Ch 3 Manufacturing Models and Metrics

Transcription

1 Ch 3 Manufacturing Models and Metrics Sections: 1. Mathematical Models of Production Performance 2. Manufacturing Costs Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 1

2 Why use metrics A system of related measures that facilitates the quantification of some particular characteristic To track performance in successive periods, Try out new technologies and systems to determine their merits, identify their problems, To compare alternative methods, and To make good decisions. Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 2

3 Production Concepts and Mathematical Models Production performance metrics: Production rate R p Cycle time T c Production capacity PC Utilization U Availability A Manufacturing lead time MLT Work-in-progress WIP Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 3

4 Operation Cycle Time Typical cycle time for a production operation: T c = T o + T h + T th where T c = cycle time, T o = processing time for the operation, T h = handling time (e.g., loading and unloading the production machine), and T th = tool handling time (e.g., time to change tools) Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 4

5 Production Rate (batch/job shop/flow) Batch production: batch time T b = T su + QT c Average production time per work unit T p = T b /Q Production rate R p = 1/T p Job shop production: For Q = 1, T p = T su + T c For quantity high production: R p = R c = 60/T p since T su /Q 0 For flow line production: T c = T r + Max T o and R c = 60/T c Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 5

6 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): PC w = ns w H n o s R p where n o = number of operations in the routing max rate of output that a production facility is able to produce under a given set of assumed operating conditions Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 6

7 Utilization: U = Utilization and Availability Q PC where Q = quantity actually produced, and PC = plant capacity the amount of output of aproduction facility relative to its capacity Availability: A = MTBF MTTR MTBF where MTBF = mean time between failures, and MTTR = mean time to repair a common measure for reliability of equipment Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 7

8 Availability - MTBF and MTTR Defined Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 8

9 Manufacturing Lead Time 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 the total time required to process a given part/product through the plant including any lost time due to delays, time spent in storage, reliability problems, and so on. Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 9

10 Work-In-Process WIP = 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 MLT AU PC SH w sh the inventory in the state of being transformed from raw material to finished product Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 10

11 Costs of Manufacturing Operations Two major categories of manufacturing costs: 1. Fixed costs - remain constant for any output level 2. Variable costs - vary in proportion to production output level Adding fixed and variable costs where TC = total costs, TC = FC + VC(Q) FC = fixed costs (e.g., building, equipment, taxes), VC = variable costs (e.g., labor, materials, utilities), Q = output level. Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 11

12 Fixed and Variable Costs Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 12

13 Manufacturing Costs Alternative classification of manufacturing costs: 1. Direct labor - wages and benefits paid to workers 2. Materials - costs of raw materials 3. Overhead - all of the other expenses associated with running the manufacturing firm Factory overhead Corporate overhead Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 13

14 Typical Manufacturing Costs Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 14

15 Overhead Rates Factory overhead rate: FOHR = FOHC DLC Corporate overhead rate: COHR = COHC DLC where DLC = direct labor costs Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 15

16 Cost of Equipment Usage Hourly cost of worker-machine system: C o = C L (1 + FOHR L ) + C m (1 + FOHR m ) where C o = hourly rate, $/hr; C L = labor rate, $/hr; FOHR L = labor factory overhead rate, C m = machine rate, $/hr; FOHR m = machine factory overhead rate Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 16