Sometimes, when you make injection molded products, you get defects, like burrs. Some of these are because of problems in the mold design and mold manufacturing, and some are because of problems in the injection molding process. Let’s find out today. Burrs mostly happen on the parting line, which is where the melt flows between the moving mold and the fixed mold, the sliding part of the slider, the gap between inserts, the ejector pin hole, and so on, and it makes too much flash on the part. This kind of burr acts like a lever during molding, which makes the burr even bigger, and it makes local depressions in the mold, and it makes a bad cycle of making the burr bigger during molding. So, if you see flash burrs at the beginning, you have to trim the mold as soon as possible.

Plastic products made by injection molding are prone to burrs during production and processing. The presence of burrs will not only affect the appearance quality of the product, but also reduce the performance and life of the product. Therefore, burr removal has become an essential task in the manufacturing process of plastic products. This article will introduce the methods of deburring injection molded plastic products to help companies better deal with the burr problem.

Ⅰ. Understand the Burrs of Injection Molded Products

The so-called burrs are what we usually call edges, burrs, etc., also called overflow. They mostly occur at the opening and closing positions of the mold, such as the parting surfaces of the movable mold and the static mold, the sliding parts of the slider, and the inserts. The flash is largely caused by the failure of the mold or the clamping force of the machine in places such as absolute gaps and ejector pin pores.

Burs happen when you’re injection molding. They’re caused by the molten injection resin overflowing from the mold’s parting surface. If the burs stick to the mold’s parting surface, they’ll mess it up. Plus, once the mold is messed up, you’ll get burs when you’re injection molding, which will also make the mold last a lot less time.

Ⅱ. Causes of Burrs in Injection Molded Products

1.Mold Problem

The mold surface is not smooth and uniform, and burrs often appear at the mold joints or where the material flow is blocked. At this time, grinding or processing the mold surface can reduce the chance of burrs. Improper mold design, such as improper gate location, may cause the plastic melt to flow unevenly in the mold, resulting in burrs or burrs.

2.Injection Molding Process Issues

The main factors that affect the generation of burrs in the injection molding process are injection pressure, injection speed, and injection volume. If these three parameters are unreasonable, burrs will easily occur. The injection molding pressure and injection volume can be gradually increased, or the injection rate can be reduced to improve the injection molding process.

3.Injection Molding Machine Equipment Problems

The injection molding machine itself can also produce burrs. If the injection molding machine is not cleaned or maintained in time, burrs are also likely to occur. Therefore, regular maintenance and cleaning of the injection molding machine can reduce the occurrence of burrs.

4.Plastic Fluidity is Too Good

It’s very simple. The fluidity of plastic is too good. In theory, this is not the cause of burrs. But when the fluidity of the plastic is too good, even the plastic with fine gaps can be drilled in, so burrs are prone to appear. In order to eliminate this burr, the melt temperature or injection pressure can be reduced, and the mold temperature or injection speed can also be reduced.

5.Too Much Melt Injected

This is not the direct cause of burrs. It is wrong to inject too much melt to prevent shrinkage. Molding should be done by increasing the injection time or holding time (referring to shrinkage).

6.Mold Surface Has Foreign Matter

If there are foreign objects on the molding surface, burrs will inevitably occur. To solve this problem, it is obvious that the mold surface should be cleaned so that the molding surface can fit tightly.

7.Caused by Mold Deflection

If the mold is not original enough, it will deflect due to injection pressure. If there is a hole near the center, burrs will develop around the hole. Burrs may also appear around the holes and runners when center gates are used to open side gates. Burrs caused by this reason are caused by poor mold making, so they are difficult to repair. Strengthening the mold can reduce burrs.

8.Insufficient Clamping Force

If the clamping force is too small compared to the projected area of the molded part, the injection pressure will cause a gap between the movable mold and the fixed mold, and burrs will appear. Especially when the side gate is placed on a hole close to the center of the part, this type of molding gate requires a large injection pressure, so it is easy to produce burrs. Lowering the injection pressure or increasing the clamping force can eliminate this defect. Depending on the situation, switching to low-pressure molding using fluid plastic can sometimes be very effective.

9.The Mold is not Closed Tightly

When the mold is not tightly closed, the plastic melt is extruded from the mold gap under high pressure, resulting in excessive flash or burrs.

10.Mold Wear

If you use it for a long time, the mold will wear out, and it will not close tightly, and it will easily produce burrs or burrs.

11.Injection Pressure is Too High

If the injection pressure is too high, the plastic melt won’t flow well, and you’ll get flash or burrs at the parting line of the mold.

12.Material Temperature is Too High

If the temperature of the material is too high, the plastic will melt too much and become too soft, which will make it flow poorly and easily produce flash or burrs at the mold parting line.

13.Part of the Mold is not Tight

First, let’s talk about the problem of the mold clamping being loose. Although the mold itself is tightly closed, when an injection machine that uses an elbow-type clamping mechanism is used to mold, the left and right sides of the mold clamping will often be unbalanced due to poor mold parallelism or poor adjustment of the clamping device. That is, only one side of the left and right sides is locked, and the other side is not tightly fitted. At this time, the tie rods (two or four cymbals) must be adjusted so that they stretch evenly. Secondly, insufficient adhesion can also result from poor fit of the mold itself, especially when there is a forming hole in the center of the part. Due to the supporting role of this part, burrs are prone to occur when the clamping force is insufficient.

Also, it’s a sliding core. Since the following core is an action mechanism, burrs often occur, so the cooperation of the sliding core is very important. Especially for Huff molds with left and right split molds, the projected area on the side is also affected by the molding pressure. If the design cannot fully withstand this pressure, burrs will often appear. The gap between the insert and the ejector pin will not only increase the vicious cycle of burrs, but also increase the ejection resistance.

Ⅲ. Troubleshooting glitch problems

1. Optimize Mold Structure

You can use polishing, grinding, EDM, and other methods to improve the smoothness of the mold surface and reduce the generation of burrs. You can also optimize the mold design, such as setting the gate position reasonably, so that the plastic melt can flow more uniformly in the mold, thereby reducing the generation of burrs or burrs.

2. Adjust the Injection Molding Process

To reduce burrs, you can adjust the injection molding process parameters, like injection pressure, injection rate, and injection volume.

3. Clean or Maintain Equipment

Cleaning or maintaining your injection molding machine can help prevent burrs from forming.
In short, there are many reasons why burrs form in injection molding, and you need to analyze the specific situation. For plastic parts that have burrs, you can use methods like hot runner spraying, grinding, and polishing to remove them.

4. Adjust Mold Closing Height

If you increase the mold closing height, you can reduce the mold gap, which will reduce the amount of flash or burrs that are created.

5. Replace the Mold

If the mold is severely worn, it is recommended to replace the mold with a new one to maintain good mold closing accuracy.

6. Reduce Injection Pressure

Lowering the injection pressure can help make the plastic melt flow better and reduce the amount of flash or burrs that are made.

7. Lower the Material Temperature

Cooling the material down can help make the plastic melt flow better and cut down on the amount of flash or burrs that are made.

8. Adjust Mold Design

If you’re seeing flash and burrs in specific areas, it could be a mold design issue. You might want to try redesigning the mold to give you more control over the shape and size of your part.

9. Optimize Process Parameters

Changing the process parameters can also affect the surface quality of the product. You can try adjusting the temperature, pressure, speed, and other parameters of the injection molding machine to get better injection molding results.

Ⅳ. Advanced Technology to Reduce Burrs

1. Manual Deburring

It is also commonly used by general enterprises, using files, sandpaper, and grinding heads as auxiliary tools. There are hand files and air files.
Features:
The labor cost is relatively expensive, the efficiency is not very high, and complex cross holes are difficult to remove.
The technical requirements for workers are not very high, and it is suitable for products with small burrs and simple product structures.

2. Mold Deburring

The product is deburred by using production molds and punches.
Features:
A certain mold (rough mold + fine mold) production cost is required, and plastic molds may also be required.
Suitable for products with relatively simple parting surfaces, the efficiency and deburring effect are better than manual work.

3. Grinding and Deburring

This type of deburring includes vibration, sandblasting, roller and other methods.
Features:
There is a problem that the removal is not very clean. The remaining burrs may need to be processed manually or combined with other methods to remove burrs.
Suitable for small batch and large batch products.

4. Freezing Deburring

Cooling makes the burrs brittle fast, and then you shoot them off.
Pros:
Expensive equipment.
Good for products with thin burrs and small quantities.

5. Thermal Deburring

It is also called thermal deburring and explosion deburring. By passing some flammable gas into the equipment furnace, and then using certain media and conditions to cause the gas to explode instantly, the energy generated by the explosion is used to dissolve and remove burrs.
Characteristics:
The equipment is expensive (millions of dollars), requires high operating technology, has low efficiency, and has serious side effects (rust, deformation).
Mainly used in some high-precision parts, such as automotive and aerospace precision parts.

6. Engraving Machine Deburring

The price of deburring equipment for engraving machines is not very expensive (tens of thousands of yuan), suitable for simple spatial structures, and the deburring positions are simple and regular.

7. Chemical Deburring

Chemical deburring is a process that uses the power of electrochemical reaction to automatically and selectively remove burrs from metal parts.
Benefits:
Perfect for those hard-to-reach internal burrs, great for small burrs (less than 7 wires thick) on pumps, valves, and other products.

8. Electrolytic Deburring

Electrolytic deburring is a way to use electrolysis to remove burrs from metal parts.
Features:
The electrolyte is corrosive, and the parts close to the burrs will also be electrolyzed. The surface will lose its original luster and even affect dimensional accuracy. The workpiece should be cleaned and rust-proofed after deburring.
Electrolytic deburring is suitable for removing burrs from hidden holes in parts or parts with complex shapes. The production efficiency is high, and the deburring time generally only takes a few seconds to tens of seconds.
Suitable for deburring gears, connecting rods, valve bodies, crankshaft oil passage openings and rounding sharp corners.

9. High-Pressure Water Jet Deburring

Water jet deburring is a high-pressure water jet that uses water as a medium. It uses the instantaneous impact force of water to remove burrs and flash generated after processing, while achieving the purpose of cleaning.
Features:
The equipment is expensive and is mainly used in the heart of automobiles and hydraulic control systems of construction machinery.

10. Ultrasonic Deburring

Ultrasonic waves create high pressure in an instant to get rid of burrs.
Features:
Primarily for small burrs. If you need a microscope to see the burrs, try using ultrasonic waves to get rid of them.

Ⅴ. Importance of Quality Control

Injection molding quality is a big deal when it comes to plastic products. It affects how the product looks, how it works, how long it lasts, and how well it sells. So, when you’re making plastic stuff, you’ve got to make sure it’s good quality.

Injection molding quality control is one of the key links in the production of plastic products. By selecting the right raw materials, controlling the injection molding process, controlling the quality of the mold, testing and acceptance, etc., we can ensure that the injection molding quality of the product meets the requirements, thereby improving the quality of the product and the competitiveness of the market.

When it comes to making sure your injection molded products are top-notch, you need to keep an eye on your injection molding process parameters. These parameters include things like injection temperature, holding pressure time, injection speed, and more. By controlling these parameters the right way, you can make sure your product quality is always on point. This is especially important when you’re making a ton of products at once. By controlling your process parameters the right way, you can make sure you’re making products fast and that they’re all the same.

Ⅵ. Conclusion

Deburring plastic products is important for quality, safety, and compliance. Different parts and requirements need different deburring methods. When you do it, you need to make sure the deburring is good enough so the surface is smooth and doesn’t mess up the next steps.
There are a lot of ways to do it, so you can pick the one that works best for you. If you keep up with what’s going on and do it right, you’ll be ahead of the game and make better stuff that makes your customers happy.