Injection molds are the heart of the plastic injection molding process. Without a proper mold, there's no injection molding — the mold defines the shape, size, surface finish, and quality of every plastic part produced. Whether you're new to injection molding or looking to optimize your process, understanding injection molds is essential.
What Is an Injection Mold?
An injection mold (also called a plastic injection mold or molding tool) is a precision-machined tool that defines the shape of a plastic part. It consists of two halves — the cavity (female side) and the core (male side) — that close together to form a hollow space. Molten plastic is injected into this space under high pressure, cooled, and ejected as a finished part.
Types of Injection Molds
Single-Cavity Molds
Produces one part per injection cycle. Ideal for prototyping, low-volume production, and complex parts. Lower tooling cost, slower output.
Multi-Cavity Molds
Produces multiple identical parts per cycle. Used for high-volume production. Higher tooling cost but lower per-part cost at scale.
Family Molds
Produces different parts in a single cycle — useful when you need multiple components of an assembly. Requires careful balancing of material flow.
Insert Molds
Metal inserts (like threaded brass inserts) are placed in the mold before injection, allowing plastic to mold around them. Common for parts requiring metal threads or conductors.
Overmolds
A second layer of plastic is molded over an existing part — commonly used for soft-grip handles, two-color parts, and sealed enclosures.
Injection Mold Materials
The material used to make an injection mold affects its cost, lifespan, and the quality of parts it produces.
Steel Molds
The most durable option — hardened steel molds can produce millions of parts. Used for high-volume production runs. Highest upfront cost ($5,000–$50,000+).
Aluminum Molds
Faster and cheaper to machine than steel — aluminum molds typically cost 30–50% less. Suitable for tens of thousands of cycles. Popular for low-to-medium volume production and prototyping.
3D Printed Molds
The lowest cost option — 3D printed plastic or resin molds can be produced for under $100 and work well for prototyping and very small runs (10–100 parts). The APSX-PIM V3 is specifically designed to work with both metal and 3D printed molds, making it the most accessible entry point for injection molding.
Key Injection Mold Components
- Cavity and Core — The two halves that form the part shape
- Sprue — The main channel through which plastic enters the mold
- Runner system — Channels that distribute plastic from the sprue to the gate
- Gate — The entry point where plastic flows into the cavity
- Ejector pins — Push the finished part out of the mold after cooling
- Cooling channels — Circulate water or coolant to solidify the plastic faster
- Vents — Allow trapped air to escape during injection
How to Design an Injection Mold
Good mold design is critical for producing quality parts. Key design principles include:
- Draft angles — Slight taper on vertical walls (1–3°) to allow easy part ejection
- Wall thickness — Uniform wall thickness prevents sink marks and warping
- Parting line — Where the two mold halves meet — should be placed to minimize visible seam lines
- Gate location — Affects material flow, weld lines, and part appearance
- Undercuts — Features that prevent straight ejection — require side actions or collapsible cores
Injection Mold Cost: What to Expect
Injection mold cost varies widely depending on material, complexity, and cavity count:
| Mold Type | Cost Range | Best For |
|---|---|---|
| 3D Printed | $10–$200 | Prototyping, 10–200 parts |
| Aluminum (simple) | $1,000–$5,000 | Low-volume, 1K–50K parts |
| Aluminum (complex) | $5,000–$15,000 | Medium volume |
| Steel (simple) | $10,000–$25,000 | High volume, 100K+ parts |
| Steel (complex) | $25,000–$100,000+ | High volume, complex parts |
APSX Injection Molds for Desktop Machines
The APSX-PIM V3 accepts standard mold sizes up to 6" × 4.8". APSX offers a range of ready-made mold options including the ASTM test bar mold and blank aluminum molds for custom machining. For even lower-cost tooling, 3D printed molds work directly with the APSX-PIM — making it possible to start injection molding for under $500 total including the mold.
Ready to get started with injection molding? Learn more about the APSX-PIM V3 or download mold drawings to have your own custom mold machined.