Pakistan Machine Tool Factory Internship Report
My Internship Report at Pakistan Machine Tool Factory (PMTF)...
Indus Institute of Higher Education www.iihe.edu.pk
Pakistan Machine Tool Factory (PMTF)
Internship Report PMTF has rich experience in Designing and Manufacturing of precision engineering goods and its facilities include Designing, Machining, Forging, Heat Treatment, Assembly, Die Casting etc.
M. Yasir Jamil Khan M. Raghib Malik
In the name of Allah most merciful, the benevolent
Indus Institute of Higher Education Internship report submitted in fulfillment of the requirements for the degree of Engineering as per the criteria for engineering program.
Venue: Pakistan Machine Tool Factory (PMTF)
Subject or Topics Covered: • CNC (Computerized Numeric Control) • NC (Numeric Control) • PLC (Programmable Logic Control) • Pneumatic & Hydraulic Controls
12th April, 2009
25th April, 2009
Belongs to: Mohammad Yasir Jamil Khan Mohammad Raghib Malik B.E Electronics Vth Semester
Forewords: The purpose of this report is to explain what we did and learned during internship period with the Pakistan Machine Tool Factory (PMTF). The report is also a requirement for the fulfillment of Indus Institute and Pakistan Engineering Council for engineering program. The report focuses primarily on the electronically controlled machines such as CNC Machines, NC Machines, PLC and Pneumatic and Hydraulic based controls, working environment, successes and short comings that the intern did encounter when handling various tasks assigned by the engineers & supervisor. The various parts of the report reflect the intern’s shortcomings, successes, observations and comments, it would be imperative to be an engineer. Therefore the report gives a number of comments and recommendations on the internship program.
It is hoped that this report would serve as a cardinal vehicle to the improvement of
Table of Contents
Introduction to PMTF……………………………………………. 05 Departments at PMTF……………………………………………. 06
NC and CNC .…...………………………………………………. 11 PLC (Programmable Logic Control)……….……………………………. 25 Hydraulic Systems..………………………………………………. 33 Pneumatic Systems.………………………………………………. 36 Abstracts…………………………………………………………… 40
A Short Introduction to PMTF:
Pakistan Machine Tool Factory (Pvt) Ltd. (PMTF) is a precision engineering goods manufacturing enterprise in Pakistan, established in technical collaboration with M/s. Oerlikon Buhrle & Co. of Switzerland who are the world's renowned manufacturers of Machine Tools. The factory came into regular production in 1971.
It is located Off National Highway, about 35 Km from Karachi City near Landhi Industrial Estate and spread over an area of 226 acres out of which 17 acres are occupied by works. The factory employs about 1900 engineers, technician, workers and other service staff. The layout of the factory is according to the best European standards. This factory is a unit of State Engineering Corporation of Pakistan and is engaged in the production of Machine Tools, Automotive Transmissions and Axles Components, Gears for Locomotives, Pressure Die Cast parts and other products.
PMTF has rich experience in Designing and Manufacturing of precision engineering goods and its facilities include Designing, Machining, Forging, Heat Treatment, Assembly, Die Casting etc.
PMTF is certified to ISO 9001.Quality Assurance System and has excellent Quality Control and Testing facilities to meet the international quality requirement.
Design Centre Machining Tool Room Material Testing Heat Treating Forging Machine Tool Rebuilding
Design Centre: Computer Aided Design & Manufacturing (CAD/CAM) facilities are installed for Product Design and Tools/Jigs/Fixtures Design and CNC Shop in 1990. Engineering software from Computer vision (USA) and Autodesk namely:
CADDS 5 Design View Personal Designer Personal Designer/Personal Machinist Micro draft Personal Data Extract Mechanical Desktop power pack (with Auto Cad)
are used for design of products, tools, jigs, fixtures, cutters, forging & die casting dies, gears, equipments, mechanical devices. Machining: The works facility consists of variety of conventional and CNC machine tools capable of performing various machining operations such as turning, planning, milling, drilling, jig boring, thread grinding, deep hole drilling, gear hobbling,
shaping and shaving, gear grinding, spiral bevel gear cutting, broaching to the close tolerances specified in the design. The maximum machining capabilities are as follows: : Max. 1000 mm dia x 4000 mm length x 800 kg wt. Shaping/Plannin : Max. 6000 mm length x 1500 mm width x 2000 g kg wt. Turning
: Max. 600 mm dia/50 mm dia max.
: 10 module x 700 mm dia max.
: Max. 400 mm dia x 2500 mm length x 500 kg wt.
Pressure Die Casting
: Max 650 ton locking force x 12 kg wt.
Besides above facilities special purpose machines are available for die-sinking, spark erosion, thread grinding, jig boring, spine rolling, vertical turning, copy milling for intricate precision components. Tool Room: The factory has a fully equipped Tool Room facility capable of manufacturing jigs & fixtures, special tools like drills, gauges, cutters and holding devices, special high precision machine tools like jig boring, thread grinding, die sinking, relieving lathes, vertical copying lathes, precision milling machines and special purpose tool grinding of Swiss and German origin supplements the facility and ensures that all specifications and tolerances essential for tool room accuracy is met. The Tool Room is linked with Tool Design Section fully equipped with computer Aided Design facilities and supported by Metrology section located in same area for precise calibration and control of tool room products. All recommended international standards are followed for toolings.
Material Testing: a. Metallographic: Complete Evaluation of : Macro and Micro Structure Non - Metallic Inclusion & segregation Case Hardening and Case Depth Photo Micrograph of Structure Failure Analysis b. Mechanical Testing: Facilities to determine: Mechanical Properties Stress - Strain Tensile and Compressive Strength Shear and Impact Test c. Chemical Testing: Complete Analysis of: Metals and Alloys Ferrous and Non Ferrous Elements Paints, Chemicals, Ores, Oils Greases etc d. Non-Destructive Testing: Determination of: Internal Cracks by Ultrasonic Testing Surface Cracks by Magnaflux and Dye - Penetration Heat Treatment: The Heat Treatment shop is the largest and the most well equipped in the country. The equipment is of French, German and Italian origin. The Facilities has : 4
- For Carburizing and Case Hardening : Five Sealed Quench Furnaces Three Gas Fired Pit-type Muffle Furnaces Two Rotary Hearth Furnaces with Quenching Press Electrically Heated Tempering Furnace For Induction Hardening: Three High Frequency and Medium Frequency Induction Hardening Machines For Surface Hardening: Flame Hardening Machine For Hardening High Speed Steel: Salt Bath Furnaces Hydraulic Presses, Shot Blasting Machines, Sand Blasting Plant are available for postheat treatment process. Forging: The Forging shop is equipped with two drop hammers of 3000 kg and 1500 kg Pneumatic hammers of 600 kg and 300 kg, Trimming press of 320 tons and 1000 tons, Friction Screw Press of 480 tons, Heating of stock for forging is done in rotary hearth furnace. Furnace car-bottom type is installed for normalizing the forged components. Removal of scales is done in Tumbler & Table type shot blasting machines. The forge shop is capable of production of forgings up to 20 kg and 200 mm in diameter. Machine Rebuilding: Machine Rebuilding is a comparatively new technology in the industrially developed countries. It should not be mixed with machine tool repair and maintenance and overhaul. The main
characteristic of Machine Rebuilding are: - The rebuilt machine has same performance and accuracy as a new machine. - The warranty period is same as for a new one. - Cost of Rebuilding is one-third of the price of new equivalent machine. PMTF has established this machine rebuilding facility in 1994 with the assistance of UNIDO experts from UK and since then has undertaken the rebuilding activity with targeted output set for 10 to 12 machines per annum. Quality Control: Inspection and Testing is carried out according to procedures established for ISO 9001 Quality Assurance System. The inspection activities are backed up with the facility for calibration of measuring and testing devices.
PMTF Products range includes: MACHINE TOOLS: 1- Heavy duty & light duty Milling Machines(Horizontal, Universal & Vertical) 2- Vertical Copying Milling & Boring Machines 3- Turret Milling Machine 4- Precision Centre Lathes 5- Universal Radial Drilling Machine (Portable) 6- Pantograph Engraving Machine 7- Special Purpose Machine Tools 8- Manual Arbor Press TRANSMISSION: 1- Gear and Shafts for Agriculture Tractors like Massey Ferguson (MF 240, MF 375),and Fiat 4
(Fiat 480, Fiat 640). 2- Traction Gears and Pinions for Locomotives 3- Gears for various Industrial applications 4- Components for Bedford Trucks & Buses etc. DIE CAST COMPONENTS: 1- Aluminum Pressure Die Cast components for Honda Motorcycle Model CD 70 & CG 125, and Suzuki Motorcycle; Model A80. 2- Aluminum Pressure Die Cast components for Domestic Appliances 3- Aluminum Pressure Die Cast components of Gas Meter for Gas distribution industries. 4- Aluminum Pressure Die Cast components for Suzuki Car Model SB 308 TEXTILE MACHINERY: 1- Ring Spinning Frame Model FA 506 MISCELLANEOUS: 1- Gears for various Industrial Applications. 2- Spares for various plants/machinery. 3- Machines / Equipments as per customer's design / requirement.
Topics Covered: N C & CNC Numerical control (NC) refers to the automation of machine tools that are operated by abstractly programmed commands encoded on a storage medium, as opposed to manually controlled via hand wheels or levers or mechanically automated via cams alone. The first NC machines were built in the 1940s and 50s, based on existing tools that were modified with motors that moved the controls to follow points fed into the system on paper tape. These early servomechanisms were rapidly augmented with analog and digital computers, creating the modern Computer Numerical Controlled (CNC) machine tools that have revolutionized the design process. In modern CNC systems, end-to-end component design is highly automated using CAD/CAM programs. The programs produce a computer file that is interpreted to extract the commands needed to operate a particular machine, and then loaded into the CNC machines for production. Since any particular component might require the use of a number of different tools - drills, saws, etc. - modern machines often combine multiple tools into a single "cell". In other cases, a number of different machines are used with an external controller and human or robotic operators that move the component from machine to machine. In either case the complex series of steps needed to produce any part is highly automated and produces a part that closely matches the original CAD design. 4
Earlier forms of automation: Cams The automation of machine tool control began in the 1800s with cams that "played" a machine tool in the way that cams had long been playing musical boxes or operating elaborate cuckoo clocks. Thomas Blanchard built his gun-stock-copying lathes (1820s-30s), and the work of people such as Christopher Miner Spencer developed the turret lathe into the screw machine (1870s). Cam-based automation had already reached a highly advanced state by World War I (1910s). However, automation via cams is fundamentally different from numerical control because it cannot be abstractly programmed. There is no direct connection between the design being produced and the machining steps needed to create it. Cams can encode information, but getting the information from the abstract level of an engineering drawing into the cam is a manual process that requires sculpting and/or machining and filing. At least two forms of abstractly programmable control had existed during the 1800s: those of the Jacquard loom and of mechanical computers pioneered by Charles Babbage and others. These developments had the potential for convergence with the automation of machine tool control starting in that century, but the convergence did not happen until many decades later. Tracer control: The application of hydraulics to cam-based automation resulted in tracing machines that used a stylus to trace a template, such as the enormous Pratt & Whitney "Keller Machine", which could copy templates several feet across. Another approach was "record and playback", pioneered at General Motors (GM) in the 1950s, which used a storage system to record the movements of a human machinist, and then play them back on demand. Analogous systems are common even today, notably the "teaching lathe" which gives 4
new machinists a hands-on feel for the process. None of these were numerically programmable, however, and required a master machinist at some point in the process, because the "programming" was physical rather than numerical. Servos and selsyns: One barrier to complete automation was the required tolerances of the machining process, which are routinely on the order of thousandths of an inch. Although it would be relatively easy to connect some sort of control to a storage device like punch cards, ensuring that the controls were moved to the correct position with the required accuracy was another issue. The movement of the tool resulted in varying forces on the controls that would mean a linear output would not result in linear motion of the tool. The key development in this area was the introduction of the servo, which produced highly accurate measurement information. Attaching two servos together produced a selsyns, where a remote servo's motions was accurately matched by another. Using a variety of mechanical or electrical systems, the output of the selsyns could be read to ensure proper movement had occurred. The first serious suggestion that selsyns could be used for machining control was made by Ernst F. W. Alexanderson, a Swedish immigrant to the U.S. working at General Electric (GE). Alexanderson had worked on the problem of torque amplification that allowed the small output of a mechanical computer to drive very large motors, which GE used as part of a larger gun laying system for US Navy ships. Like machining, gun lying requires very high accuracies, less than a degree, and the motion of the gun turrets was non-linear. In November 1931 Alexanderson suggested to the Industrial Engineering Department that the same systems could be used to drive the inputs of machine tools, allowing it to follow the outline of a template without the strong physical contact needed by existing tools like the Keller Machine. He stated that it was a 4
"matter of straight engineering development." However, the concept was ahead of its time from a business development perspective, and GE did not take the matter seriously until years later, when others had pioneered the field.
Parsons and the invention of NC: The birth of NC is generally credited to John T. Parsons, a machinist and salesman at his father's machining company, Parsons Corp. In 1942 he was told that helicopters were going to be the "next big thing" by the former head of Ford Trimotor production, Bill Stout. He called Sikorsky Aircraft to inquire about possible work, and soon got a contract to build the wooden stringers in the rotor blades. After setting up production at a disused furniture factory and ramping up production, one of the blades failed and it was traced to the spar. As at least some of the problem appeared to stem from spot welding a metal collar on the stringer to the metal spar, so Parsons suggested a new method of attaching the stringers to the spar using adhesives, never before tried on an aircraft design. But that development led to Parsons to wondering about the possibility of using stamped metal stringers instead of wood, which would be much easier to make and stronger too. The stringers for the rotors were built to a design provided by Sikorsky, which was sent to them as a series of 17 points defining the outline. Parsons then had to "fill in" the dots with a French curve to generate an outline they could use as a template to build the jigs for the wooden versions. But how to make a tool able to cut metal with that shape was a much harder problem. Parsons went to visit Wright Field to see Frank Stulen, who was the head of the Rotary Ring Branch at the 4
Propeller lab. Stulen concluded that Parsons didn't really know what he was talking about, and realizing this, Parsons hired him on the spot. Stulen started work on 1 April 1946 and hired three new engineers to join him. Stulen's brother worked at Curtis Wright Propeller, and mentioned that they were using punch card calculators for engineering calculations. Stulen decided to adopt the idea to run stress calculations on the rotors, the first detailed automated calculations on helicopter rotors. When Parsons saw what Stulen was doing with the punch card machines, he asked him if they could be used to generate an outline with 200 points instead of the 17 they were given, and offset each point by the radius of the cutting tool on a mill. If you cut at each of those points, it would produce a relatively accurate cutout of the stringer even in hard steel, and it could easily be filed down to a smooth shape. The resulting tool would be useful as a template for stamping metal stringers. Stulen had no problem doing this, and used the points to make large tables of numbers that would be taken onto the machine floor. Here, one operator read the numbers off the charts to two other operators, one each on the X and Y axis, and they would move the cutting head to that point and make a cut. This was called the "by-the-numbers method". At that point Parsons conceived of a fully automated tool. With enough points no manual working would be needed at all, but with manual operation the time saved by having the part more closely match the outline was offset by the time needed to move the controls. If the machine's inputs were attached directly to the card reader this delay, and any associated manual errors, would be removed and the number of points could be dramatically increased. Such a machine could repeatedly punch out perfectly accurate templates on command. But at the time he had no funds to develop these ideas. When one of Parsons Salesmen was on a visit to Wright Field, he was told of the problems the newly-formed US Air Force 4
was having with new jet designs. He asked if Parsons had anything to help to them. Parsons showed Lockheed their idea of an automated mill, but they were uninterested. They had already decided to use 5-axis template copiers to produce the stringers, cutting from a metal template, and had ordered the expensive cutting machine already. But as Parsons noted: Now just picture the situation for a minute. Lockheed had contracted to design a machine to make these wings. This machine had five axes of cutter movement, and each of these was tracer controlled using a template. Nobody was using my method of making templates, so just imagine what chance they were going to have of making an accurate airfoil shape with inaccurate templates. Parsons worries soon came true, and in 1949 the Air Force arranged funding for Parsons to build his machines on his own. Early work with Snyder Machine & Tool Corp proved that the system of directly driving the controls from motors failed to have the accuracy needed to set the machine for a perfectly smooth cut. Since the mechanical controls did not respond in a linear fashion, you couldn't simply drive it with a certain amount of power, because the differing forces would mean the same amount of power would not always produce the same amount of motion in the controls. No matter how many points you included, the outline would still be rough. Enter MIT: This was not an impossible problem to solve, but would require some sort of feedback system, like a selsyn, to directly measure how far the controls had actually turned. Faced with the daunting task of building such a system, in the spring of 1949 Parsons turned to the MIT Servomechanisms Laboratory, a world leader in mechanical computing and feedback 4
systems. During the war the Lab had built a number of complex motor-driven devices like the motorized gun turret systems for the B-29 and the automatic tracking system for the SCR-584 radar. They were naturally suited to building a prototype of Parsons' automated "by-the-numbers" machine. The MIT team was led by William Pease assisted by James McDonough. They quickly concluded that Parsons' design could be greatly improved; if the machine did not simply cut at points A and B, but instead moved smoothly between the points, then not only would it make a perfectly smooth cut, but could do so with many fewer points - the mill could cut lines directly instead of having to define a large number of cutting points to "simulate" it. A three-way agreement was arranged between Parsons', MIT and the Air Force, and the project officially ran from July 1949 to June 1950. The contract called for the construction of two "Card-a-matic Milling Machine’s, a prototype and a production system. Both to be handed to Parsons for attachment to one of their mills in order to develop a deliverable system for cutting stringers. Instead, in 1950 MIT bought a surplus Cincinnati Milling Machine Company "Hydro-Tel" mill of their own and arranged a new contract directly with the Air Force that froze Parsons out of further development. Parsons would later comment that he " never dreamed that anybody as reputable as MIT would deliberately go ahead and take over my project." In spite of the development being handed to MIT, Parsons filed for a patent on "Motor Controlled Apparatus for Positioning Machine Tool" on 5 May 1952, sparking a filing by MIT for a "Numerical Control Servo-System" on 14 August 1952. Parsons' received US Patent 2,820,187 on 14 January 1958, and the company sold an exclusive license to Bendix. IBM, Fujitsu and General Electric all took sub-licenses after having already started development of their own devices. 4
MIT's machine: MIT fit gears to the various hand wheel inputs and drove them with roller chains connected to motors, one for each of the machine's three axes (X, Y and depth). The associated controller consisted of five refrigerator-sized cabinets that, together, were almost as large as the mill they were connected to. Three of the cabinets contained the motor controllers, one controller for each motor, the other two the digital reading system. Unlike Parsons' original punch card design, the MIT design used standard 7-track punch tape for input. Three of the tracks were used to control the different axes of the machine, while the other four encoded various control information. The tape was read in a cabinet that also housed six relay-based hardware registers, two for each axis. With every read operation the previously read point was copied into the "starting point" register, and the newly read one into the "ending point". The tape was read continually and the number in the register increased until a "stop" instruction, four holes in a line, was encountered. The final cabinet held a clock that sent pulses through the registers, compared them, and generated output pulses that interpolated between the points. For instance, if the points were far apart the output would have pulses with every clock cycle, whereas closely spaced points would only generate pulses after multiple clock cycles. The pulses are sent into a summing register in the motor controllers, counting up by the number of pulses every time they were received. The summing registers were connected to a digital to analog 4
convertor that output increasing power to the motors as the count in the registers increased. The registers were decremented by encoders attached to the motors and the mill itself, which would reduce the count by one for every one degree of rotation. Once the second point was reached the pulses from the clock would stop, and the motors would eventually drive the mill to the encoded position. Each 1 degree rotation of the controls produced a 0.0005 inch movement of the cutting head.. The programmer could control the speed of the cut by selecting points that were closer together for slow movements, or further apart for rapid ones. The system was publicly demonstrated in September 1952, appearing in that month's Scientific American. MIT's system was an outstanding success by any technical measure, quickly making any complex cut with extremely high accuracy that could not easily be duplicated by hand. However, the system was terribly complex, including 250 vacuum tubes, 175 relays and numerous moving parts, reducing its reliability in a production setting. It was also very expensive, the total bill presented to the Air Force was $360,000.14, $2,641,727.63 in 2005 dollars. Between 1952 and 1956 the system was used to mill a number of one-off designs for various aviation firms, in order to study their potential economic impact. Proliferation of NC: The Air Force funding for the project ran out in 1953, but development was picked up by the Giddings and Lewis Machine Tool Co. In 1955 many of the MIT team left to form Concord Controls, a commercial NC company with Giddings' backing, producing the Numericord controller. Numericord was similar to the MIT design, but replaced the punch tape with a magnetic tape reader that General Electric was working on. The tape contained a number of signals of different phases, 4
which directly encoded the angle of the various controls. The tape was played at a constant speed in the controller, which set its half of the selsyns to the encoded angles while the remote side was attached to the machine controls. Designs were still encoded on paper tape, but the tapes were transferred to a reader/writer that converted them into magnetic form. The magtapes could then be used on any of the machines on the floor, where the controllers were greatly reduced in complexity. Developed to produce highly accurate dies for an aircraft skinning press, the Numericord "NC5" went into operation at G&L's plant at Fond du Lac, WI in 1955. Monarch Machine Tool also developed an NC-controlled lathe, starting in 1952. They demonstrated their machine at the 1955 Chicago Machine Tool Show, along with a number of other vendors with punch card or paper tape machines that were either fully developed or in prototype form. These included Kearney & Trekker’s Milwaukee-Matic II that could change its cutting tool under NC control. A Boeing report noted that "numerical control has proved it can reduce costs, reduce lead times, improve quality, reduce tooling and increase productivity.” In spite of these developments, and glowing reviews from the few users, uptake of NC was relatively slow. As Parsons later noted: The NC concept was so strange to manufacturers, and so slow to catch on, that the US Army itself finally had to build 120 NC machines and lease them to various manufacturers to begin popularizing its use. In 1958 the MIT published its report on the economics of NC. They concluded that the tools were competitive with human operators, but simply moved the time from the machining to the creation of the tapes. In Forces of production Noble claims that this was the whole point as far as the Air Force was concerned; moving the process off of the highly unionized 4
factory floor and into the un-unionized white collar design office. CNC arrives: Many of the commands for the experimental parts were programmed "by hand" to produce the punch tapes that were used as input. While the system was being experimented with, John Runyon made a number of subroutines on the famous Whirlwind to produce these tapes under computer control. Users could input a list of points and speeds, and the program would generate the punch tape. In one instance, this process reduced the time required to produce the instruction list and mill the part from 8 hours to 15 minutes. This led to a proposal to the Air Force to produce a generalized "programming" language for numerical control, which was accepted in June 1956. Starting in September Ross and Pople outlined a language for machine control that was based on points and lines, developing this over several years into the APT programming language. In 1957 the Aircraft Industries Association (AIA) and Air Material Command at the Wright-Patterson Air Force Base joined with MIT to standardize this work and produce a fully computer-controlled NC system. On 25 February 1959 the combined team held a press conference showing the results, including a 3D machined aluminum ash tray that was handed out in the press kit. Meanwhile, Patrick Han ratty was making similar developments at GE as part of their partnership with G&L on the Numericord. His language, PRONTO, beat APT into commercial use when it was "released" in 1958. Han ratty then went on to develop MICR magnetic ink characters that were used in cherub processing, before moving to General Motors to work on the groundbreaking DAC-1 CAD system. 4
APT was soon extended to include "real" curves in 2D-APT-II. With its release, MIT reduced its focus on CNC as it moved into CAD experiments. APT development was picked up with the AIA in San Diego, and in 1962, to Illinois Institute of Technology Research. Work on making APT an international standard started in 1963 under USASI X3.4.7, but many manufacturers of CNC machines had their own one-off additions (like PRONTO), so standardization was not completed until 1968, when there were 25 optional add-ins to the basic system. Just as APT was being released in the early 1960s, a second generation of lower-cost transistorized computers was hitting the market that were able to process much larger volumes of information in production settings. This so lowered the cost of implementing a NC system that by the mid 1960s, APT runs accounted for a third of all computer time at large aviation firms. CAD meets CNC: While the Servomechanisms Lab was in the process of developing their first mill, in 1953 MIT's Mechanical Engineering Department dropped the requirement that undergraduates take courses in drawing. The instructors formerly teaching these programs were merged into the Design Division, where an informal discussion of computerized design started. Meanwhile the Electronic Systems Laboratory, the newly rechristened Servomechanisms Laboratory, had been discussing whether or not design would ever start with paper diagrams in the future. In January 1959, an informal meeting was held involving individuals from both the Electronic Systems Laboratory and the Mechanical Engineering Department's Design Division. Formal meetings followed in April and and May, which resulted in the "Computer-Aided Design Project". In December 1959, 4
the Air Force issued a one year contract to ESL for $223,000 to fund the Project, including $20,800 earmarked for 104 hours of computer time at $200 per hour. This proved to be far too little for the ambitious program they had in mind, although their engineering calculation system, AED, was released in March 1965. In 1959 General Motors started an experimental project to digitize, store and print the many design sketches being generated in the various GM design departments. When the basic concept demonstrated that it could work, they started the DAC-1 project with IBM to develop a production version. One part of the DAC project was the direct conversion of paper diagrams into 3D models, which were then converted into APT commands and cut on milling machines. In November 1963 a trunk lid design moved from 2D paper sketch to 3D clay prototype for the first time. With the exception of the initial sketch, the design-to-production loop had been closed. Meanwhile MIT's offsite Lincoln Labs was building computers to test new transistorized designs. The ultimate goal was essentially a transistorized Whirlwind known as TX-2, but in order to test various circuit designs a smaller version known as TX-0 was built first. When construction of TX-2 started, time in TX-0 freed up and this led to a number of experiments involving interactive input and use of the machine's CRT display for graphics. Further development of these concepts led to Ivan Sutherland's groundbreaking Sketchpad program on the TX-2. Sutherland moved to the University of Utah after his Sketchpad work, but it inspired other MIT graduates to attempt the first true CAD system, Electronic Drafting Machine (EDM). It was EDM, sold to Control Data and known as "Digigraphics", that Lockheed used to build production parts for the C-5 Galaxy, the first example of an end-to-end CAD/CNC production system. 4
By 1970 there were a wide variety of CAD firms including Intergraph, Applicon, Computer vision, Auto-troll Technology, UGS Corp. and others, as well as large vendors like CDC and IBM.
Proliferation of CNC The price of computer cycles fell drastically during the 1960s with the widespread introduction of useful minicomputers. Eventually it became less expensive to handle the motor control and feedback with a computer program than it was with dedicated servo systems. Small computers were dedicated to a single mill, placing the entire process in a small box. PDP-8's and Data General Nova computers were common in these roles. The introduction of the microprocessor in the 1970s further reduced the cost of implementation, and today almost all CNC machines use some form of microprocessor to handle all operations. The introduction of lower-cost CNC machines radically changed the manufacturing industry. Curves are as easy to cut as straight lines, complex 3-D structures are relatively easy to produce, and the number of machining steps that required human action have been dramatically reduced. With the increased automation of manufacturing processes with CNC machining, considerable improvements in consistency and quality have been achieved with no strain on the operator. CNC automation reduced the frequency of errors and provided CNC operators with time to perform additional tasks. CNC automation also allows for more flexibility in the way parts are held in the manufacturing process and the time required to change the machine to produce different components. 4
During the early 1970s the Western economies were mired in slow economic growth and rising employment costs, and NC machines started to become more attractive. The major U.S. vendors were slow to respond to the demand for machines suitable for lower-cost NC systems, and into this void stepped the Germans. In 1979, sales of German machines surpassed the U.S. designs for the first time. This cycle quickly repeated itself, and by 1980 Japan had taken a leadership position, U.S. sales dropping all the time. Once sitting in the #1 position in terms of sales on a top-ten chart consisting entirely of U.S. companies in 1971, by 1987 Cincinnati Milacron was in 8th place on a chart heavily dominated by Japanese firms. Many researchers have commented that the U.S. focus on high-end applications left them in an uncompetitive situation when the economic downturn in the early 1970s led to greatly increased demand for low-cost NC systems. Unlike the U.S. companies, who had focused on the highly profitable aerospace market, German and Japanese manufacturers targeted lower-profit segments from the start and were able to enter the low-cost markets much more easily. Today Although modern data storage techniques have moved on from punch tape in almost every other role, tapes are still relatively common in CNC systems. This is because it was often easier to add a punch tape reader to a microprocessor controller than it was to re-write large libraries of tapes into a new format. One change that was implemented fairly widely was the switch from paper to mylar tapes, which are much more mechanically robust. Floppy disks, USB flash drives and local area networking have replaced the tapes to some degree, especially in larger environments that are highly integrated. 4
The proliferation of CNC led to the need for new CNC standards that were not encumbered by licensing or particular design concepts, like APT. A number of different "standards" proliferated for a time, often based around vector graphics markup languages supported by plotters. One such standard has since become very common, the "G-code" that was originally used on Gerber Scientific plotters and then adapted for CNC use. The file format became so widely used that it has been embodied in an EIA standard. In turn, G-code was supplanted by STEP-NC, a system that was deliberately designed for CNC, rather than grown from an existing plotter standard. A more recent advancement in CNC interpreters is support of logical commands, known as parametric programming. Parametric programs include both device commands as well as a control language similar to BASIC. The programmer can make if/then/else statements, loops, subprogram calls, perform various arithmetic, and manipulate variables to create a large degree of freedom within one program. An entire product line of different sizes can be programmed using logic and simple math to create and scale an entire range of parts, or create a stock part that can be scaled to any size a customer demands. As digital electronics has spread, CNC has fallen in price to the point where hobbyists can purchase any number of small CNC systems for home use. It is even possible to build your own.
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 Y axis, and a tool chuck that moves in X and Z (depth). The position of the tool is driven by motors through a series of step-down gears in order to provide highly accurate 4
movements, or in modern designs, direct-drive stepper motors. 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. Mechanical manual controls disappeared long ago. 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, pinning, gluing, fabric cutting, sewing, tape and fiber placement, routing, picking and placing (PnP), and sawing.
Programmable logic controller A programmable logic controller (PLC) or programmable controller is a digital computer used for automation of electromechanical processes, such as control of machinery on factory assembly lines, amusement rides, or lighting fixtures. PLCs are used in many industries and machines, such as packaging and semiconductor machines. Unlike generalpurpose computers, the PLC is designed for multiple inputs and output arrangements, extended temperature ranges, immunity to electrical noise, and resistance to vibration and impact. Programs to control machine operation are typically stored in battery-backed or non-volatile memory. A PLC is an example of a real time system since output results must be produced in response to input conditions within a bounded time, otherwise unintended operation will result. 4
Features: The main difference from other computers is that PLCs are armored for severe conditions (such as dust, moisture, heat, cold) and have the facility for extensive input/output (I/O) arrangements. These connect the PLC to sensors and actuators. PLCs read limit switches, analog process variables (such as temperature and pressure), and the positions of complex positioning systems. Some use machine vision. On the actuator side, PLCs operate electric motors, pneumatic or hydraulic cylinders, magnetic relays, solenoids, or analog outputs. The input/output arrangements may be built into a simple PLC, or the PLC may have external I/O modules attached to a computer network that plugs into the PLC.
System scale: A small PLC will have a fixed number of connections built in for inputs and outputs. Typically, expansions are available if the base model has insufficient I/O. Modular PLCs have a chassis (also called a rack) into which are placed modules with different functions. The processor and selection of I/O modules is customized for the particular application. Several racks can be administered by a single processor, and may have thousands of inputs and outputs. A special high speed serial I/O link is used so that racks can be distributed away from the processor, reducing the wiring costs for large plants. User interface:
PLCs may need to interact with people for the purpose of configuration, alarm reporting or everyday control. A Human-Machine Interface (HMI) is employed for this purpose. HMIs are also referred to as MMIs (Man Machine Interface) and GUI (Graphical User Interface). A simple system may use buttons and lights to interact with the user. Text displays are available as well as graphical touch screens. More complex systems use a programming and monitoring software installed on a computer, with the PLC connected via a communication interface. Communications: PLCs have built in communications ports usually 9-Pin RS232, and optionally for RS485 and Ethernet. Modbus or DF1 is usually included as one of the communications protocols. Others' options include various fieldbuses such as DeviceNet or Profibus. Other communications protocols that may be used are listed in the List of automation protocols. Most modern PLCs can communicate over a network to some other system, such as a computer running a SCADA (Supervisory Control And Data Acquisition) system or web browser. PLCs used in larger I/O systems may have peer-to-peer (P2P) communication between processors. This allows separate parts of a complex process to have individual control while allowing the subsystems to co-ordinate over the communication link. These communication links are also often used for HMI devices such as keypads or PC-type workstations. Some of today's PLCs can communicate over a wide range of media including RS-485, Coaxial, and even Ethernet for I/O control at network speeds up to 100 Mbit/s.
PLC compared with other control systems: PLCs are well-adapted to a range of automation tasks. These are typically industrial processes in manufacturing where the cost of developing and maintaining the automation system is high relative to the total cost of the automation, and where changes to the system would be expected during its operational life. PLCs contain input and output devices compatible with industrial pilot devices and controls; little electrical design is required, and the design problem centers on expressing the desired sequence of operations in ladder logic (or function chart) notation. PLC applications are typically highly customized systems so the cost of a packaged PLC is low compared to the cost of a specific custom-built controller design. On the other hand, in the case of massproduced goods, customized control systems are economic due to the lower cost of the components, which can be optimally chosen instead of a "generic" solution, and where the non-recurring engineering charges are spread over thousands or millions of units. For high volume or very simple fixed automation tasks, different techniques are used. For example, a consumer dishwasher would be controlled by an electromechanical cam timer costing only a few dollars in production quantities. A microcontroller-based design would be appropriate where hundreds or thousands of units will be produced and so the development cost (design of power supplies and input/output hardware) can be spread over many sales, and where the enduser would not need to alter the control. Automotive applications are an example; millions of units are built each year, and very few end-users alter the programming of these controllers. However, some specialty vehicles such as transit busses economically use PLCs instead of custom-designed controls, because the volumes are low and the development cost would be uneconomic.
Very complex process control, such as used in the chemical industry, may require algorithms and performance beyond the capability of even high-performance PLCs. Very high-speed or precision controls may also require customized solutions; for example, aircraft flight controls. Programmable controllers are widely used in motion control, positioning control and torque control. Some manufacturers produce motion control units to be integrated with PLC so that G-code (involving a CNC machine) can be used to instruct machine movements. PLCs may include logic for single-variable feedback analog control loop, a "proportional, integral, derivative" or "PID controller." A PID loop could be used to control the temperature of a manufacturing process, for example. Historically PLCs were usually configured with only a few analog control loops; where processes required hundreds or thousands of loops, a distributed control system (DCS) would instead be used. As PLCs have become more powerful, the boundary between DCS and PLC applications has become less distinct. PLCs have similar functionality as Remote Terminal Units. An RTU, however, usually does not support control algorithms or control loops. As hardware rapidly becomes more powerful and cheaper, RTUs, PLCs and DCSs are increasingly beginning to overlap in responsibilities, and many vendors sell RTUs with PLC-like features and vice versa. The industry has standardized on the IEC 61131-3 functional block language for creating programs to run on RTUs and PLCs, although nearly all vendors also offer proprietary alternatives and associated development environments. Digital and analog signals: Digital or discrete signals behave as binary switches, yielding simply an On or Off signal (1 or 0, True or False, respectively). Push buttons, limit switches, and photoelectric sensors are 4
examples of devices providing a discrete signal. Discrete signals are sent using either voltage or current, where a specific range is designated as On and another as Off. For example, a PLC might use 24 V DC I/O, with values above 22 V DC representing On, values below 2VDC representing Off, and intermediate values undefined. Initially, PLCs had only discrete I/O. Analog signals are like volume controls, with a range of values between zero and full-scale. These are typically interpreted as integer values (counts) by the PLC, with various ranges of accuracy depending on the device and the number of bits available to store the data. As PLCs typically use 16-bit signed binary processors, the integer values are limited between -32,768 and +32,767. Pressure, temperature, flow, and weight are often represented by analog signals. Analog signals can use voltage or current with a magnitude proportional to the value of the process signal. For example, an analog 4-20 mA or 0 - 10 V input would be converted into an integer value of 0 - 32767. Current inputs are less sensitive to electrical noise (i.e. from welders or electric motor starts) than voltage inputs. Example: As an example, say a facility needs to store water in a tank. The water is drawn from the tank by another system, as needed, and our example system must manage the water level in the tank. Using only digital signals, the PLC has two digital inputs from float switches (Low Level and High Level). When the water level is above the switch it closes a contact and passes a signal to an input. The PLC uses a digital output to open and close the inlet valve into the tank. When the water level drops enough so that the Low Level float switch is off (down), the PLC will open the valve to let more water in. Once the water level rises enough so that the High Level switch is on (up), the PLC will shut the inlet to stop the water from overflowing. This rung is an example of seal in logic. The output is sealed in until some condition breaks the circuit. |
| Low Level High Level Fill Valve | |------[/]------|------[/]----------------------(OUT)---------| | | | | | | | | | | Fill Valve | | |------[ ]------| | | | | |
An analog system might use a water pressure sensor or a load cell, and an adjustable (throttling) dripping out of the tank, the valve adjusts to slowly drip water back into the tank. In this system, to avoid 'flutter' adjustments that can wear out the valve, many PLCs incorporate "hysteresis" which essentially creates a "deadband" of activity. A technician adjusts this deadband so the valve moves only for a significant change in rate. This will in turn minimize the motion of the valve, and reduce its wear. A real system might combine both approaches, using float switches and simple valves to prevent spills, and a rate sensor and rate valve to optimize refill rates and prevent water hammer. Backup and maintenance methods can make a real system very complicated. Programming: PLC programs are typically written in a special application on a personal computer, then downloaded by a direct-connection cable or over a network to the PLC. The program is stored in the PLC either in battery-backed-up RAM or some other nonvolatile flash memory. Often, a single PLC can be programmed to replace thousands of relays. Under the IEC 61131-3 standard, PLCs can be programmed using standards-based programming languages. A graphical programming notation called Sequential Function Charts is available on certain programmable controllers. Recently, the International standard IEC 61131-3 has become popular. IEC 61131-3 currently defines five programming languages for programmable control systems: FBD (Function 4
block diagram), LD (Ladder diagram), ST (Structured text, similar to the Pascal programming language), IL (Instruction list, similar to assembly language) and SFC (Sequential function chart). These techniques emphasize logical organization of operations. While the fundamental concepts of PLC programming are common to all manufacturers, differences in I/O addressing, memory organization and instruction sets mean that PLC programs are never perfectly interchangeable between different makers. Even within the same product line of a single manufacturer, different models may not be directly compatible.
History Origin: The PLC was invented in response to the needs of the American automotive manufacturing industry. Programmable controllers were initially adopted by the automotive industry where software revision replaced the re-wiring of hard-wired control panels when production models changed. Before the PLC, control, sequencing, and safety interlock logic for manufacturing automobiles was accomplished using hundreds or thousands of relays, cam timers, and drum sequencers and dedicated closed-loop controllers. The process for updating such facilities for the yearly model change-over was very time consuming and expensive, as the relay systems needed to be rewired by skilled electricians. In 1968 GM Hydramatic (the automatic transmission division of General Motors) issued a request for proposal for an electronic replacement for hard-wired relay systems. The winning proposal came from Bedford Associates of Bedford, Massachusetts. The first PLC, designated the 084 because it was Bedford Associates' eighty-fourth project, was the result. Bedford Associates started a new company 4
dedicated to developing, manufacturing, selling, and servicing this new product: Modicum, which stood for Modular Digital Controller. One of the people who worked on that project was Dick Morley, who is considered to be the "father" of the PLC. The Modicum brand was sold in 1977 to Gould Electronics, and later acquired by German Company AEG and then by French Schneider Electric, the current owner. One of the very first 084 models built is now on display at Modicum’s headquarters in North Andover, Massachusetts. It was presented to Modicum by GM, when the unit was retired after nearly twenty years of uninterrupted service. Modicum used the 84 moniker at the end of its product range until the 984 made its appearance. The automotive industry is still one of the largest users of PLCs. Development: Early PLCs were designed to replace relay logic systems. These PLCs were programmed in "ladder logic", which strongly resembles a schematic diagram of relay logic. Modern PLCs can be programmed in a variety of ways, from ladder logic to more traditional programming languages such as BASIC and C. Another method is State Logic, a Very High Level Programming Language designed to program PLCs based on State Transition Diagrams. Many of the earliest PLCs expressed all decision making logic in simple ladder logic which appeared similar to electrical schematic diagrams. This program notation was chosen to reduce training demands for the existing technicians. Other early PLCs used a form of instruction list programming, based on a stack-based logic solver. Programming:
Early PLCs, up to the mid-1980s, were programmed using proprietary programming panels or special-purpose programming terminals, which often had dedicated function keys representing the various logical elements of PLC programs. Programs were stored on cassette tape cartridges. Facilities for printing and documentation were very minimal due to lack of memory capacity. The very oldest PLCs used non-volatile magnetic core memory. Functionality: The functionality of the PLC has evolved over the years to include sequential relay control, motion control, process control, distributed control systems and networking. The data handling, storage, processing power and communication capabilities of some modern PLCs are approximately equivalent to desktop computers. PLC-like programming combined with remote I/O hardware, allow a general-purpose desktop computer to overlap some PLCs in certain applications.
Hydraulic drive system A hydraulic or hydrostatic drive system or hydraulic power transmission is a drive or transmission system that uses hydraulic fluid under pressure to drive machinery. The term hydrostatic refers to the transfer of energy from flow and pressure, not from the kinetic energy of the flow. Such a system basically consists of three parts. The generator (e.g. a 4
hydraulic pump, driven by an electric motor, a combustion engine or a windmill); valves, filters, piping etc. (to guide and control the system); the motor (e.g. a hydraulic motor or hydraulic cylinder) to drive the machinery. Principle of a hydraulic drive: Pascal's law is the basis of hydraulic drive systems. As the pressure in the system is the same, the force that the fluid gives to the surroundings is therefore equal to pressure x area. In such a way, a small piston feels a small force and a large piston feels a large force. The same counts for a hydraulic pump with a small swept volume, that asks for a small torque, combined with a hydraulic motor with a large swept volume, that gives a large torque. In such a way a transmission with a certain ratio can be built. Most hydraulic drive systems make use of hydraulic cylinders. Here the same principle is used- a small torque can be transmitted in to a large force. By throttling the fluid between generator part and motor part, or by using hydraulic pumps and/or motors with adjustable swept volume, the ratio of the transmission can be changed easily. In case throttling is used, the efficiency of the transmission is limited; in case adjustable pumps and motors are used, the efficiency however is very large. In fact, up to around 1980, a hydraulic drive system had hardly any competition from other adjustable (electric) drive systems. Nowadays electric drive systems using electric servo-motors can be controlled 4
in an excellent way and can easily compete with rotating hydraulic drive systems. Hydraulic cylinders are in fact without competition for linear (high) forces. For these cylinders anyway hydraulic systems will remain of interest and if such a system is available, it is easy and logical to use this system also for the rotating drives of the cooling systems. Hydraulic cylinder: Hydraulic cylinders (also called linear hydraulic motors) are mechanical actuators that are used to give a linear force through a linear stroke. A hydraulic cylinder is without doubt the best known hydraulic component. Hydraulic cylinders are able to give pushing and pulling forces of millions of metric tons, with only a simple hydraulic system. Very simple hydraulic cylinders are used in presses; here the cylinder consists out of a volume in a piece of iron with a plunger pushed in it and sealed with a cover. By pumping hydraulic fluid in the volume, the plunger is pushed out with a force of plunger-area * pressure. More sophisticated cylinders have a body with end cover, a piston-rod with piston and a cylinder-head. At one side the bottom is for instance connected to a single clevis, whereas at the other side, the piston rod also is foreseen with a single clevis. The cylinder shell normally has hydraulic connections at both sides. A connection at bottom side and one at cylinder head side. If oil is pushed under the piston, the piston-rod is pushed out and oil that was between the piston and the cylinder head is pushed back to the oil-tank again. The pushing or pulling force of a hydraulic cylinder is: F = Ab * pb - Ah * ph F = Pushing Force in N Ab = (π/4) * (Bottom-diameter)^2 [in m2] Ah = (π/4) * ((Bottom-diameter)^2-(Piston-rod-diameter)^2)) [in m2] pb = pressure at bottom side in [N/m2] 4
ph = pressure at cylinder head side in [N/m2] Apart from miniature cylinders, in general, the smallest cylinder diameter is 32 mm and the smallest piston rod diameter is 16 mm. Simple hydraulic cylinders have a maximum working pressure of about 70 bar, the next step is 140 bar, 210 bar, 320/350 bar and further, the cylinders are in general custom build. The stroke of a hydraulic cylinder is limited by the manufacturing process. The majority of hydraulic cylinders have a stroke between 0,3 and 5 metres, whereas 12-15 metre stroke is also possible, but for this length only a limited number of suppliers are on the market. In case the retracted length of the cylinder is too long for the cylinder to be build in the structure. In this case telescopic cylinders can be used. One has to realize that for simple pushing applications telescopic cylinders might be available easily; for higher forces and/or double acting cylinders, they must be designed especially and are very expensive. If hydraulic cylinders are only used for pushing and the piston rod is brought in again by other means, one can also use plunger cylinders. Plunger cylinders have no sealing over the piston, or the piston does not exist. This means that only one oil connection is necessary. In general the diameter of the plunger is rather large compared with a normal piston cylinder, because this large area is needed. Whereas a hydraulic motor will always leak oil, a hydraulic cylinder does not have a leakage over the piston nor over the cylinder head sealing, so that there is no need for a mechanical brake.
Hydraulic motor: 4
The hydraulic motor is the rotary counterpart of the hydraulic cylinder. Conceptually, a hydraulic motor should be interchangeable with hydraulic pump, because it performs the opposite function -- much as the conceptual DC electric motor is interchangeable with a DC electrical generator. However, most hydraulic pumps cannot be used as hydraulic motors because they cannot be back driven. Also, a hydraulic motor is usually designed for the working pressure at both sides of the motor. Hydraulic valves: These valves are usually very heavy duty to stand up to high pressures. Some special valves can control the direction of the flow of fluid and act as a control unit for a system.
Pneumatics Pneumatics is the use of pressurized gas to affect mechanical motion. Pneumatic power is used in industry, where factory machines are commonly plumbed for compressed air; other compressed inert gases can also be used. Pneumatics also has applications in dentistry, construction, mining, and other areas. Examples of pneumatic systems: 4
• • • • • • • •
Pneumatic drill (jackhammer) used by road workers Pneumatic nail gun Electro-pneumatic action Pneumatic switches Air compressors Vacuum pump Barostat systems used in Neuro gastroenterology and for researching electricity Cable jetting, a way to install cables in ducts
Gases used in pneumatic systems: Pneumatic systems in fixed installations such as factories use compressed air because a sustainable supply can be made by compressing atmospheric air. The air usually has moisture removed and a small quantity of oil added at the compressor, to avoid corrosion of mechanical components and to lubricate them. Factory-plumbed, pneumatic-power users need not worry about poisonous leakages as the gas is commonly just air. Smaller or stand-alone systems can use other compressed gases which are an asphyxiation hazard, such as nitrogen often referred to as OFN (oxygen-free nitrogen), when supplied in cylinders. Any compressed gas other than air is an asphyxiation hazard including nitrogen, which makes up approximately 80% of air. Compressed oxygen (approx. 20% of air) would not asphyxiate, but it would be an extreme fire hazard, so is never used in pneumatically powered devices. Portable pneumatic tools and small vehicles such as Robot Wars machines and other hobbyist applications are often powered by compressed carbon dioxide because containers designed to hold it such as soda stream canisters and fire extinguishers are readily available, and the phase change 4
between liquid and gas makes it possible to obtain a larger volume of compressed gas from a lighter container than compressed air would allow. Carbon dioxide is both an asphyxiant and poisonous, and can also be a freezing hazard when vented.
Comparison to hydraulics: Both pneumatics and hydraulics are applications of fluid power. Pneumatics uses an easily compressible gas such as air or a suitable pure gas, while hydraulics uses relatively incompressible liquid media such as oil. Most industrial pneumatic applications use pressures of about 80 to 100 pounds per square inch (psi) (500 to 700 kilopascals). Hydraulics applications commonly use from 1,000 to 5,000 psi (7 to 35 MPa), but specialized applications may exceed 10,000 psi (70 MPa). Advantages of pneumatics: Simplicity of Design And Control Machines are easily designed using standard cylinders & other components. Control is as easy as it is simple ON - OFF type control. Reliability Pneumatic systems tend to have long operating lives and require very little maintenance. Because gas is compressible, the equipment is less likely to be damaged by shock. The gas in pneumatics absorbs excessive force, whereas the fluid of hydraulics directly transfers force. Storage
Compressed Gas can be stored, allowing the use of machines when electrical power is lost. Safety Very small fire hazards (compared to hydraulic oil). Machines can be designed to be overload safe. Advantages of hydraulics: • Fluid does not absorb any of the supplied energy. • Capable of moving much higher loads and providing much higher forces due to the incompressibility. • The hydraulic working fluid is basically incompressible, leading to a minimum of spring action. When hydraulic fluid flow is stopped, the slightest motion of the load releases the pressure on the load; there is no need to "bleed off" pressurized air to release the pressure on the load. Pneumatic Logic: Pneumatic logic systems are often used to control industrial processes, consisting of primary logic units such as: • And Units • Or Units • 'Relay or Booster' Units • Latching Units • 'Timer' Units Pneumatic logic is a reliable and functional control method for industrial processes. In recent years, these systems have largely been replaced by electrical control systems, due to the smaller size and lower cost of electrical components. Pneumatic devices are still used in processes where compressed air is the only energy source available or upgrade cost, safety, and other considerations outweigh the advantage of modern digital control. 4
Abstracts Successes and Short Comings Successes
There were many successes, both on our side and on the company side. Personally the following is what we succeeded on: • First, to us it was a success having been given a chance to handle work on various machines that we believe will never see like these. • Through the work that we used to do; our knowledge related to the machines was largely broadened. We can clearly understand how one can effectively study issues concerning. • We weren’t familiar practically with CNC, PLC, controls and Pneumatic Hydraulic Systems, but now we can confidently use it with ease. The Pakistan Machine Tool Factory largely succeeded a lot through our skills, competence and the overall output of my work because; • We used our skills, studies and hands too in workshops and departments. Therefore enabling to meet deadlines Short Comings There weren’t many short comings since as an intern we were given a lot of support by our supervisors and other fellow staff. Therefore the major short comings that I did face were: •
Time was limited and therefore I had to leave prematurely before the complete products of my effort were finalized.
In terms of cultural differences I must say that nobody should expect it as easy to integrate in a different culture. 4
But the difficulty was not based on the way, we were welcomed here, it was that we needed some time to feel comfortable with our new environment. Internship as a learning process: While the work we performed during this period was particularly glamorous and equally thrilling, we feel that this internship period exposed us to experiences which have significantly altered our perception of local water related issues towards a more a global holistic model.