Direct numerical control
- 1. CAD & CAMNOTES –by S.S.H.RIZVI AssistantProfessor(Mech.Engg.) UNIT-IV CNC A CNC machine is an NC machine with the added feature of an onboard computer. The onboard computer is often referred to as the machine control unit or MCU. Control units for NC machines are usually hardwired, which means that all machine functions are controlled by the physical electronic elements that are built into the controller. The onboard computer, on the other hand, is “soft” wired, which means the machine functions are encoded into the computer at the time of manufacture, and they will not be erased when the CNC machine is turned off. Computer memory that holds such information is known as ROM or read-only memory. The MCU usually has an alphanumeric keyboard for director manual data input (MDI) of part programs. Such programs are stored in RAM or the random-access memory portion of the computer. They can be played back, edited, and processed by the control. All programs residing in RAM, however, are lost when the CNC machine is turned off. These programs can be saved on auxiliary storage devices such as punched tape, magnetic tape, or magnetic disk. Newer MCU units have graphics screens that can display not only the CNC program but the cutter paths generated and any errors in the program. Direct numerical control (DNC) Direct numerical control (DNC), is a system that uses a central computer to control several machines at the same time also known as distributed numerical control (also DNC), the central computer downloads complete programs to the CNC machines, which can be workstations or PCs, and can get the information for the machine operations. The speed of the system is increased, large files can be handled and the number of machine tools used is expanded. It is a common manufacturing term for networking CNC machine tools. On some CNC machine controllers, the available memory is too small to contain the machining program (for example machining complex surfaces), so in this case the program is stored in a separate computer and sent directly to the machine, one block at a time. If the computer is connected to a number of machines it can distribute programs to different machines as required. Usually, the manufacturer of the control provides suitable DNC software. However, if this provision is not possible, some software companies provide DNC applications that fulfil the purpose. DNC networking or DNC communication is always required when CAM programs are to run on some CNC machine control. Wireless DNC is also used in place of hard-wired versions.Controls of this type are very widely used in industries with significant sheet metal fabrication, such as the automotive, appliance, and aerospace industries. Flexible manufacturing cell (FMC). FMC consists oftwo or three processing workstation and a part handling system. The part handling systemis connected to a load/unload station.It is capable of simultaneous production of different parts. FMC is a manufacturing cell or systemconsisting ofone or more CNC machines, connected by automated material handling system, pick-and-place robots and all operated underthe control of a central computer. It also has auxiliary sub-systems like component load/unload station,automatic tool handling system, tool pre-setter, component measuring station,wash station etc. Each of these will have further elements depending upon the requirement as given below, A. Workstations CNC machine tools Assembly equipment Measuring Equipment Washing stations B. Material handling Equipment Load unload stations (Palletizing) Robotics Automated Guided Vehicles (AGVs) Automated Storage and retrieval Systems (AS/RS) C. Tool systems Tool setting stations Tool transport systems D. Control system Monitoring equipments Networks
- 2. CAD & CAMNOTES –by S.S.H.RIZVI AssistantProfessor(Mech.Engg.) Flexible Manufacturing System (FMS) A flexible manufacturing system (FMS) is a manufacturing system in which there is some amount of flexibility that allows the system to react in case of changes, whether predicted or unpredicted. Flexibility in manufacturing means the ability to deal with slightly or greatly mixed parts, to allow variation in parts assembly and variations in process sequence, change the production volume and change the design of certain product being manufactured. This flexibility is generally considered to fall into two categories, which both contain numerous subcategories. The first category, machine flexibility, covers the system's ability to be changed to produce new product types, and ability to change the order of operations executed on a part. The second category is called routing flexibility, which consists of the ability to use multiple machines to perform the same operation on a part, as well as the system's ability to absorb large-scale changes, such as in volume, capacity, or capability. Most FMS consist of three main systems. The work machines which are often automated CNC machines are connected by a material handling system to optimize parts flow and the central control computer which controls material movements and machine flow. The main advantage of an FMS is its high flexibility in managing manufacturing resources like time and effort in order to manufacture a new product.The best application of an FMS is found in the production of small sets of products like those from a mass production. Advantages of FMS Reduced manufacturing cost Lower cost per unit produced, Greater labour productivity, Greater machine efficiency, Improved quality, Increased systemreliability, Reduced parts inventories, Adaptability to CAD/CAM operations. Shorter lead times Improved efficiency Increase production rate Disadvantages of FMS Initial set-up cost is high, Substantial pre-planning Requirement of skilled labour Complicated system CIM The Society of Manufacturing Engineers (SME) defined CIM as ‘CIM is the integration of the total manufacturing enterprise through the use of integrated systems and data communications coupled with new managerial philosophies that improve organizational and personal efficiency'. CIM basically involves the integration of advanced technologies such as computer aided design (CAD), computer aided manufacturing (CAM), computer numerical control (CNC), robots, automated material handling systems, etc. Today CIM has moved a step ahead by including and integrating the business improvement activities such as customer satisfaction, total quality and continuous improvement. These activities are now managed by computers. Business and marketing teams continuously feed the customer feedback to the design and production teams by using the networking systems. Based on the customer requirements, design and manufacturing teams can immediately improve the existing product design or can develop an entirely new product. Thus, the use of computers and automation technologies made the manufacturing industry capable to provide rapid response to the changing needs of customers.
- 3. CAD & CAMNOTES –by S.S.H.RIZVI AssistantProfessor(Mech.Engg.) Automated Guided Vehicles Automated guided vehicle systems (AGVs), commonly known as driverless vehicles, are turning out to be an important part of the automated manufacturing system. With the shift from mass production to mid volume and mid variety, flexible manufacturing systems are increasingly in use. They require not only machine flexibility but also material handling, storage, and retrieval flexibility. Hence, the importance of AGVs has grown in manifold. It is a battery powered driverless vehicle with programming capabilities for destination, path selection and positioning. The AGVs belongs to a class of highly flexible, intelligent, and versatile material handling systems used to transport materials from various loading locations to various unloading locations throughout the facility. The capability related to collision avoidance is nicely inbuilt in AGVS. Therefore, the vehicle comes to a dead stop before any damage is done to the personnel, materials, or structures. They are becoming an integral part of flexible manufacturing system installations. Now a day, AGVS are versatile in nature and possess flexible material handling system. They use modern microprocessor technology to guide a vehicle along a prescribed path and makes correction if the vehicle strays from the path. A system controller receives instructions directly from the host computer, communicates with other vehicles, and issues appropriate commands to each vehicle. To avoid collision, communication is necessary among the AGVs. To facilitate the communication, they are connected through a wire in the floor or by radio. Components of AGVS There are four main components of an automated guided vehicle system. They are as follows: The Vehicle: It is used to move the material within the systemwithout a human operator. The Guide Path: It guides the vehicle to move along the path. The Control Unit: It monitors and directs system operations including feedback on moves, inventory, and vehicles. The Computer Interface: It is connected with other computers and systems such as mainframe host computer, the Automated Storage and Retrieval System (AS/RS), and the Flexible Manufacturing System. Different Types of AGVS There are different types of automated guided vehicles that are able to cater different service requirements. The vehicle types include: AGVS towing vehicles AGVS unit load transporters AGVS pallet trucks AGVS forklift trucks AGVS light load transporters AGVS assembly line vehicles ROBOTS An industrial robot is a general purpose, programmable machine possessing certain anthropomorphic characteristics. Mechanical arm is the most common characteristic of an industrial arm and is used to perform various industrial tasks. Making decisions, capability to communicate with other machines, and capability to respond to sensory inputs are the important attributes of an industrial robot. These capabilities allow the robots to be more versatile in nature. It involves the coordinated control of multiple axes(joints) and use dedicated digital computers as controllers. The various reasons for the commercial and technological importance of industrial robots include the following: (i)Robots can be substituted for humans in hazardous or uncomfortable work environments. A robot performs its work cycle with a consistency and repeatability that cannot be attained by humans. (ii)Robots can be reprogrammed. When the production run of the current task is completed, a robot can be reprogrammed and equipped with necessary tooling to performan altogether different task. (iii)Robots are controlled by computers and can therefore be connected to other computer systems to achieve computer integrated manufacturing. Robot Anatomy A robot joint is a mechanism that permits relative movement between parts of a robot arm. The joints of a robot are designed to enable the robot to move its end effector along a path fromone position to another as desired. The basic movements required for the desired motion of most industrial robots are:
- 4. CAD & CAMNOTES –by S.S.H.RIZVI AssistantProfessor(Mech.Engg.) Rotational Movement This enables the robot to place its arm in any direction on a horizontal direction. Radial Movement This helps the robot to move its end effector radially to reach distant points. Vertical Movement This enables the robot to take its end effector to different heights.These degrees of freedom, in combination with others or independently, define the complete motion of the end effector. Individual joints of the robot arm are responsible for the accomplishment of different movements. The joint movements are in synergy with the relative motion of adjoining links. Depending on the nature of this relative motion, the joints are classified as prismatic or revolute . Applications of Robots Robots are widely employed in the following applications in manufacturing: A. Parts handling: it involves various activities such as: Recognizing, sorting/separating the parts Picking and placing parts at desired locations Palletizing and de-palletizing Loading and unloading of the parts on required machines B. Parts processing:this may involves many manufacturing operations such as: Routing Drilling Riveting Arc welding Grinding Flame cutting Deburring Spray painting Coating Sand blasting Dip coating Gluing Polishing Heat treatment C. Product building: this involves development and building of various products such as: Electrical motors Car bodies Solenoids Circuit boards and operations like o Bolting o Riveting o Spot welding o Seam welding o Inserting o Nailing o Fitting o Adhesive bonding o Inspection