www.robowars.org

RoboWars Australia Forum Index -> Technical Chat

aluminium heat treating


Post new topic   Reply to topic
  Author    Thread
Glen
Experienced Roboteer


Joined: 16 Jun 2004
Posts: 9479
Location: Where you least expect


 Reply with quote  
aluminium heat treating

i know theres a lot of engineers out there so i thought this would be the best place to get my head around this

im looking to get my robots rear aluminium plate heat treated to toughen it up as far as i can. but the only heat treating website i could find locally was www.heat.com.au

the heat treatings they offer made absolutely no sense to me at all in reference to robots (what temper should it be to get maximum strenght without brittlness?..) so i was hoping some people could give me some insight into this.
_________________
www.demon50s.com - Minimoto parts
http://www.youtube.com/user/HyzerGlen - Videoooozzz

Post Wed Dec 01, 2004 7:41 pm 
 View user's profile Send private message Send e-mail Visit poster's website MSN Messenger
Ajax
Experienced Roboteer


Joined: 17 Jun 2004
Posts: 298
Location: Sydney


 Reply with quote  

I beleave it is case hardening your after.

I have Case hardened Alu to help reduce the wear and make it harder to damage. But that is in a factory inviroment.

Ring them up and have a chat to them. Most of the time they will be happy to help with inquieries
_________________
It's all about the destruction.

Post Wed Dec 01, 2004 9:52 pm 
 View user's profile Send private message Send e-mail MSN Messenger ICQ Number
Spockie-Tech
Site Admin


Joined: 31 May 2004
Posts: 3160
Location: Melbourne, Australia


 Reply with quote  

Strength, Hardness and Brittleness are all different things.

From my limited knowledge of metallurgy hardness and brittleness are mutually exclusive.. The harder something gets, the more brittle it becomes.. Grade 8 Bolts have a higher yield strength than grade 5, but you shouldnt use them in place where shock loads are likely to be experienced or breakage will result in catastrophic failure.

Often a slightly stretched bolt is preferable to a snapped one.. I know that in building ultra-light aircraft, Grade 5 bolts are usually specified, since snapped bolts are not a good thing. I saw a Gyrocopter once that had been tipped over on landing with the Rotors spinning, and the main rotor head spindle bolt had stretched so much that its diameter was down to half the original at the thinnest part, but it hadnt broken !

Someone like the Kero's or MytQik might be able to speak with more authority on this subject, but in the meantime, heres a web link that looks useful.

http://aluminium.matter.org.uk/aluselect/tempers.htm
_________________
Great minds discuss ideas. Average minds discuss events. Small minds discuss people

Post Wed Dec 01, 2004 10:10 pm 
 View user's profile Send private message Send e-mail Visit poster's website MSN Messenger
Nick
Experienced Roboteer


Joined: 16 Jun 2004
Posts: 11799
Location: Sydney, NSW


 Reply with quote  

What alloy is the back panel? I had a look at some local catalogues and ALL the structural sheet and plate listed was some variation of T5 or T6 heat treated already, so your panel is likely as hard as it can get.

It will probably be cheaper to get a whole new panel in a harder grade of ali than get the existing one treated. There was an interesting comparison on the Mad Cow site between alloys 6061, 7075 and 2024. The 6061 bent and flowed, allowing other parts to be damaged. The 7075 hardly deformed at all, but the screw holes fractured due to the brittleness of the alloy. The 2024 bent a little more but didn't fracture. 2024 is the only alloy that is often NOT supplied in T6 temper I think Fortal gave a good result too.

All these grades are really hard to get locally unless you bulk order. Fortal only seems to be available in thick slabs. You might have better luck with one of the on-line metal places in the US. Its only ali, so the postage won't be that much...

The other option is to add strength by adding some angle section like you did at the front, or to replace the back with a shallow U section. Remember how badly that test bot frame as cut up? it was made from 6061 4.5mm U channel and didn't really distort until it was mostly cut thru
_________________
Australian 2015 Featherweight champion
UK 2016 Gladiator champion

Post Wed Dec 01, 2004 11:55 pm 
 View user's profile Send private message
Spockie-Tech
Site Admin


Joined: 31 May 2004
Posts: 3160
Location: Melbourne, Australia


 Reply with quote  

a quick confirmation of what nick said back from the Gyrocopter scene..

6061-T6 is what most of the Gyro structural framework is made out of. They tend to use it in 2"x2.5" rectangular extrusion with a wall thickness of around 3-5mm IIRC.

They also get 6061 in flat plate, and some guys purchase 2024-T3 for high strength high machineability parts like rotorblade hubs.

If anyone want to harass the Gyrop guys for their sources of 6061, I found their forums over at http://www.asra.org.au/forum/default.asp . There might be someone on there who knows where to get it.. if you're really unlucky, you'll run into someone who remembers me.. Laughing
_________________
Great minds discuss ideas. Average minds discuss events. Small minds discuss people

Post Thu Dec 02, 2004 12:00 am 
 View user's profile Send private message Send e-mail Visit poster's website MSN Messenger
kkeerroo
Experienced Roboteer


Joined: 17 Jun 2004
Posts: 1459
Location: Brisbane


 Reply with quote  

Ok, this is the second time I've started writing this as I was trying to make it quick and easy. Now I'll try for some thing you can understand.

Every metal is made up of crystals. When I talk about crystals I don't mean the shiney see through ones they charge a fortune for to silly women. What I mean is the way the atoms in the metal are stacked on top of each other. The atoms might be in a cube shape, or a pyrimid, or hexagon shape or what ever, and the pattern repeats it self through the metal. Now when liquid metal is cooling into a solid the atoms start to stack them selves into crystals. But because it doesn't happen straight away there will be lots of starting points all though the metal where this happens. Now none of these crystals will be facing the same direction so when they grow and bump into each other they don't join properly, so what we end up with is lots of lumps of crystals all joined together. If you've ever looked at the surface of zinc coated steel (galvabond) you'll see lots of different colors, those are the differently orriantated crystals.
Now the differnt crystals facing differnt directions are called Grains, like in wood. Where the grains (blobs of crystals) touch is called the Grain Bounderies. Now the bonds of the atoms between each other at the grain bounderies are weaker then the bonds in the crystals, so when a crack passes though the metal it'll travel along the grain bounderies. If you had a bit of metal with lots of little grains and lots of grain bounderies it would be easy for a crack to find its way though the metal, but if you big grains with not many bounderies its harder for a crack to find its way though the metal. Also crystals are able to stretch easily, but not if there are other grains getting in the way. So metal with big grains can stretch more then metal with lots of little grains. This is why soft metals are ductile and hard metals are brittle.
To get confussing we all know about phase changes in materials, eg. Solid to Liquid to Gas. Well some metals under go a Solid to Solid phase change when heated up to a certain temperture. For example plain carbon steel changes from a Body Centered Cubic crystal structure to a Face centered Cubic structure when heated up to 750 degrees. Some aliminium alloys are the same. When they change to this hotter crystal structure I beleive they become one big grain. When it cools down different points cool quicker, forming grains first, causing all those little grains to form again. Depending on how fast you cool you end up with different size grains.

Basically tempering is a process to control how big the grains in the material are. Big grains = Soft (bad) but Ductile (good). Small grains = Hard (good) but Brittle (bad).


Its lucky you didn't ask about the heat trement of steel as the post would be 4 times this length. But steel is more fun.
_________________
Get Some!!!

Secretary of the Queensland Robotics Sports Club inc.

Post Thu Dec 02, 2004 8:32 am 
 View user's profile Send private message Send e-mail Yahoo Messenger MSN Messenger
Nick
Experienced Roboteer


Joined: 16 Jun 2004
Posts: 11799
Location: Sydney, NSW


 Reply with quote  

I found some useful sites for further reading:

http://www.key-to-metals.com/Articles.htm general stuff for tech heads.

http://www.principalmetals.com/properties/step2.asp?Family=Aluminum very specific infor on all alloys including heat treatment. recommended!


Back to my suggestion about just using a more suitable alloy: I started out by trying to get 6061 like all the US guys recommend. That didn't go so well as its expensive and rare in Australia, so I looked up alternatives. As I've said before, 5083 alloy (which is used mostly for boat building) is as good as, or better choice for combat robots, particularly if the frame is welded. To quote:


quote:
When non-heat-treatable alloys are welded, microstructural damage is incurred in the HAZ (heat affect zone). Unlike the case of heat-treatable alloys (ie 6061), whose strengthening precipitates may dissolve or coarsen, the HAZ damage in non-heat-treatable alloys is limited to recovery, recrystallization and grain growth. Thus, loss in strength in the HAZ is not nearly as severe as that experienced in heat-treatable alloys.


... so 5083 has slightly higher tensile strength and makes a better welded frame than 6061 unless you spend $$$ on heat treatment. My other fave quote about 5083:


quote:
An important application for alloy 5083 is the construction of tactical military vehicles. The hulls and turrets of vehicles such as the M113 armored personnel carrier, the M2/M3 infantry and cavalry fighting vehicles, the M109 self-propelled howitzer, and AAV7A amphibians all consists of welded 5083 aluminum structures.


2024 allow would be even better for internal parts like motor and bearing mounts, just be aware that it is not weldable and usually comes in rods or bars and not in extruded sections or thin sheet. Some suppliers and fabricators like O'briens Aluminium have offcuts of 2024 that are useful sizes. O'briens will not sell cut to size 2024 or 6061, but will make waterjet parts in those alloys.
_________________
Australian 2015 Featherweight champion
UK 2016 Gladiator champion

Post Thu Dec 02, 2004 11:47 am 
 View user's profile Send private message
kkeerroo
Experienced Roboteer


Joined: 17 Jun 2004
Posts: 1459
Location: Brisbane


 Reply with quote  


quote:

I suppose oil will have a higher heat capacity than air, so will suck heat out of a hot bit of metal quicker and alter this crystal formation process as the cooling happens more rapidly. It sounds to me like slower quenching would promote even crystal growth and result in a harder final product than fast quenching would (which would probably vreate more unjoined crystals throughout the metal) ?


Bingo. Although steels are differnt then Aliminuims. The main reason they are different is the carbon in the steel. When the steel is in its hot crystal structure (called Austinite) it is able to absorb all the carbon floating around in the steel, but when it cools and the crystal structure changes (into Ferrite) the iron atom crystals become more compact and squeezes out a lot of the carbon. This loose carbon forms Fe3C7 (called Cementite). This Cementite forms into plates between the Ferrite crystals (the mixture is called Pearlite, cuase it looks like moter-of-pearl under a microscope) and is a rather hard, brittle ceramic compond and is what makes high carbon steels more harder then low carbon steels, but also more brittle.
But when you quench a bit of steel the carbon can't get out of the way of the new crystal structure quick enough and gets in the way of the iron. What you end up with is a completly random crystal structure where nothing can more. This is call Martinsite. This structure is very hard to stretch and very easy for cracks to move through, because all the crack needs to do is breack the already strained bonds between the atoms. This is why quenched steel are so hard and brittle.
Oil is the most prefered method of quenching. Caustic Soda is better though. I think vegtable oil works best of the oils. Salty water is the next best thing after that. The best swords made druing medievil times were done by pluging the red hot sword into the decapitated bodies of a captured enamy soldiers. The salty water of a human body worked better then plain water.[/quote]
_________________
Get Some!!!

Secretary of the Queensland Robotics Sports Club inc.

Post Thu Dec 02, 2004 1:10 pm 
 View user's profile Send private message Send e-mail Yahoo Messenger MSN Messenger
Totaly_Recycled
Experienced Roboteer


Joined: 15 Jun 2004
Posts: 1346


 Reply with quote  

With steel ,tempering is also important .. makeing steel hard is easy but stopping it from cracking is more trickier . Mabee the kerroos could explain how tempering in steel is done ...my simple explamitiaon is that once the steel is hardened it is taken back up to a high temp but lower than it was before it was quenched .. it is then cooled useing different methods . this makes the steel very hard but takes a litle bit of the initial hardnes out but makes the metal much less brittle .

I think Hardox is a type of tempered steel as it is tough but can stil be bent and worked with out cracking .

Post Thu Dec 02, 2004 11:22 pm 
 View user's profile Send private message
Nick
Experienced Roboteer


Joined: 16 Jun 2004
Posts: 11799
Location: Sydney, NSW


 Reply with quote  

Enough with the Hardox already! Nobody here can afford a sheet of it and IMHO, no one is ever going to find any off-cuts of thin Hardox. For diehard steel fans here is a nice alternative to Hardox: http://www.solsteel.com.au/fedur.html

Glen needs to know what he CAN use, not about unobtainium. I spent quite a long time tryiny to find more heat treatment places in Sydney and it doesn't look like there are any. Several text books suggest that heat treating ali virtually always results in warping and stressing and that this is hard to remove. Its sounding more and more like using a different material or shape is the best bet!
_________________
Australian 2015 Featherweight champion
UK 2016 Gladiator champion

Post Fri Dec 03, 2004 12:15 am 
 View user's profile Send private message
Spockie-Tech
Site Admin


Joined: 31 May 2004
Posts: 3160
Location: Melbourne, Australia


 Reply with quote  

Off-topic Hardox posts moved to another Thread..

My fault, I should have known that people who like it get all defensive about it whenever its criticised, and I bought it up.. sorry.. we now return to you the on-topic subject of aluminium hardening...

To steer things back on track, when you buy your heat treated aluminium, it usually comes with a "T" number after the alloy indicating its "temper". Eg 6061-T6, 2024-T3..

As Far as I know, "Temper" is different to "hardness" although both are created by a heating/cooling process.. My understanding of the "temper" of a metal is the amount it can be deformed or bent and still return/spring back to its original form. If you exceed its temper rating, then the bent/deformation becomes permanent. The higher the T number, the greater the temper..

Question is, is this necessarily related to hardness ? does a higher temper automatically mean a higher hardness or are they different properties ?
_________________
Great minds discuss ideas. Average minds discuss events. Small minds discuss people

Post Fri Dec 03, 2004 10:27 am 
 View user's profile Send private message Send e-mail Visit poster's website MSN Messenger
Nick
Experienced Roboteer


Joined: 16 Jun 2004
Posts: 11799
Location: Sydney, NSW


 Reply with quote  

"Temper" is both a noun and a verb, so I take it to be a process and not a rating or measurement like hardness is. You temper metal to alter it's characteristics, so a high temper is a description of more than just hardness.

I think you are confusing temper with "modulus of elasticity"


quote:
Definition : When a material is subjected to an external load it becomes distorted or strained. With metals, provided the loading is not too great, they return to their original dimensions when the load is removed, i.e. they are elastic. Within the limits of elasticity, the ratio of the linear stress to the linear strain is termed the modulus of elasticity or more commonly known as Young's Modulus.


This rating is what makes titanium such great armour; it bends, absorbing and distributing the energy, then springs back. Steel can do that too, but not as much and it weighs 1.7 times more.

I liked the Fedur composite steel more than Hardox as you get a really hard surface with a tough backing. Given the excellent performance of the tooth on Plan B's weapon, which has hard facing steel welded on the front edge, Fedur would go well as armour or weapon parts.
_________________
Australian 2015 Featherweight champion
UK 2016 Gladiator champion

Post Fri Dec 03, 2004 12:03 pm 
 View user's profile Send private message
kkeerroo
Experienced Roboteer


Joined: 17 Jun 2004
Posts: 1459
Location: Brisbane


 Reply with quote  

quote:
Originally posted by Spockie-Tech:

As Far as I know, "Temper" is different to "hardness" although both are created by a heating/cooling process.. My understanding of the "temper" of a metal is the amount it can be deformed or bent and still return/spring back to its original form. If you exceed its temper rating, then the bent/deformation becomes permanent. The higher the T number, the greater the temper..



First I've heard of this term.
Sounds more like you refering to the eleastic limit of a material. Springs are the best way to describe it as they amplify whats going on in the material.
If you aply a small load to a spring it will stretch a certain distance. Apply a bigger load and it'll stretch further. Take away the load and it spring back to its origonal length. The same thing happens in everything including rope, steel bars, glass, ect... Now the load we put on the spring is called Stress and is calculated by:
Stress = Force being applied / Cross section area it being applied on
So for some thing hanging by a rope the force is the weight of the object and the area is the cross sectional area of the rope. Pretty simple. Stress is measured in Pascals.
Back to the spring. How much the spring stretches is called Strain. Strain is actually the percentage the sample has stretched. For steel it is less then 0.01%, but for a rubber band it be over 500% .Strain has no units by the way.
If you were to put a load on a spring and measure the distance, then try a different load and keep doing that till you are able to make a pretty graph you'd be a boring person, but you'd also notice the the graph is linear (in a straight line), untill you reach a certain point. At that point the spring wont return to it origional shape. If you are like me you would have pulled a spring out of an out ball point pen once and stretched it till it was almost straight. Well the point where the spring starts to want to be straight is the point of the graph where it stops being straigh. This point is called the Maximum Yeild Strength. Before this point the material was eleastic (went back to it origional shape) and after this it was Plastic (it didn't).
Even though the material can take more load after this point Engineers consider a part to a failed if it hit this point. Ductile items tend to keep stretching after this point, but britle items break.

Sorry, this had nothing to do with Aliminium or Andrew question which I forgot about.
_________________
Get Some!!!

Secretary of the Queensland Robotics Sports Club inc.

Post Fri Dec 03, 2004 1:09 pm 
 View user's profile Send private message Send e-mail Yahoo Messenger MSN Messenger
  Display posts from previous:      

Forum Jump:
Jump to:  

Post new topic   Reply to topic
Page 1 of 1


Forum Rules:
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum

 

Last Thread | Next Thread  >
Powered by phpBB: © 2001 phpBB Group
millenniumFalcon Template By Vereor.