V
VictorLouis
Guest
Mr. Herb Belin of S&W posted this on another board where it's no longer retrievable. Moderators, I really think this should be an 'archival item', if you have such on this board.
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"I have read with much interest the many comments in
this forum pertaining to MIM, MIM Parts and the use of
same in a S&W product. So far I have come away with
several impressions and they are "people in general
don't like/trust MIM parts" and "no one has said why"
I will take a stab at this issue and see where it
goes.
As background to our decision to use MIM in some areas
of our Mfg Process we took a long hard look at our
"Life Time Service Policy". It was clear to us that
any change in any of our products such as the use of
MIM components had to show equivalent or better
performance and durability to those components that
were being replaced or the "Lifetime Service" would
haunt us forever. The second consideration was to
determine if the change was too radical a departure
from S&W mainstream design.
For the performance and durability issues we decided
that if MIM could be used for the fabrication of
revolver hammers and triggers succesfully this would
truly be an "Acid Test". There is nothing more
important to a revolvers feel than the all important
Single Action Sear that is established between the
hammer and the trigger. Mechanicaly few places in a
revolver work harder than at the point where the
hammer and trigger bear against each other. If these
surfaces wear or loose there "edge" the "feel" is
lost. Initial testing was on these two critical parts.
Over time we arrived at a point where our best
shooters could not tell the difference between a
revolver with the old style hammer and trigger and the
new MIM components. Special attention was given to
their endurance when used in our very light Magnum J
frames such as the early prototype 340 & 360 Sc's.
None of our revolvers work their components harder
than these small magnum revolvers. Throughout this
testing MIM held strong and finally we determined that
this change judged on the basis of durability and feel
was a good one.
The second area of concern to S&W was our customers
reaction to this departure from the traditional. Many
heated, intense discussions resulted but in the end
the decision was made to move ahead with MIM.
The issue of cost was only one of the considerations
in making this decision. Equally as important was the
issue of part to part uniformity and the result of
this of course is Revolver to Revolver consistancy. We
found that revolvers that used MIM hammers and
triggers required almost no Fitter intervention in
those areas during final assembly and final inspection
and Trigger Pull Monitor rejection rates dropped
markedly on finished guns. From an internal process
point of view it appeared a "Winner".
Lets shift gears for a moment and talk about the MIM
process. It is unclear to me as to the reason for many
of the negative feelings on the forum concerning MIM.
Typically when people complain and aren't specific in
the reason why, the problem is often created by a
departure from the "Traditional". Perhaps that is
indeed what is bothering some people when they view
MIM.
The term MIM stands fo Metal Injection Molding. It
holds some similaritys to Plastic Injection Molding
and many differences as well. To start we would take a
finally divided metal powder. This could be stainless
or carbon steel. Today even Titanium is being used in
some MIM fabrications. We would mix the metal powder
and a thermoplastic binder (generally a Wax) forming a
slurry of sorts when heated and inject this mix into a
precision mold and finally form what is known as
a"Green Part". This part is roughly 30% larger than
the finished part it will become at the end of the
process. Interestingly enough the Green Part at this
stage can be snaped in two with simple finger
pressure. The Green Parts are then placed in a
Sintering furnace filled with dry Hydrogen gas and the
temperature is brought almost to the melting point of
the metal being used. Over time the "Wax" in the Green
Part is evaporated, the metal fuses and the part
shrinks 30% to it's final correct dimensions. At this
stage of the process the MIM part has developed 98 to
99%of the density of the older wrought materials and a
metalurgy that is almost identical. Dimensionaly it is
finished and no machining is required. However the job
is not yet done and the MIM parts are brought to our
Heat Treat facility for hardening and in the case of
Hammers and Triggers, Case Hardening. Depending on the
particular metal alloy that was used at the start of
the process we apply a heat treat process that is the
same as would be used if the material was the older
wrought style. Final hardness, Case thickness and core
hardness are for the most part identical to parts
manufactured the older way.
Lets look for a moment at how we acheive dimensional
precision when comparing these 2 processes. The old
parts were each machined from either bar stock or a
forging. Each cut and every resulting dimension was
subject to machine variations, Cutter wear, operator
variations etc. If every operation was done exactly
right each and every time and the cutter didn't let
you down you would have produced a good part but
sometimes this didnt happen resulting in a rejected
gun and rework or in the worst case an unhappy
customer. With MIM parts you must still machine to
very high tolerances and your cutters have to be
perfect and your machinist has to be highly qualified
but all of this only has to come together one time.
That time is when the injection mold is made.
Typically a mold for this process costs S&W between
30,000 and 50,000 dollars. Once it is perfect every
part it makes mirrors this perfection and you have in
my view a wonderful manufacturing process.
Hopefully this description will help us all better
understand the MIM process.
Please forgive the spelling errors and missplaced
puncuation. I have no spell checker on this and the
phone continues to ring!
Have a Great Weekend,
Herb
Additional Point.
Currently S&W is paying about $1.20/Lb for stainless
steel barstock. Raw MIM stainless steel injectable
material costs $10.00/Lb."
-----------------------------------------------------------------------------------
"I have read with much interest the many comments in
this forum pertaining to MIM, MIM Parts and the use of
same in a S&W product. So far I have come away with
several impressions and they are "people in general
don't like/trust MIM parts" and "no one has said why"
I will take a stab at this issue and see where it
goes.
As background to our decision to use MIM in some areas
of our Mfg Process we took a long hard look at our
"Life Time Service Policy". It was clear to us that
any change in any of our products such as the use of
MIM components had to show equivalent or better
performance and durability to those components that
were being replaced or the "Lifetime Service" would
haunt us forever. The second consideration was to
determine if the change was too radical a departure
from S&W mainstream design.
For the performance and durability issues we decided
that if MIM could be used for the fabrication of
revolver hammers and triggers succesfully this would
truly be an "Acid Test". There is nothing more
important to a revolvers feel than the all important
Single Action Sear that is established between the
hammer and the trigger. Mechanicaly few places in a
revolver work harder than at the point where the
hammer and trigger bear against each other. If these
surfaces wear or loose there "edge" the "feel" is
lost. Initial testing was on these two critical parts.
Over time we arrived at a point where our best
shooters could not tell the difference between a
revolver with the old style hammer and trigger and the
new MIM components. Special attention was given to
their endurance when used in our very light Magnum J
frames such as the early prototype 340 & 360 Sc's.
None of our revolvers work their components harder
than these small magnum revolvers. Throughout this
testing MIM held strong and finally we determined that
this change judged on the basis of durability and feel
was a good one.
The second area of concern to S&W was our customers
reaction to this departure from the traditional. Many
heated, intense discussions resulted but in the end
the decision was made to move ahead with MIM.
The issue of cost was only one of the considerations
in making this decision. Equally as important was the
issue of part to part uniformity and the result of
this of course is Revolver to Revolver consistancy. We
found that revolvers that used MIM hammers and
triggers required almost no Fitter intervention in
those areas during final assembly and final inspection
and Trigger Pull Monitor rejection rates dropped
markedly on finished guns. From an internal process
point of view it appeared a "Winner".
Lets shift gears for a moment and talk about the MIM
process. It is unclear to me as to the reason for many
of the negative feelings on the forum concerning MIM.
Typically when people complain and aren't specific in
the reason why, the problem is often created by a
departure from the "Traditional". Perhaps that is
indeed what is bothering some people when they view
MIM.
The term MIM stands fo Metal Injection Molding. It
holds some similaritys to Plastic Injection Molding
and many differences as well. To start we would take a
finally divided metal powder. This could be stainless
or carbon steel. Today even Titanium is being used in
some MIM fabrications. We would mix the metal powder
and a thermoplastic binder (generally a Wax) forming a
slurry of sorts when heated and inject this mix into a
precision mold and finally form what is known as
a"Green Part". This part is roughly 30% larger than
the finished part it will become at the end of the
process. Interestingly enough the Green Part at this
stage can be snaped in two with simple finger
pressure. The Green Parts are then placed in a
Sintering furnace filled with dry Hydrogen gas and the
temperature is brought almost to the melting point of
the metal being used. Over time the "Wax" in the Green
Part is evaporated, the metal fuses and the part
shrinks 30% to it's final correct dimensions. At this
stage of the process the MIM part has developed 98 to
99%of the density of the older wrought materials and a
metalurgy that is almost identical. Dimensionaly it is
finished and no machining is required. However the job
is not yet done and the MIM parts are brought to our
Heat Treat facility for hardening and in the case of
Hammers and Triggers, Case Hardening. Depending on the
particular metal alloy that was used at the start of
the process we apply a heat treat process that is the
same as would be used if the material was the older
wrought style. Final hardness, Case thickness and core
hardness are for the most part identical to parts
manufactured the older way.
Lets look for a moment at how we acheive dimensional
precision when comparing these 2 processes. The old
parts were each machined from either bar stock or a
forging. Each cut and every resulting dimension was
subject to machine variations, Cutter wear, operator
variations etc. If every operation was done exactly
right each and every time and the cutter didn't let
you down you would have produced a good part but
sometimes this didnt happen resulting in a rejected
gun and rework or in the worst case an unhappy
customer. With MIM parts you must still machine to
very high tolerances and your cutters have to be
perfect and your machinist has to be highly qualified
but all of this only has to come together one time.
That time is when the injection mold is made.
Typically a mold for this process costs S&W between
30,000 and 50,000 dollars. Once it is perfect every
part it makes mirrors this perfection and you have in
my view a wonderful manufacturing process.
Hopefully this description will help us all better
understand the MIM process.
Please forgive the spelling errors and missplaced
puncuation. I have no spell checker on this and the
phone continues to ring!
Have a Great Weekend,
Herb
Additional Point.
Currently S&W is paying about $1.20/Lb for stainless
steel barstock. Raw MIM stainless steel injectable
material costs $10.00/Lb."
Somehow, this must've been overlooked when it was 'hand-fitted'. 
