Exam 2 Flashcards
Smaller batch sizes yields
Shorter leadtime, smaller WIP, fewer defects, greater scheduling flexibility
BUT —> requires more handling and changeovers
To achieve the benefits of small batch production you must reduce change over/set up time
Quick change methodologies
- RETAD: rapid exchange of tools and dies
- SMED: Single minute exchange of dies
- OTED: One touch exchange of dies
Most set up tasks fall into three categories
1) transfer and cleanup
2) remove and install
3) adjustment
The four steps of the SMED procedure
1) Study existing set up/change over methods
2) Convert as many internal steps to external steps as possible
3) Improve all steps
4) Abolish the set up
Step 1 of SMED: study existing method
• distinguish internal from external tasks
– internal tasks: must be done while machine is stopped
– external tasks: can be done while the machine is running
– unnecessary tasks: can be eliminated
• use kaizen team approach, review data, take notes
Step 2 of SMED: Convert internal to external
Convert any activity that can be done safely while the machine is running to external set up steps
Step 3 of SMED: Improve or shorten internal steps
• Shortening internal steps has immediate impact on reducing downtime
• improve every task in the set up procedure
• both internal and external time shortened
• the ultimate goal: it is so short that it no longer matters
-set up time should be less than or equal to tech time
Step 4 of SMED: Abolish the set up
1) redesign products/parts to eliminate changeover
2) use machines that can produce more than one kind of part at the same time
3) use less versatile multiple machines; dedicate each machine to one kind of product/part
Kanban
A Japanese word for card
– the card is an authorization for the next container of material to be produced
– a sequence of kanban PULL material through the process
– there are different sorts of signals, but they all are still kanban
Push system versus pull system
• push system: schedules are created by MRP system
– problem: schedules are often invalid or obsolete because they ignore interruptions and inventory builds up
• Pull system: worker at station 2 producer ONLY to satisfy demand from downstream, worker withdrawals needed material from station 1 only as needed
– worker at station 1 produces only to satisfy demand from station 2, withdrawals needed material from upstream as needed
Buffer stock
Enables station 2 to meet demand quickly and not have to wait on station 1
– the quantity remaining in buffer stock signals when station 1 should produce more
Guidelines for assembly area operators
- apply to all parts of kanban system
– list all the parts in the kanban system
– the MRP work order system applies to all other parts
– take only one container per part number from the kanban storage rack whenever you run out
– before taking a full container of parts, return empty to rack
Re-Order point equation
ROP = LT(D) + SS
ROP: re-order point
LT: lead time
D: demand
SS: saftey stock
Hospital system operating rules
– For users withdrawing containers: take only one item per part number from the kanban storage rack
– for providers: check daily for items remaining, when number of items remaining reaches designated minimum, replenish with required number of full containers
Two-Bin system
Start with two full bins of each kind of item
– when one bin is emptied, place an order for another bin to replenish it
– by the time the order arrives, the second bin should almost be empty
More rules for kanban operations
– A card is attached to every container
– each operation produces/replenish is only the quantity specified on the card
– only non-defective items are sent downstream
– the production process is “smoothed” to achieve level production
Steps for continuous improvement
1) Slowly decrease the number of containers until an interruption occurs
2) Identify source of the interruption
3) Slightly increase the number, eliminate cause of interruption
4) Return to step one
Equation for the number of containers in a buffer (k)
k= (replenishment quantity + safety quantity) / container quantity
Pull will not work when
In general, whenever demand or lead time or variable
– demand is unstable/highly variable
– production process is not level
– too many defectives
– long set ups and frequent breakdowns
Necessary conditions for pull production
- production on demand only
- strive for inventory reduction everywhere
– preventative maintenance program
– quality at the source
– quick set ups
– linked, somewhat synchronous operations
– somewhat level final production schedules
– cooperative effort and teamwork
– local control and visual management
More equations
Reorder point = LT * D
K = (LT*D) / Q or K = (LT*D*(1+x)) / Q or K = (LT+S)*D / Q
Process layout
Advantages
Disadvantages
• process layout: facility is arranged by department, function, or specialty
•Advantages:
-high flexibility can make many products,
-lower equipment costs (low Fixed Costs)
-higher work motivation, greater work variety, great employee involvement
-good for low volume, high variety output
• disadvantages:
– higher labor expenses and less efficient processes & equipment (high Variable Costs)
– higher inventory&material handling costs
- difficulty in scheduling and coordinating operations
Product layout
Advantages
Disadvantages
• product layout: arranged according to steps in a process, usually to make one product
• Advantages:
– low unit cost to the highway efficient equipment, booking processing, lower rates
– operations are easy to schedule and control
– little inventory, good for high-volume, low or no variety output
• Disadvantages:
– little or no flexibility, can only make one product
– labor problems: little work variety, boredom, low worker motivation
– higher equipment costs
– task interdependencies: when one task stops, all stop
Product layout versus process layout
- product layout: highly efficient, high volume, low variety, but only use for for repetitive, low variety production
- process layout: Low efficiency, low volume, high variety, but necessary for high variety production
How do you make a variety of things efficiently
Identify similarities in the process steps, then exploit that similarity
– Products with similar process steps are called the product families
A focused factory, or subplant
Is devoted to producing a product family
– operates largely autonomously from other areas of the plant
– has its own supervision, management, along with its own workers
– has its own internal planning and control functions
– often has its own support staff
– ideally small size, staffing, and space
– different forms of focus factors: focused flow lines (most repetitive), work cells, focused work centers (most variety)
Advantages/benefits of a focused factory
– smaller physical size: requires less travel and material handling waste
– smaller size operations: simpler planning and control
– more involvement: everyone is more involved which heightens communication and problem-solving
– dedication: workers perform better and are more motivated and get things done quicker
Disadvantages of focused factories
– decrease in availability of dedicated machines
– decreased machine utilization
– resistance to change
– time and expense of training workers and relocating equipment
Product quantity analysis
Purpose: identify largest volume products
– form focused factories around product family starting with the highest quantity of products
Process routing sequence
Form product families and focus factories by grouping commonly routing sequences
Cluster analysis
Create a machine matrix, rearranging rows by common products and rearranging columns by common machines
– form focused factors around clusters
– analysis ignore sequence of operations machine utilization and machine availability
Cycle time versus takt time
- cycle time: frequency between each completed unit in a process, implies a smooth uniform rate of production
- takt time: exact cycle time necessary to meet demand
Assembly cells
Most or all work is performed by the workers
Cycle time for assembly cells
CT a = the frequency between each completed unit in a process
= the time operators in the cell need to perform tasks in between stations
• when a cell has only one operator:
= sum all assembly task times at the stations + time to walk between stations
CT a = SUM(task times) + SUM(walk times)
Capacity
How much the cell can produce each day
Cell capacity = time available / CT a
To decrease cycle time and increase capacity
Add more operators, either by rabbit chase or dividing the cells into subcells
CTa(RC) = CTa for one worker / # of workers
CTa(Div) = maximum (CTa of Subcells)
Machining cells
Much of the work is performed by single cell automatic machines
When looking at CT, must consider to CT
– machine CT, operator CT
Machine CT versus operator CT
CT overall for machining cells
•Machine CT: time for machine to perform one operation before it automatically stops
mCT= runtime + load/unloading time
•Operator CT: time for operator to walk, load/unload machines, and do any other manual tasks
oCT= SUM(all manual task times) + SUM(walk times)
•CT m = Maximum (oCT, longest mCT)
Reducing waste
– Any operators trimmed from the cell are reassigned to cells elsewhere in the plant
– unless demand everywhere is in continual decline, operators are not laid off but reassigned to other cells
– best operators in the cell or reassigned first since I have the greatest skill diversity and send a message that reassignment is not a punishment but a reward
Minimum tolerable cycle time
“Cycle of woe” for many assembly line workers
– minus boring, causes mistakes, absenteeism, turnover
– instead of using 20 assemblers on a single line, form 4 cells with 5 assemblers each
Group technology
Cellular manufacturing benefits from this which is identifying commonalities among the processes for different products and parts
– grouping products that have similar processes together into product families
Quality of conformance
Output a process conforms to the requirements
– monitoring a process: inspection
When on the process to inspect?
– before and he reversed.
– before of stuff that renders inspection difficult or impossible
– before an expensive stuff
Purpose of an inspection
1) inspection for acceptance: to determine if the process is producing acceptable results, meet specifications
2) inspection for process control: to determine if the process has changed, or is no longer doing what it was
Statistical process control
Using control charts and statistics to keep a process in control
• why the variation, inspection results
– common cause: variation is caused by random factors, is inherent to the process, the process has not changed and is in control
– special cause: variation caused by non-random factors, a process has changed, it is out of control and should be stopped
The purpose of control charts
To monitor a process and identify when it might have changed, indicate when a process should be scrutinized for possible problems
– assumption: the process is being monitored already does a good job and conforms for specifications
– charts alone do not remove problems, improve quality
Process capacity
Just because of processes and control does not mean it is a good process
– to be good it must meet specifications
– specifications are the target features of a product
– process limits
– tolerance limits
• Continuous improvement: not only keeping standard deviation reduced but also moving the tolerance value is closer to the target
SPC‘s limitations
– it relies on sampling to identify changes in the process
– it can miss fleeting changes
– it can miss defects not caused by inadvertent mistakes or changes in the process
– it does not prevent inadvertent mistakes
Jidoka
No mistake or defect is allowed to proceed in the process
Andon signals
A visual signal to indicate an abnormal condition
– often it is a light that is switched to green yellow or red depending on the situation
•Types:
– Equipment: signals in the operating status of equipment
– caution: a warning that something will interrupt process flow, often associated with kanban
– paging: signals of request for forms, materials, or people
Pokayoke
Any device that:
– prevents a mistake
– stops the process or
– signals an alert that a mistake is about to happen or has already happened
Levels of mistake proofing
1) Prevent a mistake from ever occurring
2) Detect a mistake before it becomes a defect
2) Detect mistake that is caused defect but prevent defect from causing damage
Mistake proofing process steps
Plan do check act
1) document the mistake/defect
2) look for red flags: repetition, and frequent operation, high volume
3) determine the root causes: five why, cause-and-effect diagrams, mag 7 analysis tools
4) generate ideas
5) develop the device/method
Standard work
Is necessary for sustaining the gains and preventing backsliding
– is also necessary for training, monitoring, and continuous improvement
– It is difficult and often overlooked
– is measured and set by the workers
– is provisional and subject to change
– it is essential for kaizen
– always room for improvement
TPS Elements off Standard Work
1) Cycle Time: to satisfy demand, actual cycle time should be less than or equal to takt time
–TT=avil time/demand
2) procedure, tasks, and sequence: processes, operations, and individual tasks, and the sequence in which operations and tasks are performed is the standard work address
3) work in process (WIP): # of units w/in the process necessary to enable smooth flow
– clearly marked so anyone can readily see discrepancies between standard and actual WIP
Standard worksheet or work combination sheet
Shows the task within a single operation
Or shows elapsed time for sequence of tasks or operations
To make works standard it needs to be
Repetitive as much as possible
–the same steps at the same time in the same order
Obvious sign of need for improvement
If there’s a difference between the actual cycle time in the takt time
Reducing takt time
Put stress on the system so standard work is reassessed and changed
– culture is crucial with lien, and managers must understand workers
– each leader has a standard work as well, they must visit gumbo of a process to check conformance to standard work, review and shortfalls, and assess any countermeasures
