Direction please 1

[brandnew1]

i'm trying to research more on what "MISMATCH" stands for and what the number indicates.

On a forging drawing it notes: MISMATCH: .030 MAX. Talking with others the other day they indicated this would be considered a true position value.

Can someone point me in the right direction so that i can make sure parts do pass or fail in terms of what mismatch means. i don't know where in the Y14.5-1994 standard it speaks of this specifically.

thank you

 

[pmarc]

Look at ASME Y14.8:
- paras. 1.8.17 & 3.13
- figure 3-14 for explanation.

 

[brandnew1]

Thanks pmarc,

i looked over that section and saw the image and it appears to be a straight number. So as long as the number falls within the MAX, it would be good.

Now my question relates to a diametrical situation where i get two different values when comparing the mismatch. For example i get a value of .020 in the X and .005 in the Y, do i accept this since neither reaches .030 (Given: MISMATCH .030 MAX) or if this is a true position type of value do i reject?

Thanks again for the help

 

[brandnew1]

Nevermind, as i think about this more since MISMATCH appears to be a straight value, i believe a standard distance calculation should provide the information needed. So in this case of .020 and .005 the distance would be .0206, which is good.

 

[pmarc]

Both options could be correct depending on how the allowable mismatch was specified on a drawing.

For cylindrical features I would rather think of mismatch in radial direction, not in two orthogonal directions - but I have nothing from Y14.8 to support my statement.

 

[CheckerHater]

Mismatch as a diameter - love it!

I wonder what the experts have to say?

 

[dtmbiz]

Mismatch is the allowable offset of 2 mold halves coming together at the parting line.

The posted drawing allows for .030 MAX which equates to a max "step" at the parting line. There would be no X-Y measurments just the radial measurement ( y direction for posted dwg) between the two halves - the "permissible step" at the parting line.

 

[CheckerHater]

If two halves of a mold are allowed to move in relation to each other, is the movement always radial?

How about twist?

 

[pmarc]

CheckerHater,
Of course mismatch does not have to be always radial and for sure will not be. In fact in reality it will more a combination of shift, twist etc.

I was rather thinking of how the mismatch should be specified on a drawing to meet functional requirements, so in other words, how to describe theoretical boundary that must not be violated by forging surface when mismatch happens.

To have it visualized I imagined that cylindrical portion of a forging shown on OP's sketch is fitting to a round hole with .03 diametrical loose when both halves of cylinder are made at their MMC. Knowing that mismatch must occur, how should it be specified on a drawing to assure assembly? What should be the direction of mismatch measurements?

I have prepared very rough sketch of what I described:

http://files.engineering.com/getfil...00-83aa-d17e7ad3532f&file=radial_mismatch.JPG

IMO surface of GREEN half can extend (mismatch) beyond surface of BLACK half not more than .03 at every point of BLACK half's perimeter. This mismatch would have to be measured along every line that originates at the center of BLACK half and goes radially towards the outline (some of the lines were presented in BLUE).

This is the reason why I said that the mismatch should be considered in radial direction. However if the functional requirement is different (e.g. cylindrical forging is mated with square hole), then it does not make sense to measure mismatch in radial direction. It would be more reasonable to do it in two orthogonal directions x & y.

 

[brandnew1]

Hey guys,

Thanks for the input...i've learned a lot about mismatch in a short amount of time.

Let me just add the situation that has come about, based on the attached image what has me question the vendors results is that when i get a measure of the top half of parting line and compare to bottom half i measure distances as much as .040 (well above mismatch allowances - if i'm interpreting this correctly).

So when the part was first machined to blue print, the difference between Datum A to Datum B was roughly off by .030, which appears to match the original measurements.

Thus the reason why i wanted to make sure i'm interpreting Mismatch correctly.

 

[CheckerHater]

Thank you pmarc,

It looks like brandnew1 is satisfied with the explanation, but unfortunately I am not (yet).

It appears like mismatch is generally seen as "edge" feature, judging from dtmbiz's definition of "max "step" at the parting line" and brandnew1 reducing mismatch from .040 to .030 by machining the part (if I understood him correctly).

If you look in your copy of Y14.8 the Fig. 3.10-b shows mismatch as offset of features - any features, not necessarily the edges.

So it brings the bigger question: Is mismatch:

1. Control on par with Flash, or other "unspecified features" like sharp edges, burrs and other splinters
2. Control similar to locating feature of size (then diametrical tolerances may be in order)
3. Trying to control everything on one sde of parting line in relation to everyrhing on the other side of parting line.

So, when a mismatch is not a mismatch anymore?

Is there a strong opinion about interpretation of mismatch, or like I already asked, what our experts have to say?

 

[ptruitt]

I had a similar question awhile back. I started out with a sample drawing that I tweaked and resubmitted based on some valuable advise. People seemed satisfied with my second try, so maybe following that discussion thread would be helpful:

http://www.eng-tips.com/viewthread.cfm?qid=288484&page=3

Peter Truitt
Minnesota

 

[CheckerHater]

Thank you Peter,

I liked your drawing, in fact I liked your first drawing more

Unfortunately you did not use Mismatch on your drawing and the limits of using "mismatch" is exactly what I am looking for.

Something like "if it could be described using "MIN" and "MAX" (mostly MAX), then it's mismatch, but if it requires more detailed measurement, use profile"

 

[brandnew1]

Hi all,

So as i read more the question brought about i don't really think the 14.8 standard is giving much of a good example in the case i have. As asked earlier, is MISMATCH:

1. Control on par with Flash, or other "unspecified features" like sharp edges, burrs and other splinters
2. Control similar to locating feature of size (then diametrical tolerances may be in order)
3. Trying to control everything on one side of parting line in relation to everything on the other side of parting line.

i figure points 2 or 3 would be more in-order compared to just utilizing the flash. The pictures shown on the standard doesn't show anything that deal with say the center point of a forging. i actually have the example straight from the standard, however i modified it to show what i'm seeing in terms of centerlines of the forging. i hope this identifies more closely to what i'm dealing with right now