Binder jetting builds sand molds and cores directly from CAD data. A recoater spreads a thin layer of foundry sand, a print head jets liquid binder wherever the mold should be solid, and the process repeats until the job box is full. The unbound sand is then removed, and the printed mold sections and cores are assembled, coated where needed and poured with molten metal in a foundry, just like conventional sand molds. The result is a metal casting; the printed sand is a consumable tool that is broken away after pouring.
Choose printed sand molds for prototype castings, single pieces and small series of complex parts: pump housings, impellers, valve bodies, manifolds and cylinder heads with intricate cores. Because no pattern or core box is needed, the first castings can be poured soon after design release, and a design change only requires a new print. The limits are a higher cost per mold than conventional molding at volume, a sand-cast surface and the usual foundry constraints on wall thickness, feeding and shrinkage. On Uretyco, sand and investment casting are available on request; feasibility, alloy and the foundry route are confirmed in quote review.
Mold and casting properties
| Property | Typical value | Notes |
|---|---|---|
| Layer thickness | ≈ 0.25–0.4 mm | Machine- and sand-dependent; thinner layers resolve finer detail but build more slowly. |
| Sand grain size | ≈ 0.1–0.25 mm mean | Finer sand gives smoother casting surfaces but lower permeability for venting gases. |
| Sand types | Silica; ceramic and other specialty sands | Silica is standard; specialty sands with lower thermal expansion or higher refractoriness suit steel and demanding castings. |
| Binder systems | Furan, phenolic or inorganic | Chosen by the foundry to suit the alloy and pouring temperature; see the section on sands and binders. |
| Draft angles | Not required | No pattern is drawn from the mold, so zero-draft walls and undercuts are possible. |
| Minimum cast wall | ≈ 3–5 mm for aluminum and iron | Set by metal flow in sand, not by the printer; steel needs thicker walls. |
| Internal passages | Possible with printed cores | Cores need openings in the casting for location, venting and removing the sand after pouring. |
| As-cast surface | ≈ Ra 6–25 µm | Depends on sand grain, mold coating and alloy; machined faces are specified separately. |
| Casting tolerances | Per ISO 8062-3, agreed with the foundry | Printed molds have no pattern wear and reduce core shift; the tolerance grade depends on alloy, size and foundry practice. |
| Casting alloys | Aluminum, cast iron, steel, copper alloys | Available alloys depend on the foundry and are confirmed in quote review. |
| Mold size | Machine-dependent | Large molds are printed in sections and assembled before pouring. |
Values describe printed sand molds and typical sand castings and vary with the printer, sand, binder, coating, alloy and foundry practice. The mechanical properties of the part come from the alloy and the casting process, not from the mold: design to the alloy standard, for example EN 1706 or ASTM B26 for aluminum castings and EN 1561 or EN 1563 for gray and ductile iron, and agree on test bars or specimen tests where they matter.
Designing castings for printed sand molds
The printer removes most pattern and core-box constraints, but the part is still a sand casting. Design the casting, not the mold: the foundry adds gating, risers and shrinkage allowance and splits the mold into printable sections. Practical rules:
- Upload the casting: provide the as-cast geometry with machining allowances, or the finished part with the faces to be machined marked. Supply a mold design only if you have developed one with a foundry.
- Uniform walls: keep sections as even as possible, blend transitions gradually and core out heavy bosses, because thick sections and abrupt changes cause shrinkage porosity.
- Free form without draft: printed molds need no draft and allow undercuts and complex parting, so features that conventional molding cannot form can be cast in one piece.
- Cores and core removal: every internal passage needs openings in the casting for core prints, venting and removing the sand after pouring. Closed internal cavities cannot be cast.
- Slender cores: long, thin cores can break during handling or float and shift in the molten metal; give them enough section and support, or discuss alternatives with the foundry.
- Machining stock: add allowance on sealing faces, bores and datum features, and give a datum scheme so that the casting can be clamped and machined reliably.
Sands and binders
Silica sand is the standard printing medium; specialty sands with lower thermal expansion or higher refractoriness are used for steel and for castings prone to sand defects. The binder determines mold strength, gas evolution during pouring and how easily cores break down afterward. The foundry normally selects the system to suit the alloy:
| Binder system | Characteristics | Typical use |
|---|---|---|
| Furan resin | Acid-cured; good strength and accuracy; releases gases during pouring, so molds need venting | The most widely used system; aluminum, iron and many steel castings |
| Phenolic resin | Usually heat-cured after printing; good stability at high pouring temperatures | Steel and other high-temperature alloys |
| Inorganic (silicate-based) | Very little smoke and odor during pouring; cores break down easily; sensitive to humidity | Mainly aluminum castings, such as engine and structural parts |
Tolerances and surface
Casting tolerances depend on the alloy, part size and foundry and are confirmed in the quote and order review. Specify them with a casting tolerance standard such as ISO 8062-3 and put tight tolerances only on machined features, which can be toleranced like CNC parts; Uretyco's default for unspecified machining tolerances is ISO 2768-mK. Printed molds reproduce the CAD geometry without pattern wear and reduce core shift, but metal shrinkage, mold expansion and casting distortion still apply. As-cast surfaces show the sand grain; call out Ra only on machined faces that need it.
Finishing options
After pouring and cooling, the mold is broken away and the casting is cleaned. Further steps depend on the alloy and the function and are agreed in the quote.
| Finish | Effect | Notes |
|---|---|---|
| Shakeout, cut-off and fettling | Removes sand, gates, risers and flash | Standard for every sand casting; contact points are ground flush. |
| Shot blasting | Clean, uniform surface | Removes residual sand and scale; the common base finish. |
| Heat treatment | Required mechanical properties | For example T6 for A356 or annealing for steel; quenching can distort thin sections. |
| CNC machining | Fits, sealing faces, bores and threads | Needs machining allowance and a datum scheme on the drawing. |
| Impregnation | Seals porosity | For pressure-tight parts where the specification allows it. |
| Paint or powder coat | Corrosion protection and color | Castings are often pre-baked to avoid defects from gas escaping through porosity. |
Because no pattern is involved, a design change only means printing a new mold. Use the first castings to check wall thickness, soundness and machining stock before ordering more, and request a first-article inspection if the part will be repeated.
Cost and lead-time drivers
Printed molds replace the one-time pattern cost with a cost per mold, which is why they suit single pieces and small series. The main levers:
- Mold volume and job box use: printing is priced largely by the sand volume and build time a mold occupies, so compact casting layouts and printing several molds together lower the cost.
- Quantity: without pattern cost, the first castings are economical; at higher quantities, a conventional pattern with machine molding costs less per part.
- Alloy and foundry work: pouring, shakeout, fettling, heat treatment and machining often outweigh the printed mold in cost and lead time; steel needs special sands and coatings.
- Cores and assembly: multi-part molds and many cores add assembly and inspection work.
- Quality scope: first-article inspection, measurement reports, X-ray or pressure tests and material certificates are opt-in and must be part of the order scope. Feasibility and lead time are confirmed in quote review.
Printed sand molds vs. other casting routes
| Route | Tooling | Typical quantity | Surface and detail | Geometric freedom | Notes |
|---|---|---|---|---|---|
| Printed sand mold (binder jetting) | None; molds printed from CAD | Single pieces to small series | Sand-cast surface | Very high: complex cores, no draft | Higher cost per mold |
| Sand casting with a pattern | Pattern and core boxes | Small to large series | Sand-cast surface | Limited by draft, parting line and core boxes | Lowest cost per mold once the pattern exists |
| Investment casting | Wax-pattern tooling, or printed patterns for prototypes | Small to large series of smaller parts | Fine detail, smooth surface | High, but part size is limited | Wide alloy range including steels |
| CNC machining from solid | None | Single pieces to medium series | Best | Limited by tool access | No casting risk; material waste on large parts |
| Metal 3D printing (for example AlSi10Mg) | None | Single pieces, small parts | Rough, with fine detail | Highest | Expensive for large or heavy parts |
Printed molds bridge the gap between machining from solid and pattern-based casting: they make one-off and prototype castings practical and are often used before a conventional pattern is built. Investment casting gives finer surfaces on smaller parts, and printed wax or castable resin patterns play the same prototype role there.
When not to choose printed sand molds
Large series of the same casting: a conventional pattern pays off quickly. Small, finely detailed parts with walls below about 3 mm: consider investment casting or metal printing. Parts that machine economically from bar or plate. Designs not yet adapted to casting, with uneven walls, closed cavities or no way to remove core sand. Parts that need tight tolerances everywhere without machining.
Typical applications
- Prototype castings for pump housings, impellers and valve bodies.
- Cylinder heads, engine blocks and intake manifolds in development, with complex cores.
- Spare parts whose original pattern is lost or worn.
- Small series of large castings for machinery and energy equipment.
- Printed cores combined with conventional molds for complex internal passages.
- Sculptural and architectural castings.
Specifying printed sand castings on Uretyco
- 1Upload the casting model and a drawing
STEP of the as-cast part with machining allowances, or of the finished part with machined faces marked. Add a PDF drawing with datums, tolerances and the casting tolerance standard.
- 2State the alloy and condition
For example A356-T6 (EN AC-42100), EN-GJS-400-15 ductile iron or a cast steel grade, each with its governing standard.
- 3Describe quantity and stage
Prototype, single piece or small series, and whether a conventional pattern may follow; this decides between printed and conventional molds.
- 4Define quality requirements
Pressure or leak tests, X-ray, first-article inspection, measurement reports and material certificates are opt-in and should be requested at quote time.
- 5Request casting and review the quote
Sand and investment casting are available on request. Feasibility, the foundry route, the alloy and lead time are confirmed in quote review before an order is placed.
FAQ
Do I receive the sand mold or the casting?
Normally the cast metal part. The printed mold is a consumable tool that is destroyed when the casting is removed. If you need printed molds or cores for your own foundry, state it in the request; feasibility is checked in quote review.
How accurate are castings from printed molds?
Comparable to good sand castings, often with less core shift and mold mismatch because the mold comes directly from CAD data. Specify a tolerance grade under ISO 8062-3 for as-cast features, and have fits, sealing faces and bores machined.
When should I switch to a conventional pattern?
Once the design is stable and the casting is ordered repeatedly. Printed molds suit prototypes, design iterations and small series; at higher quantities, a pattern and machine molding lower the cost per part. If you state the expected annual quantities, the quote can compare both routes.
Which binder should I choose?
Usually the foundry decides based on the alloy, the casting size and its own process. Furan is the most common choice, inorganic binders suit low-emission aluminum casting, and phenolic binders are used for steel. State the alloy and any emission or cleanliness requirements, and leave the binder open unless your specification fixes it.
Related resources
- Aluminum A356 (Cast)A common alloy for sand castings.
- Molding & Casting OverviewWhen tooling pays off, and shared design rules.
- Die CastingHigh-pressure casting for large volumes.
- Castable ResinPrinted patterns for investment casting.
- Quality Control & InspectionFirst articles, reports and certificates.
- Technical Drawings & TolerancesDatums, allowances and critical dimensions.
Related materials
Composites
Full-Color Gypsum
Gypsum-based powder printed with colored binders, so full-color models come straight from the printer. Ideal for presentation, architectural and concept models; brittle and moisture-sensitive, so not for functional or frequently handled parts.
Metals
Aluminum 6061-T6
Versatile, weldable aluminum alloy with great machinability, anodizing quality, and corrosion resistance. One of the most common CNC materials.
Metals
Aluminum 7075-T6
High-strength Al-Zn-Mg-Cu alloy with roughly 1.7–1.8× the strength of 6061-T6. Machines very well but needs a protective finish and is not weldable. The choice when strength-to-weight matters most.
Metals
Stainless 304
The default austenitic stainless steel: excellent corrosion resistance indoors and in fresh water, well suited to food equipment and widely stocked. Slower to machine than aluminum because it work-hardens.
Metals
Stainless 316L
Molybdenum-alloyed, low-carbon austenitic stainless with much better chloride resistance than 304. The standard grade for marine hardware, pharmaceutical and process equipment, and welded parts in corrosive service.
Metals
Steel 1018
Low-carbon mild steel that machines and welds easily and costs little. The default steel for brackets, fixtures, pins and prototypes, provided it gets a finish: bare 1018 rusts.
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