Key takeaways
- A burr is one part of the cut edge, and the rollover, shear and fracture zones matter as much as the burr height.
- The measurement method should match the limit: a visual check cannot prove a 0.05 mm limit, and a profile projector cannot inspect a whole coil.
- Set the acceptance criterion from the function of the edge, then choose the deburring process and the sampling plan.
- Record the sample location, the edge orientation and the die stroke count, or the number cannot be compared over time.
What a burr is, and what else is on the edge
A stamped edge is not a clean square. The punch enters the strip and the material deforms before it separates. The result is a rollover at the entry, a sheared zone with a smooth vertical face, a fracture zone with a rougher angled face, and a burr at the exit. The burr is the sharp projection left where the fracture did not quite meet the die edge.
The proportions depend on the clearance, the material, the thickness and the die condition. A tight clearance gives a large shear zone and a small burr. A loose clearance gives more rollover, a rougher fracture and a larger burr. A worn die behaves like a loose clearance, so the burr grows as the tool wears.
Edge quality is the whole profile, not only the burr height. A part with a small burr but a deep rollover may not sit flat. A part with a large burr but a clean shear may still seal. The acceptance criterion should name the feature that matters, and the measurement should capture it.
Why the edge matters to the part
A burr can injure the person handling the part, but that is the least interesting reason to control it. A burr on a sealing face can cut a gasket or hold a cover off its seat. A burr in a sliding fit adds friction and wear. A burr under a coating can show through the paint or break the coating at the edge and start a corrosion site.
In electrical parts, the burr changes the contact surface and the current path. A burr on a busbar or a terminal can reduce the contact area, create a high point that relaxes under clamp load or damage the mating part. A burr inside a lamination stack can short between sheets. The acceptable burr is therefore a function of the joint, not a universal number.
There is also a commercial reason. Deburring costs money, and a drawing that says deburr all edges without a limit invites either an expensive blanket operation or a part that is not actually controlled. A specific limit on specific edges lets the supplier choose a process and lets the buyer inspect the result.
Methods for measuring a burr
The simplest method is visual and tactile: look at the edge under good light and draw a finger along it. It detects a sharp burr but says nothing about height, and it is not repeatable between inspectors. It is useful as a first check on a production line, not as evidence against a numeric limit.
A profile projector or a toolmaker's microscope gives a magnified view of a cross-section or a silhouette. It is accurate and easy to document with an image, but it needs a prepared sample and a skilled operator. A stylus profilometer traces the edge and gives a profile with a height and a width, which is useful for comparing edges over time.
Optical 3D systems, including focus variation and confocal instruments, can map the edge without contact and produce a height map. They are fast on a sample and give a good record, but the result depends on the surface finish and the lighting. Cross-sectioning gives the most direct view of the rollover, shear, fracture and burr, but it is destructive and slow.
| Method | What it gives | Best for | Limitation |
|---|---|---|---|
| Visual and tactile | Sharp or not sharp | Line-side screening | No height, inspector dependent |
| Profile projector | Magnified silhouette and image | Sample measurement and records | Needs a prepared sample |
| Stylus profilometer | Traced profile and height | Comparing edges over time | Slow, contact can deflect a thin burr |
| Optical 3D | Height map of the edge | Fast sample mapping | Sensitive to surface and lighting |
| Cross-section | Rollover, shear, fracture and burr | First article and failure analysis | Destructive and slow |
A method should be chosen with the limit and the sample size in mind, not on its own.
Defining the limit
A burr limit needs a feature, a value, a direction and a zone. The feature is the burr height or the edge break. The value is a number with a tolerance. The direction says which face the burr is measured from. The zone says which edges are covered and which are not.
ISO 13715 uses edge state symbols to describe an edge with an undefined shape, including a burr. It is a useful way to put a consistent call on a drawing without inventing a house standard. The drawing can then say that a particular edge is to be deburred to a stated height, while the rest of the profile carries a general note.
A general note such as burrs 0.1 mm maximum on all edges is common, but it is often too coarse for a sealing face and too tight for an edge that is later painted. A better drawing identifies the critical edges, gives them a limit and leaves the rest to a general requirement. The inspector then knows where to spend time.
Height is not the only number
A burr can be tall and thin or short and thick. A thin burr folds over under a gasket; a thick burr holds a cover off its seat. If the joint is sensitive, specify the edge condition and the measurement method, not only a maximum height.
Sampling and records
A burr is a die wear symptom, so the sample should be linked to the die. Record the stroke count or the production period, the cavity or station, the coil lot and the edge orientation. Without those, a number cannot be compared with the next sample or with the supplier's record.
The sample location matters. The burr on a straight edge is not the same as the burr on a corner or a small radius. Corners and narrow tabs often carry the largest burr because the material has less support. The sampling plan should include a corner, a straight edge and any edge named on the drawing as critical.
The frequency should follow the risk. A high-volume part with a tight burr limit may need a check every few thousand strokes. A low-volume part may need a check at the start and end of the run. The first article should always include a burr record, and the record should show the method and the instrument, not just a pass.
Setting acceptance by function
A sealing face needs a flat, continuous surface with no burr that can cut the gasket or hold the cover off its seat. The limit is often set by a leak test or a seat contact check, not by a burr height alone. A sliding fit needs an edge that will not score the mating part, so the burr is removed and the edge is radiused or broken.
A painted or coated edge needs a burr that the coating can cover. A tall, thin burr can break the coating at the tip and leave a bare spot. A powder coating is thicker and can bridge a small burr, but it can also leave a void at the root. The coating supplier should agree the edge condition before the first batch.
An electrical contact edge needs a smooth surface where the current crosses, and no burr that raises the contact resistance or damages the mating terminal. A handling edge needs no sharp projection, which is a safety requirement rather than a functional one. Each case leads to a different limit and a different deburring process.
Deburring processes and their effect
Tumbling and vibratory finishing remove burrs by abrasion. They round the edge as well as removing the burr, which is good for handling and coating, but they can change a sharp functional edge and they can leave media in a hole or a recess. The process needs a defined time and media, and the result should be checked on a sample.
Brushing and grinding are directional. They can remove a burr from a specific edge without touching the rest of the part, but they depend on the operator and the access. They are common for large parts and for edges that cannot go into a tumbling barrel.
Electrochemical and thermal deburring can reach edges that tools cannot, but they have their own process controls and cost. For most stampings, the choice is between doing nothing, tumbling, brushing and a secondary grind. The drawing should say which edges are critical so the supplier does not apply an expensive blanket process to the whole part.
What to put on the drawing
Name the critical edges, give a limit and a measurement method. Add a general note for the rest. If the part is plated or coated, say whether the edge condition applies before or after the finish. If the part is deburred, say which process is acceptable and which edges must not be rounded.
Ask the supplier for a burr record with the first article and a sampling plan for production. Ask how the die wear is monitored and what triggers a die service. A supplier that can show a burr trend has a process in control; a supplier that only sends a pass certificate has a measurement, not a system.
Finally, check the edge on the part that reaches the assembly, not only on the sample that was polished for the first article. A burr that is removed by handling or by a tumbling step can still be present on a batch that skipped the step. The receiving inspection should include a simple edge check on every lot.
Frequently asked questions
What is a normal burr height for a stamped part?
There is no universal number. A general stamping might run with a burr below about 0.1 mm, but the acceptable value depends on the material, the thickness, the clearance and the function of the edge. A sealing or sliding edge may need a much smaller limit or a radius.
Can I measure a burr with a caliper?
A caliper can show that a burr exists, but it cannot reliably measure the height of a thin edge. A profile projector, a stylus instrument or a cross-section gives a number that can be repeated and recorded.
Does deburring change the part dimensions?
It can. Tumbling and brushing round the edge and remove a small amount of material, which changes the edge profile and can affect a fit or a coating. If an edge is functional, specify the edge condition and check the dimension after deburring.
How often should burr be checked in production?
Base the frequency on the volume and the risk. A tight limit on a high-volume part may need a check every few thousand strokes, while a low-volume part may need a start and end check. The record should include the stroke count and the edge location.
Sources and further reading
- ISO 13715:2017, Technical drawings, edges of undefined shape, vocabulary and indication
- ISO 2768-1:1989, General tolerances, linear and angular dimensions
- Qumek stamping edge quality and inspection notes
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