Profile Tolerances and Tooling Development

[JModelsalot]

Hello all,

I am looking for some advice from people utilizing profile tolerancing schemes. I have proposed a host of drawings utilizing profile tolerances to simplify some drawings and better/more simply define what is desired from injection molded parts.

I am getting push back from vendors suggesting that a profile will make it very difficult to adjust tooling when they 3d scan parts. This makes sense as you would then need to identify what location is out and what part of tooling needs to be adjusted which is easier if you have a direct length or width of a feature.

My question is, how do people deal with this situation? For geometry that has a complex profile, it seems like a waste of time to stack positional dimensions and clutter up a drawing when you only need to know if "Box A" will fit in "Box B".

Thanks for taking a look, I'm curious to see what people have done to work through this.

 

[3DDave]

"very difficult." Yeah. Doing work is like that. They are likely looking for a bump in spending.

 

[Burunduk]

CMM and other measuring machine programs have options for graphical display of surfaces deviations on the 3D model with color maps (red=extra material, blue=lack of material) and the values displayed for deviations at the location where they occur. Also the generated measurement reports can include those surface deviations as some auxiliary data with coordinates based on a measurement coordinate system. This is actually covered in the new ASME Y14.45 standard on measurement data reporting. All this should aid manufacturing process control.

 

[JModelsalot]

I dont disagree 3DDave but what is the process for retooling once things are out of spec? How do you find the correct tooling change locations?

Is there an easy way that people in industry correlate an out of spec location on a 3d scan to a 2d drawing?

 

[JModelsalot]

@Burunduk,

That all makes sense and its why I would like to utilize profiles rather than position on something we typically call "that surface profile".

Since I'm not a mold manufacturer I'm trying to find those tools that would allow me to say, hey, you do it like this and it's not really any more difficult(hopefully less so) than what you are doing currently.

Thanks for the post.

 

[3DDave]

Uh, take a CAD model of the tooling and overlay with the 3D scan and the intended model? This is a 5 minute job.

I think you are asking "How do I set a broken bone." Like there is one method that applies to every possible break in every possible location in every bone in a person. There isn't. It takes looking at the process and the error and actually thinking about it. If they actually are unable to think about it then you need to find ones who can. Or just keep making the profile tolerance larger - I find that 3 doublings is enough for most suppliers to make compliant, though likely useless, parts.

 

[Burunduk]

JModelsalot,
I must be not understanding something.
Surface deviations that are made available as part of profile of a surface measurement tell the manufacturer where the deviation of the part surface from the nominal geometry is, what is the amount of the deviation in linear units of measure, and at what direction! (I forgot to mention - they are represented as a positive value for extra material and a negative value for a deviation that removes material). What could be better for a vendor to tell them how to adjust the tooling to make a good part? This is spoon-feeding them the info they need to do their job. Why would they prefer directly toleranced dimensions?

 

[JModelsalot]

Burunduk,

Honestly I have already thought exactly what you and 3DDave have mentioned. I posted here to see if anyone using said tolerance scheme could tell me what I must be missing.

I'm wondering if I'm up against the "thats not the way we have been doing it" mentality and people are not willing to get out of their box to do it better.

I appreciate the replies guys.

 

[Burunduk]

If you're up against the mentality of not willing to improve because improvement requires a change, you'll have a hard time trying to make the vendors like or understand profile tolerances. This might be not the kind of suggestion that you wanted - but maybe you should change the tactic, and decide that profile of a surface is your requirement, not something that you ask the vendors to agree with. You know the advantages - it must be true that profile of a surface better describes the function and provides more unambiguous definition of your part's geometrical limits. If they know this is part of the requirement, the best of them who need the job will make the effort to cooperate. It might be also a good way to select the more competent ones who will know what they are doing, understand tolerances and can be trusted for the job. Will you be able to get the back-up for it from your company?