Presentation on theme: "BASIC MECHANICAL ENGINEERING"— Presentation transcript:
1 BASIC MECHANICAL ENGINEERING UNIT VIMACHINE TOOLS
2 MACHINE TOOL Machine tool generally means a metal cutting machine. A machine tool is a power driven device used for shaping, sizing or processing a product to a desired accuracy by removing the excess material in the form of chips.The basic machining operations are turning, drilling, shaping etc…The machine tools have some essential features common to all of them, that is they have a basic structure to which are attached work holding and tool holding devices, arrangements for giving movements to the work piece and the tool for the depth of cut, cutting speed and feed and a drive.
3 There are several types of Special purpose machine tools and Standard machine tools. Special purpose machine tools are meant for specific operations or jobs such as gear cutting machines, thread grinding machines, transfer machines or machining centers.This type of machine tools are designed for only a limited number of operations.They are costlier and suited for large volume of production only.Standard machine tools are general purpose machine tools capable of performing a number of operations.Types of Standard machine tools are:Lathe machine,A drilling machineShaper machineMilling machine andA grinding machine…..
4 WORKING MOTIONS FOR SOME MACHINE TOOLS LATHEDRILLING
7 CUTTING TOOLA cutting tool has one or more sharp cutting edges and is made of a material that is harder than the work material.The cutting edge serves to separate a chip from the parent work material.There are two basic types, (a) single-point tools and(b) multiple-cutting-edge tools.
8 A single-point tool has one cutting edge and is used for operations such as turning. Multiple-cutting-edge tools have more than one cutting edge and usually achieve their motion relative to the work part by rotating.Drilling and milling use rotating multiple-cutting-edge tools.
10 Their basic operation involves rotating a work piece and traversing a sharp cutting tool across its length.Lathe is one of the most widely used machine tools in metal cutting works.These are basically designed to cut cylindrical metal stock and are able to produce screw threads, tapered work, drilled holes.It is used for machining the job (work piece) which is rotated and a cutting tool is fed to cause the cutting action.
19 Advantages:Variety of work materials.Variety of part shapes and geometric features.Dimensional accuracy.Good surface finishes.Disadvantages:Wasteful of material.Time consuming.
20 SHAPER MACHINEShaping and planing are similar operations, both involving the use of a single-point cutting tool moved linearly relative to the work part.In conventional shaping and planing, a straight, flat surface is created by this action.The difference between the two operations is, in shaping the speed motion is accomplished by moving the cutting tool; while in planing, the speed motion is accomplished by moving the work part.
23 WORKING PRINCIPLE OF SHAPER A single point cutting tool is held in the tool holder, which is mounted on the ram.The work piece 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 work piece.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.
24 The feed is given to the work piece and depth of cut is adjusted by moving the tool downward towards the work piece.The time taken during the idle stroke is less as compared to forward cutting stroke and this is obtained by quick return mechanism.
26 Types of shapes that can cut by shaping and planing: V groove,Square groove,T-slot,dovetail slot, andgear teeth.
27 Reciprocating type of machine tool - used for machining prismatic components Job is rigidly held in work holding device- tool held in tool post mounted on the ram of the machine – ram reciprocated to and fro and makes the tool to cut the material in forward strokeNo cutting of material in return stroke (Idle stroke)Forward stroke is cutting strokeReturn stroke is idle stroke
28 PRINCIPAL PARTS OF SHAPER BaseColumnCross-RailTableRamTool headVice
29 Classification of shapers Based on length of the stroke, type of driving mechanism etc shapers are classified as..Horizontal shaperUniversal shaperVertical shaperGeared shaperCrank shaperHydraulic shapers
30 Shaper operations The basic operations done on shaper are: Horizontal cuttingVertical cuttingAngular cuttingIrregular cutting
31 SHAPING MACHINECutting tool in actionPhotographic view of a shaping machine
33 Drilling MachineDrilling is a machining operation used to create a round hole in a work part. .Drilling is usually performed with a rotating cylindrical tool that has two cutting edges on its working end.The tool is called a drill or drill bit.The rotating drill feeds into the stationary work part to form a hole whose diameter is equal to the drill diameter.
34 WORKING PRINCIPLE OF DRILLING MACHINE Twist drill is the most widely used tool in modern drilling practice. It consists of a cylindrical body carrying two spiral flutes cut on it.The twist drill consists of two main parts i.e, a shank, which is gripped in the drill chuck or sleeve, and the other the body which forms the main cutting unit.WORKING PRINCIPLE OF DRILLING MACHINEThe rotating edge of the drill exerts a large force on the work piece and the hole is generated. The removal of metal in a drilling operation is by shearing and extrusion.
35 Two hole types: (a) through hole and (b) blind hole.
36 1. Base2. Column3. Radial arm4. Motor for elevating arm5. Elevating screw6. Guide ways7. Motor for driving d rill spindle8. Drill head9. Drill spindle10. Table
37 Main operating parts of drill machine BaseColumnTableDrilling head
44 Milling MachineMilling is a machining operation in which a work part is fed past a rotating cylindrical tool with multiple cutting edges,The axis of rotation of the cutting tool is perpendicular to the direction of feed.The cutting tool in milling is called a milling cutter and the cutting edges are called teeth.The conventional machine tool that performs this operation is a milling machine.
45 The geometric form created by milling is a plane surface. Variety of shapes possible, high production rates, one of the most versatile, widely used machining operations.
46 PRINCIPLE OF MILLINGIn milling machine, the metal is cut by means of a rotating cutter having multiple cutting edges. For cutting operation, the work piece is fed against the rotary cutter.As the work piece moves against the cutting edges of milling cutter, metal is removed in form chips.Machined surface is formed in one or more passes of the work.
47 Two basic types of milling operations: (a) peripheral or plain milling and (b) face milling.
48 In peripheral milling, also called plain milling, the axis of the tool is parallel to the surface being machined, and the operation is performed by cutting edges on the outside periphery of the cutter.In face milling, the axis of the cutter is perpendicular to the surface being milled, and machining is performed by cutting edges on both the end and outside periphery of the cutter.
49 Types of Milling Machines Column and knee type milling machinesFixed-bed type milling machinePlaner milling machineProduction milling machinesSpecial purpose milling machines
50 Principal parts of milling machine BaseColumnKneeSaddleTableOver armArbor supportElevating screw.
63 Abrasive ProcessesAbrasive machining involves material removal by the action of hard, abrasive particles that are usually in the form of a bonded wheel.Grinding is the most important abrasive process.Other traditional abrasive processes include honing, lapping, super finishing, polishing, and buffing.The abrasive machining processes are generally used as finishing operations
64 They can be used on all types of materials ranging from soft metals to hardened steels and hard non metallic materials such as ceramics and silicon.Some of these processes can produce extremely fine surface finishes, to μm.For certain abrasive processes, dimensions can be held to extremely close tolerances.
65 GrindingGrinding is a material removal process accomplished by abrasive particles that are contained in a bonded grinding wheel rotating at very high surface speeds.The grinding wheel is usually disk-shaped, and is precisely balanced for high rotational speeds.A grinding wheel consists of abrasive particles and bonding material.
66 The bonding material holds the particles in place and establishes the shape and structure of the wheel.The projected abrasive particles act like cutting tool tips and remove metal.Cutting edge becomes dulled and eventually get cracked.This process continues till the abrasive grains get worn out till the level of bond
67 Bond allows the remainder of the worn grains to be torn from the wheel exposing new grains.
68 WORKING PRINCIPLE OF GRINDING A grinding wheel consists of abrasive particles, bonding material and voids.The projecting abrasive particles acts like cutting tool tips and remove metal where a properly selected grinding wheel exhibits self-sharpening action.As cutting proceeds, the abrasive particles at cutting edge become cracked along the cleavage planes due to resistance offered by work piece metal which resists the cutting action.
69 WORKING PRINCIPLE OF GRINDING This process continues till the abrasive grains get worn down till the level of bond.At this point the bond allows the remainder of the worn grains to be torn from the wheel, exposing new grains which were previous below the surface of the wheel and the new grains do further cutting action.
70 Types of Grinding Machines Rough grinding or non precision grindingFloor stand or bench grindersPortable grindersSwing frame grindersAbrasive belt grindersPrecision grindingCylindrical grindersInternal grindersSurface grindersTool and cutter grindersSpecial grinding machines
75 NUMERICAL CONTROL OF MACHINE TOOLS Numerical control (NC) has been developed out of the need for higher productivity, lower cost and most precise manufacturing.In NC systems, operation instructions are inputted to the machine as numbers which are suitably cooled for storing on tapes.These instructions are then automatically carried out in the machine tool in predetermined sequence with pre-set or self-adjusted speed, feed etc with out human intervention.The definition of NC given by electronic industries association (EIA) – “A system in which actions are controlled by direct insertion of numerical data at some point. The system must automatically interpret at least some portion of this data.”
76 Numerical control (NC) is a form of programmable automation in which the mechanical actions of a piece of equipment are controlled by a program containing coded alphanumeric data.The operating principle of NC is to control the motion of the work head relative to the work part and to control the sequence in which the motions are carried out.A programme is prepared which consists of blocks, blocks consisting of combination of characters and numbers in sequence describing the position of the tool and job, the cutting speed and feed.The data converted into coded instructions which are called a Part Programme. As the job changes, the instructions of part program are also changed.
79 Basic Components of NC Machines Program of instructionController unitMachine tool
80 Program of instruction Serves as the input to the control unit which commands the machine tool to be controlled.Detailed step by step procedure which instructs the machine tool what to do.Input media can be punched cards/ magnetic disks or tape/ punched tape.Manual entry (MDI)Direct link to the computer (DNC)
81 Controller unitConsists of electronics and hardware that read and interpret the instructionsInstructions are converted into mechanical actions of the machine toolElements are 1.tape reader 2. data buffer 3. signal output to machine tool 4. feedback channel from M/C tool and 5. data decoding control area
82 Machine toolThe machine tool consists of the worktable, spindle cutting tools, work fixtures, motors and controls and other equipment needed in the machining operation.NC machining centre is an automated production equipment which can perform various operations and has special features like automatic tool changer (ATC) and automatic pallet hanger (APC) which contribute to enhanced productivity.
83 Advantages Higher machine utilisation Machining functions can be easily changedHuman error is reducedScrap rate and rework is reducedDesign changes an be easily incorporatedCan perform various operationsIncreased versatility and reliability
84 Disadvantages Requires high initial cost Maintenance costs are high Skilled and experienced personsPunched tapes are least reliable componentsCostly controller systems are utilised in the machines
85 APPLICATIONSMetal removal process like milling, drilling, boring, turning, grinding etc.Press working machine tools.Welding machines.Inspection machines.Assembly machines.Tube bending.Flame cutting.Laser beam processes.