Chapter S6: Statistical Process Control

Exceed 1

For Cpk to _________ ___, standard deviation must be less than 1/3 of the difference between the specification and the process mean (x)

Upper and lower specifications

For a process to be capable, its values must fall within ______ and _______ _______; this typically means the process capability is within +3 standard deviations from the process mean

1.0

If the Cp is less than ____, the process yields products or services that are outside their allowable tolerance

Control charts

In an ideal world, there is no need for _______ _______

5 points above or below

In general, a run of ______________ the target or centerline may suggest that an assignable, or nonrandom, variations is present

Continuous Dimensions

Infintite number of possibilities; ex: weight, speed, length, or strength

1st major decision regarding control charts

Managers must select the points in their process that need SPC; May ask "which parts of the job are criticial to success? or "which parts of the job have a tendency to become out of control?"

1.33

Many firms have chosen a Cp of ____ (a 4-sigma standard) as a target for reducing process variability

Defectives

Measuring _______ involves counting them

Distribtuion

Natural variations form a pattern

Objective

The __________ of a process control system is to provide a statistical signal when assignable causes of variation are present

3rd major decision regarding control charts

The company must set clear and specific SPC policies for employees to follow

Range

The difference between the largest and smallest items in one sample

Product Outputs

3 types of ________ ________

C-charts

A quality control chart used to control the number of defects per unit of output; use _____ _____ to control the number of defects per unit of output

Cp

A ratio for determining whether a process meets design specifications; a ratio of the specification to the process variation; since this range of values is 6 standard deviations, a capable process tolerance, which is the difference between the upper and lower specifications must be greater than or equal to 6

Variability

All processes are subject to a certain degree of ________

In Control

As long as the distribution (output measurements) remains within specified limits, the process is said to be _____ _____ and natural variations are tolerated

Run test

Available to help identify the kind of abnormalities in a process that we see

Design specifications (tolerances)

But a process that is in statistical control may not yield goods or services that meet their __________ ___________

Process distribution

By using both charts we can track changes in the ______ _______

Defects

Control charts for _______ are helpful for monitoring processes in which a large number of potential errors can occur, but the actual number that do occur is relatively small

Mean

Control charts for the ______, x bar and the range, R, are used to monitor processes that have continuous dimensions

Centered

Cp and Cpk will be the same when the process is centered

Natural and assignable variation

Distinguish two tasks for the operations manager

X-chart

The ____ ____ is sensitive to shifts in the process mean

R-chart

The ____ ____ is sensitive to shifts in the process standard deviation

Higher; greater

The ______ the process capability ratio, the ______ the likelihood the process will be within design specifications

Process capability

The ability of a process to meet design specifications, which are set by enginerring design or customer requirements

Only natural variation

The first is to ensure that the prcess is capable of operating under control with _____ ______ ______

Percent and Number

Two kinds of attribute control charts; those that measure the ______ defective in a sample called p-charts and those that count the ______ of defects called c-charts

Attributes

Typically classified as defective or nondefective; good/bad; yes/no; acceptable/unacceptable

Natural variations

Variability that affects every production process to some degree and is to be expected; also known as common cause

Assignable variation

Variation in a product process that can be traced to specific causes

Centered; capable

When the Cpk index for both the upper and lower specification limits equals 1.0; the process variation is ________ and process is ________ of producing within +3 standard deviations

X-chart; R-chart

When the sampling mean is constant and but the dispersion is increasing, the _____ _____ does not change and the ____ _____ shifts upward

X-chart; R-chart

When the sampling mean is shifting upward and the range is consistent, the _____ _____ shifts upward and the _____ _____ does not change

P-charts

A quality control chart that is used to control attributes; using _____ _____ is the chief way to control attributes

2.0

A Cpk of _______ means the process is capable of producing fewer than 3.4 defects per million

1.0

A capable process has a Cp of at least _____

R-chart

A control chart that tracts the "range" within a sample; it indicates that a grain or loss in uniformity has occurred in dispersion of a production process

Control Chart

A graphical presentation of process data over time

Out of Control

A process can be _____ ___ _______

In Control; Capable

A process can be _____ ______ and the process is ________ of producing within established control limits

In Control; Not Capable

A process can be ______ ______ and the process is ______ ______ of producing within established limits

Statistical Control

A process is said to be operating in ________ __________ when the only source of variation is common (natural) causes

Statistical Process Control (SPC)

A process used to monitor standards by taking measurements and corrective action as a product or service is being produced

Cpk

A proportion of variation between the center of the process and the nearest specification limit; measures the difference between the desired and actual dimensions of goods or services produced

X-chart

A quality control chart for variables that indicates when changes occur in the central tendency of a production process

2nd major decision regarding control charts

Managers need to decide if variable charts (X chart or R chart) or attribute charts (P chart or c chart) are appropriate; Variable charts monitor weights or dimensions. Attribute charts are more of a "yes-no"or "go-no go" gauge and tend to be less costly to implement

Monitor the process central tendency

Operations managers use control charts for averages, which _______________

Monitor the process variability

Operations managers use control charts for ranges to ______________

Process in control

Statistical process control means keeping a _______ ____ _________; the natural variation of the process must be stable

Mean and standard deviation

The normal distribution is defined by two parameters, _______ _______ __________ ___________

Special (Assignable) Causes

The process must first be brought into statistical control by detecting and eliminating ________ ( )_________

Control Charts

The purpose of _____ ______ is to help distinguish between natural variations and variations due to assignable causes

Assignable variation

The second is, of course, to identify and eliminate _____ ______, so that the processes will remain under control

Central tendency and dispersion

The two types of charts go hand in hand when monitoring variables because they measure the two critical paramters:

Process capability ratio (Cp) and Process capability index (Cpk)

There are two popular measures for quantiatively determing if a process is capable