Sand casting
Sand-mold casting routes, cores and feeding, dimensional allowances, downstream operations and application-specific acceptance.
Tags: processes, shaping, casting
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ISO 8062-3:2023 covers general tolerances and machining allowance grades for indicated casting dimensions. Its scope excludes undimensioned 3D CAD models, angular tolerances and cylindricity. Agree the grades, individual controls and inspection criteria with the foundry. Pattern contraction allowance and feeding for solidification shrinkage address separate problems. ISO 8062-3:2023 scope
Patterns form the external cavity and separate cores form internal surfaces. Foseco distinguishes horizontal cope-and-drag molds from vertical mold strings. Foseco: green sand casting
Specify the mold and core route
Green sand is a sand, clay and water system; “green” refers to its moisture-bearing, uncured condition. Its composition and molding controls affect the cavity presented to molten metal. A green sand mold can contain pre-cured cores, so the mold and core binder systems need not be identical. Foseco: green sand materials and cores
Chemically bonded molds and cores use different hardening mechanisms. Foseco distinguishes self-hardening systems, commonly called no-bake, from triggered systems activated by heat or gas. Shell molding and cold-box coremaking are examples within this broader family, not synonyms for all sand casting. Organic and inorganic binder choices also affect handling, gas generation, breakdown and reclamation. Select them with the foundry for the alloy, geometry and production route rather than treating binder substitution as an administrative change. Foseco: chemically bonded sand casting
Printed sand changes how the mold or core is made. ExOne describes selectively bonding successive sand layers directly from CAD, eliminating a physical pattern or core box for those printed elements. Printed cores can also be combined with conventional molds. The printed object is tooling for the subsequent metal casting; printer resolution does not become a guaranteed metal-part tolerance or internal soundness level. ExOne: sand molds and cores
State the alloy and delivery condition separately from this route. An aluminum casting, a ductile iron casting and a heat-treated steel casting require different material specifications and acceptance evidence even if all use sand molds.
Design the casting and the manufacturing features together
A parting surface and withdrawal direction establish how a conventional pattern leaves the mold. Draft, fillets and radii must be coordinated with functional geometry. In its steel hitch-housing tutorial, the Steel Founders' Society of America (SFSA) evaluates orientation, draft, sharp transitions and isolated heavy sections before adding the feeding and gating system. Those choices are specific design decisions; a draft value illustrated for that housing is not a universal rule for every alloy, mold or depth. SFSA: An Example in Steel Casting, pages 4–10
For a core-defined passage, communicate the required finished opening, wall around it and its relationship to machined datums. Ask the foundry to resolve support and location, assembly variation, removal access and cleanliness. A passage that can be formed but cannot be cleared or inspected may fail the intended function. Identify which holes are cast, drilled afterward or cast undersize for machining.
The gating system conveys metal into the cavity; risers are reservoirs that supply additional liquid metal during solidification. SFSA's tutorial treats flow paths, turbulence, isolated hot spots and feeder placement as connected decisions. Merely adding a larger riser does not demonstrate that a remote heavy section remains feedable. SFSA: steel casting tutorial, pages 10–19
Separate shrinkage, allowance and tolerance
Haworth distinguishes solidification shrinkage, addressed through feeding and chills, from subsequent thermal contraction, addressed through patternmaker's allowance. Its discussion concerns foundry planning; it does not justify applying one percentage to every dimension or treating volumetric shrinkage as a linear scale factor. Local restraint and the actual casting route must be considered by the foundry. Haworth: Shrinkage in sand casting, 12 May 2015
Machining allowance is additional metal reserved for removal. Tolerance is the permitted variation of the specified feature. Keep finished-part dimensions and as-cast delivery requirements distinguishable, including which surfaces will remain as cast and which establish machining locations.
ISO 8062-3:2023, edition 2, specifies general dimensional and geometrical tolerances and machining allowance grades for castings using ± tolerances for indicated dimensions. Its scope excludes undimensioned 3D CAD models, angular dimensional tolerances, cylindricity and other position tolerances. Referencing it is therefore not a complete definition of every requirement on a complex casting. Agree the applicable grades and individual controls with the foundry. ISO 8062-3:2023
Original machining example. Assume an invented concentric ring whose finished outside diameter is 100 mm and bore is 60 mm. Reserve a hypothetical 2 mm radial machining allowance on each cylindrical surface:
| Feature | Finished | Nominal as-cast target |
|---|---|---|
| Outside diameter | 100 mm | 104 mm |
| Bore diameter | 60 mm | 56 mm |
| Radial wall | 20 mm | 24 mm |
The 2 mm allowance changes each diameter by 4 mm. If the outside diameter is 1 mm below its as-cast target and the bore is 1 mm above its target, ideal concentric radial stock is 1.5 mm on each surface. That result assumes perfect location, roundness and straightness. Core shift or other geometric variation can consume local stock even when both measured diameters meet a size limit. This example selects no production tolerance or pattern contraction factor and proves no cleanup capability.
Delivery condition and acceptance
Separate shakeout and core removal, gate/riser removal, cleaning, heat treatment, repair and machining responsibilities. Define the stage at which dimensions and material properties apply. Specify whether any weld repair or impregnation is permitted and what approval and reporting it requires; do not infer permission from the process name.
For example, ASTM B26/B26M-25 covers aluminum-alloy sand castings for general-purpose applications. Its public scope warns that it may not address the mechanical properties, integrity testing and verification required for highly loaded or safety-critical applications. Naming a material standard therefore does not remove the need to specify application-specific requirements. ASTM B26/B26M-25
Haworth's inspection overview separates composition checks, radiography for internal indications and penetrant examination for surface discontinuities, with test selection and frequency driven by customer requirements. These methods answer different questions. An acceptable surface does not establish internal soundness, and an image alone supplies no agreed rejection threshold. Haworth: Casting testing and inspection, 4 December 2014
A useful manufacturing handoff contains the controlled model and drawings, alloy/condition/product-standard edition, mold/core route, critical walls and passages, finished versus as-cast dimensions, datum and machining strategy, permitted repairs, and inspection methods, locations, acceptance levels and sampling. Confirm capability on the actual component and delivery condition rather than adopting a generic process tolerance or defect-free claim.
Source versions
Reviewed 2026-11-01. ISO's record identifies edition 2, February 2023; ASTM identifies B26/B26M-25 as active. The Haworth articles display the dates above. No separate technical issue date was verified for the cited Foseco/ExOne live pages or SFSA tutorial; website copyright years and PDF hosting dates are not treated as editions. The ring example and handoff recommendations are original.