机械制造技术基础英文课件CHAPTER9

Chapter 9 Modern Manufacturing Technology
abstract
In this chapter, the main concepts, and features of modern manufacturing technology, comprising engineering and
organizational technologies, are introduced. Moreover, the sub-
technologies of it, such as material handling technology,
production management technology etc. are discussed.
9.1Introduction
9.2Engineering Technology
9.3 Production management technology 9.4 Summary
9.1 Introduction
Modern manufacturing technology is the result of the combination and merging of computer technology,Internet technology,numerical control technology,cybernetics(控制论）,system theory,robotics, manufacturing technology,and even management.With the development of this technology,modern manufacturing technology has progressed quickly,shown extreme potential and has a prosperous future.
9.1.1 Why Do We Need Modern Manufacturing Technology?
Increasing global competition has made many business leaders and policy makers turn their attention to such critical issues as
productivity and quality.Businesses seek new approaches to production
processes and manufacturing techniques and explore new boundaries of
technology.
9.1.2Areas of Modern Manufacturing
Modern manufacturing means much more than the basic fabrication technology.It involves market analysis,design,production planning,fabrication(including outsourcing),distribution and sales, customer service,and,finally,being agile enough to reconfigure the factory for the next product“six months down the road.”
The areas of modern manufacturing consist of the two subsections: engineering technologies and organizational technologies.
Engineering technologies are defined as the hardware and software of modern manufacturing systems.
Organizational technologies are defined as management and TQM（Total Quality Management) issues.
9.1.3 The Future
As mentioned above, manufacturing is much more than machining metals: manufacturing is an extended social enterprise. In the past，society has moved from an agrarian society(农耕社会）, to handcrafts in cottage industries, to operating machinery in factories, to computer automation/robotics, and finally to telemanufacturing by modem and Web.
9.2 Engineering Technology
9.2.1 Machining Automation Technology and Equipment
9.2.1.1 Numerical Control (NC) and NC Tools
Numerical Control(NC)
The two basic types of NC systems are:a point-to-point control system,which moves in a series of steps from one point to the next;a continuous path control system,which moves uniformly and evenly along the cutting path rather than through a series of horizontal and vertical steps.
There are four components in a NC system:
①The actual NC machine or so-called Processing equipment.
②A machine control unit (MCU), which is the control unit that holds the programs that instruct the NC machine,and its related control hardware that stores the program of instructions, and executes it by converting each command into mechanical actions of the processing equipment, one command at a time.
③The communication interface between the NC machine and the MCU or a program of instructions, which is coded on a suitable medium for submission to the machine control unit, to direct the actions of the processing equipment, which accomplishes steps to transform the initial workpiece into a completed part.
④A variety of accessories for performing specific jobs on the NC machine.
The actual NC machine may be a milling machine, lathe, drill, or any other type of machine tool.
The Advantages of NC machining
The Advantages of NC machining are: adaptability to the production of a variety of products, easy machining of parts with complicated forms, increase in accuracy, high productive efficiency even by unskilled workers, decrease in manufacturing lead times, decrease in work –in-process inventories, accurate calculation of work in process inventories, accurate calculation of production costs etc.
On the other hand invested capital increases. Moreover planning and scheduling operations are required.
Classification of NC machine tools
NC machine tools are classified according to the level of information processing.These are:conventional NC/computer numerical control(CNC),machining/turning centers.
9.2.1.2Computerized Numerical Control-CNC
A CNC system consists of three components: the control component,
the input component, and the output component.
The features of CNC are: storage of more than one part program, various form of program input, program editing at the machine tool, fixed cycles and programming subroutines, various form of interpolation, positioning features for setup, cutter length and size compensation, acceleration and deceleration calculations, communications interface, on-line diagnostics capability.
Some of the common features of a CNC diagnostics system are: control start-up diagnostics, malfunction and failure analysis(故障诊断与失效分析）, extended diagnostics for individual components, tool life monitoring, preventive maintenance notices（定期检修）, and programming diagnostics.
9.2.1.3 Direct Numerical Control and Distributed Numerical Control
(DNC)
The modified form of DNC is Distributed Numerical Control.It is very similar to the Direct Numerical Control except that the central computer is connected to machine control units,which have computers of themselves.
Advantages of DNC systems are:①Expansion of the manufacturing system is possible.②Part programming is made with ease.③All necessary numerical information is stored in the memory and can be used at any time.④Production information concerning tool life,production volume,etc is easily collected.⑤Number of operators is reduced and even unskilled workers can operate them easily.⑥Production efficiency is increased.
9.2.1.4 Adaptive Control for Machining
The technology for automatically optimized machining is called adaptive control (AC).
The Advantages of adaptive control for machining are:
①Increased tool life
②Improved production efficiency
However adaptive control requires a highly sensitive real time sensor system, optimum control, and a real time numerical control unit, which is relatively expensive.
9.2.2Flexible Manufacturing Systems (FMS)
9.2.2.1Introduction
FMS is the most advanced production equipment in CAM.
The following are some of the most common and important functional subsystem technological components present in an FMS:
①CNC/DNC machine tool technology.
②Tool management.
③Automated material handling.
④Communication network to integrate elements present in the FMS
(real-time control issues are also included here).
9.2.2.2 Definition and Classification
Definition
FMS is a group of machines and related equipment brought together to process a group or family of parts completely and includes the primary and secondary components for a complete FMS.
One of the most referred-to definitions of FMS is a system dealing with high level distributed data processing and automated material flow using computer-controlled machines,assembly cells,industrial robots, inspection machines and so on,together with computer integrated material-handling and storage systems.
Classification
There are three types of FMS:
①FMC (flexible machining cell) ,which consists of a machining/turning center and a robot or a pallet pool
②Flow-type FMS ,in which the work flow through several machining / turning centers is laid in a linear or loop arrangement
③Random-access type FMS ,which contains several machining / turning centers, conveyers or automatically guided vehicles (AGV), and automated warehouses.
9.2.2.3 Application Environment and Situations of FMS
FMS makes the batch type or single production automatic,and thus reduces the amount of direct labor in process and the lead time.However, FMS can handle only those products,which are similar in shape and size.In addition,it is difficult to make the equipment and controls standardization. Therefore,the FMS is most suitable for the mid-variety,mid-volume production range(中品种，中批量生产）.
Application Environment
Appropriateness of an FMS to a given production environment is extremely important and has to be established before investment commitments are made.
●when part size and mass exceed “jib crane” standards
●when production volume is in excess of two parts per hour
●when processing requires more than two machine types to complete a work piece
●when more than five machines are required
●when stage implementation is planned so that material-handling provisions can be incorporated into the first stage
Specific manufacturing situations
The specific manufacturing situations that would be suitable for the adoption of FMS were identified as early as 1973. The following are the production situations that are encompassed by FMS:
①A number of direct numerical control (DNC) machines are required.
②Some form of automated material-handling system (MHS) is used to move the work pieces into, within, and out of the FMS.
③On-line computer control is used to manage the entire FMS under the conditions of varying parts production mixes and priorities.
9.2.2.4 Components and Characteristics
A complete FMS includes the following primary components:
●potentially independent NC machine tools with work-holding fixtures ●an automated material-handling system
●supervisory computer control system and network that coordinate the functions of both the machine tools and materials handling system to achieve flexibility
●human operators
9.2.3 Material handling system
9.2.3.1 General concept
Material handling equipment includes:transport equipment, storage systems,unitizing equipment,and identification and tracking systems.
9.2.3.2 Automated Guided Vehicle Systems
Automated guided vehicle systems(AGVS)has received increased attention by the designers and engineers of automated manufacturing systems.An AGVS consists of multiple automated guided vehicles (AGV)and computers to control them.
AGV‟s are widely used in FMS as they provide flexibility in routing parts among the elements present in the system.These systems are highly complex and expensive due to the dynamic environment in which the FMS functions.
Several analytical methods have been proposed by researchers for the design and control of AGVS.However,analytical approaches cannot predict the dynamic behaviors of the AGVS with respect to time,and cannot be effectively used for controlling the FMS under investigation due to their restrictive assumptions.
Owing to the limitation of the available analytical and simulation methods,there is a need for a single and versatile tool for addressing both design and operational control issues of AGV.
9.2.3.3 Industrial Robots
Industrial robots are easily reprogram-able, automatic, mechanical manipulators operating in several degrees of freedom and performs a wide range of sequential operations. The applications of robot in manufacturing can usually be classified into one of the following categories: ⑴material handling, ⑵processing operations,⑶assembly and inspection.
Components of industrial robots
Industrial robots are equipped with: manipulator, joint drive system, control system, and end effectors.
The manipulator of an industrial robot is constructed by a series of joints and links.
Robot motion and classification
The motion patterns of robots are: pick and place type, and continuous –path control type.
According to their motions, robots are classified as follows: fixed or variable sequence robots, playback robots, NC robots, and robot system.
9.2.3.4 Automated Warehouse
A warehouse controls both material and information flow. By using automatic transfer equipment within a high-rise stack building, a warehouse, which is usually controlled by computer,
is called an automated warehouse.
Automatic transfer equipment
This is required for rapid feeding between workstations and accurate orientation and positioning,together with large flexibility and simple maintenance.It is of two types:fixed–cycle type,and free–cycle type. Control of automated warehouse
Automatic control is provided in two phases:
The control of material flow includes: operations of stacker cranes, operation of conveyers for entry and exit of items, search for the
location number to pick up specified item, instruction for the operations. The control of information flow includes: scheduling entry and exit operations, determining the location number, reporting current inventory status, processing request for particular item.
It is to be noted that for small scale automatic storage …automatic carousels‟ and automatic sorting have been developed.
9.2.4 Automatic Inspection
Major characteristics to be inspected in the manufacturing process are numbers,dimensions,shape,weight,defects and miscellaneous inspections for color,chemical composition etc.
On-line/in-process inspection
On-line/in-process inspection is achieved by performing the
inspection procedure during the manufacturing operation. As the parts are being made, the inspection procedure is measuring or gauging the parts simultaneously.
Automated measuring machine
Rapid and precise dimensional inspection is done by the automated coordinate measuring machine(CMM)oriented to computer aided inspection.
Coordinate metrology is concerned with the measurement of the actual shape and dimensions of an object and comparing these with the desired shape and dimensions,as might be specified on a part drawing.
9.2.5 Automated Assembly
Assembly is an operation in which two or more parts are brought together and fixed with either permanent or temporary fastenings.It involves:feeding,transferring,and fastening
Automated Assembly
When all the assembly operations are undertaken exclusively by machines it is called fully automated assembly. The advantages of it are: reduction of assembly time and cost, uniformity of assembled products, increase in productive efficiency, release of operative workers from
dangerous work, etc.
Flexible assembly system (FAS)
This is used for assembling mixed product types, based upon the group technology (GT) concept.
For the design of automated assembly, the following facts are
noteworthy: the number of parts should be minimized, parts should be standardized, parts should be symmetrical, separate fasteners should be avoided, straight plunging motion is preferable to
rotational, products should be designed properly so that they can be assembled step by step..
9.2.6 Communication development among elements present in the FMS Data
Typical static data sets in an FMS include configurations of machines,AGVS,and robots and their characteristics and process
mon dynamic data sets include status of machines,
AGVS,and robots that change with respect to real time.The
control algorithms act as an interface between the static and
dynamic data sets at different levels of hierarchy in the FMS.
Communication development
A fundamental building block of an FMS is data communications. Communication development in FMS is probably
the single largest and most troublesome problem area encountered by users and suppliers of factory automation systems.
However, development of communication in an FMS is a complicated task because:
①An FMS is a complex distributed system where each element has a database, and there are several elements of this kind in an FMS that have to communicate for the manufacturing of a finished product.
②Communication and compatibility between equipment from different vendors are critical. The equipment includes computers, local area networks (LANs), cell controllers, programmable logical controllers (PLC), robots, machine tools, and similar digital control devices.
Manufacturing Automation Protocol
To alleviate the complexity of communication development, many efforts are under way in Europe and the USA to develop a common set of vendor independent communication protocols,which would be usable by all types and brands of factory automation equipment.Towards this aim,Manufacturing Automation Protocol (MAP)has recently been developed.
9.3 Production management technology
9.3.1 The hierarchical nature of production control
An illustration of the hierarchical structure is presented according to the ISO-model. It illustrates the fundamental characteristics, namely, that each control function controls a minor set of functions at the lower level. It consists of six control levels: they are enterprise control, facility control, area control, cell control, workstation control, and equipment control level.
Enterprise control includes the overall strategic planning for the enterprise. In other words, it includes product portfolio planning, market strategy, and division of work between divisions in the enterprise.
9.3.2 Management technology of CIM
Computer-Integrated Manufacturing(CIM)is the increased integration of business and manufacturing functions through the application of information technology,the use of computers in all aspects of manufacturing,with integration of functions and control in a hierarchy of computer systems.
The benefits of CIM are:increase of product quality,reduction of lead times,reduction of direct labor costs,reductionof product development time,reduce of inventories,increase of overall productivity, and increase of design quality.
9.3.3 Management of FMS
A number of studies have been devoted to the management of FMS. The National Bureau of Standards broadly addresses three main aspects of problems with FMS. These are:
(1) How can the control architecture be simplified?
(2) Why is FMS difficult to configure?
(3) What can be done to ensure a consistently high level of quality in products made in these systems?
A four-step procedure is provided as a guideline to building a supportive organizational climate for the factory of the future:
(1) Educate senior management
(2) Set goals and develop strategies
(3) Establish a corporate-wide culture
(4) Develop a unified communication structure.
Managerial barriers of FMS
In summary, the main managerial barriers to successful implementation of an FMS seem to be concentrated in a few major areas. These areas include:
①Lack of top management commitment and support.
②Inadequate training and education of the personnel involved.
③Improper evaluation of the situation/environment, which presumably justified installation of the FMS.
④Lack of long-term and committed relationships with the vendors of both raw material and the FMS equipment.
⑤Lack of total commitment to the installation and implementation of the FMS.
⑥Existence of misconceptions about FMS (such as FMS being good only for large companies and only applicable to large scale production, or FMS being the panacea for all of a system problems).
9.3.4 Tool management of FMS
9.3.4.1 Definition
Owing to diversified aspects from which the tool management is viewed, the definitions of tool management vary in the literature.
It is also defined as a strategy which aims at resolving problems related to various tool activities, including: acquisition, storage, database development, selection and allocation, inspection, presetting, delivery, loading, monitoring, replacement, requirement planning, and inventory control of tools.
Despite the various orientations and approaches, there are some common goals in tool management.
9.3.4.2 Changes in tooling
Tooling is one element in an FMS that is most prone to change owing to external factors and it may often cause differences in FMS functioning.
The changes in tooling include three aspects: changes in the number of each tool type, number of different tool types, tool position in the FMS (tool crib, magazines, etc.). 。

9.3.4.3 Significance and development of tool management
Tool management is a very complicated task and is often stressed by FMS users and researchers.Despite such complexity,there are successful working FMS,whose performance has been considerably augmented with efficient tool management.
Several firms have recently developed integrated tool management systems with tremendously encouraging results.
There are still many tool management problems to be resolved.This is mainly due to the lack of comprehensive understanding of tool management which is necessary before attempting any tool-related activities,such as development of control software,design of a tool delivery system,and framing of a new storage or tool flow strategy. Modeling of the tool management can be of critical help in this respect and aids in the understanding of complex asynchronous concurrent interactions/tasks in tool management.
9.3.5 Management technology of Lean production
Lean Production: The system of organizing production developed in Japan that stresses quick tool changeover times, minimum parts and work-in-process inventories, high levels of quality and continuous
improvement. It can also be defined as an adaptation of mass production in which workers and work cells are made more flexible and efficient by adopting methods that reduce waste in all forms.
Therefore, it can be said lean production is base on four principles: minimizing waste, perfect first-time quality, flexible production lines, and continuous improvement.
9.3.6 Agile manufacturing
Agile manufacturing:A means of thriving in an environment of continuous change, by managing complex inter and intra-firm relationships through innovations in technology, information, and communication, organizational redesign and new marketing strategies.
There are four principles of agility:
To organize to master change –“an agile company is organized in a way that allows it to thrive on change and uncertainty.”
To leverage the impact of people and information-in an agile company.
To cooperate to enhance competitiveness–cooperation-internally and with other companies is an agile competitor‟s operational strategy of first choice. To enrich the customer–an agile company is perceived by its customers as enriching them in a significant way, not only itself. The products of an agile company are perceived as solutions to the customers‟ problems.
9.3.6.1Market forces and agility
These forces include: intensifying competition, fragmentation of mass markets, cooperative business relationships, changing customer expectations, and increasing societal pressures. Modern firms are dealing with these market forces by becoming agile. Becoming agile represents a working strategy for company‟s survival and its future profitability.
9.3.6.2 Reorganizing the production system for agility
Reorganizing the production system for agility involves three basic areas: the product design, marketing, and production operations.
Objectives in production operations and procedures that are consistent with an agility strategy are the following: ①to be a cost-effective, low-volume producer, ②to be able to produce to customer order, ③to master mass customization, ④to use reconfigurable and reusable processes, tooling and resources, ⑤to bring customers closer to the production process, ⑥to integrate business procedures with production,⑦and to treat production as a system that extends from suppliers through to customers.
9.3.6.3Management relationships for agility
First of all, cooperation should be the business strategy, the general policies and practices include the following: a management philosophy that promotes motivation and support among employees, trust-based relationships, an empowered workforce, shared responsibility for success or failure, and pervasive entrepreneurial spirit.
The cooperative relationships should be internal or external, and are sometimes created between competing firms.
The formation of a virtual enterprise has the following potential benefits:(1) it may provide access to resources and technologies not available in-house, (2) it may provide access to new markets and distribution channels, (3) it may reduce product development time, and (4) it accelerates technology transfer.
9.3.6.4 Comparison
TABLE11.1Comparison of Agile Manufacturing and Mass Production Mass production Agile manufacturing
Standardized products Long market life expected Produce to forecast
Low information content Single time sales
Pricing by production cost Customized products Short market life expected Produce to order
High information content Continuing relationship Pricing by customer value
TABLE11.2four principles of lean production and agile manufacturing Lean production Agile manufacturing
Minimize waste Perfect first-time quality Flexible production lines Continuous improvement Enrich the customer
Cooperate to enhance competitiveness Organize to master change Leverage the impact of people and information
9.3.7 Manufacturing Resources Planning (MRPII)
Manufacturing Resources Planning(MRP II)is a computerized method for planning,scheduling,and controlling the use of a company's resources,including raw materials,vendors,production equipment,and processes.It is a closed-loop system that integrates and coordinates all of the major functions of the business to produce the right products at the right times.The term“closed–loop system”means that MRP II incorporates feedback of data on various aspects of operating performance so that corrective action can be taken in a timely manner;that is,MRP II includes a shop floor control system.
9.3.8 Just-in-time (JIT)
Just in time(JIT)is an approach to manufacturing that stresses
the benefits inherent in a system,where the required number of each component is produced and delivered exactly to the downstream operation in the manufacturing sequence“just in time.”
The JIT production discipline has proved to be very effective in high-volume repetitive operations, as in the automotive industry.
The principal objective of JIT is to reduce inventories. To achieve it, certain requisites must be in place for a JIT production system to operate successfully. They are: a pull system of production control, small batch sizes and reduced setup times, and stable and reliable production operations.。