De-coding Statistical Process Control (SPC)

Statistical Process Control (SPC) is an industry-standard methodology for measuring, controlling quality and to solve practical problems during the manufacturing process. In a manufacturing scenario it can be applied to virtually any field of activity that is associated in some way with numbers.

Statistical Process Control - The Word Statistical means “relating to the use of numbers or more particularly drawing conclusions from numbers”. A Process is “any set of conditions or set of causes which work together to produce a given result”. The Word Control means “to keep something with in boundaries or to make something behave the way we want it to behave”.

Taken Together and applied to a Manufacturing scenario Statistical Process Control means something like this

Statistical - With the help of numbers or Data

Process - We Study the Characteristics of our Process

Control - In order to make it behave the way we want it to behave

 Statistical Process Control (SPC) is the process of overseeing and controlling how a product is produced using statistical methods in order to guarantee its quality and to ensure that the process produces uniform products at minimum waste. In other words it is statistical methodology for measuring and analysing variations and controlling quality during the manufacturing process.

The Essential components of SPC are

Process Capability Studies - The Basic use of control charts

The Process Capability Study is used by Engineers and Managers to obtain information on how the Process has performed.

 Process Control Charts - The real time use of control charts in the Manufacturing Data Collection Area

Process Control Charts are used by the Engineers and Operators on the Manufacturing area to control the process, increase yields, minimising waste / scrap and rework.

Statistical Sampling Collection or Acceptance Sampling - May or may not make use of control charts

Statistical sampling inspection is used by Inspectors as a scientific basis for accepting or rejecting a lot or product.

Statistical Design of Experiment - A procedure of comparing variables and determining their significance.

Statistical Design of Experiment popularly known as DOE is used in Research and Development problems, to study the effect of many variables at once, to throw light on mysterious causes and effects and to explore the unknown.

From the above description it is clear that Control Charts play a very significant role while strategizing SPC. This is the interface between you and your Process. Your Process communicates back to you through the control charts.

Data is a combination of noise and signals. The role of Control Chart is to minimize the noise so that voice of your process becomes clear. Today if you are not able to listen what your process is trying to convey back to you then either your control charts are not working or you are not sensitive to process.

There is no disputing the fact that Control Charts have become an integral part of the manufacturing quality control process. The charts can instantaneously analyse data from the manufacturing area, review the statistical patterns and determine if process variability falls within an acceptable range.

They are certainly not Run Charts.

To deploy Control charts, it is important that we really understand What are Control Charts, Which Charts to Use and How to Interpret them.

This is very simple yet complex. They are like what ECG or EEG means to us as Human Beings but for a Medical Expert this is the base for understanding and further investigation.

 For a Quality Professional this is very important to understand and extend deployment of Control Charts that forms foundation to their initiative of Product Quality Management, Quality Control, Process Improvement, Process Excellence, R&D, New Product Development and so on..

Quality is built onto a Process not to a Product. A Product will always be of uncompromising Quality if it has come from a stable and well managed Process. With proper deployment of SPC the investigation moves in that direction.

In an Ideal Scenario first our Focus has to ensure that the Process is in Control. This can only be achieved if we have understood our process well and post removal of special causes of variation if any.

After ensuring that our Process is in control, Second Step will be to determine the Capability of the Process. If not capable, we use our expertise to ensure that Process remains capable.

Only after the Process is in Control and Process is Capable, focus should shift to understand the Performance of the Process. If is underperforming then our expertise again is utilized to ensure that it Performs to our expectation.

Process is in Control - Process is Capable - Process is Performing , You can be remain assured of all the benefits of SPC i.e. Product Consistency, Lowering Cost of Quality, Minimizing rejection / rework, Real time operator feedback with actionable information, Improvements. This becomes then the Starting Point for initiatives like Six Sigma, Process Excellence and Manufacturing Excellence.

I will try to cover some topics on Control Charts in brief in future posts if you find them informative.

PRECISE – Enterprise Quality Management Solutions from Qsutra helps you to achieve your objectives in Real Time Data Collection, Traceability Management, Statistical Analytics, Regulatory Compliance and Reporting. Contact us at precise@qsutra.com / sudhansu@qsutra.com for details.