COMPUTER INTAGRATED MANUFACTURING

Transcription

1 COMPUTER INTAGRATED MANUFACTURING 1

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3 Production System A collection of people, equipment, and procedures organized to accomplish the manufacturing operations of a company Two categories: Facilities the factory and equipment in the facility and the way the facility is organized(plant layout) Manufacturing support systems the set of procedures used by a company to manage production and to solve technical and logistics problems in ordering materials, moving work through the factory, and ensuring that products meet quality standards 3

4 TTypes of Manufacturing Systems 1. Continuous-flow processes. Continuous dedicated production of large amount of bulk product. Continuous manufacturing is represented by chemicals, plastics, petroleum, and food industries. 2. Mass production of discrete products. Dedicated production of large quantities of one product (with perhaps limited model variations). Examples include automobiles, appliances and engine blocks. 3. Batch production. Production of medium lot sizes of the same product. The lot may be produced once or repeated periodically. Examples: books, clothing and certain industrial machinery. 4. Job-shop production. Production of low quantities, often one of a kind, of specialized products. The products are often customized and technologically complex. Examples: prototypes, aircraft, machine tools and other equipment. 7 Production quantity Continuousflow production Mass production Batch production Job shop production Product variety 4

5 Category Continuous-flow process Mass production of discrete products Automation achievements Flow process from beginning to end Sensors technology available to measure important process variables Use of sophisticated control and optimization strategies Fully computer automated lines Automated transfer machines Dial indexing machines Partially and fully automated assembly lines Industrial robots for spot welding, part handling, machine loading, spray painting, etc. Automated material handling systems Computer production monitoring Batch production Numerical control (NC), direct numerical control (DNC), computer numerical control (CNC). Adaptive control machining Robots for arc welding, parts handling, etc. CIM systems. Job shop production Numerical control, computer numerical control The Production System 5

6 Production System Facilities Facilities include the factory, production machines and tooling, material handling equipment, inspection equipment, and computer systems that control the manufacturing operations Plant layout the way the equipment is physically arranged in the factory Manufacturing systems logical groupings of equipment and workers in the factory Production line Stand-alone workstation and worker Manufacturing Support Systems Involves a cycle of information-processing activities that consists of four functions: 1. Business functions - sales and marketing, order entry, cost accounting, customer billing 2. Product design - research and development, design engineering, prototype shop 3. Manufacturing planning - process planning, production planning, MRP, capacity planning 4. Manufacturing control - shop floor control, inventory control, quality control 6

7 Information Processing Cycle in Manufacturing Support Systems Automation in Production Systems Two categories of automation in the production system: 1. Automation of manufacturing systems in the factory 2. Computerization of the manufacturing support systems 7

8 Computer Integrated Manufacturing Mechanization Mechanization is providing human operators with machinery that assist them with the muscular requirements of work. It can also refer to the use of machines to replace manual labor or animals. A step beyond mechanization is automation. The use of hand powered tools is not an example of mechanization. 8

9 What is automation? Automation Why automation is required? Which are the operations can be automated in production system? Can automation be implemented suddenly? Automation Automation can be defined as the technology concerned with the application of complex mechanical, electronic, and computer-based systems in the operation and control of manufacturing systems. 9

10 Automation Automation is the use of control systems (such as numerical control, programmable logic control, and other industrial control systems), in concert with other applications of information technology (such as computer-aided technologies [CAD, CAM,]), to control industrial machinery and processes, reducing the need for human intervention. Automation In the scope ofindustrialization, automation is a step beyondmechanization. Where asmechanizationprovided human operators with machinery to assist them with the muscular requirements of work. Automationgreatly reduces the need for human and mental requirements as well. Processes and systems can also be automated. 10

11 Automated Manufacturing Systems Examples: Automated machine tools Transfer lines Automated assembly systems Industrial robots that perform processing or assembly operations Automated material handling and storage systems to integrate manufacturing operations Automatic inspection systems for quality control Automated Manufacturing Systems Three basic types: 1. Fixed automation 2. Programmable automation 3. Flexible automation 11

12 Fixed Automation A manufacturing system in which the sequence of processing (or assembly) operations is fixed by the equipment configuration. Typical features: Suited to high production quantities High initial investment for custom-engineered equipment High production rates Relatively inflexible in accommodating product variety Programmable Automation A manufacturing system designed with the capability to change the sequence of operations to accommodate different product configurations Typical features: High investment in general purpose equipment Lower production rates than fixed automation Flexibility to deal with variations and changes in product configuration Most suitable for batch production Physical setup and part program must be changed between jobs (batches) 12

13 Flexible Automation An extension of programmable automation in which the system is capable of changing over from one job to the next with no lost time between jobs Typical features: High investment for custom-engineered system Continuous production of variable mixes of products Medium production rates Flexibility to deal with soft product variety Product Variety and Production Quantity for Three Automation Types 13

14 Reasons for Automating 1. To increase labor productivity 2. To reduce labor cost 3. To mitigate the effects of labor shortages 4. To reduce or remove routine manual and clerical tasks 5. To improve worker safety 6. To improve product quality 7. To reduce manufacturing lead time 8. To accomplish what cannot be done manually 9. To avoid the high cost of not automating Production Concepts and Mathematical Models Production rate R p Production capacity PC Utilization U Availability A Manufacturing lead time MLT Work-in-progress WIP 14

15 Production rate R p Hourly production rate Work units completed/hr Cycle time: Time that one work unit spends being processed or assembled. It is the time between when one work unit begins processing and next unit begins. Not all time is productive. Cycle time consists of i) actual machining operation time ii) workpart handling time iii) tool handling time per workpiece Operation Cycle Time Typical cycle time for a production operation: T c = T o + T h + T th where T c = cycle time, min/pc T o = processing time for the operation, min/pc T h = handling time (e.g., loading and unloading the production machine), min/pc and T th = tool handling time (e.g., time to change tools), min/pc 15

16 Tool handling time Time spent changing tools when worn out Time required for changing one tool to the next. Tool indexing time for indexable inserts or for tools on a turret lathe Tool positioning for next pass etc.. These activities do not occur every cycle They must be spread over the number of parts Production rate for batch production Time to process one batch(q units) = Setup time + processing time, i.e., T b = T su + QT c where T b = Batch processing time in min T su = Setup time required for one batch in min Q = Batch quantity, pc T c = cycle time per workunit in min/cycle T p = T b / Q, wheret p = Avg prod. Time/workunit, min/pc R p = 60 / T b, Where R p = Hourly prod rate, pc/hr 16

17 Production rate for job shop production Time to process one batch(q units) = Setup time + processing time, i.e., T b = T su + QT c For job shop production, Q = 1 So, T b = T su + T c = T p How?? T p = T b / Q, wheret p = Avg prod. Time/workunit, min/pc R p = 60 / T b, Where R p = Hourly prod rate, pc/hr Production rate for mass production Production rate = cycle rate of the machine T b = T su + QT c For mass production, Q = very large T p = T b /Q= (T su + QT c ) / Q = T su /Q + QT c /Q T p = T su /Q +T c As Q becomes very large, T su /Q 0 So, Tp = Tc WKT, Production rate is reciprocal of production time Rp = Rc = 60/Tc 17

18 Production rate for flow line mass production Production rate = cycle rate of the production line Workstations are interdependent in the line Impossible to divide total work equally among all workstations on the line. So, one station ends up with the longest operation time ( Bottle neck station). Bottle neck station sets the pace to other workstation. Work units should be moved from one workstation to next (T r ) Production rate for flow line mass production Cycle time = transfer time + longest processing time T c = T r + Max T o Where Max To = operation time at the bottle neck station i.e., The maximum of operation times for all stations on the line T r = Transfer time R c = 60/T c

19 Production capacity maximum rate of output that a production facility(or production line, work center, or group of work centers) is able to produce under a given set of assumed operating conditions Operating conditions refer to the number of shifts per day, number of days in the week (or month) that the plant operates, employment levels, and so forth. Production capacity Let PC w = the production capacity of a given facility under consideration. Let the measure of capacity = the number of units produced per week. Let n= the number of machines or work centers in the facility. A work center is a manufacturing system in the plant typically consisting of one worker and one machine. It might also be one automated machine with no worker, or multiple workers working together on a production line. It is capable of producing at a rate R P unit/hr. Each work center operates for H s hr/shift. Let S w denote the number of shifts per week. PC w = n S w H s R p

20 Production capacity If we include the possibility that each work unit is routed through n o operations, with each operation requiring a new setup on either the same or a different machine, nswh srp PC = no where n o = number of operationsin the routing Production Capacity Plant capacity for facility in which parts are made in one operation (n o = 1): PC w = n S w H s R p where PC w = weekly plant capacity, units/wk Plant capacity for facility in which parts require multiple operations (n o > 1): ns PC = w H n o s R p where n o = number of operations in the routing 20

21 Production Capacity ns PC = w H n o Equation indicates the operating parameters that affect plant capacity. Changes that can be made to increase or decrease plant capacity over the short term are: 1. Change the number of shifts per week (S). For example, Saturday shifts might be authorized to temporarily increase capacity. 2. Change the number of hours worked per shift (H). For example, overtime on each regular shift might be authorized to increase capacity. s R p Production Capacity Over the intermediate or longer term, the following changes can be made to increase plant capacity: 3. Increase the number of work centers, n, in the shop. This might be done by using equipment that was formerly not in use and hiring new workers. 4. Increase the production rate, R p by making improvements in methods or process technology. 5.Reducethenumberofoperationsn o requiredperwork unit by using combined operations, simultaneous operations, or integration of operations. 21

22 Utilization Utilization refers to the amount of output of a production facility relative to its capacity. Expressing U=Q/PC Where U= utilizationof the facility, Q = actual quantity produced by the facility during a given time period (i.e., pc/wk), and PC = production capacity for the same period (pc/wk). It is often defined as the proportion of time that the facility is operatingrelative to the time available under the definition of capacity. Utilization is usually expressed as a percentage. Availability Availabilityis defined using two other reliability terms, mean time between failure (MTBF) and mean time to repair (MTTR). The MTBF indicates the average length of time the piece of equipment runs between breakdowns. The MTTR indicates the average time required to service the equipment and put it back into operation when a breakdown occurs. 22

23 Availability Availability is defined as follows: Availability: A = MTBF MTTR MTBF where MTBF= mean time between failures, and MTTR= mean time to repair Availability is typically expressed as a percentage Availability - MTBF and MTTR Defined 23

24 1) A production machine operates at 2 shifts/day and 5 days a week at full capacity. Its production rate is 20 unit/hr. During a certain week, the machine produced 1000 parts and was idle in the remaining time, (a) Determine the production capacity of the machine, (b) What was the utilization of the machine during the week under consideration? if the availability of the machine is 90%, and the utilization of the machines is 80%. Compute the expected plant output. Solution: (a) The capacity of the machine can be determined using the assumed 80-hr week as follows: PC = 80(20) = 1600 unit/wk (b) Utilization can be determined as the ratio of the number of parts made by the machine relative to its capacity. U = 1000/1600 = (62.5%) (c) U=Q/PC or Q= UxPCxA or UAxnSHRp 2) The mean time between failures for a certain production machine is 250 hours, and the mean time to repair is 6 hours. Determine the availability of the machine. Availability: A = MTBF MTTR MTBF 3) One million units of a certain product are to be manufactured annually on dedicated production machines that run 24 hours per day. 5 days per week, 50 weeks per year, (a) If the cycle time of a machine to produce one part is 1.0 minute, how many of the dedicated machines will be required to keep up with demand? Assume that availability, utilization, and worker efficiency = 100%, and that no setup time will be lost, (b) Solve part (a) except that availability = Solution: Tc= 1 min Tb = Tsu+QTc= 0+QTc Tp= Tb/Q = Tc Rp=60/Tp = 60 Parts/Hr n= PC/SHRp = /(50x5x24x60) = 2.77 = 3 machines 24

25 Manufacturing Lead Time Manufacturing lead time (MLT) is the total time required to process a given part or product through the plant, including any lost time due to delays, time spent in storage, reliability problems, and so on. Production consists of a sequence of individual processing and assembly operations. Between the operations are material handling, storage, inspections, and other non productive activities. Divide these activities as operation and non operation elements. Non operation elements are Handling, temporary storage, inspection and other sources of delay when work unit is not in machine. Let T c = the operation cycle time at a given machine or workstation, T no = the nonoperation time associated with the same machine. n o = the number of separate operations through which the work unit must be routed T su = Setup time required to prepare each production machine for the particular product. If we assume batch production, then there are Q work units in the batch., Given these terms, we can define manufacturing lead time as MLTj = n oj ( Tsuji + Q jtcji + Tnoji ) i= 1 where MLTj = manufacturing lead time for part or product j (min). T suji = setup time for operation i (min) for the product j, Q j = quantity of part or product in the batch (pc), T cji = operation cycle time for operation i (min/pc), T noji = nonoperation time associated with operation i (min), and i indicates the operation sequence in the processing; i = I, 2,... n oj 25

26 To simplify and generalize the model, let us assume that all setup times, operation cycle times, and non operation times are equal for the n oj machines. Further, let us suppose that the batch quantities of all parts or products processed through the plant are equal and that they are all processed through the same number of machines, so that n oj = n o, With these simplifications, Eq. becomes: MLT= n o (T su + QT c + T no ) where MLT= manufacturing lead time, n o = number of operations, T su = setup time, Q = batch quantity, T c = cycle time per part, and T no = non-operation time For a job shop in which the batch size is one (Q = 1), Eq. (1.12) becomes MLT=n o (T su +T C +T no ) (1.13) For mass production, the Q term in Eq. (1.12) is very large and dominates the other terms. In the case of quantity type mass production in which a large number of units are made on a single machine (n o =1). The MLT simply becomes the operation cycle time for the machine after the setup has been completed and production begins. MLT = QxT c

27 For flow line mass production, the entire production line is set up in advance. Also, the non operation time between processing steps is simply the transfer time T r to move the part or product from one workstation to the next. The station with the longest operation time sets the pace for all stations: MLT=n o (T r +Max T o ) = n o T c Since, (T r +Max T o ) = T c (1.5) Since the number of stations is equal to the number of operations (n = n o ) Eq. (1.15) can also be stated as MLT=n(T r +Max T o ) = nt c A certain part is produced in a batch size of 100 units. The batch must be routed through five operations to complete the processing of the parts. Average setup time is 3 hr/operation, and average operation time is 6 min. Average non operation time due to handling, delays, inspections, etc., is 7 hours for each operation. Determine how many days it will take to complete the batch, assuming the plant runs one 8-hr shift/day. Solution: Given: Q = 100 units n o = 5 T su = 3hr/operation T c = 6 min T no = 7 hr/operation The manufacturing lead time is computed from Fq MLT = n o (T su + QT c + T no ) MLT = 5( X ) = 100 hours At 8 hr/day. this amounts to L00/8 = 12.5 days. 27

28 A certain part is routed through six machines in a batch production plant. The setup and operation times for each machine are given in the table below. The batch size is 100 and the average non operation time per machine is 12 hours. Determine (a) manufacturing lead time and (b) production rate for operation 3. Solution: Given: Q = 100 units n o = 5 T su = 3hr/operation T no = 12hr/machine The manufacturing lead time is computed from Fq n oj MLT = ( T i= 1 suji + Q T j cji + T noji ) A certain part is routed through six machines in a production plant. The operation times for each machine are given in the table below. Suppose the part is made in very large quantities on a production line in which an automated work handling system is used to transfer parts between machines. Transfer time between stations = 15 s. The total time required to set up the entire line is 150 hours. Assume that the operation times at the individual machines remain the same. Determine (a) manufacturing lead time for a part coming off the line.(b) production rate for operation 3. and (c) theoretical production rate for the entire production line. Solution: Given: a) MLT = no(tr+maxto) b) Rp 3 = 60/Tp ; But Tp = Tc = To c) Rp = 60/Tp; But Tp = Tc ; But Tc = Tr+Max To 28

29 Work-In-Process Work-in-process (WIP) is the quantity of parts or products currently located in the factory that either are being processed or are between processing operations. WIP is inventory that is in the state of being transformed from raw material to finished product. Work-In-Process An approximate measure of work-in-process can be obtained from the following, using terms previously defined: AU ( PC )( MLT ) WIP= SwH sh where WIP= work-in-process, pc; A= availability, U= utilization, PC= plant capacity, pc/wk; MLT= manufacturing lead time, hr; S w = shifts per week, H sh = hours per shift, hr/shift 29

30 TIP Ratio The TIP ratio measures the time that the product spends in the plant relative to its actual processing time. It is computed as the total MLT for a part divided by the sum of individual operation time for the plant. MLT TIP= T o The average part produced in a certain batch manufacturing plant must be processed sequentially through six machines on average. Twenty (20) new batches of parts are launched each week. Average operation time = 6 minutes, average setup time = 5 hours, average batch size= 25 parts, and average non operation time per batch = 10 hr/machine. There are 18 machines in the plant working in parallel. Each of the machinescanbesetupforanytypeofjobprocessedintheplant.theplantoperatesan average of 70 production hours per week. Scrap rate is negligible. Determine (a) manufacturing lead time for an average part,(b) plant capacity, and(c) plant utilization, (d) Determine the average level of work-in-process in the plant. a) MLT = no( Tsu + QxTc + Tno ) b) PC = A.U. n.swhs.rp/no c) U = Q/PC d) WIP = A.U.PC.MLT/SwHs 30