Low-pressure injection molding

Apr 13


Ieva Masaitytė

Ieva Masaitytė

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Low-Pressure Injection Molding The mainstreaming of the low-pressure injection molding machine is a matter of the present age. Typically, it is a process that uses hot liquified polyamide and polyole...


Low-Pressure Injection Molding

The mainstreaming of the low-pressure injection molding machine is a matter of the present age. Typically, Low-pressure injection molding Articles it is a process that uses hot liquified polyamide and polyolefin materials. It paves the way to protect vulnerable components prone to moisture, vibration, and dust particles and makes them flame retardant and temperature resistant. It uses reduced pressure to inject plastic into the mold and usually suitable for printed circuit boards (PCBs), cable assemblies, and sensors.

Paradoxically, conventional or high-pressure molding is slightly different from low-pressure molding and suitable for the components made to endure increased pressure. Plastic is infused at high pressure and turns into more intricate structures, providing many customized solutions. However, it involves pressures and temperatures that may damage delicate components like PCBs. 

Meanwhile, when dealing with low-pressure injection molding, pressure is kept at 100PSI. Simultaneously, the temperature ranges between 180-220°C, and the melt flow time are 10 minutes for 5 grams. 

Low-Pressure Molding in Overmolding

Overmolding refers to an injection molding process that brings about a consistent amalgamation of different materials into a solitary product. In other terms, overmolding is a process wherein formerly molded parts are re-inserted to develop a new plastic layer around the component.

The process of overmoldingincludes unprotected PCBs, loading bare, and cable assemblies into a precision-crafted tool. The cavity is then filled with a suitable low-pressure molding material. Also, it helps manufacturers encapsulate delicate components according to their requirements and have a protected and sealed product.

The low-pressure injection molding process is used in overmolding and micro injection molding to protect weak components that allow gentle protection for them (electronic assemblies). It utilizes thermoplastic materials with relatively low viscosity that permits encapsulation and overmolding of sensitive and printed circuit board assemblies. 

Since the materials used in the process are entirely adhesive in nature, this process proves to be the most feasible solution to seal circuits against moisture and dust.

Benefits of Low-Pressure Injection Molding

There are certain benefits associated with the use of low-pressure injections molding processes, and some of them are given below:

1. Reduced Number of Manufacturing Steps Required

Unlike 7 to 8 steps required to get the work done in conventional injection molding, low-pressure injection molding includes only three steps:

  • Filling (Molten polymer is injected into the empty cavity)
  • Packing (some more amount of molten material is packed into the cavity to avoid shrinkage when material cools)
  • Cooling (during cooling, material gets hardened and solidified)

Thermoplastic polyamide materials, also known as hot materials, are heated to the temperature unless they turn into liquid form and then injected into the mold to encapsulate the electronic parts. 

On the other hand, conventional injection molding includes a curing process to add safety for mold that considerably increases the cycle time; but this is not the case with low-pressure injection molding as it works on before mentioned three steps that less time.

2. Increased Resistance, Flexibility, and Stability

Low-pressure injection molding offers excellent solvent resistance, temperature, and protection to sensitive components. The water-tight encapsulation of parts makes them invincible against water.

Additionally, low-pressure injection molding offers an impressive scope for customization, and the thinner walls of material around the part make it flexible and durable.

3. Cost-Effectiveness 

While working with the high-pressure or conventional injection molding machine, it is mandatory to get a heavier mold made up of high-impact resistant material e.g. steel. In the case of a low-pressure injection molding process, the mold of much softer material (e.g., aluminum) can be used. Softer material means smaller tool machining costs and faster lead times. Besides, this material is highly durable with excellent thermal conductivity. Above and beyond, labor, raw material, and other operational costs become lower, which further cuts down the cost of injection molding.

4. Shorter-Cycles 

In the low-pressure injection molding process, the mold is filled with constant lower pressure. It does not rely on shear-thinning to facilitate and improve the flow. In case of relying on shear thinning, it might cause part failure, raw material degradation, and excessive mold corrosion, if not done properly.

On the other hand, in case of low-pressure injection molding, the slower and gentler filling of mold without any interruption causes faster and shorter cycles (rapid injection molding), as it allows cooler melt to flow farther through thinner channels of mold.

Along with this, it allows for a cooler melt that can better flow through the thinner channels. In contrast, conventional molding relies on shear-thinning and takes extra time to get cooled that adds in lead time.

The Steps of Low-Pressure Injection Molding

Mainly, there are three steps involved in low-pressure injection molding. These are as follows:

1. Machine Configuration

The first step belongs to the setting of mold. In this process, the core and cavity are joined together with their adjustment in the injection molding machine. It is made sure that both core and cavity are rightly adjusted to avoid any halt in molten material’s flow and ensure product quality. 

Here are the steps that need to be performed:

  • Mold Height
  • Mold Heating/Cooling
  • Hot runner connection (if designed with hot runner system)
  • Ejector safety sensor (if ejector pins are required)

Once the mold is set, the next step of ejection starts.

2. Ejection/Over-molding

Low-pressure overmolding thrives with the PCB assembly or electronic parts placed in a specially manufactured aluminum mold tool. These are surrounded by the liquid compound that provides them with a protective layer. 

After the completion of the overmolding process, the product is sent to be tested.

3. Demolding

Once the process is completed, the platens of mold move apart and manufactured product comes out in its final form. The manufactured product is pushed out from the mold, and process starts again with defined configuration: 

Future Perspectives and Conclusion

The global market size of injection molding machines is around $10,890 million, and a considerable part of this figure belongs to low-pressure injection molding. According to a survey conducted by Esticast Research, the global size of low-pressure injection molding is expected to grow with a compound annual growth rate (CAGR) of 6.13% by the end of 2022. 

Henceforth, when looking for a durable solution to protect delicate electric components, low-pressure injection molding comes up as an overwhelmingly suitable solution both monetarily and timely.