What to do if there are burrs in injection molding?

Time:2020-08-29 10:00:54 / Popularity: / Source:

Reasons and solutions for burrs

Most of burrs occur on split surface, that is, molten material flows between moving mold and fixed mold, sliding parts of slider, gaps between inserts, and hole of ejector pin, forming an excessive flash on the part. Such burrs, which act as a lever during molding, will further increase burrs, which will cause local depressions in mold, and a vicious circle of burrs will increase during formation. Therefore, if flash burrs are found at the beginning, mold must be trimmed as early as possible.
There are several reasons and solutions for burrs:

1. Fluidity of plastic is too good

Simple reason is that plastic is too fluid, which is not the cause of burrs in theory. However, when fluidity of plastic is too good, even fine gap plastic can be drilled in, so burrs are extremely easy to appear. To eliminate this burr, melt temperature or injection pressure can be reduced, mold temperature or injection speed can also be reduced.

2. Injecting too much melt

This is not direct cause of burrs. It is wrong to inject too much molten material in order to prevent shrinkage, and it should be formed by increasing injection time or holding time (refer to shrinkage).

3. Foreign matter on mold surface

Foreign matter on mold clamping surface will inevitably produce burrs. To solve this problem, it should obviously be cleaned on the surface of clean mold, and clamping surface can be closely adhered.

4. Caused by mold deflection

If originality of mold is insufficient, deflection will occur due to injection pressure. If there is a hole near center, burrs will be generated around hole. When center gate is used to open side gate, burrs may also occur around hole and runner. Burrs caused by this cause is caused by poor mold making, so it is difficult to repair. Reinforced molds can reduce burrs.

5. Insufficient clamping force

Compared with projected area of molded part, if clamping force is small, a gap will appear between moving and fixed molds due to injection pressure, and burrs will inevitably appear. Especially when side gate is placed on the hole near center of part, because this molding gate requires a large injection pressure, it is extremely prone to burrs. Reducing injection pressure or increasing clamping force can eliminate this defect. It is sometimes very effective to switch to low-pressure molding using a fluid plastic according to specific situation.

6. Mold is not tightly local

First of all, problem of loose clamping of moving and fixed molds is discussed. Although mold itself is tightly closed, when an injection machine using an elbow-type clamping mechanism is molded, it is often caused by poor mold parallelism or poor adjustment of clamping device, phenomena such as imbalanced clamping of left and right sides, that is, only one side of left and right sides are locked, and the other side is not closely attached. At this time, tie rods (two or four pull cymbals) must be adjusted to make them stretch uniformly. Secondly, there is also a lack of close adhesion due to poor fitting of mold itself, especially when there is a molding hole in the center of part. Due to supporting effect of this part, burrs are also prone to occur when clamping force is insufficient.
In addition, it is a sliding core. Since follow-up core is an action mechanism, burrs are often generated, so cooperation of sliding core is very important. Especially for left and right parted Huff molds, projected area on the side is also affected by molding pressure. If design is not able to fully withstand this pressure, burrs often occur. With regard to gap between inserts and ejector pin, not only vicious cycle of burrs increases, but also ejection resistance will increase.
Mold deburring, these methods are more professional
1, TRUMPF Deburrer deburring machine, this small tool can remove burrs directly on the board, and cutting edge is not oxidized. Similar to such small tools, inclination angle of 30 °, 45 °, 60 ° can be used for such gadgets, and can also be used for curved edges.
2, Lima Germany's all-round equipment, deburring and chamfering compound machine, it can deburr, chamfer, surface drawing, metal surface treatment at one time.
3, Some small tools for deburring and chamfering are available in single or small batch production.

10 easy ways to deburr

1. Artificial deburring

This method is also commonly used by general enterprises, using files, sandpaper, grinding heads as auxiliary tools. There are manual files and pneumatic files.
injection molding 
Labor cost is relatively expensive, efficiency is not very high, and it is difficult to remove complex cross holes.
Technical requirements for workers are not very high, applicable to products with small burrs and simple product structure.

2. Die deburring

Deburring is performed by using a production die and a punch.
A certain die (rough die + fine die) production cost is required, and a plastic die may also be required.
Suitable for products with simpler parting surface, better efficiency and deburring effect than artificial.

3. Grinding and deburring

This type of deburring includes vibration, sand blasting, rollers and other methods, which are currently adopted by enterprises.
There is a problem that removal is not very clean, and remaining burrs may need to be manually treated or cooperated with other methods to deburr.
Suitable for small products with larger batches.

4. Frozen deburring

Burr is quickly brittled by cooling, and then projectile is ejected to remove burr.
Price of equipment is about RMB 200,000 to RMB 300,000.
Suitable for products with smaller burr wall thickness and smaller products.

5. Hot deburring

Also called thermal deburring, explosion deburring. By passing some easy gas into an equipment furnace, then using some media and conditions to make gas explode instantly, use energy generated by explosion to dissolve and remove burrs.
Equipment is expensive (millions of dollars), requires high operating technology, low efficiency, and side effects (rust, deformation).
Mainly used in some high-precision parts and components, such as automotive and aerospace and other precision parts.

6. Deburring of engraving machine

Price of equipment is not very expensive (tens of thousands RMB), it is suitable for simple space structures, location of deburring is simple and regular.

7. Chemical deburring

Using principle of electrochemical reaction, deburring operation is automatically and selectively performed on parts made of metal materials.
Suitable for internal burrs that are difficult to remove, suitable for small burrs (thickness less than 7 wires) of pumps, valves and other products.

8.Electrolytic deburring

An electrolytic processing method for removing burrs of metal parts by using electrolytic action.
Electrolyte is corrosive, and parts near burrs are also subject to electrolysis. Surface will lose its original gloss and even affect dimensional accuracy. After deburring, workpiece should be cleaned and rust-proofed.
Electrolytic deburring is suitable for removing burrs of hidden holes in parts or parts with complex shapes. Production efficiency is high, and deburring time is generally only a few seconds to several tens of seconds.
It is suitable for deburring of gears, connecting rods, valve bodies and crankshaft oil circuit orifices, as well as rounding of sharp corners.

9. High-pressure water jet deburring

Water is used as a medium to remove burrs and flashes generated after processing by using its instant impact force, and purpose of cleaning can be achieved at the same time.
Equipment is expensive and is mainly used in the heart of cars and hydraulic control systems of construction machinery.

10. Ultrasonic deburring

Ultrasound produces instant high pressure to remove burrs.
It is mainly aimed at some microscopic burrs. Generally, if burrs need to be observed with a microscope, you can try to remove them with ultrasound.

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