NC MACHINE UPDATED TO CNC MACHINE
- 1. Introduction to Numerical Control Machining Historical perspective The development of numerical control owes much to the United States air force,which recognized the need to develop more efficient manufacturing methods for modern aircraft. Following World War II, the components used to fabricate jet aircraft became more complex and required more machining. Most of the machining involved milling operations,so the Air Force sponsered a research project at Massachusetts Institue of Technology to develop a prototype NC milling machine. This prototype was produced by retrofitting a conventional tracer mill with numerical control servomechanisms for the three axes of the machine. In March 1952, the MIT Labs held the first demonstration of the NC machine. The machine tool builders gradually began developing their own projects to introduce commercial NC units. Also,certain industry users,especially airframe builders,worked to devise numerical control machines to satisfy their own particular production needs. The Air force continued its encouragement of NC development by sponsoring additional research at MIT to design a part programming language that could be used in controlling N.C. machines.
- 2. What is Numerical Control ? Numerical control can be defined as a form of programmable automation in which process is controlled by numbers,letters and symbols. In NC,the numbers form a programme of instructions designed for a particular workpart or job. When job changes the program of instruction changes. This capability to change a program for each new job gives NC its flexibilty. Numerical control should be considered as a possible mode of controlling the operation for any production situation possesing the following characteristics : Similar workparts in terms of raw material (e.g. metal shock for machining) The work parts are produced in various sizes and geometries. The workparts are produced in batches of small to medium size quantities. A sequence of similar processing steps is required to complete the operation on each workpiece. Many machining jobs meet these conditions. The machined workparts are metal, they are specified in many different sizes and shapes,nad most machined parts produced in the industry today are made in small to medium size lots sizes. To produce each parts a sequence of drilling operations may be required ar aseries of turning or milling operations. The suitability of NC for these kinds of jobs is the reason of tremendous growth of numerical control in metal working industry over the last 25 years.
- 3. Basic components of NC system An operational numerical control systemconsists ofthe following three basic components: 1. Program of instructions. 2. Controller unit, also called machine tool unit. 3. Machine tool or other controlled process. The program of instructions serves as input to the controller unit, which in turn commands the machine tool or other process to be controlled. Program of Instructions. The program of instructions is the detailed step by step set of instructions which tell the machine what to do. It is coded in numerical or symbolic form on some type of input medium that can be interpreted by the controller unit. The most common one is the 1-inch-wide punched tape. Over the years,other forms of input media has been used,including punched cards,magnetic tape, and even 35mm motion picturefilm. There are two other methods of input to the NC systemwhich should be mentioned. The first is by manual entry of instructional data to the controller unit. This is time consuming and is rarely used except as an auxillary means of control or when one or a very limited no. of parts to be made. The second method of input is by means of a direct ling with the computer. This is called direct numerical control, or DNC. ControllerUnit The second basic component of NC systemis the controller unit. This consists ofelectronics and hardware that read and interpret the program of instructionsand convert it to mechanical actions of the machine to ol. The typical elements of the controller unit include the tape reader, a data buffer, signal output channels to the machine tool,and the sequencecontrols to coodinate the overall operation of the foregoing elements. The tape reader is an electrical-mechanical device for the winding and reading the punched tape containing the program of instructions.The signal output channels are connected to the servomotores and othercontrols in machine tools.Most N.C. tools today are provided with positive feedback controls for this purposeand are referred as closed loop systems. However there has been growth in the open loop systems which do not make use of feedback signals to the controller unit. The advocates ofthe open loop concept claim that the realiblity of the systemis great enough that the feedback controls are not needed. Machine Tool The third basic component of an NC systemis the machine tool or othercontrolled process.It is part of the NC systemwhich performs useful work. In the most common example of an NC system,one designed to perform machining operations,The machine tool consists ofthe worktable and spindle as well as the motorsand controls necessary to drive them. It also includes the cutting tools,work fixtures and other auxillary equipment needed in machining operation.
- 4. ABSTRACT Main article: Numerical control The first NC machines were built in the 1940s and 1950s, based on existing tools that were modified with motors that moved the controls to follow points fed into the system on punched tape. These early servomechanisms were rapidly augmented with analog and digital computers, creating the modern CNC machine tools that have revolutionized the machining processes. NUMERICAL CONTROL Numerical control (NC) is the automation of machine tools that are operated by precisely programmed commands encoded on a storage medium, as opposed to controlled manually via hand w heels or levers, or mechanically automated via cams alone. Most NC today is computer numerical control (CNC), in w hich computers play an integralpart of the control . In modern CNC systems, end-to-end component design is highly automated using computer-aided design (CAD) and computer-aided manufacturing (CAM) programs. The programs produce a computer file that is interpreted to extract the commands needed to operate a particular machine via a post processor, and then loaded into the CNC machines for production. Since any particular component might require the use of a number of different tools – drills, saw s, etc., modern machines often combine multiple tools into a single "cell". In other installations, a number of different machines are used w ith an externalcontroller and human or robotic operators that move the component frommachine to machine. In either case, the series of steps needed to produce any part is highly automated and produces a part that closely matches the original CAD design.
- 5. CNC MACHINES
- 6. Description Modern CNC mills differ little in concept from the original model built at MIT in 1952. Mills typically consist of a table that moves in the X and Y axes, and a tool spindle that moves in the Z (depth). The position of the tool is driven by motors through a series of step-down gears in order to provide highly accurate movements, or in modern designs, direct-drive stepper motor or servo motors. Open-loop control works as long as the forces are kept small enough and speeds are not too great. On commercial metalworking machines closed loop controls are standard and required in order to provide the accuracy, speed, and repeatability demanded. As the controller hardware evolved, the mills themselves also evolved. One change has been to enclose the entire mechanism in a large box as a safety measure, often with additional safety interlocks to ensure the operator is far enough from the working piece for safe operation. Most new CNC systems built today are completely electronically controlled. CNC-like systems are now used for any process that can be described as a series of movements and operations. These include laser cutting, welding, friction stir welding, ultrasonic welding, flame and plasma cutting, bending, spinning, hole-punching, pinning, gluing, fabric cutting, sewing, tape and fiber placement, routing, picking and placing (PnP), and sawing.
- 7. Examples of CNC machines CHAPTER:-01 Mills CNC mills use computer controls to cut different materials. They are able to translate programs consisting of specific number and letters to move the spindle to various locations and depths. Many use G-code, which is a standardized programming language that many CNC machines understand, while others use proprietary languages created by their manufacturers. These proprietary languages while often simpler than G-code are not transferable to other machines.
- 8. CHAPTER:-02 Lathe Lathes are machines that cut spinning pieces of metal. CNC lathes are able to make fast, precision cuts using indexable tools and drills with complicated programs for parts that normally cannot be cut on manual lathes. These machines often include 12 tool holders and coolant pumps to cut down on tool wear. CNC lathes have similar control specifications to CNC mills and can often read G-code as well as the manufacturer's proprietary programming language. .
- 9. CHAPTER:-03 Electric dischargemachining Electric discharge machining (EDM), sometimes colloquially also referred to as spark machining, spark eroding, burning, die sinking, or wire erosion, is a manufacturing process in which a desired shape is obtained using electrical discharges (sparks). Material is removed from the workpiece by a series of rapidly recurring current discharges between two electrodes, separated by a dielectric fluid and subject to an electric voltage. One of the electrodes is called the tool-electrode, or simply the "tool" or "electrode," while the other is called the workpiece-electrode, or "workpiece." When the distance between the two electrodes is reduced, the intensity of the electric field in the space between the electrodes becomes greater than the strength of the dielectric (at least in some point(s)), which breaks, allowing current to flow between the two electrodes. This phenomenon is the same as the breakdown of a capacitor. As a result, material is removed from both the electrodes. Once the current flow stops (or it is stopped – depending on the type of generator), new liquid dielectric is usually conveyed into the inter-electrode volume enabling the solid particles (debris) to be carried away and the insulating proprieties of the dielectric to be restored. Adding new liquid dielectric in the inter-electrode volume is commonly referred to as flushing. Also, after a current flow, a difference of potential between the two electrodes is restored to what it was before the breakdown, so that a new liquid dielectric breakdown can occur. Wire EDM Also known as wire cutting EDM, wire burning EDM, or traveling wire EDM, this process uses spark erosionto machine or remove material with a traveling wire electrode from any electrically conductive material. The wire electrode usually consists of brass or zinc-coated brass material. Sinker EDM Sinker EDM, also called cavity type EDM or volume EDM, consists of an electrode and workpiece submerged in an insulating liquid—often oil but sometimes other dielectric fluids. The electrode and workpiece are connected to a suitable power supply, which generates an electrical potential between the two parts. As the electrode approaches the workpiece, dielectric breakdown occurs in the fluid forming aplasma channel) and a small spark jumps.
- 10. CHAPTER:-04 Water jet cutters A water jet cutter, also known as a waterjet, is a tool capable of slicing into metal or other materials (such asgranite) by using a jet of water at high velocity and pressure, or a mixture of water and an abrasive substance, such as sand. It is often used during fabrication or manufacture of parts for machinery and other devices. Waterjet is the preferred method when the materials being cut are sensitive to the high temperatures generated by other methods. It has found applications in a diverse number of industries from mining to aerospace where it is used for operations such as cutting, shaping, carving, and reaming.
- 11. Other CNC tools Many other tools have CNC variants, including: Drills EDMs Embroidery machines Lathes Milling machines Wood routers Sheet metal works (Turret punch) Wire bending machines Hot-wire foam cutters Plasma cutters Water jet cutters Laser cutting Oxy-fuel Surface grinders Cylindrical grinders 3D Printing Induction hardening machines submerged welding knife cutting glass cutting