There are various causes of molding defects, but if there is no problem with the molding machine or peripheral equipment used, most are errors in molding condition settings or mold design.
We would like to explain each molding defect based on the following flat plate molding samples.
Air bubbles are generated inside a molded product.
This phenomenon occurs because air bubbles generated inside the resin are not fully removed from the mold during the molding process.
＞Molding conditions
Cylinder temperature is too high, injection pressure is insufficient, mold temperature is too low, injection speed is too fast, or metering/residual volume is insufficient.
Injection speed is too fast, or there is insufficient metering/residual volume.
>Mold
Runner gate is too narrow, gate position is inappropriate, etc.
This refers to the distorted state of a molded product immediately after it is removed from the mold.
This can occur when the product is cooled unevenly during the cooling process or when internal distortion is large.
＞Molding conditions
Cylinder temperature is too low, temperature distribution of mold temperature is too large, cooling time is too short (deformation occurs during ejection), screw back pressure is insufficient, etc.
deformation), insufficient screw back pressure, etc.
>Mold
Inadequate gate shape, position, or number of points, inadequate cooling circuit, inadequate ejector position or number of ejectors, etc.
Insufficient draft angle, etc.
Molding material does not fully fill the mold, resulting in a partially chipped molded product.
This occurs when the mold is not filled with sufficient resin.
＞Molding conditions
Insufficient injection force, insufficient injection speed, resin or mold temperature setting too low
Insufficient metering, etc.
>Mold
Runner/gate flow resistance is too high, or gate layout is such that gas or air is entrapped.
Insufficient metering, etc.
(This is a condition in which foreign matter or black spots occur on the surface or inside of a product.
Countermeasures vary greatly depending on the identity of the foreign matter or black spot.
Foreign matter: metal pieces, dust, rubber pieces, fibers, other resins
Black spots: Burnt resin (carbonized material), dirt
＞Molding conditions
Insufficient purging of material during material change, insufficient cleaning of barrel and hopper, resin noise too high
>Mold
Insufficient maintenance, galling on inserts, nests, etc.
This is a thin line that occurs at the meeting point of the molten plastic flow in the mold.
Weld lines are formed when the meeting points do not completely melt together.
Weld lines themselves can occur in general molding, but if the depth of the line is too deep, the strength of the plastic will be reduced and there is a risk of breakage from the weld area.
If the weld line is too deep, there is a risk of breakage from the weld area.
＞Molding conditions
Cylinder temperature and mold temperature may be too low, or injection speed may be insufficient.
＞Mold
Inadequate gate position and number, insufficient venting, etc.
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