What is the key difference between SPC and MSA?

 

There is a difference between giving up and knowing when enough is enough: Unknown

 

Introduction

There can always be a difference of opinion. There can always be contrasting thought in the way in which we want to reach a particular destination. There can always be divergent strategies to achieve a particular goal.

The most important thing is our intentions. As long as our intentions are correct, in spite of the difference in thoughts, we can work as a team and achieve whatever we are aiming for.

Objective

SPC (Statistical Process Control) and MSA (Measurement System Analysis) are 2 key pillars for a manufacturing process to ensure process control so that desired quality of product and services can be achieved. Although both are statistical tools still, they have their distinct purposes which are generally not clearly understood like at times we apply the same principles of SPC study (mean and range chart-all points within control limits) for MSA study too!

By understanding the key difference between SPC and MSA study, we can effectively implement them and can take desired benefits.  

Definitions:

SPC (Statistical Process Control): It is a collection of statistical techniques intended to understand the behaviour of a process. 

MSA (Measurement Systems Analysis): It is an experimental process that determines the viability of an evaluation/measurement technique for use on a specific part characteristic. 

Detailed Information

In the highly competitive environment of the manufacturing sector, organizations are challenged with four simultaneous and equally momentous goals (PQCD):

  1. P-Productivity: Produce sustainable volume
  2. Q-Quality: Provide high-quality products, meeting or exceeding customer expectations
  3. C-Cost: Cost-effectiveness
  4. D-Delivery: Delivery on time

By monitoring the processes and measurement system systematically, SPC and MSA studies help the organizations to have predictable product and service quality. Following are some of the key difference between SPC and MSA:

S.No. SPC MSA
1 The key purpose is to establish a controlled manufacturing process by the use of statistical techniques to reduce process variation.  The key purpose is whether your measurement system variability is small compared with the process variability and whether your measurement system is capable of distinguishing between different parts.
2 To monitor the performance of the manufacturing process To monitor the performance of the measurement system
3 To identify the common and special causes in the process To identify the variation in the process due to SWIPE (Standard, Workpiece, Instrument, Person, Equipment)
4 The key output is Cp and CpK The key output is G R&R for Variable and Kappa Value for Attribute study
5 It is the requirement of the Process It is the requirement before conducting an SPC study
6 Monitor CTQ (Critical to Quality) and CTP (Critical to Process) characteristics Measure variation present in all types of measuring, inspection and test equipment
7 a customer requirement or defined during DFMEA and PFMEA study Not a customer requirement but to fulfil customer requirement for the process, an MSA study is conducted
8 AIAG manual (2nd Edition) to be followed unless the customer has their requirement AIAG manual (4th Edition) to be followed unless the customer has their requirement
9 In the X-bar chart, all the points should be within UCL and LCL to demonstrate that there are only common causes In the X-bar chart, more than 50% of the points should fall outside UCL and LCL to demonstrate that the measurement system is effective
10 As per Clause 9.1.1.2 of IATF As per Clause 7.1.5.1.1 of IATF
11 The number of samples is 100 which are subdivided into 20 or 25 subgroups The number of samples is 10 and the number of appraisees is 2 or 3
12 Used to solve process problems before making defective products Garbage in, Garbage out; Wrong measurement, wrong result
13 The aim is not to allow defects to be produced Measure possible biases from operator, instrument, method etc.

Present Challenges:

  • How many organizations have benefitted by using SPC and MSA studies apart from fulfilling IATF 16949 requirements?
  • How many organizations conduct SPC and MSA study as a preventive tool and not as postmortem?
  • How many organizations have understood their graphical interpretations?
  • How many organizations use it as a cost-saving tool?

References:

IATF 16949: 2016

Industry Experts

SPC Manual- 2nd Edition

MSA Manual- 4th Edition

This is the 104th article of this Quality Management series. Every weekend, you will find useful information that will make your Management System journey Productive. Please share it with your colleagues too.

Your genuine feedback and response are extremely valuable. Please suggest topics for the coming weeks.

 

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