Knowledge Base

Plastic Molding Manufacturing Process: 3 Ways to Reduce Scrap Parts

Apr 25, 2022, 12:39 PM by The Stoner Molding Solutions Team
Your plastic molding manufacturing process would produce perfect parts during every molding cycle in an ideal world—with no imperfections and zero waste. The blow or injection molders on your team would be happier, productivity and profits would skyrocket, and you wouldn’t face the stress of figuring out what’s causing so many scrap parts during the molding process.

Plastic bottles on a blow-molding machine.Your plastic molding manufacturing process would produce perfect parts during every molding cycle in an ideal world—with no imperfections and zero waste. The blow or injection molders on your team would be happier, productivity and profits would skyrocket, and you wouldn’t face the stress of figuring out what’s causing so many scrap parts during the molding process.

Unfortunately, we don’t live in a perfect world, and whether caused by human error, machine malfunctions, or inferior mold release products, waste is part of the plastic molding process. While you may not be able to get to zero scraps and waste, there are some steps you can take to reduce the amount of scrap your process produces.

1. Choose the Right Molding Products

First, are you using the right molding products? Having a high-quality and peer-tested mold release agent, mold cleaner, and processing aid can make a difference in your plastic molding manufacturing process. Stoner Molding Solutions has been the leader in the industrial molding sector for over 80 years.

Our industry-leading experts and chemists design and engineer the best products on the market. We can even work with you to create custom formulations tailored to your production requirements and help you reduce scrap.

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Mold Release Agents

If you’re dealing with sticking parts, cracking, and excess build-up on your molds, then you are likely using the wrong mold release agent or too much of the right one. Stoner has mold release agents specifically designed for the thermoplastics industry. Whether you need a conventional sacrificial coating or a semi-permanent release agent, we have the formulation you need to optimize your production and reduce scrap parts. With our products, your final piece will release wholly from the mold, without imperfections that lead to scrap.

Mold Cleaners

If you’re producing a large volume of plastic parts but aren’t taking the time to clean your mold properly, you’re doing a disservice to your entire rotational or injection molding process. Cleaning your mold with industry-leading mold cleaners from Stoner Molding removes any residual material, rust, and product build-up to ensure that the mold release agent can bond adequately, giving you the perfect release every time.

Processing Aids

Did you know that the right processing aid can reduce your scrap by up to 40% for rotational molding operations? We developed Stoner RotoFlow to solve quality and production challenges faced by the rotational molding industry, like reaching the inserts, tight radii, threads, and deep cavities of hard-to-fill parts. This product increases the flow of polyolefin and nylon resins to produce fully molded parts and eliminate voids, pinholes, bridging, and other imperfections.

Injection molding operations can benefit from ejector pin lubrication using Stoner Molding’s E436 Mold Release & Ejector Pin Lube. This product provides the durable mold release coating your tooling needs while also lubricating the ejector pins to easily push the part off the mold.

2. Recycle Scrap Parts, if Possible

The second tip to reduce scrap in your plastic molding manufacturing process is to recycle your scrap parts. If your operation performs plastic injection molding, smaller scrap plastic material, like sprues and runners, can be added back to the hopper with other plastic pellets to start the molding process over again. These heavy injection molding machines will melt the scrap part again so that it can continue injecting molten plastic into the cavity image.

Some blow molding for thin-walled objects may also be able to recycle defective parts or excess plastic by putting them back into the hopper that feeds into the machine forming the part. The deflasher removes the extra tail in a closed-loop system, and that part is provided back into the system. It is ground and reused to create another batch of products.

3. Optimize the Manufacturing Process

The third way to reduce scrap is to optimize your plastic molding manufacturing process. Optimizing the process can be as simple as trying a sample of one of Stoner Molding’s mold release products, cleaners, or processing aids to see just how well it performs. Another way to optimize the manufacturing process is to keep detailed records, particularly around scrap parts. Ask yourself these questions:

  • Does a certain machine produce more scrap parts than others? Perhaps it’s reached the end of its molding life or needs servicing. Things like a malfunctioning feed system, inconsistent screw-stop action or speed, variable injection pressure, and insufficient cycle and cooling times can all lead to scrap parts.
  • Do less experienced molding operators generate more scrap pieces than your veteran molders? Maybe they need more on-the-job training and tips from those with more experience.
  • Are scrap parts happening because of too much build-up? Stay on top of build-up by using multiple light coats of release spray and perform preventative maintenance when required.
  • Is the plastic molding manufacturing process documented and followed by all? If not, use this opportunity to define best practices and procedures and ensure all employees adhere to them.
  • Is the injection unit maintaining a consistent melt temperature? The wrong temperature changes cavity pressure, cycle time, and injection time. Your plastic parts will display imperfections like splay, burning, flashing, and bubbles if the temperature is imbalanced.

Bring Scrap Parts Down to Near-Zero in Your Plastic Molding Manufacturing Process

You want to see parts free from defects when a mold is opened. Molding more parts in less time allows for high performance from your machines and operators and a shorter lead time for your customers. So, if you’re tired of flow marks, sink marks, part delamination, and other molding issues that cause you to scrap parts, it’s time to analyze your plastic molding manufacturing process and see where you can improve.

Your tooling costs hundreds of thousands of dollars, so you need to use the best molding products to extend their life and reduce the number of scrap parts in your heavy injection molding process. If you need more tips on reducing scrap parts or finding the right molding products to optimize your manufacturing process, contact our experts!

We’ll be glad to listen to your molding woes and suggest the appropriate steps to eliminate or decrease that stress at your job. After all, you deserve a molding operation that controls its scrap output to remain competitive in your field.

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