If you ever want to manufacture a part that is strong, durable, lightweight, and resistant to chemical and physical factors, consider using ABS injection molding.
Belonging to a market that is expected to reach 144,599 kilotons by the end of 2023 with a compound annual growth rate (CAGR) of over 3.5% across the next five years, this type of plastic injection molding process is experiencing increased usage in several industries.
This is an ultimate guide to the process of manufacturing parts using ABS plastic injection molding. You will also learn more about various aspects to consider when opting for this method, as well as the different techniques used to ensure you get the right result.
A discussion of the advantages, disadvantages, and the problems faced during the ABS molding process follows, after which we highlight how our ISO:9001 and ISO8 injection molding services offer the ideal solution for all your plastic manufacturing demands.
What is ABS Injection Molding?
ABS injection molding refers to the process of obtaining molded products by using acrylonitrile butadiene styrene (ABS) plastic, which is first melted using heat and then injected into a mold, before being cooled and solidified.
The ABS molding procedure begins with the feeding of ABS pellets or granules into a hopper. A reciprocating screw feeds it along the barrel, where the heaters melt the pellets and inject them through a nozzle into the mold cavity.
The molten ABS thus takes the shape of the mold, and is allowed to cool down and solidify. The mold then opens, allowing you to take out the manufactured part before the process is repeated.
Why is ABS Used in Injection Molding?
ABS is used in injection molding due to a combination of properties it gains from each of its three monomers. The acrylonitrile part (leftmost in the above diagram) of its structure imparts resistance to chemicals and heat, as well as hardness.
The butadiene (middle) portion gives it impact resistance and toughness, while the styrene (rightmost part) contributes to its glossy, impermeable, rigid surface.
These properties make ABS a thermoplastic, which refers to plastics that do not burn when heated. Rather, they become liquid at a certain elevated temperature and solidify when cooled.
This elevated temperature, known as the liquefying temperature, is 105°C (221°F) for ABS.
Moreover, ABS is inexpensive when compared to other materials. It is also possible to obtain molded parts in a particular color or a combination of colors.
What Are the Applications of ABS Injection Molding?
If you take a look at your surroundings, there is a strong likelihood that you are using products made with ABS plastic on a daily basis.
Its ease of molding, durability, low production cost, and resistance against physical and chemical changes makes it a perfect material to use on a consumer as well as on industrial level.
Among the most widely used ABS products at home are Lego blocks, refrigerator liners, keyboard keys, food processors, and vacuum cleaners.
In addition to the abovementioned qualities, ABS also enables these products to be painted as per requirement, resulting in all those colorful Legos you once used to play with.
ABS plastic finds its use in the manufacturing of pipes and fittings, as well as rigid casings on several power tools. All these take advantage of its high resistance to impact.
Vehicle parts need to be as light as possible so that the engine does not have to move all that extra weight along. Therefore, ABS is often used in the manufacture of several car components, such as bumpers, pillar trims, car door handles, fuel covers, seatbelt parts, and instrument panels.
Being an electrical insulator, ABS plastic is widely used to make computer and printer accessories as well as safety enclosures for wall sockets and power tools.
Considerations in ABS Plastic Injection Molding Process
Until now, you have learnt what ABS injection molding is as well as where it is used. However, before you proceed with various techniques, there are some factors you must consider to ensure you get the best results regarding your desired product.
1. Consider ABS Plastic Parts Design
Prior to starting the ABS molding process, you must ensure several things about the part to be designed. Firstly, make sure that the wall thickness of the part to be manufactured is uniform.
Usually, a range of 1.14 to 3.56 mm is suggested. Avoiding sudden changes in the wall thickness prevents the buildup of large stresses in the part. Moreover, ribs can be added to increase strength.
You can also reduce stress concentrations by increasing the radius. But do practice caution, as extremely large radii can cause shrinkage to occur. Experts suggest that the minimum radius should be at least 30% of the wall thickness.
2. Dry ABS Material Before Processing
You are also advised to dry the plastic before starting the ABS injection molding process. Not doing so may result in longer cycle times, greater operating costs, and cloudy parts being produced.
However, the hygroscopic ABS may still absorb water from the atmosphere, often as much as 0.4% of the composition.
In that case, you should use temperatures around 90°C to dry it for 3 to 4 hours, so that the moisture content drops to around 0.05%.
Not doing so may cause easily separating thin layers to form on the surface of the part, which is a sign of delamination. This reduces the strength of the molded ABS part.
3. Molding Temperature Control
As mentioned earlier, ABS is a thermoplastic, which means it melts when heated to its liquefying temperature.
However, applying excessive heat to it during ABS molding may break the chemical bonds holding its structure together, resulting in the formation of brown granules on the molded parts.
However, if the parts need high gloss, you should keep the molding temperature high to ensure that. Also note that ABS molding requires higher temperatures (around 200°C) than other materials.
4. Injection Pressure
When you melt ABS, its structure causes it to flow into the mold with some resistance. This is due to its viscous property, which necessitates the use of high injection pressure. However, you should strike a balance between the pressure ranges.
This is because at very high pressures, parts can stick due to friction, while very low pressures cause mold shrinkage to increase. These factors result in high production costs (due to the extra removal procedure required) or lower-quality parts being produced (due to part dimensions not being met).
5. Injection Molding Speed
Just like injection pressure needs to be balanced, injection molding speed needs to be within a specific range as well.
High speeds have the same effect as high temperatures, that is, they cause thermal decomposition of the ABS structure. They may also cause discoloration and a weld line to form on the part, resulting in a poor general finish.
On the other hand, low speeds result in incomplete filling of the mold by the ABS, which affects the dimensions of the part produced.
What Are the ABS Injection Molding Techniques?
1. Thin-Walled Parts
Thin parts must be manufactured at high injection molding pressures. This is because increasing the temperature in this manner causes the viscosity of ABS to increase, thus affecting the flow of the molten ABS into the mold.
2. Large-Hollow Parts
If you want to produce large and hollow arts, the parameters such as thickness and internal volumes are important to get right. You should make such parts using water or gas at high pressures, which firmly press the molten ABS against the walls of the mold to produce a better finish.
3. Thick-Walled Parts
Using regular plastic injection molding methods to make thick-walled parts often results in the formation of sink marks on the manufactured parts. You can avoid this by using compression injection molding, in which the melted plastic is injected into a partially opened mold.
This prevents internal stresses from developing, thus reducing the occurrence of sink marks. Or otherwise, you can tweak the mold walls to make them thinner so that the thick-walled part has a better finish.
4. Multi Material
Multi-material is a type of injection molding in which two or more different materials are molded into one plastic part. Common techniques to achieve this include multi-component molding, multi-shot molding, insert molding, and over molding.
Materials that are near their melting points have to be used so that, in their molten state, they can flow into the mold. Multi-material injection molding is used to make toothbrushes and power tools.
What Are the Advantages of ABS Injection Molding?
The robustness of ABS plastic makes it a favorite among the manufacturers. Some of the benefits include:
1. High Productivity – Efficiency
You may have noticed that the whole process, from the feeding of ABS granules from the hopper to the unclamping of the mold once the part has been molded and solidified, is highly automated.
This enables ABS plastic injection molding to have high efficiency compared to other manufacturing methods. High production rates, which lead to higher revenue, also contribute to making it a favored choice.
2. Design of Complex Parts
The part produced depends on the mold, which can be altered according to the specifications needed. Wall thickness and internal diameters can easily be controlled using computer-aided design (CAD) or computer-aided manufacturing (CAM), which seamlessly integrate with the control panel of the machine.
3. Increased Strength
ABS plastic owes its high strength to the various types of bonds found in its structure. This is a property that it also imparts to the parts it produces. Thus, making it suitable for applications that require increased strength and durability.
4. Flexibility of Color and Material
As shown before, ABS is easily colored. This is why you can find ABS products in a wide spectrum of colors depending upon the application.
Although it is best to avoid using such products outdoors owing to their degradation by UV light from the sun, this problem can be dealt with using paint or electroplating.
5. Decreased Waste
Larger production rates result in minimal waste being produced. For a factory running it throughout the year, it eventually adds up to a low cost of material wasted, thus further increasing the profit.
6. Low Cost of Labor
This is another factor that positively contributes to the financial aspect of the ABS molding. As a result of high levels of automation, you don’t need to employ many workers to operate a single machine. This results in a low cost of labor, thus increasing savings.
What Are the Disadvantages of ABS Injection Molding?
However, you must be mindful of several disadvantages of using ABS plastic injection molding to produce your parts. Some of them are discussed below:
1. High Tooling Costs and Extended Lead Times for Setup
As the parts become more complex, the time you would need to design the mold increases. Once that stage has been completed, the production of the mold becomes expensive.
Therefore, you must keep in mind the high initial costs of the whole project before starting it. To make it feasible from a financial perspective, you need to ensure that you produce enough parts to balance the costs and then return a profit.
2. Partial Design Limitations
Since the process of plastic injection molding has been developed across numerous decades, experts have devised several guidelines to ensure best practices are followed in order to obtain high-quality products.
In doing so, they have also developed limits on several aspects of the part design, such as wall thickness and internal radius. Depending on the complexity of your part, these limitations might affect your design. This is why you should carefully study them before designing your part.
3. Costly Small-Run Parts are a Possibility
As stated earlier, injection molding works best at high levels of production. If your part is highly specialized, your production rate may be low. Therefore, you would need to sell at a high price to generate enough revenue to offset the costs.
As a general rule, remember that the more specialized a part is, the less the demand there will be for it, necessitating a high sale price to breakeven.
What are the Common Problems in ABS Injection Molding?
As with any other manufacturing process, you might experience several problems when working with ABS injection molding. These are outlined below:
When the heating temperature goes beyond the plasticizing temperature of ABS, the plastic becomes more viscous, that is, more resistant to flow, due to large friction forces in the material.
Hence, you should ensure that the temperature does not go beyond this level, as the friction forces may affect the production of thin-walled parts.
2. Thermal Degradation
As mentioned before, thermoplastics lose their chemical structure at extremely high temperatures, which further makes temperature control one of the most important facets of ABS injection molding.
The last component of ABS molding prior to its unclamping is the cooling process, in which the molten plastic solidifies in the mold. The formation of internal stresses due to inadequate or uneven cooling causes warping, which is evidenced by the inward curve of the walls of the produced part.
To avoid it, ensure that you give sufficient time for cooling, and that the cooling channels are evenly spread out.
4. Sink Marks
Sink marks are another result of uneven cooling. They appear as dents in the thicker sections and are caused by the inner portions of the part contracting at a different rate than the outer portions.
Extremely high temperatures and low pressures in the mold cavity can also cause sink marks. To prevent them, you can reduce the thickness of the thicker sections so that the part is evenly cooled, ensure proper rib thickness of the part, or increase the pressure used.
What Material is Used for Injection Molding?
Since injection molding involves the melting and solidifying of a material at high temperatures and pressures, thermoplastics are ideal materials you can use in the process.
This article discussed ABS, but other similar plastics such as polycarbonate, polystyrene, polypropylene, nylon, and high-density polyethylene can be used as well. Furthermore, you can also strengthen the plastic using carbon fiber or glass.
In cases where you need to inject metals, a plastic binder or filler is required for a smooth flow of the metal into the mold.
The metal product that forms would have to undergo additional processes such as cleaning and thermal debinding to remove the binder material. Sintering is then used to densify the metal particles.
Kemal’s Custom ABS Plastic Injection Molding Services
At Kemal, we take pride in offering the perfect solution for all your custom plastic production needs. Top-quality parts produced in minimum lead times at low-cost rates are hallmarks of our services.
Our advanced manufacturing setup houses the right technology to produce consistent parts with the same mold.
If you are still unsure, we offer a free consultation service where our expert will ensure all your queries regarding the mold, the process, and the product are appropriately answered.
We also offer instant quote services while guaranteeing the confidentiality of your uploaded designs. Contact us today to get ahead of your competition!