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250 Part IV: Quality AssuranceEnvironment Personnel EquipmentDefect(s) underinvestigationTechniques ormethodsMaterialsFigure 19.2 Initial form of a cause-and-effect diagram.Environment Personnel EquipmentWorkers underpaid Not enough training No proper maintenancePart IV.BNo funds forresearchNot enough workersLack of managementcommunicationTechniques ormethodsLack of propersupervisionSupervisors notknowledgeableLack ofcommunicationHandling ofshipmentDesign not wellplannedLack of SPC onlineMaterialsFigure 19.3 A completed cause-and-effect diagram.Machines are oldSoftware not updatedDefect(s) underinvestigationImproper inspectionImproper distributionMishandling of rawmaterialToo many suppliersUsing a brainstorming session, the team brings up all possible causes undereach category. For example, under the environment category, causes could includethe management’s attitude, their unwillingness to release any funds for research,unwillingness to change suppliers, non-cooperation among middle and top management,or something similar. Under the personnel category, causes could includelack of proper training for workers, supervisors who are not helpful in solvingproblems, lack of communication between workers and supervisors, or workerswho are afraid of asking their supervisors questions for fear of repercussions ontheir jobs, promotions, or raises. Once all possible causes under each major categoryare listed in the cause-and-effect diagram, the next step is to isolate one ormore common causes and then eliminate them. Thus, for example, in the abovecase a completed cause-and-effect diagram might appear as shown in Figure 19.3.
Chapter 19: B. Statistical Process Control 251The defect concentration diagram proved to be of great use when the daughter of oneof the authors made a claim with a transportation company. In 2001, the author shippeda car from Boston, Massachusetts, to his daughter in San Jose, California. After receivingthe car, she found that the front bumper’s paint was damaged. She filed a claim with thetransportation company for the damage, but the company turned it down simply statingthat this damage was not caused by the company. Fortunately a couple of days later, shefound similar damage symmetrically opposite under the back bumper. She again calledthe company and explained that this damage had clearly been done by the belts thatwere used to hold the car in transportation. This time the company could not turn downher claim since she could prove scientifically, using a defect concentration diagram, thatthe damage was caused by the transportation company.DEFECT CONCENTRATION DIAGRAMA defect concentration diagram is a visual representation of the product understudy that depicts all defects. This diagram helps workers to determine if thereare any patterns or particular locations where the defects occur and what kindsof defects are occurring, minor or major. The patterns or particular locations mayhelp the workers to find the specific causes for such defects. It is important thatthe diagram shows the product from different angles. For example, if the productis shaped as a rectangular prism and defects are found on the surface, thenthe diagram should show all six faces, very clearly indicating the location of thedefects. In Figure 19.4 the two diagonally opposite edges are damaged, whichclearly could have happened in transportation or moving this item from the productionarea to the storage area.RUN CHARTIn any SPC procedure it is very important to detect any trends that may be presentin the data. Run charts help to identify such trends by plotting data over a certainperiod of time. For example, if the proportion of nonconforming parts producedfrom shift to shift is perceived to be a problem, we may plot the number of nonconformingparts against the shifts for a certain period of time to determine if thereare any trends. Trends usually help us to identify the causes of nonconformities.The run chart is particularly useful when the data are collected from a productionprocess over a certain period of time.Part IV.BTopBottomFront Back Left RightFigure 19.4 A damaged item shaped as a rectangular prism.
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Chapter 19: B. Statistical Process Control 251
The defect concentration diagram proved to be of great use when the daughter of one
of the authors made a claim with a transportation company. In 2001, the author shipped
a car from Boston, Massachusetts, to his daughter in San Jose, California. After receiving
the car, she found that the front bumper’s paint was damaged. She filed a claim with the
transportation company for the damage, but the company turned it down simply stating
that this damage was not caused by the company. Fortunately a couple of days later, she
found similar damage symmetrically opposite under the back bumper. She again called
the company and explained that this damage had clearly been done by the belts that
were used to hold the car in transportation. This time the company could not turn down
her claim since she could prove scientifically, using a defect concentration diagram, that
the damage was caused by the transportation company.
DEFECT CONCENTRATION DIAGRAM
A defect concentration diagram is a visual representation of the product under
study that depicts all defects. This diagram helps workers to determine if there
are any patterns or particular locations where the defects occur and what kinds
of defects are occurring, minor or major. The patterns or particular locations may
help the workers to find the specific causes for such defects. It is important that
the diagram shows the product from different angles. For example, if the product
is shaped as a rectangular prism and defects are found on the surface, then
the diagram should show all six faces, very clearly indicating the location of the
defects. In Figure 19.4 the two diagonally opposite edges are damaged, which
clearly could have happened in transportation or moving this item from the production
area to the storage area.
RUN CHART
In any SPC procedure it is very important to detect any trends that may be present
in the data. Run charts help to identify such trends by plotting data over a certain
period of time. For example, if the proportion of nonconforming parts produced
from shift to shift is perceived to be a problem, we may plot the number of nonconforming
parts against the shifts for a certain period of time to determine if there
are any trends. Trends usually help us to identify the causes of nonconformities.
The run chart is particularly useful when the data are collected from a production
process over a certain period of time.
Part IV.B
Top
Bottom
Front Back Left Right
Figure 19.4 A damaged item shaped as a rectangular prism.
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