Low volume Reaction Injection Molding (RIM), a rapid molding process for making unreinforced thermoset parts rapidly in an environment of low pressure and room temperature, is widely applied to produce large-sized plastic car parts. 

RIM has several advantages as the following:

1. It can produce large, lightweight, and thin-walled complex parts.

The viscosity of the mixture injected into the mold is much lower than that of the molten thermoplastic polymer used in the traditional injection molding process. So that large, light, and thin-walled items can be processed using RIM.

2. The wall thickness can vary from 4 mm to 30 mm within the same part without distortion.

Many medical products, with relatively thick walls or uneven wall thickness, are not suitable for traditional injection molding. As the surface curves are complex, they don't fit for the blister molding process either. However, RIM can inject thick-walled products, and the wall thickness can be uneven for one part. The normal infusion wall thickness (5-6mm) can be up to about 30mm thick.

As the RIM product is the overall molding out, compared to vacuum casting, the products via RIM embrace smaller shrinkage and deformation rates, and stable sizes.

3. It is easy to do surface treatments on RIM parts.

The process of demolding requires the use of a mold release. After demolding, the part surface product will be bright in some areas and matte in others. And it is very easy to deal with. After that, it is easy to do a variety of surface treatments, such as painting, electroplating, silk screening, etc.

4. It has high production efficiency.

The RIM equipment has a high degree of automation. A microcomputer program controls the movement program, and the process can be adjusted without stopping the machine. Therefore, the production efficiency is high.

5. Its cost is lower than that of mass production.

The lighter and thinner products require less clamping force. Therefore it requires smaller-sized equipment. Mold materials are also cheaper than conventional injection molds, such as resin, ABS, and aluminum. The production cycle time is also much shorter. So production costs are much lower.

There are also other low-volume production methods involving molds and injection processes at X Rapid Technologies. Here is an overview for your better understanding.

Low Volume Reaction Injection Molding Low Volume Vacuum Casting Low Volume Rapid Tooling
Mold ABS, Resin, Aluminum, etc Silicone ABS, Silicone, Aluminum, Steel, etc
Part Materials

HD RIM4210/1100 PU Resin

YU-Heng RIM5236 PU Resin

AXSON RIM875/900 PU Resin

Hei-Cast PU resin series

AXSON PU resin series

Pelnox PU resin series

Any plastics and rubber material of actual production grades
Normal Production Volume per Mold About 100 shots 15-20 shots About 1,000 shots

Different Wall Thickness

Within One Part Available or Not

Yes Yes Yes
Applications To make automobile bumpers, medical products, radio and TV cabinets, computer cases, furniture, sporting equipment, appliances, business-machine housings, etc Small quantities of plastic-like or rubber-like prototypes or end-use products The production of light usage or the short-run manufacturing of large parts for the automotive, aerospace and aircraft, and shipbuilding industries

X Rapid Technologies has produced lots of bumper parts for our clients. In the automotive industry, low-volume injection molding is generally applied to make large and medium-sized plastic parts such as steering wheels, dashboards, bumpers, seat cushions, etc. Typically, they are used in new design tests, market tests, exhibitions, short-run end-use products, etc. There are also many applications in the car modification market. RIM is particularly suitable for an annual need of small production runs of tens, hundreds, or thousands of pieces.

Low volume reaction injection molding works on the following principle:

Pre-formulated two-component liquid raw materials are mixed by a metering pump at a specific ratio into a mixing head, then continuously injected into the mold to react and cure. By changing the pump speed, the raw material mix ratio can be adjusted and the injection volume is controlled by the pump's unit exhalation volume and injection time. The curing time in the reaction injection mold is mainly determined by the formulation of the raw materials and the size of the product. The production time for each piece takes 15-30 minutes. 

The most common brands of RIM materials are BAYER, BASF, HUNTSMAN, AXNSON, etc. The material properties of the products produced are generally similar to PP or ABS. It is possible to modify the density, hardness, and elasticity of the material. Depending on the customers' requirements, the properties can be controlled. 

In this case, the mold of low-volume reaction injection molding was in aluminum material. Usually, an aluminum mold can last for 500-5,000 shots.

Aluminum mold for car bumper parts

Low Volume Reaction Injection Molding for Car Bumper


Low volume reaction injection molding car bumper parts in ABS-like PU material

Low Volume Reaction Injection Molding for Car Bumper

Low Volume Reaction Injection Molding for Car Bumper

Low Volume Reaction Injection Molding for Car Bumper

These parts were made in ABS-like PU material with just one layer of paint because the client planned to use them to test the structure of the new design. So the parts didn’t need to be good-looking. In other cases, parts for trade fairs and market tests need to be well finished to be esthetic.