The Ultimate Guide to Gas Assist Injection Molding

 

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.

10 Frequently Asked Questions About Unscrewing Molds

 Unscrewing molds are essential in the manufacturing of threaded parts, offering precision and efficiency in production processes. Here, we address 10 frequently asked questions about unscrewing molds to provide a comprehensive understanding of their functionality and benefits.

 

1. What Are Unscrewing Molds?

 

Unscrewing molds are specialized molds used in injection molding to create threaded parts. Unlike traditional molds, they incorporate mechanisms that allow for the precise formation and removal of threads by unscrewing the part from the mold after the injection process.

 

2. How Do Unscrewing Molds Work?

 

Unscrewing molds operate by using rotating cores that match the thread pattern of the molded part. After the plastic material is injected and cooled, the rotating cores unscrew the part from the mold, ensuring that the threads are not damaged during removal.

 

3. What Are the Benefits of Using Unscrewing Molds?

 

The key benefits of unscrewing molds include:

 

- Precision: Accurate thread formation without post-processing.

- Efficiency: Faster production cycles for threaded parts.

- Consistency: Uniformity in thread dimensions across multiple parts.

- Versatility: Suitable for various thread designs and sizes.

 

4. What Types of Products Use Unscrewing Molds Design?

 

Unscrewing molds are commonly used in producing a wide range of threaded products such as bottle caps, medical syringes, automotive parts, and various consumer goods that require precise threading.

 

5. What Materials Can Be Used with Unscrewing Molds?

 

Unscrewing molds can handle a variety of thermoplastic materials, including polypropylene, polyethylene, polystyrene, and more. The choice of material depends on the specific application and the properties required for the final product.

 

6. How Do You Maintain Unscrewing Molds?

 

Proper maintenance of unscrewing molds is crucial for their longevity and performance. Key maintenance tasks include:

 

- Regular Cleaning: Removing residue and buildup from the mold surfaces.

- Lubrication: Ensuring moving parts are well-lubricated to prevent wear.

- Inspection: Routine checks for wear and tear on threads and cores.

- Alignment: Verifying that all components are properly aligned to prevent defects.

 

7. What Are the Challenges of Using Unscrewing Molds?

 

While unscrewing molds offer numerous benefits, they also present some challenges, such as:

 

- Complexity: More intricate design and manufacturing processes.

- Cost: Higher initial investment compared to standard molds.

- Maintenance: Requires diligent maintenance to avoid operational issues.

 

8. How Do Unscrewing Molds Compare to Traditional Molds?

 

Unscrewing molds differ from traditional molds in their ability to produce threaded parts directly during the molding process. Traditional molds may require secondary operations to add threads, whereas unscrewing molds integrate this step, saving time and improving accuracy.

 

9. Can Unscrewing Molds Be Customized?

 

Yes, unscrewing molds can be customized to meet specific production needs. Customization options include varying thread patterns, mold sizes, and core designs to accommodate different products and materials. Working with an experienced mold manufacturer is essential for effective customization.

 

10. What Industries Benefit Most from Unscrewing Molds?

 

Industries that frequently benefit from unscrewing molds include:

 

- Packaging: For caps and closures.

- Medical: For syringes and other threaded medical devices.

- Automotive: For threaded components in vehicles.

- Consumer Goods: For products requiring precision threading.

 

Conclusion

 

Unscrewing molds are invaluable tools for manufacturing threaded parts, offering precision, efficiency, and consistency. By addressing these frequently asked questions, we hope to provide a clearer understanding of their benefits and operational considerations. Whether you are in the packaging, medical, automotive, or consumer goods industry, unscrewing molds can significantly enhance your production capabilities.

Introduction to Injection Molding of Thermoset BMC

 BMC is the abbreviation of glass fiber reinforced unsaturated polycrystalline thermosetting plastic. It is currently the most widely used type of reinforced thermosetting plastic.

 

Whether it is screw type or plunger type, an extrusion type feeding device must be attached to force the material into the barrel. This feeding device mostly uses plunger type pressure-feeding.

 

Characteristics and applications of BMC Molding

 

BMC has good physical, electrical and mechanical properties, so it has a wide range of applications. For example, it can be used to make mechanical parts such as gearbox components, intake pipes, valve covers, bumpers, etc.; in applications that require earthquake resistance, flame retardancy, aesthetics, Durable aviation, construction, furniture, etc. are also widely used; in its traditional electrical field, its uses are becoming more and more extensive.

4) Mold clamping device

 

1) Feeding system

Several mold clamping devices, such as mechanical, hydraulic and fully hydraulic, are mostly used.

 

5)Mold

2)Injection molding system

 

Because the injection volume of the plunger injection molding machine is accurate and constant, the glass fiber is dispersed in the melt with less damage. Therefore, the plunger injection molding machine is used more often, but the exhaust is inconvenient.

BMC injection molding is somewhat different from ordinary thermoplastic and thermosetting injection molding. The main reason is that BMC has a lower shrinkage rate, so the mold cavity size should be changed.

 

3)Heating system

In BMC injection molding, it is very important to control the temperature of the barrel. There must be a control system to control the temperature to ensure that the temperature from the feeding section to the nozzle is optimal. Currently, constant temperature water or constant temperature oil is used for heating. Electric heating can also be used.

 

BMC’s injection molding process

 

1) Barrel temperature and mold temperature

During injection molding, BMC is required to maintain low viscosity flow behavior for a long time under the barrel temperature; generally, the barrel temperature should be able to meet the lower limit of BMC. The temperature of the barrel is generally divided into two or three stages of control. The temperature near the hopper is lower and the temperature near the nozzle is higher. Generally the difference is 20-60C, and the mold temperature is generally controlled at 135~185C;.

 

2) Injection pressure

Because BMC has poor fluidity, fast solidification, and complex mold structure, the injection pressure should be higher, generally 80~16 OMPao.

 

3)Injection speed

Increasing the injection speed will help improve the surface quality of plastic parts and shorten the curing time, but it is not conducive to exhaust and increase the degree of glass fiber orientation. - Therefore, a lower injection speed should be used while ensuring the surface quality of the plastic part, usually 1.8-3.5m/min.

 

4) Screw speed and back pressure

If a screw injection molding machine is used, the screw will cause greater damage to the glass fiber when injecting BMC. In order to minimize the damage to the glass fiber, the screw speed should be selected at a low value, generally 20~5Or/min. According to the viscosity of BMC, it is appropriate to use low back pressure, generally 1.4-2.0MPa.

 

5) Molding cycle

Due to the different size and complexity of plastic parts, the process time of each stage is also different. Generally, the injection time is 2~20s and the heat preservation time is 10-20s/mm (thickness).

What Is Gas Assisted Molding?

 Gas Assisted Molding (GAM) is an advanced injection molding technique used to manufacture plastic parts with complex shapes and hollow sections. This process involves injecting a pressurized gas, usually nitrogen, into the molten plastic inside the mold. Here’s a detailed explanation of how gas assisted molding works, its advantages, applications, and key considerations:

 

How Gas Assisted Molding Works

 

1. Injection Phase:

   - The molding process begins by injecting molten plastic into the mold cavity, similar to traditional injection molding.

   - The plastic partially fills the cavity, leaving some areas unfilled to be expanded by the gas.

 

2. Gas Injection Phase:

   - Once the plastic is partially injected, pressurized gas (typically nitrogen) is introduced into the mold.

   - The gas pushes the molten plastic towards the mold walls, creating a hollow section inside the part.

 

3. Packing and Holding Phase:

   - The gas continues to exert pressure, ensuring the plastic fully conforms to the mold’s surface and compensating for material shrinkage.

   - This phase helps achieve a consistent wall thickness and reduces the risk of sink marks and warping.

 

4. Cooling and Ejection Phase:

   - After the part has sufficiently cooled and solidified, the gas pressure is released.

   - The mold opens, and the finished part is ejected.

 

Advantages of Gas Assisted Injection Molding

 

1. Material and Cost Savings:

   - Reduces the amount of plastic required by creating hollow sections, leading to significant material savings.

   - Lower material usage translates to cost savings and lighter parts.

 

2. Improved Quality:

   - Reduces internal stresses and warping by evenly distributing the plastic within the mold.

   - Minimizes surface defects like sink marks and enhances the aesthetic quality of the parts.

 

3. Enhanced Design Flexibility:

   - Allows for the creation of complex geometries and intricate designs that are difficult or impossible with traditional injection molding.

   - Facilitates the production of parts with varying wall thicknesses.

 

4. Cycle Time Reduction:

   - Faster cooling times due to the reduced volume of plastic.

   - Increased production efficiency and reduced cycle times.

 

5. Structural Benefits:

   - Produces parts with higher stiffness-to-weight ratios.

   - Hollow sections can enhance the structural integrity of parts without adding extra weight.

 

Applications of Gas Assisted Molding

 

Gas assisted molding is widely used across various industries due to its versatility and the quality of parts it produces. Some common applications include:

 

1. Automotive Industry:

   - Production of lightweight components like handles, trim parts, and structural elements.

   - Enhances fuel efficiency by reducing the weight of automotive parts.

 

2. Consumer Goods:

   - Manufacturing of durable and aesthetically pleasing items such as furniture, appliance housings, and electronic enclosures.

   - Ideal for producing ergonomic and visually appealing products.

 

3. Industrial Components:

   - Creation of robust and lightweight industrial parts like tool handles, machine covers, and equipment casings.

   - Suitable for parts that require complex shapes and consistent quality.

 

4. Medical Devices:

   - Used to produce medical equipment and components that require precise and complex designs.

   - Ensures high quality and reliability for medical applications.

 

Key Considerations

 

1. Material Selection:

   - Not all plastics are suitable for gas assisted molding. Materials should have good melt flow properties and the ability to form a solid skin quickly.

   - Commonly used materials include polypropylene (PP), acrylonitrile butadiene styrene (ABS), and polycarbonate (PC).

 

2. Mold Design:

   - Mold design is critical to ensure proper gas flow and effective plastic distribution.

   - Considerations include gas injection points, venting, and the ability to withstand high gas pressures.

 

3. Process Control:

   - Precise control over gas pressure, injection timing, and plastic flow is essential to achieve consistent quality.

   - Advanced monitoring and control systems are often employed to manage these parameters.

 

4. Cost Implications:

   - Initial setup costs for gas assisted molding can be higher due to specialized equipment and mold modifications.

   - However, the long-term benefits of material savings and improved part quality often outweigh these initial expenses.

 

Conclusion

 

Gas Assisted Molding is a sophisticated injection molding technique that offers numerous benefits, including material savings, improved part quality, and enhanced design flexibility. Its ability to produce complex, lightweight, and high-quality parts makes it a valuable process in various industries. Understanding the principles, advantages, and considerations of gas assisted molding can help manufacturers leverage this technology to optimize their production processes and achieve superior results.