Low-pressure infusion processing: an excellent solution for rapid trial production and small batch production

Low-pressure injection molding, also known as Reaction Injection Molding (RIM), is a new manufacturing technology widely used in the rapid production of injection-molded parts. It uses a two-component polyurethane material that is mixed and then injected into a quick mold at low pressure and room temperature, forming a product through chemical and physical processes such as polymerization, cross-linking, and solidification. Low-pressure injection molding has the advantages of high efficiency, short production cycle, simple process, and low cost. It is suitable for small-batch tryouts in product development, as well as small-batch production of relatively simple structural parts and large thick-walled or uneven thickness products.

Advantages of Low-pressure Injection Molding in Rapid Prototyping and Small-batch Production:

During the research and development phase, low-pressure injection molding provides a quick and cost-effective way for rapid prototyping and can help companies get results and make adjustments quickly. Moreover, for small-batch production, low-pressure injection molding can reduce mold costs and material waste, lower production costs, improve production efficiency, and shorten production cycles. Compared with other manufacturing techniques, low-pressure injection molding can flexibly and quickly produce complex parts, which is a significant advantage, especially in the production of complex parts.

Considerations for Use:

Although low-pressure injection molding has stable and reliable product performance, it is essential to consider the selection and performance of materials, and control process parameters such as temperature, injection thickness, and injection speed before use. Additionally, maintenance of molds and equipment is necessary to ensure product quality.

Materials Used:

Low-pressure injection molding typically uses a two-component polyurethane material with similar physical properties to polypropylene (PP) or acrylonitrile-butadiene-styrene (ABS), which has advantages such as aging resistance, high impact resistance, and high adaptability. The commonly used materials on the market include HD-PU4210, DCP-RIM, AXSON-RIM 875, etc., which can be selected according to specific production needs. In addition to polyurethane, aluminum oxide melt is also a commonly used material for low-pressure injection molding, which can also achieve good effects.

Advantages of KAIAO Company in Reaction Injection Molding:

KAIAO Company is a professional injection molding manufacturer with years of experience in reaction injection molding. The company has several reaction injection molding machines and corresponding mold-making capabilities, allowing it to design and manufacture molds according to customer requirements, providing integrated services such as product development, material selection, and production. KAIAO has strict control over the entire process to ensure product quality and stability, which has been recognized and trusted by customers. Additionally, KAIAO has in-depth research on the properties and usage of various materials and continuously innovates and develops new materials and processes to meet customers' ever-changing needs.

Process of Reaction Injection Molding:

The process of RIM includes the mixing of monomers or prepolymers in a liquid state in a certain ratio and injection into the mold using a metering pump. The assembled mold is rapidly reacted and cross-linked within the mold, and the product is formed. The simplified process can be divided into storage → metering → mixing → injection → curing → demolding → post-processing.

(1) Storage. The two components of the liquid used in the RIM process are usually stored at a certain temperature in two separate reservoirs, which are usually pressure vessels. When it is not formed, the stock liquid is usually circulated continuously in the reservoir, heat exchanger and mixing head at a low pressure of 0.2~ 0.3MPa. For polyurethane, the temperature of the stock solution is generally 20~40℃, and the temperature control accuracy is ±1℃.

(2) Measurement. The measurement of the two-component stock liquid is generally completed by the hydraulic system, which is composed of pumps, valves and accessories (piping system for controlling liquid materials and oil circuit system for controlling the work of the distribution cylinder). During injection, the pressure needs to be converted into the pressure required for injection by a high and low pressure conversion device. The bulk liquid is measured with a hydraulic quantitative pump, and the measurement accuracy is required to be at least ± 1.5%, and it is best to control it at ± 1%.

(3) Mixing. In RIM product molding, the quality of the product is largely determined by the mixing quality of the mixing head, and the production capacity is completely determined by the mixing quality of the mixing head. Generally, the pressure used is about 10MPa to obtain a better mixing effect.

(4) Mold filling. Reaction injection material filling is characterized by a high rate of material flow. For this reason, the viscosity of the stock solution is not required to be too high, for example, the viscosity of the polyurethane mixture when filling the mold is about 0.1Pa.s. Flow control: 600g/s.

(5) Curing. The polyurethane two-component mixture has high reactivity after injection into the mold cavity, and can be cured in a very short time. However, due to the poor thermal conductivity of the plastic, a large amount of reaction heat can not be distributed in time, so that the internal temperature of the molding is much higher than the surface temperature, resulting in the solidification of the molding from the inside out. In order to prevent the temperature in the cavity from being too high (not higher than the thermal decomposition temperature of the resin), the heat transfer function of the mold should be given full play to dissipate heat. The curing time in the reaction injection mold is mainly determined by the formula of the molding material and the size of the product. In addition, the reaction injection product needs to undergo secondary heat curing after it is removed from the mold.

Explicit details of the process steps were also discussed in the earlier Chinese version of the article.

In summary, low-pressure injection molding is an extremely practical manufacturing technology that can help enterprises quickly prototype and produce parts, reduce costs, and improve production efficiency. As a professional injection molding manufacturer with years of experience, KAI-O Company provides high-quality and efficient services to customers. Moreover, KAI-O is continuously introducing new technologies and materials to meet customer needs.

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