Single-cavity and Multi-cavity Injection Molding

When it comes to injection molding, it is important for engineers and designers to make the ultimate decision on cavity number, single-cavity or multi-cavity mold, mainly based on the timeframe and quantity demanded, hence seldom interchangeable.

The choice of mold’s cavity number has a significant impact on the cost-effectiveness and productivity of the final product (Photo: Micro Systems) 

What is a Cavity in a mold?

An injection mold includes 2 parts: core and cavity. The elevated portion of the mold is the core, while the recessed portion is the cavity. During the injection molding process, the space between the core and cavity is filled with the hot, molten plastic material, which is then solidified into the final form. The core and cavity mold designs are essential to the successful molding of the product, making the final shape and appearance of the molded product. 

Once the mold has been created, the production process can now start. The mold’s cavity and core are first clamped, or pushed, together, then comes the process of injecting molten plastic into the mold. After settling and cooling, the plastic can fill the mold and solidify. Finally, ejector pins release the item from the mold when it opens, and the final molded product could be collected for the next steps. 

Single-cavity or Multi-cavity mold?

The main difference between single-cavity and multi-cavity molds is simply the number of cavities within the mold. Since there is only one cavity for plastic resin injection, single-cavity molds only manufacture one product every cycle. 

Multi-cavity molds, on the other hand, feature at least two cavities and two cores, all identical and produced in symmetrical pairs with even numbers, with a theoretical upper limit of hundreds of microscopic cores and cavities. Due to the abundance of cavities, with multi-cavity molds, a single manufacturing cycle can produce dozens or even hundreds of completed pieces, depending on the molding machine’s capability.

Benefits of Single-cavity mold

• Single-cavity injection molds are generally less expensive to produce than multi-cavity molds as the former could be smaller hence take less material and product cost to make. 
• Single-cavity molds could be more simple to make and design, hence the lead time is shorter to get the mold, suitable for rapid manufacturing methods. 
• Can produce both small and large size parts 
• Injection molding operations could be better managed by molders and tool producers, hence enhancing the quality of plastic injection-molded products. Unlike multi-cavity molds, the problems, if any, in the cavity will not affect other cavities and parts. 

Benefits of Multi-cavity mold

• Shorter production time for the desired number of parts required, as multi-cavity molds could make many items with a single mold. 
• Multi-cavity molds utilise cycle time more efficiently, producing more parts with the same mold within the shot guarantee, hence significantly suitable for large-volume production. 
• Multi-cavity molds can produce a cheaper per-unit moulding cost (while the initial mould cost could be more expensive) as multiple parts are produced in a unit time. 
• Multi-cavity molds could raise the consistency and quality control for mass production, as they reduce the chances of having defects compared to producing the number of parts using different single-cavity molds. 
• A eight-cavity mold could have a lower total cost of ownership (TCO) to make than eight separated single-cavity molds. 
• Multi-cavity molds could save space within the manufacturing facilities as they are smaller compared to the number of single-cavity molds to make the same amount of parts in the same amount of unit time.

Key takeaway

Choosing single-cavity or multi-cavity molds for an injection molding project depends on several factors, including but not limited to: The material and design complexity of the final parts, Machine capacity and capability and The initial tooling cost. A multi-cavity mold is typically the better choice when a lot of comparable components need to be made quickly. However, manufacturers need to be aware of the higher initial mold cost, longer time to get the mold manufactured, and higher maintenance and risks. On the other hand, a single-cavity mold is more cost-effective for a new product in the short-run with a limited budget, or if the part quality is the most important factor. Customers should hence discuss in depth with the mold designers and manufacturers to go through every step of the part production and life-cycle, such that the most suitable mould type could be chosen to maximize the cost-effectiveness and time-length of the project. 

Micro Systems has 20 years of experience in micro mold projects for medical, pharmaceutical and optics markets, from mold design, mold manufacture, micro metrology to micro molding. All our molds are manufactured in house and we can utilize diamond cutting techniques which enable us to produce ultra precision micro features with integrated optical areas and surface finishes as low as 5-7 Nm Ra. Our team of experts in the UK and Singapore will work with you from the very first step of your project, to ensure that our molds meet all of your highest expectations.

• High standards of control – ISO Class 7 Cleanrooms.
• ISO 9001 and ISO 13485
• Pilot molds to 32 cavity production molds
• In-house production
• Fast-cycling medical molds
• Fully validated production molding

Micro Systems specializes in the design, manufacture and validation of ultra precision micro molds for the medical, pharmaceutical and optical markets, at the same time, the development and use of micro and nano technologies in the design and manufacture of injection molded components. We have a dedicated micro molding facility, and have ISO13485 and ISO9001 certifications, and an ISO Class 7 Cleanroom. For more information, please Contact us or visit our website.