Plastic Injection Molding Process

The plastic injection molding process is adaptable, making it versatile enough to produce anything from a simple plastic cup to car and laptops parts. While there are some alternatives to injection molding – like 3D printing and spin casting – injection molding remains the most reliable way to produce plastic goods. Because of this, injection molding is still the technique most often used to produce plastic goods in the 21st century.

But what is injection molding exactly? What does the typical injection molding process look like? And what exactly is it that makes injection molding so much more adaptable (and hence more versatile) than other options?

What Is Plastic Injection Molding?

Plastic injection molding is a technique used to shape plastic in the form of the object you’re aiming to produce. During the injection molding process, thermoplastic polymers are injected into a mold cavity. To do this, pellets of a material are heated so they can be injected into the cavity in a liquid state. This hot liquid is then left to cool in the mold so the part can properly set. Once one part is ejected from the mold, another cycle can promptly begin.

Although injection molding can also be used for metals and glass, it’s a particularly popular production process for manufacturing plastic parts.

The steps in an injection molding process cycle include clamping, injection, cooling and ejection.

During clamping, the injection mold is prepared for a cycle by tightly clamping the two halves that form the mold cavity into place. This ensures that the molded part will have a smooth appearance and ideally the molded part should have almost no line where the different halves came together, as this shows that the mold might not be clamping tightly enough.

Once the mold halves are clamped together, the mold is ready to form a part. Before the polymer is injected into the mold, the pellets are heated to form a liquid. The liquid polymer is then injected into the mold through a nozzle. This is the injection stage of molding process, which is the second stage in a four stage cycle.

Next, the part is left to cool in the mold for a predetermined amount of time. The cooling stage can take anywhere from a few seconds to a few minutes depending on the polymer being used to produce a part. While some polymers need hardly any time to cool at all, others can take a few minutes. It all depends on the part being produced.

Once a part has cooled, the injection mold is opened and the part is ejected from the mold. The mold will clamp again and prepare for its next cycle.

Because manufacturers know how long the cycle on their molds are, they can accurately predict the amount of parts a mold will produce every hour. This helps manufacturers know exactly how many parts they’ll be able to produce every day, week and month with a fully functional mold.

Why Is Plastic Injection Molding So Popular?

As mentioned above, plastic injection molding is a very predictable process. This predictability also makes the process dependable, as injection molding companies will know exactly how many parts they can expect from every mold they own.

Based on the amount of parts each mold is able to produce, manufacturers can calculate how many molds they need to in order to produce enough parts for their production line to operate at its intended capacity.

It should also be possible for manufacturers to estimate the amount of parts they can produce with a mold during its entire lifetime, making it easier to calculate whether or not a mold will generate enough income to cover its own costs with profit added.

All this is fine and well, but for injection molds to be reliable and predictable they must be maintained according to a maintenance schedule.

Unfortunately, some manufacturers run their molds till they break down. This might be because they’re just inherently stingy, but often times it was recommended to them by financial advisors in their company. The problem is that finance and engineering are worlds apart.

As mold manufacturers, we know that regular mold maintenance can extend the lifetime of your molds and help them operate optimally at all times. Yes, mold maintenance is an expense, but it’s not one you can cut to save money. If molding plastic parts is an integral part of your business, the condition of your molds in undoubtedly important. Cutting on maintenance by working molds till they break down will hurt your company.

It’s ironic that predictability, which is one of the advantages of injection molding, isn’t considered by many molders when overworking their molds. Fact is, a mold that works till it breaks down can’t always be repaired, and the halt in production from the broken mold can’t be scheduled because you won’t know for certain when it will break down.

When looking at it like that, it’s hard to understand why working a mold till it breaks could be considered a viable way to save money. Perhaps it’s time that molders look further into the issue of maintenance to establish what really works best.

But apart from the predictability of plastic injection molding, the process is also very versatile. Thousands of polymers can be used for injection molding purposes, and injection molds can be adapted for different uses. Which is why the process is as effective for the automotive industry as it is for the medical industry. With micro-molding technology, injection molding can even produce even very small parts with surprising accuracy.

To conclude, injection molding is popular mainly because no other manufacturing process allows manufacturers produce a lot of parts in a relatively short amount of time, all while maintaining the desired level of part integrity.

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