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Single-cavity vs. multi-cavity injection molding

One of the most widely-used methods in plastic parts manufacturing today, injection molding can facilitate large, cost-effective production runs of identical parts. In fact, in most cases, injection molding is the most cost-effective method for producing plastic parts in medium to high volumes. For this reason, it’s frequently preferred over other methods of manufacturing, including CNC machining, urethane casting, and die casting.

Injection molding may be facilitated by means of a single- or multi-cavity mold. While the processes of both single- and multi-cavity injection molding require the same basic set of operations in the same chronology, the two are generally used to meet different demand or timeline requirements and are therefore rarely interchangeable. Choosing whether to use a single- or multi-cavity injection mold is vital to the success of a project. Here are common use cases, advantages, and disadvantages of each.

The injection molding process

Injection molding begins with creating the mold itself. The mold, which will later be filled with melted plastic to create the desired part, represents the most complex component of the injection molding process. Fortunately, it only needs to be created once.

Single-cavity vs. multi-cavity injection molding
The mold may feature either one cavity or multiple cavities, each of which can be used to create a single part. As such, a single-cavity mold produces one product per cycle, while a multi-cavity mold produces more than one.

Once the mold has been made, injection molding becomes an easily-replicated six-step process. The first step is clamping, or pushing the mold’s two clamshell-like halves together. Next is injection, in which plastic is melted down and inserted into the mold. Dwelling and cooling, which allow the plastic to fill the mold and solidify, follow. Finally, the mold opens, and ejector pins remove the part.

Choosing whether a single- or multi-cavity mold is best-suited for a given project tends to be more complex than one might expect.

Choosing a single- or multi-cavity mold

In general, the choice between a single- or multi-cavity mold comes down to timeframe and demand. When many identical parts are needed within a set time frame, a multi-cavity mold is often the better choice. Multi-cavity molds enable manufacturers to create more parts, faster — a clear advantage of using multiple cavities at once.

However, multi-cavity molds aren’t always the best fit for a given project. A multi-cavity mold requires a far more substantial upfront investment than a single-cavity mold. It is more cost-intensive to create multi-cavity molds because they require more material, labor, and energy resources than a single-cavity mold. While the investment in a multi-cavity injection mold can certainly pay off if producing parts at high volumes, at lower volumes, it may make more sense to opt for a single-cavity mold.

Multi-cavity molds require more substantial lead time, as they take longer to create than single-cavity molds. In addition, maintenance costs and risk is higher with multi-cavity molds; if one cavity breaks or has a flaw, the entire mold can become unusable, which can significantly impact time-to-market.

Designing with the right mold in mind

It’s always wise to know your market and have a firm understanding of the demand for your product so you can design and manufacture to minimize your costs.  This is especially true when it comes to injection molding. Given the time and substantial cost required to create a mold, it’s vital that product teams do their due diligence and select the mold type that best suits the product and the demand in the marketplace.

Fortunately, an experienced design partner like Fast Radius can help make those decisions easier. We’re experts in the process of creating the perfect mold — and in Design for Manufacturing (DFM) principles. If you’re ready to get started with injection molding, contact us today.

You can learn more about injection molding, CNC machining, and our other service offerings in the Fast Radius resource center.

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