A cause-and-effect diagram is useful to help us sort out the causes of problems and organize the mutual relationship.
3-5Quality data always have dispersion.
We are producing large quantity of products witty
Great numbers of parts and materials. So, the quality of these products always have some amount of dispersion.
Excellent products should have less dispersion of quality, and if not, customers will suffer inconvenience.
For example, when the specification says This electric bulb has 2000 hours life. it means only mean value.
When 100 bulbs are tested, some bulbs have maximum life more than 2500 hours, and some have minimum life less than 1500 hours.
We can show this dispersion as "Histogram" shown here, and with this histogram, we can know the percentage of defective bulb, when the given standard is minimum 1600and hours.
Q.C. people lay more stress on dispersion than mean value.
Dispersion comes from dispersion of materials, operations and machines, etc.
Let's start analyzing the cause of dispersion from this Histogram.
3-6 Analysis of the data. --- part 1. (Stratification)
Any products that we produce have dispersion in performance, or dimensions. Our theme is to minimize this dispersion, and we have to know the cause of dispersion, but final data itself usually tells nothing about causes.
One of the practical ways to find out causes is stratification. When the diameter of the shaft of certain machine has excess dispersion, and if they are made by two machines, we have to stratify the data corresponding to each machine.
Then, we can find difference between machine 4 and B, and if adjustment of machine A is incorrect, we can easily adjust it.
This is one example of '1stratification't1 and if we stratify the data from various points of view, we will be able to find out the most effective causes.
Important points are,
(1) Stratification is based on cause-and-effect diagram.
(2) Stratify the data from various points of view.
(3) After the stratification, check the difference of dispersion.
3-7Analysis of the data. Part 2. (Scatter diagram, Control chart)
(1) Scatter diagram,
To know the relationship between cause and effect, (for example, relationship between torque of air driver and air pressure,) it is convenient to draw a scatter
Diagram, plotting data of the cause on the horizontal axe, data of the effect on the vertical axe. We can see the relationship clearly, and it is helpful to solve the problem.
(2) Control chart,
Dispersion includes types of causes. One is inevitable cause, (like dispersion caused by ordinary machine.) and another is unusual cause. (Like dispersion caused by different quality of the material.)
We have to control the latter, and find the variation of these causes by control chart.
Let's study control chart, because it is Very helpful when we are accustomed to use it.
Chapter 4. Basic steps of Quality assurance
4-1Let's study relationship between Product Quality and your job.
Each process of operation is responsible for final product Quality.
For example, even a small operation like picking up the parts could cause defective products, because of rusting mg by grease of finger, or deformation when it is pinched. Before producing defective products, let's study the causes of possible defects in your job, by actual samp1es or experiments. If we know these concrete causes well, we can avoid unnecessary causes of defects.
It is also helpful to study causes of defects in the past, and listen to the lecture of technical engineer about important point of Quality.
4-2Let's standardize operation of the job. (Operation standard)
To produce the products with minimum dispersion, each process of operation and procedure should be kept same as constant as possible, no matter when and who' will do it.
Oral explanation or memory of each people is not always reliable, therefore, we have to standardize them as "Operation standard".
It is important not to describe them by imagination.
We have to try the job actually to find out essential points of the job, and describe them as the operation standard.
Quality control in workshop begins from describing the "Operation standard".
Operation standard should be corrected when ever better methods are found, or circumstances are changed.
Let's make the operation standard easy to understand with necessary drawing, and keep it in certain place for easy reference.
4-3Enough training of the job is necessary.
"Do you know how to solder?"
"Do you understand when and how poor soldering happens?"
"Can you solder perfectly without any defectives?'1 There are three steps until we can do something perfectly, "To know", "To understand" and "To be able to do". To reach the third step or to be a professional worker, hard training is necessary. So, basically, before working in the workshop, we have to be well trained until we can produce excellent lent products.
Now, let's consider about Quality Control,
"Do you know what is Quality Control?"
"Do you understand which points are more difficult to carry out Quality Control?"
"Are you carrying out Quality Control successfully?''
4-4Let's build the quality in the process.
Some says, "Our products are very reliable because of severe inspection". Is it correct?
It is a great loss to select defective products by severe inspection after producing certain number of defective products. First, we have to make an effort to establish a system not to produce defective products.
Moreover, there are some products whose characteristics will not allow to be selected by total inspection, like explosive power of the bomb.
Basically, the quality of the products must be assured in each process.
We have to assure the quality of products that we produce by total inspection if it allows, but we should realize that the inspection is only to select, but not to build the quality.
4-5 Let's study the function of the inspection.
To assure the quality, inspection plays important part when defectives are inevitable.
Inspection is not a test, but it should have three factors.
1.To decide the criterion of judgment appropriately clearly.
2.To evaluate the quality by testing.
3.To compare the test results to the criterion, and to judge whether acceptance or rejection.
We sometimes have problems with lack of definite criterion.
The results and data of the inspection should be utilized for improvement of original processes. There are two types of inspection, total inspection and sampling inspection. The former is usually for the outgoing inspection, and the latter is mainly for the incoming inspection of the parts.
Total inspection
⊙In the case where the quality of each product should be assured.
⊙Large number of defects is included.
⊙The cost of inspection is cheap enough to inspect all the products.
Sampling inspection
⊙In order to reduce the cost of inspection, estimate the quality level from partial sample, and judge if they might bring bigger risk to the next process or not.
4-6Maintenance of tools, machines and measuring instruments.
We are utilizing many kinds of tools, machines, and measuring instruments in our workshop.
Today, machines are widely operated automatically by electronic devices.
But if these machines are operated in wrong condition, bunch of defective products will be mass-produced. Simple tools also possibly mass-produce defective products, if it is worn out.
And if measuring instruments were wrong whole system of quality assurance is meaningless.
We have to set up the checking system, deciding important checkpoints for each tool and machine, and preparing checksheet to check them periodically.
Before having problems by wrong machine, let's set up the system to prevent these
4-7Let's promote "Fool-proof".
We are always trying to do our best, but natura1ly we are not the almighty and unable to everything perfect, sometimes make mistakes.
But, if 100 persons make 1% mistakes each, it means almost 100% defects in total. So we have to consider the countermeasures as some devices to alarm or unable to operate the machine when we make mistake.
This is called "Fool-proof", and if all employees try to improve their job we can make great progress in reducing defectives caused by careless mistakes, and as a matter of fact this activity is achieving success in many companies.
Example,
When packing the product, small attachment parts, instruction book, or guarantee card are apt to be forgotten. To prevent this case, touch switches are attached to each parts box, and if operator doesn't touch the every touch switches when picking up the parts and if he missed to touch of these switches, the stopper does not allow to proceed the carton box.
4-8 Quick response against abnormal phenomenon.
In our daily operations, we can easily notice something abnormal when it happens. But usually they are neglected if they do not disturb the operation directly, and these neglect, if not reported to their boss, often cause the greater damage.
For example, when tightening a screw to the plastic parts, the operator felt some difficulty, and he adjusted air pressure of the torque driver to continue his job.
But, actually, the cause was that the pin of the mold was broken, and the hole of the plastic parts became shallower.
Several months later, all of the products became defective because of cracking caused by excess stress of the screw.
⊙If any abnormal situation is found, inform it to your boss immediately.
⊙If any abnormal situation is found, trace it until you can get the real cause.
⊙If the problem seems serious, take action to the relating sections until the decision of re-check or suspension of shipment is made.
⊙The speed of taking action for countermeasures represents the level of Quality Control.
Chapter 5. Let's promote Q.C. Circle activities.
5-1 Let's build up the workshop filled with humanity.
A female worker, who presented an achieved result of her Q.C. Circle activities at Q.C. Circle conference inner company, told us, "When I get a child in the future. I would like to tell my deep impression to him/her!" Why was she impressed so deeply? It might not be easy to understand without such an experience, but when we imagine, she might have felt great satisfaction by achievement of the subject by participating with her whole capability, and by being recognized the results by all people in the company.
The essence of Q.C. Circle activity is not mere offer of physical labor, but the participation of each individual with their wisdom and good idea to make their own workshop better.
Through this activity, everyone comes to feel that he/she can feel worth working through Q.C. Circle activity.
5-2Lets study about Q.C. and Q.C. Circle.
Then, how is the Q.C. Circle being carried out?
It begins from studying.
We have to study the basic knowledge about improvement workshop, statistical ineth6ds, etc. This booklet is hoped to be helpful to study the base And it is also very helpful to study some examples of actual activities in other companies in or outside your country, since Q.C. activities are actively conducted in Japan, U.S.A. Europe and south East Asia.
And the leaders of Q.C. Circle should study about the role of leadership, responsibility and activities leaders.
5-3 Organization of the group, and selection of the leader.
The basic idea of Q.C. Circle activity lies in independent voluntary activity by the people in workshop.
So, it is desirable that somebody strongly motivated will take leadership to organize the group with full support of his section.
Of course, adequate support and advice of supervisor or staff will expedite the activities.
Several members or about ten members are adequate to activate the group, and it is easier to promote the activities if all members belong to the same section with the same target. If all members of the section willingly participate in, that means leadership of the leader is excellent., and the activity will become positive.
Of course, the interest and support of top management have great power to promote Q.C. Circle activities.
5-4 Setting up a target, and promotion of the activity.
It is a usual case to start the activity from studying Q.C. and when it get to certain level, decide the target of activity. In the beginning, it's better to choose the target from daily, familiar problems, ex. To prevent parts from falling, in order to get cooperation of everybody easier.
It is recommended that the meeting be held once a. week or every few weeks, depending upon the situation of thc group, but better not have longer interval to the next meeting in order to continue the activity smoothly.
It's better to hold the meeting in their workshop where they have the subject to discuss.
Activity should be such arranged that every member has a role assigned so that all members' idea is adopted. Throughout the activity, support of supervisor and staff is fully useful.
5-5 Summarizing and reporting.
When an improvement activity comes to the end, confirm the effect comparing to the initial situation. If it is necessary to increase the effect, continue the activity. If sufficient effects are obtained, summarize the process of the activity. This is important for leaving on record the story of everyone's effort
The result will be reported to their supervisor, and when Q.C. Circle conference is held, prepare for it and participate. For preparation, everyone will play each part, preparing the chart, actual sample, and practice the way of presentation, in order to obtain better understanding of their effort.
It can be said that nobody can get deep impression after the presentation without such an experience.
It is hoped that vivid Q.C. circle activity of your workshop will be conducted.
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