Unit 7_STATISTICAL QUALITY CONTROL
P Chart
A chart that can be used to track defective and non-defective components in a manufacturing process
Variable Chart
A chart that contains data which represents measurements taken from the process such as temperature, pressure, pH or weight.
Attribute Chart
A chart which makes use of discrete data classifying the number of items conforming and the number of items failing to conform to any specified requirements.
C Chart
A type of chart used when identifying the total count of defects per unit that occurred during the sampling period.
Statistical Quality Control
A way of monitoring a process to maintain consistent quality and thereby reduce failure cost.
sampling the finished items that are to be shipped
Acceptance sampling after the process involves _________ either to a customer or a distributor/wholesaler.
randomly inspecting the raw materials received in the warehouse
Acceptance sampling before the process involves sampling materials received from a supplier such as _____________.
specification, production, inspection
Additionally, statistical quality control makes use of control charts which may influence decision related to the function of ___________________.
Quality
Generally means that the finish product consistently meets the requirements established for it such as the requirements set forth by the FDA and the official compendia.
Quality Control Chart
Graphical representation of certain descriptive statistics for specific quantitative measurements of the manufacturing process.
mathematical loss of probability
Statistical Quality Control relies on using ______________. These losses have something to do with the probability of something occurring either naturally or because of outside influence.
Mean
The most common measure of central tendency.
Control chart
The most commonly used
Statistical Quality Control
The techniques that are vital for monitoring the inherent variations that are present in all manufacturing processes.
1) Descriptive Statistics 2) Statistical process control (SPC) 3) Acceptance sampling
The three (3) main pillars in the METHODOLOGY and TOOLS OF SQC
C Chart
The type of control chart that allows the practitioner to assign each sample more than one defect.
Histogram Pareto Chart Defect Concentration Diagram Control Chart Cause and Effect Diagram Scatter Diagram Stratification
Tools used for SPC
Inspection
refers the comparison of certain
Control charts
Statistical quality control information about
I chart
Used to track the process LEVEL and detect the presence of special causes
Control limits
_________ are so placed in the quality control charts as to disclose the presence or absence of assignable causes.
lower dotted line
refers as the lower control limit (LCL) and is also three standard deviation below the center line
NP Chart
A chart used when each data point is based on the same sample size.
NP Chart
A chart used when identifying the total count of defective units or unit that may have one or more defects with a constant sampling size.
Variable Chart
A chart which makes use of actual records of numerical measurement on a full continuous scale such as meter, grams, liter
Statistical Quality Control
A valuable tool that can be used to help maintain consistent quality while keeping failure cost down.
P chart
An example of an attribute chart is the control chart for fraction defective known as _____.
Detecting error at inspection Uniform quality of production (higher customer satisfaction) Reduces inspection costs (by keeping an eye on the quality of the products, defects are caught before product shipment or before delivery consignments) Reduces the number of rejects (saves the cost of material) Basis for attainable specifications Determining the capability of the manufacturing process (this is because statistical quality control enables operators to determine how much and what kind of variation is occurring in the process) Understanding and Appreciation of quality control
BENEFITS OF STATISTICAL QUALITY CONTROL
subgroup
Each point on the graph represents a ________; that is, a group of units produced under the same set of conditions (**For example, you want to chart a particular measurement from your process... if you collect
I chart MR chart (moving range)
Examples of Variable control charts for individual data
S chart X-bar chart R chart Mnemonic: SeXbaRr
Examples of Variable control charts for subgroup data
99.7%
If the process is in control, the six standard deviations spread between the upper and lower control limits will encompass __% of the values in a normal distribution with its mean at the center line.
individual measurement
In I chart and MR chart, each point on the graph represents ________________________.
problem in the process
In any process, there is always some amount of variations because of these natural variations. No product is exactly the same all the time but if there is too much and too little variation, what result or indication this may cause?
Quality Control Chart
It consists of solid line and two horizontally parallel lines on either side of the solid line.
Control chart
It is a graphical display that provides a basis for deciding whether the variation in the output of a process is due to common causes which are randomly occurring variations or out of the ordinary assignable causes.
Control charts
It is a graphical representation of certain descriptive statistics for specific quantitative measurements of the manufacturing process.
Standard Deviation
It is a measure of the spread of scores within a set of data. Specifically, it shows how much your data is spread out around the mean.
Statistical process control (SPC)
It is performed during production usually based on the analysis of the goods produced rather than the manufacturing equipment.
Control solid line
It is the target value of the historical process average and/or range in quality control chart.
statistical tools
It is the use of ______________ and techniques to monitor and maintain product quality in industries such as food, pharmaceuticals and many manufacturing environments.
Range
It refers to the difference between the highest and lowest score in a distribution.
Acceptance sampling
It refers to the process of randomly inspecting a certain number of items from a batch or lot in order to decide whether to accept or reject an entire batch.
lowest possible cost
One goal of every process plan is to produce a quality product at the_______________.
failure cost
One of the biggest costs a manufacturing company can encounter is the cost associated with producing defective products, that is commonly referred to as________.
pre-defined limits
Products are carried out via SPC to determine if production processes are continuing to operate within ________________.
U CHART
Similar to a c-chart, this chart is also used to track the total count of defects per unit that occur during the sampling period and can track a sample having more than one defect
Random sampling
Statistical process control (SPC) involves statistical analysis of products from the production line via what type of sampling?
C Chart U Chart P Chart NP Chart Mnemonic: CUP N' Pee
TYPES OF CONTROL CHART USED TO ANALYZE ATTRIBUTE DATA
1) Proper sampling 2) Determining quality variation of the sample 3) Making inferences 1. Proper sampling **proper selection of a subset of items or products or units of products from within a total population or total number of items to estimate the characteristic of the whole population 2. Determining quality variation of the sample **involves inspection of the characteristics and overall quality of our products. 3. Making inferences **Giving disposition to the entire batch whether to accept or reject or continue with the process or not. Correct decisions correspond to accepting a good quality lot and rejecting a poor-quality lot. Because ampling is being used, the probabilities of erroneous decisions need to be considered.
The STEPS INVOLVED IN DOING STATISTICAL QUALITY CONTROL
U CHART
The chart used when the number of samples of each sampling period may vary significantly and used to plot the rate of defectives (number of defectives/number of units inspected)
Control limits
These are boundaries within which the process is controlled while the operators typically do not calculate limits.
Inferences
These are conclusions to the entire
two dotted parallel lines
These are the lines that indicate the limits within practically all observed results should fall as long as the process is under normal variation or is considered statistically controlled.
R chart, S chart
These charts are used to track process variation and detect unexpected variation
R chart, S chart
These charts help to determine if a process is stable and predictable.
Control charts
These charts provide a visual representation of what is occurring in the process.
Variable control charts for individual data
They are used when measurements are expensive, production volume is low, or products have a long cycle time. ** Example: to test the impact strength of parts (destructive testing)
Control charts
They provide information that the operator can use to maintain product quality and they can serve as a documentation of quality for the customer.
NP Chart
This chart follows the same principle as the p chart, but actually plots the number of
Variable Chart
This chart plots continuous
I chart
This chart plots individual OBSERVATIONS over time
MR Chart (Moving range chart)
This chart plots the MOVING RANGE over time
X-bar chart
This chart plots the process MEAN over time.
R chart
This chart plots the process RANGE over time.
S chart
This chart plots the process STANDARD DEVIATION over time.
P Chart
This chart plots the proportion ("p") of the data falling into the relevant category over time
X-bar chart
This chart shows how the mean or average changes overtime
R chart
This chart shows how the range of the
Attribute data **Examples 1) Number of products that either passed or failed a standard test. 2) Number of complaints received from customers 3) Proportion of technical support calls due to installation problems
This data provides a count of how many times something specific occurred, or of how many times something fit in a certain category.
Statistical Quality Control
This enable operators to determine how much and what kind of variation is occurring in the process.
failure cost
This includes the cost of replacing defective product, cost of scrap material from the production process, cost resulting from return product and cost associated with lost sales and costumers.
Acceptance sampling
This involves batch sampling by inspection.
Descriptive Statistics
This involves describing quality characteristics and relationships. They are used to describe the attributes of a
Statistical process control (SPC)
This involves inspecting random samples of output from process for characteristic.
NP Chart
This is a special version of the p chart.
C Chart
This is similar to the np chart that is used with a constant sample size (i.e., per day,
P Chart
This type of chart shows the proportion of non-conforming units in a certain category or requirements (i.e., subgroups of varying sizes)
variable data, attribute data
To determine whether abnormal variation exist, information is collected from the process plotted on control charts and analyzed. One factor that dictates the type of control chart to be used is whether the data collected form the process in these two basic quality control charts. These two basic quality control charts include?
normal circumstances
Too little variation may seem like a good thing, but statistically it should NOT occur under______________.
1) Variable control charts for subgroup data 2) Variable control charts for individual data
Two main types of variable control charts
S chart
Used to monitor the process variability as the standard deviation when measuring sub
MR Chart (Moving range chart)
Used to track the process VARIATION and detect the presence of special causes
X-bar chart
Used to track the process level and detect the presence of special causes affecting the mean
P Chart
Used when each unit can be considered pass or fail, no matter the number of defects and this chart shows the number of tracked failures (np) divided by the number of total units (n).
Statistical process control (SPC)
Uses sampling and statistical methods to monitor the quality of an ongoing process.
Equipment Material People Environment Regulatory requirement Mnemonic: EMPER a. Equipment b. Material - Ex: Changes in raw materials can cause changes in the process c. People - Ex: One operator might do something different from another causing variation d. Environment - Ex: Increase/decrease in ambient temp could affect the cooling capacity at a certain step in the process. e. Regulatory requirement - Ex: the requirements become more restrictive; it may become harder to produce a product that meets those requirements.
What are the FACTORS that can influence processes?
before/after the process
What makes acceptance sampling different from statistical process control is that acceptance sampling is performed ___________ rather than during the process.
unstable or out of statistical control
When abnormal variation is present, the process may be ___________________.
statistically controlled
When only normal variation is present in the process, the process is considered as
Random/Normal Variation
occurs normally or randomly in the process
Special/Abnormal Variation
referred to as assignable variation since it can be assigned to a specific cost or problem
upper dotted line
refers as the upper control limit (UCL) in quality control chart, which is normally three standard deviations above the center line
Mean
refers to the average value of a group of numbers
consumer's risk
refers to the error of accepting a poor-quality lot creates a problem for the consumer
producer's risk
refers to the error of rejecting good quality lot creates a problem for the producer.
Standard Deviation
refers to the measure of the amount of variation or dispersion of a set of values.
Statistical Quality Control
refers to the use of statistical methods in the monitoring and maintaining of the quality of products and services.