Slide 1

Unit 2 Manufacturing Operations Sections: 1.Manufacturing Industries and Products 2.Manufacturing Operations 3.Production Facilities 4.Product/Production Relationships 5.Lean Production 6.Manufacturing Metrics Manufacturing Lead Time Rate of Production Production Capacity Work in Progress Design Times Utilisation/Availability Slide 2 Industrial Automation Architecture Level 0 Level 1 Level 2 Level 3 Level 4 Industrial Automation (Shop Floor) Business Information (Business Office) Slide 3 Manufacturing Lead Time Raw Materials Work in Progress Finished Goods Transport Machine Group StoresInspect Operating Times Non-operating Times Slide 4 Manufacturing Lead Time Time 95% Moving and Waiting 70% Positioning, Loading 5% On Machine 30% Cutting 1.5% of total time - adds value e.g. Set-up Time Slide 5 Manufacturing Lead Time Operation Time Non-operation Time n1 n2 n3 Time T o = Operation Time per Machine T no = Non-operation Time per Machine n m = Number of Machines MLT = n m ( T o + T no ) Slide 6 Manufacturing Lead Time Q = Number of parts MLT = n m ( QT o + T no ) n1 n2 n3 Pallet of six parts Slide 7 Manufacturing Lead Time n1 n2 n3 Pallet of six parts T su = Set-up Time MLT = n m ( QT o + T no + T su ) Slide 8 Manufacturing Lead Time Order #1 Order #2 Process Plan (Routing) Slide 9 Manufacturing Lead Time In practice Q, T su, T o, T no and n m will vary considerably for different order quantities, process routing to find average or aggregate values before carrying out analysis. e.g.: Slide 10 Operation Times Operation time has three elements: T m = Actual Machining Time T h = Workpiece Handling Time T th = Tool Handling Time T o = T m + T h + T th Slide 11 Rate of Production Total Batch Time per Machine Tsu + QTo Average Production Time per Part Tp = Tsu + QTo Q Rate of Production Rp = 1/Tp Slide 12 Lead Times Mass Production (Tsu + Tno -> 0) Job Shop (Q -> 1) Slide 13 Production Capacity Production Capacity, P c P c = WS w HR p W = number of work centres Sw = Number of shifts per week H = Hours per shift R p = Rate of production (units per hour) If process plan requires N m machines: P c = WS w HR p / N m Slide 14 Demand Rate Weekly Demand Rate D w = WS w HR p / N m WS w H = D w N m / R p Three ways of adjusting capacity W (number of work centres) S w (number of shifts per week) H (number of hours per shift i.e. overtime) Slide 15 Work In Progress WIP :Amount of product currently located in the factory that is either being processed or is in between processing operations Generally: WIP = P C U (MLT) / S w H Slide 16 WIP Ratio WIP Ratio = WIP / Number of Machines Processing WIP Ratio = PC U Sw H (MLT) W U QTo Tsu + QTo Ideal ratio: 1:1 Slide 17 Design Model Design Process generally involves six stages Recognition of need Definition of Problem Synthesis Analysis and Optimisation Evaluation Presentation Slide 18 Design Model Many engineering hours spent in Design Let T 1 = Time spent producing one unit of product T 2 = Time spent planning and setting up production T 3 = Time spent on design B = Aggregate number of batches produced Q = Aggregate batch size Slide 19 Design Model Aggregate total time spent during life of product TT LC = BQT 1 + BT 2 + T 3 Average time spent on each product T LC = T 1 + T 2 /Q + T 3 /BQ Slide 20 Design Model In Mass Production and Batch Production T2 and T3 can be spread out among large number of units - dominant factor is T1 - automation is important In Job Shop Production all three times are important. T2 and T3 may become dominant terms - CAD/CAM is important Slide 21 Worked Problem 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 min., 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 machines can be set up for any type of job processed in the plant. The plant operates an average of 70 production hours per week. Scrap rate is negligible. Determine (a) manufacturing lead time for an average part, (b) plant capacity, (c) plant utilization. (d) How would you expect the nonoperation time to be affected by the plant utilization? Slide 22 Solution (a) MLT = 6(5 + 25(0.1) + 10) = 105 hr (b) T p = (5 + 25 x 0.1)/25 = 0.30 hr/pc, R p = 3.333 pc/hr. PC = 70(18)(3.333)/6 = 700 pc/week (c) Parts launched per week = 20 x 25 = 500 pc/week. Utilization U = 500/700 = 0.7143 = 71.43% (d) As utilization increases towards 100%, we would expect the nonoperation time to increase. When the workload in the shop grows, the shop becomes busier, but it usually takes longer to get the jobs out. As utilization decreases, we would expect the nonoperation time to decrease. Slide 23 Utilisation Utilisation, U = Output/Capacity Utilization: U = where Q = quantity actually produced PC = plant capacity Slide 24 Availability Availability: A = where MTBF = mean time between failures, and MTTR = mean time to repair Slide 25 Costs of Manufacturing Operations Fixed costs - remain constant for any output level Variable costs - vary in proportion to production output level Adding fixed and variable costs TC = FC + VC(Q) where TC = total costs FC = fixed costs (e.g., building, equipment, taxes) VC = variable costs (e.g., labor, materials, utilities) Q = output level Slide 26 Costs Quantity, Q Method 1: Manual Method 2: Automated Breakeven Point FC 2 FC 1 VC 2 VC 1 Breakeven Point Slide 27 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 Slide 28 Typical Manufacturing Costs Slide 29 Overhead Rates Factory overhead rate: FOHR = Corporate overhead rate: COHR = where DLC = direct labor costs Slide 30 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 Slide 31 Worked Problem The break-even point is to be determined for two production methods, one a manual method and the other automated. The manual method requires two workers at 9.00/hr each. Together, they produce at a rate of 36 units/hr. The automated method has an initial cost of 125,000, a 4-year service life, no salvage value, and annual maintenance costs = 3000. No labour (except for maintenance) is required to operate the machine, but the power required to run the machine is 50 kW (when running). Cost of electric power is 0.05/kWh. If the production rate for the automated machine is 100 units/hr, determine the break-even point for the two methods, using a rate of return = 25%. The solution requires familiarity with the Uniform Annual Cost (UAC) method of determining an annual amount payable (A) on a principle sum (P). Slide 32 Solution Manual method: variable cost = (2 workers)(9.00/hr)/(36 pc/hr) = 0.50/pc Total cost as a function of Q is TC = 0.50 Q assuming no fixed costs. Automated method: (A/P,25%,4) = = (0.4234) UAC = 125,000(A/P,25%,4) + 3000 = 125,000(0.4234) + 3000 = 55,930/yr Variable cost = = 0.025/pc Total cost as a function of Q = 55,930 + 0.025 Q Break even point: 0.50 Q = 55,930 + 0.025 Q, 0.475Q = 55,930, Q = 117,747 pc/yr Hours of operation per year: Manual: H = = 3270.76 hr/yr. Comment: This would require two shifts. Automated: H = = 1177.47 hr/yr. Comment: Plenty of additional capacity in one shift beyond the break-even point.