Bending Hardox

[Max]

Hi,
I was wondering how hard it is to put a 90 degree bend in Hardox? Specifically 6mm thickness, a strip around 100mm wide, is it any harder to bend than regular steel or will it need heating before/after/during bending?
Also what kind if bend radius can I expect?

[Eventorizon]

http://www.hardox.com/Handling/Bending1/

That is what SSAB has to say on the subject.

[marco]

cut it half way with a grinder and then bend it manualy ...

[Eventorizon]

Doesn't that kind of defeat the point? If you have to make it thinner to bend it then the corner is only as strong as the thin section so you may as well be using thinner material anyway, and if you stick a weld on the inside you end up ruining its properties. I'm not saying don't do it, but there may be/probably are better alternatives.

A company I used to work for invested in a whole new breakpress specifically for hardox and domex as it was worth the initial out lay in comparison to all the work they had to do in mild steel.

[Max]

Doesn't that kind of defeat the point? If you have to make it thinner to bend it then the corner is only as strong as the thin section so you may as well be using thinner material anyway, and if you stick a weld on the inside you end up ruining its properties. I'm not saying don't do it, but there may be/probably are better alternatives.

Yeah this was my thinking, I'd heard that welding ruins its properties which I why I wanted to bend it in the first place rather than just weld two sheets together but it would make bending easier.
It is probably worth going along with the grinder to make a small indent to ensure it bends on the line. I'll have a word with the metal workers to see if they think they can bend it as they've got a hydraulic line bender but not sure if it can deal with this sort of thickness or this hardness of material.

[adz600]

Xerox scoop is 4mm bent hardox , but we used a 200 ton press with a v form, standard small press will struggle alot

[adz600]

Ceros

[SSAB_TechnicalDev_UK]

Hi everyone,
I work for SSAB (the manufacturer of Hardox) as the technical development manager for the UK market. Having seen your interest in the use of Hardox in fighting robots and bending related questions, I just wanted to share some pointers in regard to grade selection and fabrication. My experience of robots fighting is pretty much watching Robot Wars many years ago...so my assumptions may be very incorrect.
Basics of what gives Hardox strength -
Hardox gets its strength from quenching i.e. cooling the steel after rolling from around 900 degress C to room temperature in a matter of seconds, depending on the grade. This has the effect of "locking in" the Carbon atoms in the atomic lattice structure. This gives it a very high strength and hardness level. A useful rule of thumb is the Tensile Strength / 3 gives the hardness level in HBW. It then undergoes some tempering (in a large oven) at fairly low temperatures (in comparison to conventional practices), hence, there is a heating limit of 250 degrees C on Hardox. Heating it above this temperature will essentally enable the "locked in" carbon atoms to migrate and the martensitic structure is gradually lost as the temperature increases. So when fabricating Hardox, i.e. welding, thermal cutting, machining, many of our recommendations revolve around minimising the temperature. For example;
Welding - we recommend minimising the heat input (product of volts and amps) to minimise the extent of the Heat Affected Zone and also improve toughness in the joint - something I assume would be important in a fighting robot which could be subjected to high dynamic loads. SSAB WeldCalc can help with this, its a free online software which visually plots your welding settings and tells you if they are optimal. If you want access to this please send me an email - bottom of post.
Thermal cutting - tips such as underwatter cutting with an oxy torch (or even feeding water with a water hose) whilst cutting reduced the HAZ by about 30%, which means that the softened zone from cutting is 30% less giving you a longer life in that edge. Maybe if you were making a flipping arm that flips the opponent and scrapes the floor, this preserved hardness would be beneficial
Machining - the use of plenty of coolant whilst machining is very beneficial to both the thread strength and the drill bit. Usually about 10% coolant mix is sufficient, but I would consider 20% mix for grades Hardox 550 and above.
Selecting the grade
Skin of robot - I would suggest either Hardox 450 or, preferably, Hardox 500. As has already been suggested, bending is always much better than welding, since a weld is essentially a point defect, so from a durability perspective a bend is always better.
Some comments on bending Hardox -
Bending high-strength steel is different to mild steel, as has already been highlighted. The reason is that the high-strength steel follows the punch much more closely than mild steel, since it has a higher capacity for local straining. This means that the relationship between punch radius is critical since it strongly dictates the strains on the outer radius, which, if high enough, leads to “fissures”, which can eventually lead to cracks and failure. On the other hand, bending performance and weldability is a strong indicator of quality, so when it comes to Wear Plate, Hardox is very user friendly. Another thing to consider when bending Hardox is springback i.e. you ned to overbend it by a certain amount of degrees to get the desired angle. A good rule of thumb for this is about 1 degree per 100MPa of yield strength, i.e. expect to overbend by about 15 degrees. This can vary from equipment type, so a quick test run is always recommended. Also, when it comes to required bending force, it can often be less in comparison to conventional steel since you can use a thinner material (or upgraded) and the bending force is proportial to the thickness squared. See links at end of post.

A final note on material selection. Generally speaking, the smaller your part is e.g. a damaging spike or saw-shaped ram, the higher in grade you can use. So you could consider a Hardox 600 in certain small parts, which would give you very high hardness and possibly a competitive edge. However, as mentioned, ensure to consider the processing effects, abrasive water jet is by far the best for small critical parts since the bulk hardness is preserved, or even a laser cut is also fantastic. Of course, it needs to be within budget, so apologies if I’m suggesting practices that are beyond scope.

Please drop me an email if you would like more information related to high strength steels.

Bending force calculator - BendCalc
http://www.ssab.com/en/Products--Ser...App-functions/

Upgrading rule of thumb - how much weight can be saved going from conventional steel to HSS
http://www.ssab.com/en/Products--Ser...d-films/Tools/


Good luck.
Email – aaron.middleton@ssab.com
Regards,
Aaron

[Ellis]

Just want to say hi there Aaron, cheers for your informative post, very interesting. Hope you stick around, we all love Hardox here!

[marco]

Hardox or Raex ( almost the same ) ...

[cliveb]

Hi Aaron

Welcome to the forum, just like to say that we here at Team Toon are always happy to see new people posting on here. Loved the informative post from you.

We currently have a vacancy within our Team for a sponsor or supplier of sample materials. Please feel free to contact us for further details and you and your fine company could be part of Team Toon at the 2015 Robot Wars World Championship.

[adz600]

Hi Aaron also like to say welcome to the forum and clives sale pitch, you will be a valuable asset for the robot community. Talking about hardox I managed to get 4 small 2mm 450 hardox plates form Pegasus profiles last month any chance you might know of any more 2mm floating around seems very difficult to get ?

thanks Adam

[typhoon_driver]

I'm sure many robots have similar spaces for sponsored suppliers of materials

[Garfie489]

Before it was painted, Manta looked like it had got Hardox sponsorship :P