How to check concavity presence in a flat strip in a 50 mm length

How to check concavity presence in a flat strip in a 50 mm lengthThat depends: What is the requirement? More data, please.

I.e: Is it supposed to be concave or is this a deviation from a flatness reqirement?

If it is a flatness deviation, there are several ways, depending on the requirement. The simplest way would be to put it on a flat surface and measure the gap between surface and part.

/Claes

Hi

Find the drawing attached, concavity measurment is required in the flat portions.

First step is to ensure presence of concavity, next step is to measure the concavity, spec is 50 micron max

That specification is rubbish I am afraid.

There is no such thing as 'concavity' for a start. If the area of the part has to have some form/shape then this should be specified in terms of technical dimensions/references - not some made up word like concavity.

The sentence that is should be concave in the flat area is a contradiction in terms in itself !

Its impossible to measure because it is not correctly technically specified - throw it back to the drawing office !!

I would try this: set a couple of 1,2,3, blocks on a surface plate and then "straddle" the part on the blocks as seen in view labeled "cross section A-A" so that the flat area sets on the blocks, but there is a gap wide enough to sweep a dial indicator underneath (on the "flat area"). I would use a .0001 in. indicator. Your total indicator reading should be less than 0.05 mm. Hope this helps.

Hi, it is pretty common to have a concave or convex requirement for a flat surface area. No surface is flat. The easiest way (tolerance of 50um) to measure is use a form tracer or strip chart recorder or maybe an optical system.

K.

Hi, it is pretty common to have a concave or convex requirement for a flat surface area.


I've never seen it specified like this. I'm with M Greenaway--the drawing makes no sense on any level. If a prescribed area of the part is supposed to be flat, there should be flatness callout and associated tolerance. If flatness is allowed in only one axis or direction, that should be called out in association with the flatness specification. As it is, there's no telling what was intended.

Well, I disagree. For example for roller bearings, the surfaces are flat. Under magnification these surface have a concave or convex form.The drawing specifies a concavity requirement for the surface in microns. A tracing device is used to measure this form requirement. For certain surfaces a min and max concavity is specified and for some surfaces convexity is not allowed.

K.

I've never seen it specified like this. I'm with M Greenaway--the drawing makes no sense on any level. If a prescribed area of the part is supposed to be flat, there should be flatness callout and associated tolerance. If flatness is allowed in only one axis or direction, that should be called out in association with the flatness specification. As it is, there's no telling what was intended.


I have to agree. In general on this drawing, I'm seeing a whole lot of "should"s and targets, i.e. "this area should be concave", and "concaved amount of flat area should be carried out molding targeting 0.05 max" which means to me that is what the customer would like, but is not a solid requirement. I thought at first that there may just be a translation issue, but they have used "shall" in one of their notes, which tells me they may be aware of the difference.

If I were the QE on this part, I would take it back to the customer for clarification of what they need.

it is pretty common to have a concave or convex requirement for a flat surface area. No surface is flat. I agree that no surface is flat, but the question is what you are aiming for: A flat surface or a shape? In psavijay's case a shape seems to be desired? The question is whether it is within tolerance or not.

...the surfaces are flat. Under magnification these surface have a concave or convex form.Um... I would assume that the shape stays the same regardless of magnification... Anyway: Once more, the question is what one is aiming for. Should the surface be flat or have a certain shape?

If I were the QE on this part, I would take it back to the customer for clarification of what they need.So would I. The flat and concave surface really threw me off track...

Slightly :topic: but interesting: Is this a new part or something psavijay's company has been producing for years? If the product works some caution should be excercised when updating the drawing.

/Claes

I have seen similar callouts before. The customer typically wants a flat surface, but recognizes that no surface is perfectly flat. Therefore, they want any deviation from flat to go in a specific direction. Since this part has a punched hole in this surface that will cause some degree of concavity in a consistent direction, the net effect is to specify from which direction the hole must be punched.

In similar parts that are secured with fasteners to another surface, a surface curve one direction will result in a preload on the fastener to flatten the surface while a curve in the opposite direction will not preload it.

In a GDT world, a Profile callout with phantom lines should have been used to illustrate the intent.

Pls bear with my delayed response. First of all thanks to all responded.

This part is new, under development in my organisation, all the requirement mentioned in the drawing is based on customer requirements (Customer is Japan based).

Manufacturing process is Blanking, Bending in mechanical press and Austempering heat treatment, We do have surf tester, profile tracer to check the profile shape, concavity and flat length. But the problem is Process capability, A team is working on improving process capability in Bending and Heat treatment, I am planning, want to introduce some simple solution to measure the concavity (Time taken in surf tester 2 min/ component and checking Process is scan the profile, draw the profile graph, scale it, measure it from graph).
Customer requirement- if the process is not capable introduce 100% inspection per month qty requirement 50000, So I want to find some solution for measurment.

Still we are unable to set the inspection technique. Any solution, Please help.

I will start of the conversation on the measurement technique with this (expecting all kinds of additional opinions to follow):

To measure for concavity for the part, the most correct way I would propose a fixture with 3 posts (see Fixture 1 sketch attached) that would establish the the plane on the same side of the part (3 point define a plane). You will have to suply a force on the top of the part to keep it in place. I would keep the singe post towards the transition, and also keep it away from the transition, as any interference by the transition to the location the post is at, will be error.

I would then zero out a balanced indicator or test indicator at a location very close to one of the posts, and scan the surface, expecting the data to go negative as concave. Any positive numbers would be convex, and a problem.

Another, less accurate but easier to accomplish approach, would be a fixture with 3 posts (see Fixture 2 sketch attached) that would establish the the plane on the opposite side of the part. It will be affected by material thickness variation, but is a lot easier to set up and measure.

I would then zero out a balanced indicator or test indicator at a location directly above one of the posts, and scan the surface, expecting the data to go negative as concave. Any positive numbers would be convex, and a problem.

Can you use optical flats to validate your flatness callout?

Can you use optical flats to validate your flatness callout?

:agree1: Good idea - but be careful if there are any burrs on the surface!

Customer requirement- if the process is not capable introduce 100% inspection per month qty requirement 50000, So I want to find some solution for measurement.

If you find you need to do 100% inspection, either laser or optical may be fast enough to automate to verify the surface. There are laser and vision systems set up for high speed inspections...just need to get the right sources for quotes.

If you find you need to do 100% inspection, either laser or optical may be fast enough to automate to verify the surface. There are laser and vision systems set up for high speed inspections...just need to get the right sources for quotes.


Thanks bobdoering,

I will try first the one with indicator and will come back.

Raj