|
Happy New year
to all from Handy & Harman. 
Our best wishes
for a safe and prosperous 2005.
Brazing as a means to make a
part.
The last newsletter talked about brazing as a way of joining
two or more metals into a permanent assembly. And we've limited our
discussion to the situations where you have a metal assembly in mind from
the outset, from initial product concept through finished piece. Now let's
discuss brazing from a very different point of view. Think about the parts
your customers fabricate, and consider where any of those parts now made as
monolithic units, might not be made more efficiently as brazed assemblies.
Consider this real-life story...
A company was fabricating thousands of small, closed-end metal
cylinders. The part looked like this:
For years the cylinders were
machined out of solid bar stock, with considerable labor required to drill
and bore the blind holes. Finally, someone suggested that the cylinder was
actually two parts--bar stock cut-offs brazed into lengths of stock tubing:
The assembly is a lot less
expensive to make than the machined part and it works just as well.
Think Brazing at the beginning.
The time to consider brazing is
at the beginning, when you're first planning or designing a metal
component. Ask yourself if the part should be made as a single unit, or if
it can better be made as an assembly of simple components. The
"assembly" approach may help you eliminate expensive casting,
forging and machining operations. It may save materials. It may enable you
to use low-cost stock forms--sheet, tube, rod, stampings or extrusions. It
will almost invariably be lighter in weight than the monolithic part, and
will probably work better as the metals in the assembly can be selected to
match their functions. Let's look at some typical metal "parts."
First we'll see how they're made by conventional casting, forging and
machining methods. And then we'll see how they could be made better and
more economically as brazed assemblies.
From casting to sheet metal.
You're designing a housing,
with threaded holes in the flange. You could make it as a casting. But
consider instead making it as a brazed assembly, joining bar stock sections
to a sheet metal deep draw:
The brazed assembly works just
as well as the casting. And it's a lot cheaper to make, because you're
putting the thickness only where you really need it--in the flange and not
the shell. You save weight, materials and labor.
From forging to brazing.
You're planning a part--a
hardened cam on a steel camshaft. Should you machine the unit out of a
solid bar of tool steel? That's a lot of lathe chips. Perhaps forge the
piece, and then finish-machine it?
Still a lot work. After
hardening, the cam has to be drawn and the shaft ends annealed. How about
making the cam and shaft separately and then join them mechanically as an
assembly?
You're on the right track. By
substituting cold rolled for tool steel in the shaft, you're saving on
material cost. But machining is still somewhat involved, and locking
device, such as a set screw, is subject to loosening under vibration. Now
try the "assembly" approach again, but this time use a brazed
joint instead of a mechanical one.
Simplest of all. No keyway, no
key, no set screw. Minimum material, minimum labor and a strong, permanent,
vibration-proof bond,
The awkward elbow.
Extensions or projections on
metal parts require excessive material (expensive!), and then a lot of work
to machine away the unwanted metal (twice as expensive!). Consider what
happens when you make an elbow shaped part from solid stock...
You're paying for metal you
don't want, and the labor of getting rid of it. There's an easier way. Make
the "part" as a brazed assembly, joining together standard tubing
and bar stock components:
The assembly will be just as
strong as the machined part. And you'll save materials, labor and weight.
(The more awkward and complex the extension, the more you'll save.)
From hard to easy.
You have to design a leak-tight
component, with complex configuration. You can plan it as a cored
casting...
It will be lead-tight, but a
cored casting is an expensive one. An open casting is a lot cheaper to
make. So why not make it that way?
By using brazing, you've
replaced the complex cored casting with a simple open casting and a metal
stamping. Machining is easier, and brazing's capillary action assures you
of a leak-tight bond.
From casting to stock parts.
Let's say you're designing a base
plate with a threaded coupling. You can make it in one piece as a
casting...
Material cost is low, but material
choice is limited. Weight is excessive, machining extensive, and the
finished part may be weak and brittle. Consider making the "part"
as a brazed assembly of stock elements...
Machining is minimal--the base
plate is a stamping and the coupling a screw machine part. Weight is down
to the bone, too, because the thickness is only where it's needed, in the
threaded coupling. Material can be matched to function. And the assembly
will undoubtedly be stronger than the casting.
Two metals are better than one.
The ability of brazing to join
dissimilar metals is helpful in many applications, but in some instances
it's quite critical. A classic example is the carbide metal-cutting tool.
The tool could be made entirely of carbide. But carbide is expensive.
What's more, though carbide is fine for the cutting tip, you don't really
want to use it for the tool shank. It's too hard and brittle to withstand
shock. Brazing solves the problem...
By brazing, you've reduced
material cost--obviously. But even more--you're now using metals perfectly
suited to their functions. Hard carbide at the cutting edge, and
shock-resistant tool steel for the shank.
Freedom for the designer.
We started this section with a
question: "When do you think brazing?" And we've indicated,
through just a few of the many possible examples, that you think brazing at
the beginning--at the design stage. The fact is--brazing liberates the
designer. It enables him to design for function, for light weight, for selective
use of metals, and for production economy, The designer who's fully aware
of the possibilities of brazing thinks less and less in terms of castings,
forgings and parts machined from solid metal, He thinks more and more in
terms of brazed assemblies, which combine plate or sheet stock, standard
tubing and bar, stampings and screw machine parts, Assemblies based on the
use of such elements are generally lighter in weight, less expensive to
fabricate, and at least equal in performance to metal parts made as monolithic
units.
|
