Water-Assist Injection Molding (WAIM)
ABSTRACT:
This article provides an introduction to the benefits of water-assist injection molding (WAIM), as well as to
some of the key differences between WAIM and gas-assist injection molding. A detailed animation quickly
introduces the reader to a typical WAIM process, its equipment and configuration. The article also
contains links to WAIM-optimized materials and opportunities for more detailed education on WAIM.
Water-assist injection molding (WAIM) is one of
the latest and most promising developments in
“assisted” injection molding. As in the established
gas-assist injection molding process,WAIM
technology uses a fluid under pressure to core out
a hollow plastic part in the mold. Because of
similarities between the two processes, both
provide several of the same benefits:
 Lower material costs
 Lower tool cost
 More part consolidation and less finishing
than with un-assisted injection molding or
metals.
The differences between water and gas, however,
enable WAIM to introduce significant
improvements of its own:
 50% faster cooling cycle time than with
gas-assist molding
 Up to 25% thinner wall sections, based on
resin / composition
Molders may also combine gas-assist and waterassist technology in sequence to achieve further
benefits in certain applications.
Advantages of WAIM Technology
Cooling
WAIM reduces cooling cycle time to as little as
half that of gas-assist molding both because of the
properties of water and the structure of the
process. To begin with, the thermal conductivity of
water is 40 times greater than that of gas; its heat
capacity, four times greater. After injection, the
continuous flow of water coring out the hollow
section cools plastic from the inside at the same
time that the mold tool’s metal cools the plastic
from the outside. Although the mold tool performs
the same cooling function in gas-assist, injected
gas simply cannot cool as well as water can. In
fact, studies performed by BASF demonstrate that
the temperature of parts molded with gas-assist
continues to rise after demolding. The
temperature of WAIM-molded parts drops. In
addition, WAIM creates thinner walls that cool
faster.
Thinner walls, less material.
Compared to gas, water has higher viscosity and
is incompressible. In WAIM, water compresses
plastic uniformly into thinner walls – approximately
25% thinner than is typical in gas-assist molding.
Uniformity of wall thickness around bends and
other geometric shapes is a particular advantage
of WAIM. Thinner walls directly correlate to
materials savings; uniform walls, directly to
uniform strength.
Material surface and performance.
Even with hygroscopic resins, such as
polyamides, the water injection process does not
have a negative effect on material characteristics
– probably because the rapid cooling with WAIM
prevents water ingress. The molecular weights of
WAIM-molded resins are comparable to those
measured in gas-assist-molded resins. In studies
conducted by BASF, both polyamides and
polyesters at 25% regrind levels exhibit expected
molecular weight retention over five heat histories.
And the water-assist-molded parts can be
successfully powder-coated or painted.
Proven process technology, materials.
WAIM has been under development for some 10
to 15 years and is already successfully
commercialized in Europe. In North America,
BASF Corporation has built upon its European
experience and established WAIM technology and
application development capabilities. At its Budd
Lake, New Jersey, location, the company can
perform pilot-scale WAIM, gas-assist injection
molding, or the combination of the two processes
(GAS-WAIM). BASF has already optimized
several resin grades* (LINK) specifically for use in
WAIM or GAS-WAIM, and in several product
applications.
Applications.
WAIM is especially well suited for a number of
hollow-parts applications:
• Automotive fluid handling tubes for oils and
coolants
• Automotive door handles
• Oven and refrigerator handles
• Chain saw handles
• Office furniture chair arms
• Structural components in many industries.
Learn More About WAIM.
Every new processing technology comes with a
learning curve. Because WAIM resembles gasassist injection molding, molders already familiar
with gas-assist should grasp the intricacies of
WAIM most quickly. Before launching a successful
WAIM operation, however, some details regarding
equipment, process variations, materials and
applications (and investment) require explanation
and mastering.
Fortunately, several companies in Europe – and
now North America – have already done much of
the research and development work to ensure this
technology’s value and viability. In
addition,courses are available to help molders
master WAIM.