of the part. The critical dimensions of the part were machined
inside of the slide-core mechanism during the injection molding
process. A high speed computer numerically-controlled electronic discharge machine was used for final machining, since it
can control tolerance to less than 3.0 microns.
The next step in the mold fabrication process was a testing
and debugging phase, which incorporated a dry run and analysis
of product first off the tool. Once parts that met the dimensional
specification were molded, key process parameters were identified and logged to define the perfect process window.
Following internal validation and functional testing, the parts
were sent to the customer for their evaluation. The cost of the
plastic valve set was near parity to the amortized life-time cost
of a metal valve set. When the cost of the autoclave/steriliza-tion process following each procedure was considered, the cost
of the disposable, single-use valve set was lower than then per
procedure cost of using reusable parts. However, the real value
of the use of a single-use, disposable valve set was the contamination risks it mitigates for patients.
The primary challenge in this project wasn’t related to
resources or technical capabilities. Instead, the challenge was
cognitive. The contract manufacturer’s team needed to design
an innovative approach that utilized existing equipment and
tools in ways that eliminated the tolerance constraints found
in traditional approaches to tooling design. Software modeling
tools were critical in designing the tool, hot runner, and cooling
system. Mold-flow analysis and DoEs were performed to
optimize the design and molding parameters. Molding process
simulations were also done to test design assumptions prior
to tool fabrication and to enable the tool designers to easily
demonstrate the likely performance of the tool to the engineering team during the design process.
Integrating design, design analysis, tooling, and injection
molding expertise enabled the team to develop a viable solution
applicable to invasive medical devices used in surgical and/or
diagnostic procedures. MDT
used for a cushioning effect, in order to develop a spring
that provided the same “feel” to doctors as the metal spring.
Designing the Mold
The most significant challenge involved mold design. The
design of plastic components is fundamentally different from
that of metal components because the manufacturing process is different. Fabricated metal parts are formed through
machining, which supports very tight tolerances, precisely
formed groves, and sharp corners with 90 degree edges to
achieve a tight seal. Conversely, plastic parts are formed via
an injection molding process, which traditionally has wider
tolerances and delivers a less precise cylindrical form.
The tolerance for the components used in the suction
valve assembly was 5.0 microns, which gave a window of
± 2.0 microns. When a part is injection molded, there is a
possibility of non-centering. Additionally, cylindrical molded parts are typically not a perfectly shaped cylinder. The
initial parts did not have the required tolerance, and as a
result, there was leakage in the activation button.
The team decided to change the mold and the molding
concept. The two-cavity mold was redesigned to include a
slide-core mechanism for forming the cylindrical portion
Software modeling was critical in designing a tool, hot runner, and
cooling system that met the project’s requirements.