Many people sometimes confuse Cmk and Cpk. An easy way to distinguish the two is to remember the ‘M’ in Cmk lets you know that it is the Machine Capability Index and the ‘P’ in Cpk lets you know that it is the Process Capability Index.

Overview: What is a machine capability index?

It is an index that is pulled from the observations of an uninterrupted production run. The machine capability index is a short-term index and is used as a measurement tool for determining how effective machine improvement efforts are.

4 benefits of a machine capability index

There are several benefits of utilizing a machine capability index. Let’s take you through a few of them:

1. Authentication

It provides verification of a new machine.

2. Helps track improvements

Using a machine capability index verifies the efficiency of machine improvements to determine if they sufficiently benefit processes.

3. Constant verification

With a machine capability index, existing machines receive continual verification to ensure everything is on the right track.

4. Forecasting

A machine capability serves as a valuable tool forecasting trends and as an indicator.

Why is a machine capability index important to understand?

There are several reasons to understand a machine capability index:

Added confidence

A Cmk study is meant to minimize variation, so running a new machine through the index can assure additional confidence that the new machine can hold up.

It paves the way for a long-term index.

Before you can determine the long-term effectiveness of a machine, you need to first know how it does on an initial run. A machine capability index is a good key for how the initial run will go and give you insight prior to running a long-term index.

Having a thorough knowledge of capability indices can be crucial.

Capability indices do more than just help you meet the requirements. They focus on continued improvement and can lead to the constant betterment of your machines and processes.

An industry example of a machine capability index:

An operations manager is asked to approve a new machine in a shop that will cut back on costs. To determine if the machine is going to make the cut, a machine capability index is utilized. The value of the index is found to be 2.0 and the new machine is accepted as part of production.

3 best practices when thinking about machine capability index

Here are some practices to keep in mind when it comes to machine capability index:

1. Prepare accordingly

In order for a machine capability index to be reliable, the capability study needs to be adequately planned, sufficiently performed, and thoroughly evaluated.

2. Remember it is a short-term index.

A machine capability index is typically geared towards new machines and has limits to what it can tell you. It should not be used as a long-term index of how things are going.

3. If you already know other capability indices, Cmk is fairly simple.

If you already know the two most common capability indices, Cpk and Ppk, Cmk follows the same general formula and should be easy to add to your knowledge base.

Frequently Asked Questions (FAQ) about a machine capability index

What is the difference between machine capability and process capability?

Machine capability is a measure specifically geared towards the quality of a machine respective of its specs. Process capability takes into account anything that might affect the ability of a machine to perform, including its environment. Other factors of variation a process capability index may take into account are machine, operator, method, material, and measurement. Machine capability indices only factor in machine and measurement and are thereby more suited for a short-term indexing.

What does Cmk stand for?

The Cm refers to the spread of a machine’s performance in comparison to the width of the tolerance. The k accounts for shifting and location in relation to the tolerance.

How many measurements are used in a machine capability index?

The standard is 20-50 consecutive measurements.

How do I interpret the results of the index?

Put simply, the higher number the better. A minimum of 1.67 or 2 is the typical requirement in order to approve the use of a machine.

Implementing a machine capability index

Now that you have had an introduction to the benefits of running a machine capability index, you have knowledge of a tool in your belt for determining the initial improvement the new machine adds to your business processes.

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