THIẾT KẾ CHẾ TẠO KHUÔN MẪU ĐỦ 25 BÀI_SPKT-2-EN

DEFECTS IN INJECTION MOLDING PRODUCTS


1)

Products deviations size
Reason

The variables that influence shrinkage

- Shrinkage in molding.

If the thickness of the product increases, the shrinkage increases

- shrinkage after the product removed from the mold.

- Pressure:
+

Long retention time and maximum pressure higher, lower shrinkage.

-Temperature:
+

If the temperature increases, the shrinkage increases in the process of injection

-

Molecular orientation in injection molding:

+ The molecular orientation due to shear modulus and is retained by the combination with the

process of cooling


2) Products warping
Reason

The variables that influence

Solution

- Shrinkage change across products

- Thickness difference in product

- Increased time and pressure

- Products take off too soon, therefore the product

-

- Controlled the temperature on the surface of the

is not shaped

+ The material compression uneven.

mold

- Mold design inconsistent and thickness difference

-

- Test the structure of product and the accuracy of

in product

+ High mold temperature would make that the

Influence of pressure

Influence of temperature

product

product cool slowly => warping increases.

-

Influence of Molecular orientation:

+ The orientation is not the same => very high
risk of warping.

- Avoid internal stress by choosing materials and
shapes products


3)

Focus Bubble

Description

- The gas bubbles form the hole inside product or

Reason

-

make products that are not filled completely.

When products have the gas line focus, Air

Solution

-

is pushed into one place cause air bubbles.

-

The air is left in the product in the area
product filled final cause air bubbles.

Design thickness of production in the appropriate
positionĐổi vị trí cổng phun.

-

Reduce speed injection.

Optimized exhaust system.
Reduce the pressure lossy of the screw or reduced
pressure by reducing the speed.

-

If there are air bubbles, you need to put them in
areas that can exhaust or more the entrance to the
exhaust sound.


4)

Products with the dimples.

Reason

-

Material shrinkage.
Where the crust of hard enough to not be shrinkage, the product will form
a hollow inner part

Solution

-

Change the parameters pressed (pressure, temperature, time).
Changes plastic shrinkage coefficient smaller.

5)

The phenomenon of injection lack :
Reason

Solution

- Melting temperature, mold temperature and injection speed too low.

- Increased melting temperature or temperature mold and injection speed.

-

-

Plastics are not flexible
Valve exhaust system mismatch: The air in the mold is not drained.
Product thickness too small or too long
Lack of raw materials (installation screw itinerary insufficient).
Low injection pressure.

- The glossy surface of the mold should not hinder the flow.

Increased volume injection (injection volume is too small, no buffer).
Install matching between injection pressure and injection volume,
increased

injection pressure.

-

Improved exhaust valve system, reducing mold clamping force.
Increased the size channel system (runner).

- If the temperature is low, increase the temperature mold.


6) Products with burrs
Reason

-

Solution

Moldmaking inaccuracies, errors between the two halves of the mold too

-

big or mold damage.

-

Mold clamping force is too low

- Reduce the injection pressure, speed injection or pressure smaller

mold too high.

-

- Mold does not close by: mold mounting unmatched, with channels (due to

-

- Melting temperature, cylinder temperature, injection speed or pressure in the

dirt, corrosion).

Repair mold and Correct damaged places
Mold clamping forces higher or change larger machine.

Reduced melting temperature and mold temperature.
Check the correct surface fabrication closed mold.
Select the appropriate port position.


7) Products have welded
Reason

-

Similar to the product not filling the mold

Solution

-

Check the exhaust system of mold or adding gas drainage.

-

Design unreasonable gateway.

- Can be designed to take the road to the location weldline unseen.

-

The air is trapped

- Use materials with lower viscosity.

-

Influence of color, the position weldline usually affects the mechanical

- Identification of specific areas by analyzing MOLDFLOW

properties.


8) Products with many wrinkles

Reason
- Surface product uneven

-

Injection pressure is low . Mold temperature is too high.

- Gateway is size too small or high

Cách khắc phục

-

Reduced thickness.
Make multiple tendon


9) Surface peeling, scratch, uneven

Description

-

Reason

The surface is separated into sheets, flake

-

Very difficult to identify because the surface is

- The dirt incompatible with thermoplastic.

not cracked.
- The surface is damaged when using hard objects
scratch lightly.

High shear modulus layers formed.

Solution

- Increased temperature and decreased speed
injection


10) Cracks
Reason

-

The impact from the outside, appears as the power grab.
Due to residual stresses form . Internal stress in the parameters by pressing
inappropriate.

Solution
- Reduce the force on mold or using thermoplastic less susceptible to stress

-

Review the design of products to improve the flow.
Increase the mold surface temperature and melting temperature of the

- Because of structural weaknesses products difficult to obtain products from

plastic, reducing pressure maintenance, reset the time and injection speed

the mold or adhesive partial product in the mold.

accordingly.

-

- Reduce the injection pressure, reduced pressure compression.
Reduce mold temperature, check the temperature uniformity mold.


11) Products with black burn marks
Reason

-

High pressure injection
The temperature of the plastic is too high.
Air is trapped in the mold.

Solution

-

Reduce injection pressure, injection speed.
Check the exhaust system.