What is the difference between Critical Dimension and Control Dimension

M

Monica_B

#1
Hello everybody,

I'm new in the forum and this is my first post.

Can anybody clarify me what the difference between "Critical Dimension" and "Control Dimension" is?
In my company there are permanent discussions and different opinions about this topic. :(

Thanks in advance for your support.

Best regards,
Monica
 
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Stijloor

Staff member
Super Moderator
#2
Hello everybody,

I'm new in the forum and this is my first post.

Can anybody clarify me what the difference between "Critical Dimension" and "Control Dimension" is?
In my company there are permanent discussions and different opinions about this topic. :(

Thanks in advance for your support.

Best regards,

Monica
Two options:
  1. If this is customer-related terminology, ask them for their definition.
  2. If this is company-specific terminology, come to a consensus agreement on the definitions.
 

qusys

Trusted Information Resource
#3
Hello everybody,

I'm new in the forum and this is my first post.

Can anybody clarify me what the difference between "Critical Dimension" and "Control Dimension" is?
In my company there are permanent discussions and different opinions about this topic. :(

Thanks in advance for your support.

Best regards,
Monica
Agree with Stijloor.
In any case , "critical dimension" is used, expecially in the mfg flow and control plan/fmea where you have to check or measured something that impact product quality, but I have never heard "control dimension". Probably the latter should be "dimension control", something linked with your operativity but probably not as much "critical" as the former.Please let us know more details.:bigwave:
 
M

Monica_B

#4
Dear Stijloor and qusys,

thanks for your reply. The terminology is a specific internal terminology in my company. As mentioned, it is an unclear topic because there is so far no written definition (e.g. guidelines) of "Critical Dimension" and "Control Dimension". Therefore everybody, both in QM as in the Development Dept., interprets these terms differently. Generally in the drawing the critical dimensions are circled and the Control Dimensions are identified with the notation "SPC". But nobody can clarify exactly the difference between them.
Is there any standard (e.g ISO) definition of critical, important, control dimensions?

BR from Germany,

Monica
 

Stijloor

Staff member
Super Moderator
#5
Dear Stijloor and qusys,

thanks for your reply. The terminology is a specific internal terminology in my company. As mentioned, it is an unclear topic because there is so far no written definition (e.g. guidelines) of "Critical Dimension" and "Control Dimension". Therefore everybody, both in QM as in the Development Dept., interprets these terms differently. Generally in the drawing the critical dimensions are circled and the Control Dimensions are identified with the notation "SPC". But nobody can clarify exactly the difference between them.
Is there any standard (e.g ISO) definition of critical, important, control dimensions?

BR from Germany,



Monica

For example, in automotive supplier land, the customer may indicate various characteristics (including dimensions) that they consider "special" because too much variation can cause problems. In addition, the automotive supplier has also an obligation to study the specifications and determine which ones they consider "special." These characteristics are often determined through design and process FMEA's and must be included in the control plan to mitigate risk. A supplier may choose to control these special characteristics through the use of SPC techniques such as appropriate control charts as well as through other means.

Unless you must deal with customer specific requirements, the decision on how to determine, interpret, and control, is your company's decision. So, get all the stakeholders together, come to a consensus decision, and GO with it.

Hope this helps.

Stijloor.
 

TWA - not the airline

Trusted Information Resource
#7
Monica,

I guess you're talking about "Pr?fma?" which means a dimension that needs to be verified on the part/product and therefore is specially marked in the drawing by a circle around it. This is defined in DIN 406 I think and to my knowledge there is no international equivalent to this. I'm not sure whether a "Pr?fma?" needs 100% verification and if not, how the sampling rate would be shown in a drawing.

For me (coming from the medical device industry), critical dimensions are those that have a high impact on product risk and/or quality as defined in the risk analysis. Therefore you need to have a very good control on them; however that does not necessarily mean you need to verify/check them on the actual part (which would make it a test or check dimension or "Pr?fma?"). A validated process with a high capability might actually be more appropriate to control a critical dimension... Also I do not use drawings alone to define necessary in-process or final QC control steps, I always have a seperate test instructions document.
 
M

Monica_B

#8
Yes, exactly: in German is called ?Pr?fma?. I have checked the definition of Pr?fma? in the DIN 406: in the ?2.19 the ?check dimension? is defined as ?dimension designated as requiring particular consideration when the scope or stringency of inspection is specified.? But, as you mentioned, there is not any hint about the frequency of the verification in the serial production.
I see that the DIN 406 refers to the ISO 129. Anyhow I could find any definition of control dimension in the ISO norm.
Best regards,
Monica
 
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