02b. Manufacturing Operations
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Transcript of 02b. Manufacturing Operations
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
Industrial AutomationArchitecture
Transformation ProcessRaw
MaterialPart or Product
PowerTools
MachinesLabour
Scrap or Waste
Level 0
Level 1
Level 2
Level 3
Level 4
Industrial Automation(Shop Floor)
Business Information(Business Office)
Manufacturing Lead Time
RawMaterials
Work inProgress
FinishedGoods
Transport
MachineGroup
Stores Inspect
•Operating Times•Non-operating Times
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
Manufacturing Lead Time
Operation TimeNon-operation Time
n1n1 n2n2 n3n3
Time
To = Operation Time per MachineTno = Non-operation Time per Machinenm = Number of Machines
MLT = nm ( To + Tno )
Manufacturing Lead Time
Q = Number of parts
MLT = nm ( QTo + Tno )
n1n1 n2n2 n3n3
Pallet of six parts
Manufacturing Lead Time
n1n1 n2n2 n3n3
Pallet of six parts
Tsu = Set-up Time
MLT = nm ( QTo + Tno + Tsu )
Manufacturing Lead Time
Order #1
Order #2
Process Plan (Routing)
Manufacturing Lead Time
In practice
Q, Tsu, To, Tno and nm will vary considerablyfor different order quantities, process routing to find average or aggregatevalues before carrying out analysis. e.g.:
QQi
i1
nq
nQ
Operation Times
Operation time has three elements:
Tm = Actual Machining TimeTh = Workpiece Handling TimeTth = Tool Handling Time
To = Tm + Th + Tth
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
Lead Times
MLT (Tsui QToi Tnoi)i1
nq
MLT (Tsu QTo Tno)nm
MLT (Tsu To Tno )nm
Mass Production (Tsu + Tno -> 0)
MLT nm(TransferTime Longest(To ))MLT nmQTo
Job Shop (Q -> 1)
Production Capacity
Production Capacity, Pc
Pc = WSwHRp
W = number of work centresSw = Number of shifts per weekH = Hours per shiftRp = Rate of production (units per hour)
If process plan requires Nm machines:
Pc = WSwHRp / Nm
Demand Rate
Weekly Demand Rate
Dw = WSwHRp / Nm
WSwH = DwNm/ Rp
Three ways of adjusting capacity
W (number of work centres)Sw (number of shifts per week)H (number of hours per shift i.e. overtime)
Work In Progress
WIP : Amount of product currently locatedin the factory that is either being processedor is in between processing operations
Generally:
WIP = PC U (MLT) / Sw H
WIP Ratio
WIP Ratio = WIP / Number of Machines Processing
WIP Ratio =
PC USw H
(MLT)
W UQToTsu + QTo
Ideal ratio: 1:1
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?
Solution
(a) MLT = 6(5 + 25(0.1) + 10) = 105 hr
(b) Tp = (5 + 25 x 0.1)/25 = 0.30 hr/pc, Rp = 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.
Utilisation
PC
Q
Utilisation, U = Output/Capacity
Utilization: U =
where
Q = quantity actually produced
PC = plant capacity
Availability
Availability: A =
where MTBF = mean time between failures, and MTTR = mean time to repair
MTBF
MTTRMTBF
Costs of Manufacturing Operations
Fixed costs - remain constant for any output level Variable costs - vary in proportion to production output
levelAdding fixed and variable costs
TC = FC + VC(Q)where TC = total costsFC = fixed costs (e.g., building, equipment, taxes)VC = variable costs (e.g., labor, materials, utilities)Q = output level
Costs
Quantity, Q
Method 1:Manual
Method 2:Automated
Breakeven Point
FC2
FC1
VC2
VC 1
Breakeven Point
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
Overhead Rates
Factory overhead rate:
FOHR =
Corporate overhead rate:
COHR =
where
DLC = direct labor costs
DLC
FOHC
DLC
COHC
Cost of Equipment Usage
Hourly cost of worker-machine system:
Co = CL(1 + FOHRL) + Cm(1 + FOHRm)
where
Co = hourly rate, €/hr
CL = labor rate, €/hr
FOHRL = labor factory overhead rate
Cm = machine rate, €/hr
FOHRm = machine factory overhead rate
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).
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.