Dievestigation- Designing stamped parts

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Dievestigation- Designing stamped parts Powered By Docstoc
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When you design stamping parts, do you consider how the design affects
manufacturing costs? All too often stamped parts are designed to have certain features
and tolerances with little consideration given to the effect these features have on the
manufacturing process and costs. To optimize cost savings, you must take into
account how the design interacts with and affects downstream processes. The failure
or success of a stamping operation begins with a good, cost-effective part design.

Metal and Downstream Operations
Among the factors that affect downstream operations and influence cost are the type
and thickness of the metal you specify to make the part. The selected material has a
direct impact on several aspects of the manufacturing process. So what should you
consider before making your decision?

1. The metal's ability to make and shape the partJust because a part is designed to be
made from a certain material, there is absolutely no guarantee that it can be done.
Some product designs I have seen made my head spin just looking at them. One
example is deep-drawn shapes designed to be made from special armor plating having
yield strengths above 200,000 PSI. Another example is high-tensile, hard stainless
steel parts 8 in. in diameter and 0.020 in. thick with a flatness tolerance of 0.003 in.
TIR. These are just a couple of instances of specifying materials without fully
considering the manufacturing process. I'm not saying that these geometries can't be
made from these materials, but they most likely can't be made using a conventional
sheet metal stamping process.

2. The consistency of the part geometryMetals with great tolerances within a given
specification behave differently when subjected to the various metal cutting and
forming processes. The result is inconsistent part geometry.

I find it very interesting that parts frequently are designed with tolerances that are
tighter than the metal is held to. In other words, stampers often are expected to create
a consistently shaped part using a process in which many of the input variables are
inconsistent. I was once taught that whatever tolerance was expected from the end
product, the process that makes it must have a tolerance that is 10 times less than the
end product.

3. The press type and tonnage neededHigher-strength materials, such as advanced
high-strength and stainless steel, require greater forming and cutting forces. In
addition, certain materials, such as stainless steel, are best-suited to slower forming
and drawing speeds. Parts with a small hole-to-thickness ratio require a rigid press
with very little ram-to-bolster deflection.

4. The type of tool steel neededMaterials such as high-strength and martensitic grades
of steel require the die to be made from premium tool steel grades like powdered
metals and solid carbide. These premium tool steel grades not only cost more, but
require more machining time to produce. Also, certain die components may need to be
coated. This also inflates the tooling cost and increases the time necessary to complete
the tooling.

5. Tool steel geometryParts designed from heavy metal gauges require larger, stronger
sections of tool steel. It also may be necessary to key in all tool steel sections to
reduce the deflection during cutting and forming the metal. Additional heels often are
needed in the tools used to process these heavier materials.

6. The number of stations required to make the partCertain metal types and
thicknesses may require more stations than others. For example, designing a formed
part out of high-strength steel may require one or more re qualifying stations or re
strike operations.

7. Additional special operationsWhen using some grades of superalloys, such as
INCONEL?, you may need an additional annealing operation between forming
stations. This increases manufacturing costs and slows down production. This is why
aircraft parts are so expensive.

8. The lubricant needed to form and cut the metalHow does the metal type that the
part is made from affect the lubricant used in the tooling? It's simple; higher-strength
metals generate more friction than their low-carbon counterparts. As a result, they
require lubricants that do not break down or "burn off" during the metal cutting or
forming process.

High-strength steel grades often necessitate adding extreme-pressure additives such as
sulfur to the lubricant. These additives not only increase lubricant cost, but they often
create welding problems during the assembly process. In addition, using bright
stainless steel requires the lubricant to have special wetting agents to help it stick to
the metal.

9. Additional material needed to make the partParts made from high-strength steel,
such as dual- and triple-phase steel, often have more springback problems than
low-carbon steel. To help reduce the amount of springback, it frequently is necessary
to increase the strain or stretch levels in the part. Achieving this often calls for the part
geometry to be drawn or stretched into the finished geometry, which may require
excess material on the part's perimeter so that it can be stretched over a punch. This
extra material later is trimmed away and discarded as scrap.

Making the part from thicker-gauge low-carbon steel can reduce the need for
stretching and drawing dies, but keep in mind that the finished part will now weigh
more. Also keep in mind that metal is purchased by the pound or ton. Parts made from
thicker metals will cost more.
As you can clearly see, the metal used to make the stamping parts have a significant
effect on the tooling and manufacturing costs. Next time you're choosing a metal for
your part design, consider how many factors your decision affects. It all begins with
the product designer. A product designer's decisions can make or break a metal
stamping process.

				
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posted:4/6/2011
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