КОНТРОЛЬНЫЙ ПИСЬМЕННЫЙ ПЕРЕВОД НАУЧНОГО ТЕКСТА ПО СПЕЦИАЛЬНОСТИ
Automation of manufacturing process
Kalpakjian Serope. Manufacturing engineering and technology. – USA, Addison-Wesley Publishing Company, Inc, 1999. – 1199 p.
Автоматизация производственных процессов
Калпакджан Сероп. Машиностроительное производство и технология. – США, Издательская компания Эдисон-Уэсли, 1999. – 1199 с.
Выполнил:
магистрант кафедры МАХП
группы 226-М1.3
Аскаров И.В
Проверил:
доцент кафедры иностранных языков
в профессиональной коммуникации
Булатова Ирина Михайловна
Казань, 2017
AUTOMATION OF MANUFACTURING PROCESSES
Until about four decades ago, most manufacturing operations were carried out on traditional machinery, such as lathes, milling machines, and presses, which lacked flexibility and required considerable skilled labor. Each time a different product was manufactured, the machinery had to be retooled, and the movement of materials had to be rearranged. The development of new products and parts with complex shapes required numerous trial-and-error attempts by the operator to set the proper processing parameters on the machine. Furthermore, because of human involvement, making parts that were exactly alike was difficult.
These circumstances meant that processing methods were generally inefficient and that labor costs were a significant portion of overall production costs. The need for reducing the labor share of product cost gradually became apparent, as was the need to improve the efficiency and flexibility of manufacturing operations. This need was particularly significant in terms of increased competition, both nationally and from other industrialized countries.
Productivity also became a major concern. Defined as the optimum use of all resources - materials, energy, capital, labor, and technology - or as output per employee per hour, productivity basically measures operating efficiency. With rapid advances in the science and technology of manufacturing and their gradual; implementation, the efficiency of manufacturing operations began to improve and the percentage of total cost represented by labor costs declined.
How can productivity be improved? Mechanization of machinery and operations had reached its peak by the 1940s. Mechanization runs a process or operation with the use of various mechanical, hydraulic, pneumatic or electrical devices. Note that, in mechanized systems, the operator still directly controls the process, and must check each step of the machine's performance. If a tool breaks during machining, if parts overheat during heat treatment, if surface finish begins to deteriorate during grinding, and if dimensional tolerances become too large in metal forming, the operator has to intervene and change one or more process parameters.
The next step in improving the efficiency of manufacturing operations was automation, from the Greek word automates, meaning self-acting. The word automation was coined in the mid-1940s by the U.S. automobile industry to indicate automatic handling of parts between production machines, together with their continuous processing at the machines. During the past three decades, major advances and breakthroughs in the types and extent of automation have occurred. These important developments were made possible largely through rapid advances in the capacity and sophistication of control systems and computers.
Automation can generally be defined as the process of following a predetermined sequence of operations with little or no human labor, using specialized equipment and devices that perform and control manufacturing processes. The meaning and concept of automation has been variously interpreted as follows:
· Semiautomatic or automatic material handling, workpiece loading and unloading in machines and workholding fixtures, and use of other labor-saving devices.
· Automatic cycle control of machines and equipment, including use of mechanical devices, numerical control of machines, and use of computers.
· Complete computer-based control of all aspects of manufacturing operations from raw materials to the finished product.
Automation, in its full sense, is achieved through the use of a variety of devices, sensors, actuators, techniques, and equipment that are capable of observing the manufacturing process, making decisions concerning the changes that should be made in the operation, and controlling all aspects of the operation. Automation is and will continue to be an evolutionary,rather than a revolutionary, concept. All of us are familiar with the evolution of automation, beginning with hand tools and hand-operated simple machines, continuing to mechanized processes and machines, and finally moving to higher levels of automation.
Automation in manufacturing plants has been implemented successfully in the following basic areas of activity:
· Manufacturing processes. Machining, forging, cold extrusion, and grinding operations are examples of processes that have been automated extensively.
· Material handling. Materials and parts in various stages of completion are moved throughout a plant by computer-controlled equipment without human guidance.
· Inspection. Parts are automatically inspected for quality, dimensional accuracy, and surface finish, either at the time of manufacturing (in-process inspection); or after they are made (post process inspection).
· Assembly. Individually manufactured parts are automatically assembled into a product.
· Packaging. Products are packaged automatically.
Automation has several primary goals:
· Integrate various aspects of manufacturing operations, so as to improve product quality and uniformity, minimize cycle times and effort, and thus reduce labor costs.
· Improve productivity by reducing manufacturing costs through better control of production. Parts are loaded, fed, and unloaded on machines more efficiently. Machines are used more effectively and production is organized more efficiently.
· Reduce human involvement, boredom, and possibilities of human error.
· Reduce workpiece damage caused by manual handling of parts.
· Raise the level of safety for personnel, especially under hazardous working conditions.
· Economize on floor space in the manufacturing plant by arranging machines, material movement, and related equipment more efficiently.
Automation can be applied to manufacturing all types of goods, from raw materials to finished products, and in all types of production from job shops to large manufacturing facilities. The decision to automate a new or existing production facility requires the following additional considerations:
· Type of product manufactured.
· Quantity and rate of production required.
· The particular phase of manufacturing operation to be automated.
· High initial cost of equipment.
· Reliability and maintenance problems associated with automated systems.
· Economics.
NUMERICAL CONTROL
Numerical control (NC) is a method of controlling the movements of machine components by directly inserting coded instructions in the form of numerical data (numbers and letters) into the system. The system automatically interprets these data and converts it to output signals. These signals, in turn, control various machine components, such as turning spindles on and off, changing tools, moving the workpiece or the tools along specific paths, and turning cutting fluids on and off.
In order to appreciate the importance of numerical control of machines, let's briefly review how a process such as machining has been carried out traditionally. After studying the working drawings of a part, the operator sets up the appropriate process parameters (such as cutting speed, feed, depth of cut, cutting fluid, and so on), determines the sequence of operations to be performed, clamps the workpiece in a workholding device such as a chuck, and proceeds to make the part. Depending on part shape and the dimensional accuracy specified, this approach usually requires skilled operators. Furthermore, the machining procedure followed may depend on the particular operator, and because of the possibilities of human error, the parts produced by the same operator may not all be identical. Part quality may thus depend on the particular operator or even the same operator on different days or different hours of the day. Because of our increased concern with product quality and reducing manufacturing costs, such variability and its effects on product quality are no longer acceptable. This situation can be eliminated by numerical control of the machining operation.
In numerical control, data concerning all aspects of the machining operation, such as locations, speeds, feeds, and cutting fluid, are stored on magnetic tape, cassette, floppy or hard disks, or paper or plastic tape. Data are stored on punched 25-mm (1-in.) wide paper or plastic tape, as originally developed and still used. The concept of NC control is that holes in the tape represent specific information in the form of alphanumeric codes. The presence (on) or absence (off) of these holes is read by sensing devices in the control panel, which then actuate relays and other devices (called hard-wired controls). These devices control various mechanical and electrical systems in the machine. This method eliminates manual setting of machine positions and tool paths or the use of templates and other mechanical guides and devices. Complex operations, such as turning a part having various contours and die sinking in a milling machine, can be carried out.
Numerical control has had a major impact on all aspects of manufacturing operations. It is a widely applied technology, particularly in the following areas:
· Machining centers.
· Milling, turning, boring, drilling, and grinding.
· Electrical-discharge, laser-beam, and electron-beam machining.
· Assembly operations.
Numerical control machines are now used extensively in small- and medium-quantity production (typically 500 parts or less) of a wide variety of parts in small shops and large manufacturing facilities. Older machines can be retrofitted with numerical control.
Numerical control has the following advantages over conventional methods of machine control:
· Flexibility of operation and ability to produce complex shapes with good dimensional accuracy, repeatability, reduced scrap loss, and high production rates, productivity, and product quality.
· Tooling costs are reduced, since templates and other fixtures are not required.
· Machine adjustments are easy to make with minicomputers and digital readouts.
· More operations can be performed with each setup, and less lead time for setup and machining is required compared to conventional methods.
· Programs can be prepared rapidly and can be recalled at any time utilizing microprocessors.
· Less paperwork is involved.
· Faster prototype production is possible.
· Required operator skill is less, and the operator has more time to attend to other tasks in the work area.
In the next step in the development of numerical control, the control hardware mounted on the NC machine was converted to local computer control with software. Two types of computerized systems were developed: direct numerical control and computer numerical control.
In direct numerical control (DNC), as originally conceived and developed in the 1960s, several machines are directly controlled step by step by a central main frame computer. In this system, the operator has access to the central computer through a remote terminal. Thus handling tapes and the need for computers on each machine are eliminated. With DNC, the status of all machines in a manufacturing facility could be monitored and assessed from the central computer. However, DNC had the crucial disadvantage that if the computer went down, all the machines became inoperative.
A more recent definition of DNC includes the use of a central computer serving as the control system over a number of individual computer numerical control machines with onboard minicomputers. This system provides large memory and computational capabilities, thus offering flexibility, while overcoming the previous disadvantage of DNC.
Computer numerical control (CNC) is a system in which a minicomputer or microprocessor is an integral part of the control panel of a machine or equipment (onboard computer). The part program may be prepared at a remote site by the programmer. However, the machine operator can now easily and manually program onboard computers. The operator can modify the programs directly, prepare programs for different parts, and store the programs. Because of the availability of small computers with large memory, microprocessors, and program editing capabilities, CNC systems are widely used today. We cannot overstate the importance of the availability of low-cost, programmable controllers in the successful implementation of CNC in manufacturing plants.
The advantages of CNC over conventional NC systems are:
· Increased flexibility. The machine can produce a certain part, followed by other parts with different shapes and at reduced cost.
· Greater accuracy.
· More versatility. Editing and debugging programs, reprogramming, and plotting and printing part shape are simpler.
A program for numerical control consists of a sequence of directions that causes an NC machine to carry out a certain operation, machining being the most commonly used process. Programming for NC may be done by an internal programming department, on the shop floor, or purchased from an outside source. Also, programming may be done manually or with computer assistance.
The program contains instructions and commands. Geometric instructions pertain to relative movements between the tool and the workpiece. Processing instructions pertain to spindle speeds, feeds, tools, and so on. Travel instructions pertain to the type of interpolation and slow or rapid movements of the tool or worktable. Switching commands pertain to on/off position for coolant supplies, spindle rotation, direction of spindle rotation, tool changes, workpiece feeding, clamping, and so on.
Manual part programming consists of first calculating dimensional relationships of the tool, workpiece, and work table, based on the engineering drawings of the part, and manufacturing operations to be performed and their sequence. A program sheet is then prepared, which consists of the necessary information to carry out the operation, such as cutting tools, spindle speeds, feeds, depth of cut, cutting fluids, power, and tool or workpiece relative positions and movements. Based on this information, the part program is prepared.
Manual programming can be done by someone knowledgeable about the particular process and able to understand, read, and change part programs. However, the work is tedious, time consuming, and uneconomical - and is used mostly in simple applications.
Computer-aided part programming involves special symbolic programming languages that determine the coordinate points of corners, edges, and surfaces of the part. Programming languageis the means of communicating with the computer and involves the use of symbolic characters. The programmer describes the component to be processed in this language, and the computer converts it to commands for the NC machine. Several languages having various features and applications are commercially available.
Computer-aided part programming has the following significant advantages over manual methods:
· Use of relatively easy to use symbolic language. Several programs have been developed: ADAPT, MINIAPT, UNIAPT, AUTOSPOT and AUTOMAP.
· Reduced programming time. Programming is capable of accommodating a large amount of data concerning machine characteristics and process variables, such as power, speeds, feed, tool shape, compensation for tool shape changes, tool wear, deflections, and coolant use.
· Reduced possibility of human error, which can occur in manual programming.
· Capability of simple changeover of machining sequence or from machine to machine.
· Lower cost because less time is required for programming.
Because numerical control involves the insertion of data concerning workpiece materials and processing parameters, programming must be done by operators or programmers who are knowledgeable about the relevant aspects of the manufacturing processes being used.