Page 36 - Plastics Nuews October 2017

FEATuRES
FEATuRES

Will 3D Printing be the Demise of Plastic Injection Moulding

Plastic injection molding is a tried and true method of production that is in no danger of going
away anytime soon.

ome observers of the at where 3D printed tooling inserts may fi t into the
Splastics manufacturing big picture, and concluded that there were still signifi
industry, especially those cant issues with both metal inserts (surface fi nish and
with a vested interest, machine cost) and polymer inserts (surface fi nish as
would like to have you well as poor strength and heat transfer).
believe that 3D printing is Quality
going to be the demise of
injection molding. While One of the key limitations of 3D printing is the inability
there are certainly cases to make parts with the same physical properties as
where 3D printing makes conventional injection molded parts. Although the
sense, the reports of the number of various materials available for 3D printing
death of injection molding have been greatly exaggerated. seems to be constantly increasing, it is still limited
compared to all the various plastic materials that can
Plastic injection molding is a tried and true method of be injection molded. While a 3D printed prototype might
production that is in no danger of going away anytime be acceptable for evaluating its shape, there is no way
soon. It is a basic, dependable method of producing high to test the material characteristics if your prototype is
quality plastic parts. Despite recent improvements in not the same material as the production part will be.
the technology of 3D printing and those likely to emerge
in the future, the fact is that more than 80% of plastic Another issue cited in Kazmer’s study was surface
parts used in products today have to be injection molded. finish. While the surface fi nish of the part may vary
The answer to the question, “Which manufacturing according to how good (expensive) the 3D printer is,
method is best for my part?” is, “It depends.” It depends it is still no match for the smooth surfaces attainable
on variables like quantity, quality and cost. Quantity with polished steel injection molds. Last, but certainly
David Kazmer, Professor of Plastics Engineering at the not least in the list of quality diff erences, is the issue
University of Massachusetts Lowell, said in a published of tolerances. Although the ability of 3D printing to
paper that 3D printing currently makes sense for the hold tighter part tolerances is expected to improve
most rapid “procurement time to quantity” for a small with advanced process designs (like parallel printing)
quantity of 50 or fewer units. So for production runs, and optimization, today the part quality achieved in
injection molding is still the best manufacturing method, 3D printing is inferior compared to injection molding.
especially considering the long production time involved Cost
for 3D printing compared to injection molding. There
is an emerging “hybrid” practice of 3D printing the The overall cost of a 3D printed part compared to an
mold tooling inserts only, then producing the parts with injection molded part is tied to the quantity being
injection molding. produced, assuming the aforementioned quality issues
do not preclude 3D printing as an option out of the
For certain limited applications, 3D printed inserts can gate. In the study at Lowell, the cost of 3D printing 300
be employed as a test mold for product development and of a certain size part was $20 each. The piece price of
very limited quantities. A 3D printed mold may last for injection molding a million such units with a steel mold
typically just 60 to 180 pieces. Kazmer’s study looked was just $1.13 each.

Plastics News | Octob er 2017 36