Plastic injection molding is a popular process in making parts. The process allows you to produce more at a low cost. There is a wide range of materials to choose from that can meet the application’s needs. Using the right material and design, the process can give you the same strength and hardness as metal. Plastic injection molding can have a lot of benefits. But, it’s essential to keep in mind that it can also have a lot of injection molding defects problems. Some of which is due to bad mold design or operators who are not familiar with certain types of materials or molds.

Injection molding defects may not only cause by an error in the molding process. But, also due to materials used. It could also be on the way they handle the material before using it to make the item. The flaws in this category can be minor in the look of the molded item, or they can weaken the part. They may cause damage to how they made the products.

Below are some of the injection molding defects due to the materials usedand ways to avoid them.

Delamination!

Other terms for delamination are layering or lamination. It is when the surface layers of a molded part peel off. It usually occurs in the gate area but may also happen in any part of the molded item. The defect can be small or big.

Causes of Delamination

The first thing to do is to look at the materials you will place on the mold. Here are a few things that can cause this defect or other problems.

• Separation and parts that don’t fit well can happen when dirt or foreign materials are in the molten plastic. This is because it can’t bond with the plastic.

• Plastics that don’t mix: Double-shot molding and over molding two plastics that don’t work well can cause them to separate.

• Too Much Moisture: Plastics need different drying conditions than other materials. Applying the right amount of heat removes the plastic pellets’ surface moisture to avoid delaminating.

Tips to Avoid Delamination

You need to figure out first what caused it to solve this issue in molded parts. Your company can help you choose the right plastic for your project. This can keep the layers of polymer from separating or breaking apart.

The producer must be extra careful to make sure that the materials that go into the mold are perfect and free from dirt.

If the processing tool is not working properly, the molding company must fix it. It can be hard to deal with this issue in injection molding. But, if you work with a firm that cares about making high-quality parts, you will get durable and high-quality components.

StepRapid has been making high-quality plastic injection parts for clients all over the world for a long time now. in the meanwhile, we also experienced a lot of injection molding defects.

Weld Lines–injection molding defects

During molding, when two or more flow fronts can’t “knit” together or “weld,” the weld line is the line where they meet. These lines are found around holes or barriers, and they weaken the molded part in those places.

Causes of Weld Lines

When designing a component, a few things can lead to weld lines. Some of these factors are:

• Pressure. A wide weld line can happen if the pressure is not strong enough to push the flow and meld it back together. If your machine is broken or you set it up wrong, these things could happen. It could also be because of problems with how the mold was made.

• Temperature. If the temperature isn’t high enough, you may start to have early hardening. This is when things start to stick together. You might see some parts harden during the process while the rest of the parts move on. As a result, you get weld lines.

The temperature might reduce in various areas that require resin to flow continuously. Some of these places are the mold, runners that go to the mold, and the machine that makes plastic.

• Mold design. When you make a mold with a bad design, you might see weld lines in different parts of your design. Some common mistakes in mold design that can cause knit lines are having the wrong wall thickness and having the gates in the wrong places.

• Speed. Slowly, the resin will move through the mold. So the fronts may not cool at the same time. Knit lines could form if one cools before the other.

• Impurity. Moving it through the mold is not easy if the material has impurities. It only means that a part may flow faster than the others.

• Too much mold release. If there’s too much mold release, you may need to use more pressure to move it through the machine, which could hurt it. Weld lines could form if the speed doesn’t go up.

How to Get Rid of Knit Line?

You can avoid welding lines in plastic injection moldng, by making sure there is only one front during the molding process. You can also get rid of the knit by making sure the line is well covered. These tips can help you do this:

Change How the Part Looks

If you want to do this, you can make the walls thicker. It will help with pressure transmission, and this will make sure there is a higher melting point. When you thicken the walls of the parts, you can slow down how quickly the resin cools. This gives the resin more time to spread to the part that isn’t covered before the resin cools and hardens, making it stronger.

There are, however, some rules you need to follow. If you do, you might end up with sink marks.

You can also cut down on the thickness ratio of the parts. It will spread out more quickly if there is less flow. This will close the weld line.

You can also change the size and position of the gate. Keep the part that makes you knit as far away from the edge of your design as possible. If you keep it too close to the edge, it might fall off.

Change the Mold Design

You can change the design of the mold by making the gate and runners bigger. You should also make sure there is no air trapped in the weld line injection molding. If you don’t get rid of the air, it will leave empty spaces in your part design, which will weaken it even more. You can get the air out of the weld line area by putting a vent there.

You can alter the gate design to modify the mold’s design. It helps to avoid welding lines being molded or making sure they form closer to the gate under a lot of pressure and a lot of heat.

Adjusting the Mold Conditions

Another way to make sure there are no injection molding weld lines is to change the molding conditions. Temperature, injection speed, and injection pressure are some of the things to keep in mind.

The weld line may be more noticeable if the melt temperature is too low or if the speed and pressure of the injection are too low. So, you can get rid of the weld line by making these conditions better.

Warping–injection molding defects

Warpage is one of the most common problems with plastic injection molding, and it can be not very good. When a part is ejected from a mold, and there is a lot of distortion afterward, this is called a “defect.”

If there are different shrinkage rates or a mechanical force, such as when the part is ejected, the warped part can bend or twist. They must know how to avoid warping because it can cost a lot of money to change the tooling or the material.

Causes of Warping

Fill rate, temperature changes, and cavity pressure are the three main issues when it comes to this one. But, many things can cause warpage because of these problems, such as:

• Mold Problem: When trying to figure out what’s wrong, moldis usually the first thing to look at, but it’s not always the case. A gatethat isn’t in the right place can cause the flow to go in the wrong direction, which can cause welding lines or air pockets. Uneven cooling can cause different shrink rates, which can cause warpage.

• Parts of the design that don’t work well: There are different shrink rates because of localized stress or if the part doesn’t have any strengthening ribs, making it less rigid. Some shapes warp more than others. Engineers need to keep this in mind, too.

• Machine Problems: A machine mistake, like when the injection screw moves slowly while filling the mold, can put more stress on the part, which can cause it to warp.

• Issues in processing parameters: If you have a low or high injection rate, it can cause stress that warps the item. Reducing cooling time can also be bad because a part thrown out while the object is still hot may warp.

• Wrong Material Used: Polyethylene, polypropylene, and plastics with a crystalline structure are more likely to warp compared to amorphous plastics like polystyrene and polycarbonate.

To avoid warpage, a company needs to thoroughlyunderstand the injection molding process from start to finish.

How to Reduce and Avoid Warping in Plastic Injection Molding?

Mitigating warpage starts with addressing issues with temperature, tools, and materials. Working with the company early on is the best way to ensure that fixing problems doesn’t hurt your business. During the design phase, fixing problems has the least effect on your bottom line.

An engineer will ensure that the right materials, tool design, processes, and machine settings will work together to avoid warpage during the prototyping phase. But, if warpage happens even though there are safeguards, engineers will look at where and how much warpage is there and how warpage affects parts to find out who isto blame.

The best way to keep plastic injection molding from warping is to work with a company that has done this before. Because this defect can come from a lot of different places, you need to trust your production to a company that has had a lot of success in the past.

At StepRapid, they can help you with your prototype development, production, and quality assurance because they have a lot of experience in a wide range of industries and a strong desire to make strong and durable parts.

Final Thoughts About injection molding defects

At present, the best way to produce high-quality parts fast and without spending a lot is done through injection molding. Many companies have benefited a lot from this. But it is not always a smooth process. You may encounter some issues like injection molding defects which are caused by wrong materials used or machine errors.

Injection molding can have a lot of benefits but can also cause problems. Some of which is due to bad mold design or operators who are not familiar with certain materials. Separation and parts that don’t fit well can happen when dirt or foreign materials are in the molten plastic. StepRapid has been making high-quality plastic injection parts for clients all over the world.

Weld lines are caused when two or more flow fronts can’t “knit” together. Common mistakes in mold design include having the wrong wall thickness and gates in the wrong places. You can avoid welding lines in plastic injection molding by making sure there is only one front during the molding process.

Engineers must know how to avoid warping. Warpage is one of the most common problems with plastic injection molding. Fill rate, temperature changes, and cavity pressure are the three main issues when it comes to this one.

Some shapes warp more than others. Engineers need to keep this in mind. A company needs to keep a thorough understanding of the injection molding process from start to finish. Warpage can come from issues with temperature, tools, and materials.

The best way to avoid warpage and all the injection molding defects you might encounter during the production of parts is to work with a company that has done this before.