CHAPTER 7

Process Analysis: Interfering Factors and Action

The enemy of the best is good

– Stephen R. Covey

Process interference

Any incident that happens sporadically in a process is process interference. Different types of sporadic incidents are known. But their occurrence in terms of frequency and timing are not known. Hence, they are termed as sporadic incidents. Each interference is potentially a source of defect as it can adversely affect the process and/or in-process items. In our experience, enough attention is not given to this major source of defect arising out of process interference.

This chapter deals with the approach as under for defect prevention arising due to process interferences such as

1. Make an exhaustive checklist of process interference.
2. For a given process, carry out an applicability analysis.
3. Stipulate the measures to control defects as relevant to each interfering factor found relevant to the process.
4. Enforce the control measures.

The above is applicable to a manufacturing process. Similar approach holds good for any non-manufacturing process as well. All the four steps are briefly discussed in this chapter.

Checklist of interfering factors

Table 7.1 gives a checklist of interfering factors as applicable to a manufacturing process. This list is not exhaustive and needs to be updated as and when necessary.

TABLE 7.1 Checklist of Interfering Factors

Interferences: applicability and analysis

For a given process, all interferences listed in Table 7.1 may not occur and the interference that can occur may not cause a defect to the in-process product and affect the process.

Therefore, it is necessary to carry out an interference applicability analysis for each process. This analysis comprises the following steps.

1. Take a process.
2. Consider, at any given time, one type of process interference listed in Table 7.1.
3. Find answers to the following questions and ensure that the answers are databased.
   1. Does the interference affect the process?
   2. If the answer is ‘No’, ignore.
   3. If the answer is ‘Yes’, record the following information.
      1. In what way it affects the process?
      2. What actions need to be taken to correct the process?
   4. Does the interference affect the in-process product?
   5. If the answer is ‘No’, ignore.
   6. If the answer is ‘Yes’, record the following information.
      1. In what way it affects the product?
      2. Is the affected product fit for subsequent processing?
      3. If it does not fit, should the affected in-process product be discarded/scrapped?
      4. If it fits, can the affected in-process product be straight away taken up for processing or should they be checked, reworked, rechecked and accepted before taking up for processing.
      5. If latter is the course of action, document the details covering method of checking and rework procedure.
   7. Information generated in (iii) and (iv) need to be appropriately incorporated in the process instruction.
4. Repeat the exercises (1)–(3) for each of the interference listed in Table 7.1.
5. With steps (1)–(4), the following would be known for a given process:
   1. The interference factors applicable to the process.
   2. The measures to be taken for the process with respect to each interference factor.
   3. The measures to be taken for the in-process material with respect to each interference factor.

Illustrative examples

The following mindset is common and any failure detected is dismissed as ‘communication gap’.

1. What is there to inform? It is all obvious.
2. Why expect someone to inform us or insist on communicating? We have the knowledge and experience to find out.

This commonly found deficiency is also covered in the illustration. Three illustrations given here explain the application of interference analysis.

Illustration 1

TABLE 7.2 Process: XYZ; Interference: Power Failure

Illustration 2

Name of the process: Grinding

Make provision in the format to record the ‘issues’ to be informed. Those issues that are process-specific and shift-specific are to be pre-printed in the format.

It is a means to prevent defects arising due to ‘communication gap’.

Illustration 3

The format in Tables 7.3 and 7.4 deals with the way the interferences mentioned therein are controlled.

The following points can be noted from the illustrative examples:

1. Each format is devised in such a way that it can be used for a week/month. Thus, paper requirement can be kept to a minimum.
2. Instructions on the mode of control/handling the process and product for each type of interference can be pre-printed in the format. Thus, it also serves as a tool to teach, self-learn.
3. ‘Forgetfulness’ is another cause for failure to take timely action. The format devised as in Table 7.2 minimises faults due to forgetfulness and pins down responsibility as well as accountability for failures due to forgetfulness.
4. Provision is made for authenticating every detail (recorded by the operator’s signature). This ensures accountability. Recording is limited to a ‘tick’ or Yes/No.

TABLE 7.3 Process XYZ; Interference: Restart after Maintenance/Long Stoppage

TABLE 7.4 Process: XYZ; Interference: Chemical Addition

Process owner must review the interference-control record every day to ensure compliance as well as effectiveness of compliance.

Relevance to continual improvement project/problem

For a given continual improvement project/problem, the process where it is located should be identified. For that process, adopt the following steps to prevent defects from interfering factors.

1. Make a list of all the suspected possible interference factors similar to the one shown in Table 7.1.
2. Analyse each factor to decide whether it is an interfering factor or not. After such analysis, arrive at the list of applicable factors.
3. Carry out the analysis for each applicability factor through steps (1)–(4) as already stated and introduce appropriate measures of defect.

Conclusion

In conclusion, this chapter states that over a period of time certain practices, methods, outlook and habits would have been established. These will have a grip over the minds of the persons concerned. No one would normally take any initiative to review these and update/change them. This tendency to continue the past without review for their continued satisfactory status itself can be a source of ‘defects’. Thus, another major step in the prevention of defects is process review. This is the subject matter of Chapter 8.