manufacturing systems

MANUFACTURINGSYSTEMS

NUMPON MAHAYOTSANUN DEPARTMENT OF MECHANICAL ENGINEERINGKHON KAEN UNIVERSITY

introduction

INTRODUCTION

page 2

Manufacturing consists of a large number of interdependent activities with distinct entities, such as, materials, tools, machines, controls, and people. Consequently, manufacturing should be regarded as a large and complex system, consisting of numerous diverse physical and human elements. In a manufacturing system, a change or disturbance anywhere in the system requires that it adjusts itself system-wide in order to continue functioning effectively or efficiently. The manufacturing system must also be capable of producing the modified product on a short lead time and, preferably, with relatively small major capital investment in machinery and tooling.

Batch production usually involves lot sizes between 100 and 5000 and utilizes machinery similar to that used for small-batch production, but with specially designed fixtures for higher production rates. Mass production generally in-volves quantities over 100,000 and requires special-pur-pose machinery and automated equipment for transferring materials and parts.

Production quantity or volume is crucial in determining the type of machinery and the level of automation required to produce parts economically. Total production quantity is defined as the total number of parts to be produced. Pro-duction rate is defined as the number of parts produced per unit time. Small quantities can be manufactured in job shops. These operations have high part variety, meaning that different parts can be produced in a short time without extensive changes in tooling and in operations. On the oth-

Automation is generally defined as the process of hav-ing machines follow a predetermined sequence of opera-tions with little or no human involvement, using specialized equipment and devices that perform and control manufac-turing processes.

On the other hand, machinery in job shops generally re-quires skilled labor, and the production quantity and rate are low; as a result, the cost per part can be high. Quantities for small-batch production typically range from 10 to 100, using general-purpose machines and machining centers.

introduction

NUMERICAL CONTROL

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Schematic illustration of the components of (a) an open-loop, and (b) a closed-loop control system for a numerical control ma-chine. (DAC is digital-to-analog converter.)

adaptive control helps (a) optimize production rate, (b) op-timize product quality, and (c) minimize production costs. Application of AC in manufacturing is particularly important in situations where workpiece dimensions and quality are not uniform, such as a poor casting or an improperly heat-treated part.

control various machine components. In computer numeri-cal control (CNC), the control hardware follows directions received from local computer software. Computer numeri-cal control is a system in which a control microcomputer (onboard computer) is an integral part of a machine or piece of equipment. The machine operator can easily and manual-ly program the onboard computer, can modify the programs directly, prepare programs for different parts, and store the programs.

Numerical control (NC) is a method of controlling the movements of machine components by directly inserting coded instructions, in the form of numbers and letters, into the system. The system automatically interprets these data and converts them to output signals. These signals, in turn,

In adaptive control (AC), the operating parameters au-tomatically adapt themselves to conform to new circum-stances, such as changes in the dynamics of the particular process and any disturbances that may arise. This approach is basically a feedback system. In manufacturing operations

LEFT: Schematic illustration of the major components of a numerical control machine tool.

BOTTOM: Schematic illustration of the application of adaptive control (AC) for a turning operation.

introduction

MATERIAL HANDLING

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(a) A self-guided vehicle (Tugger type). This vehicle can be arranged in a variety of configurations to pull caster-mounted cars; it has a laser sensor to ensure that the vehicle operates safely around people and various obstructions. (b) A self-guided vehicle configured with forks for use in a warehouse.

from machine to machine, from inspection to assembly and to inventory, and finally shipment. Material handling opera-tions must be repeatable and reliable. Important aspects of material handling are summarized below:

1. Methods of material handling. Several factors must be considered in selecting an appropriate material-handling method for a particular manufacturing operation: (a) shape, size, weight, and characteristics (b) Distance, position, ori-

Material handling is defined as the functions and sys-tems associated with the transportation, storage, and con-trol of materials and parts in the total manufacturing cycle of a product. During this cycle, raw materials and parts (work-in-progress) are typically moved from storage to machines,

entation (c) path conditions (d) level of automation and con-trol (e) operator skill (f) economic considerations.

2. Equipment. Several types of equipment can be used to move materials: conveyors, rollers, monorails, carts, forklift trucks, automated guided vehicles, and various mechanical, electrical, magnetic, pneumatic, and hydraulic devices and manipulators.

3. Automated guided vehicles (AGV). This transport sys-tem has high flexibility and is capable of efficient delivery to different workstations. AGVs are guided automatically along pathways with in-floor wiring or tapes or fluorescent-painted strips. Some systems may require additional opera-tor guidance. Autonomous guidance involves no wiring or tapes and uses various optical, ultrasonic, and inertial tech-niques with onboard controllers. Routing of the AGV can be controlled and monitored from a central computer.

4. Coding systems. Various coding systems have been developed to locate and identify parts and subassemblies throughout the manufacturing system and to correctly transfer them to their appropriate stations: (a) bar coding (b) magnetic strips (c) radio frequency (RF) tags (d) Acous-tic waves, optical character recognition, and machine vision.

LEFT: Automated guided vehicle (AGV)

introduction

INDUSTRIAL ROBOTS

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(a) Schematic of a six-axis KR-30 KUKA robot; the payload at the wrist is 30 kg and repeatability is ±0.15 mm (±0.006 in.). The robot has mechanical brakes on all of its axes. (b) The work envelope of the KUKA robot, as viewed from the side.

dent actuators that use an electrical, pneumatic, or hydrau-lic power supply; each has its own characteristics, advan-tages, and limitations.

4. Control system. The control system is the brain of a robot. The control system is the communications and in-formation processing system that gives commands for the movements of the robot; it stores data to initiate and termi-nate movements of the manipulators.

1. Manipulator (arm and wrist). The manipulator is a me-chanical unit that provides motions (trajectories) similar to those of a human arm and hand, using various devices such as linkages, gears, and joints.

2. End effector. The end of the wrist in a robot is equipped with an end effector, also called end-of-arm tooling, end ef-fectors can be custom made to meed special handling re-quirements. Mechanical grippers are the most commonly

An industrial robot has been defined as a reprogram-mable multifunctional manipulator designed to move mate-rials, parts, tools, or other devices by means of variable pro-grammed motions and to perform a variety of other tasks. Here are the basic components of an industrial robot:

used end effectors and are equipped with two or more fin-gers.

3. Power supply. Each motion of the manipulator, in linear and rotational axes, is controlled and regulated by indepen-

Various devices and tools that can be attached to end effectors to perform a vari-ety of operations.

introduction

SENSOR TECHNOLOGY

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A toolholder equipped with thrust-force and torque sensors (\it smart tool holder), capable of continuously monitoring the machin-ing operation.

Sensors are also classified as follows:1. Tactile sensing involves the continuous sensing of vary-ing contact forces, commonly by an array of sensors. 2. Visual sensing (machine vision; computer vision) in-volves cameras that optically sense the presence and shape of an object.3. Smart sensors have the capability to perform a logic function, conduct two-way communication, and make deci-sions and take appropriate actions.

-fered to computers. Analog-to-digital converters (ADCs) are used for interfacing analog sensors with computers. Sensors may be classified as follows: 1. Mechanical sensors, which measure such quantities as position, shape, velocity, force, torque, pressure, vibration, strain, and mass.2. Electrical sensors, which measure voltage, current, charge, and conductivity.3. Magnetic sensors, which measure magnetic field, flux,

A sensor is a device that produces a signal in response to detection or measurement of a specific quantity or a prop-erty. Analog sensors produce a signal, such as voltage, that is proportional to the measured quantity. Digital sensors have digital (numeric) outputs that can directly be trans-

and permeability.4. Thermal sensors, which measure temperature, flux, con-ductivity, and specific heat. 5. Acoustic, ultrasonic, chemical, optical, radiation, la-ser, and fiber-optic sensors.

LEFT: A robot gripper with tactile sensors.BOTTOM: Applications of machine vision.

introduction

FLEXIBLE FIXTURING

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PAGE 12: Components of a modular workholding system. PAGE 13: Schematic illustration of an adjustable-force clamping system. The clamping force is sensed by the strain gage, and the system automatically adjusts this force.

Fixtures are generally designed for specific purposes; clamps are simple functional devices; jigs have various ref-erence surfaces and points for accurate alignment of parts and tools and are widely used in mass production. These devices may be used for actual manufacturing operations, or they may be used to hold workpieces for purposes of measurement and inspection, where the part is not subject-ed to any forces. Workholding devices have certain ranges of capacity; for example, (a) a specific collet can accommo-date rods or bars only within a certain range of diameters; (b) four-jaw chucks can accommodate square or prismatic workpieces of various sizes; and (c) other devices and fixr-tures are designed and made for specific workpiece shapes and dimensions and for specific tasks, called dedicated fix-tures. The emergence of flexible manufacturing systems has necessitated the design and use of workholding devices and fixtures that have built-in flexibility.

1. Modular fixturing. Modular fixturing is often used for small or moderate lot sizes. These modular fixtures are usu-ally based on tooling plates or blocks configured with grid holes or T-slots upon which a fixture is constructed. A num-ber of other standard components, such as locating pins, adjustable stops, workpiece supports, V-blocks, clamps, and springs, can be mounted onto the base plate or block to quickly produce a fixture.

2. Tombstone fixtures. Also referred to as pedestal-fixtures, tombstone fixtures have between two and six vertical faces onto which parts can be mounted. Tombstone fixtures are typically used in automated or robot-assisted manufactur-ing; the machine tool performs the desired operations on the part or parts on one face, then flips or rotates the tomb-stone to begin work on other parts. These fixtures allow feeding more than one part into a machine but are not as flexible as other fixturing approaches.

3. Bed-of-nails device. This fixture consists of a series of

air-actuated pins that conform to the shape of the external part surfaces. Each pin moves as necessary to conform the shape at its point of contact with the part; the pins are then mechanically locked against the part. The fixture is compact and has high stiffness and is reconfigurable.

4. Adjustable-force clamping. In this system, referred to as an adjustable-force clamping system, the strain gage at-tached to the clamp senses the magnitude of the clamping force; the system then adjusts this force to keep the work-piece securely clamped to the workpiece.

5. Phase-change materials. There are two basic methods to hold irregularly shaped or curved workpieces in a me-dium, other than hard tooling: (a). A low-melting-point metal is used as the clamp-ing medium. For example, an irregularly shaped workpiece is partially dipped into molten lead and allowed to set. After setting, the assembly is clamped in a simple fixture. (b). The supporting medium is either a magneto-rheological (MR) or electrorehological (ER) fluid. In the MR application, magnetic particles are suspended in a non-magnetic fluid. Surfactants are added to maintain dispersal of powders. After the workpiece is immersed in the fluid, an external magnetic field is applied, whereby the particles are polarized and the behavior of the fluid changes from a liquid to a solid. After the part is processed, it is retrieved after removing the external magnetic field. In the ER application, the fluid is a suspension of fine dielectric particles in a liquid with a low dielectric constant. After applying an electrical field, the liquid becomes a solid.

introduction

ASSEMBLY SYSTEMS

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Transfer systems for automated assembly: (a) rotary indexing machine, and (b) in-line indexing machine.

continues operating until the next buffer is full or the previ-ous buffer is empty. Also, if for some reason one station be-comes inoperative, the assembly line continues to operate until all the parts in the buffer have been used up. (c) Continuous systems. The product is assembled while moving at a constant speed on pallets or similar workpiece carriers. The parts to be assembled are brought to the prod-uct by various workheads, and their movements are syn-chronized with the continuous movement of the product.

1. Manual assembly uses simple tools and is generally economical for relatively small lots.

2. High-speed automated assembly uses transfer mecha-nisms designed specifically for assembly operations. (a) Synchronous systems, also called indexing systems. In-dividual parts and components are supplied and assembled at a constant rate at fixed individual stations. These systems can operate in either a fully automatic mode or a semiauto-

Some products are simple and have only two or three com-ponents to assemble. Most products, however, consist of many parts, and their assembly requires considerable care and planning. There are three basic methods of assembly: manual, high-speed automatic, and robotic.

matic mode. However, a breakdown of one station will shut down the whole assembly operation. (b) Nonsynchronous systems. Each station operates in-depndently, and any imbalance in product flow is accom-modated in storage (buffer) between stations. The station

Examples of guides to ensure that parts are properly oriented for automated as-sembly.

introduction

COMPUTER-INTEGRATED MANUFACTURING(CIM)

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A schematic illustration of a computer-integrated manufacturing system.

specifications).2. Data management attributes (creator, revision level, and part number).3. Production data (manufacturing processes used in mak-ing parts and products).4. Operational data (scheduling, lot sizes, and assembly re-quirements).5. Resources data (capital, machines, equipment, tooling, and personnel, and the capabilities of these resources).

systems consist of the following:1. Business planning and support.2. Product design.3. Manufacturing process planning.4. Process automation and control.5. Factory-floor monitoring systems.

The subsystems are designed, developed, and implemented in such a manner that the output of one subsystem serves

Computer-integrated manufacturing is a broad term used to describe the computerized integration of product design, planning, production, distribution, and manage-ment. Computer-integrated manufacturing systems consist of subsystems that are integrated into a whole. These sub-

as the input to another subsystem. An effective computer-integrated manufacturing system requires a single, large da-tabase that is shared by members of the entire organization. A database typically consists of the following information:1. Product data (part shape, dimensions, tolerances, and


introduction

COMPUTER-AIDED DESIGN AND ENGINEER-ING (CAD/CAE)

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aided design and computur-aided manufacturing are often combined into CAD/CAM systems. This combination allows information transfer from the design stage to the planning stage for the manufacture of a product, without the need to manually reenter the data on part geometry.

of the database by allowing several applications to share the information in the database. These applications include, for example, (a) finite-element analysis of stresses, strains, deflections, and temperature distribution in structures and load-bearing members, (b) the generation, storage, and re-trieval of NC data, and (c) the design of integrated circuits and various electronic devices.

Computer-aided design (CAD) involves the use of computers to create design drawings and geometric mod-els of products and components and is associated with interactive computer graphics, known as a CAD system. Computer-aided engineering (CAE) simplifies the creating

Computer-aided manufacturing (CAM) involves the use of computers and computer technology to assist in all phases of manufacturing, including process and produc-tion planning, scheduling, manufacture, quality control, and management. Because of the obvious benefits, computer-

Various type of modeling for CAD

introduction

GROUP TECHNOLOGY

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(a) Two parts with identical geometries but with different manufacturing attributes. (b) Four parts with similar manufacturing at-tributes but with different geometries.

component consist of the following: a. Primary processes. b. Secondary processes and finishing operations. c. Process capabilities, such as dimensional toler-ances and surface finish. d. Sequence of operations performed. e. Tools, dies, fixtures, and machinery. f. Production volume and production rate.

families by classification and coding (C/C) systems. This process is a critical and complex first step in GT, and it is done according to the part’s design and manufacturing at-tributes:

1. Design attributes pertain to similarities in geometric features and consist of the following: a. External and internal shapes and dimensions. b. Aspect ratio.

Many parts have certain similarities in their shape and in their method of manufacture. Group technology (GT) is a concept that seeks to take advantage of the design and processing similarities among the parts to be produced. In group technology, parts are identified and grouped into

d. Surface finish. e. Part function.2. Manufacturing attributes pertain to similarities in the methods and the sequence of the operations performed on the part. The manufacturing attributes of a particular

(a) Functional layout of machine tools in a traditional plant; arrows in-dicate the flow of materials and parts in various stages of completion. (b) Group-technology (cellular) layout.

introduction

CELLULAR MANUFACTURING

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Schematic view of an attended flexible manufacturing cell, showing various machine tools and an inspection station. Note the worker positions and the flow of parts in progress from machine to machine.

in any order. This highly automated system is capable of optimizing each step of the total manufacturing operation.

eral machines, each of which performs a different operation on a part. The significant benefits of cellular manufactur-ing are (a) the economics of reduced work in progress, (b) improved productivity, and (c) the ability to readily detect product quality problems right away.

In a flexible manufacturing system (FMS), all major elements of manufacturing are integrated into a highly au-

The concept of group technology can effectively be imple-mented in a cellular manufacturing, which consists of one or more manufacturing cells. A manufacturing cell is a small unit consisting of one or more workstations. A workstation typically contains either one machine or sev-

tomated system. FMS consists of a number manufacturing cells, each containing an industrial robot and an automated material-handling system, all interfaced with a central com-puter or fileserver. The flexibility of FMS is such that it can handle a variety of part configurations and produce them

A schematic illustration of a flexible manufacturing system, showing two machining centers, a coordi-nate measuring machine, and two automated guided vehicles.

introduction

JUST-IN-TIME MANUFACTURING

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2. Produce parts just in time to be made into subassemblies.3. Produce subassemblies just in time to be assembled into finished products.4. Produce and deliver finished products just in time to be sold.

time manufacturing is a pull system, meaning that parts are produced to order, and the production is matched with demand. Consequently, there are no stockpiles, and the ex-tra motions and expenses involved in stockpiling parts and then retrieving them from storage are eliminated. Moreover, parts are inspected in real time either automatically or by the worker as they are being manufactured and are used within a short period of time. In this way, control is maintained continuously over production, immediately identifying de-

In traditional manufacturing operations, the parts are made in batches, placed in inventory, and used when necessary. This approach, known as a push system, means that parts are made according to a schedule and are in inventory to be used if and when they are needed. In contrast, just-in-

fective parts or process variation. Adjustments can then be made rapidly to make a uniform, high-quality product.The just-in-time production (JIT) concept has the following goals:1. Receive supplies just in time to be used.

introduction

LEAN MANUFACTURING

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5. Minimizing or eliminating product transportation, be-cause it represents an activity that adds no value.6. Performing time and motion studies to identify inefficient workers or unnecessary product movements.7. Eliminating defects.

of customer, and optimizes processes to maximize added value. The focus of lean production is on the entire process flow and not just the improvement of one or more individual operations. Typical wastes to be considered and reduced or preferably eliminated include the following:1. Eliminating inventory (using JIT methods) because in-ventory represents cost, leads to defects, and reduces re-sponsiveness to changing market demands.2. Eliminating waiting time, which may be caused by unbal-

Lean manufacturing is a systematic approach to iden-tifying and eliminating waste in every area of manufactur-ing, through continuous improvement, and emphasizing product flow in a pull system. Lean production requires that a manufacturer review all its activities from the viewpoint

anced work loads, quality problems, and unplanned main-tenance.3. Maximizing the efficiency of workers at all times.4. Eliminating unnecessary processes and steps, because they represent costs.

REFERENCES

- S. Kalpakjian, S. R. S. (2003). Manufacturing Engineering and Technology. New Jersey, Pearson Prentice Hall.- Groover, M. P. (2010). Principles of Modern Manufacturing: Materials, Pro-cesses, and Systems, John Wiley & Sons Ltd.

manufacturing systems

Documents

manufacturing system

smallbatch production

production costs

mass production

control hardware

adaptive control

total production quantity

closedloop control system