Plastic injection molding flaws are still quite prevalent on any shop floor that uses the injection molding process extensively. Because of its design flexibility in producing parts in bulk, the injection technique is very useful for many plastic manufacturers. However, errors can occur at any time, whether they are minor or major, and they are always present.
Injection flaws are difficult to avoid. Defects can be caused by a variety of factors, including process issues, human error, tooling issues, excess or insufficient material, design flaws, or a combination of all of these.
Every problem, however, has a quick fix. So simply addressing the issue is half the battle. The top five flaws that you should never overlook are listed below.
Table of Contents
1. Sink Marks
Sink marks are among the most noticeable sterile injection molding flaws. It is most commonly found on the relatively thick parts of the molded component. It typically appears as divots or bouts of depression and is extremely difficult to prevent.
Sink marks are caused primarily by insufficient cooling time prior to ejection of the moulded component, low pressure in molding cavities, and an excessively high molding temperature at the gates.
They can be avoided by continuing to increase the cooling time and putting the part in the mold for a longer period of time. A slight reduction in mold temperature can also be beneficial. Sink marks should be greatly reduced by designing a mold with thinner component walls.
2. Discoloration
Discoloration indicates that the color of the molded components is different from the intended color. The discoloration is a prevalent injection molding defect that does not affect the stability or shape of the molded part but is limited to a few streaks of strange color discovered anywhere on the molded part’s surface. It is common in electric components such as mv breaker.
The discoloration is commonly caused by vestige pallets in the hopper, residual resin in the nozzle, or a mold from an earlier production run. Reasons such as improper masterbatch mixing and low thermal conductivity of the coloring agent can occasionally cause discoloration.
It can be avoided by ensuring that the quality cnc machine for mold making, nozzle, hopper, and mold are thoroughly cleaned between each production run and that any leftover resins or materials are removed.
It will also make a dramatic contribution to using a color agent with high thermal conductivity. Using a purging compound to remove excess material from the machine is a good idea.
3. Vacuum Voids
It’s indeed accurately what it appears to be. Air trapped in the mold cavity can be seen as most commonly a “bubble” in the fully completed component. Some of the most common causes of air pockets are insufficient cooling, material contraction, and insufficient injection pressure.
Because air pockets aren’t easily visible, they pose a significant risk to the product’s integrity. Prevention can be accomplished by adhering to a layout policy of having the wall thickness below 6 millimeters.
In other cases, moving the gate to the thickest part of the mold can help prevent premature cooling, which is the primary cause of uneven shrinkage. Increasing the air pressure can also be beneficial because it will force air out of the material.
4. Warping
Warping refers to the imbalanced contraction and deformation of molded products even during the molding process. When uneven stress is maintained but compressibility occurs in various parts of the molded component, warping occurs.
Undue stress causes flexion on the portion, which is especially noticeable with flat-surfaced products. Premature cooling is one of the primary causes of warping. Excessive temperature and the material’s poor thermal conductivity also play a role in warpage.
In some cases, the irregular wall thickness in the mold can also contribute to warping. It can be avoided by reducing the temperature of either the material or the mold. A sustained and lengthy sufficient cooling process will aid in the prevention of imbalanced stress and strain on the material. During the cooling process, swapping to a material with excellent thermal conductivity is also a good option.
5. Flow Lines
The most common injection molding defect in mode components is flow lines. Flow lines are typically visible on the component’s relatively narrow sections as discolored “bands” or perhaps even “wavy” discoloration.
They could also show up at mold and gate points of entry. Flow marks aren’t going to derail the product’s completeness, but they can be unappealing to see.
The most major reason for flow lines is insufficient variability in the cooling speed of the material as it propagates inside the mold. Any differences in wall thickness could indeed end up causing the materials to cool at an unusually fast rate.
While molten plastic cools quickly during the injection molding process, flow marks are unavoidable when the injection rate is low. Because of the slow speed, the plastic solidifies and becomes soupy while still going to fill the mold, starting to cause the flow “wave” or “band” to appear.
You can avoid it by continuing to increase the injection pace, material strain, and material temperature to make sure that the material properly fills the mold. Or by relocating mold gates to distance increases between them and the coolant, preventing the material from cooling too early in the injection cycle.
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