Lower tooling cost, smaller series — and the only route to heat treated strength.

Gravity die casting

Gravity fill into a permanent steel mould. Chosen when the part is to be heat treated, when sections are heavy, or when volume is too low to carry a pressure die.

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Gravity casting · aluminium

Gravity die casting in Norway

Gravity die casting in Norway means a permanent steel mould that the melt runs into under its own weight, not under pressure. It is a slower process — and that is precisely why the part can be heat treated afterwards.

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The principle

Why slower is an advantage

In pressure die casting the metal is injected so fast that air is entrained and stays trapped in the section. The part is dense enough and strong enough for most purposes — but heat it in a treatment furnace and the trapped gas expands and raises blisters under the surface. That is why pressure die cast parts normally are not heat treated.

Gravity die casting fills the mould calmly, under gravity. Less air is entrained, so the part will take a solution treatment and an age. That is where the strength comes from: a heat treated gravity cast aluminium part has substantially higher tensile and ultimate strength than the same part as cast.

One of the brackets in our portfolio is exactly this. It could have been pressure die cast — that would have been faster and given a better surface. But it has to take more than pressure die casting delivers, and then gravity is the right process. We choose the process from what the part has to withstand, not from what is quick.

Process choice

Gravity or pressure?

We have both, and the choice is a technical decision, not a question of which machine is free.

Gravity or pressure?
Kriterium	Gravity die casting	Pressure die casting (HPDC)
Filling	Gravity	High pressure
Cycle time	Minutes per shot	Seconds to tens of seconds
Wall thickness	Needs heavier section	Handles thin walls and complex geometry
Surface	Rougher	Fine, often finished with no rework
Heat treatment	Possible — gives high strength	Normally not possible
Tooling cost	Lower	Higher
Viable from	Smaller series	Larger series
Used here for	Brackets that will be heat treated	Most parts — brackets and housings

Suitability

When gravity is right — and when it is not

Choose gravity die casting when

The part must be heat treated to reach its strength requirement.
The series is too small to carry a pressure die — gravity works at a fifth to a tenth of the volume.
Sections are heavy, and the part has no thin features that need pressure to fill.
The tooling budget is tight in a start-up phase.

Choose pressure die casting instead when

Walls are thin or the geometry is complex.
Volume is high and cycle time dominates the price.
The surface has to be fine straight from the die.
The part is to be cast in zinc. Zinc runs in a die casting machine.

Design

What to know before you design for gravity

Gravity is not pressure die casting in slow motion. It is a different process, and the part should be designed for it from the start.

Heavier sections, not thinner. The melt fills under gravity alone, with no pressure behind it. Tight, thin features do not fill reliably. Where pressure die casting handles thin walls, gravity needs a minimum for the metal to reach before it freezes.

A rougher surface. A gravity cast part comes out with more visible texture than a die cast one. If the face has to look good, it must be blasted, machined or coated. Allow for it in the costing.

Direction of solidification matters more. With no pressure, the part has to be fed by gravity as it freezes. That places demands on how heavy and light sections sit relative to each other, and it is one of the things we look for in the review.

The alloy is often a different one. The classic gravity alloys are chosen because they can be heat treated. The most common is EN AC-42100, AlSi7Mg0.3 — see the alloy table for standard values in the as-cast and heat treated conditions.

Datablad

Specifications — gravity die casting

Machine park

Processes in house: Pressure die casting (aluminium and zinc), gravity die casting, CNC turning, CNC milling, boring, heat treatment, blasting
Processes we do not have: Sand casting, toolmaking, anodising, powder coating
CAM software: Autodesk Fusion 360
Number of die casting machines: Available on request
Clamping force: Available on request
Hot or cold chamber: Available on request
Maximum shot weight: Available on request
Platen size and maximum die height: Available on request
Gravity casting stations: Available on request
Maximum mould size, gravity: Available on request
Melting furnaces and melting capacity: Available on request
CNC lathes: Available on request
Maximum turning diameter and length: Available on request
CNC mills: Available on request
Milling work envelope: Available on request
Boring machine: Available on request
Heat treatment furnace: Available on request
Blasting equipment: Available on request
Automation: Available on request
Machining operations: CNC turning, CNC milling, boring, tapping, sawing, grinding
Machining experience: More than 30 years år
Number of axes, milling: Available on request
Heat treatment applies to: Gravity die cast aluminium parts
Heat treatment — effect: Higher tensile strength and higher ultimate strength
Tempers we run: Available on request
Blasting: In house
Anodising: Via subcontractor — aluminium only, zinc cannot be anodised
Powder coating: Via subcontractor
Finishing subcontractors: Available on request
Die ownership: The customer owns the tool. We procure it, specify it for our machines and maintain it.
Typical tooling cost: Available on request
Die life, aluminium: Available on request
Die life, zinc: Available on request
Storage and insurance of customer-owned dies: Available on request
Shift pattern: Available on request

Alloys

Metals: Aluminium and zinc
Feedstock form: Ingot from established suppliers
Aluminium supplier: Metallco, Toten, Norway — secondary aluminium realloyed against international standards
Aluminium melting point: 660 °C °C
Aluminium casting temperature: 680–700 °C °C
Alloy selection: Made together with the customer, as part of the design review
Aluminium alloys, pressure die casting: Available on request
Aluminium alloys, gravity: Available on request
Zinc alloys: Available on request
Customer-specified alloy: Available on request
Material certificate: Available on request
Melt and batch traceability: Available on request
Recycled content: Available on request

Part sizes

Part weight: From a few grams to several kilos Estimat
Maximum part envelope: Available on request
Maximum projected area: Available on request
Minimum wall thickness, aluminium: Available on request
Minimum wall thickness, zinc: Available on request
Minimum wall thickness, gravity: Available on request
Minimum draft angle: Available on request
Minimum cored hole: Available on request
Insert casting: Available on request
Multi-cavity tooling: Available on request

Series and lead time

Response to an enquiry: Within 24 hours timer
Formal quotation with final files: Within 24 hours timer
Indicative minimum series, pressure die casting: A few thousand parts per year or per order
Indicative minimum series, gravity: A fifth to a tenth of the pressure die casting volume
Typical series size in production: Available on request
Lead time from tool order to first sample: Available on request
Time from sample to approved series start: Available on request
Lead time in running series: Available on request
Annual capacity: Available on request
Available capacity: Available on request
Call-off and stock holding: Available on request
Added lead time for external finishing: Available on request
Prototypes and pre-series: Available on request

Does the part need heat treatment?

Then gravity is probably the right process. Send the drawing and we will confirm it.

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