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Introduction to Mechanical Engineering Module-2 1. Machine Tool Operations A machine tool may be defined as a power driven machine to produce a product by removing the excess material using a cutting tool. The excess material removed is called as chips. Various machine tools are available, all these tools perform specific machining operations like, turning, milling, key slots, gear cutting, shaping etc. Among them most common machine tools used are, Lathe, Milling Machine, Drilling Machine, etc,. Lathe is a common machine tool used in almost all the machining, using special attachments almost all the operations can be achieved. 1.1. Working Principle of lathe Lathe is considered as one of the oldest machine tools and is widely used in industries. It is called as mother of machine tools. It is said that the first screw cutting lathe was developed by an Englishman named Henry Maudslay in the year 1797. Every individual part performs an important task in a lathe. Some important parts of a lathe are, Bed, Headstock, Spindle, Tailstock, Carriage, Lead screw, Feed rod. HEAD STOCK SPINDLE COMPOUND REST as TAIL STOCK = CARRIAGE LEAD SCREW A "A CROSS SLIDE | T-FEED GEARING ——— Fig:2.1 Parts of lathe machine Dept. of Mech, Sri Venkateshwara College of Engineering, Bengaluru, 562157 Introduction to Mechanical Engineering Bed: It forms the base of the machine. It is made of cast iron and its top surface is machined accurately and precisely. Headstock: It is mounted permanently on the inner guide ways at the left hand side of the leg bed. It houses a hollow spindle and the mechanism for driving the spindle at multiple speeds. Spindle: It rotates on two large bearings housed on the headstock casting. Tailstock: It is located on the inner guide ways at the right side of the bed opposite to the headstock. Carriage: It is located between the headstock and tailstock on the lathe bed guide ways. Lead screw: It is a long threaded shaft used as master screw. It is brought into operation during thread cutting to move the carriage to a calculated distance. Feed rod: It is placed parallel to the lead screw on the front side of the bed. It is a long shaft which has a key way along its length. Feed rod is a power transmission mechanism used for precise linear movement of the carriage along the longitudinal axis of the lathe. 1.2. Lathe operations: 1.2.1. Turning. huck Revolving Workpiece - Se ee \é—Tool Fig:2.2 Turning Operation It is the most common type of operation in all lathe machine operations. Turning is the operation of removing the excess material from the work piece to produce a cylindrical surface to the desired length. Dept. of Mech, Sri Venkateshwara College of Engineering, Bengaluru, 562157 Introduction to Mechanical Engineering against the slowly rotating work piece such that the serrations are formed on the work piece surface. Workpiece Head stock ——_.| 1.3. Working principles of Knurling tool Movement Fig: 2.4 Knurling operation Drilling Machine. impressions of tool Dead center Feed When the power is given to the motor, the spindle rotates and thereby the stepped pulley attached to it also rotates. On the other end, one more stepped pulley is attached and is used to increase or decrease the speed of the rotational motion. Handle co - |. _-Dnill head and Motor }__}— |_-Spindle ~—Dnill chuck _—Dnill bit |__| “Work table “Column Base Dept. of Mech, Sri Venkateshwara College of Engineering, Bengaluru, 562157 Introduction to Mechanical Engineering Fig:2.5 Parts of drilling machine Now, a V-belt is placed in between the stepped pulleys so as to drive the power transmission. Now the drill bit also rotates which was placed in the chuck and which was in connection with the spindle. As the Pulleys rotates, the spindle also rotates which can rotate the drill bit. Now, by the rotation of hand-wheel, the spindle moves up and down in the vertical direction in order to give the necessary amount of feed to the work and this drill bit is used to make the holes on the component placed in the machine vice. 1.4. Drilling operations: 1.4.1. Drilling This is the operation of making a circular hole by _ removing a volume of metal from the job by a rotating, cutting tool called drill. Drilling removes solid metal from the job to produce a circular hole. Before drilling, the hole is located by drawing two lines at right angle and a center punch is used to make an indentation for the drill point at the center to help the drill in getting started. x A suitable drill is held in the drill machine and SS the drill machine is adjusted to operate at the correct cutting speed. The drill machine is started and the drill starts 4 rotating. Cutting fluid is made to flow liberally __ Fig: 2.6 Drilling operations and the cut is started. The rotating drill bit is made to feed into the job. The hole, depending upon its length, may be drilled in one or more steps. 1.4.2. Boring Boring is performed in a drilling ~< machine for reasons stated as under. To enlarge a hole by means of an adjustable cutting tool with only one cutting edge. g 5--) To finish a hole accurately and to < { bring it to the required size. To machine internal surface of a hole already produced in casting. N Fig: 2.7 Boring Operation Dept. of Mech, Sri Venkateshwara College of Engineering, Bengaluru, 562157 Introduction to Mechanical Engineering i Pe Cutter i} I Arbor 1 Work H ble _| i 5 ares Hl. y, Knee Braces (optional) \.-~Elevating Screw. \ Base Fig:2.9 Parts of Milling Machine 1.6. Milling operations: 1.6.1. Plane milling Plain milling is common type of milling machine operation, producing a simple, flat, horizontal surface parallel to the axis of rotation of a plain milling cutter. Plain milling is performed to produce a plain, flat, horizontal surface parallel to the axis of rotation of a plain milling cutter. The operation is also known as slab milling. Slab Milling Cutter |}_Work wer Fig:2.10 Plane Milling Operation Arbor. fl To perform the operation, the work and the cutter are secured properly on the machine. Dept. of Mech, Sri Venkateshwara College of Engineering, Bengaluru, 562157 Introduction to Mechanical Engineering The depth of cut is set by rotating the vertical feed screw of the table and the machine is started afier selecting the right speed and feed. 1.6.2. Slot milling Fig:2.11(a) Slot Milling Operation Fig:2.11(b) Workpiece atter Slot Milling Operation In this operation slotting cutter is used to produce the slot of given width corresponding to cutter size. The cutter is placed exactly at the centre line of the workpicce and then cut is taken. Slot milling operation can be achieved by both vertical and horizontal milling machines. In both the cases knee is used to give the depth of cut. Fig 2.11 (a) and (b) shows the slot milling operation and work piece after the slot milling operation respectively. Dept. of Mech, Sri Venkateshwara College of Engineering, Bengaluru, 562157 Introduction to Mechanical Engineering Input Devices Part Programs Display Unit [Data Processing, Control Loop Unit Unit silo S8/)s Miscell B18 iscellaneous Motion Data . 2 2 Function i = o||s g\|2 3 2) )> Feedback System Fig:2.12 (b) Components of CNC Machine A CNC System consists of the following elements: 1. Input Device . MCU or Machine Control Unit Machine Tool Driving System Feedback devices Display Unit DARWN = Input Device: The part program is entered into the MCU through the input device. There are various input devices used on a CNC Machine such as a) USB (Universal Serial Bus) Flash drive: Here the USB flash drives transfer data to the control. USB is very common nowadays and its use is increased in modern computers. b) ~~ Serial Communication: A serial communication port connects a computer system and a CNC Machine tool through an interface called RS-232. Most machines have RS-232 port and an RS-232 cable connects the computer and the CNC Machine to transfer data from the computer to the CNC Machine. c) Ethernet Communication: The Ethernet communication is a more reliable and efficient means of transferring part programs from Computer to the CNC Control. d) Conversational Programming: This is another way to input part programs to the controller through a keyboard. Dept. of Mech, Sri Venkateshwara College of Engineering, Bengaluru, 562157 Introduction to Mechanical Engineering 2. MCU Or Machine Control Unit: The Machine Control Unit or the MCU is the heart of the CNC System. It consists of the following components: a) b). c). d). Central Processing Unit: CPU is the brain of the MCU & it comprises of: A control section that retrieves data from the memory and generates signals which in turn activates all MCU components. An ALU (Arithmetic Logic Unit) that performs integer arithmetic operations like addition, subtraction, multiplication, counting etc.. CNC Memory: The memory of the CNC is divided into Main Memory which consists of Read Only Memory (ROM) and Random Access Memory (RAM). The ROM stores the Operating System Software and machine interface programs. The RAM stores the Part programs. Secondary Memory such as Hard disks which is used to store large programs and which can be used by the main memory when required. Input/output Interface: The Input/output interface or the /O interface establishes communication between the machine operator, the components of the CNC system and other connected computers. The Operator control panel is the interface through which the machine operator communicates with the CNC system Machine tool controls: A Machine Tool consists of various axes such as X, Y, Z, A, B, C and a spindle which rotates at the designed RPM. The position and velocity control of each of the axis and the rotational speed control are accomplished by certain hardware components in the MCU. Sequence controls for auxiliary functions: Apart from the general functions like spindle speed, feed rate, etc, certain auxiliary functions like emergency stop, tool changing function, ctc are carried out under part programs. 3. Machine Tool: This can be any type of machine tool such as a Machining center, a turning center, a lathe, milling machine, etc. Dept. of Mech, Sri Venkateshwara College of Engineering, Bengaluru, 562157 Introduction to Mechanical Engineering 2.4. Applications of CNC 1. Machine Tool Applications: 2. Milling, drilling, turning, grinding, boring, 3. Punch presses, EDM profile cutter 4, Laser Cutting Machine 5. Aerospace Applications 6. Component insertion machine in clectronics 7. Drafting Machines (x-y plotters) 8. Coordinate Measuring Machine (CMM) 9. Tape laying Machine for Polymer Composites 10.Filament Winding Machine for Polymer Composites 2.5. 3D Printing 3D printing is a process where a digital model created using computer-aided design software (CAD) is turned into a physical three-dimensional object by adding material a layer at a time. 3D printing is also known as additive manufacturing because material is added during the process of manufacturing to form the object. The opposite of this, known as subtractive manufacturing, is where material is cut away from a sheet or a block of material to form the object, for example manufacturing processes such as milling or laser cutting. Additive manufacturing wastes very little material compared to subtractive manufacturing. The way that 3D printing forms an object in layers allows for objects to be created with very complex geometries that simply could not be manufactured in any other way 2.6. Advantages of 3D Printing 1. Setting up the production system is simpler because it involves fewer stages. There wouldn’t be a need to store inventory in firms. Assembling products can be a simultaneous process to production Layer by layer production allows for much greater flexibility and creativity in the design process. 5. Parts can be completely re-designed so that they are stronger in the areas that they need to be and lighter overall. AYN Dept. of Mech, Sri Venkateshwara College of Engineering, Bengaluru, 562157 Introduction to Mechanical Engineering 6. 3D Printing significantly speeds up the design and prototyping proce 2.7.Limitations of 3D Printing 1. Expensive hardware and expensive materials. This leads to expensive parts, thus making it hard if you were to compete with mass production. 2. It also requires a CAD designer to create what the customer has in mind, and can be expensive if the part is very intricate. 3. 3D Printing is not the answer to every type of production method; 4. Another major disadvantage of 3D printing is that the highly capable printers may potentially replace highly skilled workers, shifting entire companics and countries to people-less production. Differences betwe: 2.8.Difference between subtractive and additive manufacturing dditive and Additive Manufacturing Subtractive Manufacturing 1. Here layer by layer material is added one over another to build desired solid 3-D product 2. Complex shapes can be easily fabricated using additive manufacturing techniques. 3. This manufacturing concept is usually suitable for materials having low melting point, such as plastic. 4. Volumetric density (thus weight) of the constructive material of final component can be controlled during operation. 5. No material wastage takes place in these processes. 6. These processes are applicable to a narrow range of materials. 1. Here layer by layer material is gradually removed from a solid block to fabricate 3-D product 2. Subtractive manufacturing processes have limited ability in fabricating complex shapes. 3. This manufacturing concept can be applied to all solid materials irrespective of melting point. 4. These processes are associated with material wastage in the form of chips, scraps, dissolved ions, vapors, etc. 5. To act as good lubricant, the cutting fluid should possess high lubricity. 6. These processes can efficiently handle a wide variety of materials. \www.difference.minaprem.com 2.9. Applications of 3D printing Here are some examples of the various industries that 3D Printing is utilized. 1. Automotive a. Special Tooling and Fixtures for unique parts b. Make prototypes for parts to test c. Can make customized pieces for specific cars Dept. of Mech, Sri Venkateshwara College of Engineering, Bengaluru, 562157 
