High-Pressure Die Casting (HPDC) Ingate, Runner & Gating Vector Prepress Guide
Master the principles of NADCA high-pressure gating design, PQ² machine-die matching, tangential fan runners, vacuum venting channels, and CNC DXF vector toolpath preparation for H13 tool steel dies.
1. Fundamentals of High-Pressure Die Casting Gating
In high-pressure die casting (HPDC), molten metal (aluminum, magnesium, zinc) is injected under high pressure ($30 - 100\,\text{MPa}$) at velocities exceeding $30 - 70\,\text{m/s}$ through narrow ingates to fill complex, thin-walled die cavities in 10 to 60 milliseconds. The design of the gating system—including the biscuit, runner tree, tangential fan gates, and overflows—dictates flow pattern, porosity levels, and surface finish.
$$t_f = K \cdot \left(\frac{T_m - T_l + S \cdot Z}{T_l - T_d}\right) \cdot T$$
Where $t_f$ is maximum allowable fill time (s), $K$ is NADCA alloy constant (0.0346 for Al, 0.0240 for Mg), $T_m$ is metal pouring temp (°C), $T_l$ is liquidus temp, $T_d$ is die surface temp, $S$ is max fraction of solid metal allowed at end of fill (~20–25%), $Z$ is conversion factor (4.8°C/% solid), and $T$ is nominal wall thickness (mm).
2. PQ² Machine-to-Die Matching Theory
The $PQ^2$ diagram plots metal hydraulic pressure $P$ against the square of flow rate $Q^2$. Stable die filling occurs at the intersection of two characteristic curves:
- Machine Characteristic Line: Defined by maximum hydraulic accumulator pressure ($P_{\text{max}}$) and dry shot plunger speed ($Q_{\text{max}}^2$). Expressed as $P = P_{\text{max}} - K_m \cdot Q^2$.
- Die Resistance Curve: Governed by Bernoulli's flow equation through the ingate constriction: $P = \frac{\rho}{2 C_d^2 A_g^2} \cdot Q^2$.
If the intersection falls below the minimum required gate velocity ($v_g < 30\,\text{m/s}$ for Al), cold shuts, flow lines, and blistering occur. If it exceeds maximum gate velocity ($v_g > 65\,\text{m/s}$), die erosion (soldering) and cavitation wear rapidly degrade H13 tool steel cavity inserts.
3. Gating Design & Critical Parameters by Alloy
| Alloy Family | Recommended Gate Velocity $v_g$ | Max Solidification Time Factor ($K$) | Pouring Temp ($T_m$) | Die Operating Temp ($T_d$) |
|---|---|---|---|---|
| Aluminum A380 / A383 | 35 - 55 m/s | 0.0346 | 650 - 680°C | 180 - 240°C |
| Aluminum AlSi10Mg | 40 - 60 m/s | 0.0340 | 660 - 690°C | 200 - 260°C |
| Magnesium AZ91D / AM60 | 45 - 85 m/s | 0.0240 | 640 - 670°C | 220 - 280°C |
| Zinc Zamak 3 / Zamak 5 | 30 - 45 m/s | 0.0210 | 420 - 440°C | 140 - 190°C |
4. Runner & Ingate CAD Vector Rules for Toolmakers
- Tangential Runner Cross-Section: Runner area must decrease proportionally along the branch length: $A_{\text{runner}}(x) = 1.35 \cdot A_g \cdot (1 - x/L)$ to ensure uniform exit pressure along continuous fan gates.
- Ingate Land Length: Keep ingate land thickness short ($L_{\text{land}} = 0.8 - 1.5\,\text{mm}$) with a 30°–45° relief taper to facilitate clean degating.
- Air Vent & Chill Block Sizing: Total vent area must equal at least 25% of total ingate area, incorporating zigzag chill vents ($0.12 - 0.18\,\text{mm}$ deep for Al, $0.06 - 0.10\,\text{mm}$ for Mg) to flash-freeze metal while exhausting cavity gases.
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