Page 72 - Plastics News May 2024

IN THE NEWS

Injection molders can boost confidence used to prepare, inject, and pressur- time. Wasted resin. Inconsistent qual-
and trust from their OEM customer by ize a shot. At Freudenberg Medical, ity later. Little documentation that will
adopting the proactive mindset of a re- we provide operators with specific aid future setups.
searcher (why) rather than the reactive instructions during the NPI phase on
mindset of an operator (how). which variables to change, in what Beware the speed trap.
order, and how much. This process Quite often, companies set up their
Focus on the process of making was created based on 40 years of ex- machines to run at maximum pressure
consistent components. perience with medical device precision and/or flow limits. However, usually
injection molding and focuses on the
Plastic is a life-changing and transfor- when settings are “dialed in” at or near
mational material, although it can be process parameters maximum levels, problems occur shot
finicky. You might assume that a hop- No matter how small or large the medi- to shot, during the next shift, or are
per of pellets is as chemically consist- cal device injection molding project we even discovered the next day.
ent as salt. That's unfortunately not the are starting, we have rules for each of We recommend a focus on flow con-
case. Resins coming from the same these process parameters that cannot trol so high quality, repeatability, cavity
supplier and same location can vary be compromised. balance, and a consistent flow path can
by batch, and even within a batch. This be maintained during the first 95% of
is why molders who operate on a “set Medical device injection molding filling, and for a consistent pack chan-
it and forget it” principle using nar- fill studies done the right way. nel during the last 5% and beyond.
row processing parameters eventually Raw materials may vary by batch, While some people focus on applying
get a nasty surprise with components but thermoplastic polymers are quite a specific pressure, we emphasize ve-
that are not consistent. After that their predictable in that there are only four locity and observe thermoplastic pres-
hands are tied on how to properly re- “levers” you can pull to manipulate its sure. Ultimately you want to be meas-
store the parts. final form — temperature, pressure, uring the output not the settings of the
In the absence of a robust process, flow rate, and cooling rate/time. Most machine!
molders also tend to spend a lot of molders use melt flow index (MFI) or
time up front fidgeting with settings do a rheological study to evaluate how One thing at a time…
and running test cycles instead of the plastic will flow and perform during One of the most critical mistakes
stepping back and refining their setup injection, but the results tend to have molders make is adjusting more than
and test procedures. Again, this in- little correlation with part quality. one variable or phase at a time. When
evitably leads to more scrap + more In my 40+ years working in medical producing full parts, many param-
downtime = higher costs and missed device injection molding, I have ob- eters can be changed to try and “fix”
commitments. served that far too many operators a problem, but it is almost impossible
spend days, weeks, or even months to know how an adjustment affected
Define the rules and stay within doing these initial tests. They make an the process if you change two things
the guardrails. adjustment, start a machine cycle, take at the same time! Isolating the variable

The key to improving part consistency samples, walk away, wait for QC feed- in check is key.
is to refine and narrow the parameters back, and make more changes. Wasted

Injection screw cushion should be minimal to
Pressure should be adjusted to properly pack reduce the amount of variable material being
the part, not to fix flash, sticking, or sinks. Im- pushed through. Image courtesy of RJG Inc.
age courtesy of RJG Inc. via Freudenberg Medi- via Freudenberg Medical.
cal.

72 74 PL MAY 2024Y 2024 MAY 2024 PLASTICS NEWS 73
PLASTICS NEWSASTICS NEWS
MA