Gordon,

I have a question on the tolerance capability level for thermal spray processes
.
I would like to know, what is the best tolerance (i.e. +/- 0.00x) that can be achieved with HVOF or Air Plasma?

For my process
1. APS - I could achieve a deposition rate in the range of 0.001"~0.003" per pass.

2. HVOF - I could achieve a deposition rate in the range of 0.00025 ~0.0005

Any information would be appreciated!

Thanks.

Regards,
Alex

Hi Alex

Generally speaking on simple substrate parts within a few 0.001" should possible. There are many factors that could influence the thickness tolerance:

• Substrate geometry
• Gun manipulation (manual, robotic etc.)
• Overall coating thickness needed
• Coating application rate and thickness per pass
• Surface preparation roughness
• Powder type, particle size and spray parameters
• Texture of particular coating
• General accuracy of equipment and measurement systems
  

Setting a tolerance could also be influence by your finishing method or whether the coating is to be used as sprayed.

Really it comes down to determining practical tolerances for each particular job. I suspect you may be production spraying, in which case you may be more experienced/qualified to answer your own question than myself

Gordon,

Thanks for lighting my way. My intention is to have a standard of the tolerance limit as a guidance to the measurement system when performing Guage R&R(Repeatbability & Reproducibility)

what you said is true. All the factors are critical and are also sources of variation.

As measurement of coating thickness is a process and like any process, is subject to variation. The product of measurement process is a number, which we will use as data. The measuring tools and skills of the technician is very important to decide the have got the thickness measurement right.

Another factor would be the instrument used by technician difference with the one used by the Inspectors. So alot of the sources of variation could contribute to the defective data of the thickness measurement.

By knowing the tolerance limit as least we can minimize the thickness overmax or undermin problem. Anyway, this is just a small matter.

Thanks for the advice, I will set the tolerance limit based on our in-house spraying capability.

Regards,
Alex

Alexangel1226 Wrote:Gordon,

Thanks for lighting my way. My intention is to have a standard of the tolerance limit as a guidance to the measurement system when performing Guage R&R(Repeatbability & Reproducibility)

what you said is true. All the factors are critical and are also sources of variation.

As measurement of coating thickness is a process and like any process, is subject to variation. The product of measurement process is a number, which we will use as data. The measuring tools and skills of the technician is very important to decide the have got the thickness measurement right.

Another factor would be the instrument used by technician difference with the one used by the Inspectors. So alot of the sources of variation could contribute to the defective data of the thickness measurement.

By knowing the tolerance limit as least we can minimize the thickness overmax or undermin problem. Anyway, this is just a small matter.

Thanks for the advice, I will set the tolerance limit based on our in-house spraying capability.

Regards,
Alex

Adding just a "historical" story from my days in Sweden. In this job shop spray operators were doing the coating job and the finishing was done by the machine workers. After years of struggle on when the work allowance on a sprayed coating was optimal, they decided that the final measurement of the work peace had to be made by the finishing operator.
br bhe

bhellman Wrote:

Alexangel1226 Wrote:Gordon,

Thanks for lighting my way. My intention is to have a standard of the tolerance limit as a guidance to the measurement system when performing Guage R&R(Repeatbability & Reproducibility)

what you said is true. All the factors are critical and are also sources of variation.

As measurement of coating thickness is a process and like any process, is subject to variation. The product of measurement process is a number, which we will use as data. The measuring tools and skills of the technician is very important to decide the have got the thickness measurement right.

Another factor would be the instrument used by technician difference with the one used by the Inspectors. So alot of the sources of variation could contribute to the defective data of the thickness measurement.

By knowing the tolerance limit as least we can minimize the thickness overmax or undermin problem. Anyway, this is just a small matter.

Thanks for the advice, I will set the tolerance limit based on our in-house spraying capability.

Regards,
Alex

Adding just a "historical" story from my days in Sweden. In this job shop spray operators were doing the coating job and the finishing was done by the machine workers. After years of struggle on when the work allowance on a sprayed coating was optimal, they decided that the final measurement of the work peace had to be made by the finishing operator.
br bhe

hello everybody
me i use the weight for tolerance on hvof ;i mean +10g/-10g a mn of carbide .in general we use 100g/mn

hvofhamid Wrote:hello everybody
me i use the weight for tolerance on hvof ;i mean +10g/-10g a mn of carbide .in general we use 100g/mn

hello every body
i think gordon has resumed all factors in his intervention,I will just give some details.
-more pressure of gaz can help to loose powder
-distance of proection=turbulence and less of powder adhrence
-angle of projection can be responsible " "
-rugosity
-speed of robot
-also the size of diametre you are coating must have a good speed of robot and rotation
excuse my bad english
have nice time to all

HvoFhamid,

Thanks for your opinion sharing.

What I read from you is you control the feedrate and set a torelence for it. Right?

Well, as feedrate always fluctuates esp when we use a close loop hopper, it does have a high low range and probably we can fix it and high/low alrm, or system cut-off..

But this rreading does not necessarily translate into coating thickness measurement, because the deposition rate is vaque. Unless u know it, then ok, e.g x g/min = y deposition rate.

What I am trying to say is, the actual in house spraying capability is more critical and practical to used as tolerance setting on thickness I guess. With all factors that is affecting the thickness build up, we should use the set parameter e.g: rot, diameter,gun traverse speed, powder feedrate for diff powder..to develop the tolerance.

Second thought of it..if we could achieve 0.001"/pass spraying..I think it is perfectly fine to ignore this matter as the tolerance seems too insignificant. and control it on doc just put 0.001 +/- 0.0002" is good enough. =)

Regards,
Alex

Alexangel1226 Wrote:HvoFhamid,

Thanks for your opinion sharing.

What I read from you is you control the feedrate and set a torelence for it. Right?

Well, as feedrate always fluctuates esp when we use a close loop hopper, it does have a high low range and probably we can fix it and high/low alrm, or system cut-off..

But this rreading does not necessarily translate into coating thickness measurement, because the deposition rate is vaque. Unless u know it, then ok, e.g x g/min = y deposition rate.

What I am trying to say is, the actual in house spraying capability is more critical and practical to used as tolerance setting on thickness I guess. With all factors that is affecting the thickness build up, we should use the set parameter e.g: rot, diameter,gun traverse speed, powder feedrate for diff powder..to develop the tolerance.

Second thought of it..if we could achieve 0.001"/pass spraying..I think it is perfectly fine to ignore this matter as the tolerance seems too insignificant. and control it on doc just put 0.001 +/- 0.0002" is good enough. =)

Regards,
Alex

excuse me i will talk in french ,de tout facon un micron ou 2 micron ne gene en rien ton revetement ,vu qu il va etre rectifié
les 10 g de tolerance me permette juste d ajuster le nombre de passe que je dois faire sur un diametre quelconque.si ton distributeur de poudre a la bonne pression ,et que tu n a pas de fuite sur ton circuit de poudre, et que tu a une bonne machine ,ton revetement sera impecable
avec mes respect hvofhamid