How Do Low-Pressure Die Casting and Gravity Die Casting Differ?

MACCHINAZIONE CNC in resina epossidica

Low-pressure die casting and gravity die casting are two foundational metal-forming processes, each built on distinct mechanical principles. While both shape molten metal into finished parts using molds, their approaches to filling cavities—one driven by controlled pressure, the other by natural gravity—create stark differences in quality, efficienza, e costo. Per i produttori, choosing between them means balancing needs like part strength, volume di produzione, e budget. But what exactly sets their workflows apart? How do these differences impact end-product performance? And which process is right for your specific application? This article answers these questions with detailed comparisons and actionable guidance.

1. Principi principali: The Fundamental Contrast in Filling Mechanisms

The biggest divide between the two processes lies in how molten metal is delivered to the mold cavity—a difference that shapes every other aspect of their operation.

UN. Casting da dado a bassa pressione

  • Driving Force: Usi dry compressed air or inert gas (PER ESEMPIO., azoto) to apply controlled pressure (typically 0.02–0.15MPa) to a sealed crucible holding molten metal.
  • Filling Process: Pressure forces metal up a vertical liquid lift tube and into the mold cavity from the bottom up. This creates a slow, steady “laminar flow” (no turbulent splashing), ensuring the cavity fills completely without trapping air.
  • Solidificazione: The pressure is maintained during cooling (pressure-holding crystallization). This pushes remaining molten metal into shrinkage gaps, eliminating defects like pores or voids.

B. Gravità muore casting

  • Driving Force: Relies solely on metal’s own weight (gravità)—no external pressure is applied.
  • Filling Process: Molten metal is poured into a sprue (funnel-shaped inlet) at the top of the mold. It flows downward through runners and gates into the cavity via “natural flow”—filling speed depends on the mold’s design and metal’s fluidity.
  • Solidificazione: Cooling happens passively, with no pressure to counteract shrinkage. This means thicker sections may develop small shrinkage pores, though the slow filling reduces gas entrainment compared to high-pressure methods.

2. Side-by-Side Process Comparison: Key Operational Differences

To understand how these processes perform in practice, let’s break down their workflows, parametri, and constraints in a clear, data-driven table:

Process AspectCasting da dado a bassa pressioneGravità muore casting
Filling ModeBottom-up laminar flow; pressure-controlled (0.02–0.15MPa).Top-down gravity flow; nessuna pressione esterna.
Filling SpeedLento, uniforme (typically 5–15cm/s); adjustable via pressure.Variabile (depends on mold design); faster than low-pressure but slower than high-pressure die casting.
Metal Fluidity RequirementDa basso a medio; works with most non-ferrous alloys (alluminio, magnesio).Alto; requires alloys with good flowability (PER ESEMPIO., alluminio, rame) to fill cavities via gravity alone.
Mold Design ComplexityAlto; needs sealed crucibles, liquid lift tubes, and pressure ports.Basso; semplici sistemi materozza-canale-cancello (nessun componente correlato alla pressione).
Tempo del cicloPiù lungo (60–120 secondi per parte); comprende l'aumento e il mantenimento della pressione.Moderare (45–90 secondi per parte); faster than low-pressure but slower than high-pressure die casting.
Tasso di rifiutiBasso (5–8%); non c'è bisogno di alzate (metallo extra per alimentare il ritiro).Più alto (10–15%); potrebbe richiedere montanti per parti con pareti spesse, aumento dello spreco di materiale.

3. Prestazione & Qualità: Which Delivers Better Results?

Il meccanismo di riempimento influisce direttamente sulla qualità della parte, Proprietà meccaniche, e tassi di difetto. Di seguito è riportato un confronto dettagliato dei principali parametri prestazionali:

Metrica delle prestazioniCasting da dado a bassa pressioneGravità muore casting
Densità parzialeAlto (Densità teorica ≥99,5%.); la pressione elimina i pori da ritiro.Moderare (98–99%); piccoli pori possono formarsi in sezioni spesse.
Resistenza alla trazioneSuperiore (PER ESEMPIO., 280–320MPa for aluminum alloys); dense structure boosts strength.Bene (PER ESEMPIO., 240–280MPa for aluminum alloys); slightly lower due to minor porosity.
Finitura superficialeEccellente (Ra 1.6–3.2μm); smooth filling avoids surface defects like cold shuts.Moderare (Ra 3.2–6.3μm); may have minor surface irregularities from uneven flow.
Tasso di difettoBasso (2–5% scrap rate); minimal oxidation or gas defects.Moderare (5–10% scrap rate); risks include cold shuts (from slow flow) or shrinkage pores.
Heat Treatment CompatibilityEccellente; uniform structure resists deformation during heat treatment (PER ESEMPIO., T6).Bene; can be heat-treated but may require pre-inspection to avoid pore expansion.

4. Applicazioni: Matching Process to Part Needs

Each process excels in specific scenarios, based on part design, materiale, e requisiti di prestazione. The table below maps processes to ideal use cases:

Part RequirementPrefer Low-Pressure Die CastingPrefer Gravity Die Casting
Ad alta resistenza, Safety-Critical PartsRuote automobilistiche, engine blocks/covers (need density and strength to withstand loads).None—safety parts require the higher density of low-pressure casting.
Large Thin-Walled ComponentsMissile housings, Parti strutturali dell'aeromobile (laminar flow prevents thin-section voids).Not suitable—gravity flow can’t fill thin walls (≤3mm) uniformly.
Thick-Walled, Forme sempliciNone—overkill for low-performance thick parts.Rail transit accessories (PER ESEMPIO., bogie brackets), robot structural parts, ship propeller hubs (sezioni spesse, low complexity).
Sensibile ai costi, Medium-Volume PartsNone—higher equipment costs make it uneconomical for low-margin parts.Beni di consumo (PER ESEMPIO., large cookware), valvole industriali (Design semplice, volume medio).
Non-Ferrous Alloy PartsIdeal for aluminum, magnesio, and copper alloys (controllable flow suits these materials).Best for aluminum and copper alloys (buona fluidità); less suitable for low-fluidity alloys.

5. Cost Analysis: Upfront Investment vs. Risparmio a lungo termine

Cost is a critical factor for manufacturers. Below is a breakdown of equipment, muffa, and per-part costs (based on aluminum alloy parts, 10,000-part batch):

Categoria dei costiCasting da dado a bassa pressioneGravità muore casting
Equipment InvestmentAlto (\(150,000- )300,000); includes sealed crucibles, pressure control systems, and lift tubes.Basso (\(50,000- )100,000); simple melting furnaces and open molds.
Costo della muffaAlto (\(15,000- )40,000); complex designs with sealed cavities and lift tubes.Basso (\(5,000- )15,000); semplice, open designs with minimal features.
Per-Part Material CostBasso (\(0.4- )0.6/kg); no risers reduce waste.Moderare (\(0.5- )0.7/kg); risers increase material usage.
Labor CostModerare; requires trained operators to monitor pressure (1–2 operators/line).Basso; simple process needs minimal supervision (1 operator/2 lines).
Total Batch Cost~ (30,000- )60,000~ (15,000- )30,000

6. Yigu Technology’s Perspective on the Two Processes

Alla tecnologia Yigu, we see low-pressure and gravity die casting as complementary tools—each solving unique manufacturing challenges. For automotive clients needing high-strength wheels, our low-pressure casting lines (equipped with real-time pressure monitoring) deliver parts with 99.8% density and <3% scrap rates, meeting IATF 16949 standard. For rail transit clients, our gravity casting solutions cut upfront costs by 50% while producing durable brackets that pass 100,000-cycle load tests.

We’re optimizing both processes: 1) Adding AI to low-pressure systems to auto-adjust pressure for different part thicknesses (riducendo il tempo ciclo di 15%); 2) Developing modular gravity molds that switch between part designs in 30 minuti (ideal for small-batch production). Our goal is to tailor each process to the client’s “pain points”—whether it’s quality, costo, or flexibility—instead of forcing a one-size-fits-all solution.

Domande frequenti

  1. Can gravity die casting be used for thin-walled parts (PER ESEMPIO., 2mm di spessore)?

No—gravity-driven flow can’t fill thin walls uniformly, leading to voids or incomplete filling. Parti a parete sottile (≤3mm) require low-pressure die casting, which uses controlled pressure to push metal into narrow cavities without gaps.

  1. Is low-pressure die casting worth the higher upfront cost for medium-volume production (PER ESEMPIO., 5,000 parti/anno)?

It depends on part value: For high-value parts (PER ESEMPIO., ruote automobilistiche, where defects cost $100+/part), yes—lower scrap rates and better quality offset equipment costs. For low-value parts (PER ESEMPIO., Staffe semplici), gravity casting is more economical, even with higher material waste.

  1. Which process is better for magnesium alloys—low-pressure or gravity die casting?

Low-pressure casting is better. Magnesium is prone to oxidation, and low-pressure’s sealed crucible and inert gas protection reduce oxidation by 80% compared to gravity casting (which exposes molten magnesium to air during pouring). This ensures magnesium parts meet corrosion-resistance standards (PER ESEMPIO., ASTM B94).

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