Low Pressure Die Casting (LPDC) - Process & Applications

Low pressure die casting (LPDC) fills a permanent steel die from below. Molten metal sits in a furnace under controlled gas pressure (typically 0.03–0.1 MPa). Pressure pushes metal up a riser tube into the cavity in a slow, laminar flow — unlike high-pressure die casting, where metal is injected at very high velocity.

LPDC is chosen when low porosity and T6 heat treatment matter more than the thinnest walls or the fastest cycle times.

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How LPDC Works

1. Die close — The die is mounted above the holding furnace; the riser tube connects the furnace to the gate at the bottom of the cavity.
2. Pressurized fill — Dry air or nitrogen raises furnace pressure; metal rises through the tube and fills the cavity from the lowest point upward.
3. Solidification under pressure — Pressure is maintained while the casting solidifies, feeding shrinkage in thick sections.
4. Pressure release and eject — Furnace pressure drops; metal in the tube solidifies as a stalk; the die opens and the casting is removed.
5. Trim and finish — Gate, riser, and stalk are removed; CNC machining and heat treatment follow as required.

Because fill is gentle, there is little turbulence and minimal air entrapment compared with standard HPDC.

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LPDC vs High Pressure Die Casting (HPDC)

Parameter	LPDC	HPDC (cold chamber)
Fill mechanism	Bottom fill, low pressure	Horizontal injection, high velocity
Typical gate velocity	Low, laminar	20–60 m/s at gate
Gas porosity	Very low	Higher unless VADC used
T6 heat treatment	Routinely feasible	Restricted on standard HPDC; VADC improves
Minimum wall (aluminum)	~3–4 mm typical	~1.2 mm achievable
Cycle time	Slower (minutes)	Faster (30–120 s)
Tooling cost	Higher than gravity, lower than complex multi-slide HPDC	Moderate to high
Best volumes	Medium to high	High volume

For a full comparison of all casting types, see types of die casting.

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LPDC vs Gravity Die Casting

Both processes can produce low-porosity aluminum suitable for T6 treatment. Differences:

	LPDC	Gravity die casting
Fill control	Pressurized, repeatable	Pour or tilt under gravity
Feeding pressure	Maintained during solidification	Risers and gravity head only
Automation	Highly automated production cells	Often semi-automatic
Typical parts	Wheels, structural nodes, discs	Manifolds, covers, thick-wall housings

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Alloys and Mechanical Properties

LPDC is used primarily for aluminum (A356, A319, A413) and some magnesium programs. Typical goals:

• T6 heat treatment after casting — solution treat, quench, age
• Tensile strength gains of roughly 35–45% over as-cast in heat-treatable alloys
• Pressure-tight or fatigue-sensitive sections without impregnation

Example: A319 friction discs produced by LPDC plus T6 for compressor applications — see compressor friction disc.

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When to Specify LPDC

Choose LPDC when the drawing requires:

• Heat-treated mechanical properties (yield/tensile targets HPDC cannot meet without vacuum)
• Low internal porosity for structural or rotating components
• Moderate wall thickness (generally ≥3 mm average) and less extreme thin-wall detail than phone housings

Stay with HPDC when:

• Very thin walls, complex slides, or highest annual volumes at lowest piece cost
• Cosmetic Class A surfaces with shortest cycle time
• Zinc or small magnesium parts suited to hot- or cold-chamber HPDC

For borderline programs, KastMfg compares LPDC, vacuum-assisted HPDC, and gravity die casting during quoting.

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KastMfg LPDC Capability

KastMfg runs LPDC for selected aluminum programs where T6 and porosity requirements exceed standard HPDC — including communication equipment structural castings and compressor-related components.

Representative work:

• Handle body for communication equipment — A356, low-pressure fill, CNC finish
• Compressor friction disc — A319 LPDC with full T6 and machined friction faces

Post-cast services on the same campus: CNC machining, heat treatment, surface finishing, and quality inspection.

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Frequently Asked Questions

Is LPDC the same as low-pressure permanent mold casting?

Yes. LPDC, low-pressure permanent mold casting, and “low-pressure aluminum casting” refer to the same family of upward-fill processes.

Can LPDC parts be welded?

Porosity is lower than HPDC, but weldability still depends on alloy and porosity level. Machined joints and mechanical assembly are common; discuss weld requirements at RFQ.

How does LPDC relate to misruns and blisters?

Slow fill reduces misrun risk in thick, well-fed sections but still requires correct gating and temperature. Low porosity makes T6 blistering far less likely than on standard HPDC — see misrun and short shot for fill-related defects on fast-fill processes.

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LPDC and process selection: yaoqingpu1983@gmail.com | +86 138 1403 4409 | Request a quote