Some Common 2-Step Plastic Injection Mould Defects and How to Avoid Them

When it comes to a 2-step plastic injection mould process, there is a lot of room for errors. These errors can range from small surface defects to bigger problems that can affect the safety, functionality, and performance of the product.

These problems can be either caused by material use, moulding process, tooling design, or a combination of all three of them. Therefore, it is extremely important to identify these problems at the earliest so that you can avoid them.

This is why we have come up with this guide for you. Here, we will discuss all the common problems that can arise and how to avoid them. So, let’s get started!

A Bit about the 2-Step Plastic Injection Mould Process

The 2-step plastic injection mould process is also called the multi-shape injection measure. The whole interaction relies on various kinds of plastics in just a solitary machining cycle. Thus, it turns into a critical interaction for multicolour, multi-material, and other complex plastic parts.

Some Common 2-Step Plastic Injection Mould Defects

There is a huge list of 2-step plastic injection mould defects. While some of them are easy to address, others can be extremely costly to fix. Let’s take a look at these defects below.

1.      Flow Lines

The flow lines look like a wavy pattern with a slightly different color than the surrounding area. Moreover, you can generally spot them on narrower sections of the moulded product.

The main reason behind the formation of these lines is the variation that takes place in the cooling speed of the material. When it flows in different directions through the entire mould, flow lines may occur. In addition to this, differences in the thickness of the wall can also result in the material cooling down at different rates. This would leave flow lines behind.

So, if you want to avoid this problem, all you need to do is increase the velocity of the injection, material temperature, and pressure. This will ensure that the material fills the entire mould before its cooling.

2.      Burn Marks

Burn marks are typically black or rusted marks or discolouration that appears on the surface or the edge of the plastic moulded part. Generally, these marks do not affect the integrity of the product as long as the plastic is not completely burned to the point of degradation.

One of the major causes of the burn marks in the 2-step plastic injection mould is the resin or the trapped air. When the resin overheats in the mould cavity during the process of injection, it then results in burn marks.

To avoid the defect of the burn marks in the moulded components, you should lower the mould and melt temperature to avoid the problem of overheating. Moreover, you can also reduce the speed of the injection. This will greatly reduce the chances of the trapping of the air inside the mould.

3.      Warping

Warping is a distortion that can happen in injection moulded items when various pieces of a part recoil unevenly. Similarly as wood can twist when it dries unevenly, plastic and different materials can twist during the cooling system when lopsided shrinkage puts unnecessary weight on various spaces of the formed part.

One of the primary drivers for twisting in injection moulded plastic and comparative materials is that cooling happens excessively fast. Injection moulding imperfections like regularly unreasonable temperature or low warm conductivity of the liquid material can deteriorate the issue.

Different occasions form configuration can add to distorting when the dividers of the shape are not of uniform thickness—shrinkage increments with divider thickness.

You can very easily avoid warping in the moulded products. All you need to do is make sure that the cooling process is gradual and long enough. This will help you in preventing uneven stress on the material. Other than that, you can even try to lower the temperature of the mould or the material.

4.      Sink Marks

Sink marks are small depressions or recesses on a flat surface of a moulded part. They occur during the process of a 2-step plastic injection mould.

These sink marks possibly occur if the inner part of a moulded product shrinks. That’s because when the component shrinks, it pulls out the material outside inward.

To avoid sink marks from occurring in the moulded products, you should increase the holding time and pressure. This will allow the material near the surface part to cool down. You can also increase the cooling time if you want to limit the shrinkage.

Final Words

If you are not careful during the process of the 2-step plastic injection mould, it can ruin your entire product. Therefore, it is extremely important to watch out for the defects and avoid them. Still, got any questions regarding the moulding process? Please feel free to contact us!

The Cost of Injection Molding Material

Injection mold or molding is a process of manufacturing that helps manufacturers produce parts in big volumes. Manufacturers inject melted materials into the mold to complete this process. It is also a widely used mass manufacturing process to create various identical items (thousands or even more).

Injection molding materials can be elastomers and plastics, etc. Injection molding is the fastest and precise method of producing identical parts or components in very large quantities. Today, we will take a look at the average cost of the injection molding material. Before that, we will take a look at how it works.

How Does Injection Mold Process Work?

The very first injection mold process involves creating the mold itself. Most molds are metal, usually steel or aluminum, and are precision-machined for matching the product features that you want to produce.

After creating the mold, the mold-maker fed the part material into the heated barrel. Then, it is mixed with the help of a helical-looking screw. The heating band melts the mold material inside the barrel.

The molten plastic or molten metal material is served into the cavity of the mold where it cools down and hardens to match the mold’s shape.

You can reduce the time of cooling by using cooling lines circulating the oil or water from the outside temperature controller. The tools of mold are fixed on platens (or mold plates) that open up after solidification of the material.

It also helps ejector pins in ejecting the component from the mold. You can combine separate materials in one component in an injection molding type, two-shot mold. You can use this technique for adding a softer touch to your products.

Moreover, this technique is also useful in adding colors to a component. It is an ideal approach for producing items with diverse performance characteristics.

It is possible to make molds with multiple or single cavities. A multiple cavities mold can include identical components in every single cavity. Or, you can use it to produce components of various geometries. Aluminum molds aren’t ideal for large production volumes or components with thin dimensional tolerances.

It is because they have mediocre mechanical properties. They are also susceptible to damage, deformation, and wear because of the clamping and injection forces.

The steel molds are highly durable, but they are expensive than aluminum molds. Thus, the process of injection mold needs vigilant design, including features and the shape of the component.

Injection Mold Material Cost

The cost of the injection molding material depends on how much you spend to create how many parts. For instance, if you produce 400,000 components after spending #20,000 on the steel mold, your cost on the mold for a single component will be around 5 cents.

However, there are a few other costs as well that will incur. Those include the material you use and the labor. All these things impact the cost of your injection molding project.

The most common materials for injection molding include:

• Polyamide
• Polyethylene
• Polypropylene
• ABS (Acrylonitrile Butadiene Styrene)
• ……

These materials are so common because all these materials are durable and affordable. Your product itself is the best decision-maker in deciding which material to choose to create the product. Apart from that, the material selection also depends on for what purpose you will use the product. 

In addition, various factors impact injection molding’s final price, including complexity and size. 

Most Expensive Injection Molding Materials

The most expensive injection molding materials include Polycarbonate, Teflon, Polysulfone, PEEK, Acetal, and Polyurethane. These materials come with special properties and are usually stronger, making them an ideal choice for specialized use.

Other components and additives can make them more durable. However, their price will also go up.

Injection Molding Materials That Cost Low

When we talk about the least expensive materials, they are polyethylene and polypropylene. These materials are highly versatile and perfect for making various things from car batteries to milk jugs. Polyethylene and polypropylene are the materials that we usually use every day. So, their low cost is a great advantage for mass production.

You must choose the right material for your injection molding project. As not all materials are suitable for all products. It is the product function that helps you determine what material you should choose. Before choosing a material, you should learn about all available options. It will help you identify the most suitable material for the product you want to make.

Injection Molding Considerations

There are several considerations to look at when starting your injection molding project. Here are those important considerations:

Financial: For injection molding manufacturers, the starting price can be a bit high. It also includes the mold and machinery costs.

Production Quantity: You must decide how many components you want to manufacture. Moreover, it will help you decide whether or not injection mold is a highly cost-effective production method.

Design Factors: You can make the injection molding easier by minimizing the parts number and making the geometry of the items simple. Additionally, the mold design tool is critical in preventing flaws during the production phase.

Production Considerations: Minimizing your cycle time would assist in production. Using hot runner mold machines with appropriate tooling is also important. Using hot runner machines and small changes can result in production savings. You can also save costs by minimizing assembly requirements, particularly if you want to produce parts in huge numbers.

How to Reduce Mold Costs

Some people find injection molding a highly expensive process. However, you can reduce the costs of mold in several ways. Those include:

• Eliminating undercuts
• Using the core cavity method
• Removing unnecessary features
• Designing self-mate parts
• Reducing cosmetic finishes
• Monitoring DFM analysis
• Considering part sizes

You can also modify existing molds for re-use and use multiple cavities of mold to reduce mold costs.

Final Words

The cost of injection mold depends on the material you choose and how many parts you want to manufacture. Apart from the material cost, there are also other costs, such as labor costs that you must also consider. However, you can reduce the cost by considering a few things that we discussed in this article. For a successful injection molding process, it is essential to choose the most suitable material according to the product you want to manufacture.

To learn more about the injection molding process, please click here.

Internal plastic thread carries high accuracy due to forced ejection and auto screwing

In comparison to auto unscrewing injection plastic molding, forced molding in injection processes happens in three different conditions. The forced injection is perfect for the material that is soft as glue. For instance, the materials like PVC, PP, and PE work well with this process.

One of the most vivid differences between auto unscrewing injection and forced ejection is the difference in the shape of the tooth profile. The tooth profile of forced ejection carries a circular shape. The height of the tooth profile in forced ejection also appears to be considerably smaller in comparison to the unscrewing.

In auto unscrewing injection, some points are of integral value. It includes:

Analysis Of the Plastic Parts

The analysis of the plastic parts in auto unscrewing injection molding focuses on the plastic part that acts as a connecting pipe. This, connected pipe happens to join and connect the mechanical products. ABS is the material that manufacturers commonly use.

The most striking feature of this plastic is that it has a shrinkage rate of only 0.5%. Furthermore, plastic parts in molding injection processes are cylindrical parts. For all these parts, the most prominent feature is the presence of threads both inside and outside in a continuous pattern. The unit for the internal thread is M20 and that of the outer thread is M44. Hence, for an auto unscrewing injection, the teeth are triangular and thus there is no chance of ejecting the plastic forcibly. Releasing the mold appears to be the most difficult step in mold designs.

Analysis Of the Mold Structure

There are two ways to analyze the mold structure in auto unscrewing injection molding. Let us discuss each here:

First Case

Here the plastic part acts as a rotating body. Also, the customer is looking for 4 cavities for a project. Therefore, according to the rules and mechanism, the scenario would be, according to the assembly position of the plastic parts on the product, the production of external thread happens because of the side pulling and parting mechanism in ejection. However, on the other hand, the internal threads, adopt the formula of “motor ten chains ten sprockets”. This mechanism is the source to have internal threads.

Second Case

There are certain cases and models where we can only set the cavity of the model as per horizontal shape. This happens because of the structure of the mold. Here, we see that a plastic part makes itself the part of a circulating rotating body. Moreover, for a large end face, the gate design appears to be the best choice. In this case, the pouring system of the mold appears to go through the main channel, a gate, and a flow distribution channel.

Analyzing the Design of the Mold Part

In the auto unscrewing injection molding process, the moveable mold carries the shape of a mosaic structure.  This structure helps much in easing the overall manufacturing and also venting the cavity of the mold.

Here the mold consists of ratings 24 and 26. Moreover, for the sake of machining cavities, the combined machining method is also used. However, the mosaic structure is capable and conducive to exhaust.

Auto Screwing Thread Mechanism and Ejection System

If we are to discuss the most difficult and complex core structure in injection molding, the auto unscrewing injection happens to be the one. To work it the right way, the automatic thread removal mechanism works and it carries the structure of motor ten roller chain ten sprocket ten thread core.

By this, it means that motor 23 drives the roller chain 22. Furthermore, the roller chain 22 in turn drives the sprocket 16. Whereas, the sprocket 16 eventually drives the large sprocket shaft number 18 with the help of key 19. After that, the large sprocket shaft helps in driving the core 25 with the help of a square wedge.

We also observe that during the rotation of the threaded core, there is an attachment of reinforcing rib, which helps in playing a critical role by stopping the rotation. To do this, the plastic part in the system moves up and away from the model cavity, which is moving, in the axial direction. In the last step, using the ejector pin, we cab push the bypass in the gating system.

However, to connect the bypass to the plastic part, there is wide use of a gate. Through this, you can get the plastic move out of the box. The ejection system of this auto screwing mold and injection carries the mold using ejector pin 15. It also includes an ejector fixing plate of number 12 and so on.

Design Of the Temperature Control System

If you are looking at the mold quality of the plastic parts in auto unscrewing injection molding, the very first thing that affects the quality is the temperature control system. Furthermore, the temperature control system in the injection molding process also directly affects labor productivity.

Therefore, it is a recommendation that if someone needs to avoid affecting the melt-filling, it is the best practice to reach rapid cooling and balanced cooling. This is to be done as much as possible.

The moving side in the molding process gets colling by cooling water pipes. However, as an alternative, the fixed mold gets cooling through the use of a water well plus water pipe. Thus, if we achieve this status, then we can safely claim that the product appears to be the best in plastic quality. Otherwise, there is no guarantee for this.

 

Advantages of Transmission Method

We have seen that the power source in all this auto unscrewing injection molding process is the electric motor. Hence, the transmission method for is motor ten single-row roller chain plus three arc-linear tooth sprockets. To use this method, we consequently get the advantage such as:

• The average transmission ratio of the model appears to be accurate without causing any possible slippage.
• It carries a compact structure and holds low pressure on the shaft.
• High transmission efficiency 98%.
• Lower bearing cost.