel-shaped cavity at the top of the mould into which the molten metal is poured. Sprue: The passage through which the molten metal from the pouring basin reaches the mould cavity. In many cases, it controls the flow of metal into the mould. Runner: The passageways in the parting plane through which molten metal flow is regulated before they reach the mould cavity. Gate: The actual entry point through which molten metal enters the mould cavity. Riser: It is a reservoir of molten metal provided in the casting, so that hot metal can flow back into the mould cavity, when there is a reduction in volume of metal due to solidification. Sand-Mould-Making Procedure 1. First, a bottom board is placed either on the moulding platform or on the floor, making the surface even. The drag-moulding flask is kept upside down on the bottom board along with the drag part of the pattern at the centre of the flask on the board. There should be enough clearance between the pattern and the walls of the flask, which should be of the order of 50 to 100 mm. 2. Dry-facing sand is sprinkled over the board and pattern to provide a nonsticky layer. Freshly prepared moulding sand of requisite quality is now poured into the drag and on the pattern to a thickness of 30 to 50 mm. 3. Rest of the drag flask is completely filled with the backing sand and uniformly rammed to compact the sand. The ramming of the sand should be done properly, so as not to compact it too hard, which makes the escape of gases difficult, nor too loose, so that mould would not have enough strength. 4. After the ramming is over, the excess sand in the flask is completely scrapped using a flat bar to the level of the flask edges. Now, with a vent wire, which is a wire of 1 to 2 mm diameter with a pointed end, vent holes are made in the drag to the full depth of the flask as well as to the pattern to facilitate the removal of gases during casting solidification. This completes the preparation of the drag. 5. The finished drag flask is now rolled over, to the bottom board exposing the pattern as shown in Fig. 5. 6. Using a slick, the edges of sand around the pattern is repaired, and cope-half of the pattern is placed over the drag pattern, aligning it with the help of dowel pins. The cope flask on top of the drag is located aligning again with the help of the pins. 7. The dry-parting sand is sprinkled all over the drag and on the pattern. A sprue pin for making the sprue passage is located at a small distance of about 50 mm from the pattern. Also, a riser pin, if required, is kept at an appropriate place. 8. Freshly prepared moulding sand similar to that of the drag along with the backing sand is sprinkled. The sand is thoroughly rammed, excess sand scraped and vent holes are made all over in the cope as in the drag. 9. The sprue pin and the riser pin are carefully withdrawn from the flask. Later, the pouring basin is cut near the top of the sprue. 10. The cope is separated from the drag and any loose sand on the cope-and-drag interface of the drag is blown off with the help of bellows. 11. Now the cope and the drag-pattern halves are withdrawn by using the draw spikes and rapping the pattern all around to slightly enlarge the mould cavity, so that the mould walls are not spoiled by the withdrawing pattern. 12. The runners and the gates are cut in the mould carefully without spoiling the mould. Any excess or loose sand found in the runners and mould cavity is blown away using the bellows. Now the facing sand in the form of a paste is applied all over the mould cavity and the runners, which would give the finished casting a good surface finish. 13. The mould now, as shown in Fig. is ready for pouring. HAND TOOLS USED IN FOUNDRY SHOP In foundry shop, mould making, melting of metal and further casting steps are carried out. Hand riddle Hand riddle consists of a screen of standard circular wire mesh equipped with circular wooden frame. It is generally used for cleaning the sand for removing foreign material such as nails, shot metal, splinters of wood etc. from it. Even power operated riddles are available for riddling large volume of sand. Shovel Shovel consists of a steel pan fitted with a long wooden handle. It is used in mixing, tempering and conditioning the foundry sand by hand. It is also used for moving and transforming the molding sand to the container and molding box or flask. Rammers Rammers are required for striking the molding sand mass in the molding box to pack or compact it uniformly all around the pattern. Sprue pin Sprue pin is a tapered rod of wood or iron which is placed or pushed in cope to join mold cavity while the molding sand in the cope is being rammed. Later its withdrawal from cope produce a vertical hole in molding sand, called sprue through which the molten metal is poured into the mould using gating system. Strike off bar Strike off bar is a flat bar having straight edge and is made of wood or iron. It is used to strike off or remove the excess sand from the top of a molding box after completion of ramming thereby making its surface plane and smooth. Draw spike Draw spike is a tapered steel rod having a loop or ring at its one end and a sharp point at the other. It may have screw threads on the end to engage metal pattern for it withdrawal from the mold. Vent rod Vent rod is shown is a thin spiked steel rod or wire carrying a pointed edge at one end and a wooden handle or a bent loop at the other. After ramming and striking off the excess sand it is utilized to pierce series of small holes in the molding sand in the cope portion. The series of pierced small holes are called vents holes which allow the exit or escape of steam and gases during pouring mold and solidifying of the molten metal for getting a sound casting. Gate cutter Gate cutter is a small shaped piece of sheet metal commonly used to cut runners and feeding gates for connecting sprue hole with the mold cavity. Bellows Bellows gun is hand operated leather made device equipped with compressed air jet to blow or pump air when operated. It is used to blow away the loose or unwanted sand from the surfaces of mold cavities. Patterns A pattern is a replica of the object to be made by the casting process, with some modifications. The dimensions of the pattern are different from the final dimensions of the casting required. Pattern size = casting size ± allowances. Allowances Shrinkage Allowance Machining Allowance Draft Allowance Shake allowance Distortion Allowance All metals shrink when cooling except perhaps bismuth.  Shrinkage of metal during casting will takes place in three stages 1. Shrinkage of molten metal when reducing from pouring temp to freezing temp. (Liquid Shrinkage) 2. Shrinkage of molten metal during freezing. (Liquid Shrinkage) 3. Shrinkage of solid metal when reducing from freezing temp to room temp. (Solid Shrinkage) Pouring Temp. = Freezing Temp. (Melting Temp.) + (150-200) °C. Liquid shrinkage is compensated by providing riser during mould making. Metal in the riser should solidify in the end. Riser volume must be sufficient for compensating shrinkage in casting. Shrinkage allowance is provided on the pattern to compensate the solid shrinkages. Machining Allowance The finish and accuracy achieved in sandcasting are generally poor and, therefore, when the casting is functionally required to be of good surface finish or dimensionally accurate, it is generally achieved by subsequent machining. Also, ferrous materials would have scales on the skin, which are to be removed by cleaning. Hence, extra material is to be provided which is to be subsequently removed by the machining or cleaning process. Pattern Materials The usual pattern materials are wood, metal and plastics. The most commonly used pattern material is wood, the main reason being the easy availability and the low weight. Also, it can be easily shaped and is relatively cheap. But the main disadvantage of wood is its absorption of moisture as a result of which distortions and dimensional changes occur. Ingredients of Moulding Sand The main ingredients of any moulding sand are, the silica grains (SiO2), the clay (as binder), and moisture (to activate the clay and provide plasticity). Besides, some other materials are also added to these to enhance the specific properties of moulding sands. E.g., Coal Dust It is basically used for providing better surface finish to the castings. This when comes into contact with the molten metal would provide a gaseous envelope to keep the molten metal from fusing with the sand thus providing good surface finish. Questions 1. Explain in brief different steps in casting. 2. What is the reason of wide application of casting? 3. Draw a neat sketch of a sand mould. Briefly describe various parts of sand mould. 4. What is the use of a pattern? 5. How does a pattern differ from actual casting product? 6. Why is allowance provided over pattern? 7. Why is riser prepared in sand mould? 8. Which is the most commonly used pattern material? Why? 9. What are the ingredients of moulding sand?