Plastic injection molding is a manufacturing process widely used for producing parts in high volumes with high precision. The success of this process heavily depends on thoughtful design considerations that influence both the quality of the final product and the efficiency of the manufacturing process. Below are key design factors to consider:

1. Part Geometry and Wall Thickness

Designing parts with uniform wall thickness is crucial. Variations in thickness can lead to issues such as warping, sink marks, or other defects due to inconsistent cooling times. Thinner walls are more feasible with small parts rather than large ones. The limiting factor in wall thinness is the tendency for the plastic material in thin walls to cool and solidify before the mold is filled. Walls should also be as uniform in thickness as possible to avoid warpage from uneven shrinkage. When changes in wall thickness are unavoidable, the transition should be gradual and not abrupt.

2. Draft Angles

Incorporating draft angles in the design facilitates the easy ejection of the molded part from the mold. Without adequate draft, parts may experience higher friction during ejection, leading to defects or damage. Draft angles should be used on interior and exterior walls of the part along the pulling direction. The minimum allowable draft angle is harder to quantify, but in most instances, 1 degree per side will be sufficient; however, between 2 degrees and 5 degrees per side would be preferable. Even a small draft angle, such as 0.25 degrees, is preferable to none at all.

3. Radii and Fillets

Sharp corners in a design can lead to stress concentrations, which may cause material failure or defects. Incorporating generous radii and fillets at corners distributes stress more evenly and enhances the structural integrity of the part. It is recommended that an inside radius be a minimum of one times the thickness. At corners, the suggested inside radius is 0.5 times the material thickness, and the outside radius is 1.5 times the material thickness. A bigger radius should be used if the part design allows.

4. Undercuts

Undercuts are features that prevent the easy removal of a part from the mold and can complicate the molding process. They may require additional mechanisms in the mold, such as slides or lifters, increasing the complexity and cost of mold fabrication. Therefore, undercuts should be avoided whenever possible. If unavoidable, their design should be carefully planned to facilitate efficient molding and ejection.

5. Gate Design

The gate is the entry point through which molten plastic enters the mold cavity. Its design significantly impacts the filling pattern, part quality, and ease of post-molding processing. Gate size should be balanced to ensure adequate filling without excessive pressure or material wastage. Common gate types include edge gates, pin gates, and submarine gates, each suitable for different part geometries and applications.

6. Cooling System Design

Efficient cooling is essential to reduce cycle times and ensure uniform part quality. Designing the mold with conformal cooling channels—cooling passages that follow the shape of the mold—can significantly improve cooling efficiency. This approach leads to faster cooling rates, reduced cycle times, and improved part quality.

7. Ejection System

The ejection system is responsible for removing the molded part from the mold cavity after cooling. Common ejection methods include ejector pins, sleeves, and blades. The choice of ejection system depends on the part’s geometry and material. Proper design ensures that the part is ejected smoothly without damage and that the ejection mechanism does not leave marks on the part’s surface.

8. Material Selection

Choosing the appropriate material is fundamental to the part’s performance and manufacturability. Factors such as mechanical properties, thermal stability, chemical resistance, and cost should be considered. Additionally, the material’s flow characteristics affect the ease with which it fills the mold cavity, influencing the design of the gating system and the overall molding process.

9. Tolerances and Fits

While injection molding can achieve high precision, specifying tight tolerances can increase manufacturing costs and complexity. Designers should assess the functional requirements of the part to determine acceptable tolerance levels, balancing performance needs with cost-effectiveness.

10. Design for Manufacturability (DFM)

Integrating DFM principles involves designing parts with consideration for the injection molding process capabilities and limitations. This approach includes simplifying part geometry, minimizing the number of parts, and designing for ease of assembly. Collaborating with mold designers and manufacturers during the design phase helps identify potential manufacturing challenges and optimize the design for efficient production.

Conclusion

Designing plastic parts for injection molding requires a comprehensive understanding of both material properties and manufacturing processes. By considering factors such as part geometry, wall thickness, draft angles, and cooling system design, designers can create parts that are not only functional and aesthetically pleasing but also cost-effective and manufacturable. Early collaboration with experienced mold designers and manufacturers can further enhance the design’s feasibility, leading to successful injection molding outcomes.

Two-shot injection molding, also known as dual-shot molding, offers advantages like the ability to combine different materials and colors in a single part, creating complex designs with enhanced functionality, but comes with drawbacks including high initial tooling costs and the need for specialized molds, making it most suitable for high-volume production runs.

There are a variety of manufacturing methods used to create products using plastic polymers, including two-shot injection molding, compression thermoset molding and extrusion. While all of these are viable manufacturing processes, there are several advantages to this process that make it the top choice for many plastics manufacturers. The process is relatively simple; one material is injected into a mold in order to make the initial section of the product, followed by a second injection of a secondary material that is compatible with the original material. There are three good reasons many manufacturers use this method of manufacturing plastics or polymers.

Advantages of two-shot injection molding

Two-shot injection molding  is cost-effective

The two-step process needs only one machine cycle, rotating the initial mold out of the way and putting the secondary mold around the product so that the second, compatible thermoplastic can be inserted into the second mold. Because the technique uses only one cycle instead of separate machine cycles, it costs less for any production run and requires fewer employees to make the finished product while delivering more items per run. It also ensures a strong bond between the materials without the need for further assembly down the line.

Enhanced product quality

Two-shot injection molding enhances the quality of most thermoplastic items in several ways:

ㆍImproved esthetics: Items look better and are more appealing to the consumer when they are crafted of different colored plastics or polymers. The merchandise looks more expensive if it utilizes more than one color or texture
ㆍImproved ergonomics: Because the process allows for the use of soft-touch surfaces, the resulting items can have ergonomically designed handles or other parts. This is particularly important for tools, medical devices, and other hand-held items.
ㆍEnhanced sealing capabilities: It provides for a better seal when silicone plastics and other rubbery materials are used for gaskets and other parts that require a strong seal.
ㆍCombination of hard and soft polymers: It lets you combine both hard and soft polymers for outstanding comfort and utility for even the smallest of products.
ㆍReduced misalignments: It can greatly reduce the number of misalignments when compared to over-molding or more traditional insert processes.
ㆍComplex mold designs: It enables manufacturers to create more complex mold designs using multiple materials that can’t be effectively bonded using other processes.
ㆍExceptionally strong bond: The bond created is exceptionally strong, creating a product that is more durable, more reliable, and with longer life.

Versatility

Product manufacturers favor a wide range of applications for two-shot injection molding, including automotive interior parts, medical equipment, tools, and toys. It allows manufacturers to combine various materials and colors to create a strong and attractive final product. Some materials can be effectively combined with this process, including silicone and thermoplastics, nylon and thermoplastic elastomers, or hard nylon and soft-touch materials.

Two-shot injection molding can solve your company’s product production difficulties. An experienced plastic manufacturer can guide you from concept to finished product and ensure a cost-effective solution.

Producing an assembly with multiple components

Compared to other methods of plastic molding, two-shot is ultimately a more cost-efficient way of producing an assembly with multiple components. Here’s why:

Part Consolidation: Two-shot injection molding reduces the number of components in a finished assembly, eliminating an average of $40K in development, engineering, and validation costs associated with each additional part number.

Improved Efficiency: Two-shot molding allows multiple components to be molded with a single tool, reducing the amount of labor needed to run your parts and eliminating the need to weld or join components after the molding process.

Improved Quality: Two-shot is carried out within a single tool, allowing for lower tolerances than other molding processes, a high level of accuracy and repeat-ability, and reduced scrap rates.

Complex Moldings: Two-shot injection molding allows for the creation of complex mold designs that incorporate multiple materials for functionality that cannot be achieved through other molding processes.

Disadvantages of two-shot injection molding

1) High tooling costs and long setup lead times. Up-front costs are high due to the design, testing, and tooling required. There is the initial design and prototyping (probably via CNC or 3D printing), then the design of a prototype mold tool to produce replicas of the part in volume. Lastly, and only after extensive testing during both stages, you can finally inject mold a part.

2) Part design restrictions. Plastic parts must be designed with injection molding consideration and must follow the basic rules of injection molding, for example:

Avoid undercuts and sharp edges as much as possible

Use uniform wall thicknesses to prevent inconsistencies in the cooling process resulting in defects like sink marks.

Draft angles are encouraged for better de-molding.

Don’t forget, because tools are typically made from steel or aluminum, it can be difficult to make design changes. If you need to add plastic to the part, you can make the tool cavity larger by cutting away steel or aluminum. But in order to take away plastic, you need to decrease the size of the tool cavity by adding aluminum or metal to it. This is extremely difficult and in many cases might mean scrapping the tool (or part of it) and starting over.

Also, the weight and size of the part will determine the tool size and necessary press size. The larger the part, the more difficult and expensive it will be.

3) Small runs of parts can be costly. Due to the complexity of tooling, and the necessity to rid the machine of all previous material before the next product can be made, the setup time can be quite lengthy. Therefore small runs of parts have traditionally always been thought of as too expensive to injection mold.

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Gas assist injection molding is a process that uses pressurized gas to create hollow plastic parts. The gas is introduced into the mold cavity after the plastic has been injected. The gas pressure helps the part solidify and reduces surface blemishes.

What is Gas Assist Injection Molding?

Gas assist injection molding (GAIM) is an enhanced injection molding process often applied for complex parts, large parts and parts requiring an attractive, cosmetic finish.

The types of parts benefiting most from this process include:

• large panels
• enclosures
• handles
• doors and bezels
• tube or rod-shaped parts

How Does Gas Assist Work?

The gas assist process is introduced at the finish of the mold filling stage while the resin is still liquid.  Pressurized gas (usually nitrogen) is used in place of pack pressure from the molding machine.  The pressure from the gas completes the filling of the mold cavity, forcing an even distribution of molten resin against the mold. The gas is held inside during the entire cooling phase and then is vented, leaving a hollow void.  For internal gas-assist molding, the void is inside the plastic.  For external gas assist molding, the void is on the outside surface, typically the backside of a part.

Benefits with Gas Assist

The gas-assist process gets results when part design elements make the part difficult to manufacture using straight injection molding.  GAIM allows for more design flexibility while still being able to provide these benefits:

• Thin-walled parts with greater strength and rigidity
• Creation of hollowed out areas, reducing part weight
• Reduction of molded-in stress for improved dimensional stability
• Better surface finish with no sink marks
• Less part shrinkage and reduced warpage

Design Advantages with Gas Assist

1. Complex Designs

For the design engineer, using GAIM expands design options and helps to minimize design changes to make the part manufacturable using injection molding. One of the greatest benefits is the ability to produce complex parts.  Oftentimes with straight injection molding, parts having different wall thicknesses are molded separately and assembled later.

GAIM allows multiple parts to be combined into one, reducing the need for secondary assembly processes – even if the parts have different wall thicknesses.  This is because gas-assist allows heavy wall sections to intersect thinner ones. Support ribs and bosses can achieve tighter tolerances and be designed larger without fear of sink marks. Gas channels are directed toward these areas and the consistent pressure during the cooling phase eliminates sink marks, associated with these support features, on the front side of the part.

2. Metal Replacement

Gas-assist allows the production of thin-walled components that have solid but hollow areas.  The resulting strength and lightweight part can often replace metal fabricated or die cast parts, and reduce product cost.

3. Large parts

The introduction of gas pressure aids in mold filling, providing uniform pressure throughout the part that lasts through the cooling stage. The result is a part with less shrinkage and reduced warpage. Part weight can also be reduced by creating hollowed out areas.

4. Cosmetic finishes

Where an attractive finished surface is required, gas-assist prevents sink areas that eliminate or at least minimize secondary operations to improve part appearance including sanding and priming.

5. Hollow parts

The gas can create hollowed out areas within parts like handles, which decreases part weight and still provides strength.

Cost Benefits with Gas Assist

1. Extended Tool Life

With gas-assist, lower clamping force is required because lower pressures are used.  This results in less mold wear extending the life of the tool.

2. Less Energy Cost

With lower clamping force required, larger molds can be used in smaller presses.  Smaller presses consume less power and help to decrease the cost of manufacturing the part.

3. Less Machine Time

A more rapid cooling period helps to reduce cycle time which in turn lowers manufacturing expense per part.

4. Lower Material Cost

Less material is used to produce the part because hollow areas inside of the part are created with the gas and with less resin used, the part cost is lowered.

5. Quality Results

With gas-assist injection molding, the process is typically easier to control than conventional injection molding. A dependable, repeatable process provides consistent production results and less waste.

Common pitfalls

There are many common pitfalls when it comes to Gas Assisted Injection Moulding. Firstly, it is more complex and more expensive to set up than ordinary injection molding. if the tooling price of injection mold shocks you, gas-assisted injection molds will blow you away. Also, by introducing gas into the molding mix, this variable must be precisely tracked, managed and controlled. Without experienced machine operators and technicians, the molding process could go disastrously wrong. The control of the gas also contributes to variable wall thicknesses, especially in tight corners and this is something you generally want to avoid.

Gas Assist Tool Design

If you want to achieve high-quality results, make sure you get the tool design right.

Regardless of what injection molding process will be used, it is important to engage your molder during the early stages of part design in the design for manufacturing (DFM) phase. Tooling cost, timeline, and resulting part quality will be directly impacted by the quality and efficacy of the tool.  When determining the optimal way to mold apart, engineers will consider all product requirements including application, resin selection, and cost considerations. Mold flow analysis is used to find design constraints so that adjustments can be made. When the tooling engineer determines gas-assist is the best solution, the tool will be designed with gas channels built into the mold that will allow the addition of nitrogen gas during the molding process. Determining your molding method early will conserve tooling costs and help to maintain project timelines.  Getting your molder involved early will be critical to a cost-effective, high-quality product.

To learn more about this process or to receive assistance with your project, contact WIT MOLD.

Precision injection molding has become a cornerstone in the manufacturing industry, particularly for high-tech projects requiring large-scale production. This process offers a blend of cost-effectiveness, intricate design capabilities, and enhanced efficiency. As industries continue to demand more complex components, precision injection molding has proven to be an ideal choice, delivering parts that are both high in quality and precision. WIT MOLD, a leader in this field, excels in providing seamless solutions for large-scale manufacturing needs, ensuring reliability and excellence.

Cost-Effectiveness for Large-Scale Production

One of the primary reasons businesses choose precision injection molding is its cost-effectiveness, especially for large-scale production runs. While the initial cost of creating the mold may seem high, the process becomes significantly more affordable as production volumes increase. The ability to produce thousands or even millions of parts from a single mold makes the per-unit cost drop substantially. This makes injection molding an ideal option for companies looking to keep production costs low without compromising on quality. The efficiency of the process also reduces the need for excessive labor or additional steps, further driving down overall costs.

Ability to Handle Complex Designs

In today’s competitive market, the demand for complex, high-performance parts is ever-increasing. Precision injection molding excels in producing components that require intricate detailing and tight tolerances. Whether it’s thin-walled parts, parts with intricate geometries, or components that need to be produced in multiple materials, injection molding offers unmatched flexibility in handling complex designs. This makes it an excellent choice for industries like electronics, automotive, medical devices, and consumer goods, where component complexity is critical.

Moreover, the precision with which the process can produce these parts ensures that every component meets the exact specifications required. Whether you are creating delicate parts with micro-features or robust, heavy-duty components, precision injection molding can accommodate a wide range of design specifications. This level of precision is particularly valuable for high-tech applications, where the integrity of the final product is non-negotiable.

Strength and Durability of Molds

Precision injection molding uses highly durable molds that can withstand repeated use over long production cycles. These molds are designed to endure the high pressures involved in the injection process, ensuring that they can be used for thousands or even millions of cycles without degradation. The longevity of these molds contributes significantly to the cost-effectiveness of the process, as they do not need to be replaced frequently.

Furthermore, the materials used in injection molding can be chosen to meet the specific strength and durability requirements of the part. Whether you need parts that can withstand extreme temperatures, resist corrosion, or handle heavy loads, the selection of appropriate materials ensures that the molded parts will perform consistently throughout their lifespan.

Efficiency in Production

The efficiency of precision injection molding is another reason why it is a preferred method for large-scale manufacturing. The process is highly automated, reducing the need for manual labor and minimizing human error. Once the mold is created, it can be used to produce thousands of identical parts with minimal intervention. This not only speeds up the manufacturing process but also ensures consistency and uniformity across all units.

Additionally, the cycle time for injection molding is relatively short, which means that businesses can produce large quantities of parts in a shorter time frame. This efficiency is especially valuable in industries where time-to-market is critical. By utilizing precision injection molding, companies can meet tight deadlines while maintaining high-quality standards.

Design Freedom and Flexibility

One of the standout advantages of precision injection molding is the design freedom it offers. The process allows for complex geometries, undercuts, and the integration of multiple features in a single part. This flexibility enables designers to explore a range of creative possibilities without being limited by the manufacturing process.

Injection molding also supports the use of various materials, including thermoplastics, thermosets, and elastomers. This diversity opens up new opportunities for product development, enabling manufacturers to select materials that best suit their specific needs. Additionally, multi-material molding capabilities allow for the creation of parts that combine different properties in a single component, further enhancing their functionality.

Why WIT MOLD is the Best Choice for Your Project

WIT MOLD stands out as a reliable supplier of precision injection molding services, offering seamless and efficient experiences in large-scale production. With extensive expertise in handling complex and high-tech projects, WIT MOLD ensures that every component meets the highest standards of quality and precision. Whether you are looking to produce small or large quantities, WIT MOLD’s state-of-the-art technology and experienced team can help bring your vision to life.

If you are looking for a trusted supplier to handle your precision injection molding needs, contact us today. We are committed to providing you with the best manufacturing solutions to meet your project requirements.