When it comes to plastic machined parts, quality goes beyond what you can easily see. Often, a part might look right, it may pass initial quality
control tests and it might even perform well in the field at
first. But two weeks or two months down the road, something goes wrong.
The problem may not be in the design. It might be in
the manufacturing process, especially if the manufacturer
also makes metal parts rather than focusing exclusively on
machined plastic parts.
While a metal machinist may be capable of making a plastic
machined part, choosing the wrong machininst may result in a
product failing in the field. Contamination risks and a lack of
plastics expertise can contribute to problems that often don’t
arise until after a part is already in the hands of the customer.
Here are a few points to consider before hiring a metal
machinist to make a plastic machined part:
• Metal Contamination. Making a plastic part on a machine
that also crafts metal parts can lead to contamination. No
matter how well a company cleans its equipment, it’s difficult
to get every tiny fragment of metal off a machine. Those fragments can become embedded in a plastic part and cause them
to degrade over time. Just imagine a $2 million machine short
circuited in the field, and after taking the whole machine
apart, the manufacturer discovers a small metal fragment in
one of the machined plastic parts. That little piece is all it
takes to create a major problem.
• Oil Contamination. What is good for metal can wreak havoc
on plastic. Metal machining often requires the use of oil-
based cutting fluids. Even the cleanliest of manufacturers will
have trouble removing all of the oil residue from a machine
before running a plastic part. Many plastics are highly sen-
sitive to petroleum-based cutting fluids and will degrade if
they come into contact with them. Also, many plastics are
hydroscopic and will absorb the cutting oils. These problems
can be hard to spot at first glance. One medical analytics
company found this out the hard way. They had a product
that failed in the field, they thought, due to static. After closer
examination, they discovered that one of the plastic parts had
tiny cracks due to crazing, a degradation due to cutting oils.
The cracks were so tiny that they were only visible when the
part was viewed under a microscope.
• Materials Knowledge. A good plastics machining compa-
ny will be knowledgeable about what types of plastics
are best for what uses and will be up on the latest mate-
rials — expertise that a metal machinist likely won’t
have. A plastics machining expert can share information
on what plastics perform best according to factors such
as humidity, abrasion resistance and thermo sensitivity.
By Alex Curtiss
The Right Parts
Need the Right
Wonder why plastic parts are failing in the field? Take a closer look at the