What is SPC?

SPC is stand for Statistical Process Control. 

SPC is a tool used for continuous improvement. SPC used to maintain quality by monitoring the process and well detect the possible occurrence of the error before it actually happened and we'll detective.

It is one of the core tool of IATF16949. Other core tool of IATF16949 are:

1. APQP: Advance Product Quality Planning
2. PPAP: Production Part Approval Planning
3. MSA: Measurement System Analysis
4. FMEA : Failure Mode and Effective Analysis 

The SPC process is better than other quality tools because it is based on detection and prevention rather than the correction of problems after they have occurred, it means it help us to detect the fault or give indication before error actually occur, which means we can correct the process or the job size before any error occur in our job. It is real time process, so machine operator can easily identify the trend of the job and take corrective action before generation of any NG product. SPC is not only useful for manufacturing process but also helpful in the non-manufacturing process. But here we only discuss about manufacturing process.

SPC is Statistical / Mathematical tools to monitor and control the quality of a product. It worked by collecting data from machine or the process related to size of job manufactured. These data is converted into control charts or Some charts, these charts indicates about the process and with the help of this we can change or correct the process, so that, process remain on the mean.

Why to use SPC?

Now a days, use of SPC is in great trend because it help us to save the material from getting scrap and rework. When we able to reduce the rejection which in turn able to increase the production and profitability of a company will increase. It is based on real time data and operator also analysis the data and detect the trend on the process, by using this trend operator will change the process if the trend going in wrong direction before the manufacturing of non-confirmative product. SPC turns manufacturing process from detection to prevention based so that in early stage only product manufactured at mean position before it goes towards non-confirmative side.

Important tool of SPC are:

1. Control Chart
2. Normal Distribution

1. Control Chart:

Most popular tool of SPC is Control Chart. Control Chart is developed by Quality Guru Walter Shewhart in 1920. Control Chart help us to indicate trend/patterns that occur in the process and to enable the organization to affect the patterns and decrease waste and nonconformities. To prepare control chart we require data, these data also include some deviation (also known as variation), no two identical jobs have same measurement value there is always some variation.

When data is deviated from its mean position is known as variation:

Variation is of two types:

1. Common Cause
2. Special Cause

1 Common Cause or Non-assignable cause:

 These are also known as Natural causes as they are naturally occurred in the process and it is very difficult to eliminate common causes. These causes do not damage the process but actually produce a statistical stable process.

2 Special Cause or assignable cause:

These causes occur randomly at any point of time and Special cause is difficult to predict. These are causes where we have to pay more attention and work over it to eliminate the cause, if these causes are eliminated from the process, then process called as stable process. 

In Control Chart we can be able to identify when the special cause occurred. Once identified these special causes, work to be done to eliminate this special cause. Control Chart is continuous activity and it is full day activity, this chart is displayed at the front of machine so that any one can able to see and analysis the data and if required can improve the process.

Normal Distribution:

Normal distribution is a bell-shaped curve that directly relates to the frequency of occurrence of the measured data, usually middle range cover with most occurrences range, and fewer at the either side and which form a shape like “Bell”, hence it is also called as Bell distribution.

Now we are able to understand about SPC (Statical Process Control), now how to implement SPC in the system or the process.

SPC must be implement in following phases: 

1. The first phase is the initial establishment of the process.
2. The second phase is the regular production use of the process. In the second phase, a decision of the period to be examined must be made, depending upon the type of part manufactures and cycle time of part and change in 5M&E conditions (Man, Machine, Material, Method, Movement, Environment) and also consider wear rate of parts used during manufacturing process, such as Machine parts and tooling.
3. Once SPC is established now it is important that everyone using SPC should be aware and trained, so that they can analysis the control chart and identify the special cause and work to eliminate the special cause.