Place ejector pins at structural areas like ribs, bosses, and vertical walls to avoid flexing or puncturing the part.
The boundary where the two halves of the mold (cavity and core) meet. Selecting a proper parting line is crucial to minimize flashing and ensure clean part release.
Ideal for prototyping and low-to-medium volume production runs (up to 10,000 parts). Aluminum offers rapid machining turnarounds and superior thermal conductivity, which slashes cycle times. However, it cannot withstand abrasive glass-filled resins. Pre-Hardened Steel (e.g., P20, NAK80)
Air must escape as plastic fills the mold. If not, the air compresses, heats up, and causes (burn marks) or incomplete filling. injection mold design guide
Once the part cools, the mold opens, and the ejection system physically pushes the part off the core. Ejector Pins and Sleeves
As molten plastic fills the mold, it displaces trapped air and gases. Inadequate venting leads to short shots, burn marks (diesel effect), and poor weld line strength. Vent Dimensions
The (prototype vs. multi-cavity mass production). Share public link Place ejector pins at structural areas like ribs,
Ribs add structural stiffness without increasing wall thickness. Bosses create mechanical fastening points.
The plastic must flow from the gate to the farthest point without freezing. The flow length divided by wall thickness should be ≤ 150:1 for most materials. If you need a long rib, keep it at 0.6x the nominal wall thickness.
A successful mold design guide doesn't just teach you how to fill a cavity; it teaches you how to think like the plastic. The polymer doesn't want to flow, it hates sharp corners, and it shrinks unpredictably. Your job is to outsmart it with geometry, cooling, and venting. Pre-Hardened Steel (e
| Material | Shrinkage (in/in) | Key Design Consideration | | :--- | :--- | :--- | | ABS | 0.004 – 0.007 | Good flow, easy draft. | | Polypropylene (PP) | 0.010 – 0.025 | High shrinkage. Requires large drafts. | | Polycarbonate (PC) | 0.005 – 0.007 | High viscosity. Requires larger gates. | | Nylon (PA6/66) | 0.007 – 0.020 | Hygroscopic (absorbs water = swells). | | POM (Delrin) | 0.018 – 0.025 | Very high shrinkage. |
: This is the most critical rule. Aim for consistent walls between 1–4 mm. Non-uniform walls lead to "sink marks" (surface depressions) and "warpage" because thick sections cool slower than thin ones. Draft Angles
The primary entry point into the mold. It must be tapered (typically 2 to 4 degrees) to allow clean extraction and must have a cold slug well at its base to catch the initial, colder plastic drop. Runner Systems Runners distribute plastic from the sprue to the gates.
The expected (prototype vs. mass production)