Statistical Quality Control

Uses statistical techniques and sampling in monitoring and testing of quality of goods and services

Acceptance Sampling

It relies primarly on inspection/test of previously produced items. It determins weather to accept or reject a product.

Statistical Process Control

It is a statistical quality control that occurs during production. It determins if the process is operating within acceptable limits.

Inspection

Apraisal of a good or service against a standard.

3 Stages of Inspection

Statistical Process Control Planning Process

Where to inspect

On Site VS In Lab

Random Variation

Natural variations in the output of processes created by countless minor errors

Assignable Variations

A variation whose source can be identified

Control chart

A time ordered plot of a sample statistic that is used to distinguish between random and assignable variation.

Control Limits

The deviding lines between random and non random variations

Type I Error

Concluding that a process changes whan it has not

Type II error

Concluding that a process is in control when it is actualy not

5 Steps in designing a control Chart

- Determine a sample size

- Obtain 20 to 25 samples

- Establish and graph preliminar control limits

- Plot sample stats values on control chart

- if any point are outside the control limits, investigate and correct

Control Charts for Variables

**Sample mean **

Monitor the mean of a process

**Sample Range **

Monitor the dispersion of a process

Control Charts for attributs

**p-Chart**

- Measure the proportion of deffects in a process

- from a binomial distribution: measure success or failure

**c-Chart **

- Measurs the number of deffect per unit

- From a poisson distribution

Design Specification

A range of acceptable values established by engineering design or customer requierment

Process Variability

Actual variability in a process for a product

Process Capability

The ability of a process to meet design spacifications

Capability analysis

determins wether the process output falls within the design specifications

Capable process

The output falls within specifications

4 possible strategies if a process is incapable

- Redesign process or reduce variability

- Use an alternative process

- use 100% inspection

- Relax design specifications

six sigma quality

A more advance version of problem solving/ Continuous improvement. It also refers to the goal of acheiving process variability so small that the half width of the design specification is 6 sigma