Gravity casting is a permanent-mold casting method where molten non‑ferrous alloy is introduced into a reusable metal die under gravity only (no high‑pressure ramming). In common usage it is often called gravity die casting (GDC) or permanent mold casting, and it sits in the broader “casting” family alongside sand casting, investment casting, and low‑pressure die casting (LPDC). Typical alloys include aluminum alloys (e.g., A356), magnesium alloys, and zinc alloys.
Process flow and key controls
Tooling and coating: machine heated metal dies, apply die release to manage heat and facilitate ejection; use sand cores for internal cavities where needed.
Pouring: gravity fill via top gating, tilting/rotary pouring, or ladle dosing; control metal velocity and turbulence to avoid oxide defects.
Solidification: design for directional solidification; use chills, risers, and controlled cooling (e.g., water/graphite spray) to feed shrinkage and minimize porosity.
Finishing: trim, deburr, heat treat (e.g., T5/T6), machining, and surface treatment per specification.
Process simulation tools (e.g., Inspire Cast) are widely used to position gates/risers, set gravity direction, and assess filling and feeding before trials.
Equipment and tooling
Machines: tilting/rotary gravity casting machines enable smooth filling and better venting; common tilt range 0°–90°; automated cycles improve repeatability.
Dies: heat‑treated tool steels with water/oil cooling channels; coatings reduce friction and improve release.
Cores: preformed sand cores allow complex internal features; steel pins/inserts can be cast‑in for functional features.
Automation: integrated molding, clamping, rotation, cooling, and ejection sequences reduce variability and labor.
Advantages and limitations
Advantages: better dimensional accuracy and surface finish than sand casting; thinner walls achievable; faster than many sand processes; excellent repeatability with proven tooling; supports complex internal forms via sand cores and inserts.
Limitations: higher tooling cost than sand; no mold collapsibility, so hot‑tear risk at sharp section transitions; slower filling than HPDC, so gating/venting must be optimized; generally lower production rate than HPDC/LPDC.
When to choose and typical applications
Choose gravity casting when you need a balance of mechanical properties, surface quality, and cost for medium runs of aluminum/magnesium structural parts.
For very high production of thin‑wall, complex parts where cycle time dominates, LPDC/HPDC may be better despite porosity/heat‑treat constraints.
For maximum pressure tightness/ductility with near‑net shape and minimal porosity, squeeze casting is an established alternative to both GDC and HPDC.
Typical parts: aluminum alloy casting cylinder heads, automotive parts and pump valve housings, hardware, and kitchen/medical components; wheels are commonly produced by gravity casting, LPDC, or forging depending on performance and cost targets.