Question 1

Statistical Process Control and Process Variation

Accepted Answer

In typical manufacturing quality methods, measurements are compared to specification limits and the result is a pass/fail decision. There is no indication of process variation. It is important to establish a normal variation pattern for the process and maintain it by continual process monitoring. If there is a deviation from a normal variation, then a disturbance has occurred and process adjustments must be made.

SPC supplies the techniques for measuring, recording, analyzing and decision making. When all disturbances or special causes of variation are eliminated the process is in statistical control. However, SPC is much more than just analyzing manufacturing processes. It’s not just the implementation of control charts. It must be seen as a total manufacturing quality program.

Question 2

Where did SPC come from?

Accepted Answer

In spite of SPC coming to the fore in western industries during the 1980’s, the origins of SPC lay in the twenties in America. Walter Shewhart (Bell Telephone Laboratories, USA in 1924) developed statistical quality control methods for the improvement of manufacturing quality. These methods were incorporated into a management philosophy by Dr. W.E. Deming (a younger colleague of Shewhart). Just prior to World War II American industrial management did not pay very much attention to Deming and his views on statistical techniques and open management style. However, Japan’s post-war efforts to increase production, and to compete with western industries, found Deming’s philosophy attractive. Top Japanese management concluded that they had to improve quality, and invited Deming to lecture in Japan in the early 1950’s.

The successful tour, lead to a few companies implementing the Deming methodologies and within a few month’s their quality and productivity increased. This, in turn, led to a greater proliferation of these techniques in Japan.It was the commitment of top Japanese management, the realization of the rewards of SPC implementation plus the philosophies of Deming that are the basis of Japanese competitive advantage as we know it today.Deming stated that a quality product can only be made if all the processes in a company are under control, therefore everybody in a company is responsible for quality. The knowledge on the shop floor has to be used and the walls between departments have to be torn down. It is the responsibility of management to allow operators to work with the best methods, the best machines, etc.In 1981 Deming appeared in a documentary on American television named: “If Japan can, why can’t we?”

There was a considerable reaction and for the first time managers in America listened to his philosophy. It was quickly proven that SPC could also give beneficial results in western industries. However, despite increased attention on this side of the globe; SPC is still in a preliminary implementation stage.

Deming has summarized his philosophy in 14 rules of management, these are given below:

Create constancy of purpose toward improvement of product and service with the aim to become competitive, stay in business and provide jobs.
Adopt the new philosophy. We are in a new economic age, created by Japan. A transformation of the Western style of management is necessary to halt the continued decline of the industry.
Cease dependence on inspection to achieve quality. Eliminate the need for mass inspection by building quality into the product in the first place.
End the practice of awarding business on the basis of price. Purchasing, design, manufacturing and sales departments must work with the chosen suppliers so as to minimize total cost, not initial cost.
Improve constantly, and forever, every activity in the company so as to improve quality and productivity and thus constantly decrease costs.
Institute education and training on the job, including management.
Institute improved supervision. The aim of supervision should be to help people and machines do a better job.
Drive out fear so that everyone may work effectively for the company.
Break down the barriers between departments. People in research, design, sales and production must work as a team to tackle production and usage problems that may be encountered with the product or service.
Eliminate slogans, exhortations and targets for the workforce asking for new levels of productivity and zero defects. The bulk of the causes of low quality and low productivity belong to the system and will not be in the direct control of the workforce.
Eliminate work standards that prescribe numerical quotas. Instead, use resources and supportive supervision, using the methods to be described for the job.
Remove the barriers that rob the hourly worker of the right to pride of workmanship. The responsibility of supervision must be changed from sheer numbers to quality. Equally, remove barriers that rob people in management and engineering of their right to pride of workmanship.
Institute a vigorous program of education and retraining. New skills are required for changes in techniques, materials, and services.
Put everybody in the organization to work in teams to accomplish the transformation.

Question 3

From product inspection to Statistical Process Control

Accepted Answer

Traditionally manufacturers have accepted that every product has to have tolerance limits because it is impossible to manufacture products without variation. Tolerance limits have been used historically as the basis for quality control i.e. product test results are either inside or outside of them. Intermediates and end-products are therefore inspected after manufacture and either pass or fail. With mass production, every product is checked and people use sampling plans to check if a lot can be shipped to the customer.

The problem with these methods is that variation is not taken into account and in case of inspection in the warehouse that inspection is not immediately after a product is produced so people are not able to correct problems instantly and are also not able to find the root cause because the people doing the inspection are normally not the people in production.

SPC aims to eliminate all disturbances in a process, reduce variation, and produce on target, thus leading to continual process improvement.Errors in the process such as tool wear, wrong adjustments, wrong materials etc. will be found at an early stage thus enabling production with less variation and reduced scrap levels.

Question 4

Industry Requirements and Implementation

Accepted Answer

More and more industries and customers are requiring SPC implementation. It is mandatory in automotive (IATF 16949, VDA), semiconductor, aerospace (AS13006), medical device etc. To get the benefits from a SPC implementation you need to implement SPC real-time. Data should be gathered on the shop floor and SPC results should be available instantly for operators and manufacturing support. This means you need to address SPC automation in an early stage of the implementation. This is also important to make sure SPC is implemented efficiently. You do not want to lose expensive engineering time on gathering and processing Excel documents to get an SPC analysis after the fact.

Typical aspects which need to be considered during real-time SPC implementation and automation are:

Required functionality
Integration in the organization (3 levels)
Integration in the IT architecture (ERP, MES, hard and software, Big data)
Integration with other quality software (FMEA, MSA, OEE, CAPA)
Integration with gages and measurement systems (Camera’s, PLC, CMM etc)
Specific industry or company requirements (FDA, IATF 16949, AS13006, Legal requirements, multiple languages, centralization, reporting
Training and (local) support

Question 5

Results of SPC Implementations

Accepted Answer

Over the last 40 years we have seen high results with SPC implementations. Some examples:

A pharmaceutical company gained more than 900K yearly in scrap reduction and more accurate dosing
A solar company increased income with 700K by increasing the yield per solar cell
A food company reduced overweight with 1%
A semiconductor company completely eliminated end of line inspection
A medical device company integrated SPC with OEE and Big data and saw a 25% productivity increase in 3 months

Not all companies will see these high results but typically we always see better communication, more efficient data entry, analysis and reporting and improved quality.

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