Cast in Steel Thor's Hammer
The Cast in Steel competition is put on by The Steel Founders’ Society of America each year. Last year, we competed to make a Bowie Knife. This year students from across the US will be challenged to make Thor's Hammer.
Our design this year is highly influenced by Norse mythology. We have adapted the classic design of the curved top face of the hammer with hammer faces that are not perpendicular to the handle. Additionally, the bottom surface of the hammer has a curve to a point where it meets the handle. Other aesthetic choices are the use of Nordic runes to spell the initials of all of the students that are on the team and the use of a brass coin that will have the tree of life embossed.
By using a brass coin insert, we are able to do that portion of the casting on campus. This will let students on the teams get to do some of the casting themselves, as we are not able to do factory visits currently.
The hammer and coins will be 3D printed in PLA. The hammer will be investment cast in steel and the coins will be cast in a solid-flask process in brass.
Hammer Design
Two designs for the hammer were proposed and went through an initial test print to see what it would look like in real life, shown below:
CAD Design A
Test Print Design A
CAD Design B
Test Print Design B
The team voted to move forward with a modified version of Design A that would maintain the side profile, but would have a narrower face of the hammer and only one rib down the middle. The decision to move to one rib was found after running stress test simulations to see where stress concentrations would build up. By having a solid piece of material from the center of the hammer face to the handle, the load can be primarily directed straight through the hammer.
The next step of the project was to mass produce these 3D printed patterns.
Mass Production of Patterns
A total of 13 successful prints were completed across four 3D printers.
The print time on the hammers was approximately 16 hours.
Due to the use of new components that had not been thoroughly tested beforehand and user error, there were 3 failed prints and 1 recovered print. The recovered print had the microSD card removed during printing, stopping the printer. However, the display on the printer showed the current z-height, so by going through the G-Code and removing all of the lines prior to that z-height, the print was able to continue. There was slight evidence of material squished out of the side of the print since the nozzle went over the same area twice, but the hammer was salvageable nonetheless.
Other issues that required troubleshooting were: bed adhesion being too weak or too strong, finding the balance of minimal infill while still retaining part rigidity, and clean support material removal.
Gating Design
While producing patterns, we also had to design the gating for when they would be cast. Our industry partner suggested using a standard tree that would allow for 6 hammers to be cast on a single tree. Our job was then to design the gates that would connect our hammers to the standard tree.
After about a dozen different designs, we landed at the gating design on the left. There are four connection points where the gating reaches the hammer and meet at the four areas of largest metal volume on the part.
This design allowed for nonturbulent metal flow, and enough metal behind the part to feed solidification shrinkage in our simulations.
Gating Simulation
Gating simulation was done using SOLIDCast 8 with between 6-8million nodes on each simulated tree.
Figure 1 on the left shows the setup for the gating simulation. The red portion is the gating/riser/sprue that will fill the hammers. The green cylinder at the top is just the cross sectional area of the pour.
Figure 2 shows the simulation halfway through its calculation, showing a temperature gradient, where lighter colors are hotter and darker colors are cooler.
Figure 3 shows the solidification time results of the simulation, where darker colors are where the material solidifies first and the lighter areas are what solidify last. With this gating design, there is a consistent gradient from the thinnest areas of the part solidifying first to the thicker areas solidifying last.
Figure 4 shows the material density results, with blue being 100% dense and lighter colors being less dense. With this gating design, there were no areas of porosity shown in the simulation.
VPQZ9262.MP4The video on the left shows the full animation of the casting simulation.
This shows the nonturbulent flow of the metal, with no 'waterfall effect' as well as the temperature of the metal as it pours and solidifies.
Gating Assembly
With the gating design complete and the 3D printed patterns shipped to Aurora Casting, it was time to assemble the gating trees.
The visible 3D printed layer lines were smoothed over with wax and the wax gating was attached to the hammers.
Not pictured is the assembled tree with all 6 hammers.
Coin Insert Design and 3D Printing
Due to the ability to run many different versions of parts on a 3D printer, each student got to design their own custom coin inserts to be on their hammers.
A few of these different designs are shown on the left.
The coins will be cast in brass using solid-flask investment casting.