Presentation on theme: "from Prof. Goldsman’s lecture notes"— Presentation transcript:
1 from Prof. Goldsman’s lecture notes Process Flowfrom Prof. Goldsman’s lecture notes
2 Main Concerns… Transform inputs into outputs Internal measurement (process performance) versus External measurement (customer satisfaction)Productivity level (output/input)Which one is controllable by the managers?Remember …“Work smart, not hard”Systematic approach: find easier and better ways to accomplish a taskSteps: Identify problems -- Obtain facts -- Question the facts -- Develop and test an improved method -- Simulate the method -- Apply the method -- Review the methodLet’s look into the flow…
3 Chart Types Process Flow Chart Left-Hand-Right Hand Charts (analyze the work performed by one person at one specific WS)Multiple Activity Chart (>= 2 objects/persons are shown)Work Distribution Chart (all activities/person/ department)Operation Process ChartGantt Chart
4 Process Flow Diagram Elementary School Middle School State Exam High PassGeorgiaTechFail
8 Process Flow Concepts Process boundaries Process flow rate: R (Throughput)Process inventory: I (WIP, Inventory, Bottleneck)Unit flow time: T (on average, amount of time a flow unit spends within the system)Little’s LawFlow unitWhat is the flow unit in a kitchen in restaurant, gas station pump, gas station, or clothes store?
9 Process Flow Concepts (Cont’d) Inventory:What are the inventory in a …University?Gas station?Kitchen in a restaurant?Flowtime for a particular item in a system:= time it leaves system - time it enters systemUsually is on average, the amount of time a flow unit spends in systemi.e. how long does a dollar remains in your checking account?
10 Process Flow Concepts (Cont’d) Throughput: rate of flow unit through a pointWhat is the throughput in …A Kitchen in a restaurant?Gas station?Gas pump?Clothes store?
11 Sneak Preview … Let’s observe a bank teller, What do we actually observe?
12 Sneak Preview … (Cont’d) We can observe:Events:Arrive at the “in” queueLeave the “in” queue, starts serviceFinishes service, enter the “out” queueLeave the “out” queueArrival ProcessServiceProcess
13 Sneak Preview … (Cont’d) Averaged them out over time,VOILA! Little’s Law!Rate in = rate out (steady state)Similar to physics (v x t = d)Applicable to most systems even those with variabilityThroughput rate x flowtime = inventoryR x T = I or I = R x TNow, how can we determine the inventory in a university?
14 Process Flow Concepts (Cont’d) Bottleneck:Definition: reduce rate, reduce throughputIn a university?Flowlines usually have bottlenecks -- Assembly Line BalancingJobshops are more complex; less easily applicableOften become unclear when variability exists
15 Ok.. Little’s Law is awesome... BUT, what about resource requirements? How much capacity is “required”?Estimating capacity requirementOperation Capacity Required = R x (resource/flow unit) -- utilizationExample: labor hours req’d =200 pc/day x .25 hrs/pc = 50 hrs/dayor 7.14 workers -- at 100% utilization
16 Utilization isn’t 100%Whenever the inventory goes to zero, the process is idle, thus the utilization is less than 100%Thus, estimate the utilization to be less than 100%Revisit the previous example:Suppose utilization is 75%, the labor hours req’d is…66.67 hrs/day or 9.52 workers
17 Look at a “network” of processes… and apply theoretical CPM
18 Process Flow Process Flow Graph Process Flow Chart Shows only the structure of the flowUsed to “map” the actual path and document resource usageProcess Flow ChartShows the structure of the flows and detailed operation informationUsed to “document” times and distances, and identify unquantified delays
20 Critical Path ConceptCalculate the longest path in the process flow graph = Critical Path
21 Flow Time EfficiencyTheoretical Flow Time (T*)= Σ quantified process times on the longest pathActual Flow Time, T, is never less than T*, why?Thus, the flow time efficiency is T*/T should be >, <, or = 1?The inverse of flow time efficiency is called the “x factor”
22 How to Improve It? Focus on Critical Path! Reduce work content of operations on critical pathIncrease lot size to reduce the number of setupsReduce product reworkReduce or eliminate inspection“Balancing” the CP and non-CP
23 Dilbert ObservationIf you are evaluated on the basis of flow time efficiency, i.e., T*/T, one way to make your efficiency better is to increase T* while holding T constantWhat do you think?
24 What about the maximum rate at which units can be produced?