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About:
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What is <a href="https://www.doush-dass.com/" target="_self">Injection Molding</a>:
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Injection Molding is a manufacturing process for producing parts in large volume. It is
most typically used in mass-production processes where the same part is being created
thousands or even millions of times in succession.
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Why Use Injection Molding:
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The principal advantage of injection molding is the ability to scale production en masse.
Once the initial costs have been paid the price per unit during injection molded
manufacturing is extremely low. The price also tends to drop drastically as more parts are
produced. Other advantages include the following:
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Injection Molding produces low scrap rates relative to traditional manufacturing
processes like CNC <a href="http://www.doush-dass.com/rubber-machine/" target="_self">rubber
machining</a> which cut away substantial percentages of an original plastic block or sheet.
This however can be a negative relative to additive manufacturing processes like 3D printing
that have even lower scrap rates.
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Note: waste plastic from injection molding manufacturing typically comes consistently
from four areas:
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The sprue
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The runners
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The gate locations
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Any overflow material that leaks out of the part cavity itself (a condition called
“flash”).
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A sprue is simply the channel that guides molten plastic from the nozzle of the injection
molding machine to the entry point for the entire <a href="http://www.doush-dass.com/rubber-
machine/rubber-injection-machine/" target="_self">rubber injection mach</a>ine tool. It is a
separate part from the mold tool itself.
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A runner is a system of channels that meet up with the sprue, typically within or as part
of the mold tool, that guides the molten plastic into the part cavities within the mold tool.
There are two principal categories of runners (hot and cold) which you can read about here.
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Lastly, the gate is the part of the channel after the runner that leads directly into the
part cavity. After an injection mold cycle (typically only seconds long) the entirety of the
molten plastic will cool leaving solid plastic in the sprue, runners, gates, part cavities
themselves, as well as a little bit of overflow potentially on the edges of the parts (if the
seal isn’t 100% right).
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Thermoset material, such as an epoxy resin that cures once exposed to air, is a material
that cures and would burn after curing if one attempt is made to melt it. Thermoplastic
material by contrast, is a plastic material that can be melted, cool and solidify, and then
be melted again without burning.
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With thermoplastic materials the material can be recycled are used again. Sometimes this
happens right on the factory floor. They grind up the sprues/runners and any reject parts.
Then they add that material back into the raw material that goes into the injection molding
press. This material is referred to as "re-grind".
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Typically, quality control departments will limit the amount of regrind that is allowed
to be placed back into the press. (Some performance properties of the plastic can degrade as
it is molded over and over). Or, if they have a lot of it, a factory can sell this re-grind
to some other factory who can use it. Typically regrind material is used for low-quality
parts that don't need high performance properties.
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Injection Molding is very repeatable. That is, the second part you produce is going to be
practically identical to the first one etc. This is a wonderful characteristic when trying to
produce brand consistency and part reliability in high volume production.
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