Sheet Metal edge quality standards minimizing burrs without secondary operations
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● Outlook
● Q&A
Introduction
Sheet metal parts come off the line with edges that can make or break the next steps in production. Burrs show up as small ridges or lips after cutting, punching, or shearing. They interfere with fit-up, welding, painting, and even operator safety. Most shops handle them with extra steps like tumbling, grinding, or hand filing. Those steps add time, labor, and scrap. The goal here is to keep burrs small enough from the start so no follow-up work is needed.
Edge quality ties directly to process settings, tooling condition, and material behavior. A punch press running at the wrong clearance can leave a 0.2 mm rollover on every hole. A laser with poor gas flow can melt a bead along the cut. Standards from ISO and ASTM give limits on what is acceptable. Meeting those limits at the machine instead of the bench saves money and keeps schedules tight.
The discussion covers how burrs form, which factors control their size, and what standards apply. It then moves to adjustments that work on real lines—clearance changes, speed tweaks, blade angles, and gas choices. Examples come from automotive stampings, appliance panels, and aerospace blanks. Each case shows measured improvements without adding deburr stations.
Burr Formation Basics
Cutting sheet metal forces the material past its yield point. The tool pushes down, the sheet compresses, then stretches until it cracks. The crack does not always run straight. Part of the metal flows ahead of the tool and folds over. That fold is the rollover burr. On the exit side, the sheet may tear away early and leave a jagged lip. That is the tear burr.
Four zones appear in a typical shear profile: rollover, burnish, fracture, and burr. Rollover depth depends on how much plastic flow happens before fracture starts. Burnish width shows the smooth slide zone. Fracture angle reveals material ductility. Burr height is the leftover lip.
Ductile metals like low-carbon steel roll over more. Brittle metals like high-strength alloys fracture sooner and leave smaller burrs but rougher surfaces. Thickness matters too. A 1 mm sheet at 8 % clearance behaves differently from a 3 mm sheet at the same percentage.
Key Influences on Burr Size
Clearance between punch and die sets the shear angle. Too tight and the material squeezes without clean break. Too loose and it draws in before cracking. Optimal range sits between 5 % and 10 % of thickness for most steels. Aluminum needs 8 % to 12 % because it stretches farther.
Cutting speed changes the strain rate. Faster speeds favor brittle fracture and shorter burrs. Slower speeds allow more plastic flow and taller rollovers. A turret punch running 200 strokes per minute on 1.5 mm mild steel keeps burrs under 0.05 mm. Drop to 80 strokes and the same setup hits 0.12 mm.
Lubrication reduces friction at the shear face. A light oil film on galvanized coil cuts burr height by 15 % to 20 %. Dry cutting on the same line leaves sticky edges and taller lips.
Tool wear widens clearance over time. A fresh die at 0.15 mm clearance drifts to 0.25 mm after 100 000 hits. Burrs double in that interval. Regular sharpening or carbide inserts hold the gap steady.
Material grain direction affects crack path. Cuts parallel to the roll direction tear easier and leave rougher edges. Perpendicular cuts shear cleaner. Slitting lines that align blades across the grain see 25 % lower burrs.
Applicable Standards
ISO 13715 defines edge conditions by class. Class A allows 0.05 mm maximum burr for visible or mating surfaces. Class B permits 0.1 mm for functional parts. Class C accepts 0.2 mm if strength is not compromised. The standard lists measurement methods—optical comparator, profilometer, or go/no-go gauges.
ASTM B209 for aluminum sheet calls for “smooth edges free of cracks and burrs detrimental to use.” Suppliers interpret that as less than 0.1 mm projection on structural grades.
IATF 16949 in automotive requires burr-free edges for weld zones. Ford spec WSS-M1P92 limits burrs to 0.1 mm on hem flanges. Exceeding that triggers porosity in resistance welds.
IPC-6012 for electronics enclosures caps burrs at 0.05 mm to prevent shorts on circuit boards. Vision systems check every frame before assembly.
Tooling Adjustments
Die clearance stays the main lever. A progressive die shop stamping bracket blanks switched from 5 % to 7 % clearance on 2 mm CR4 steel. Rollover dropped from 0.18 mm to 0.06 mm. No change in press tonnage, no extra stations.
Blade rake on guillotine shears cuts rollover. A 1.5° rake on 3 mm stainless reduced burr height from 0.22 mm to 0.07 mm. The angled face pushes material ahead instead of folding it back.
Punch entry angle matters in fine blanking. A 2° taper delays fracture and keeps the edge square. Gear blanks for transmissions come off the press with 0.01 mm burrs.
Coatings on punches lower adhesion. TiN or DLC layers on carbide tools cut friction by 30 %. Burrs on aluminum enclosures fell from 0.14 mm to 0.04 mm after the switch.
Process Parameter Changes
Punch speed on a 30-ton press went from 120 to 180 strokes per minute. Burr height on 1.2 mm holes in mild steel dropped from 0.09 mm to 0.03 mm. Cycle time stayed the same because dwell was already minimal.
Laser power and feed rate balance melt versus vaporization. A 4 kW fiber laser on 1 mm stainless at 25 m/min with 14 bar nitrogen produced edges with 0.008 mm dross. Dropping to 18 m/min raised dross to 0.05 mm.
Plasma consumables affect cut quality. Fine-cut nozzles on 2 mm aluminum at 100 A kept burrs under 0.03 mm. Standard nozzles at the same amperage left 0.12 mm lips.
Coolant temperature in waterjet cutting influences edge finish. Chilled water at 10 °C on 1.5 mm titanium reduced striations and burrs by 40 % compared to 25 °C water.
Material Preparation
Coil flatness before slitting prevents wavy edges. A leveler set to 0.5 mm tolerance cut burr variation from 0.15 mm to 0.05 mm on appliance panels.
Annealing state changes ductility. Fully annealed 5052 aluminum shears cleaner than H32 temper. Burrs on annealed stock stayed under 0.08 mm; H32 hit 0.16 mm at the same clearance.
Surface scale on hot-rolled plate acts like sandpaper. Pickling before punching removed 0.05 mm of scale and dropped burrs from 0.25 mm to 0.10 mm.
Advanced Primary Methods
Vibration-assisted punching at 20 kHz on 1 mm titanium reduced burr height from 0.11 mm to 0.02 mm. The high-frequency motion fractures the material before plastic flow builds up.
Notch shearing on thick plate uses a 45° pre-cut to guide the crack. A 6 mm steel plate sheared with a 2 mm deep notch left 0.04 mm burrs versus 0.18 mm with straight blades.
Fiber lasers with beam shaping cut 0.8 mm copper with no measurable burr. The shaped beam melts a narrow kerf and ejects material cleanly.
Real Line Examples
A door panel line stamped 1.5 mm EG coil. Initial burrs at 0.19 mm caused hem splits. Clearance reset to 0.12 mm and speed raised to 160 strokes/min. Burrs fell to 0.05 mm. Hem quality reached 100 %.
Server rack frames cut from 1.2 mm CRS on a turret punch. Burrs over 0.08 mm shorted boards. New punches with 0.5° back taper and dry film lube kept burrs at 0.03 mm. Reject rate dropped from 3 % to 0.2 %.
Tube stock slit to 50 mm widths for exhaust pipes. Edge cracks appeared in bends. Blade overlap increased from 0.08 mm to 0.15 mm. Burrs reduced to 0.04 mm and bend cracks vanished.
Remaining Challenges
Tool life limits how long optimal clearance lasts. Carbide dies wear slower but cost more. Shops balance upfront price against scrap savings.
Material variation from coil to coil changes burr response. Inline thickness gauges and automatic clearance adjustment help.
High-speed lines vibrate and loosen settings. Dampers and rigid frames maintain stability.
Outlook
Sensors on presses now measure punch force in real time. When force drifts, the system tweaks clearance by 0.01 mm steps. Early tests show burrs stay under 0.05 mm for full runs.
Hybrid machines combine laser and mechanical shear. The laser pre-scores the edge; the shear finishes the cut. Burrs on 2 mm stainless measure 0.005 mm.
Dry processes with ionized air instead of oil meet green targets. Burr performance matches wet cutting in trials.
Conclusion
Burr control starts at the cutting tool. Clearance, speed, lubrication, and material prep set the edge condition. Standards give the target; process tweaks hit it. Shops that measure edges after every die change and adjust on the fly eliminate secondary deburring. The savings in labor, scrap, and schedule make the effort pay off fast. Edge quality is not an add-on—it is built into the primary operation.
Q&A
Q: What clearance range works best for 1 mm stainless steel in punching?
A: Use 0.06 mm to 0.09 mm (6 % to 9 %). Check with a plug gauge after 10 000 hits.
Q: How does laser focus position affect dross on aluminum?
A: Keep focus 0.5 mm below the surface. Above that melts extra material and raises dross.
Q: Why do burrs grow taller mid-coil on a slitting line?
A: Coil camber shifts blade overlap. Add side guides and tension control to hold alignment.
Q: Can I use the same die for mild steel and aluminum?
A: No—aluminum needs larger clearance. Separate dies or adjustable shims prevent rollover.
Q: What quick check confirms ISO Class B edges?
A: Run a 0.1 mm feeler gauge along the edge. If it catches, measure with a profilometer.