Bending Abrasive Resistant Steels
AR Steels are becoming more popular everyday. Used in mining, transportation, military, agricultural and many other applications, they represent a great opportunity for fabricators.
Knowing how to bend and work this materials requires experience and study. The following is a collection of years of experience on the fabrication of these alloys
Not only are these alloys harder and therefore resistant to abrasion, some are also ductile enough to be fabricated, and so they are being used on structural fabrication.
The best example being transportation, where a lighter truck means more profitability per load/transport.
Mining industry people know all about abrasion. Imagine how much steel is scrapped away during the loading of a truck when tons of mineral rock are thrown in a bucket.
Eventually this scraped material starts compromising the shape and structural holding of the bucket itself. So, the less it's scraped the longer the bucket is useful, secure and profitable. Basically there is a need to make the bucket "thougher”
Though still Ductile
Special alloys and heat treatment make AR steels very resistant
What about ductility and malleability? Ductility is the ability of a given material to withstand deformation under traction without cracking, while malleability is the ability to withstand compression.
as we know, in press brake bending we have both traction and compression.
Many AR steels have good ductility and malleability. In fabrication we are interested in its' ductility. These material can be deformed without cracking but we must know the rules that apply to avoid cracks or material failure.
The key aspect to remember is that AR steels are tougher and less ductile than MS or SS steels.
It's vital to remember that we need to account for a lot of springback on these alloys.
The other fundamental aspect to keep in mind is that we want to avoid cracks. In order to avoid cracks we must diminish pressure by enlarging the surface on which we apply the PB force.
pressure = force over a given area.
We need a lot of force because these materials are hard, so we must enlarge the area where this force is applied.
This is why we need larger V openings and larger upper radius
To keep in mind (rules of thumb)
- Thickness / V open ratio: There is NO unique rule for all AR steels , but know that V openings need to be at least 10 times a thickness when bending AR steels. Some materials even require a V= 20 x Thickness. The harder the material, the larger the V required. Luckily most suppliers have run tests and provide a chart for each material type. So ask for those charts when buying AR steel.
- Punch radius / material thickness ratio: Again, this is not a unique ratio for all AR steels, BUT the radius of upper tools need to be very large compared to normal MS bending. Usually the ratio starts from 4 times and can go up to 12 or 14 times the thickness, depending on the material specs.
- Springback: Every AR steel will be different, but in any case it will be far grater than what we’re used on mild steel. As a rule of thumb consider to go from 15° to 25° degrees. Such springback requires 60° tools to compensate for the lost degrees.
- Grain or roll direction: Bending along the grain or against it makes a great difference on AR steels. Not choosing the correct punch radius according to grain direction usually results in material cracks. So before you start cutting, make sure you know how you will bend the part and what direction the grain goes, then choose your tools and program your PB accordingly
Some AR steels fabrication instructions from steel suppliers
Always ask your steel supplier for the specific data sheet for what you are purchasing