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Editor's Note: CR4 would like to thank PJ Sikorsky, Metallurgical Consultant, for contributing this blog entry, which originally ran here.
I can't
begin to remember how many times over the past 30 years I've felt the bile rise
in my system as I've heard design engineers suggest that it doesn't matter what
material(s) are used to build parts and components. I suppose it's natural for
any of us to feel unloved and underappreciated in our professional endeavors.
As a materials engineer working for two different major manufacturers over my
career I often felt that materials selection was not given as much attention
during the design process as it deserved. There are 5 repetitive problems I
have observed related to material(s) selection over my career:
1.
Material Selection after the part/component is 'designed'.
2. Material Selections not reviewed over time.
3. Materials copied from old designs.
4. Material substitutions fail.
5. Bad material selections - the gift that keeps on taking.
In the
remainder of this blog post I'll briefly describe each of these problems. I'll
devote subsequent posts to each of these issues individually in more detail.
1.
Material Selection after the part/component is 'designed'.
Many times
a design engineer comes to the materials engineer after lines are committed to
paper and the part is 'designed' - the question often is 'Okay, what should we
make this out of?' The shortcoming of this approach is that once parts are
designed, materials options are limited. Done right, Material Selection is
integral with the design process and parts are designed around specific
material characteristics.
2.
Material Selections are not reviewed over time.
 Even when Material
Selection is done right, the materials world is a dynamic place and what makes
sense today, may not make sense tomorrow. For many years copper was less
expensive per pound than aluminum (for most of my career, copper was
$0.65/pound while aluminum was around $1.00/pound), today copper is 4.5 times
more expensive than aluminum per pound - does copper still make sense for heat
exchanger tubing or headers or connecting tubing now that aluminum is so much
less expensive? Maybe, maybe not, but it is obviously a different question now
than it was before.
3.
Materials copied from old designs
This is
similar to #2 above, but it also can create problems for other reasons: What is
the right material for a one pound widget may not be the right material for an
'identical' 10 pound widget - material properties do not necessarily scale with
the geometry of a part. Where a part is manufactured may impact the material
selection - what makes sense for a part made in the US, may not be appropriate
for a part made in China.
4.
Materials substitutions fail.
Whether we
try to convert parts from metal to plastic, or from metal castings to powdered
metal, materials substitutions fail. The primary reason is that when materials
change, part design needs to change. A plastic gear, even though it may serve
the same function as a metal gear, if designed properly, should look different
than a plastic gear. If we simply try to drop in a plastic material into the
same geometry as a part that was originally made from metal we are almost
assured of failure.
5. Bad
Material Selection - the gift that keeps on taking
Oftentimes
during the development process, problems are discovered too late in the game to
'redesign' parts before going into production. Instead, we call on some
materials 'magic' and we implement special coatings, or heat treatments or
exotic materials into the existing designs just to get us into production. Our
intentions are always good - we say we'll come back later and redesign the
parts so that we can revert to more standard/affordable materials - but the
reality is that we rarely have the time to go back and redesign and instead we
pay for the premium material throughout the life of the component design, and
in those cases where we simply copy material selections from old designs into
new designs, we pay the premium forever.
With raw
material costs accounting for 50-80% of piece part cost it seems intuitive that
choosing the 'right' material is critical to managing cost, yet we often treat
this part of the design process as an afterthought. We'll explore each of the
repetitive problems described above in more detail in subsequent posts and
we're available to help you improve Material Selection.
- PJ Sikorsky
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