Free WinSPC Trial Request a Demo

Ask the Expert

How Does SPC Complement My Automatic Inspection System?

 

 

More companies are leveraging high speed vision systems to inspect multiple quality characteristics on their products.

Read more...

Hypothesis and Equivalence Testing

 

 

This article will review statistical hypothesis testing in general and then introduce equivalence testing and its application.

Read more...

Beyond the Usual Benefits of SPC

 

 

When Statistical Process Control is applied properly, tremendous benefits in profitability and process understanding are achieved.

Read more...

How Undetected Process Changes Can Ruin Product Reliability

 

 

So how does process control (or the lack of it) affect product reliability? Reliability is defined as the probability that a material, component, or system will perform its intended function under defined operating conditions for a specified period of time. (By Steven Wachs, Principal Statistician, Integral Concepts.)

Read more...

Optimizing product target weights of foods and beverages

 

 

In order to maximize profitability while complying with government regulations regarding net package contents, food manufacturers and packagers must achieve an optimal balance.

Read more...

Resolving a complex manufacturing problem with statistical methods

 

 

In this case, we address $1.2 million worth of annual process variation.

Read more...

How to reduce warranty costs using tools that predict product and process performance

 

 

Looking just at the auto industry, GM has recalled roughly 3 million vehicles this year in the U.S. alone. In 2009, GM recalled roughly 2.2 million vehicles.

Read more...

Prioritizing prevention

 

 

While enormous dollars are spent reacting to problems, Quality teams can excel to new heights by focusing on prevention: of product failures, of scrap, and of other inefficiencies.

Read more...

How do I implement SPC for short production runs? - Part 1

 

 

Traditional SPC methods were developed to support high volume production and long production runs. However, with the trend toward product specialization, product diversity, and flexible manufacturing, short production runs have become more common. Applying SPC in the traditional manner presents challenges in short production runs because by the time enough datails are collected to establish valid control charts, the production run may be over.

Read more...

How do I implement SPC for short production runs? - Part 2

 

 

In last month’s article, we introduced the concept of utilizing Deviation from Nominal (DNOM) control charts for short production runs. These charts allow us to monitor process characteristics over time even when the units being controlled have varying nominal values. DNOM charts assume that the process variability (i.e. standard deviation) does not vary significantly by part type. However, often this assumption does not hold. Characteristics with larger nominal values tend to have more variation than characteristics with smaller nominal values. This month we discuss how to test whether or not significant differences in variability exist and if so, how to modify the DNOM methods and charts to handle this situation.

Read more...

Pre-Control: No Substitute for Statistical Process Control

 

 

Many advocate the replacement of SPC with more simplistic approaches such as "Pre-Control." Unfortunately, in a manufacturing world of increasing complexity, and with a global market demanding the highest quality and reliability, applying "simple" tools at the expense tools with considerably more value (and really not very complex or difficult) doesn't cut it.

Read more...

Where do the typical control chart signals come from?

 

 

The purpose of control charting is to regularly monitor a process so that significant process changes may be detected.

Read more...

Misapplications of SPC…and the consequences

 

 

Many manufacturing leaders believe that their production personnel use SPC properly, but the evidence suggests otherwise.

Read more...

How do I choose the appropriate type of control chart?

 

 

Many factors should be considered when choosing a control chart for a given application.

Read more...

How should the subgroup size be selected for an X-bar chart? - Part 1

 

 

The key is to specify a subgroup size so that significant shifts are detected with high probability and that insignificant shifts are unlikely to produce a signal.

Read more...

How should the subgroup size be selected for an X-bar chart? - Part 2

 

 

Last month’s article focused on the conceptual application of appropriate sample sizes for X-bar charts. This month we describe the sample size formula and its application in detail. 

Read more...

What is a standard deviation and how do I compute it?

 

 

Most manufacturers would rate product quality as a key driver of their overall ability to satisfy customers and compete in a global market.

Read more...

How do I know what process characteristics to control?

 

 

Clearly, controlling everything is not feasible or a smart use of limited resources.

Read more...

What is the relationship between process stability and process capability?

 

 

Nothing and everything. Though they are not directly linked, statistician and SPC expert Steven Wachs cautions that without evidence of process stability, capability data is useless.

Read more...

Can I chart deviation-from-target, and when would it make sense to do this?

 

 

You can chart deviation-from-target. You do this by creating a Target chart, a chart that plots the deviation of subgroup values from a target value.

Read more...

Why is Cpk data important, and how can my company benefit from tracking it?

 

 

To answer that, we need to start off with what these capability indices represent. Capability indices characterize a process as compared to a specification.

Read more...

What is the Cpm index and how does it relate to Cpk?

 

 

In my last column, I was asked about a capability index called Cpk. Cpk is a measure of a process' ability to conform to specification. A Cpk = 1 means that if nothing changes, 99.73% of the process output will be within specification, as in Figure 1.

Read more...

My company is instituting Lean systems - Part 1

 

 

What is SPC's role, if any, in the world of Lean Manufacturing? Is SPC 'lean'?

Read more...

My company is instituting Lean systems - Part 2

 

 

Last month I began to answer this question by examining some of the 14 Principles of Lean Manufacturing according to Jeffery Liker. Let's continue that examination.

Read more...

What is the difference between specification limits and control limits?

 

 

This is a crucial distinction that is frequently confused. Basically, specification limits have to do with the voice of the customer while control limits have to do with the voice of the process.

Read more...

What is the philosophy of Process Control (rather than Product Control)?

 

 

Ask people involved with the design and manufacture of a product the following question: "What is Quality?" Many, if not most, of the responses will be some form of the following: "Quality is ensuring that our products meet the customer (or engineering) specifications. Unfortunately, this leads to a "conformance to specifications" or a "Product Control" approach to quality.

Read more...

"How do I test my data for normality?"

 

 

Before applying statistical methods that assume normality, it is necessary to perform a normality test on the data.

Read more...

Can control charts detect small process shifts?

 

 

Typical control charts, such as Xbar & R and X & Mr, indicate whether or not a process is statistically stable.

Read more...

SPC 101: Differentiating between Cpk and Ppk values

 

 

Just like control charts tell us about the stability of the process, capability analyses tell us about process capability.

Read more...

What does an out-of-control process indicate?

 

 

Control charts are one of the most popular SPC tools used by manufacturers. They are used to determine whether a process is in or out of control.

Read more...