What Is Statistical Process
Control?
Control Chart
Statistical
Process Control is a set of methods for controlling and monitoring quality,
also detecting quality variation during process.
As per ISO 9000:2015 Quality Management System-
process is a set of interrelated or interacting activities which transforms
inputs into outputs.
Note 1: inputs to a
process are generally outputs of other processes
Note 2: processes in an
organization are generally planned and carried out under controlled conditions
to add value.
SPC- is an easy method to monitor the process is “in-control”.
Further to work with SPC, what we need is called
data. The data can be Quantitative and
Qualitative. There are two types Quantitative data-
Variable data (continuous
Data)
Attributes data (discrete
Data)
Variable data characteristically are those that can be
measured like length, volume, pressure and time. Sample size in variable data
is less .
Attributes data are countable in discrete units or
number of occurrences. They can be divided as good or bad products. Typically
it includes number of defects/defectives/scrap items etc. Sample size in
attribute data is large.
You must be wondering what is the significance of SPC.
With real-time SPC one can:
- Dramatically reduce variability
and scrap
- Scientifically improve
productivity
- Reduce costs
- Uncover hidden process
Quality deviation
- Instantly react to process
changes
- Make real-time decisions
Well! there are
so many tools claiming for the Quality
but the question still arises is “How”.
We can do by measuring ROI. May be it’s a new term for
few of you, let’s have a brief explanation on it.
ROI is an abbreviation of Return
on Investment.
It is a performance measure. It
is used to evaluate the efficiency of an investment or compare the efficiency
of a number of different investments.
Now lets start on-
How to Measure the ROI of a Real-Time
SPC Solution
1. Start identifying the major areas leading to nonproductive- like waste
(scraps, reworks, over stocks..), Equipment downtime (Changing of parts,
breakdown time..), processes/ products incapable of meeting customers’
requirements, personnel competency, inefficiency at your facility and/or unit
lines etc.
2. Do Cross verification-
Ask questions before making
any decision. If require take help of your accounts department and team to
verify collected data. Since it is critical factor on which further steps has
to be taken.
The following question will
be certainly helpful to you for such steps.
Like-
a. Do you really know your costs of quality.
b. What category does the work fall in -Process/service/product/area?
c. Are the right kind of data being collected with respect to right
process/service/product/area?
d. Has the data Cross verified to know it’s stand on true ground?
e. Can this data be useful to improve your area of work?
f.
Are decisions being made on
true data which is causing the issue?
g. Did you really found the cause of quality issue?
h. Can you accurately predict output result of your task?
3. It’s now time to quantify the value of an SPC solution.
What are SPC Tools?
As
discussed before SPC is a set of methods for
controlling and monitoring quality, also detecting quality variation during
process. Here is a
brief descriptions on SPC tools are -
Control
Charts are used to analyze process performance over time. Control charts will
give you data on control values/results and calculate mean, bias and sigma lines
to evaluate the stability of the process. There are two types of cause
variation depicted by help of control charts. They are - Special
cause variation and Common
cause variation
Histogram
Histograms is used to show
the spread, or dispersion, of variable data. It works as per customers demand.
Since, the upper specification (USL) and lower specification limits (LSL) are
defined by the customer. Any result or value outside of the specification
limits represent that don't meet customer requirements. for more detail follow histogram-analysis
Pareto Chart
Pareto charts combine
a sorted bar graph with a cumulative line graph. Pareto Charts are used to
counts of defect data or error types by using 80/20 rule.
Fishbone Diagram
Fishbone diagrams used to
document the root cause analysis of an issue. Start with a problem statement and
then ask at least 5 Whys until you get to the root cause.
Scatter Plot
Scatter
Plots are used to show the correlation or cause-effect relationship between two
sets of data.
If the points are clustered
along the trend line, then there's probably a strong correlation. If it is
dispersed on the graph, there is no correlation.
Flowchart
Flowcharts show the current
and improved process flow. One of the key benefits is this process helps in better
understand in achieving a standard process and also often leads to identifying
obvious problems that can be corrected quickly.
For any organization whether in manufacturing/service, productivity will increase only by meeting the customers' requirements by controlling quality, segregating the good from the bad. By using SPC tools wisely at pre-process control or control at design stage/process stage will prove to be really oriented towards prevention of such quality defects.
Conclusion-
SPC is important to-
- Reduce scrap and rework
- Improve quality of product/ services
- Increase productivity
- Compete in today’s market
References-
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