30lb Combat: Materials

Metals

Aluminums

2024 Al

2024 Aluminum is mostly the material of choice for many robot frames in iRobotics. It has a good balance of strength and toughness, meaning that it is resistant to fracture and permenant deformation.

7075 Al

High strength and stiffness aluminum alloy. However, it has lower elongation at break comapred to other aluminums, which means it will tend to break and crack more than other aluminums, which will just deform instead. Depending on your application, this might be favorable or unfavorable. For instance, it could be a good choice for a bottom plate that needs to be stiff and should not deform (which could high center the robot). However, 7075 would be less advantageous compared to another alloy like 2024 for exterior aluminum armor panels, as it would tend to break apart easier than other aluminums.

6061 Al

Cheap, easy to machine, but lower strength than the other options.

Steels

AR Steels (600/500/400)

AR: Abrasion Resistant. The number in the name refers to its hardness. As with most steels, higher hardness leads to higher strength and resistance to damage, but increased brittleness.

Often the material of choice for robot weapons and armor.

Titaniums

Ti-6Al-4V “Grade 5”

Twice as strong as mild steel but half the weight. This is the material of choice when aluminum is too soft for a component and steel is too heavy. Commonly used for armor, cleats, and mounting plates. While very strong and tough, it has a hrc rating of 34C which is lower than most weapons. In addition, the material is very expensive and difficult to machine. Machining precautions: Titanium rapidly work hardens when drilled. Use low speeds, moderate pressure, and plenty of coolant. Carbide tooling is preferred

Welding titanium is exceedingly difficult due to its affinity for oxygen. If any portion of the material comes into contact with oxygen while above 400 degrees, it will become brittle and fracture on impact. Cleanliness is a MUST, all parts need to be cleaned with a wire brush then wiped with acetone. Grade 2 filler rods should be used for ductility and wiped with an acetone soaked rag. Weld in half inch sections with a trailing shield, high gas flow rate, and >12 second post flow. Gas coverage on the back of weld surface is absolutely critical. If not welding tube, parts should be welded in an inert chamber. Silver and straw colored welds are acceptable, any other will be brittle.

“Commercially Pure Titaniums”

Encompassing grades 1-4, these materials are easily formable but have less than half the strength of grade 5.

Unsuitable for combat