Proof of machine performance and process capability according to SPC Manual (VDA/AIAG) & ISO 22514-2

Requried course: Introduction to statistics

In industrial production, a machine capability analysis is carried out first, particularly for new products or significant changes to the applied production technology. This study helps you find out whether the production equipment is generally suitable to manufacture the respective product. Only if this is the case, you conduct a process capability analysis. The result of this analysis tells you whether the production remains stable under long-term conditions.

The proof of machine performance, process performance or process capability is an essential part of quality assurance in industrial production. We provide you with the necessary knowledge in this training course by using software programs and by showing you how to apply these procedures based on practical examples.

This machine performance and process capability training is based on ISO 22514-2. At the same time, this course can be considered as SPC manual training, as it incorporates all the principles and methods of the soon-to-be-published harmonised SPC manual, a joint guideline from the VDA and the AIAG.

Our training program on machine performance and process capability in detail

Referenced standards
Terms, definitions
SPC control loop and influence quantities
Principles of tolerance and responsibility
Preparing production equipment for machine performance studies
Measurement process capability
Machine performance
Preliminary process performance
Process capability
Documenting results
Calculating and interpreting statistics P_m, P_mk, P_p, P_pk, C_p, C_pk in production
Situation-related limits
Interpreting results
Stability study
Consideration of various special cases

Further information

What is the difference between machine performance, process performance and process capability?

A machine performance study is also referred as a short-term capability analysis. It is used solely to determine whether the machine or production equipment is basically suitable for manufacturing the respective product, e.g., prior to a new series production run or in the event of significant changes to an existing production process. This is a one-time analysis and serves only to assess the influences caused by the machine.

This is usually followed by a preliminary process performance study to determine whether the results of the machine performance study conducted previously change in actual series production. All influences (men, material, environment, etc.) are considered here. Preliminary process performance can also be applied if a machine performance study is not possible.

Finally, a process capability analysis or long-term analysis is used to determine whether production remains stable in the long term under real conditions.

What do process capability and machine performance have to do with the SPC manual and ISO 22514-2?

The statistical procedures for the acceptance of machines and production equipment as well as for process qualification are defined and described in the new SPC manual to be published by the German Association of the Automotive Industry (VDA) and the Automotive Industry Action Group (AIAG) as well as in ISO 22514-2. The statistics required to determine machine performance, process performance and process capability include

Machine performance index P_m and minimum machine performance index P_mk
Process performance index for processes not meeting stability requirements P_p and minimum process performance index for processes not meeting stability requirements P_pk
Process capability index for processes meeting stability requirements C_p and minimum process capability for processes meeting stability requirements C_pk.

Correct calculation and interpretation of these values ensure that the measurement and test results are reliable, thereby helping you to avoid wrong decisions. It is therefore important to adhere to these standards or the associated company guidelines.

What are the statistics of a machine performance study or a process capability analysis?

You calculate the machine performance indexindex Pm and the minimum machine performance index Pmk in a machine performance study to determine short-term capability.

The process performance index for processes not meeting stability requirements _{P_p} and minimum process erformance index for processes not meeting stability requirements P_pk as well as the _{process capability index} for processes meeting stability requirements Cp and minimum process capability index for processes meeting stability requirements Cpk are statistics of capability analyses to deterine process performance (short-term) and process capability (long-term). A process is considered as unstable when at least one parameter varies over time.

Company guidelines often use their own designations and symbols for these parameters. For this reason, it is important to carefully review the relevant specifications and requirements and to agree on a common approach in customer-supplier relationships.

How many parts are necessary to determine machine performance, process performance or process capability?

A machine performance study usually requires at least 50 parts. A minimum of 100 parts is recommended for calculating preliminary process performance. For long-term process capability, the specific number of parts is not important. It is important that a sufficiently long period of time is monitored under normal series conditions so that all possible influence quantities can be considered. A minimum of 20 production days is recommended.

Company guidelines often contain approaches and requirements that are not entirely consistent with general standards and guidelines. It is therefore important to check the required time frame and scope of data in advance and to agree on a common approach in a customer-supplier relationship.