Final Qual (Lean) Flashcards
Takt Time
versus Cycle Time
What is their relationship?
Takt Time = Max time between successive outputs from a process, as determined by demand
T = 1/demand rate
= Time Period/Demand Units within time period
Cycle Time = average time between successive outputs from a process or step OPERATING at capacity
(recall kristens cookies)
= 1/capacity
Cycle Time must be LESS than takt time in order to meet demand
Made to Order products (time spent waiting?)
Equal to Flow TIme
Load Balancing
Moving around tasks across steps and increasing # of resources within steps to balance load (and therefore bottleneck resource)
Toyota Production System (TPS)
Guiding Principles
- Zero Non-value added activities = “Muda”
* value is equal to whatever the customer wants (e.g. Dinsey World)
* Seven Sources of Waste = TIMWOOD
- Zero Non-value added activities = “Muda”
- Zero defects
- Zero breakdowns
- Zero setup
(low as possible)
TPS
Seven Sources of Waste (Muda)
+ 1 bonus
TIMWOOD
- Transportation (internally –> should optimize layout of “gemba”)
- Inventory (a) inventory hides problems, like inefficient load balancing, b) inventory introduces risks, like obsolete products
- Motion - optimize ergonomics according to the “right way” to perform tasks (workers shouldn’t have to move around a lot)
- Waiting - resources waiting for flow units, flow units waiting for resources
- Over-production - producing too much too soon (excess inventory)
- Over-processing (unnecessary and redundant processes)
- Defect - requires rework - do it right the first time
- # 8) underutilized talent (mismatch of people and their jobs)
TPS
JIT (just-in-time)
3 steps?
Goal:
- supply matches/synchronize with demand
- give customers what they need when they need it
- Achieve a one unit at a time flow = Heijunka (opposite of batch processing)
- Mixed Model Production and frequent production of smaller batches - mixing together production variants (R R R M instead of all Rs then all Ms)
- Advantages:
- lean uses excess labour, machines, and overtime to provide the hedge, instead of excess inventory (Safety stock) –> excess labour and overtime are CHEAPER than excess inventory
- Frequent production of smaller batches reduces setup and changeover times
- Improves setup processes
- Produce at a rate of customer demand = Takt time
* no use of forecasts; sync production with customer demand - implement a pull system - Kanban
- Kanban = control system in which production and the delivery of parts are TRIGGERED by downstream consumption
- Kanban refers to the card attached to each container (carries inventory between process steps)
- Advantages:
- there can never be more inventory between two resources than what has been authorized by the kanban cards
- Amount of Inventory = # of Kanban Cards
- therefore, the amount of inventory becomes a decision variable
- there can never be more inventory between two resources than what has been authorized by the kanban cards
TPS
Is JIT appropriate for every production system?
What are some disadvantages of JIT?
NO
Conditions ripe for JIT:
- stable, repetitive manufacturing environment
NOT suitable for:
- high variability in demand
- made-to-order production
- high set up times (recall JIT requires frequent setups)
Disadvantages of JIT?
- JIT is vulnerable to shutdowns and breakdowns
- JIT is also hard to accommodate frequent new production introductions
TPS
JIT myths
- JIT requires suppliers to be close to the plant…
- Not true - JIT can be applied in the plant, while still holding raw material inventory for distant suppliers
- JIT uses single-sourcing for all components…
- few suppliers for all components, but closer communication and partnership
- JIT pushes inventory to suppliers…
- not in the JIT philosophy
- Workers enjoy working in JIT plants
- repetitive work is boring no matter what
TPS
Quality Management
3 steps
Goal:
- Eliminate defects in order to operate with minimum buffers and avoid waste of rework
3 Steps:
- Defect Prevention - Poka Yoke
- fool proofing by making mistakes in assembly physically impossible (e.g. cut out shaped boxes)
- Rapid Defect Detection - Jidoka and Andon Cord
- pull cord to immediately stop the line and prevent the defect from going to further stages
- Jidoka = “building quality in”
- Strong worker responsibility with respect to quality
TPS
Inventory Reduction
How fast? How can this be established?
Goal:
- Recede inventory to expose defects
- fix underlying root cause of the defects
Inventory reduction should be down SLOWLY and with caution
- arbitrarily reducing inventory causes high changeover costs and/or equipment starvation
- reduce the number of kanban cards to gradually reduce inventory and expose problems
- Recall: River Analology with inventory problems beneath the water
Kaizen
Process Improvement
Question
An employee in a restaurant spends her time on the following:
- Waiting for a customer order
- taking the order
- forwarding the order to the kitchen
- waiting for the kitchen to confirm the order
- bringing the food to the customer
- serving the customer
- collecting the payment
Which of these time commitments are waste, which are non-value-added (but necessary) work, and which are value-added work?
Waste: TIMWOOD
- Waiting for kitchen to confirm the order
Non-value adding:
- waiting for customer
- collecting payment
Value-Added:
- Taking order
- Forwarding order to the kitchen (internal transport)
- Serving the customer
- Bringing food to customer (can’t eliminate this step)
Question
How does the use of Kanban result in a pull system?
- Kanban cards are used to manage inventory
- there can never be more inventory between two resources than what has been authorized by the kanban cards
- Use Kanban cards to pull in exactly what is needed to respond to a customer’s demand (not forecasted demand)
- This is contrasted with the traditional approach that uses a push system, where products are created in batches based on forecasts
Question
A production process has 2 machines. The first machine has a capacity of 100 units/hour and the second machine has a capacity of 60 units/hour. Demand for the process is 100 units/hour
A) in a push process, what would be the first machine’s utilization? What would happen to the process inventory?
A) Throughout Rate = MIN ( process capacity, demand rate)
= MIN (60/h, 100) = 60/h
First machine’s utilization = Throughout/Capacity of Pool
= 60/100 = 0.6
If there’s a buffer, first machine would produce a lot more than required
B) Pull system:
- first machine will only process a unit when the second machine can take it => operate at the rate at which the final step needs to operate it => won’t have build up inventory
Question
A manufacturer of auto parts has just learned about the Toyota Production System and is trying to implement lean operations. Traditionally, there has been no control on the amount of WIP inventory between stages (been known to exceed 500 parts between some stages). As a first step, the WIP inventory between stages is limited to a max of 20 parts. What, if any, impact does does this have on the output from the factory in the short term? Using lessons learned from the river analogy, how should the manufacturer manage buffers?
- Inventory is being reduced very quickly from 500 parts down to 20 parts
- this can expose a lot of problems, much like how the river’s water level falls rapidly and reveals many rocks (aka inventory problems like scrap, vendor problems, change orders, backlogs, machine downtime etc.)
- instead, if the inventory between steps is reduced slowly, this allows for more time to fix the problems as you come across them
