Cast In Steel: Thor's Hammer
The Cast In Steel Competition is an annual competition run by the Steel Founders' Society of America (SFSA). Each year colleges from around the country are tasked with casting a different object out of steel. Each team partners with an industrial casting company to produce their designs.
This year's challenge was to cast Thor's Hammer. The constraints on what qualified as Thor's Hammer were minimal. The hammer had to be under 6lbs, and have a handle length of less than 20 inches.
Research
Our process began with assembling historical details on Thor's Hammer. We researched historical Viking hammers as well as their depictions. We found that Viking weapons and runes were full of detail, so we decided that investment casting was a good choice, since investment casting is known for it's detail. We also noted the profile of many of the hammers depicted in historical works, which had rounded features and etchings on the sides.
Brainstorming
As a group we began to create CAD models of various shapes and profiles we liked. The picture on the right was the first model I designed. I tried to capture some of the curves of the Viking hammer designs I saw, but ultimately I was dissatisfied with the final result.
Through some other designs we developed the idea of adding pockets to the bottom of our design to reduce the overall weight of the hammer. That way we could increase the size of our hammer design.
For my second idea I came up with the design pictured here on the left. I tried to capture the anchor shape that many hammers online featured. I was much more satisfied with the profile of this design, which felt a lot more regal and strong. I kept the square corners of my previous design, which I felt gave some definition the the hammer faces.
As a group, we decided this profile was a strong candidate, and went forward trying to optimize it for casting. I took ownership of the CAD design from this point, implementing the features we wanted changed, added, or removed.
Brass Inserts and Runes
To add a color and details, we decided to add a brass "coin" insert to the center of the hammer. This coin has a depiction of the world tree on it, which is an important aspect of Viking religion. This brass insert would be cast by team members in Cal Poly's casting lab.
We wanted to add a personal touch to the design. So I added the initials of all 8 team members to the hammer in the form of Viking runes along the sides.
Pocketing and Simulations
I tested two different forms of pockets on the underside of the hammer. The creation of these pockets was based on the simulation I ran on the right. This is a shape optimization simulation, which shows where weight can be reduced with minimal sacrifice to rigidity when force is applied to the front of the hammer. The simulation shows that material around the left and right sides of the hammer are lass critical, while material in the center is much more critical to the hammer's rigidity.
Based on the first simulation, I began working on two different pocket designs. The first featured three half depth triangular pockets, with smaller ribs in between them. The second design used two full depth pockets with a much larger rib in the center.
I ran both designs were ran through Finite Element Analysis Simulations to get feel for their relative strength upon a large force being applied to the front. This was my first time running simulations in Fusion 360, and I was blown away by the simplicity and detailed results. The results of the many tests allowed us to see where stress was concentrated, and adjust the design in these areas. Both pocketing designs underwent many, many iterations to optimize each of them.
While I liked the look of the triple pocket design much more, the simulated strength difference between the two designs was negligible. As a team we consulted our contact Andrew at Aurora Casting, the company who would ultimately be casting our design. His input was that the two pocket design would be easier to cast since the rib was larger. Due to this advice, we chose the two pocket design as our model continuing forward.
Andrew also advised us to angle the walls and rib such that they were wider at the base and thinner at the top. This way, the thinner parts would cool first, and there would be less chance of heat pockets forming in the middle of the ribs. We wanted the model to cool in a way where heat was drawn outward from the model into the gates to prevent variations in porosity that could cause shrinking, cracks and weak points.
Final Hammer
Aurora Casting manufactured 12 hammers for our team, and we sent one hammer to compete in the Cast In Steel competition. Aurora handled all of the 3D printing, sealing, gating, investment molding, casting and finishing of the hammer heads. The image on the right shows a 3D printed hammer with the gating attached. Covid-19 restrictions prevented our team from getting more involved in the production of the hammer head, but we still were able create the brass coin inserts as a team.
Each brass coin was 3d printed with gating, and then investment was added to create a mold. After casting the coins in brass, each coin was released from the mold and sand blasted. Then, multiple rounds of sanding and polishing were used to get a smooth reflective finish on the embossed design.
Final Hammer
The coins were attached to the hammer with epoxy, and the wooden handle was inserted and secured. The handle was received a leather wrap to improve grip and add some visual flair. This completed our final hammer, which was shipped to the competition for judging. The final hammer is featured below, and our judges video can be found here.
My Hammer
Aurora Casting was nice enough to produce multiple hammer heads so that each team member could have a hammer of their own. For my personal hammer, I used two brass coins with personal designs embossed, and added some laser etched designs to my handle. I also CNC cut a stand made of clear polycarbonate to hold the hammer.
