Keep in mind cars/trucks are welded everyday by body shops. A close friend
of mine has been in the business for over 20 years and has had to go to
classes to weld on modern cars, but the process is much the same. Many of
the advances in steel strength in the last few years has more to do with
forming processes than the alloy.
wrote in message ...
In article ,
Eric R Snow wrote:
On Tue, 01 Mar 2005 13:48:23 -0800, Grant Erwin
wrote:
I have this buddy with a dump truck (handy thing to have). It's actually
a one-ton pickup with a dump bed, which means when I borrow it I'm
covered
on my insurance - barely, but covered. The bed raises and lowers with a
Knapheide hydraulic unit, hinged all the way at the back. The main
channels
of the bed line up with the main channels of the truck frame. He wants
two
(or maybe four) pieces of heavy flat bar to be attached to the truck
frame
rails so that they stick up on either side and guide the bed rails down
dead
onto the truck frame rails.
So I'm looking at attaching probably 3"x5/8" steel flat bar to the main
rails of a truck frame. I've heard you should never weld to such a frame,
that the heat would wreck the temper of the steel. I've always heard you
have to bolt to the frame. The hydraulic unit is indeed bolted to the
frame. Yet, I wonder -- is this really true? Welding is faster & thus
would be cheaper, and Navy ships weld on HY-80 armor plating routinely,
which is surely at least as high carbon as the truck frame.
Comments? I have to bid this job and don't want to screw it up but don't
want to lose the bid or waste his money either.
GWE
Greetings Grant,
I know that newer vehicles use heat treated frames. This allows
lighter frames to be used. I don't know what year this became
universal for American auto makers but it has been several years. The
reason that welding is a bad thing is because the heat affected zone
will get weaker. If I recall correctly the actual alloying elements
were present in minute quantities and the heat treat was not done the
way normal steel is. The thing that makes this steel so attractive is
the low amount of alloying elements and the lighter gauge. Apparently
these two money saving features more than offset the cost of heat
treat. I betcha Ed knows.
ERS
From what I reacall from my materials classes, most modern frames (and
unibody designs) are made from so called HSLA (High Strength Low Alloy)
steel. The great strength they have is from a very tightly controled alloy
mix. If you get the alloy ratios even slightly wrong, you loose most of
the
strength. The problem with welding is that you are melting the metals and
adding some other filler metal. There is no telling what the alloy will be
at this point, but I can almost gaurantee it won't be right. As a result,
you have a weak weld and as far as the frame is concerned, any place you
welded, you might as well have cut. Of course, it is possible to weld the
stuff, if you know the alloy compositions you are working with and use the
proper techniques and fillers... that is how the factory does it. Then you
get into heat treating and the like. Keep in mind that the frame was
probably cold worked (which makes the material tougher) and possibly
tempered (to keep it from cracking). A weld is a casting, so you are not
ging to have any kind of desireable (or really controlable) microstructure
compared with the rest of the frame. Again, with the proper techniques,
materials, and information, it is doable, but odds are you won't be able
to
get that info or equipment. I think you are better off bolting rather than
welding.
-- Joe
--
Joseph M. Krzeszewski Mechanical Engineering and stuff
Jack of All Trades, Master of None... Yet