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To further confirm the benefits that were being reported in numerous field tests, we requested Case Western Reserve University, under the auspices of Professor John Wallace, to conduct their traditional Dip Tank Test. This test evaluates the performance of the MetaLL ifeÒ process in relation to edge cracking of H13 materials.
A specimen is prepared from H13 material that measures 2" x 2" x 7". The specimen is then austenitized at 1900°F for one and one-half hours and then oil quenched. This is followed by tempering cycles at about 1100°F for one hour and an oil quench to give the final hardness value of 46 HRC. The model is then surface ground and polished so each corner had a .010" radius with
all corners square to within +/- .003" of an inch. The corner radius is formed on each corner by manually stoning with successive grits of 240, 320, 400, and 600 grit papers along the length of the corners of the block. The papers are clamped in a V-notch block to achieve the required radius and checked with a radius gauge at each corner. |
Each dip tank test cycle consists of a 12 second immersion in 380 aluminum alloy, followed by 24 seconds of air cooling out of the molten metal solution. The specimen is internally cooled at a rate of one gallon per minute. The aluminum alloy is maintained in a gas-fired crucible furnace at an average temperature of 1300°F which is monitored by two CHROMEL*- ALUMEL* thermocouples. Just before
another immersion, a water based die lubricant diluted to 50:1 is sprayed onto the specimen surface. This test is meant to simulate most of the conditions present in an aluminum die casting operation.
*( CHROMEL and ALUMEL are registered trademarks of Hoskins Manufacturing Company)
While molten metal heating and environment, internal water cooling, and lubricant spraying of the die material are present, the mechanical effects due to pressure against the die walls and die erosion due to high metal velocity are not. The thermal effects or differences in external and internal steel temperature obtained in this test, however, are more severe than conditions encountered in normal
die casting operations.
The specimen is tested for a total of 15,000 cycles. After every 5,000 cycles the specimen is removed from the testing unit, and fatigue crack initiation and growth are evaluated. Oxide layers are removed by polishing in the same manner as previously described. Cracks that initiate along the edge of both the MetaLL ifeÒ processed and unprocessed corners are measured within the center three inches of each corner to eliminate end effects. Crack
measurements are obtained at a magnification of 100X using a Leitz micro hardness tester.
Two crack parameters are then calculated to characterize thermal fatigue behavior of the sample specimens. The average maximum crack length, d (in microns), is the sum of the longest crack initiated from the edge on each corner subjected to a specific treatment ( MetaLL ifeÒ v/s unprocessed) divided by the number of corners that received the treatment. Total crack area is the number of cracks (n) in each 25
micron (u) length interval multiplied by the square of the average crack length for that interval (d2). These are then added to give End2.
MetaLL ifeÒ Test Results
After the 15,000 cycles were completed on the MetaLL ifeÒ specimen, the total average crack area of corners "B" and "D" that were not treated averaged 50.74. Corners
"A" and "C" that were treated averaged only 13.34 total crack area. This amounts to 380.36% less total crack area or a 3.8 times reduction in cracking. In addition the average Maximum Crack length was 22.22% less on the MetaLL ifeÒ processed corners.
It is important to also note that due to a specifications communication problem
between the testing lab and Badger Metal Tech, it was necessary to polish and
remove all topography on corner "B" so that opposite corners instead of adjacent sides would be used for the test. Even though the "B" corner was polished considerably to remove the MetaLL ifeÒ topography, this corner still had less soldering and 314.88% less total crack area after 15,000 cycles than corner "D" which
received no processing. Had this "B" corner never been MetaLL ifeÒ processed, the total average crack area of treated to untreated would have been well over 400% or 4 times less, and the maximum crack
length would have been 33.33% less. This gives strong confirmation that even after significant polishing to remove visual topography that the benefits of the MetaLL ifeÒ process still remain. This has been a frequently asked question by zinc die casters that require a hardware finish on their castings
and want to polish the die after MetaLL ifeÒ processing.
Our test results from the field have for some time confirmed MetaLL ifeÒ does close and help keep closed thermal heat checks and minor crackes on USED dies. With this test there is now confirmation that MetaLL ifeÒ also significantly retards the initiation of thermal stress heat checking on NEW tooling.
The results of the test were then plotted and compared with identical testing of various heat treat methods, steel types, and surface treatments. The MetaLL ifeÒ corners had both a significantly lower total crack area and shorter crack length than other specimens tested using alternative steels
and treatments under identical conditions.
Independent testing is continuing. At Case Western Reserve University, the attributes of MetaLL ifeÒ and its correlation to the thermal fatigue effects of H13 EDM surfaces are being evaluated. Ohio State's Net Shape Engineering
Research Center is involved in a testing program as well to evaluate the beneifts of applying MetaLL ifeÒ to stop soldering and retard die erosion. Badger Bulletins will be published as more information regarding these tests become
available. Please call or email us if you have any questions regarding this test or other aspects of the MetaLL ifeÒ process.
Click HERE for the Charpy Impact Lab Test.
You may
download or print a hard copy of the Diptank test along with other
brochures.
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