Fine blanking
Three-force fine blanking, functional edge quality, tool and material dependencies, secondary operations and production acceptance.
Tags: processes, shaping, blanking
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An ideal 4.00 mm section with 0.25 mm rollover and 0.15 mm fracture has 3.60 mm of continuous shear if the remaining height is uninterrupted. That is 90% of thickness but falls 0.20 mm short of a 3.80 mm functional contact requirement. Check the specified sections around the contour and measure projecting burr separately.
Feintool's three-force tooling uses vee-ring holding force and counterforce to restrain the sheet before cutting. Smaller conventional die clearance alone cannot reproduce that restraint. Feintool: process schematic, printed pp. 4–5
Three forces and the tooling system
| Function | Role in the route | Information to request |
|---|---|---|
| Cutting punch | Separates the required contour | Cutting geometry, stroke and capacity for the actual part |
| Vee-ring/blank holder | Indents and restrains surrounding material | Ring arrangement, force and permitted witness locations |
| Counterpunch | Supports the component during separation | Counterforce, motion and ejection sequence |
The three actions must be compatible with the tool and press. Feintool also describes combining fine blanking and forming in progressive tooling. The result can reduce subsequent operations, but a brochure's ready-to-install claim does not establish that heat treatment, cleaning, deburring or final sizing is unnecessary for a particular drawing. Feintool: combined process capability
Ask the supplier to identify which features are blanked, pierced, formed, coined or machined, and in which operation. The finished-part model alone does not show the strip carrier, scrap bridges, ring impressions or loading/ejection needs. Freeze those interfaces with the tool designer before treating a quotation as a production commitment.
A smooth edge is not the whole acceptance requirement
Distinguish the useful sheared zone, entry rollover or die roll, any fractured region, and exit burr. Define the contact length and edge geometry actually needed for a bearing, tooth flank or locating feature. A nominal through-thickness dimension can pass while the intended working edge is too short or locally interrupted.
Nürnberger and colleagues' original study, published November 19, 2022, compares vee-ring arrangements using 6 mm S355MC sheet and nominal 60 mm disks. It evaluates cut-surface characteristics, surface hardness and residual stresses as separate outcomes. This is evidence that the tool configuration affects more than external size; it is not a transferable fatigue allowable for every fine-blanked gear. Original study: scope and experimental setup
The study uses a 0.5% relative die clearance: its nominal 60 mm die and 59.94 mm punch differ by 0.06 mm in diameter, corresponding to 0.03 mm per side for 6 mm sheet. The distinction between diametral difference and radial clearance matters. These are the paper's test dimensions, not recommended production settings. Tool edge preparation, blanking versus piercing and material state must remain part of the selected route. Same study, §4.2
For drawing release, identify whether rollover, burr or a ring witness can remain on a functional surface. State the measuring direction and permitted edge treatment. Deburring can change a small functional corner, so define the finished condition rather than approving an unspecified cleanup operation.
Material, lubrication and tool condition
Specify grade, incoming condition, thickness tolerance, surface and rolling direction. Do not use the strength associated with rolled stock as proof of finished-part performance after local deformation, subsequent heat treatment and finishing. Confirm the actual material range used for qualification.
Feintool's lubricant guide treats friction as a system involving tool steel/coating, work material and lubricant. It identifies wear and breakage of contact elements as tool-life limits, and explicitly says that lubricant recommendations alone do not guarantee correct functioning: tool machining/coating, cutting speed and material condition also matter. A named oil or its viscosity is therefore not a complete process specification. Feintool: lubrication guide, printed pp. 2–5
Record the qualified lubricant application, tool condition and maintenance interval. Compare parts across that interval and after tool service. A first-off sample from fresh tooling does not establish sustained dimensional or edge capability. Include lubricant removal and compatibility with subsequent coating, bonding or cleanliness requirements in the agreed route.
Secondary features and route economics
Precision Resource describes progressive tooling that combines forms, bends, coining, countersinks and counterbores. Its supplier guidance also states that achievable tolerances depend on material, thickness, geometry and volume. These capabilities support evaluating feature integration, rather than assuming every feature can be completed in one station. Precision Resource: tooling and application limits
Compare cost through the accepted final part: dedicated tooling, strip utilization, setup, production rate, maintenance, secondary processing and inspection. Precision Resource identifies part-specific tooling cost as a reason some low-volume jobs are unsuitable. Include a production quantity and replenishment pattern when comparing fine blanking with machining or another route. Same supplier: production-volume guidance
Original functional-edge calculation
Assume a hypothetical 4.00 mm sheet section has 0.25 mm entry rollover and 0.15 mm fractured region, measured as distinct non-overlapping portions along thickness. Suppose the remaining region is verified smooth shear, with no other interruptions:
useful shear height = 4.00 − 0.25 − 0.15 = 3.60 mm
sheared fraction = 3.60 / 4.00 = 90%
If the drawing requires 3.80 mm continuous functional contact, this section falls short by 0.20 mm, despite its 90% sheared fraction. A percentage requirement and an absolute functional height are different requirements. An exit burr projecting beyond the sheet is measured separately; it is not simply subtracted from sheet thickness in this model.
Define sectioning, sampling locations and treatment of discontinuities. Establish load, tool life and fatigue evidence separately.
Production handoff and acceptance
Supply four groups of information:
- Material: grade/specification and edition, incoming condition, thickness range, surface, rolling direction and traceable lot.
- Final geometry: datums, profiles and hole locations, flatness, functional edge height/squareness, rollover/burr limits and permitted witnesses.
- Route: press/tool configuration, integrated forming features, secondary operations, heat treatment, cleaning and finishing.
- Acceptance: measurement stage and locations, sampling, relevant hardness/material or functional tests, and evidence across tool-service intervals.
Separate dimensional conformance, flatness, edge condition and application performance. A smooth cut surface does not itself establish a fatigue rating or the adequacy of every local feature. Confirm the delivered condition against the drawing and contract.
The Feintool technology brochure prints FIH 500.E.03.2019 on its back cover; the lubricant brochure prints FIH 350.E.07.2020. Retain these document codes separately from the embedded lubricant product-information sheets dated January 20, 2020. The live supplier pages have no separately verified issue date. The research paper has its own verified publication date. The functional-edge calculation and handoff structure are original.