The latter, generally forming a simply supported beam, also has minimal deformation. When using two cores, their diameters should differ slightly to prevent misalignment and ensure smooth mating surfaces. Blind holes, formed with a cantilever beam core, are more prone to bending under the impact of the molten plastic, leading to irregularly shaped holes. Generally, the depth of a blind hole should not exceed twice its diameter. For blind holes with diameters of 1.5mm or less, the depth should not exceed the diameter. The wall thickness at the bottom of a blind hole should be at least one-sixth of the hole diameter to avoid shrinkage.

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.

The principle of a snap-fit involves pushing a protruding part of one component past an obstacle on another component. This process involves elastic deformation, and once the obstacle is cleared, the parts snap back into their original shape and lock together, as shown in Figure 9. Snap-fit connections can be either permanent or releasable.

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.

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.

If the internal corner is rounded and the external corner is sharp, the area at the turn will still be thicker than other parts, leading to shrinkage. A solution is to round both internal and external corners to achieve uniform wall thickness. In this case, the external radius is the sum of the internal radius and the base wall thickness.

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.

Interference fits, used to connect holes and shafts, are effective for transmitting torque and other forces. This type of connection is convenient and straightforward. The primary consideration in designing interference fits is the amount of interference: too little interference leads to unreliable connections, while too much makes assembly difficult and increases the risk of cracking.

The design principles for corner radii also apply to cantilever snap-fits. In these snap-fits, the cantilever arm needs to bend and fit into place. If the radius of the corner (R) is too small, it can lead to excessive stress concentration, making the product prone to breaking when bent. Conversely, if R is too large, it can result in shrinkage marks and voids. Therefore, there is a specific ratio between the corner radius and wall thickness, typically ranging from 0.2 to 0.6, with an ideal value around 0.5.

Most plastic products can achieve high precision in dimensional tolerances. However, materials with high shrinkage rates or softer materials can be more challenging to control. Product design must consider the use environment, plastic material, and product shape to set appropriate tolerances. As customer demands increase, the concept of fit and finish must evolve. The goal is to achieve a balance between fit, precision, and aesthetics.

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.

Injection molding is generally categorized into three quality levels: general-purpose, medium precision, and high precision.

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.

Additionally, designers must consider the flow path, the distance the molten material travels from the gate to all parts of the cavity. Generally, there’s a proportional relationship between flow path and wall thickness. A larger wall thickness means a longer flow path. If the ratio of flow path to wall thickness is too high, material shortage or incomplete filling can occur far from the gate. Therefore, increasing wall thickness might be necessary in some cases.

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.

Experienced product designers deeply understand injection molding processes and consider numerous factors in plastic part design. This article focuses on essential elements such as wall thickness, draft angles, ribs, holes, pillars, snaps, interference fits, and tolerances in plastic molded part design.

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.

Annular snap-fits use a ring’s internal protrusions to engage with a shaft’s groove. Based on the release angle, they can be either releasable or non-releasable. The ring expands elastically during insertion and removal, typically made from materials with good elasticity.

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.

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.

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.

Draft angles are crucial in determining the magnitude of ejection forces. Since injection-molded parts often adhere to the convex mold due to cooling shrinkage, equal draft angles on both concave and convex molds ensure uniform wall thickness and prevent the part from sticking to the hotter concave mold after ejection. In special cases where the part is required to stick to the concave mold post-ejection, the draft angle on the adjoining concave part can be reduced, or an undercut can be deliberately added to the concave mold.

Determining the appropriate wall thickness is crucial. Other features like ribs and fillets reference the wall thickness. The wall thickness of a plastic product depends on various requirements, including the external forces it must withstand, support for other parts, properties of the plastic material, weight, electrical performance, dimensional accuracy, stability, and assembly requirements.

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).

Typically, the wall thickness for thermoplastic materials ranges from 1 to 6mm, with 2 to 3mm being most common. For larger parts, thicknesses can exceed 6mm. Table 1 shows recommended values for the wall thickness of various thermoplastics.

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.

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.

In addition to interference fits, other methods for joining plastic parts include heat staking, welding, and ultrasonic welding. Each of these methods has its own set of advantages and is suitable for different applications based on the material properties and the requirements of the assembly.

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.

When designing interference fits, it’s important to consider the tolerances of the hole and shaft, as well as the operating temperature, since temperature variations can significantly affect the interference amount. Most shafts are metallic, and to ensure a reliable connection, it’s common to add knurling or grooves on the mating shaft. The general formula for calculating interference is:

There are no inherently bad materials, only inappropriate choices for specific applications. Designers must thoroughly understand the properties of available materials and carefully test them to study their impact on the performance of molded products.

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%.

In many cases, designers can use ribs to modify the overall wall thickness, which not only saves material and reduces production costs but also shortens cooling time. Cooling time is approximately proportional to wall thickness.

However, you must be mindful of several disadvantages of using ABS plastic injection molding to produce your parts. Some of them are discussed below:

To achieve uniform stiffness in all directions, the simplest method is to add ribs both longitudinally and transversely, intersecting at right angles. However, this can increase wall thickness at intersections, leading to greater shrinkage. A common solution is to add a round hole at the intersection to create uniform wall thickness, as shown in Figure 5.

Where S is the design stress, v is Poisson’s ratio, E is the elastic modulus, and K is a geometric coefficient calculated as: K = (1 + (d/D)²) / (1 – (d/D)²).

There’s no fixed value for draft angles; they are usually determined based on experience. Highly polished outer walls can have draft angles as small as 1/8 or 1/4 degree. For deeper or textured parts, the draft angle should increase correspondingly. Conventionally, an additional 1 degree of draft angle is required for every 0.025mm depth of texture.

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.

The strength of plastic parts does not solely depend on increased wall thickness. In fact, increased thickness can lead to internal stresses due to shrinkage, thereby reducing strength. The key to enhancing the strength of plastic parts lies in their stiffness. This is often achieved through a combination of thin-wall styles and strategically placed ribs to increase the section modulus.

On the other hand, low speeds result in incomplete filling of the mold by the ABS, which affects the dimensions of the part produced.

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.

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.

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.

Side holes are typically formed using side cores, which can increase mold costs and maintenance, especially if the side cores are long and prone to breaking. If feasible, the design can be improved as shown in Figure 6, to mitigate these issues.

From the analysis, it’s evident that the thickness of the rib should be minimized within limits. If the rib is too thin, its height must be increased to maintain stiffness. However, excessively thin ribs can lead to deformation under pressure, difficulties in filling during molding, and sticking to the mold. The radius of the rib’s base should not be too small to avoid stress concentration.

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.

In summary, this article has covered various critical aspects of structural design for injection molded parts, including wall thickness, draft angles, ribs, holes, bosses, snap-fits, interference fits, tolerances, and rounded corners. Each of these elements plays a vital role in the overall functionality, durability, and quality of the final product.

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.

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.

Where S is the design stress, v is Poisson’s ratio, E is the elastic modulus, and K is a geometric coefficient calculated as:

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.

Many bosses are used to connect self-tapping screws. The internal threads on these bosses are formed through cold flow processing, which deforms the plastic without cutting it. The size of the threaded boss must be sufficient to withstand the screw’s insertion force and the load it carries. The hole diameter in the boss should ensure that the screw remains secure under specific torque and vibration conditions.

There are various types of holes, such as through holes, blind holes, and stepped holes. From an assembly perspective, through holes are more common and easier to produce than blind holes. In terms of mold design, through holes are structurally more straightforward. They can be formed with cores fixed in both the movable and fixed parts of the mold, or with a single core in either part. The former creates two cantilever beams under the action of the molten plastic, but with short arms, resulting in minimal deformation.

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.

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.

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.

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.

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.

A simplified estimation method from a foreign website is recommended, based on the nominal diameter of the screw. First, identify the material used, then apply the corresponding coefficient from the table to the screw’s nominal diameter to determine the appropriate size.

As with any other manufacturing process, you might experience several problems when working with ABS injection molding. These are outlined below:

Incorporating holes in plastic parts for assembly or functionality is common. The size and placement of these holes should ideally not compromise the product’s strength or add complexity to the manufacturing process. Key factors to consider:

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.

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.

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.

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.

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.

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.

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.

However, it’s important to remember that structural design is also influenced by environmental factors, specific conditions, and unique requirements of each project. These factors necessitate a tailored approach to each design challenge.

The maximum allowable deflection for a uniform section snap-fit can be calculated using: Y = el² / (1.5t). This formula assumes deformation only in the snap hook. In practice, some deformation also occurs near the snap-fit, which can be considered a safety factor.

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.

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.

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.

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.

The butadiene (middle) portion gives it impact resistance and toughness, while the styrene (rightmost part) contributes to its glossy, impermeable, rigid surface.

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.

Ideally, bosses should not be designed as isolated cylinders. They should be connected to outer walls or used in conjunction with ribs. This approach enhances the strength of the boss and facilitates smoother flow of the plastic material. The connection to the outer wall should be a thin-wall connection to avoid shrinkage.

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.

Generally, the radius of the rib’s root should be at least 40% of the rib thickness. The rib thickness should be between 50% and 75% of the base material’s wall thickness, with the higher ratio limited to materials with low shrinkage rates. The height of the rib should be less than five times the thickness of the base material. Ribs must have draft angles and be oriented in the direction of ejection or use movable mold components. The spacing between ribs should be more than twice the thickness of the base material.

Snap-fit assembly is a convenient, cost-effective, and environmentally friendly method of connection. The snap-fit components are molded simultaneously with the product, eliminating the need for additional fasteners like screws. Assembly simply involves snapping the corresponding parts together.

Some thermoplastics, especially PA6 and PA66, are highly hygroscopic, which can significantly affect their mechanical properties and dimensional stability.

The base of the boss where it meets the base material should have a fillet radius of 0.4 to 0.6 times the thickness of the base material. The wall thickness of the boss should be between 0.5 and 0.75 times the thickness of the base material. The top of the boss should have a chamfer for ease of screw installation. Draft angles are also necessary on bosses. These design requirements are similar to those for ribs, making bosses a variant of ribs. Refer to Figures 7 and 8 for these relationships.

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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.

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 most commonly used materials in injection molding are thermoplastics, which are divided into amorphous and semi-crystalline plastics. These two categories differ significantly in molecular structure and performance affected by crystallization. Semi-crystalline thermoplastics are typically used for parts requiring high mechanical strength, while amorphous thermoplastics, less prone to bending, are often used for casings.

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.

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.

However, adding ribs results in increased thickness at the junction with the main wall. This thickness typically depends on the largest inscribed circle, determined by the rib thickness and the radius of the root fillet. With a base material thickness of 4mm, changing the rib thickness and root fillet radius alters the diameter of the largest inscribed circle. Figure 4 illustrates how local increases in wall thickness can lead to shrinkage deformation on the back, affecting the appearance. Proper design can reduce the likelihood of surface indentations, thus improving part quality.

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.

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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.

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.

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.

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.

At the onset of designing an injection-molded product, it’s crucial to establish the ejection direction and parting line. This ensures minimal core-pulling mechanisms and reduces the impact of parting lines on the appearance. Once the ejection direction is set, structures like ribs, snaps, and protrusions should align with it to avoid core pulling, reduce seam lines, and extend mold life. The appropriate parting line can then be chosen to enhance appearance and performance.

Moreover, while larger draft angles generally facilitate easier ejection, it’s vital to maintain dimensional accuracy. The dimensional errors caused by draft angles must stay within the precision range. For parts with significant shrinkage or complex shapes, larger draft angles should be considered.

The outer diameter of the boss must withstand the circumferential force generated during screw tightening without breaking. To facilitate screw insertion, a recess is often created at the top of the boss, slightly larger than the nominal diameter of the thread. Calculating the dimensions of a boss can be complex.

Uniform wall thickness is a key principle in plastic part design. Uneven thickness can cause inconsistent melt flow and cooling shrinkage, leading to defects like sink marks, voids, warping, or even cracking. It can also result in shrinkage marks, internal stresses, distortion, color variations, or differences in transparency. Thinner walls may compromise strength and rigidity during use and assembly. Economically, overly thick parts increase material costs and production time. Areas with thicker plastic cool slower, leading to sink marks. Figure 1 illustrates uniform wall thickness design.

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.

Two critical angles in snap-fit design are the retraction side and the entrance side. Generally, a larger retraction side is preferred for a more secure fit. When the retraction side approaches 90 degrees, the snap-fit becomes permanent, as shown in Figure 11.

Sharp corners often lead to defects and stress concentration in plastic parts, which can cause fractures under load or impact. Larger rounded corners (fillets) offer a solution to this problem. They not only reduce stress concentration but also facilitate smoother flow of the plastic during molding and easier ejection of the finished product.

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.

For releasable snap-fits, the release force can be calculated using the same formulas, substituting angle a with angle b.

Among the most widely used ABS products at home are Lego blocks, refrigerator liners, keyboard keys, food processors, and vacuum cleaners.

Bosses, typically protruding from the wall thickness, are used for assembling products, separating objects, and supporting other parts. Hollow bosses can accommodate inserts or tighten screws. These applications require sufficient strength to withstand pressure without cracking. Bosses are generally cylindrical, as this shape is easier to mold and offers better mechanical properties.

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.

Thermoplastics are available in unreinforced, glass fiber reinforced, and mineral or glass bead filled varieties. Glass fibers mainly enhance strength, rigidity, and temperature resistance; minerals and glass fibers reduce warping but offer lower reinforcement. Specific changes in properties due to reinforcements should be confirmed with material suppliers or through experimentation.

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.

The goal of this comprehensive overview is to equip aspiring and practicing structural design engineers with the knowledge and insights needed to excel in their field. By understanding and applying these principles, designers can create more effective, reliable, and high-quality injection molded parts.

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.

If a transition from thicker to thinner sections is unavoidable, it should be gradual, maintaining a maximum ratio of 3:1 in wall thickness, as shown in Figure 2.

Sharp angles often lead to defects and stress concentration in parts. These areas are prone to unwanted material accumulation during post-processing treatments like electroplating or painting. Stress concentration can cause fractures under load or impact. Therefore, it’s advisable to avoid sharp angles in design. Figure 3 provides an example of sharp angle design.

Considerations related to processing and assembly are crucial. Integrating multiple functions into a single component can save on costly assembly expenses. This principle is beneficial for calculating production costs. High-performance materials (rigidity, toughness) can allow for thinner walls, shortening production cycles. Therefore, listing all standards and systematically evaluating them is essential.

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.

During ejection from the mold, the part must overcome ejection and opening forces. Opening refers to the part’s detachment from the cavity. As the part cools inside the mold, it shrinks, causing the hole walls to grip the core tightly. Friction between the part and core, vacuum adhesion at the hole bottom, and other factors make ejection forces significantly greater than opening forces. Excessive ejection forces can deform the part, cause whitening, wrinkling, and surface abrasions.

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.

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.

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.