Application of Datum Target Areas

[koodsg]

Hi guys,
Got messed up with the datum target areas definition and inspection methods. Could some one clarify on this?

There is necessity to use the datum target area to establish a primary datum surface A.
But
from design side the datum target area defined as dia of 50mm,
from manufacturing made the tool with the 50mm X 25mm rectangle tool index.

When I check the ASMY14.5 says the datum target area is tool target area, and not much clear definition with example.

My confusion is
Is the actual tool index target area must be the same as designed circular datum target area?
(or)
Is the smaller actual tool index target area allowed to fit inside the design defined datum target area? (in this case what is the minimum datum target area allowed by inspection tool?)

Some one help me to understand the exact definition of tool index of datum target according to ASMY14.5 or ISO?

See pictures shows the more details.

Thank you.

 

[tbuelna]

Your sketch does not provide enough information. It appears the intent of your fixture is to register the part at four contact points that comprise datum reference feature A. Your example is bit unusual since the primary datum points are located on a concave part surface. So your fixture should probably use something like spherical tooling balls for the locating features. And the contact points of the tooling balls should lie within the 50mm diameter target area defined in your sketch.

The minimum number of points required to establish a primary datum is typically three. By using more than the optimum number of constraints required, you may encounter a situation where the part does not contact all four gage surfaces of the fixture in a free-state condition.

 

[koodsg]

Thank you tbuelna,
Sorry for insufficient information

Yeah I agree with you an theoretical no deflection component needs just the three points to establish the primary datum, more than three will be state of free-condition.

In my case, Cargo door assembly is designed for this datum targets, which is monolithic structure approximately 250kg. If the spherical tooling balls (leads the Point contact) is used it might damage the skin due to the self weight thin skin. Current inspection method used is assembly jig, Quality used more then 4 target area's.

In case of the point contact of tool index the datum target point can be defined in the drawing.
and I reckon the datum target area inspection should use only datum target area's contact in the index.

My confusion is as I have explained in previous
the deviation allowed between the design defined datum target area and manufacturing (quality) physical tooling target size.
Cant found in ASME14.5 or ISO.

 

[tbuelna]

The plan view shown in your sketch of the inspection fixture would seem to conform with the datum target locations shown in the plan view of the part. But what is not shown is definition of the 4 inspection fixture points in the direction normal to the sketch plane.

 

[koodsg]

Here is the reference of ASME:

4.24.4 Datum Target Areas
Where it is determined that an area is necessary to
assure establishment of the simulated datum (that is,
where spherical or pointed pins would be inadequate),
a target area of the desired shape is specified. The datum
target area is indicated by section lines inside a phantom
outline of the desired shape, with controlling dimensions
added. The basic size of the area is given in the
upper half of the datum target symbol. See Figs. 3-9 and
4-48. Where it becomes impracticable to delineate a target
area in the upper half of the datum target symbol,
the method of indication shown in Figs. 3-6, 4-42, and
4-47 or basic dimensions may be used to define the shape
and size of the datum target area.


Cant find the reference for the rectangle datum target area in ASME,
[highlight #EF2929]clarification required for the size of the inspection tooling datum targets deviations accepted (tooling Pins)[/highlight]

Figure 4-48 is attached

 

[tbuelna]

I think you are a bit confused. The design of the inspection fixture must conform to what is defined on your part drawing. The plan view of your part sketch shows dimensional limits for the primary datum point locations on the part surface. So the dimensions of the mating locating features of the inspection fixture must agree. While it appears that the part datum points agree with fixture datum points in a plan view, there is no way to know if they also agree in other orientations.

 

[drawoh]

koodsg,

Someone has borrowed my copy of ASME 14.5-2009. According to ASME Y14.5M-1994, the datum target area specifies the area of contact. Your fixture must contact the whole specified area. The 25[×]50mm tool indices are wrong.

The contact area specification is optional. If you leave it out, tbuelna's suggestion of spherical tooling balls becomes functional.

If your part is rigid, you need only three points to define a primary datum. Read up on Free State Variation. Your four points can be valid if you provide clamping information. Perhaps you can specify the maximum force required to engage all four datum targets. Your datums are supposed to simulate how your part will be installed.

--
JHG

 

[3DDave]

The point of specifying a location and a size for a target point is so that various members of the team have a single description of the means to establish the datums. If manufacturing or inspection uses something else it is possible to accept an unusable part or reject a useable one.

I suspect there is a lot of information missing from the simplified example of your part. Four points on a part that has cylindricity will force an orientation of that surface that is likely not what is desired in this case.

There is also insufficient description of how the targets are to account for the curvature.

It's possible the item is meant to be restrained to conform, but there is not enough info to know.

TL;DR - the targets used in manufacturing and inspection should be the same as on the drawing.

 

[tbuelna]

I can see where there might be some confusion. Each of the four primary datum target areas shown in the OP sketch are 50mm in diameter. If you follow the letter of ASME Y14.5-2009, the part being inspected with this fixture must have conformal contact over the entire 50mm (or almost 2 inch) diameter surface area of all four datum locations. To achieve this condition of restraint would likely require a substantial amount of clamping force applied to the part.