An investment casting tree (also called a cluster or assembly) is a central wax sprue with multiple wax patterns attached to it, all cast as one unit. The tree design directly affects casting yield, defect rate, and per-part cost.
Tree components:
| Component |
Function |
Design Consideration |
| Sprue (main) |
Vertical central column; molten metal flows down through it |
Diameter must be large enough for metal to feed all patterns before solidifying |
| Runner (cross) |
Horizontal bars connecting patterns to sprue |
Positioned to ensure even metal flow to all patterns |
| Gate |
Short connection between runner and individual pattern |
Thickness and shape control solidification direction |
| Pattern |
The wax replica of the final part |
Orientation affects surface quality and dimensional accuracy |
Gating types for investment casting:
| Gate Type |
Description |
Best For |
| Direct gate |
Pattern attached directly to sprue |
Simple, thick-walled parts |
| Runner gate |
Pattern attached to horizontal runner |
Multiple small parts, even distribution |
| Tangential gate |
Gate enters pattern at an angle |
Round parts, impellers, rotating components |
| Stepped gate |
Gate with gradual cross-section change |
Parts with varying wall thickness |
Tree size limits:
| Factor |
Typical Range |
Constraint |
| Patterns per tree |
4-100+ |
Shell handling weight, furnace capacity |
| Tree weight (shell + metal) |
5-50 kg |
Manual or robotic handling capability |
| Tree height |
200-600 mm |
Shell building tank depth, furnace height |
Quick Q: What is an investment casting tree?
A tree (or cluster) is an assembly of multiple wax patterns attached to a central wax sprue. The entire tree is shelled, dewaxed, and cast as one unit — producing multiple parts per pour. Tree design (spacing, gating, orientation) is critical for casting quality and yield. A well-designed tree can achieve 60-85% metal yield (parts ÷ total metal poured).