Test 2 Flashcards
(96 cards)
1
Q
What are the necessary conditions for pull production?
A
- Continuous, stable demand
- Uniform (level) production schedules
- Short setup times
- Limited product variety
- Continuous flow
- Equipment must be reliable
2
Q
What strategies could you implement if you have seasonal demand
A
- Don’t vertically integrate (excess inventory)
- Modular design
3
Q
True or False: A small buffer stock is good for pull production
A
True, otherwise could lead to increases in lead time (can start work immediately as soon as the order begins with small buffer stock)
4
Q
What is a Kanban System
A
Uses simple cards to strictly control production, means ‘card you can see’, maintains inventory levels, if all material is consumed a signal is sent to produce and deliver new material, it is a ‘pull’ system where products are made on demand
5
Q
What are the rules of Kanban
A
- Downstream operations withdraw only the quantity of items needed from upstream operations. This quantity is controlled by the number of cards
- Each operation produces items in the quantity and sequence indicated by the cards
- A card must be attached to a container. No withdrawal or production is permitted without a Kanban
- Only non-defective items are sent downstream. Defective items are withheld and the process stopped until the source of defectives is remedied
- The production process is smoothed to achieve level production. Small demand variations are accommodated in the system by adjusting the number of cards
- The number of cards is gradually reduced to decrease WIP and expose areas that are wasteful and in need of improvement
6
Q
What is the two-bin Kanban system
A
Material is held in two bins (A and B), material used to satisfy demand is withdrawn from B, when bin B is empty authorization is sent down to fill another bin, in the meantime material is drawn from A to satisfy production
7
Q
What is a reorder point (ROP)
A
A replenishment order, placed whenever inventory falls below a specified level, used in Kanban, denoted as:
ROP = D(LT) + SS, where:
- D = Demand/Consumption Rate (units/time)
- LT = Lead Time (elapsed time between order and replenishment). Time required to replenish the buffer
- SS = Safety Stock (units)
8
Q
What is lead time (in Kanban/pull systems)
A
Time required to replenish a container, comprised of two components:
- Conveyance Time (C) to move empty container upstream and full container downstream
- Production Time (P) to setup and produce required parts
This time can be variable, and formulas are estimates only
9
Q
In Kanban, what if the distance between two stations is further apart? What can be done about this?
A
If workstations are not close to each other, a buffer could be split into an inbound buffer and an outbound buffer, can synchronize production between upstream and downstream processes
10
Q
What is conveyance time
A
Time that the C-Kanban waits in the kanban mailbox downstream to be retrieved
+
Time it takes to move C-Kanban upstream
+
Time it takes to move C-Kanban downstream with a bin of parts
+
Time it waits in the downstream buffer until the C-Kanban is retrieved and put back into the Kanban mailbox to be retrieved again
11
Q
What is production time, P
A
Time that the P-Kanban waits in the P-Kanban mailbox
+
Time it takes to move the P-Kanban upstream to the first operation
+
Time it takes the P-Kanban to wait at the first operation
+
Time it takes to refill the container (setup + run + in-process waiting time)
+
Time it takes to move the full container to the outbound buffer
+
Time the container waits in the buffer
12
Q
How do you facilitate continuous improvement in Kanban (4 steps)
A
- Slowly decrease the number of containers until an interruption occurs (or, slowly decrease the units per container)
- Identify the source of the interruption
- Increase the number slightly; try to eliminate the cause of the interruption
- After the cause has been eliminated, return to step 1
13
Q
Fill in the blank: Demand cannot be greater than the _____________ of the ____________ machine
A
Capacity, slowest
14
Q
Fill in the blank: To adapt to increasing demand, lean systems are designed with ____________ capacity, and are run below ________ utilization
A
Excess, 100%
15
Q
Is this a pull or push production trait: Every operation requires a schedule
A
Push
16
Q
Is this a pull or push production trait: Only final operation requires a schedule
A
Pull
17
Q
Is this a pull or push production trait: Decentralized control
A
Pull
18
Q
Is this a pull or push production trait: Every part needs a schedule
A
Push
19
Q
Is this a pull or push production trait: Every part needs a schedule
A
Push
20
Q
Is this a pull or push production trait: Centralized planning
A
Push
21
Q
Is this a pull or push production trait: Centralized planning
A
Push
22
Q
Is this a pull or push production trait: Batch and queue
A
Push
23
Q
Is this a pull or push production trait: Flow
A
Pull
24
Q
When does pull not work? Give 5 examples
A
- When assembly involves anything that causes the assembly time per unit to vary
- When operations require setups that cannot be simplified or significantly shortened
- The product is made in so many options and demand for each option is small or unstable (impractical to carry buffer stocks for all parts everywhere in process)
- High defect rate causes too many interruptions to permit continuous flow and defect level cannot be significantly reduced
- Products must be produced in integrated batches throughout the process for reasons of quality control or certification (e.g. pharmaceuticals)
25
True or False: In reality, every process has elements of push and pull
True
26
True or False: Standard procedures are changed only when a better way is found
True
27
Class question: What does “buy-in” mean to you? (in terms of shop floor involvement and employee participation in general)
You’re working towards a common goal, and you respect each others perspectives, but does not necessarily mean that everyone is at 100% agreement
28
What is a standard operation
A detailed specification of all tasks, procedures, and operations
29
What elements are included in a standard operation
- Required cycle time (takt time)
- Completion time per unit
- Production capacity (cell CT)
- Standard Operations Routine
- Standard quantity of WIP
30
What is completion time per unit (CTU)
Total time required to complete one unit at a workstation, cell or operation. CTU for a task is the average task time. CTU for an operation is the sum of the tasks CTUs. Includes machine and manual time. Used to determine worker and machine operation times in a workcell
31
What is standard task time for a manual task
An estimation made by measuring the actual time and adjusting it by a performance factor (ability of worker) and an allowance factor (unavoidable delays)
32
What is actual cycle time (ACT)
Time to perform operation, walk around cell, retrieve materials. Compared to the takt time, which is based on demand
33
What is a standard operations routine (SOR)
Specifies sequence in which tasks will be performed. Types of SORs include single repeated operation, multiple repeated operations, or multiple non-repeated operations. An SOR for a work-cell incorporates machine CT and worker CT
34
If actual CT is less than the required CT, there will be _________
Idle time, this is an opportunity to reduce number of workers or assign additional tasks
35
Define standard quantity of WIP
Minimum quantity of WIP for process to function, consists of items being processed in each operation plus any items held between operations
36
Define a Standard Operations Sheet (SOS)
Contains standard operations information in one place (completion time, routine, standard quantity WIP, require/actual CT, diagrams, etc.)
37
What does the SOS do? Name three things
1. Informs workers concerning the SOR, completion times
2. Helps supervisor assess whether the operations are being done according to standards
3. Serves as a tool to evaluate performance and improvements, powerful tool when used in conjunction with OEE strategies
38
What are the goals in work cell design?
Eliminate:
- Walking
- Waiting
- Out-of-cycle activities
(in other words, eliminate waste)
39
True or False: A rabbit chase work-cell can be used in a machining cell
False, this is impossible (machines are operated out of sequence), rabbit chase is only applicable to assembly cells
40
True or False: Cycle times among multiple workers in one work-cell must be as equal as possible
True
41
What are the two types of work-cells?
Assembly (hard to automate, mostly manual) and machining (simpler, easier to automate)
42
True or False: Actual cycle time should be close to required cycle time in work-cells
True (~95% of Takt time)
43
What are some methods of increasing capacity for a work-cell
- Add workers and divide cell into sub-cells
- Limit: One worker at each station
- Overall cycle time is equal to cycle time of slowest sub-cell
44
If a work-cell is divided between two workers, and the first has a cycle time of 99 seconds while the second has a cycle time of 85 seconds, what is the actual cycle time of the cell
99 seconds (whatever the slowest operation is)
45
What are decouplers in terms of machining work-cells
Holds one or more parts to allow operation of all machines within a work-cell if the line is not perfectly balanced
46
What are the advantages of decouplers
- Allows machines in series to operate somewhat independently
- Limits WIP
- Facilitates automatic inspection
- Facilitates part feeding to next station
- Allows bypassing, branching, or converging flows
47
True or False: SPC and ZQC cannot be used together
False, SPC and ZQC are complimentary
48
What is attribute data and variable data, and what is the difference between them?
Attribute data measures things like the defective vs. non-defective parts as well as the number of passes vs. fails. Variable data, however, measures how defective something is or how well/poorly the passes and fails were
49
What is poka yoke
It means error proofing. It is a scheme or device used in source inspection to prevent defects and comes in two types: one detects/warns about a problem, while the other prevents a problem
50
What are some types of Poka Yokes
- Contact Poka Yoke (use physical attribute to detect/prevent error, i.e. part only fits one way)
- Count Poka Yoke (ensure correct number of actions is completed, i.e. counter)
- Sequence Poka Yoke (ensure all steps in sequence are completed in correct order)
51
What is screening
100% inspection to eliminate defects to catch and correct errors, achieved through self-checks or successive checks
52
What is automatic inspection
Checks for defects through automation, used a lot in the electronic industry
53
What is non-destructive testing
Performed where destructive testing of the product is not desired, can include die penetrant testing, eddy current testing, x-ray testing, and ultrasonic testing
54
What are visual quality aids
Visually-obvious defect references for workers, typically used where it is difficult to quantify a good vs. bad part or if there can be many simultaneous possible defects, often used for paints and coatings where defects must be visually assessed and the assessment is qualitative
55
What are the requirements for self-checking and successive-checking
- Check targets (workers know what to check)
- Feedback and action (when defect is spotted, worker responsible is immediately notified and problem is corrected)
- Defects are prevented from moving to the next operation
56
What are the elements of a product inspection
- Inspection process (internal/external)
- Inspection measurement (sensory/physical)
- Population inspected (all/sample)
- Inspection judgement (subjective/objective)
- Quality characteristics (variables/attributes)
57
What is bias (not opinion-based)
The average difference between the parameter and the true value
58
What is precision
The standard deviation of the parameter
59
What is acceptance sampling
Traditional approach to quality, assumes there is an ‘acceptable quality level’, uses sampling and probability to determine whether quality is acceptable or not, accept/reject entire lot based on sample results
60
Define Setup (as in 'short setup time')
Setup is the elapsed time between making the last good part of item A to the first good part of item B
61
What are the benefits of setup reduction
- Better quality
- Lower cost (less time)
- Better flexibility
- Better worker utilization
- Shorter lead time and more capacity
- Less process variability
62
Fill in the Blank: In order to minimize setup time, the _______ associated with reduced setup time, cycle time, and labour expenses must be greater than the __________________________ associated with the equipment increased cost associated with the additional equipment and maintenance costs
Savings, capital investment
63
What are internal setups versus external setups?
Internal: A step that must be performed while the machine or operation is stopped
External: A step that can be performed when the machine is running
(ideally, all internal steps are converted to external steps)
64
Describe the SMED methodology
Stands for Single Minute Exchange of Dies. The methodology is to identify internal and external steps, convert internal to external steps, improve all aspects of the setup operation, and abolish setup
65
Describe a Type 1 setup
Retrieving, preparing, and checking materials, tools, etc. before AND after the setup
66
Describe a Type 2 setup
Mounting tools, parts, etc., PRIOR to the next batch, and removing tools, parts, etc., AFTER completion of the last batch
67
Describe a Type 3 setup
Measuring, setting, and calibrating machine tools, fixtures and parts to perform the operation
68
Describe a Type 4 setup
Producing a first-off part after initial machine settings, measuring the piece, adjusting the machine, then producing another test piece until the operation meets production requirements (usually accompanied by verification by quality personnel and an associated delay)
69
Out of the four types of setups, which are internal and which are external
Most type 1 steps are external. Most type 2, 3, and 4 steps are internal
70
What are some strategies to improving internal setups?
Parallel setup tasks (two people > one person), quick-attachment devices (toggle clamps, bar clamps, etc.), and eliminating adjustments
71
What are some strategies to improving external setups?
Store fixtures near the machine (minimize travel), prepare setup kits and carts, improve material handling
72
What are the three types of maintenance in Total Productive Maintenance (TPM)
- Preventative Maintenance (keep equipment running properly)
- Maintenance Prevention (improve equipment to reduce maintenance requirements)
- Maintainability Improvement (simplify maintenance that is required)
73
What metric can be used to determine how quick and easy it is to maintain and repair a piece of equipment?
Mean Time to Repair (MTTR), defined as total repair time over number of repairs
74
What metric can be used to determine how reliable a piece of equipment is?
Mean Time Between Failure (MTBF), defined as total running time over number of failures. This value can be used to determine the probability that an item will not fail before a certain time (e^(time/MTBF))
75
What metric can be used to determine the proportion of time a machine is actually available out of time it should be available?
Availability (A), defined as actual running time over planned running time. It could also be defined as:
A = MTBF/(MTBF + MTTR)
Breakdowns directly reduce this metric
76
Define rate efficiency
Rate Efficiency (RE) is defined as:
RE = Actual Production Volume * Actual Cycle Time / Actual Running Time
It measures how effectively a process is using its time. Slow setups directly reduce this metric
77
Define speed efficiency
Speed Efficiency (SE) is defined as:
SE = Design Cycle Time / Actual Cycle Time
It tells us if the system is producing at the same rate that we designed it to. Slow machine operation directly reduces this metric
78
Define performance efficiency
Performance Efficiency (PE) is defined as:
PE = RE * SE
Helps determine overall performance efficiency. If it is lower than 1, then there are two potential causes:
1) Low Rate Efficiency: Not enough production is happening for the time spent running.
2) Low Speed Efficiency: The process is running slower than its design capacity
79
What metric can be used to determine the percentage of good parts out of total produced
Quality rate (Q), sometimes called 'yield'. High defect rate directly reduces this metric
80
Define overall equipment effectiveness
Overall Equipment Effectiveness (OEE) is defined as:
OEE = A * PE * Q
It can be improved by:
- Fewer breakdowns and faster repair
- Faster setups
- Improved machine operation
- Elimination of defects
81
Define capacity vs utilization
Capacity: Total output a machine CAN produce
Utilization: Actual output
82
List some sources of machine idle time
- Waiting for a part to work on (starved)
- Waiting for a finished part to be unloaded (blocked)
- Waiting for an operator
83
What are the seven elements of a Preventative Maintenance (PM) program?
1. Maintain normal operating conditions (operate at normal/reduced capacity, conform to standard operating procedures)
2. Maintain equipment requirements (simple adjustments, bolt tightening, lubrication)
3. Keep equipment and area clean and organized (operators keeping machines clean)
4. Monitor equipment daily (operators responsible for monitoring equipment, operators trained in machine operation, structure, adjustments, and daily checkpoints for inspection)
5. Schedule time for PM (allow 15-30 minutes at start or end of every shift, also schedule weekly/monthly/quarterly/yearly PM)
6. Manage equipment information (track breakdowns, repairs, costs)
7. Use predictive (on demand) maintenance (use sensors that help indicate potential problems on equipment)
84
What are the basic types of layouts
- Fixed position layout
- Process layout
- Product layout
85
Where would a fixed position layout be used
Used in projects where the product cannot be moved
86
What is a process layout
Machines grouped by the process they perform
87
What is a product layout
Linear arrangement of workstations to produce a specific product
88
What are the types of hybrid layouts
- Cellular layout
- Flexible manufacturing systems
- Mixed-model assembly lines
89
How do you establish a cellular layout
1. Identify families of parts with similar flow paths
2. Group machines into cells based on part families
3. Arrange cells so parts movement is minimized
4. Locate large shared machines at point of use
90
What are the components of a focused factory layout
- Focused flow lines (when parts in family have nearly the same process sequence and processing times)
- Workcells (more flexible, when parts have greater differences)
- Focused workcentres (used when its not practical to rearrange machines, individual machines are dedicated to particular families)
91
What strategies could you use to establish product and machine groups?
- Group technology coding and classification (use GT codes)
- Cluster analysis (grouping achieved by visual inspection of process plans)
- Production Flow Analysis (PFA) (Similar to cluster analysis, uses matrix methods to find clusters)
92
List some production strategies and their associated lead times
- Engineer to order (LT: months)
- Make to order (LT: weeks)
- Assemble to order (LT: days)
- Make to stock
93
What is machine cycle time (MCT)
Setup time plus operation time of a machine, setup time includes the unload time, changeover time, and loading time
94
What is worker cycle time (WCT)
The time for a worker to complete a trip around the cell, which includes the time to unload, time to change over, time to load, time to start machine, and walk time between stations
95
True or False: The machining cell cycle time (CTm) depends on what takes longer, the WCT or the MCT
True
96
