(1) Flexible Manufacturing Automation

2016-10-07

Production Management

Flexible Manufacturing Automation (1) 1. Introduction 2. Need for Flexible Manufacturing Systems 3. Organizational categories of flexible manufacturing

Wacław Skoczyński room 2.17 B-4, tel. 71 320 26 39 [email protected]

Bibliography: 1. Groover M.P.: Automation, Production Systems and Computer-Integrated Manufacturing. Third Edition. Prentiece Hall International. London, 2008 2. Krzyżanowski J.: Flexible Manufacturing Automation , Oficyna Wyd. Politechniki Wrocławskiej, Wrocław, 2011 3. Luggen W.W.: Flexible manufacturing cells and systems, Prentice-Hall Inc. Engelwood Cliffs, NJ, 1991 4. Kief H.B.: FFS-Handbuch, 4. überarbeitete Auflage, Carl Hanser Verlag, München, Wien, 1998

Course Outline: 1. Introduction 2. Need for Flexible Manufacturing Systems 3. Organizational categories of flexible manufacturing 4. Functional structure of flexible manufacturing system 5. Machining subsystem 6. Tool management 7. Workpiece subsystem 8. FMS logistic system (automated material movement and storage) 9. FMS information system 10. FMS supervising and diagnostics system 11. FMS availability

Issues concerning the development of manufacturing systems The technological transformation of the information society is associated with considerable changes in the demands on machine tools, requiring new solutions for the inherent conflict in design between precision and productivity. For mechanical manufacturing, this results in constantly growing demands for precision in machine tools. The real demands identified from surveys of customers and manufacturers in this respect are: • An increase in availability as a result of prescient maintenance (status and process monitoring; intelligent maintenance; diagnostic functions). • Highly economic manufacturing (life-cycle costs) as a result of functionoriented design (improved performance due to dynamics, flexibility as a result of reconfigurability).

Optimal use of resources

The development of achievable machining accuracy

acc. to EROWA

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From production cell to integrated manufacturing

The concept of automated systems can be applied to various levels of factory operations.

acc. to EROWA

Levels of automation and control in manufacturing (1) Device level. This is the lowest level in our automation hierarchy. It includes the actuators, sensors, and other hardware components that comprise the machine level. The devices are combined into the individual control loops of the machine, for example, the feedback control loop for one axis of a CNC machine or one joint of an industrial robot. Machine level. Hardware at the device level is assembled into individual machines. Examples include CNC machine tools and similar production equipment, industrial robots, powered conveyors, and automated guided vehicles. Control functions at this level include performing the sequence of steps in the program of instructions in the correct order and making sure that each step is properly executed.

Figure 4.6 Five levels of automation and control in manufacturing

Levels of automation and control in manufacturing (2) Plant level. This is the factory or production systems level. It receives instructions from the corporate information system and translates them into operational plans for production. Likely functions include order processing, process planning, inventory control, purchasing, material requirements planning, shop floor control, and quality control. Enterprise level. This is the highest level, consisting of the corporate information system. It is concerned with all of the functions necessary to manage the company: marketing and sales, accounting, design, research, aggregate planning, and master production scheduling.

Cell or system level. This is the manufacturing cell or system level, which operates under instructions from the plant level. A manufacturing cell or system is a group of machines or workstations connected and supported by a material handling system, computer, and other equipment appropriate to the manufacturing process. Production lines are included in this level. Functions include part dispatching and machine loading, coordination among machines and material handling system, and collecting and evaluating inspection data.

Strategies for automation and process improvement (acc. to Groover) (useful for automation or just for simplification of processes) 1. Specialization of operations. 2. Combined operations. 3. Simultaneous operations. 4. Integration of operations. 5. Increased flexibility. 6. Improved material handling and storage. 7. On-line inspection. 8. Process control and optimization. 9. Plant operations control. 10. Computer-integrated manufacturing (CIM).

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Strategies for automation and process improvement (1) • Specialization of operations. The first strategy involves the use of special-purpose equipment designed to perform one operation with the greatest possible efficiency. This is analogous to the Specialization of labor, which is employed to improve labor productivity. • Combined operations. Production occurs as a sequence of operations. Complex parts may require dozens or even hundreds of processing steps. The strategy of combined operations involves reducing the number of distinct production machines or workstations through which the part must be routed. This is accomplished by performing more than one operation at a given machine, thereby reducing the number of separate machines needed. Since each machine typically involves a setup, setup time can usually be saved by this strategy. Material handling effort, nonoperation time, waiting time, and manufacturing lead time are all reduced. • Simultaneous operations. A logical extension of the combined operations strategy is to simultaneously perform the operations that are combined at one workstation. In effect, two or more processing (or assembly) operations are being performed simultaneously on the same workpart, thus reducing total processing time.

Strategies for automation and process improvement (3) • On-line inspection. Inspection for quality of work is traditionally performed after the process is completed. This means that any poor-quality product has already been produced by the time it is inspected. Incorporating inspection into the manufacturing process permits corrections to the process as the product is being made. This reduces scrap and brings the overall quality of the product closer to the nominal specifications intended by the designer. • Process control and optimization. This includes a wide range of control schemes intended to operate the individual processes and associated equipment more efficiently. By this strategy, the individual process times can be reduced and product quality can be improved.

Strategies for automation and process improvement (2) • Integration o f operations. This strategy involves linking several workstations together into a single integrated mechanism, using automated work handling devices to transfer parts between stations. In effect, this reduces the number of separate work centers through which the product must be scheduled. With more than one workstation, several parts can be processed simultaneously, thereby increasing the overall output of the system. • Increased flexibility. This strategy attempts to achieve maximum utilization of equipment for job shop and medium-volume situations by using the same equipment for a variety of parts or products. It involves the use of flexible automation concepts. Prime objectives are to reduce setup time and programming time for the production machine. This normally translates into lower manufacturing lead time and less work-in-process. • Improved material handling and storage. A great opportunity for reducing nonproductive time exists in the use of automated material handling and storage systems. Typical benefits include reduced work-in-process and shorter manufacturing lead times.

Strategies for automation and process improvement (4) • Plant operations control. Whereas the previous strategy was concerned with the control of the individual manufacturing process, this strategy is concerned with control at the plant level. It attempts to manage and coordinate the aggregate operations in the plant more efficiently. Its implementation usually involves a high level of computer networking within the factory. • Computer-integrated manufacturing (CIM). Taking the previous strategy one level higher, we have the integration of factory operations with engineering design and the business functions of the firm. CIM involves extensive use of computer applications, computer data bases, and computer networking throughout the enterprise.

Flexible manufacturing systems - Historical Note The flexible manufacturing system was first conceptualized for machining, and it required the prior development of numerical control. The concept is credited to David Williamson, a British engineer employed by Molins during the mid 1960s. Molins applied for a patent for the invention that was granted in 1965. The concept was called System 24 because it was believed that the group of machine tools comprising the system could operate 24 hours a day, 16 hours of which would be unattended by human workers. The original concept included computer control of the NC machines, production of a variety of parts, and use of tool magazines that could hold various tools for different machining operations. One of the first flexible manufacturing systems to be installed in the United States was a machining system at Ingersoll-Rand Company in Roanoke, Virginia, in the late 1960s by Sundstrand. Other systems introduced soon after included a Kearney & Trecker FMS at Caterpillar Tractor and Cincinnati Milacron's "Variable Mission System." Most of the early FMS installations in the United States were in large companies that had the financial resources to make the major investments necessary. They also possessed the prerequisite experience in NC machine tools, computer systems, and manufacturing systems to pioneer the new FMS technology. Flexible manufacturing systems were also installed in other countries around the world (Germany in 1969, USSR (now Russia) in 1972, Japan in 1972).

1. Introduction The Flexible Manufacturing Automation is a stage in the process of production technology development which is connected with the introduction of computer technique and first of all the data acquisition and processing to the production automation process. Definitions of Flexible Manufacturing Systems: 1. A series of automatic machine tools or items of fabrication equipment linked together with an automatic material handling, a common hierarchical digital programmed computer control, and provision for random fabrication of parts or assemblies that fall within predetermined families. 2. A technology which will help achieve leaner factories with better response times, lower unit costs, and higher quality under an improved level of management and central control.

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WHAT IS A FLEXIBLE MANUFACTURING SYSTEM?

2. FMS is a randomly loaded automated system based on group technology manufacturing linking integrated computer control and a group of machines to automatically produce and handle (move) parts for continuous serial processing. 3. FMS combines microelectronics and mechanical engineering to bring the economics of scale to batch work. A central on-line computer controls the machine tools, other workstations, and the transfer of components and tooling. The computer also provides monitoring and information control. This combination of flexibility and overall control makes possible the production of a wide range of products in small numbers. 4. FMS is a process under control to produce varieties of components or products within its stated capability and to a predetermined schedule.

Historic approach to the system The basic system approach is a still actual Aristotelian contention that the whole is more than the sum of parts. In the course of the scientific revolution in XVI-XVII centuries a new approach was accepted. Descartes formulated one of the main bases of this approach as follows: each problem should be disrupted on so many separated simple elements as much as it is possible. It is based on the reduction of a complex cases and their disintegration into elements. This method resulted in a great success in the science and technologies; however, it functioned well only when observed occurrences could be divided onto isolated causal chains that means into relations, which occurred between two or more variables. At the end of the 1920-s, one of the originators of the general theory of systems, Ludwig von Bertalanffy wrote: Since the basic feature of the organized whole is just its organization, the traditional methods of investigation and description of particular elements and proceedings cannot give a full explanation of occurrences of functioning this whole. They do not give namely any information about the coordination of particular parts and proceedings. In addition, therefore the main task must be exerted in discovering the regulations, which rule the systems on all levels of their organization. The above statement can be concisely produced as follow: to understand the functioning of the organized whole, we must know both: their parts as well as relations between themselves.

A flexible manufacturing system (FMS) is a highly automated group technology machine cell, consisting of a group of processing workstations (usually CNC machine tools), interconnected by an automated material handling and storage system, and controlled by a distributed computer system. The reason the FMS is called flexible is that it is capable of processing a variety of different part styles simultaneously at the various workstations, and the mix of part styles and quantities of production can be adjusted in response to changing demand patterns. An FMS relies on the principles of group technology. No manufacturing system can be completely flexible. There are limits to the range of parts or products that can be made in an FMS. Accordingly, a flexible manufacturing system is designed to produce parts (or products) within a defined range of styles, sizes, and processes. In other words, an FMS is capable of producing a single part family or a limited range of part families. A more appropriate term for FMS would be flexible automated manufacturing system. The use of the word "automated" would distinguish this type of production technology from other manufacturing systems that are flexible but not automated, such as a manned group technology machine cell. The word "flexible" would distinguish it from other manufacturing systems that are highly automated but not flexible, such as a conventional transfer line.

System S consists of a set of elements with their behaviors and mutual connections between elements as well as between elements and surroundings Output E3

Political and legal surroundings

R57

Relation

Material flow

R14 E4

E7

R24

Element

Information flow

Output

R67

E2

E6

System System (subsystem) border

System surroundings

Figure 1.1 Structure of a system

SURROUNDINGS

Energy

Heat

Information

Information

Row material, blanks

Auxiliary materials Cutting tools Workholders

Parts Chips

Technological surroundings

R47

R46

Cutting tools Workholders

Enterprise as system

E1 R21

Auxiliary materials

Energy flow

Subsystem

E5 R34

Manufacturing system is a material, information and organization structure aimed to manufacture of predetermined product family Economic surroundings

R35

Element

MANUFACTURING SYSTEM

Another definitions of FMS 1. A FMS is a group of NC machine tools, which can randomly process a group of parts, having automated material handling equipment and central computer control to dynamically balance resource utilization so, that the systems can be adapt automatically to changes in parts production, mixes, and levels of output. (Definition used by Kearney and Trecker Co.).

Five main functional areas: 1. Workpiece system 2. Cutting tool system 3. Kinematical system 4. Energetic system 5. Information system

Social and cultural surroundings

Figure 1.2 System surroundings of an enterprise

Figure 1.3 Block diagram of a machine tool as manufacturing system acc. to G.Spur

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The main streams of a manufacturing process The material stream on the entry to the system consists of semi-products, tools and liquids suitable to be used as well as exploitations materials. On the way out, the stream consists of ready-made products, partly or completely worn-out tools, contaminated and used coolant, waste products and chips. Similarly, the information stream at its entry contains the following: information about the manufacturing process of particular pieces, NC programs on particular machine tools, possible NC programs for other installations, information about setting tools and conditions of cutting edges. On the exit, the part of information remains unchanged, and part (for example concerning tools) is actualized. All functions realized in manufacturing require the expenditure of energy that was expressed as the transfer of energy flow. The system is actually fed from electric installation and from the control installation of compressed air. The flow of energy at the exit becomes then the heat and the air decompressed to a level of atmospheric pressure.

Some discoveries that influenced the development of manufacturing automation (2): 1949-1952 - John Persons has developed rules for numerical controlled machine tools and launched at MIT the first NC machine tool 1954 - The Bendix company began commercial production of CNC milling machines (control using the tube circuits), 1958 - Industrial installations (in the U.S.) conventional automated machining lines controlled mechanically, electrically and hydraulically 1958 - IBM developed the first machine tool programming language APT 1965 - development of an automatic tool change 1969 - Installation of the first DNC systems 1970 - automatic change of workpiece pallet

Some discoveries that influenced the development of manufacturing automation (1): The fourteenth century – set of playing bells controlled by drums with pins, 1808 - Joseph M. Jacquard applied punched metal cards to the automatic control of weaving machines (example of removable data storage device), 1863 - M. Fourneaux patented automatic piano controlled by paper perforated tape (paper storage medium, control of auxiliary functions), 1920 - INDEX company - automatic lathe controlled by cam, 1923 - the first diagnostic and supervision systems 1938 - Claude E. Shannon developed the theoretical basis for the automatic processing and data transmission (the elements of computer operations and numerical controls) 1946 - John W.Mauchly i Presper Eckert put into service electronic digital machine "ENIAC" (the basis of electronic data processing)

2. Need for Flexible Manufacturing Systems The process of manufacturing technology development is a result of simultaneous affecting of technical possibilities given by the current technological conditions in the industry, as well as of the market demands. Both spheres are not independent but significantly coupled together. This process is besides stimulated by economic calculation. This statement can by formulated as follows: the technical possibilities are a set of necessary conditions whereas market demands and economic calculation form a set of conditions sufficient to ensure a qualitative change in process of manufacturing technology development.

Productivity by small and middle batches

Development phases of production facilities (1)

1950

Classical machine tools

NC machine tools

1960

1970

Connected machine tools

Flexible manufacturing systems

1980

Computer integrated manufacturing

1990

2000

Figure 2.1. Development phases of means of production in the second half of XX century (acc. to Kief)

The first phase covering the decade of 1950-1960, is the period of development of production of the conventional machine tools. They had to replace the machinery destroyed in many countries because of war operations (or dismantled in the aggressor countries in the frame of the war reparations, as in Germany). Following the war damages, the demand for all industrial products was significant. Products were purchased to use them in relatively long period. Therefore, the producer had to assume, that the period of use of the product should be appropriately long. In the industry of machine tools, there was a trend to produce automatic machine tools, to make long series of products. Batch production was rather not in question. The second phase in the years of 1960-1970 was an animated period in all developed countries. The increased demand created the tendency to modernize the industry and to rationalize production. New generation of machine tools, more precise and efficient, replaced the old machines. Numerically controlled (NC) machine tools appeared in the engineering, requested mainly by the aviation industry, which intended to introduce a new generation of aircrafts. The beginning of the third phase, which covers the years 1970-1980, marked the stagnation in the world economy, causing recession in many industrial branches, excessively curbing research and development. The hitherto existing market of producers changes into market of customers. The main tendencies, which appeared in the industry, are shown, in Fig. 2.2.

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The actions aimed at rationalizing the production in the first two phases of development The actions were concentrated on the shortening of main times and on the increase of their part in general time of making the product through shortening of auxiliary times. This was achieved through the following: • Improving the cutting ability of tools and thus increasing the machining efficiency; for example, applying of ceramic tool insert, • Increasing the power of machine tools, • Automation of tool change, • Inventing multiple tool heads and several supports, • Automation of part change.

Product variety

1970

Product life cycle

1980

1990

1970

Product complexity

1970

1980

1990

Required target dates

1980

1990

1970

1980

1990

Figure 2.2. Market trends stimulating the development of flexible manufacturing

5%

3

4

On a machine

5

95% Moving and waiting An average part’s time in the shop

6% 4% 12% 44%

2

1

34%

The time an average part spends on a machine

Figure 2.3. Breakdown of 8760 available hours in a calendar year to a manufacturing operation: 1 - inefficient use of second and third shifts, 2 - weekends, holidays, and vacations, 3 - machine and work setup, 4 - machining, 5 - unforeseen problems (breakdown, downtime)

Development phases of production facilities (2) In the United States, there appeared some concepts worked out for manufacturing systems in medium and short series production. Based on direct control, they used one computer and several combined NC machine tools. (Concept of DNC – Direct Numerical Control). This idea leads to fourth phase in the decade of 1980 – 1990. The still increasing market requested the flexibility and production efficiency. This puts on the first place the problem of coordinating the activity of different manufacturing equipment and functional sphere of manufacturing system, for example NC machine tools, setting tools equipment, tools store, transport means etc. It became quickly evident, that there is a need for comprehensive solution of the problem of “integrated manufacturing” (CIM), which appear in the fifth phase of development in the beginning of the 1990-s.

In cut

Load/Unload/Gage/Idle

Approximately 1,5%

Approximately 3,5%

Figure 2.4. Breakdown of the time spent by an average part in the shop

The actions aimed at rationalizing the production in the third and fours phase of development • Shifting the tool exchange time to the main time (realization of tool exchanging during the machining time), • Reducing the waiting time of machine tool (for example for changing the tool, etc.), • Reducing of standstill times, • Changing the NC program without stopping the operation, • Automation of tool management and tool delivery to the machine, • Automation of tool data transfer from the preset area, after automatic tool gauging, into the FMS tool system database and then to the MCU. All actions for automation the operation of the system simultaneously fulfill the main requirements in enabling the reduction of the unproductive times of machining tools: • Working unmanned during the night hours and holidays, • Working during shift breaks, • Minimizing the personnel during the third shift.

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THE 10 TYPES OF MANUFACTURING FLEXIBILITY 1. Machine flexibility Various operations performed without set-up change 2. Material handling flexibility Number of used paths per total number of possible paths between all machines

3. Operation flexibility Number of different processing plans available for part fabrication 4. Process flexibility Set of part types that can be produced without major set-up changes,

LIMITS OF MANUFACTURING FLEXIBILITY 1. Limited part types in predetermined product mix 2. Limited system capacity 3. Limited range of possible machining operations 4. Limited range of possible machining accuracy

i.e. part-mix flexibility

5. Product flexibility Ease (time and cost) of introducing products into existing product mix 6. Routing flexibility Number of feasible routes of all part types/Number of part types 7. Volume flexibility The ability to vary production volume profitably within production capacity

8. Expansion flexibility Easy (effort and cost) of augmenting capacity and/or capability, when needed, trough physical changes to the system 9. Control program flexibility The ability of a system to run virtually uninterrupted (e.g. during the second and third shifts) due to the availability of intelligent machines and system control software 10. Production flexibility Number of all part types that can be produced without adding major capital equipment

COMPLETENESS OF MANUFACTURING PROCESS REALIZED IN THE SYSTEM 1. Relation of number of operations possible to be realized in the system, to the whole number of operations necessary to complete machining of the workpiece, or 2. Relation of the sum of operational time duration of operations realized in the system, to the whole time necessary to complete machining of workpiece The grade of completeness is a number within the range between 0 and 1

Some basic definitions related to CIM

Figure 1.6 A typical automation migration strategy. Phase 1: manual production with single independent workstations. Phase 2: automated production stations with manual handling between stations. Phase 3: automated integrated production with automated handling between stations. Key: Aut = automated workstation.

Automation of the manufacturing support systems is aimed at reducing the amount of manual and clerical effort in product design, manufacturing planning and control, and the business functions of the firm. Nearly all modern manufacturing support systems are implemented using computers. Indeed, computer technology is used to implement automation of the manufacturing systems in the factory as well. The term computer-integrated manufacturing (CIM) denotes the pervasive use of computer systems to design the products, plan the production, control the operations, and perform the various information-processing functions needed in a manufacturing firm. True CIM involves integrating all of these functions in one system that operates throughout the enterprise. Other terms are used to identify specific elements of the CIM system. For example, computer-aided design (CAD) denotes the use of computer systems to support the product design function. Computer-aided manufacturing (CAM) denotes the use of computer systems to perform functions related to manufacturing engineering, such as process planning and numerical control part programming. Computer-integrated manufacturing involves the information-processing activities that provide the data and knowledge required to successfully produce the product. They are accomplished to implement the four basic manufacturing support functions identified earlier: (1) business functions, (2) product design, (3) manufacturing planning, and (4) manufacturing control.

A typical automation migration strategy Phase 1: Manual production using single-station manned cells operating independently. This is used for introduction of the new product for reasons already mentioned: quick and low-cost tooling to get started. Phase 2: Automated production using single-station automated cells operating independently. As demand for the product grows, and it becomes clear that automation can be justified, then the single stations are automated to reduce labor and increase production rate. Work units are still moved between workstations manually. Phase 3: Automated integrated production using a multi-station automated system with serial operations and automated transfer of work units between stations. When the company is certain that the product will be produced in mass quantities and for several years, then integration of the single-station automated cells is warranted to further reduce labor and increase production rate.

Row material, blank

Machining Nr 1

Operation

Machining

Machining

Machining

Nr 2

Nr 3

Nr 4

Operation Moving

Operation Moving

Operation Moving

Moving

Figure 2.5. Placing of person in conventional manufacturing process

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Data input Supervision

DNC Computer

FMS system console-control room

Host computer

CNC CNC A u to m a t e d t r a n s p o r t

CNC

CNC Machined part

Blank M2

M1

Parts

Multimachine attendance

CAQ

CAQ

M4

M3

Multimachine attendance

ASO111 FMC MC

Preliminary assembly

ASO22 MC

Final assembly

Epedition

CAQ Transport

Figure 2.6. The role of person in manufacturing, using automated machine tools

Figure 2.7. The role of person in flexibly automated manufacturing

Advantages of automation migration strategy: - It allows introduction of the new product in the shortest possible time, since production cells based on manual workstations are the easiest to design and implement - It allows automation to be introduced gradually (in planned phases), as demand for the product grows, engineering changes in the product are made, and time is provided to do a thorough design job on the automated manufacturing system - It avoids the commitment to a high level of automation from the start, since there is always a risk that demand for the product will not justify it.

Figure 1.5 Types of automation relative to production quantity and product variety

Fixed automation Fixed automation is a system in which the sequence of processing (or assembly) operations is fixed by the equipment configuration. Each operation in the sequence is usually simple, involving perhaps a plain linear or rotational motion or an uncomplicated combination of the two, such as the feeding of a rotating spindle. It is the integration and coordination of many such operations into one piece of equipment that makes the system complex. Typical features of fixed automation are (1) high initial investment for custom-engineered equipment, (2) high production rates, and (3) relative inflexibility of the equipment to accommodate product variety. The economic justification for fixed automation is found in products that are produced in very large quantities and at high production rates. The high initial cost of the equipment can be spread over a very large number of units, thus making the unit cost attractive compared with alternative methods of production. Examples of fixed automation include machining transfer lines and automated assembly machines.

Programmable Automation In programmable automation, the production equipment is designed with the capability to change the sequence of operations to accommodate different product configurations. The operation sequence is controlled by a program, which is a set of instructions coded so that they can be read and interpreted by the system. New programs can be prepared and entered into the equipment to produce new products. Some of the features that characterize programmable automation include (1) high investment in general purpose equipment, (2) lower production rates than fixed automation, (3) flexibility to deal with variations and changes in product configuration, and (4) high suitability for batch production. Programmable automated production systems are used in Iow- and medium-volume production. The parts or products are typically made in batches. To produce each new batch of a different product, the system must be reprogrammed with the set of machine instructions that correspond to the new product. The physical setup of the machine must also be changed: Tools must be loaded, fixtures must be attached to the machine table, and the required machine settings must be entered. This changeover procedure takes time. Examples of programmable automation include numerically controlled (NC) machine tools, industrial robots, and programmable logic controllers.

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3. Organizational categories of flexible manufacturing

Flexible Automation Flexible automation is an extension of programmable automation. A flexible automated system is capable of producing a variety of parts (or products) with virtually no time lost for changeovers from one part style to the next. There is no lost production time while reprogramming the system and altering the physical setup (tooling, fixtures, machine settings). Accordingly, the system can produce various mixes and schedules of parts or products instead of requiring that they be made in batches. What makes flexible automation possible is that the differences between parts processed by the system are not significant, so the amount of changeover required between styles is minimal. The features of flexible automation include (1) high investment for a custom-engineered system, (2) continuous production of variable mixtures of products, (3) medium production rates, and (4) flexibility to deal with product design variations. Examples of flexible automation are the flexible manufacturing systems for performing machining operations.

Every producer tends to gain a maximum profit out of manufactured products. For this achievement of purpose indispensable condition, in an unmonopolistic situation, is the market competitiveness. The most important element of competitiveness, at comparable utilitarian values of products produced by different producers, is the price. Therefore, one of the reason of manufacturing technology development is the trend for sinking the manufacturing costs. Possibility of their determining depend on four fundamental factors characterizing production: - production volume (batch number), - production capacity, - part variety, - manufacturing flexibility. On these factors depends effective application of individual organizational form of production.

3. Organizational forms of flexible manufacturing Variety

high

Conventional transfer line

3

1

low C)

high

2 low

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B)

A)

Flexible manufacturing system (FMS) Flexible manufacturing island Flexible manufacturing cell

Flexibility

Production capacity

Special system Flexible transfer line

Machining centre

NC machine tool

low

Standard general-purpose machine

low

high

Volume

high

Figure 3.1 Use ranges of various organizational form of manufacturing:

Figure 3.2. Functional structure of a machining center: 1 – machine tool, 2 – tool magazine, 3 – tool changer, 4 – pallet shuttle

A) Programmable automation, B) Flexible automation, C) Fixed automation

Machining center

1 5

Machining center is a numerically controlled machine tool of high automation degree. It has at least 3 NC axes (translatory motion) and often additionally one or two NC rotary axes. The first machining centers were designed with the destination to work with rotary tools. Therefore, under this denomination and without additional defining they are accepted as the milling machine centers. They are prepared to suit many various machining operations like drilling, milling, boring, threading, or reaming. They possess appropriately wide range of rotational speeds and feeds, and are equipped with great capacity tool magazines (60 to 120 tools) and automatic tool changers. To shorten the auxiliary times they may be provided with automatic pallet changer, whereas fixing and releasing the machined workpieces is made manually within the duration of machining another part.

2 3 4

Figure 3.3. Functional structure of a manufacturing cell: 1 – machining center, 2 – automatic work changer, 3 – tool magazine, 4 – automated pallet movement system, 5 – chip disposal system

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Manufacturing cell Manufacturing cell is a machining centre with broadened range of automation, enabling unmanned operation of a limited part inventory. Part changing is running automatically until inventory is finished. The required capacity of part store depends first on the machining time of one workpiece.

b)

a)

Manufacturing cells are provided with integrated program of installations to carry out monitoring of machining operations and supervising thereof; this refers to the condition of tools in order to change them in case of worn out state, or damage, as well as the machining process with the aim to protect the whole system. Manufacturing cells do not require a DNC computer if only the CNC memory capacity is adequate to introduce the machining programs of all workpieces to be machined during the unmanned continuous operation. It’s also necessary to ensure chips removal during this time. The structures of a manufacturing cell may be based on various machining centers.

Flexible manufacturing island

O

PR

The flexible manufacturing island – FMI in comparison to the machining centre and manufacturing cell is a system consisting of many machine tools and other manufacturing equipment, which from design point of view forms separated part of production department. A flexible manufacturing island enables to carry out all necessary machining operations. The workpieces of certain limited spectrum create principally a group of technological similar parts. In FMI there are included besides NC machine tools (and other equipment) also conventional machine tools manually operated, particularly to make seldom carried out operations which are not worth of automation. A team of appropriately trained personnel operates FMI, whereas this does not mean a rigid division of work-range between particular workers. As a rule, every worker should be able to solve each problem pertaining to island’s operation. It is one of conditions of its flexibility. Often the weakness of FMI is that the machine tools included in the island are not fully utilized.

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Production planning

Traffic management and control

Human resources management

Flexible manufacturing island

Island personnel

Means of production

Work order processing

Material resources management

Part family

System availability maintain

Quality control management

Tool management

Figure 3.5. Organization of flexible manufacturing island

The concept of flexible manufacturing with the highest grade of automation is the Flexible Manufacturing System - FMS. It consists of a group (5-10) of highly automated machine tools which – working independently of themselves - realize in due measure, complete machining operations of the same, or similar parts. The machine tools are connected each other with a transport system, and the whole system is controlled usually by a host computer.

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T IO N D IVI S I O DUC N

Flexible manufacturing system

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Figure 3.4. Flexible manufacturing cells: a) milling, b) turning

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Figure 3.6. The main units of a flexible manufacturing system: 1 – part store, 2 – fixture store, 3 – fixture/pallet assembly building station, 4 – queue area, 5 – pallet moving system, 6 – machine tool, 7 – cutting tool store, 8 – tool preset gauge, 9 – control system, 10 – cutting tool moving system, 11 – supervising station

It enables the following: • Fully automated manufacturing, • Making various machining operations of workpieces belonging to a part family, • Machining the workpieces of variable batches volumes, • Avoiding breaks in production caused by operators interference. To use fully these possibilities, there is a need of a developed system of supervision and diagnostics. In FMS, we can employ with a different arrangement of machine tools and other manufacturing equipment.

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a) Basic types of FMS layouts

C)

b) Closed-loop system

In-line system

d) Open-field system

Ladder-type system

load

c)

Appropriate transport system

Larry cart car Shuttle

Conveyor

Basic FMS layout types (1) In-line structure is most often applied by larry car transport. The machine tools and other equipment are placed on both sides of transport line. Advantage of the system is a compact structure (well-utilized work space) and ease to expand (through extension of transport line). Its disadvantage is a not easy access to machine tools by servicing and maintenance works and in case of removing the results of failure in system functioning.

unload

Automated guided vehicle

Conveyor

Closed loop structure here the transport path is in the form of closed oval, round or rectangle circuit of conveyor system. The workstations are located outside of this circuit. Pallets remain in continuous circulation until the end of machining. Thereafter, they usually leave circulation through the washing stand and return to beyond the unloading stand. Advantages and disadvantages are similar to those of linear structure.

Figure 3.7. Basic FMS layout types

a)

Basic FMS layout types (2) Open-field system in which the manufacturing equipment is freely spaced on a given surface according to conditions of technology, or system requirements. The transport system, connecting particular workstations is realized by: • Automated Guided Vehicles (AGV), most often wire-guided, or • Robots, in case of small numbers of machines and little surface being under operation. Advantages: free access to particular stations and good possibility to expansion. Disadvantages: large surface occupied and long transport ways. Ladder-type structure its specific feature is, that pallets run on conveyor round all the machine tools waiting on buffer sections until appropriate machine tool will be free. In transport systems are used most often gravity roll conveyors with a double belt (Bosch). After machining, the pallet with work-piece is delivered onto conveyor and returns to behind unloading station. The great disadvantage of this structure is that each machine tool is surrounded by transport system and the access to it is very difficult. Due to this fact, this structure is not recommended.

1

2

b)

3

Figure 3.8. Flexible production lines structures: a) single row line, b) closed loop line, c) line with compensation store 1 – loading, 2 – unloading, 3 – central load/unload station, 4 – compensation store with loading/unloading possibility

c) 1 4

4 2

Flexible manufacturing lines Flexible production line – FPL is distinguished from conventional lines first of all by the use of NC machine tools and other equipment like robots and manipulators. Machine tools are situated one by one along the transport path. The parts follow then from one stand to another in beforehand ordered sequence and are machined according to the following various machining program. Flexibility of line, results from the ease of resetting the tools to machine various product batches, and the easiness of programming the machining procedure and of possibility to expand the line and retain the existing machine tools and the ways of material flow. By changing the structural system of FPL, one can increase in certain limited range its flexibility. The line with compensation stores gives namely the possibility to part loading and unloading without the necessity to pass through the all stations. The flexibility of line can be also increased using transport system, which allows omitting certain stations, or passing without making machining operations.

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