Rapid tooling technology is a new technology developed with the emergence of rapid prototyping technology. Low pressure injection molding of rapid tooling refers to the process in which the bicomponent materials with high chemical activity and low relative molecular weight are mixed in a certain proportion and injected into the closed mold under low pressure (0.4 ~ 0.5MPa), which completes the chemical reactions such as polymerization, crosslinking and curing, and finally forms products after cooling and solidification. It is the process of low pressure perfusion molding (RIM) technology in rapid tooling products molding Field development. The product material is generally polyurethane resin, which has the properties of thermosetting material after molding - the product quality is closely related to the mold structure, filling process, mold temperature, initial temperature of raw materials, material mixing ratio, mixing uniformity, curing time, etc.
               

　　低壓灌注成型的工藝流程及成型原理

　　Technological process and forming principle of low pressure pouring molding

　　快速模具低壓灌注成型是指將聚氨酯樹脂注射進快速模具并固化成型的過程。可使用硅膠模具、聚氨酯模具、環氧樹脂模具、ABS模具及鋁合金模具。低壓灌注成型設備主要由控制箱、定量泵、混合頭及噴嘴等組成。工藝流程見圖1。低壓灌注成型設備在0.4~0.5MPA的低壓下將雙組分的聚氨酯材料用定量泵送入混合頭，經撞擊混合后再注入模具。混合后的雙組分材料在模具內快速反應，進行聚合交聯固化。為保證材料充分固化，減少制品變形，一般在注射完成后，需要將模具移到烘箱內進行后固化，約1.5~2.0小時后脫模得到制品。通常一副模具的制作周期為3~4天，可生產100~500件左右產品。按照工藝要求，模具和材料在注射前均應加熱。由于雙組分材料的固化反應，在成型過程的初始階段，整個反應體系的溫度還將進一步上升，出現放熱現象。

　　Low pressure injection molding of rapid tooling refers to the process of injecting polyurethane resin into rapid tooling and curing molding. Silicone mold, polyurethane mold, epoxy resin mold, ABS mold and aluminum alloy mold can be used. Low pressure injection molding equipment is mainly composed of control box, quantitative pump, mixing head and nozzle. The process flow is shown in Figure 1. Under the low pressure of 0.4 ~ 0.5MPa, the two-component polyurethane material is pumped into the mixing head by a quantitative pump, and then injected into the mold after impact mixing. After mixing, the two-component materials react rapidly in the mold and are polymerized and crosslinked. In order to ensure that the material is fully solidified and reduce the deformation of the product, the mold should be moved to the oven for post curing after the injection, and the product can be demoulded after about 1.5 ~ 2.0 hours. Generally, the production cycle of a pair of dies is 3-4 days, which can produce about 100-500 pieces of products. According to the process requirements, the mold and material should be heated before injection. Due to the curing reaction of the two-component material, the temperature of the whole reaction system will rise further and exothermic phenomenon will appear in the initial stage of the molding process.

　　低壓灌注成型使用的材料主要以聚氨酯材料為主。改變材料的混合比例，可獲得不同的材料彈性模量，從而得到所需要的材料特性!固化后的材料物理性能類似于普通熱塑性材料ABS、PP或PS。適合于較大壁厚（>4mm）及不均勻壁厚制品的生產.

　　Polyurethane is the main material used in low pressure injection molding. The physical properties of cured materials are similar to those of ordinary thermoplastic materials ABS, PP or PS. It is suitable for the production of larger wall thickness (> 4mm) and non-uniform wall thickness products

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