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VDI What does this mean in surface finish terms?

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Q. Our company is a supplier to the automotive industry worldwide. We are a plastic injection moulding company in the North East of the UK and manufacture our own mould tools. For surface finishes on our tooling we have used VDI comparator blocks. Can anybody tell me what the initials "VDI" stand for?

Cheers.

Graeme Hutton
Plastic Injection Molding & Tools - Stockton on Tees, Cleveland, UK

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Q. I also want to know about the VDI finish and its conversion in Ra value. Is it EDM related term if yes then how is it controlled?

Waiting for your positive response,

Faizal
designing - Udaipur, Rajasthan, India


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Q. Same questions as previously posted by others: a formal comparison of VDI to Ra? information on VDI - what is it?

Ray Smith
- Huntingdon, UK


April 30, 2013

A. Hi. VDI = Verein Deutscher Ingenieure, the Society of German Engineers. There is a VDI scale for surface finishes, which is widely but not exclusively used in the EDM field. My lack of German has hampered my search for a cross reference chart or a description of what the VDI scale is about, but hopefully a reader will help.

Regards,

pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Brick, New Jersey


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A. I had the same problem with VDI grades. The solution came from Rubert & co. England. They offer EDM finish scale to VDI 3400 standard. It comes with comparison table Ra values. For more information: http://www.rubert.co.uk/comparison.php

Jaakko Havola
Medical equipment - Helsinki, Finland

----
Ed. note: Update April 2013 -- The referenced link no longer works, and it appears that that website no longer includes any such charts.



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A. I have the same problem to find a correspondence between VDI and Ra, and after some search I made this comparison table :

VDI   RA (in micrometer)
10    0.32
12    0.4
15    0.56
18    0.8
21    1.12
22    1.26
24    1.6
27    2.24
30    3.15
33    4.5
36    6.3
39    9
42   12.5
45   18

Best Regards.

David Bourdin
- Bobigny, France


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Q. We have the VDI 3400.39 grain call out on a print for a part we are to supply. Can anyone tell me the depth of this grain and the draft required to eject the part with this grain?

Sabrina Arsenault
- Barrie, Ontario, Canada


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A. Bayer Plastics has some good Information about surfaces and injection molding available on their web- Site.

According to a (German) Document the VDI surfaces correspond to the following Ra / Rz Values and require the following drafting angles:

VDI;   Ra;     Rz;    DA-PA;   DA-PC;   DA-ABS
12;    0,40;   1,5;   0;      1,0;     0,5
15;    0,56;   2,4;   0,5;     1,0;     0,5
18;    0,80;   3,3;   0,5;     1,0;     0,5
21;    1,12;   4,7;   0,5;     1,0;     0,5
24;    1,60;   6,5;   0,5;     1,5;     1,0
27;    2,24;  10,5;   1,0;     2,0;     1,5
30;    3,15;  12,5;   1,5;     2,0;     2,0
33;    4,50;  17,5;   2,0;     3,0;     2,5
36;    6,30;  24,0;   2,5;     4,0;     3,0
39;    9,00;  34,0;   3,0;     5,0;     4,0
42;   12,50;  48,0;   4,0;     6,0;     5,0
45;   18,00;  69,0;   5,0;     7,0

DA-PA = Drafting Angle for Polyamide
DA-PC = Drafting Angle for Polycarbonate
DA-ABS = Drafting Angle for Acrilnitrile-Butadiene-Styrol

glass reinforced materials require more drafting

Lorenz Wiedemar
- Langendorf, Switzerland


February 22, 2012

But be careful: The table with the VDI related draft angles Mr. Lorenz Wiedemar provided (he says it's from BAYER plastics) is possibly not right!

For example:

STANDEX International communicates that their VDI 36 equivalent (MT 11540) requires minimum 3,5 even for PA !!
So just ask your surface supplier BEFORE being fooled by this table (like me).

Simon Mueller
- Fuerth, Bavaria, Germany


February 22, 2012

Hi, Simon. Thanks!

I have never found any surface standards for which "conversion" or "substitution" is actually possible. Rather, it is like comparing people's height vs. weight, or torque vs. horsepower -- one parameter tends to "track" the other, but cannot actually be converted. We see this in Ra vs Rz where the "conversion factor" must be low in one direction to be relatively safe and much higher in the other direction to be relatively safe because they are simply not the same thing.

My unfortunate lack of German prevents me from understanding VDI standards and how they translate to other systems, but it would greatly surprise me if there is an actual conversion rather than "usually roughly equivalent to somewhere around . . ."   :-)

Regards,

pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Brick, New Jersey


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A. VDI = 20log(10Ra)

James Lai
- JB, Malaysia


April 4, 2011

A. Nr is the number of roughness or the class, using VDI d

Nr=20*log(10*Ra)

Try with the equivalence table.

Aitor

Aitor Ruiz
- Basq Country (north of Spain)

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A. VDI Table
In the following, you can determine the roughness for your application according to VDI table.

VDI3400 Ra = AA = CLA              ISO1302 Rt
0-45    µm       µinch    N3-N10   µm
-----  -----    -----    -----    -----
0    |  0.1   |   4    |   N3   |
1    |  0.11  |   4.4  |        |
2    |  0.12  |   4.8  |        |
3    |  0.14  |   5.6  |        |
4    |  0.16  |   6.4  |        |
5    |  0.18  |   7.2  |   N4   |
6    |  0.2   |   8    |        |
7    |  0.22  |   8.8  |        |  
8    |  0.25  |  10    |        |
9    |  0.28  |  11.2  |        | 
10   |  0.32  |  12.8  |        |  
11   |  0.35  |  14    |   N5   |
12   |  0.4   |  16    |        |  1.6
13   |  0.45  |  18    |        |
14   |  0.5   |  20    |        |
15   |  0.56  |  22.4  |        |  3.2
16   |  0.63  |  25.2  |        | 
17   |  0.7   |  28    |        |
18   |  0.8   |  32    |   N6   |  5
19   |  0.9   |  36    |        |
20   |  1     |  40    |        |
21   |  1.12  |  44.8  |        |  7.5
22   |  1.26  |  50.4  |        | 
23   |  1.4   |  56    |        |
24   |  1.62  |  63    |        |  12
25   |  1.8   |  72    |   N7   |
26   |  2     |  80    |        |
27   |  2.2   |  88    |        |  16
28   |  2.5   | 100    |        |
29   |  2.8   | 112    |        |
30   |  3.2   | 125    |   N8   |  20
31   |  3.5   | 140    |        |
32   |  4     | 160    |        |
33   |  4.5   | 180    |        |  25
34   |  5     | 200    |        |
35   |  5.6   | 224    |        |
36   |  6.3   | 250    |   N9   |  37
37   |  7     | 280    |        |
38   |  8     | 320    |        |
39   |  9     | 360    |        |  46
40   | 10     | 100    |        |
41   | 11.2   | 448    |        |
42   | 12.6   | 500    |   N10  |  60
43   | 14     | 560    |        |
44   | 16     | 640    |        |
45   | 18     | 760    |        |  85
Qijin Wu
- Nanjing Jiansu Province, P.R.China


August 16, 2008

Q. Besides surface finishing of VDI standards, there is another standard SPL-2, would like to know the relation of VDI versus SPL-2, how to convert SPL-2 into VDI?

Cherwei Li
- Penang


October 27, 2008

Q. Hello, is there anybody who knows how is possible to compare VDI scale to SPI scale?

Paolo Aprile
Datasensor - Bologna, Italy



April 29, 2013

Q. Hi, can anyone help me with VDI 27 (RA 2.24) finish? I need to know if it's like mirror polished or just EDM textured finish.
I am trying to order plastic molds and need Mirror finish polish for better clarity of molded parts, my mold maker says that VDI 27 is just EDM textured finish.
Any documented help on this will be highly appreciated.

Abdul Sina
- Dubai UAE
  ^- Privately contact this inquirer -^


June 4, 2013

A. VDI is a textured finish usually from spark eroding, for polished finish you should work on microns, lower the number higher the polish

Daniel David Wood
- Blyth England

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