Guide
Die casting vs sand casting vs investment casting: which process fits your part?
Die casting is the process of forcing molten nonferrous metal under high pressure into a reusable, two-half steel die. Sand casting pours metal by gravity into a mold of bonded sand that is broken up after every pour. Investment casting pours metal into a one-piece ceramic shell built up around a wax pattern, which is melted out first. All three make near-net-shape metal parts, and they part ways on volume, alloy, size and how much precision comes straight out of the mold.
By Saola Manufacturing engineering team · Published · Updated
This guide is for engineers and sourcing managers deciding which process to quote. It uses government and standards-body references, a volume-first decision order, and the usual path from a sand-cast prototype to a die-cast production part.
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Which casting process should you choose first?
Decide on alloy and annual volume before anything else: die casting suits large volumes of small-to-medium aluminum, zinc or magnesium parts, sand casting suits low volumes, big parts and almost any alloy, and investment casting suits small, intricate parts in alloys such as steel that a die cannot take.
The two filters remove options outright. A steel or stainless callout rules out die casting, and a few dozen parts a year rarely pay for a hardened steel die. Then work through the rest:
- Size and weight. Very large castings point to sand. Small, detailed parts point to die or investment casting.
- Walls, detail and finish. Thin walls, crisp detail and a smooth as-cast surface favor die casting (nonferrous) or investment casting (including steels and titanium).
- Machining after casting. Count the faces that will be machined anyway. If most functional features are machined, as-cast precision matters less than stock allowance and datums.
How do die, sand and investment casting compare on cost, size, walls and tolerance?
On a published benchmark, die casting is the cheapest process per part in quantity and the most expensive for a handful of parts, sand casting is the reverse, and investment casting sits at the high end in quantity but reproduces fine detail and, per NADCA, accepts a wide variety of alloys.
The most useful public comparison is a table the US Department of Energy reproduced in its metalcasting industry profile, taken from American Foundrymen’s Society data (DOE Office of Industrial Technologies, 1999, Table 2-1). The rows below are copied from it for the three processes this guide covers. Treat them as order-of-magnitude benchmarks: the underlying data is decades old, foundry practice has improved since, and none of these figures replaces a tolerance grade on your drawing.
| Property | Green sand | Die casting | Investment casting |
|---|---|---|---|
| Relative cost in quantity | Low | Lowest | Highest |
| Relative cost for a small number | Lowest | Highest | Medium |
| Permissible casting weight | Up to 1 ton | 60 lb | Ounces to 100 lb |
| Thinnest section castable (in) | 1/10 | 1/32 | 1/16 |
| Typical dimensional tolerance (in) | 0.012 | 0.01 | 0.01 |
| Surface finish | Fair to good | Best | Very good |
| Alloys that can be cast | Unlimited | Aluminum base and lower-melting metals preferable | Limited |
Two readings hold up regardless of the data’s age. Cost runs in opposite directions: the die is expensive to build and cheap to run, while a sand mold is cheap to make but has to be made again for every casting. And the headline tolerances are close together; the real difference is repeatability from part to part, which a steel die holds better than a mold that is rebuilt each cycle.
The same DOE report also shows how the industry divides the work: the various forms of sand casting made up about 60% of American castings by weight, permanent mold and die casting together about 20%, and investment casting about 7% (DOE, 1999). Sand dominates tonnage because iron and steel dominate tonnage, and most iron castings are sand cast.
NADCA puts the die-versus-investment trade-off in plain terms: die casting tooling costs more at the start, overall production costs are considerably lower in high volume, and die cast parts are generally more consistently precise because investment casting relies on gravity pouring (NADCA, die casting vs investment casting). This guide does not quote die or pattern prices; ask each supplier to itemize tooling separately from the piece price so the break-even can be checked.
Which alloys can each process cast?
Die casting is limited to nonferrous alloys with relatively low melting points, chiefly aluminum, zinc and magnesium. Green sand is the most alloy-tolerant route, taking iron and steel as well as nonferrous metals, and investment casting accepts a wide variety of alloys, including costly ones such as titanium.
According to NADCA, the bulk of North American die casting uses just four alloy families: aluminum, magnesium, zinc, and the zinc-aluminum grades. All of them melt well below copper-base metals, iron and steel, a property that makes them practical to shoot into steel dies (NADCA, introduction to alloys). Aluminum is shot on cold chamber machines, where a hydraulic plunger forces the metal into the locked die at high pressure (NADCA, cold chamber process); zinc runs on hot chamber machines.
Even within aluminum, the alloy usually changes when a part moves between processes. The Aluminum Association registers every casting alloy against the processes it is meant for, with the product codes D for die casting, P for permanent mold, S for sand and I for investment casting. The table below shows the split for the alloys most often seen on US drawings. The companion ASTM product specifications follow the same split: ASTM B26 for aluminum sand castings, B108 for permanent mold castings and B85 for die castings.
| Alloy | Registered for | Silicon | Iron | Copper | Magnesium |
|---|---|---|---|---|---|
| 356.0 | Sand and permanent mold | 6.5–7.5 | 0.6 | 0.25 | 0.20–0.45 |
| A356.0 | Sand and permanent mold | 6.5–7.5 | 0.20 | 0.20 | 0.25–0.45 |
| 380.0 | Die casting | 7.5–9.5 | 2.0 | 3.0–4.0 | 0.10 |
| A380.0 | Die casting | 7.5–9.5 | 1.3 | 3.0–4.0 | 0.10 |
The contrast is deliberate. The sand and permanent mold alloys keep iron and copper low and carry magnesium, which is what lets 356 and A356 respond to heat treatment. The die-casting alloys allow far more iron, which helps keep molten aluminum from soldering to the die steel, and add copper for strength in the as-cast condition. So a part drawn in A356 cannot simply be quoted as a die casting in the same alloy: the drawing alloy, and often the temper and property requirements, have to be reviewed. The ADC12 vs A380 guide covers how the Asian die-casting grade maps onto A380.
How do NADCA and ISO 8062-3 tolerances apply to each process?
NADCA’s Product Specification Standards are written for conventional high-pressure die castings, while ISO 8062-3 is a general casting standard, so a sand or investment casting should carry an ISO 8062-3 grade or explicit tolerances rather than a NADCA callout.
NADCA describes its standards manual as specification, design and production guidance for conventional high-pressure die castings, covering standard and precision tolerances, GD&T and quality provisions (NADCA, Product Specification Standards). A die-cast drawing can therefore say which NADCA tolerance level applies, standard or precision, for features left as cast.
ISO 8062-3 works differently. It assigns a dimensional casting tolerance grade (DCTG) and a machining allowance grade to the whole casting through one general note, whatever the process. The 2023 edition revised the title and scope, added definitions for draft angle, and replaced the grade DCTG 16 with DCTG 15wt to make the wall-thickness concept explicit (ISO 8062-3:2023; changes as summarized in BSI's record for BS EN ISO 8062-3:2023). If an older drawing still calls DCTG 16, update it before quoting.
Which grade each process can hold depends on the alloy, part size and foundry practice, and the grade tables sit inside the standard, which ISO sells; this page does not reproduce them. The practical rule: pick the grade your function needs, write it on the drawing, and ask each supplier to confirm in writing that it will hold that grade on the as-cast features. Tighten only the features that need it, and send those to machining. The ISO 2768 and NADCA tolerance guide shows how the general-tolerance note and the casting note fit together on one drawing.
When should a part move from sand casting to die casting?
Move when the forecast volume is high enough to spread the cost of a steel die, the part can be made in a die-casting alloy, and the design can be reworked for die casting’s thinner walls, draft and parting line.
Many programs start in sand for good reasons: a sand pattern is cheap and quick to change while the design is still moving, and the first units rarely justify hard tooling. The move to die casting is less a process swap than a redesign, and it goes more smoothly in steps:
- Freeze the function, not the geometry. List the features that matter: sealing faces, bores, mounting points and datums. Everything else can change to suit the die.
- Review the alloy. If the sand part is in A356 or another heat-treated grade, check whether an as-cast die-casting alloy such as A380 or ADC12 meets the strength and corrosion requirement, and change the drawing callout formally.
- Redesign for the die. Thin and even out walls, add draft, place the parting line and ejector pins where they do no harm, and replace sand cores with slides or machined features.
- Re-baseline tolerances. Swap the ISO 8062-3 grade for the NADCA level you need on as-cast features, and keep machining allowance only where a face will be cut.
- Settle the tooling terms before the die is cut. Write down who owns the die, where it is kept, who pays for maintenance and repair, and how it is released if you move the work. This is ordinary contracting practice, not something to leave to a quote footnote.
- Qualify the first die-cast lot. Run a first article inspection against the new drawing, including porosity checks on machined faces, before retiring the sand pattern.
When does investment casting beat both die and sand casting?
Investment casting wins on small, intricate parts in alloys a die cannot handle, such as carbon or stainless steel, and on complex shapes that would otherwise have to be welded up from several pieces.
NADCA notes that investment casting can economically produce extremely complex or unique parts that would otherwise need welding or other costly secondary processes, and that its one-time molds accept a wide variety of alloys (NADCA). The DOE profile adds that investment casting is noted for smooth, detailed surfaces and good dimensional accuracy, and is used for castings in expensive materials such as titanium (DOE, 1999).
The cost is in the cycle: every casting needs its own wax pattern and a ceramic shell built up in dipped and dried coats, so the piece price stays high even in quantity. For an aluminum or zinc part with the same geometry and a large annual volume, die casting is usually the better economic answer. For a stainless valve body, a steel lever with an integral boss, or a nickel-alloy part near its temperature limit, investment casting is often the only near-net option.
How should you source a casting program that spans more than one process?
Qualify each process on its own terms and send every supplier the same drawing package, with the alloy standard, the casting tolerance system and the machined faces stated explicitly.
Each process has its own failure modes: core shift and wall variation in sand castings, porosity on machined and sealing faces in die castings, fine-feature dimensions in investment castings. Put the matching inspection requirement on the drawing or purchase order.
If you are moving castings out of China to a supplier in Vietnam or elsewhere in Southeast Asia, ask each supplier to state which processes it runs itself and which it places with partners, and where the casting and the machining physically happen, because both affect inspection access and origin documentation. For our part: Saola runs CNC turning and milling at its lead CNC plant; die casting in ADC12 aluminum and Zamak 3 zinc, sand casting, stamping and surface finishing are placed with partner plants and managed by Saola, and the quote names the production site and origin. See the die casting page for the part families, or send a drawing for a quote and say which process you have in mind.
Frequently asked
Is die casting always cheaper than sand casting?
No. Die casting is cheaper per part only once the volume is high enough to spread the die cost. For small quantities, sand casting is usually the cheapest route because the pattern costs far less than a steel die.
Can steel parts be die cast?
Not in normal production. High-pressure die casting is built around aluminum, zinc, magnesium and similar lower-melting alloys. Steel parts are sand cast, investment cast, forged or machined.
Is investment casting the same as lost-wax casting?
Yes. Investment casting is the industrial form of the lost-wax process: a wax pattern is coated in ceramic, the wax is melted out, and metal is poured into the shell that remains.
Can I keep A356 when I move a sand-cast part to die casting?
Usually not. The Aluminum Association registers A356.0 for sand and permanent mold castings, not die castings, so the move normally means changing the drawing to a die-casting alloy such as A380 and checking that its as-cast properties meet the requirement.
Which tolerance note should a sand casting drawing carry?
An ISO 8062-3 casting tolerance grade and machining allowance grade, or explicit tolerances on each feature. NADCA tolerance levels are written for high-pressure die castings.
Sources
- Energy and Environmental Profile of the U.S. Metalcasting Industry, including Table 2-1 (comparison of casting methods) and Table 1-4, Energetics, Inc. for the US Department of Energy, Office of Industrial Technologies, September 1999
- Designations and Chemical Composition Limits for Aluminum Alloys in the Form of Castings and Ingot (Pink Sheets), The Aluminum Association, revised August 2025
- ASTM B26/B26M-18e1, Standard Specification for Aluminum-Alloy Sand Castings (scope), ASTM International, 2018
- ASTM B108/B108M-19, Standard Specification for Aluminum-Alloy Permanent Mold Castings (scope), ASTM International, 2019
- ASTM B85/B85M-18e1, Standard Specification for Aluminum-Alloy Die Castings (scope), ASTM International, 2018
- ISO 8062-3:2023, general dimensional and geometrical tolerances and machining allowances for castings (abstract), ISO, edition 2, 2023; summary of changes from the BSI Knowledge record for BS EN ISO 8062-3:2023
- Product Specification Standards for Die Castings, NADCA, accessed September 2026
- Die Casting vs Foundry Casting and Investment Casting, NADCA Design, accessed September 2026
- Introduction to Alloys, NADCA Design, accessed September 2026
- Cold Chamber Process, NADCA Design, accessed September 2026