Zinc plating spec too tight 2

[unp1]

Plating spec for a screw machine part is .00025-.00040 zinc & yellow chromate. Is this too tight spec? Our maker in China has difficulty in meeting the spec. They are saying that it is too tight. Is it true? Thanks.

 

[TVP]

If the values that you provided are in inches, then they convert to 6-10 micrometers. This is a reasonable specification, especially for threaded components. GMW3044 requires that the maximum thickness be less than 2x the minimum, which would only give an additional 2 micrometers for your example. A yellow chromate is typically only 0.2-0.5 micrometers thick, so this does not add very much to the total thickness.

 

[unp1]

Hi TVP,

Yes, the values are in inches, but this part is not a threaded part. Thanks.

 

[limct]

It's rather common to see 5 microns tolerance specified for such finishing, eg. 0.003~0.008. Your's requirement is around 4 micronsand should not be an issue.
I believe their concern is over the geometry of your components, is your part looks complicated? or is it a long shaft with relatively small diameter?

Best regards,
ct

 

[unp1]

Hi limct,

My part is a very simple and small screw machine part. It is a new part, so I submitted a PPAP (ISIR) with 5 samples. The required spec is .00025"-.00040" thick zinc yellow chromate. My samples were .00032"-.00042" thick. The PPAP was rejected by our customer who is a large US based electrical industry giant. They want the plating thickness strictly between .00025"-.00040". My Chinese vendor says that this tolerance it too tight and we can't work with this type of tolerance.

It is really frustrating for me. We have contacts in Asian countries and get the screw machine parts and other products from there for our US customers. China is a new addition for us. I really had bad experiences with Chinese vendors; Korean and Taiwanese are ok. Due to heavy pricing pressure from US customers, we have to choose Chinese vendors. In the beginning, they (Chinese) agree for a project. They don’t even look at the drawings carefully. Once the project starts, they find all the strict requirements mentioned on the drawings. They don’t follow the material and finish specs mentioned on the drawing; rather they just follow the Chinese industry standards. We reject the samples. This happen few times and they want to drop the project. We have to do compromise, price increase and such things that are favorable to them. They are ISO 9000 and QS 9000 certified by registrars like BSI, but many times their responsible person asks us stupid questions which we never can imagine. They ask us questions like, “instead of 1141 (or 1144) mentioned on the drawing; can we use 12L14, there won’t be any problem because we here in China use 12L14 for screw machine parts. It is a very common material!” In one incidence, they submitted a plating cert and 6 out of 11 samples were non-conforming because the thickness was below the spec. I rejected the part and in response of the rejection, they told me that the average plating thickness of the 11 samples is within the spec and so it should not be rejected. It was a big surprise for me. After a project has already been started and few months have passed, they are willing to drop the low volume (EAU) parts even though the annual usage quantity was given to them for all the parts with RFQ. Usually their strategy is grab the project anyhow, start the project and at a later stage, do only high volume and easy to manufacture parts. At this point, we are at a point of no return and have no other choice but to give them rise in the price. Their quality is not comparable with US manufacturer. I can see clear difference between US made and Chinese made parts. I even never satisfied with a Chinese made consumer product. Last year I bought a room heater. I had to try four or five different good brands to find a good quality heater. Each heater I tried, I found quality problems that can’t be tolerated. I have seen Chinese products and have experienced Chinese manufacturers, now I don’t have trust on them or their products.

I am just expressing my experiences here and am sure that many of the readers of Eng-Tips Forums also had bad experiences with Chinese. When my vendor told me about the above problem of plating thickness, I decided to put it on this forum to know if what they are saying is really true. Thanks.

 

[limct]

Hi Unp1,
I can tell you frustation, because I did experience the same issue with some kind of the Chinese experts. My advise to you is, do watch out the followings criteria when you're dealing with Chinese sub con.
1) heat treatment
2) precision plating
3) when material strength / propery (magnetic, grain size..etc) is important

My experience tells me that proper audit and extensive monitoring is required for projects running in China. Good luck.
P.s. like the old folk says "A fall in the pit, a gain in your wit".

Best regards,
ct

 

[TVP]

unp1,

I think there are many people who share your frustration when forced to work with new suppliers. It isn't just Chinese suppliers that have these problems-- it also occurs in North America and Europe when the supplier is not technically competent. They do not understand all of the drawing requirements, and complain when their parts are rejected for not meeting the requirements. I feel your pain.

 

[unp1]

Hi limct and TVP,

Thanks for your comments, I feel better now!