When buyers search “casting and foundry,” they’re usually trying to solve a real problem: who should make my metal parts—and what capability do I actually need? The confusion comes from the fact that foundry, casting, and castings are related, but they are not the same thing.
This guide clarifies the difference, explains what actually happens inside a foundry, and shows where aluminum die casting fits—so your RFQs, quotes, and quality expectations line up from day one.
- A foundry is the facility/company that melts metal and produces cast parts (and often offers machining, finishing, and inspection).
- Casting is the manufacturing process of forming a part by solidifying molten metal in a mold or die.
- Castings are the finished parts you buy.
If you’re sourcing aluminum die cast parts, the important question isn’t the vocabulary—it’s whether the supplier has die casting capability (machines + tooling + process control + inspection) to meet your tolerances, appearance, and leak-tight requirements.
What is Casting?
Casting means shaping a part by pouring or injecting molten metal into a cavity (a mold or die), letting it solidify, and then removing the part.
Common casting processes include sand casting, investment casting, permanent mold casting, and high-pressure die casting. If your part is thin-wall, high-volume, or needs strong dimensional repeatability, aluminum die casting is often the right branch of “casting” to specify.
Foundry vs Casting vs Castings
| Term | What it means (in practice) | Typical equipment you should see | What it includes | What it does NOT automatically include | What buyers should ask (RFQ-ready) |
|---|---|---|---|---|---|
| Foundry | The facility/company that melts metal and produces cast parts (may also provide machining/finishing/QC) | Melting/holding furnace, metal handling, casting cell(s) (HPDC machines if die casting), trimming/deflashing, deburring/finishing, inspection area; often CNC, leak test, X-ray/CT (capability varies) | Manufacturing capability + production control + QA system; may include DFM support and tooling management | “Foundry” ≠ “die casting” by default. Also not automatically: machining, coating/anodizing, leak test, X-ray/CT, full traceability, or specific documentation | Which processes do you run (HPDC / gravity / sand / investment)? Which alloys? Tonnage range (if HPDC)? Vacuum capability? In-house tooling or outsourced? CNC capacity? Leak test method? CMM? X-ray/CT access? Typical lead time and monthly capacity? |
| Casting | The manufacturing method: forming parts by solidifying molten metal in a mold/die | Depends on method: sand molding line, shell/investment line, permanent mold stations, or HPDC machine + die | Multiple process options with different cost/tolerance/surface/volume fit | “Casting” doesn’t specify quality level, alloy, finish, tolerance, inspection plan, or whether parts are leak-tight | Which casting process matches my part’s geometry (thin-wall/ribs/bosses), volume, tolerance, cosmetic needs, and sealing requirement? What design rules apply (min wall, draft, radii, parting line)? What are typical defect risks and how are they controlled? |
| Castings | The delivered parts + acceptance standard (what you receive and how it’s judged) | Final inspection tools: gauges/CMM, leak test rigs, surface inspection standards; packaging/traceability setup | As-cast or machined parts; may include trimming, deburring, surface finishing, coating, assembly, packing, lot traceability, inspection reports | A “casting” is not automatically: machined, cosmetic-grade, leak-tight, internally inspected, or delivered with reports | Are parts delivered as-cast or machined? What inspection reports come with each lot (FAI/CMM, material cert, leak test record, X-ray/CT if required)? What cosmetic zones/standards apply? What’s the sampling plan and dispute rule for borderline results? What traceability and packaging spec do you support? |
Foundry vs Casting vs Castings What’s the difference?
Think of it this way:
- Foundry = “who & where” (the manufacturer and facility)
- Casting = “how” (the forming method)
- Castings = “what you receive” (the produced components)
In RFQs, problems happen when these get mixed:
- A buyer says “I need a foundry,” but doesn’t specify die casting vs sand casting.
- A supplier replies “we do casting,” but their casting method doesn’t match your requirements (thin walls, appearance, leak-tightness, tight tolerances, high volume).
- Both sides assume different inspection or finishing steps are “included.”
Clear language prevents expensive re-quotes, wrong process selection, and quality disputes.
What happens in a foundry? The foundry process step by step
Different foundries run different processes, but the workflow usually follows the same backbone. Here’s a practical view—focused on what matters to buyers.
Step 1: Material selection and charge preparation
A foundry starts with metal input: primary ingot, certified alloy, and controlled internal return (re-melt). For buyers, what matters is consistency—the same alloy chemistry and melt practice produce stable mechanical properties and predictable machining behavior.
Step 2: Melting and holding (melt control)
Metal is melted, then held at controlled conditions. This is where foundries manage:
- temperature stability,
- melt cleanliness,
- and consistency from batch to batch.
Even before a part is made, melt control influences internal quality and repeatability—especially for parts that will be machined or leak-tested.
Step 3: Molding or die/tool setup (depends on process)
This step looks different by casting method:
- Sand casting uses sand molds and cores.
- Investment casting uses wax patterns and ceramic shells.
- Die casting uses hardened steel dies in a die casting machine.
For aluminum die casting, tooling is a major part of capability: die design, gating, venting/vacuum strategy, cooling, and ejection must match the part and quality targets.
Step 4: Pouring or injection and filling
- In many foundry processes, molten metal is poured into a mold.
- In high-pressure die casting (HPDC), molten aluminum is injected at high speed/pressure into a steel die.
For buyers, the key is that HPDC is designed for repeatability and efficiency, but it also requires strong process control (shot profile, intensification timing, die temperature management) to hit leak-tightness and cosmetic goals consistently.
Step 5: Solidification and cooling control
As the metal solidifies, the foundry controls cooling behavior. Poor control here can create issues such as shrinkage sensitivity, distortion, or cosmetic inconsistency. Strong foundries treat solidification as an engineered outcome—not an accident.
Step 6: Ejection / shakeout and trimming
The part is removed from the mold/die and then:
- runners/gates are removed,
- flash is trimmed,
- and edges are finished (deburring).
In die casting, trimming and deburring are often integrated into a standardized cell to keep output consistent.
Step 7: Finishing, machining, and surface treatment (as required)
Many cast parts need secondary operations:
- CNC machining for critical dimensions,
- surface finishing (shot blast, polishing),
- coating (powder coating, anodizing, plating).
The important buyer question: are these done in-house or through qualified partners, and how is quality controlled across steps?
Step 8: Inspection, testing, and documentation
A capable foundry can provide the inspection evidence you need:
- dimensional reports (CMM),
- visual standards,
- internal inspection when required (X-ray/CT),
- functional tests (especially leak/pressure tests for housings).
Where aluminum die casting fits in a foundry
Many companies call themselves “aluminum foundries,” but their actual processes can differ. A die casting foundry (or die casting shop) is specialized for HPDC.
Why die casting is different
Aluminum die casting is typically chosen for:
- high-volume production,
- thin-wall geometry,
- consistent dimensions across large runs,
- good surface finish (depending on tool and process),
- and cost efficiency at scale.
But it comes with its own engineering realities: die design, thermal control, venting/vacuum, and quality validation are central—not optional.
Typical die casting workcell (what “capability” looks like)
A modern aluminum die casting line often includes:
- die casting machine (tonnage matched to part),
- die temperature and spray control,
- vacuum/venting setup where required,
- trimming/deflashing equipment,
- inspection stations (visual + gauges/CMM),
- and a controlled process record.
What buyers usually care about for aluminum die castings
- Tolerances & repeatability (especially after machining)
- Cosmetics (surface appearance, sink, flow lines, texture requirements)
- Leak-tightness (housings, valve bodies, manifolds)
- Machining stability (material behavior, porosity risk zones)
- Documentation (first article, inspection reports, traceability)
Types of foundries and casting processes
Foundries by metal category
- Ferrous foundries: iron/steel castings
- Non-ferrous foundries: aluminum, zinc, magnesium, copper alloys
If you source aluminum die cast parts, you’re typically working with non-ferrous foundries with HPDC capability.
Casting processes buyers commonly see
- Sand casting: flexible shapes, often lower tooling cost, typically lower production rate
- Investment casting: high detail, complex shapes, often higher cost and longer cycle
- Permanent mold / gravity casting: metal mold, moderate production, good quality for some geometries
- High-pressure die casting (HPDC): high volume, thin walls, high repeatability when controlled well
A foundry may run one or several of these. Never assume “foundry” automatically means “die casting.”
Foundry equipment buyers should recognize and what it tells you
When you evaluate a supplier, equipment reveals the true boundary of capability.
- Melting/holding system: stability and melt practice
- Tooling/mold capability: whether the supplier can build and maintain dies for production consistency
- Trimming and finishing: whether post-casting operations are standardized
- Machining capability: whether tight tolerances are supported reliably
- Inspection tools: CMM, leak testing, and (when needed) internal inspection capability
A supplier can say “we do casting,” but equipment tells you whether they can meet your quality definition.
Quality and inspection in a foundry how castings are verified
For buyers, inspection matters most when it aligns with function:
Visual and surface checks
Appearance standards should be defined: acceptable surface texture, cosmetic zones, and allowable minor marks. A good foundry asks for your expectations rather than guessing.
Dimensional control (repeatability)
Expect:
- first article inspection (FAI),
- critical dimension control,
- and trend monitoring across production (not only “one part passed once”).
Internal inspection (when needed)
X-ray/CT is not always required, but it becomes important when your part’s function depends on internal integrity (leak-tightness, high stress zones, safety-related parts).
Leak and pressure tests (for housings and sealed parts)
If your part must seal, the inspection plan should reflect that:
- define the test method and pass/fail criteria,
- define which surfaces are sealing-critical,
- and align sampling and escalation rules.
How to choose the right foundry for aluminum die casting parts
Here’s a buyer-friendly checklist that prevents most quoting and production issues.
What to send for an accurate RFQ
- 3D model (STEP/IGES) + 2D drawing (key tolerances/GD&T)
- alloy requirement (or performance requirements if flexible)
- annual volume and production rhythm
- machining plan (what gets cut, and where)
- surface/appearance requirements and cosmetic zones
- functional requirements: leak/pressure test, temperature, load, corrosion, etc.
What a capable die casting foundry should offer
- DFM feedback (hot spots, wall transitions, gating/venting implications)
- tooling strategy and sample plan
- first article validation approach (dimensions + functional test strategy)
- stable production control (process records + corrective action discipline)
Red flags
- quoting without asking about critical dimensions or functional requirements
- “we can do everything” with no evidence of inspection method or validation plan
- no clarity on what’s included (machining/finishing/testing/documentation)
Conclusion
A foundry is the manufacturing organization and facility; casting is the process; castings are the parts you buy. Once those are clear, sourcing becomes much easier—especially for aluminum die casting, where tooling, process stability, and inspection planning determine whether you get consistent parts at scale.
If you’re sourcing aluminum die cast components, the fastest path to a clean launch is to share your drawing, functional requirements, and volume expectations early—so the die casting strategy and validation plan match your real needs.
Send your 3D/2D files, target alloy, annual volume, and any leak/appearance/tolerance requirements. We’ll review manufacturability and propose a die casting + machining + inspection plan that fits your application.
FAQ
1) Is a foundry the same as a machine shop?
Not exactly. A foundry’s core job is melting metal and producing cast parts. A machine shop’s core job is machining material (CNC turning/milling). Some die casting foundries also run machining in-house, but you should confirm scope: casting only, or casting + machining + finishing + inspection.
2) Is a steel mill considered a foundry?
No. A steel mill focuses on making steel products (sheet, plate, bar, coil). A foundry focuses on producing shaped parts by casting molten metal into a mold or die. Both handle molten metal, but the end products and process chain are different.
3) Which casting process is best for thin-wall aluminum parts?
High-pressure die casting is commonly chosen for thin-wall, high-volume aluminum parts because it supports fast cycle times and repeatable geometry when tooling and process control are done well. The “best” choice still depends on function (leak-tightness, strength needs, surface requirements) and volume.
4) What files should I send to a foundry for an RFQ (STEP/IGES/2D/GD&T)?
At minimum: a 3D model (STEP/IGES) and a 2D drawing showing critical dimensions/tolerances (including GD&T if applicable). Add the alloy requirement (or performance target), annual volume, machining plan, surface requirements, and any functional tests (leak/pressure).
5) Why do die casting quotes separate tooling cost and part price?
Because the die (tooling) is a major one-time investment that enables production. Part price reflects cycle time, alloy consumption, trimming/finishing, inspection, and secondary operations (machining/coating). Separating them makes program economics and ownership clearer.
6) How do foundries check porosity and leakage in aluminum castings?
Common methods include visual inspection, dimensional inspection, functional leak/pressure testing, and internal inspection when required (X-ray/CT or sectioning on samples). For leak-tight parts, the test method and acceptance criteria should be defined up front.
7) Can a die casting foundry handle machining and surface finishing in-house?
Some can, some cannot. Many die casting suppliers offer machining and finishing either internally or through qualified partners. The key is to confirm responsibility and control: who runs it, how it’s inspected, and what documentation you’ll receive.
8) What should I ask if my part requires tight tolerances or cosmetic surfaces?
Ask how critical dimensions are achieved (as-cast vs machined), what the first article plan is, what process controls are used to maintain repeatability, and how cosmetic zones are defined and approved (samples, reference standards, acceptable variation). For appearance-critical parts, request sample-based approvals early.
