Fabricant d'injection de plastique: défauts et causes de moulage par injection

Chaque fabricant d'injection plastiquevise à produire des pièces de haute qualité, robustes et fiables. Après tout, la qualité du produit aura un impact direct sur sa marque. Pour garantir des produits de haute qualité, ils utilisent une série de techniques, mettent en œuvre les 5 M et passent du temps à détecter la cause des défauts.

Different types of defects lead to different problems in the part. The manufacturer must eliminate these defects as soon as possible. To eradicate the problem, they find its cause.  Only when they find the reason, will they be able to generate effective solutions.

Of course, there are many different types of defects, however, we will focus on the most common ones. In this article, we will talk about the most common defect along with their causes.

Injection Molding Defects and Causes

You must have heard that a certain injection mold part did not serve its purpose. It did not live up to the expectation. As a manufacturer, you would have done everything in your power to overcome the problem. Despite the rigorous work, you might not be able to resolve the issue.

Vous pourriez être surpris d'apprendre que de nombreuses pièces en plastique n'arrivent pas sur le marché. Ce qui est plus intéressant, c'est que les défauts présents dans ces pièces ne sont pas dus à une défaillance de l'équipement. Au contraire, cela est dû au manque de compréhension des propriétés des matériaux.

Les fabricants ne savent pas comment ces propriétés réagiraient pendant le processus de moulage. Par conséquent, il est important d'avoir une connaissance complète des causes de l'échec ou du succès des pièces lorsqu'elles sont mises en œuvre dans leur environnement prévu.

Le manque de connaissances en matière de traitement des matériaux, de mauvaises conceptions de moules, un équipement peu fiable et une connaissance limitée des contraintes de conception conduisent à une série de problèmes. Voici quelques défauts courants et leurs causes respectives.

Lignes de flux

Flow lines are the wavy pattern that you often see on the narrower sections of the molded parts. These lines are slightly different in color in comparison to their surrounding. In some cases, flow lines come out as ring-shaped bands.

Flow marks may have no impact on the product’s robustness. However, they do have an adverse impact on the aesthetic sense of the product. Flow lines may be acceptable for certain products, but they are unacceptable for others.

For instance, for a toy car pumper, flow lines might work. On the contrary, they are undesirable for high-end sunglasses.

Flow lines are the result of limited knowledge regarding the cooling speed of the material while it flows throughout the mold in different directions. In addition, the differences in the thickness of the walls can result in the material to cool at different rates. Thus, resulting in flow lines.

Weld Lines

Weld lines are generally seen at places where molten material tends to coverage after it is separated into two different directions in the mold. These lines are usually not thicker than a hair. They might not be prominent, but they signify weak material bonding.

This results in a lack of robustness and reliability in terms of parts and their components.

Cavity Pressure

Part’s dimension has a direct impact on cavity pressure. It means changes in the cavity pressure would mean changes in the dimension of the parts. An important thing to understand here is that less variation means better dimensional control.

When you incorporate high cavity pressure, it means you do not want the parts to shrink much. During all this, the other values do remain the same.  When it comes to shrinking, you should be familiar with universal law.

The law states that a plastic shrinks more in the perpendicular direction of the flow then it does in the direction of the plastic flow. Generally, when the molders are playing around with the equipment settings to find optimal settings at which the gate freezes, they often end up with cavity pressure error.

To remove the error, they need to keep on reversing the process until the defect is gone. However, doing this might result in the other three processes interfering with the final product properties. Thus, this results in a lot of rework for the fabricants d'injection plastique prennent and a lack of reliability for the customer.

Burn Marks

You might have come across molded plastic parts with rust-colored or black discoloration on the surface or the edge. The good news is that burn marks may not affect the integrity of the product. Nevertheless, they are not pleasing to the eye.

Of course, if you burn the plastic to the extent of degradation, it is bound to have a negative impact on the overall quality of the plastic component.

There are two major causes of burn marks. Either the resin itself can cause or the trapped air can lead to this problem. Once there is overheating in the mold cavity it then results in the burns.

Air Pockets

You might have seen trapped air bubbles appearing on top of the finished surface of the molded part. These air bubbles are basically air pockets.  Although, quality control professionals consider it a minor defect, yet a large number of air pockets can eventually affect the reliability and robustness.

Therefore, it is important to pay close heed to its cause. The major reason for voids is the inadequate molding pressure that is responsible for releasing the trapped air out of the mold cavity.  Some minor reasons include the fast cooling of the mold walls and significant change in the density of the material.

Warping

The uneven shrinking of components or their different parts leads to the deformation, warping.  The concept is similar to the drying of wood. When wood tries, it becomes uneven. It happens to plastic and other components during the cooling down process.

Different parts face undue stress because of shrinkage. Thus, this results in twisting and bending of different areas of the parts as they cool.

The major reason for warping is the fast speed of cooling. What makes the problem worse is the low thermal conductivity or excessive temperature. Furthermore, mold designs can also cause warping.

Uneven thickness of the mold walls would lead to uneven coolness, thus warping would occur.

Sink Marks

Have you ever seen small recesses inconsistent and flat surfaces? These recesses are sink marks. They happen due to the shrinking of the material. When the component’s inner part shrinks and brings in the material from outside, it leads to these marks.

Sink marks occur when the material takes too long to cool down. The slow cooling of the process results in the outside material to be dragged inside. Therefore, it is vital to have just the right temperature.

Jetting

Plastic injection manufacturers often claim about jetting. It is basically a deformation in the parts. The deformation occurs when the molten material enters the mold at once or it cools before the rest of the cavity is filled.

The high injection pressure along with the quick cooling element leads to this particular problem.

Short Shot

Si vous ne remplissez pas complètement la cavité du moule avec le plastique fondu, cela entraînera un court tir. Le produit final serait incomplet et présenterait des défauts. Ceci est courant, mais l'un des défauts les plus coûteux.

Cela aurait un impact direct sur la fonctionnalité du produit. Dans la plupart des cas, cela rendrait la pièce inutile. Ainsi, le fabricant d'injection plastique finirait par payer un supplément.

La raison principale de ce défaut est que la machine a des portes ou des passages obstrués. Cela peut se produire même en raison de portes étroites. En outre, le manque de température appropriée et de matériau visqueux peut entraîner ce défaut particulier.

L'air emprisonné avec une pression d'injection insuffisante peut également conduire à un tir court.

À emporter

As an experienced fabricant d'injection plastique, you need to eliminate these common defects. Doing this would help you come up with high-quality and robust products. It will also ensure that you have a name in the market.

Si nous pouvons vous aider avec votre projet, veuillez nous appeler au 0086-769-82821468 ou par e-mail un .