Introduction: In injection molding, burrs are a common injection molding defects that can occur. Some are caused by problems with the mold design and manufacturing, while others are caused by issues with the injection molding process.

Today, we’re going to take a look at why burrs happen. Burrs usually occur on the parting line, which is where the molten material flows between the moving and stationary molds, the sliding part of the slide, the gap between the inserts, the ejector pin hole, etc., causing excessive flash on the parts.

This flash acts as a lever during molding, which will further increase the flash, causing local depression of the mold, forming a vicious cycle of increased flash during molding. Injection molding defects usually occur in excessive injection pressure, resulting in burrs in the mold cavity gap.

Therefore, if flash is found at the beginning, the mold must be trimmed as soon as possible. This article mainly discusses the causes of flash and how to solve it.

What are the Causes of Burrs?

Insufficient Clamping Force

If the clamping force is small compared to the projected area of the molded part, the injection pressure will cause a gap between the moving and stationary molds, resulting in flash.

This is especially true when the side gate is placed near the center of the part, as this type of gate requires higher injection pressure and is more likely to cause flash.

You can fix this problem by lowering the injection pressure or increasing the clamping force. Sometimes, if you use a plastic that flows well for low-pressure molding, it works really well.

The Local Mold is Not Tightly Matched

Let’s talk about the problem of loose clamping of the dynamic and static molds. Although the mold itself is clamped tightly, when we use an injection molding machine with a toggle-type clamping mechanism to mold, it is often due to poor mold parallelism or poor adjustment of the clamping device.

Such as unbalanced clamping on the left and right sides, that is, only one side of the left and right sides is locked, and the other side is not tightly attached. At this time, we must adjust the tie rods (two or four tie rods) to balance and expand.

Also, there is another loose fit caused by poor mold matching. Especially when there is a molding hole in the center of the part, due to the supporting role of this part, burrs are also prone to appear when the clamping force is not enough.

Another type is the sliding core. Because the moving core is a moving mechanism, burrs often occur, so the matching of the sliding core is very important. Especially for the left and right split half mold, the projected area of its side is also affected by the molding pressure.

If the design cannot fully withstand this pressure, burrs will often appear. Regarding the gap between the inserts and the ejector pin, not only will the burrs increase in a vicious cycle, but also the ejection resistance will increase.

Caused by Mold Deflection

If the mold isn’t original enough, it will be deflected by the injection pressure. At this time, if there is a hole near the center, burrs will be generated around the hole; and when the side gate is opened using the center hole, burrs will also be generated around the hole and the runner.The burrs caused by this reason are caused by poor mold manufacturing, so it is difficult to repair. Reinforcement of the mold can reduce the burrs.

Unreasonable Mold Structure

The structure of the mold has a big impact on the quality of the molded parts. If the mold structure is not good, the molded parts will have burrs. For example, if there are sharp corners in the mold, the material will be squeezed and stretched, and burrs will be formed.

Mold design is one of the important factors affecting product quality. In the design of mold structure, the structure and processing accuracy requirements of the mold are not sufficiently considered, resulting in uneven mold surface processing, insufficient starting angle and other problems, which will cause burrs.

Poor Mold Surface Treatment

When you use the mold surface, it will wear out and get cracks from the heat. If you don’t treat the mold surface right, you’ll get burrs too.

Foreign Matter on the Mold Surface

If there is foreign matter on the mold mating surface, burrs will inevitably be generated. Therefore, we need to check the surface of the mold before the mold starts production.In addition, after the mold is produced, we must also pay attention to cleaning it in time and doing daily maintenance, which will not only reduce the occurrence of mold problems, but also extend the service life of the mold.

Too Much Melt Injection

Normally, it won’t happen. Usually, when you’re adjusting the machine parameters, because you’re short on material locally or you’re injecting too much melt to prevent shrinkage, the mold will bulge, and you’ll get flash.That’s the wrong way to do it. You need to increase the injection time or the holding time to mold it.

Plastic Fluidity is Too Good

Just because the melt flow is good doesn’t mean you’ll have flash. However, if the melt flow is too good, it can get into the tiniest gaps and cause flash. To get rid of flash, you can lower the melt temperature or injection pressure, or lower the mold temperature or injection speed.

Raw Material Quality Problems

Burr of injection molded parts may be caused by the problem of raw materials. For example, the plastic particles of different sizes and too many impurities will affect the molding quality of injection molded parts. At this time, it is necessary to start with the selection and screening of raw materials and drying treatment.

Improper Material Selection

The materials you choose are also important for injection molding success. If the plastic you pick melts at too high a temperature, it can cause poor plastic flow and create burrs. Impurities in the material can also cause burrs.

Improper Control of Injection Molding Temperature And Pressure

Before you start injection molding, you need to control the injection molding temperature and pressure. If the temperature and pressure are too high or too low, it will affect the quality of the molded product.For example, if the temperature is too high, the plastic will not flow well, and if the temperature is too low, the product will have a poor surface finish and will have a lot of burrs.

Injection pressure is a very important factor in the injection molding process. If the injection pressure is unstable, the molten plastic will not flow smoothly, causing the plastic to be squeezed and sheared in the mold, resulting in burrs.

Unreasonable Injection Molding Process Parameters

The generation of injection molded part burrs is also related to the parameters of the injection molding process.For example, unreasonable settings of parameters such as injection temperature, pressure, and speed will cause injection molded part burrs. The solution is to adjust each parameter one by one according to the specific situation to ensure the quality of injection molding.

If the injection molding process is not standardized or improperly operated, it will also cause injection molded part burrs. For example, unstable temperature during injection molding, too long injection time, etc., will have a negative impact on injection molded parts.

Mold Structure Design Problems

The generation of burrs on injection molded parts may also be related to the design of the mold structure. The part of the mold where burrs appear may be due to residual gas remaining in the mold or there may be holes in the mold.The mold needs to be checked and improved to ensure that the mold structure meets the requirements of the injection molding process.

Injection Molding Machine Equipment Problems

The generation of injection molded part burrs may also be related to problems with the injection molding machine equipment itself.If the injection molding machine has problems such as unstable pressure and uneven temperature, it will cause burrs on the injection molded parts. At this time, the injection molding machine needs to be inspected and repaired.

What are the Ways to Avoid And Solve the Burrs on Injection Molded Parts?

Improve Mold Structure

To avoid burrs, it’s important to improve the mold structure. When designing the mold, pay attention to the processing of edge transitions and minimize the contact surface of the mold to reduce extrusion and shearing.To improve the mold surface accuracy and processing quality, and reduce the generation of burrs, you can improve and design the mold based on the deficiencies in the mold structure and processing accuracy.

Mold Deburring

Before you start injection molding, you need to prepare the mold surface to keep it smooth and flat and prevent burrs from forming.Deburring is done by using production molds and punches. It requires a certain mold (rough mold + fine mold) production cost, and may also require a plastic mold. It is suitable for products with simple parting surfaces, and the efficiency and deburring effect are better than manual.

Correct Selection of Plastic Materials

The key to solving the burr problem is to choose the right plastic material. Select the material according to the characteristics and requirements of the injection molded product, and pay attention to the purity and melting point of the material.

Use the Right Material

The choice of material will also affect the quality of the product surface. Some materials are prone to burrs, while others are relatively less likely to produce burrs.Therefore, when choosing injection molding materials, consider the characteristics and applicability of the material and choose those materials that are less likely to produce burrs.

When it comes to mold manufacturing, picking the right molding material is also the key to reducing burrs. Choosing some good materials, such as wear-resistant materials, can effectively reduce the wear of the mold surface and avoid the generation of burrs.

Reasonably Set the Injection Pressure

To avoid burrs, you need to stabilize the injection pressure during the injection molding process. During the injection molding process, the injection pressure should be set reasonably according to the properties of the plastic material and the structure of the mold to ensure that the plastic flows smoothly.

Implement a Standardized Injection Molding Process

Before injection molding, you can control the injection temperature and pressure to avoid burrs. Also, you need to adjust the mold temperature and pressure properly.To avoid burrs, you need to have a standardized injection molding process. When you’re doing injection molding, you need to control things like temperature, injection time, and injection speed. You don’t want to do anything wrong or have anything weird happen.

Make the mold design and manufacturing better: By making the mold design and manufacturing better, you can make less burrs. First, make sure the mold outlet design is good so you don’t have burrs. Second, make the mold processing more accurate, make the mold surface better, and make less burrs.

Adjust Injection Molding Process Parameters

To reduce burrs, it’s important to set reasonable injection molding process parameters. You can adjust the injection molding temperature, injection molding pressure, injection molding speed, and other parameters appropriately to reduce the burrs on the product surface.In addition, you can also use some special injection molding processes, such as multi-stage injection molding, reverse injection molding, etc., to reduce the generation of burrs.

Post-Processing Process

If there are burrs on the product, you can use some post-processing methods to remove the burrs. Common post-processing methods include grinding, polishing, sandblasting, etc.Through these methods, the burrs on the surface of the product can be effectively removed, and the quality of the product can be improved.

Periodic Trimming of Large Plastic Burrs

To prevent large burrs caused by scratches from falling off, it is necessary to trim them regularly with a blade. At the same time, it is recommended to check the source of the burrs,Such as whether the burrs are caused by employees using too sharp tools to scratch them, or whether the burrs are caused by improper operation.

The advantages of this method are that it is easy to operate and does not require special investment, but the trimming method is inefficient and not suitable for small burrs.

Manual Deburring

General enterprises also use this method, using files, sandpaper, and grinding heads as auxiliary tools. There are manual files and pneumatic files.The labor cost is relatively high, the efficiency is not very high, and it is difficult to remove complex cross holes. The technical requirements for workers are not very high, and it is suitable for products with small burrs and simple product structures.、

Grinding And Deburring

This type of deburring includes vibration, sandblasting, rollers and other methods. The methods currently used by enterprises are:There is a problem of not removing cleanly, and the remaining burrs may need to be manually processed or deburred with other methods. Suitable for small and large batches of products.

Freezing Deburring

The burrs are quickly made brittle by cooling, and then the projectile is shot out to remove the burrs. The equipment price is about 200,000 to 300,000 yuan. It is suitable for products with thin walls and small volumes.

Thermal Deburring

Also known as thermal deburring and explosion deburring. By passing some flammable gas into the equipment furnace, and then using certain media and conditions to make the gas explode instantly, the energy generated by the explosion is used to dissolve and remove the burrs.

The equipment is expensive (millions of dollars), has high operating technology requirements, low efficiency, and large side effects (rust, deformation). It is mainly used in some high-precision parts, such as precision parts for automobiles and aerospace.

Chemical Deburring

Using the principle of electrochemical reaction, metal parts are automatically and selectively deburred. Suitable for internal burrs that are difficult to remove, and small burrs (thickness less than 7 wire) of products such as pumps and valves.

Electrolytic Deburring

A method of electrolytic processing that uses electrolysis to remove burrs from metal parts. The electrolyte is corrosive, and the parts close to the burrs will also be electrolyzed. The surface will lose its original gloss and even affect the dimensional accuracy.

After deburring, the workpiece should be cleaned and rust-proofed. Electrolytic deburring is suitable for removing burrs from hidden holes or complex-shaped parts. It has high production efficiency, and the deburring time generally only takes a few seconds to tens of seconds.It is suitable for deburring gears, connecting rods, valve bodies, crankshaft oil channel orifices, and rounding sharp corners.

High-Pressure Water Jet Deburring

Using water as the medium, it uses the instantaneous impact force of water to remove burrs and flash generated after processing, and at the same time achieve the purpose of cleaning.The equipment is expensive and is mainly used in the heart of automobiles and hydraulic control systems of engineering machinery.

Summary

This article is about the causes of burrs in injection molded products and their solutions. Burrs are mainly caused by insufficient clamping force, loose mold fit, mold deflection, unreasonable structure, poor surface treatment, raw material problems, and improper control of injection molding parameters.

To solve these problems, it is recommended to improve the mold structure and design, select suitable materials, reasonably set the injection pressure, implement standardized injection molding process, and adopt post-processing processes such as grinding and polishing.

In addition, by optimizing process parameters and regular trimming, the appearance of burrs can be effectively reduced and the overall quality of injection molded parts can be improved.