One of the prototypes that we have produced recently is moving closer to production. The prototype showcases the extraordinary elastic properties of Liquidmetal as a clamp. To protect customer confidentiality, we have disguised the geometry but are reporting actual results. We hope these will be of interest to other existing and potential customers.
In the first prototypes, two clamp spring designs were evaluated. A comparable steel solution would be expected to lose efficacy within 100 cycles, as the steel would yield and the clamp force would decrease. For this prototype design, a goal of at least 200 cycles without a decrease in the clamp force was specified. The clamp needed to be opened to create a gap close to the diameter of the circular clamp when closed (about 12mm).
There were some production issues in creating these challenging prototypes, and the consistency of our initial parts was not what we would have liked. However, the objectives of the prototype were met: create a molding strategy that worked and test material properties.
We tested two specimens of each design and found:
- Design 1, specimen 1: Failed after 977 cycles
- Design 1, specimen 2: Failed after 791 cycles
- Design 2, specimen 1: Failed after 636 cycles
- Design 2, specimen 2: Failed after 1240 cycles
This is obviously a dramatic improvement on their existing solution – even our worst result was a 6-fold improvement.
Of course, it should be noted that this application is designed to take the spring to the breaking limit with each cycle. We have recently run some independent fatigue tests which we show in this graph:
This shows that our material gets 10,000 cycles at a stress that would cause Titanium to yield (880Pa). Incidentally, we are doing some interesting work on alloys that are tougher.
There were several other encouraging factors for us.
One of these was the remarkable validation of our FEA simulations. The graphs below show the actual (red) vs. simulated (blue) clamp force as a function of displacement:
(the anomalous red point at the end was the fixture bottoming out)
We, therefore, are able to predict the clamp force of a non-trivial geometry under a variety of strain conditions with a high level of confidence.
A second encouraging result is the relative consistency of the force over time. Recall that the specification was for just 200 cycles. Also, note that our Liquidmetal clamps are smaller than the existing steel product. The existing steel product is made bigger to prevent the clamp from taking a set too easily. If our geometry were made from stainless steel, the clamps would deform when fully opened.
It can be seen that the Liquidmetal clamps hold their set for 600 cycles. Clamp Design 1, specimen 1 showed a decrease in force after 600 cycles. Specimen 2 of the same design showed an anomalous increase in force after 400 cycles (this has not yet been accounted for). Both clamps from the second design maintained their maximum force for the duration of the test, with only a very small decrease. There were no significant changes in the clamp opening for any of the specimens.
More detailed analyses are ongoing, and the customer is working to perform further tests. They are aiming to create an even smaller clamp in an application where space is at a premium and existing materials have not been able to deliver the required performance. Liquidmetal is excited to see this application move into production soon.