When sourcing aluminum cast parts, a common question is whether HPDC, LPDC or gravity die casting (GDC) should be used.
The answer should not be based on production volume or part size alone.
Part geometry, quality requirements, alloy, machining, appearance, production volume, tooling and supplier capability all need to be considered together.
Here are five practical factors to review when comparing these casting processes.
HPDC, LPDC and GDC: What Is the Difference?
HPDC — High Pressure Die Casting
HPDC fills a metal die with molten metal at high speed and pressure.
It is widely used for parts requiring complex geometry and efficient mass production.
Depending on the part and its quality requirements, however, internal quality, gating and overflow design, vacuum assistance and downstream machining may require careful consideration.
LPDC — Low Pressure Die Casting
LPDC uses relatively low pressure to introduce molten metal into the die.
Its controlled filling and solidification characteristics can make it a useful option for certain part geometries and internal-quality requirements.
The actual suitability still needs to be evaluated together with equipment, tooling and production requirements.
GDC — Gravity Die Casting
Gravity die casting fills a permanent metal mould primarily by gravity.
Depending on part geometry, volume and quality requirements, it can provide an alternative to HPDC or LPDC.
It can also be useful for some components requiring cores, but the final decision should be based on the actual part specification and the supplier’s process capability.
5 Factors to Check When Selecting a Casting Process
1. Part Geometry and Size
Start with the overall dimensions, weight, wall sections and complexity of the part.
A single dimension should not determine the casting process.
Filling behaviour, solidification, die release, tooling construction and required machining should also be considered.
2. Quality Requirements
Identify which characteristics are critical: dimensional requirements, internal quality, leak tightness, mechanical performance or appearance.
Even for similar geometries, different quality requirements may lead to different casting concepts or process choices.
3. Alloy and Secondary Operations
The specified alloy is only one consideration.
Heat treatment, machining and surface finishing may also influence process selection.
For sourcing decisions, it is better to evaluate the complete manufacturing route rather than the casting operation alone.
4. Production Volume and Tooling
Production volume is important, but there is no universal production threshold at which HPDC automatically becomes the correct choice.
Tooling investment, productivity, equipment, part cost and die maintenance should be evaluated together for the specific project.
5. Supplier Equipment and Process Capability
Several casting processes may appear feasible from the drawing alone, but stable mass production is a separate question.
Supplier equipment, experience with similar parts, tooling capability, process control, machining and quality management should therefore be reviewed before making the final decision.
Do Not Select a Casting Process by Tolerance Grade Alone
Standards such as ISO 8062-3 may be referenced when defining dimensional and geometrical tolerances for castings.
However, a tolerance grade should not be used as a simple rule such as “HPDC equals this grade” or “LPDC equals that grade.”
Actual capability depends on the part geometry, datum concept, machined features, tooling design and manufacturing process.
Critical dimensions should therefore be discussed with the supplier against the actual drawing and production conditions.
Start with the Drawing and Project Requirements
HPDC, LPDC and GDC each have different characteristics, but the process name alone does not determine quality, cost or productivity.
For RFQs to Chinese suppliers, a practical sequence is:
Drawing and 3D Data → Alloy → Quality Requirements → Production Volume → Secondary Operations → Equipment and Process Capability
This makes it easier to compare feasible manufacturing routes based on the actual project rather than on generic process tables.
Conclusion
Selecting an aluminum casting process requires more than comparing HPDC, LPDC and GDC using fixed numerical benchmarks.
The more reliable approach is to evaluate the part requirements together with the actual manufacturing conditions.
For sourcing from China, supplier equipment, tooling capability and process control should also be considered to determine whether the proposed process can support stable production.
Related: engineering decision factors for comparing feasible casting processes
Frequently Asked Questions
Should HPDC always be selected for high-volume production?
No. Production volume is important, but part geometry, quality requirements, tooling, equipment, productivity and secondary operations also need to be considered.
Which process provides the best dimensional accuracy: HPDC, LPDC or GDC?
There is no universal answer based on the process name alone. Achievable dimensional accuracy depends on factors including part geometry, tooling, datum strategy, process capability and whether machining is required.
What information should I provide before asking a supplier to recommend a casting process?
Provide the drawing or 3D data, alloy, annual volume, critical quality requirements, secondary processing or surface treatment requirements, and relevant application conditions.