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How to Improve Plastic Injection Mold Cycle Times with Proper Procedures, Maintenance, and Cleaning

Aug 11, 2022, 17:46 PM by The Stoner Molding Solutions Team
If you own or manage a plastic injection molding operation, you know that the longer the cycle time takes, the more money you waste. You’re likely always looking for ways to improve cycle times, through methods like shortening certain process stages, experimenting with new mold release agents, or improving your plastic injection mold cleaning procedures.
The inside of a plastic injection mold.

If you own or manage a plastic injection molding operation, you know that the longer the cycle time takes, the more money you waste. You’re likely always looking for ways to improve cycle times, through methods like shortening certain process stages, experimenting with new mold release agents, or improving your plastic injection mold cleaning procedures. But sometimes, this trial-and-error approach can be frustrating and cause more time to be wasted during your production schedule.

At Stoner Molding Solutions, we understand that you want to eliminate as much downtime as possible and operate at optimal cycle times to improve your operations. That’s why we’ve designed injection molding release agents, cleaners, and lubricants to meet your needs. We’ve been in the mold release industry since 1942 and have the experience, knowledge, and experts to help you release more products in less time.

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What Is Cycle Time in Injection Molding?

Before we get into the nitty gritty of plastic molding cycle time and how to improve it, let’s look at what cycle time is, so you know what you’re trying to measure. Cycle time in the injection molding industry refers to the total time required to complete all stages of the injection molding process. The stages include:

  • Fill Time—The time between the moment when the mold is clamped shut and how long it takes the mold to be filled with the melted polymer. The machine largely controls this stage.
  • Packing Time—Also known as the holding time, this stage encompasses the time it takes for the pressure to be applied to the melted polymer to compress it and force in more material. Approximately 5 to 25% more polymer is packed into the mold at this stage.
  • Cooling Time—The time required when the mold is held shut, and the polymer cools and hardens. The cooling time is typically the longest part of the injection molding process.
  • Open Time—The stage in the process where the mold opens, air rushes in to break the seal of the molded part from the mold surface, and the ejector pins push the piece out. This stage also includes prepping the mold for the next molding cycle by spot cleaning molds with high-quality mold cleaner and reapplying injection molding release agents, if necessary. The mold is then clamped shut for the next process.

What Is a Normal Injection Mold Cycle Length?

There is not a normal cycle length for injection molding. Each cycle depends on several factors, including the size and complexity of the part being molded, the polymer type and any additives introduced, the mold itself, and a host of other factors. It even depends on which plastic injection mold cleaning, release, and lubricant agents you use.

There is no magic number. The cycle time could last two seconds to two minutes, but thicker parts may take five to 10 minutes to complete. You can measure the average cycle length for your molding operations by timing it from when the mold is clamped shut to when operators finish prepping for the next cycle. Once you figure out how long your unique process takes, you can start trying to improve your injection molding cycle time.

What Affects Cycle Time in Injection Molding?

A hand holding a bunch of small baby blue plastic pellets.As we stated in the previous section, several factors could affect the cycle time in your injection molding operations. Some factors include:

  • Mold release agents
  • Ejector pin lubricants
  • Cleaning solutions
  • Mold cleaning processes
  • Preventative maintenance frequency
  • The people operating the machine
  • The plastic you use (certain polymers don’t solidify as quickly)
  • Wall thickness
  • Mold temperature

That’s why when you want to improve your injection molding cycle times, you must carefully evaluate each aspect of the process to see where you can make improvements.

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Are There Any Challenges to Reducing Cycle Time?

As a word of caution, before you attempt to reduce cycle times, you may find yourself molding fewer inferior parts. For example, if you decrease the cooling time and try to eject a piece before it completely hardens, you may damage the mold. It could also warp the part when demolding, so you must take steps to reduce cycle time without sacrificing part quality or decreasing mold life.

How Can I Improve the Productivity in My Injection Molding Process?

You can do many things to improve your injection molding cycle times. Some of these steps involve the molding cycle itself, and others focus on your team, training, and maintenance procedures.

1. Ensure your Team is Properly Trained

If newer operators take more time in the molding cycle than more experienced operators, it’s time to give the newbies a training partner. The more experienced operator likely has some tips and tricks that can make the process faster and help the newer operator.

Additionally, provide ongoing training and documentation on proper plastic injection mold cleaning procedures, maintenance, and cycle information to keep standard operating procedures fresh in everyone’s mind.

2. Perform Routine Mold Maintenance

Just like cars need oil changes after a certain number of miles or months, injection molding machines need routine mold maintenance after so many cycles. Cleaning after a set number of cycles extends the working life of the mold and ensures that it will continue producing high-quality parts. Skipping this step will decrease the life of your expensive injection mold and cause cycle times to be longer.

3. Reduce Scrap Parts

You may be able to get a low cycle time with some of these steps, but if that means you’re producing more scrap parts, are you really reducing cycle time? Instead, you need to improve your cycle time while also reducing scrap parts. You can minimize scrap by using the right molding products, recycling the scrap parts if possible, and optimizing your overall manufacturing process.

4. Use the Right Molding Products

Two cans of Stoner Mold Cleaner sit on a workbench while a worker cleans a mold beside them.Like the last step to reduce scrap, using the right molding products can help you improve your cycle time. When parts release quickly and wholly from the mold, there is no wasted time trying to get the piece out or cleaning excess resin from the mold surface. At Stoner Molding Solutions, we have various molding products specifically designed for the injection molding industry, including:

  • Mold Release Agents—Release agents come in different formulations for injection molding. From solvent-based releases to silicone-free releases, our mold release sprays are designed to allow multiple releases per application and provide a solution to sticking parts, cracking, and build-up.
  • Lubricants—Our penetrating lubricants reduce friction and prevent sticking for faster, quieter, and more efficient molding operations. They can clean, lubricate, and protect most metal surfaces while penetrating between close tolerances.
  • Plastic Injection Mold Cleaning Products—A meticulously cleaned mold is the first step to ensuring that your molding process runs smoothly. With cleaners specially formulated for the injection molding industry, you can count on your cycles to run faster and more smoothly.

5. Experiment with Slightly Shorter Hold Times

Since each polymer and part being molded is different, you can sometimes shorten hold times and still produce higher quality parts. Start by reducing the hold time for a few seconds to see if it affects part quality. If the piece still meets your standards, then you may be able to reduce the time even more. Keep experimenting until you find that hold-time sweet spot.

For More Plastic Injection Mold Cleaning and Maintenance Tips, Trust Stoner Molding Solutions

When it comes to plastic injection molding, even reducing certain steps by a fraction of a second to a few seconds will help to improve your cycle times and increase your efficiency. But you can’t do that without the right advice from experts in the thermoplastics field. That’s why you need Stoner Molding Solutions. With our plastic injection mold cleaning products and release agents, you can easily mold more parts in less time. If you combine that with some of our other tips in this blog post, you’ll be well on your way to getting the optimal cycle time for your molded parts. Get in touch with our experts today to learn more ways to reduce cycle time and find the right products for your plastic injection molding operations.

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