Hi!: somebody wrote here about a Chinese press machine he owned,
being able to provide several tons of pressure. The question is:
would this machine be able to produce parts such as body panels and
other steel, or aliminium, body parts of a car? Wit the current 3D
copiers, having one copier and a press of sufficient size would
allow making, part by part, a replica of any old car you may wish,
just the time and the money to make the casts or matrix would be
needed, and an original or a blue print to be used as pattern. Any
comment on this? Thank you, best regards. Salut † Jose Gros-Aymerich
Madrid, Spain

Pressing steel fenders takes many tons of force.

3D printing in steel or aluminum takes a long time and the machine to
do it is expensive. For one off parts use an English wheel.

Paul Lamar

Hi Paul: thanks for your response. My idea was not directly printing
the parts in a 3D copier, but using the copier as a first step in
preparing a cast to be used with the chinese press to make body parts
from sheet steel or aluminum, in the 60's, a machine for preparing
casts, by grinding in an Iron block, that followed the contour of
anything used as pattern, costed here around 9'000 Euros, when an
inside town bus ticket was 10 cents of an Euro. Regards. Salut †

Jose Gros-Aymerich Spain

Jose, the economics of various fabrication strategies depends on the
dimensions of your desired parts, and the quantities needed. It is
pretty unlikely that anything in the home built aircraft situation
(short of going into the business like Vans or Zenith) will justify
the costs associated with 3D printing. For flat profile parts IE ribs
and such, a good wood shop router, bits, and band saw on MDF material
are plenty for making dies. There was an article in EAA Experimenter
outlining a pseudo hydroforming technique for forming flat profile
parts, using a high powered press and strips of rubber in a die box,
but the big caveat there was that as the part area got larger so too
does the force required to form the part and also the die box to
contain the forces of the compressing rubber. The weight of the
containment box for a 20"x 12" wing rib I calculated to be around 250
lbs. Conventional sheet metal forming methods are cheaper, quicker to
get right, and proven over many years. Perhaps a CNC router to make
an MDF blank, which could then either be used directly for a limited
run of rib like structures, or as a casting blank for an aluminum die
for a longer die life? There are some CNC routers out there for about
$1000 or so that could do a rib size piece in MDF. Parts with great
depth like cowls and such use good old fashioned English wheel and
other old world craftsman sheet fabrication techniques. As Paul said
the, forces involved in stamping metal (even Aluminum) are quite
large, and the die material must therefore withstand the many
thousands of pounds per square inch of pressure to achieve fully
developed stamping details. In the article, for the
pseudo-hydroforming, I think the baseline was in the order of 1200
lbs per sq in of part surface area. Have you gotten any quotes for 3D
printing services, and what materials can they print?

C. Smith


Craig, where he used the word "cast" I think he meant stamping die.
IMHO He suggest making stamping dies with metal "printing".

Basically 3D printing in aluminum, Ti or steel is wire feed welding
on a 2D plotter with a 3rd vertical axis added. One weld bead on top
of the last weld bead. Probably in an argon temperature controlled
atmosphere. One tiny piece of metal at a time.

This is why it takes days to make something useful. An easy and
relatively cheap machine to make with a PC computer control. Finish
is an issue and it would probably be hand sanded for a stamping die.

The step file format from 3D programs like Rhino and Solid works is
probably what is used to control the stepper servos.


Paul Lamar

BTW any old NC mill would make a good 3D printer when combined with a
MIG welder. The spindle does not need to turn. -- Paul Lamar

In basic principal, yes. The devil is in the details. What will be
the actual metallurgical properties of the finished piece? What
about surface finish, dimensional tolerance? All of those will
require trial and error, a learning curve. So look at the costs
involved. NC Mill, $5-10K? The best DMLS machines (direct metal laser
scintering) are many times that. From what I've seen first hand, DMLS
is about the only method that produces ready to use product, with
minimal post processing, has documented process/metallurgical
properties of process. It's easy to say you can do this or that in
principal, but another thing altogether to actually DO it. I just
looked at a CNC router suppliers used machines they range in price
form $17K-95K. There are lots of hobbiest websites offering do it
yourself solutions, cheaper, but still in the thousands of dollars in
investment. A basic Carvewright setup starts around $1800. If you can
find someone local with a carvewright you may be able to get them to
make patterns fairly cheaply. C. Smith


Many thnks to all of you for the detailed responses, the implicit
concept in my question was using this procedure: 3D printing of a
cast, then passing it to any hard material, and using the cast with a
press to shape sheets of metal, and from the parts pressed, make
replicas of some special old cars, that can be produced in small
series if somebody is willing to pay for it.

As a matter of  fact, one of the cars that first came into my mind
when asking this question was the French 'Panhard Dyna', who
installed a flat twin, air cooled, 850 cc engine giving 45 HP and a
top speed of 150 kph, some 90 mph.

As you know, patents have an expiry date of 20, never more than 30
years, books and printed material are protected until 70 years after
the author's death, but the field of classic cars lovers is very big
and wide, and 'Variation is the spice' or the Blondie's song:
'Dreamin' is free' applies.

Regards. Salut †

Jose Gros-Aymerich Madrid, Spain



Paul,

Years ago (mid-1960's) I worked for an aerospace firm that used an old method to shape some large sheet metal panels.  Non-critical pieces, that didn't require the wall thickness precision of hydro-forming, were made by drop forging.

Male & female dies were cast from lead & fastened inside steel frames. The steel frames were mounted in a tower fabricated from I beams & angle iron. The top (male) die was hoisted to drop height where a pawl snapped into place restraining it. A piece of sheet metal would be placed on the bottom die & the die dropped.

The dies were used for short runs (=< 10-15 pieces) before they deformed to an out of spec condition. After that they were melted down and new dies cast from the molten lead to repeat the process.

The foundry patterns were fabricated from wood. The dies were sand-cast (probably using a fine greensand & bentonite mix nearest the pattern for smoothness) as I recall.

Old timers on the shop floor told me this method had been used to form body panel sheet metal for the car industry in Detroit many years back so it should work for this application.

Regards,

Jack Hilditch