Closed-die forging

The worked volume budget adds 80 cm³ finished part, 10 cm³ machining stock, 8 cm³ flash and trim, and 2 cm³ other loss. That gives 79.58 mm billet length at 40.0 mm diameter. A flashless route needs its own preform and loss budget, including the allowance for complete die fill.

Commercial use of closed-die forging often includes impression dies with flash. FIA uses the term for the enclosed, flashless variant. Specify the route and delivered condition. FIA, Product Design Guide for Forging, §5.2.2

Impressions, preforms and flash

In conventional impression-die forging, material fills shaped die cavities and excess material enters the parting-line flash region. Supplier DEECO describes flash cooling and restricting further outward flow, followed by trimming. Some geometries require preformed billets; a single finishing impression is not a universal process sequence. DEECO’s copper/aluminum examples should not be interpreted as a one-blow rule for steel, titanium or complex shapes. DEECO: closed-die forging

Enclosed impression dies do not deliberately provide a flash reservoir. FIA explains that workpiece volume must be tightly controlled to fill the cavity without extreme pressures. Small clearance fins remain possible. Near-net forging may still produce flash. FIA guide, §§5.2.2.2–5.2.2.3

For either route, review how the billet is distributed into ribs, bosses, webs and flanges. Adequate total volume does not prove that material can reach every cavity. Preform geometry, placement, die geometry and the forming sequence determine the available flow paths. A billet-volume check is an input to process development, not proof of complete fill. Van Tyne and Walters, Understanding Geometrical Forging Defects, April 2007

Geometry and thermal processing

Agree the parting line, die-opening direction, draft, radii, transitions and machining locations with the forger before freezing the finished-part design. A sharp finished corner may need to be machined from a more generous forged transition. Likewise, a finished hole may be drilled or machined from a pierced or solid region. Do not assume every CAD surface is reproduced directly by the impression.

The forging drawing and the finished drawing serve different purposes. ASM’s 2005 handbook chapter distinguishes machining stock, die wear, die match, die closure/thickness, straightness, radii and flash-extension tolerances. One general “forging tolerance” cannot describe all these effects. Define datums and inspection stages so that material remains available around the complete finished envelope. ASM, Forging Design Dimensions and Tolerances, Vol. 14A, pp. 820–823

Closed-die describes tooling confinement rather than a universal temperature. A quotation should identify the alloy and incoming condition, hot/warm/cold route where applicable, heating controls, forming sequence and post-forging thermal condition. The final properties need to match the actual section and heat treatment. FIA’s property discussion explicitly notes effects of section size, hardenability, heat treatment and cooling history. FIA guide, §3.6.2 and Table 3-3

Grain flow is a design variable

Forging can orient material flow around the component, but the useful direction must correspond to the loads and final geometry. FIA relates flow optimization to loading and describes etched flow lines associated with oriented constituents. Directional properties still require verification. FIA guide, §3.2.1 and glossary

Machining can change the relationship between the forged flow pattern and the final surface. Where directional behavior is important, agree the required flow pattern, retained envelope and specimen location/orientation. Neither a favorable macroetched picture nor the word “forged” establishes a fatigue allowable, defect-free interior or the properties of every local section. Request the evidence appropriate to the application.

Laps, incomplete fill and process development

Van Tyne and Walters distinguish several mechanisms for laps: material flowing into itself, flow-by, and peeling at a tooling contact. Their examples show that die and preform changes can prevent the defect. Underfill and shape errors likewise require examination of the process rather than assuming that additional force or billet mass will solve every problem. Die deflection, wear and placement also belong in diagnosis. April 2007 article, pp. 1–4

Transvalor’s May 1, 2018 FORGE description identifies forging-sequence development, defect prediction and yield optimization as simulation uses. Simulation can compare candidate routes before tooling trials; the result remains dependent on its material, thermal, friction and tooling inputs. Agree how predicted fill, loads and flow are checked against actual trial forgings. Transvalor: FORGE for closed-die forging

Original bounded billet-volume example

Assume a room-temperature volume budget for a hypothetical forging is:

For a cylindrical billet of 40.0 mm diameter, ignoring end shape and dimensional variation:

length = 100,000 / [π × 40.0² / 4] = 79.58 mm

The assumed finished-volume yield is 80 / 100 = 80%. A 1.0 mm cut-length change at that diameter changes billet volume by 1.257 cm³, or 1.257% of the nominal budget. This illustrates why cutoff control matters; it establishes neither an acceptable tolerance nor the flash volume needed for filling.

Removing the assumed 8 cm³ flash term does not automatically produce a valid 92 cm³ flashless billet. The enclosed route may require different preforms, machining stock and losses. Also distinguish cold billet dimensions from hot cavity dimensions and account for actual density if converting the budget to mass. These assumptions are arithmetic examples, not a production recipe or press-tonnage calculation.

Inspection and release

Specify material traceability, final heat-treatment condition, dimensional inspection after the relevant operations, and any required mechanical or metallographic tests. Separate surface examination from internal examination and state acceptance criteria rather than merely requesting “NDT.”

For steel forgings, ASTM A275/A275M-23 addresses magnetic-particle examination and explicitly does not supply acceptance standards or recommended quality levels. ASTM A388/A388M-26 addresses ultrasonic examination of steel forgings and requires the ultrasonic quality level to be stated in the order. These are scoped examples, not instructions to apply either method to every alloy or geometry. ASTM A275/A275M-23, ASTM A388/A388M-26

Define whether indications, surface cleanup, remaining machining stock and final dimensions are assessed before or after heat treatment, trimming and machining. Establish permitted repair or removal procedures contractually. A passing external dimension cannot establish internal soundness, and a material certificate alone does not verify local fill or flow.

The manufacturing handoff should include finished and forging drawings, material specification and edition, quantities, load-critical regions, machining datums, retained stock, thermal condition, inspection stages and acceptance requirements. DEECO’s offered machining, surface finishing and plating illustrate that delivery may include secondary operations; agree which are actually included. DEECO service scope

The FIA PDF and DEECO page have no independently verified technical issue date here. The ASM chapter is published in 2005, the defects article prints April 2007, and Transvalor prints May 1, 2018; these dates identify the cited material rather than a universal current process specification.

Related reference

Manufacturing processes