Structural Foam Injection Molding Process

Structural foam molding is a low-pressure foam injection molding process in which molten resin is injected with nitrogen or a chemical blowing agent. The resin is then injected into the cavity without overfilling or filling it. The blowing agent or gas then expands to push the molten resin to the end of the cavity. As the part cools, the internal pressure of the foaming action absorbs internal shrinkage and reduces sinkage on the ribs or heavy sections.

 

Structural foam molding is a low-pressure injection molding process that can produce very large structural parts. Molten plastic is mixed with a blowing agent and injected into the mold to "foam" the plastic. Structural foam injection molding is ideal for large parts because the foam bubbles in the resin matrix squeeze out the resin, reducing the incidence of side-sinking of the part. Structural foam molded parts are typically thick, with wall thicknesses approaching 0.250 inches, making them ideal for fabricating invisible plastic structural components. Visible parts require sanding, painting and finishing.

 

The molding process for structural foam parts is very similar to traditional reactive injection molding methods. The two components, such as polyol and isocyanate (which combine to form polyurethane) are stored in separate containers in liquid form. They are mixed together to form a resin, which is then injected into a pre-prepared mold and cured by a chemical reaction.

 

In addition to the polyol and isocyanate, inert gas or chemical blowing agent is added to the mixture during the injection process. This changes the nature of the chemical reaction that ultimately occurs.

 

Compared to standard solid polyurethane reaction injection molding, fewer polyols and isocyanates are used, so the resin does not completely fill the mold. Instead, the gas or blowing agent is activated by the reaction between the two components. It expands and fills the blank space of the mold with foam. This produces a "honeycomb" texture called the structural foam core. The surface cells collapse as they come into contact with the mold walls, forming a solid surface layer on the outside of the material.

 

Benefits of Structural Foam Molding

There are many benefits to using the foam injection molding process, including.

 

Uses less energy - The process uses less energy per pound of plastic, and there is a less raw material in the finished product.

Lower molding costs - Part weight can be reduced by up to 15%, resulting in lower material costs without compromising structural integrity.

Greater product design capabilities - smaller parts with contrasting functions can be combined into one part to reduce costs and increase efficiency.

Raw material savings - low-pressure molding consumes less raw material than comparable methods.

Family molds run together - Because of the larger platen size, family molds can be run together to create complete assemblies without waiting.

Improved dimensional stability- Low-pressure injection combined with expanded nitrogen produces parts with less internal stress. The result is a foam injection molded product that stays straighter and has greater dimensional stability when subjected to temperature changes and prolonged exposure to weather.

Improved weight-to-weight strength - The structural properties of molten resin cores can improve performance per pound of plastic.

Wide range of materials - WIT MOLD's low-cost molding capabilities allow the use of many types of resins.

Efficient and cost-effective - Our structural molding process provides an efficient and cost-effective way to produce advanced quality, easily repeatable parts for your next foam injection molding project.

 

Contact WIT MOLD today about your structural foam molding project.

 

Advantages and disadvantages of plastic injection moulding

The plastic injection molding industry is very popular among manufacturers, but like any type of manufacturing method, it also has its own advantages and disadvantages. The advantages of plastic injection molding focus on high precision and high repeatability. At the same time, it combines high speed, low single piece cost and a wide variety of plastics to choose from. Disadvantages include higher initial costs and delivery times than some other processes.

 

Plastic molding advantages

1. Precision plastic injection molding part

Plastic injection molding is very suitable for very complex parts. Compared with other technologies, molding allows you to integrate more functions with very small tolerances. Look at the picture on the right. You can hold this mold in the palm of your hand. It has bosses, ribs, metal inserts, side cores and holes. The tool has sliding closing function. This is a small part of a large number of functions! It is impractical to use plastic manufacturing, and it is impossible to use vacuum forming process.

2. High repeatability

Once your mold is finished, you can make the same product again and again. Then again. A properly made mold tool has a long service life as long as it is handled by the molding machine installer!

3. Low single piece cost

Although the initial investment of plastic injection molding tools is very high, the subsequent single piece cost is very low. Other plastic processing technologies may require multiple operations, such as polishing, while injection molding can be completed at one time. If you choose to CNC the above parts, the cost of each part will be as high as hundreds of pounds. If you want to put into full production, injection molding is your best choice.

4. Fast

The cycle time can be as low as 10 seconds. Combined with multi impression injection molding tools, you can get a large number of products very quickly. The upper part takes longer because it is a professional material and has many functions that need to be molded correctly, but you can still get 70 parts per cavity per hour in about 50 seconds. CNC processing takes half a day at a time - 3D printing takes longer!

5. Material selection

If injection molding is really good at one thing, it is the ability to customize materials and finishes according to almost any type of requirements. You can choose from plastics, thermoplastic rubber, chemical resistant plastics, biodegradable plastics and many other materials, so be sure to find out what you need from the parts, and you will have many choices.

You can also choose almost any conceivable color, or choose from a variety of finishes, whether for aesthetic or functional purposes.

6. Special surface treatment, engraving and printing

In addition to a range of colors, injection molding tools can also be made into special finishes, which will be displayed on the mold. Almost any finish you like, such as leather appearance, soft touch, spark, high gloss, everything. You can also engrave a logo or other text in the tool. Finally, you can print your mold because a range of inks can print well on plastic.

7.Eco-Friendly

A well-designed mould can produce parts without runners by using hot runner systems. Commonly most moulds produce runners for every part moulded. A majority of the moulders recycle these runners by grinding for reuse.

 

Now that we know why injection molding is so effective, let's take a look at some of its shortcomings to provide you with a more comprehensive understanding.

 

Disadvantages of plastic molding

1. High initial cost

As we mentioned earlier, injection molding can be very cost-effective, especially for larger production runs, because the cost of a part is relatively low.

However, before you actually manufacture, you need to design and create your own mold, which may take a lot of time and manpower to perform correctly.

Nevertheless, even if the process may be complex, once completed, you can quickly produce thousands of parts using molds.

2. Initial delivery time

From the product concept to the final part, it may take months of design, review, testing and tool manufacturing. Once the mold is completed, as mentioned in the advantage, it takes only a little time to produce the required parts, especially when you have a multi cavity / embossing mold.

But even if the mold development project may take time, once completed, the process will become very fast and reliable. If you know what you're looking for and have past experience, you can significantly reduce time.

3. Size limit of large parts

Huge machines are needed to make plastic injection molding. Very large parts require huge mold tools and are very expensive to manufacture. In this case, processes such as plastic manufacturing may be a better choice, depending on the type of product required.

4. Design restrictions

Plastic molds need to be designed very carefully to avoid tool problems such as undercut (which will significantly increase mold cost), locking features and insufficient drawing modulus (what is the drawing angle of plastic molds?). The wall design needs to consider the material and temperature, otherwise the mold may not be fully filled. The placement of ejector and cooling pipeline needs to be considered to ensure the beauty of the product.Unless an experienced design team works with mold manufacturers and raw material suppliers to handle the required parts, plastic injection molded parts may be almost unlimited.

 

WIT MOLD is a very professional mold design and mold manufacturer located in southern China, and has passed the ISO2009:2015 international quality standard certification. We started to build complete molds in 2011, specializing in the production of different types of injection molds, which are mainly exported to North America and Europe.Our longstanding experience allows us to help you choose the best manufacturing process for your new project. We also share our knowledge on our plastic moulding advice pages. Or just:Get a Quote now !

What is Unscrewing Mold?

 

 

One of the most unique types of injection molds is unscrewing molds. Unscrewing molding is a unique injection molding process with mold technology that includes movement and rotation to produce threaded components. Some plastic parts such as caps and closures with detailed threads cannot be removed using standard knock-off methods. After they are molded, parts need to be carefully unscrewed from mold to avoid damaging the threads.

The unscrewing molds are part of everyday use, which may cause you to think that you won’t need to spend much time considering the required design. To demonstrate the wide use of this particular mold type, the following is a shortlist of the types of products that use unscrewing molds in the design:

 

• Bottle and milk caps

• Condition and shampoo lids

• Prescription medication bottles

• Medical supplies

• Sprinkler and showerheads

• Screws, nuts, and bolts

 

Here’s How It Works:

• First, the plastic is injected into the tool. After the plastic has cooled, the threaded core starts to unscrew. The unscrewing mechanism works off of a rack and pinion and is powered by a hydraulic cylinder.

• The rack turns three sets of gears which then retracts the threaded core into the ejector box.

• Once the threaded core is fully unscrewed, the mold opens and the ejector system pushes a stripper plate forward to eject the part.

• After the part is fully ejected, the hydraulic cylinder reverses, screwing the threaded core back into the molding position, and the process repeats.

 

What factors need to be considered?

When you need one of these types of plastic molds, there are several things you have to determine to make sure you get the right fit for your product and budget.

 

Volume

 

The volume of the product will probably determine many different aspects of the final product, including the thread count, the size of the part, and the type of material that will be used during production. While other factors are important, the design of the various unscrewing molds is more complex and costly than many of the other types of molds.

 

Ease of Removal

 

The ease by which an unscrewing mold should be removed from the final product is an important factor to consider in the design. Water bottles have only a few threads, sometimes only two or three because they need to be easy to remove. To ensure that the tops do not fall off easily, the threads are spaced out a bit more. An unscrewing mold on a medical device will likely need a lot of threads that are evenly spaced and very difficult to pull off of the device. The material required for these two vastly different uses is affected by how easily the part should be removed from the product.

 

The Threads

 

The number of threads is going to vary based on the final product. Water bottles do not require a high thread count because they are relatively light and should be easily removed. If the unscrewing mold is for a plastic part under the hood of a car, it needs to have a higher thread count to be more durable. The number of threads required plays a large role in the final cost of production, so it needs to be tested to ensure it meets the needs of the final product.

 

WIT MOLD is a very professional mold design and mold maker located South of China, certified ISO2009:2015 international quality standard. Reach out to us for a Rapid Quote to take advantage of this new offering for your internally threaded plastic parts.

How Does Injection Moulding Work?

As a growing branch of the plastic industry, plastic injection molding is the most commonly used process in the production of plastic parts. Plastic injection molding process is fast, aiming at mass production of the same plastic product in a short time. In the plastic industry, it is used to manufacture a variety of items, such as car bumpers, wheeled dustbins, bottle caps, spools, toys, musical instruments, auto parts, remote controls, electronic products, chairs, mechanical parts, storage containers and medical equipment

 

What is injection molding?

Injection moulding is a manufacturing process for producing parts by injecting molten material into a mould, or mold. Injection moulding can be performed with a host of materials mainly including metals (for which the process is called die-casting), glasses, elastomers, confections, and most commonly thermoplastic and thermosetting polymers. Material for the part is fed into a heated barrel, mixed (using a helical screw), and injected into a mould cavity, where it cools and hardens to the configuration of the cavity.  After a product is designed, usually by an industrial designer or an engineer, moulds are made by a mould-maker (or toolmaker) from metal, usually either steel or aluminium, and precision-machined to form the features of the desired part. Injection moulding is widely used for manufacturing a variety of parts, from the smallest components to entire body panels of cars. Advances in 3D printing technology, using photopolymers that do not melt during the injection moulding of some lower-temperature thermoplastics, can be used for some simple injection moulds.

Injection molding uses a special machine, which is composed of injection unit, mold and fixture. Parts to be injection molded must be designed very carefully to facilitate the molding process; The material used for the part, the required shape and characteristics of the part, the material of the die and the characteristics of the forming machine must be taken into account. This wide range of design considerations and possibilities promotes the versatility of injection molding.

 

How does injection molding work?

Although the injection molding process is complex, it can actually be broken down into several basic steps to help understand how it works and why it is so effective.

The injection molding machine is composed of three main parts: feed hopper, screw and heating barrel. The working principle of the machine is to take plastic powder or particles and operate them according to requirements and dimensions to form them into parts.

When the feed hopper receives plastic particles, it will use the friction of the screw to generate heat. Once the plastic reaches the correct temperature, it is injected into the mold cavity, where it finally cools and forms according to the mold design.

If necessary, parts can be manufactured from a variety of materials using advanced injection molding technology (e.g. repeated injection). You can also use insert molding to add plastic parts to existing parts made of other materials.

The basic principle behind the injection molding process seems simple, but in fact, it is a very complex process, requiring appropriate equipment and appropriate expertise. However, if implemented properly, injection molding can consistently produce excellent results even for the most challenging manufacturing projects.

 

Step by step procedure

In the pretreatment stage, the design, shape, color and quality of plastic products must be planned. Injection molding companies determine the type of plastic they will use to produce.

1. Mold setting

In the initial step, the parts are arranged by robot or hand. The two halves of the mold first need to be carefully closed by the clamping part. Hydraulic press is used for clamping.

2. Plastic extrusion

The second step involves the melting of small plastic particles as raw plastic. They were evicted from a very hot room. Extrusion is done with the help of screw tools. Due to the flow change of molten plastic placed in the mold, it is necessary to accurately estimate the injection time.

3. Forming process

Plastic molding means providing the desired shape. The melted plastic is now injected into the mold. The temperature shall be controlled as required.

The forming process is very complex. The whole process must be carried out carefully and pay attention to the pressure of the die clamp. Only experienced manufacturers can operate the injection molding machine effectively without causing any harm. Incorrect timing and management can damage plastic parts.

4. Cooling and demoulding of parts

The plastic part is kept in the mold until it cools and becomes the desired solid shape. During the cooling phase, the plastic may shrink a little. When the required cooling time is over, the half mold can be opened.

The cooling time estimate depends on the material properties of the plastics used in the process. The solid part is then ejected by compressed air or mechanically. Mechanical and mechanical forces are applied when the part is removed from the mold. This is how plastic injection molding works. This process can quickly produce millions of the best quality parts.

5. Post processing

Runner is a channel used to fill the mold cavity and is automatically removed from the part. Finally, finish the product for final use. The flash part is trimmed from the plastic product by using a knife.

The cycle time is processed in seconds. It has produced a mass application of more than 5000 parts. The delivery time of injection molding is 2 to 4 months. The final parts are then counted and weighted. Then the plastic products are transported to different areas.

 

In A Nut Shell,Plastic injection molding works as the best equipment to design unique and high-quality parts at an efficient speed. It gives flexibility to plastic manufactures to make durable and complex shape products at very cost-friendly rates.