metaletch application sheet. - universal marking grid whitepaper 2… · the universal marking...
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Electrochemical
Strain Grid Marking
Moving Marking Technology Forward
Strain Grid Marking Equipment
Strain grid marking has become, over the years, the standard method for analysing stress in sheet metal forming.
We manufacture two power units capable of producing the large, geometric patterns required for analysis. These
patterns are laid down directly on to the surface of the sheet, prior to forming, by oxidising the material with
electro-chemistry. This process is favoured, due to the ease of marking and speed of operation. More importantly
however, the process is stress free, and ` forms a permanent mark without compromising the structure of the
material. Most metals form a dark oxide mark that can be measured with ease once the sheet metal is formed.
The ME96 and ME3000TSG Strain grid kits are designed specifically for strain grid marking applications and are
supplied as complete marking kits ready for use. The choice of machine will depend on the area that is to be
marked.
ME96 This is our heavy-duty strain grid marking kit. The machine can deliver 100amps output and can be used with our
largest strain grid stencils. Supplied with pistol roller with trigger operated output control.
Contents:-
Part Number Description Quantity
ME96 100 amp marking unit 1
UC10 & UC11 100 amp output cables (head cable UC10 is mounted into pistol
grip handle. EC11 Earth cable with clip. Cables 2m long
1 pr
UC8 output cables for hand marking. Cables 1m long. 1pr
R0ll280 280mm long single roller 50mm in diameter with pistol grip
handle and trigger
1
FP5D21p 280mm x 500mm pack of felt pads 1pk of 5
SG Strain grid stencil - customers choice 1
HM5 13mm x 31 mm hand marker 1
HM5/1 Spare felt / grid pads for HM5 1pk of 10
Mains cable and plug appropriate for country of use 1
ME8 1L of ME8 non-neutralising electrolyte for ferrous metal marking 1
ME5 lL of ME5 electrolyte for non-ferrous metal marking 1
MN2 lL neutraliser for ME5 electrolyte 1
ME3000TSG.
This machine gives a 20amp output and is
suited for relatively small strain grid
applications, typically 100mm wide marks. The
marking output can be set for continuous
output, or timed. The machine is supplied in a
high quality wooden instrument case with all
accessories required for marking including four
strain grid stencils. The kit also contains stencil
paper and an HM5 hand marker which are used
for part marking the test pieces.
Contents:-
Part Number Description Quantity
ME3000T20SG 20 amp marking unit 1
ME3000 kitbox Wooden kit box 1
UC8 1m long output cables 1pr
R0ll4 or
RM3
100mm wide roller or
100m wide rocker marker
1
FP2D21p 150mm x 200mm pack of felt pads 1pk of 5
SG77A Strain grid stencil 1
SG77B Strain grid stencil 1
SG77C Strain grid stencil 1
SG77D Strain grid stencil 1
HM5 13mm x 31 mm hand marker 1
HM5/1 Spare felt / grid pads for HM5 1pk of 10
FS8 Footswitch for timer control operation 1
Mains cable and plug appropriate for country of use 1
ME8 125 125ml of ME8 non-neutralising electrolyte for ferrous metal
marking
2 x 125ml
ME5 125ml of ME5 electrolyte for non-ferrous metal marking 1 x 125ml
MN2 125ml neutraliser for ME5 electrolyte 1 x 125ml
Note: Photo shows BRSK stencil tape as option for marking text on parts. Used with P-Touch printers.
Universal Marking Systems Application Information
This technique is used in many press-shops to reduce the time and costs of die try-out and to
transform press trouble-shooting from a series or random guesses into logical process. The
rudiments of this approach are described here.
Why circle grid analysis? In sheet metal forming we are looking at the permanent plastic
deformation of sheets by stretching, usually, in a complex way. If the sheet is marked in a non-
directional pattern (circles) then any deformation can be measured. If the pattern were, for
example, squares, then fruitful measurements would be impossible (fig.1).
It is necessary to cover a reasonable area - 250mm x 250mm, for example - when studying
sheet metal deformation, for the critical region of the stamping cannot be precisely pinpointed:
besides it can shift due to
variations in press setting and
lubrication, for instance.
How do we analyse what we
see?
A simple example is shown in
figure 2, considering only major
strain (or elongation).
It is now clear, even at this early
stage, why this approach is
termed circle grid analysis. But
one important point has not been settled. The circle size and pattern. The importance of circle
size is also demonstrated in figure 2.
If the original circle diameter had
been 50 units (assuming no space
between circles) then our analysis
would have shown 26%
elongation - and missed the
important peak of strain of 80%.
Widely spaced circles could also
miss peak strains, which could
occur between them.
An acceptable, well-tried design is
I 0
I 1
I 2
I 0
?
I 1 = M a j o r s t r e t c h
I 2 = M i n o r s t r e t c h
F i g u r e 1 .
U s e f u l i n f o r m a t i o n c a n b e d e r i v e d f r o m c i r c l e s , b u t n o t
s q u a r e s .
I 0
I 1 I 1 I 1 I 1 I 1
1 0 1 3 1 8 1 2 1 0
0 0 . 3 0 . 8 0 . 2 0
0 % 3 0 % 8 0 % 2 0 % 0 %
I 0 = 1 0 u n i t s
M a j o r s t r e t c h
S t r a i n e = I 1 - I 0
E l o n g a t i o n I 0
[ s t r a i n x 1 0 0 ]
F i g u r e 2
that of 0.1” or 2.0mm diameter circles, close but not touching, in arrays of four, delimited in a
square matrix for easy identification.
Other patterns approximating this concept are also acceptable.
Summarising at this stage: to be able to identify regions of high strain is useful in itself, but
stain measurements from deformed small-diameter circles can provide far more useful
information. Firstly, we must consider both major and minor strains. For a given major strain,
e1, the minor strain e2, can be positive, zero or negative.
This is illustrated in figure 3.
The point of supreme importance here is that if, on a split
pressing, a deformed circle, close fracture, but not distorted
by it, is measured and the major and minor strains
(elongation’s) calculated and this is done for a wide range of
strain combinations. The resultant plot of e1 vs. e2 is termed
a Forming Limit Diagram (Figure 4) and it separates
successful strain combinations.
The FLD’s can be constructed in the
laboratory using a stretch-forming press
and sheet metal blanks of varying widths
to give different strain combinations at a
fracture.
Different metals naturally give different
FLD’s. FLD’s for low alloy steels,
aluminium alloys and titanium sheet, for
example, gives FLD’s of widely differing
shapes and levels.
Conveniently, the shape of the FLD’s for the type of sheet steel used in the motorcar, domestic
appliance, container, etc., industries are very similar and fairly represented by figure 4. The
level of FLD however changes with steel grades - the best grade giving the highest, or putting it
more correctly, the major strain (e1) at a minor strain of zero (e2=0) is greater for a better steel
grade (this strain state is known as plane
strain).
Studying figure 5 it is clear that major strain
alone is an inadequate parameter, for e1 = 40%
would represent success at e2 = 40%, failure at
e2 = 0 and not a whisper of a problem at e2 = -
20%.
+ e 1 + e 1 + e 1
- e 2 e 2 = 0 + e 2
M i n o r s t r a i n s c a n b e n e g a t i v e , z e r o , p o s i t i v e .
F i g u r e 4 .
A f o r m i n g l i m i t d i a g r a m ( F L D )
0
0 . 1
0 . 2
0 . 3
0 . 4
0 . 5
0 . 6
0 . 7
- 0 . 5 0 0 . 5
M a j o r s t r a i n
+ e 1
Typical of sheet
steel
Minor strain -e2 Major strain +e2
Succeed
Fail
Fail
Succeed
0
2 0
4 0
6 0
8 0
1 0 0
- 5 0 0 5 0
X Y
( S c a t t e r ) 1
% Elongation
Figure 5.
The importance of the minor strain
It is often instructive to represent the
strains in a panel by a plot of major
values taken in the critical area shown
in figure 6, with the values approaching
a ‘ ceiling’ - this will be the minor strain
limit from the FLD. Assume for a
moment that this is a die- try out
situation. It is now possible to see how
close a successful pressing is to failure.
If too close then action should be taken
before putting tools into production.
Take now a production splitting
problem represented in figure 8. The problem is now to move a ‘below the line’ and this can be
done in various ways by press adjustment, by lubrication, by changing the sheet metal. Until
the advent of FLD, it had now been
realised that failure could be
changed to success by increasing
the total strain, i.e. increasing e2
by the route A C.
The FLD is the most important
contribution to sheet metal forming
technology of the last 30 years and
now accepted in the press-shops of
the world as a method for firstly,
assigning a degree of severity to a
pressing and, secondly, as a logical
approach to remedying production stamping problems in the press shop.
LimitMajor
Strain
Only critical circles shown
Figure 6.
Severity point - how near is the part to failure?
Figure 7
0
10
20
30
40
50
60
70
80
-40 -20 0 20 40
B
A
C
Marking Information
The Universal Marking Systems strain grid marking equipment can be used on ferrous and non-
ferrous metals, producing either an oxide or etched mark on the test piece. The marking
process is quite simple and fast and is ideal for on-site testing. It is important to follow the
instructions of the equipment and solutions being used. Please contact us or your local Agent
or distributor for copies of our product sheets.
Ferrous metals.
There are a number of electrolytes that can be used, but ME8 is good choice due to its non-
neutralising properties. It will produce a good dark oxide mark on most grades steels. For a
very black mark on mild steels, then ME3 can be used but care must be taken to neutralise the
mark afterwards. For stainless steels, then ME6 is a good electrolyte to use, again neutralising
is important.
Non-ferrous metals.
ME5 is a good general-purpose electrolyte that will produce a white or grey oxide mark on
aluminium or can be used to etched mark. Neutralising must be done after marking.
Technique.
1. Use a large flat workspace for the marking process
allowing room for the test piece and the equipment
to be set-up and used safely.
2. Lay the test piece on the flat surface and degrease
and wipe dry.
3. Position the equipment close enough to the test
piece so the output cables reach easily.
4. Place the stencil onto the test piece in the correct area where the analysis is to be taken
after pressing or forming.
5. Lay the felt pad on top of the stencil
6. Soak the felt pad in fresh electrolyte. Use the roller marker to distribute the electrolyte over
the complete area of the felt pad.
7. Using a tissue, soak up any excess electrolyte that may over spill onto the test piece.
8. Set the marking unit for marking. According to oxide or etch marking and for the electrolyte
that is being used.
9. Place the roller marker on the felt pad close to the edge.
10. Depress the trigger on the pistol grip (ME96 roller marker) and gently using the weight of
the roller. Roll over the length of the stencil pattern several times.
11. Gently, lift the corner of the stencil to see if the
mark is clear. If not roll over the stencil again
until the desired mark is obtained.
12. Remover the felt and stencil
13. Place them in a tray if they are to be used again
or wash them out in cold running water and
store carefully.
14. Dry the test piece with clean tissue.
15. If required, neutralise with the appropriate
neutralising solution (MN1 for ferrous metals or MN4 as an immersion neutraliser or MN2
for non-ferrous metals).
Press or form the test piece
and measure the results.
Measuring the results.
The simplest way is to use our Universal Marking Systems Mylar rules. These are graduated in
the percentage of stretch of the circle. Optical measuring systems are also available.
Universal Marking Systems Strain Grid stencil sizes
Universal Marking Systems Strain grid stencils are produced in three standard sizes.
Size Stencil size Pattern size
A 150mm x 300mm 100mm x 280mm
B 300mm x 300mm 250mm x 280mm
C 500mm x 300mm 400mm x 280mm
Strain grid ref. No. Pattern style. Example of Pattern
SG01 6.1mm circles
SG01 5mm circles
SG02
SG03 20mm circles
SG04 0.25 inch circles
SG05* 2.5mm circles
SG5a 1mm circles (I.D)
SG06 2mm increments
SG07
SG08 5mm circles in 12.5 mm squares
SG09 10mm circles
SG10 2mm circles
SG11 2.5mm circles
SG12 0.5inch circles
SG13* 6.4mm circles in
15mm squares
SG14 1mm squares
SG15 20mm circles
SG16 5mm circles
SG17 15mm circles overlapping
SG18* 3/4 inch squares with 1 inch circles
SG19 10mm circles
SG20* 2mm circles in 6mm squares
SG21 2mm circles in 6mm squares
SG22 0.1 inch circles in 0.25 inch squares
SG23 10mm circles
SG24* 10mm circles on 8mm squares
SG25 20mm squares
SG26* 0.1inch circles
SG27* 8mm circles
SG28 5.5mm increments
SG29* 5 mm circles
SG30* 5mm circles
SG31 5mm circles
SG32 5mm circles with 2.5mm squares
SG33-500 5mm squares
SG34* 0.1 inch circles
SG35* 0.1 inch circles As above
SG36* 0.1 inch circles As above
SG37 0.1 inch circles As above
SG38* 0.1 inch circles As above
SG39 10mm circles in 5mm squares
SG40 13/64 inch circles in 1/2 inch squares
SG41* 5mm circles with 2.5mm squares
SG42* 10mm circles with 5mm squares
SG43 2mm squares
SG44 5mm circles in 12.5mm square
SG45 1mm circles
SG46 0.25mm dot
SG47 5mm grid – special 50mm x 50mm pattern size
SG48 5mm grid – special 50mm x 35mm pattern size
SG49 2.5mm grid – special 50mm x 50mm pattern
size
SG50 2.5mm grid – special 50mm x 35mm pattern
size
SG51 5mm circles
SG52 4mm grid
Please note:
Maximum width of strain grid stencil now available is 300mm
It is possible to manufacture additional grid designs. Please submit specification
for confirmation
Strain grid stencils for ME3000TSG strain grid marking kits
Strain grid
ref. No.
Marking size Stencil size Pattern style
SG77A 159mm x 97mm 198mm 137mm 6mm circles
SG77B 125mm x 90mm 165mm x 130mm 2.5mm circles
SG77C 131mm x 90mm 171mm x 103mm 5mm circles
SG77D 135mm x 92mm 175mm x 132mm 2.5mm circles in 6mm
squares
Marking size
Stencil size
Universal Marking Systems Ltd. Head Office: Mount Road, Feltham, Middx. TW13 6AR. ENGLAND
Sales - Tel. 020 8898-4884/5 Fax. 020 8898-9891. e-mail: [email protected] www.ums.co.uk