SIU IT 208 - CHAPTER 21 – PRODUCTION CONTROL

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CHAPTER 21 – PRODUCTION CONTROLCHARACTERISTICS OF DIFFERENT TYPES OF FACILITIES The most important factor in manufacturing is the rate of production, because it determines which manufacturing processes will be the most efficient for any given product. (Table 21-1)1. PIECEWORK PRODUCTION  Defined as the fabrication of one complete unit at a time. Utilization of equipment is not a great concern since the equipment is not usually shared or tied up continuously for the production run.  Piecework facilities are often batch processes in which products are made individually. 1.1. Jigs and Fixtures 1.1.1. A fixture is a device that is individually designed to hold a specific workpiece in place. Its specific job is to facilitate setup or to make holding easier. 1.1.1.1. Ex. - Use a fixture to hold a particular plug at an angle for easier soldering. 1.1.2. A jig is a fixture that establishes certain critical location dimensions on theworkpiece. 1.1.2.1. Ex. – Using a jig for the holding and drilling precise holes (into a casting) for the shafts of a three dimensional mechanism.1.1.3. Workholder is the general term for either a jig or a fixture. A miter box ora bench vise might be a workholder.1.2. Desirable Characteristics of Workholders (skip)1.3. Inspection/Dimensioning (skip)1.4. Inspection is the act of determining whether or not the size, shape, and location of all features of the workpiece are consistent with the drawings or otherspecifications. Inspections are performed by machinists or operators.2. SMALL BATCH PRODUCTION (1-20 parts/hr.) At this rate of production, completed parts begin to take up a significant amount of space before they can be shipped and raw materials are needed at a faster rate than they are with piecework.  Boredom becomes a concern and not only affects the quality of the product, but safety is also affected.2.1. Numerical Control is a way of controlling the action of machines by giving them a set of instructions in numerical form. 12.2. Computerized Numerical Control  Can be programmed to control several production machines Can store programs and data that would allow it to track the wear of the cutting tools and automatically compensate for that wear.  Machines were designed with a tool carrier so that tools could be changed by computer control.  Feeds and speeds now had to be controlled electronically rather than mechanically. 2.2.1. Some Problems of CNC 2.2.1.1. New machines are very expensive and only 5% of the part’s total manufacturing time is it actually on the machine. 2.2.1.2. Only profitable if it frees up time to supervise more machines or tospend time with the human activities that computers cannot do well 3. LARGE BATCH OR CONTINUOUS PROCESSES (20-200 parts/hr.) No longer does one person see the part from start to finish. Scheduling is an important part of this type of manufacturing.  Inspect the parts frequently to detect trends in parts not meeting standards and take corrective action before the parts were a so far from the specifications that they are scrap.3.1. Computer-Aided Drafting/ Computer-Automated Manufacturing 3.1.1. Computer-Aided Drafting is a method of drafting that uses a computer todraw on the screen as instructed by an operator. The computer acts only as an “electronic drafting board”; it does not do anything on its own. 3.1.2. Computer Automated Engineering (CAE) is a system that uses a computer to make design drawings, but additionally is capable of doing engineering analysis of the designed object.  Determine the volume and weight of the part and locate its center of mass. Do a complete structural analysis of the product.  Determine clearances and allowances between matching parts.  Devise the optimum steps for the manufacture of the product.  Create the commands for the computer controlled machines that make the product.  Keep the inventory records and other documentation for the product3.1.3. Computer-Automated Manufacturing is an approach to organizing a manufacturing plant so that all possible analyses, decisions, and actions are assigned to a master computer. 3.1.4. Typical Computer Operations in CAM 2 Control the inventory.  Direct the transportation of raw materials, completed products, and parts atdifferent stages during manufacture.  Create machine maintenance schedules.  Control the automatic inspection  Maintain documentation  Control the actions of robots. 3.2. Robotics Robots have five essential components: 1) Manipulator - the part of the machine that actually handles the tool, material, or part. 2) Actuators - respond to the signals from the controller, causing the manipulator to perform its assigned function. 3) Sensors - detect the positions of the various components of the arm and hand and feed data back to the controller. 4) Controllers - computers that send control signals to the manipulators and respond to the data fed back to them by the sensors.5) Power supplies - provide the energy that drives the controllers, sensors, manipulators, and actuators. 3.2.1. Use of Robots 3.2.1.1. Manipulators – The robot manipulator must duplicate essentially every movement of the human arm and hand. 3.2.1.2. Actuators. The “muscles” of the robot mechanism. These may be powered by air, hydraulic fluid, electricity, magnetism, or a vacuum. 3.2.1.2.1. Air-operated and vacuum-operated (pneumatic) mechanisms are usually small and limited by the amount of force they can exert, but they are inexpensive to construct and operate. 3.2.1.2.2. Hydraulic mechanisms are capable of exerting large forces, are high powered, and are amazingly quick for their size. They do tend to be messy due to the inevitable leakage of hydraulic fluid. 3.2.1.2.3. Electrically driven mechanisms are appropriate for light duty. They are very accurate, precise, and clean. 3.2.1.2.4. Magnetically driven actuators such as solenoids are very quick but are limited by the amount of force they can exert on the workpiece. 3.2.1.3. Computer Functions. The “brain” of the robot is the computer that controls the robot. 33.2.1.4. Control System Functions. If the computer is the ‘brain” of the robotics system, then the control system is its “nervous system.” 3.2.1.5. Robot Functions. Through its end-of-arm device (“hand”), the robot either picks up the workpiece and does something with it. 3.3. Quality Assurance Through Automated Inspection 3.3.1. Quality Control


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