Apr 16/19

Thin Walled Plastic Injection Molding: How to Do It Faster, Better, Stronger

There are many interesting trends in the manufacturing industry.

Experts have noted that domestic manufacturing is making a comeback. Labor costs overseas combined with shipping costs are increasing to such an extent that they are neutralizing any cost advantages.

Even though there are changes in the industry, plastic injection molding is here to stay. That’s because it is one of the most basic and reliable methods for manufacturing plastic components.

Plastic injection molding has a sterling reputation for producing sturdy end products for a wide range of industries, from food to automotive. The demand for lighter and thinner parts makes this industry one of the most sought after in manufacturing. As such, engineers and scientists continue to innovate, trying to produce stronger, lighter, and thinner materials.

What is the key to successful thin-walled injection molding? In this article, you will learn the science and techniques required to manufacture faster, better and stronger.

Design It Right — Uniform Wall Thickness

When you’re making parts that are extremely thin, it’s important that the design of the wall thickness is as uniform as possible. Sometimes, there is a need to deliberately design the wall thickness to vary.

When that is the case, it’s important that the variation is not too steep. Gradual variations can be applied to ensure stability and strength. The variation should not exceed 10%.

Variations in thickness should be avoided wherever possible. If there are variations, the part is vulnerable to warping and cracking during the cooling process. Furthermore, the flow of molten resin through the tool into the mold may lead to air pockets and uneven areas.

Using the right tool and mold configuration is the smartest way to go in order to ensure uniform wall thickness throughout the part.

Use the Right Ingredients

Depending on the purpose intended for a plastic part, the right resin will be needed. There are thousands to choose from, and each one will have its own strength and thickness characteristics.

If you want a quality product, you need to work with others that can advise you on the best materials that will suit your product design and function.

It will help if you’re familiar with some basic material properties. For example, the hardness is measured on a scale from 0 to 100. There are two scales for soft and hard materials.

Another important variable to grasp is material flexibility. A common mistake is to assume that hard materials are rigid and that flexible materials are soft. Flexibility is the ability to bend under stress without breaking.

A familiar example of hard and flexible material is the plastic that is used to make the common school ruler. Another important variable is the material weight, which is determined by the density of the plastic polymer. Don’t try to select the right material on your own, use expert advice from the industry.

If you use the wrong material with the wrong strength and thickness characteristics, you’ll fail from the start.

Go with the Flow

This is all about physics. The thinner and smaller your product is, the faster the resin has to be delivered to the mold for the product to be within your quality control standards.

This is because with such a small amount of material and at a high temperature, when it is delivered to the mold, it will set quickly. If the speed is too slow, then the final product will be inconsistent and flawed.

High temperature, and especially high speed require high pressure. The pressure has to be consistent and sufficient to drive the material through the tool you’re using to deliver it to another surface. That of course, means you need the right equipment.

Equipment Considerations

If you’re making very small parts, such as 1mm thick, the mold fill time could be about 0.5 seconds and the pressure 30,000 psi. You will need equipment that can fit this type of specification.

It’s also important to think about the clamping force over the projected area as well as the use of extra heavy platens. These serve the purpose of preventing any flex during the manufacturing process.

Don’t Shoot in the Dark

The percentage of the barrel capacity that should be injected as a shot into the mold should be carefully calculated based on the material type used and the design of the mold itself.

As a general rule, the value should fall between thirty percent to seventy percent. Lower values are riskier as more material will remain in the barrel longer, and that can lead to degradation and ultimately, a poorer outcome.

Don’t guess it, follow the physics and calculate it, or rely on your manufacturing partner to guide you.

Expert Advice on Plastic Injection Molding

In this article, you have read about some of the science and techniques you need to keep in mind when using plastic injection molding or designing parts that will be produced using this method.

As you can see, it’s not simple, and there are many variables to keep in mind. With the right expert advice though, you can design and manufacture high-quality and consistent parts.

For more advice or to ask questions, get in touch here.

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