Control - Six Sigma Statistical Process Control Basics

Which categories of variables should teams consider for control?

- Variables that are most difficult to hold - Variables that are salient or known - Variables representing a critical dimension of the product or process - Variables tied to customer, organizational, or regulatory imperatives

Which examples of variables are good candidates for SPC?

A six sigma team determines that poor batches of raw material are the result of a special cause variation Customer surveys at a call venter show that hold times are a major source of customer complaints Teams have noticed that historically tube diameter on a coolant system varies significantly A mfg wants to adjust the temperature at which a flame retardant material used by consumers combust

Which statements accurately describe SPC?

As a source of information on process behavior, it's one of several tools you'll need to implement continuous improvement It can be overused It employs control charts as the preferred tool It allows process owners to have control over the process

Match the control chart types to when they are used

C - Defects are in equally sized subgroups Xbar and R - The subgroups contrain two to ten measurements Xbar and s - The subgroups contain more than 10 measurements p - defectives are in unequally sized subgroups imR - The subgroups contain a single measurement

Match each selection criteria with the corresponding example

Critical dimension of the product: A variable related to the ability of a device with GPS to sync to satellite signals Tied to key imperatives: An aspect of a service has generated customer complaints Salient or known variables: A defect that occurs each time a night shift falls on a Friday night Difficult to hold or maintain: Computer crashes are associated with high defect rates

Match each key element with a description of it's role in control charts

Data point - Represents the status of a process characteristic at a point in time Control limits - Identifies the range of variation that can be ascribed to common causes Center line - The mathematical average of all the samples plotted Axes - Represents a timeline and the variable of interest

How can you tell when a process is remaining in control?

Data points remain within specified control limits Measurements of the mean and std deviation remain consistent over time

What actions are involved in the transfer of control plan responsibilities from the SS team to the process owner

Establish documentation process for control Secure understanding and agreement from involved personnel Update all work instructions with reaction plans Integrate the control plan with related process

A six sigma team at a pressure gauge manufacturer is completing a control plan What are some examples of information you might find in the control plan?

Plastic injection molding control plan customer #3121: Gleedon auto manufacturing The injection molding process encompasses four operations : mixing polymer, injecting cooling and buffing Revised August 1 revision 2.1 The person in charge of the process

What are the objectives of SPC?

Reducing the cost of variation in a process by controlling and improving process performance Using quality control tools to monitor a process's performance Using statistical analysis to help identify sources of variation

Match the common and special causes variation categories to the corresponding examples.

Special cause: - Machine malfunction - Power Surge - Operator falls asleep Common Cause: - A lack of clearly defined standard operating procedures - Poor maintenance of machines - Poor lighting and excessive noise on the shop

Which considerations should you keep in mind when determining an appropriate subgroup size?

Teams need to have significant history of the process when selecting subgroup size Service processes typically have a sample of one large subgroups may contain dependent data or special cause variation Small subgroups are more economical but can't detect larger process shifts easily

Which statements accurately reflect the characteristics of control plans?

The control plan is a singlem accessible document Control plans outline the checking monitoring and response plan for a process Control plans can cover a single process or a family of processes Control plans include categories of information such a critical customer requirements, indicators, specifications and targets

What are the key properties of rational subgroups?

The observations within a subgroups are from a single stable process The subgroups are formed from observations made in a time ordered sequence The observations comprising the subgroup are independent

What other information would the team typically include in the control plan?

Upper specification limit is 2.7 Model #25150 pressure gauge A high repeat customer rate determines a KPOV Temperature tensile strength and length are important inputs A less than 1% defect rate is required