Process Config - Line Balancing/Little's Law/SF & LT/DBR Flashcards
Give 5 negative things that will occur if you don’t optimise the flow of resources through an operation.
1) Queues
2) Long process times
3) High costs
4) Inflexible operations
5) Unpredictable and confused flow patterns
The nature of any process is influenced by what and what
The volume and variety of what it has to process
Define long and thin processes
A process designed to have many sequential stages, each performing a relatively small part of the task
Define short and fat processes
A process with relatively few sequential stages, each of which performs a relatively large part of the total task
Define WIP
Number of units in the queue of a process - i.e. number of units waiting to be processed.
Define line balancing
The attempt to equalise the load on each station or part of a line layout or mass process.
Define bottle neck
the capacity constraining stage in a process - it acts as the drum and governs the output of the whole process
Define balancing loss
The percentage of time used for non-productive purposes compared to the total time invested in making a product.
Define Little’s law
The mathematical relationship b/w Through Put time, WIP and Cycle time
Define Work Content
The total amount of time required to produce a unit of output
Define through put time
The time for a unit to move through a process
Define through put efficiency
WC/Throughput time * 100
What is one of the most important design decisions in product layout?
Line balancing
What happens if the line is unbalanced?
It increases effective cycle time of the operation. The effectiveness of the line balancing activity is measured by balancing loss.
What does balancing loss measure?
The time wasters through the unequal allocation of work as a percentage
Name the 5 advantages of Long and Thin processes
1) Controlled Flow
2) Simple materials handling
3) Lower capital requirement
4) Greater efficiency
5) Higher space utilisation
Name the 4 disadvantages of Long and Thin processes
1) Exposed to breakdowns
2) Non-flexible
3) Too much standardisation can cause high turnover
What are the 4 advantages of short and fat processes?
1) higher mix flexibility
2) higher volume flexibility
3) greater robustness
4) less monotonous
What are the 4 disadvantages of short and fat processes?
1) Training times
2) Equipment needs
3) Duplication of resources
4) Reliant on employees
What does DBR concept do in operations?
Helps to decide exactly where in a process control should occur.
What should be the control point in a process?
The bottle neck
What is the bottleneck usually called?
The drum because it sets the beat for the rest of the process to follow
Why is the buffer meant to be kept in front of the bottleneck?
To ensure that the bottleneck always has something to work on
What impact does a bottle neck have on a process?
Affects the output of the whole process.
Is it worthwhile for parts of the process before the bottle neck to work to their full capacity?
No.
What does the rope do?
Communicates to the stages before the bottle neck to ensure that they don’t produce work that will accumulate at the point where the bottle neck is constraining the flow.
What does the DBR concept do for operations managers?
Helps managers to realise that the speed at which the system can produce is limited by the slowest link
What is SPC?
It is about measuring whether you have variation in the process. This variation maybe common cause variation (normal) or special cause variation (abnormal and needs to be investigated further).
Define capable process
Where the control limits fit within the process specification
Define incapable process
Where either or both the control limits exist outside the process specification
Define natural variation
The variation that exists in the process without any adjustment
Define special event
A recorded data point that falls outside the control limits - needs to be investigated
Define a run of seven
A statistically significant series of data points that indicate that the process has changed it’s performance - either negatively or positively
Why do we use SPC?
To understand variation in the process. If we don’t understand variation and respond inappropriately we can exacerbate the problem.
What is the purpose of a control chart?
To detect the change in the performance of a process. It provides a dynamic view of the both the change in the absolute level of performance (average, mean, measure of central tendency) and the level of variation within a process (the deviation).
The standard deviation in a CC assumes what?
That the process is normally distributed.
What axis is time on a CC chart?
X axis
Describe the 5 exception rules in SPC
1) Is there a point which falls above or below our control limits (UCL/LCL)
2) Is there a run of 7 consecutive points above or below the mean? This indicates the process is slowly changing over time. At this point it is worth splitting the data set and recalculate on the points after the change in process.
3) 2 consecutive points in UWL/LWL. Needs investigation but not recalculation of the warning/control limits
4) Is there a cyclical pattern? Seasonality may explain the variation.
5) Peaks and troughs may indicate a process out of control.
