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Rapid Injection Molding: Everything You Need To Know

How to improve low volume injection molding for plastic prototype manufacturers? Most answer is surely rapid injection molding. This post looks into the basics of the rapid injection molding, its advantages, and its modern-day applications.

An Overview

Rapid Injection Molding (RIM) is a manufacturing technique that is carried out by injecting thermosetting resins in a rapid injection mold to make the required shape and product. The process is pretty much like the traditional production injecting molding. The process uses a host of different materials including metals, elastomers, thermoplastics, glasses, and thermosetting polymers. The material, for instance, glass is first put into the heated barrel where it is mixed and then carefully injected into the mold cavity. In the mold cavity, the prototyping material cools and hardens to the shape and dimensions of the cavity resulting in the final part.
What makes this process ‘rapid’ is the technology used to produce the mold, which is made of aluminum instead of the traditional steel that is being used in making molds. These rapid injection molds greatly reduce the turnaround time and the production cost.

What Are the Basic Components for Rapid Injection Molding?

The schematics figure below shows the basic components for RIM. The basic components for RIM are quite similar to the standard injection molding. The components for this process are (starting from left to right);
  1. Ram
  2. Screw
  3. Hopper
  4. Barrel
  5. Heaters
  6. Materials
  7. Nozzle
  8. Mold
  9. The finished part

2D diagram with all the essential components for RIM

Injection Molding Basics

In order to make injection molding parts via rapid injection molding, the CAD models by the manufacturers or the design engineers are directly sent over to the production floor where the prototype injecting molding takes place. The molds in RIM are typically fabricated from aluminum and not steel. For low volume plastic molding, resins of different plastics can be used as well. The mold used to make metal parts can be used to make plastic parts as well. This dramatically lowers the turnaround time.

RIM uses side-action and hand-load inserts along with much simple over-molding and insert molding. In order to improve the mold features over the edges and corners, Electrical discharge machining. All these rapid prototyping techniques allow for the parts to be made in a matter of a few weeks as opposed to months when traditional injection molding methods were used.

Common Applications for Rapid Injection Molding

Though RIM is primarily used to make injected molded parts much faster and cheaper than the conventional injection molding, there are several other applications for RIM as well. The RIM is used to carry out different test functions during product development with production-grade parts as well as to test different materials. RIM is a method of choice by many prototype developers and several CAD designers. RIM is also used to leverage low volume plastic molding.

Molded rapid injected molded parts via this method are stronger and have a better finish as opposed to the ones made via conventional injection molding. RIM is also used by many manufacturers to manage the volatility in demand in the market and to leverage low volume production for on-demand parts.

Complex geometries easily made with RIM

Rapid Injection Molding Advantages

Rapid prototype injection molding process and the injection molded parts have significant advantages over the traditional molding processes which include quick turn injection molding and small run injection molding.
  1. RIM is both time- and cost-effective
  2. Different materials can be used over the same mold
  3. The surface finish from RIM varies and can be adjusted to the requirement of the client
  4. RIM has better precision as opposed to conventional molding methods
  5. Complex geometries and designs can be made by RIM with ease
  6. The parts made from RIM are much stronger and durable
  7. From low volume injection molding to batch production, RIM can meet the demand quite easily
  8. The waste from RIM is to the minimal as only required amount of material can be injected in the cavity for molding
  9. Higher grade aluminum such as QC-10 and QC-7 have closed the gap between aluminum and steel. The aluminum molds of today can produce hundreds of thousands of parts in a life cycle with no wear.

RIM can be used to make parts with multiple layers

What Impacts the Pricing of RIM Parts?

For the client, it is important for them to know what certain things directly affects their product pricing. Here are several aspects that affect prototype pricing;

  1. Annual volume – Volumes over 100,000 per year will require the need for multi-tooling. This, on the one hand, may significantly increase the tooling price; however, the price per piece can be 60% lower per additional cavity. For the clients, it is important to accurately specify their annual volume so that they do not incur extra tooling cost.
  2. Surface Finish – Prototype injection molding can easily carry out all sorts of surface finishes. Better the finish, the higher the price. For parts that are hidden in the assembly and their finish do not add to the aesthetics of the product, then money can be saved using rough surface finish such as 320 sandpaper finish.
  3. Part complexity – Complexity of the design and model, can dramatically increase the cost of the tool and the product. The more surfaces and faces your CAD model have, the higher the cost. The product designers must consider this when adding blends or any unneeded features to the product.

Are There Any limitations to Rapid Injection Molding/Tooling?

It all depends on the prototype manufacturer you select. Some rapid injection mold manufacturer cut corners in order to become so-called rapid manufacturers. By this approach, they often tend to compromise the life of both the product and the tool. However, at Wayken, we do not cut out any essential steps from conventional injection molding. By using modern technology, common mold components, well trained and experienced staff along with proven and streamlined process flow gives us a huge competitive edge over our competitors in the market. Therefore, it gives Waken the ability to call our injection molding process as “rapid.”