The cost of making injection mold tooling is inarguably part of the biggest expense lines and fixed costs in mass plastic part production. So delicate is the injection mold tooling that a single error in its design will be reflected in all the copies of the part that will be made from the tool.
More often than not, the high precision and accuracy required for mold tooling means that tools will be fabricated with sophisticated CNC machines. When it comes to parts that have multiple components, tooling design can be made to incorporate more than one part, such that, one injection molding cycle produces more than one part. Today, we take a look at the three most popular mold cavity concepts, when to use what, and the advantages of each of these approached.
Single-cavity Mold
A single-cavity mold is a mold that makes only one component per injection molding cycle. Most injection molding projects are achieved with single-cavity injection molding. The concept is like every injection molding operation in that the molten resin flows through the runner system into the single cavity. The mold is filled and left to cool, after which the final product is ejected.
The following are the advantages and disadvantages associated with single-cavity injection molding techniques:
| Advantages | Disadvantages |
| Lower upfront cost for mold design and manufacture | The landing cost per part may become higher over the life cycle of the mold |
| Relatively shorter leadtimes to make the mold | Not suitable or not sustainability for large volumes |
| Cost-effective for low volume production (1-1000) parts | |
| Excellent for bridge tooling solutions |
Single-cavity molds are commonly used when:
• Launching new products where market demand cannot be determined
• Special or limited-edition products with small volumes
• Intricate parts with complex geometries where control over molding parameters is desired
• Projects with flexible leadtime requirements
• Budget productions where lower upfront cost is imperative
Multi-cavity Molds
Multi-cavity molds are injection molding tooling designed to house two or more copies of the same part. Multi-cavity molds can produce multiple units of the same part in a single injection molding cycle, using multiple impressions of the part in the same mold tool.
The process for multi-cavity molds is such that the molten plastic flows into each cavity in the mold using similar fill, pack hold and cooling parameters. After the process has been completed, multiple parts are ejected from the mold tool.
The following are the advantages and disadvantages associated with multi-cavity injection molding techniques:
| Advantages | Disadvantages |
| Lower price per part over the useful life of the mold when compared with single-cavity molds | Higher upfront costs due to design complexity and additional engineering |
| Excellent for higher-volume projects | More frequent and demanding maintenance |
| Quicker leadtimes and high part output per injection molding cycle | Relatively longer leadtimes for mold design and manufacture |
Multi-cavity molds are commonly used when:
• Making up to 500,000 parts in a year
• High volume production that places emphasis on the lowest possible cost per part
• Projects where upfront costs can be sizeable
• Projects that demand quick production and shorter leadtimes
Family Molds
Family cavity molds are actually multi-cavity molds that house two or more cavities within the mold tooling to produce multiple pieces of a part in a single injection molding cycle. Unlike multi-cavity molds, family mold will make different component parts of a product within the same mold tool.
They are particularly used for molding operations that call for the manufacture of various components parts for a larger or composite product. They also serve assembly halves of a plastic part design that will be snapped together to make a single complex parts.
The following are the advantages and disadvantages associated with family cavity injection molding techniques:
| Advantages | Disadvantages |
| Excellent cost-effectiveness over the mold tool life span | Higher upfront costs due to design complexity and additional engineering |
| Lower tooling cost in the longer run | Significantly higher engineering and operational parameter variabilities |
| Ability to make several distinct parts in one-go | Higher susceptibility to part defects |
| Quicker leadtimes from making multiple part types in one injection molding cycle | Relatively longer leadtimes for mold design and manufacture |
Family molds are commonly used when:
• Making products with numerous parts and components to be made from the same material, color and other uniform cosmetic attributes
• Quick market entry and leadtimes are critical to launch and success
• High volume production for parts whose designs are less likely to be reviewed in the near future
• Working with an expert mold manufacturer that can mitigate the chances of part defects that may occur from using the mold tooling concept.
First Part Injection Molding Services in China
FirstPart offers high quality, thermoplastic injection molding service for all your plastic part projects in China. We also offer low-volume manufacturing that serve small quantities from 50 to 10000 parts and produce for mass production. Our engineers are always available to advice on the best processes, materials and design optimization to ensure cost-savings, quick turnaround and the production of parts that are 100 percent defect and issue free.
