HENLI application guide ยท Precision parts leveling
Leveling Perforated Metal and Etched Mesh: 4-Hi or 6-Hi?
Choose around the finished partโnot the roller-stack label. Compare flatness, surface protection, and the evidence a meaningful sample trial should provide.
Technical guide ยท Updated September 20, 2026
Choosing a precision parts leveler for perforated metal starts with two separate requirements: how flat the finished part must be, and what condition its surface must retain. A sheet can meet the flatness requirement yet fail inspection because of roller marks, scratches, or coating damage.
01 / THE FINISHED PART
Start with the part after perforation or etching
Coil preparation and finished-part leveling address different stages of production. Material that looks flat before punching may distort after holes are made or after the part is separated from the surrounding strip.
Perforation changes the sheet's stiffness and can introduce or redistribute stress. Etching removes material and may expose distortion associated with the incoming material and the etched geometry. Narrow bridges, dense hole patterns, and solid borders can respond differently within the same part.
Start with the symptom and the stage where it first appears.
Shape changes after perforation
Compare the part before and after punching, etching, cutting, or separation. Note whether distortion follows dense hole patterns, narrow bridges, or solid borders. Flat incoming sheet does not establish the condition of the finished part.
Flat, but visibly marked
Assess the affected face separately from shape. Distinguish roller lines from scratches, indentations, gloss variation, or coating damage. Compare parts before and after leveling and handling.
Distortion in two directions
Record the sheet orientation, hole pattern, and direction of bow, edge waves, or twist. Distortion along and across a part does not automatically justify a second pass.
A roller leveler applies successive alternating bends to improve shape within its operating capability. It does not automatically correct every local defect or leave every part free of residual stress. If the problem begins later in production, see why stamped parts can warp even after coil leveling.
02 / THE ROLLER STRUCTURE
What do 4-Hi and 6-Hi mean?
These terms describe the roll layers in the upper and lower stacksโnot the total number of working rollers along the feed path. A machine's work-roll count and its stack arrangement are separate specifications.
4-Hi 2+2 roll layers
Backup rolls support the work rolls directly.
6-Hi 3+3 roll layers
Full-length intermediate rolls separate work rolls from backup contact.
In a typical 4-Hi arrangement, backup rolls support the working rolls directly. In a typical 6-Hi arrangement, full-length intermediate rolls sit between them. This additional layer can help reduce the transfer of backup-roll contact patterns to the work rolls, which is relevant to appearance-sensitive material. B&K's leveler technical FAQ describes this distinction; individual machine construction still needs to be checked.
Neither arrangement eliminates the need for clean, suitable roller surfaces and controlled material handling. Dirt, damaged rolls, unsuitable contact conditions, and downstream handling can mark material regardless of the stack label.
03 / TWO ACCEPTANCE CRITERIA
Flatness and surface quality need separate acceptance criteria
โFlat and no scratchesโ is a useful starting request, but it is not a complete acceptance specification.
How flat is the finished part?
For flatness, define the finished part dimensions, permitted deviation, measurement area, and measurement method. Agree whether the part is checked in its free state or in an application-specific fixture, and at which production stage. Do not compare a clamped result with a free-state requirement.
What surface condition is acceptable?
For surface quality, identify the inspected face or faces and the defects that are unacceptable. A visible roller line, a scratch, gloss variation, coating damage, and an indentation are not interchangeable descriptions. Reference samples or agreed photographs can make the acceptance standard clearer.
For prepainted steel, anodized aluminum, coated parts, or film-protected material, also confirm the actual finish and film condition during leveling. Do not assume that protective film makes any roller arrangement suitable. Both the film and the underlying surface need evaluation.
Inspect the same trial parts for both requirements. Passing one does not cancel a failure in the other.
04 / THE SELECTION
How should you choose between 4-Hi and 6-Hi?
Treat the choice as a testable engineering decision, not a contest between a basic machine and a more expensive one.
Prove the required result
A suitable 4-Hi configuration may be worth evaluating when its material capacity covers the application and the required surface finish can be demonstrated in trials. There is no reason to reject it solely because another proposal has more support layers.
Examine surface-sensitive support
A 6-Hi configuration deserves closer evaluation when surface appearance is particularly sensitive or when the support arrangement needs to limit the influence of backup-roll contact on the working rolls. That still does not establish the machine's suitability for the required width, material strength, thickness, or hole pattern.
Capacity is more than a stack label
Finally, compare the total production requirement: required throughput, handling of individual parts, inspection access, maintenance, and floor space. A more complex specification only adds value if it addresses a demonstrated requirement.
Roller diameter is another part of the selection. A diameter appropriate for one material and width is not automatically suitable for a thinner, wider, or stronger sheet. Hole patterns also affect how the part responds. Use the roller diameter selection guide for the broader relationship between thickness, strength, width, diameter, and support.
05 / THE PROCESS
Does a perforated sheet need leveling in two directions?
Not necessarily. A sheet can show distortion in more than one direction, but that observation alone does not establish the correct number of passes or a cross-direction processing method.
Record the orientation of the original sheet, the hole pattern, and the direction of the observed distortion. If a trial includes more than one pass or a change of orientation, record the result after each stage. Evaluate the finished shape and surface together with the added handling and cycle time.
Do not describe one-pass or two-pass performance as universal. The qualified process must suit the particular machine, part geometry, and acceptance requirement. Any trial sequence or adjustment should be agreed with the equipment supplier and performed by trained personnel under the machine's safety procedures.
06 / THE SAMPLE TRIAL
What should you send for a meaningful sample trial?
A drawing and material thickness alone are not enough. Prepare the following information before confirming a leveler configuration:
- Material grade and condition
Include alloy or steel grade, aluminum temper where applicable, and available mechanical properties. A grade name alone may not describe the leveling response.
- Thickness, width, and part dimensions
State the full production range and identify the combinations that need validation.
- Hole or mesh drawing
Show hole dimensions, spacing, open area, solid borders, and narrow connecting bridges.
- Incoming condition
Supply representative parts after the actual punching or etching process, with photographs of the distortion.
- Surface specification
Identify coating, anodizing, film, inspected faces, and permitted or prohibited marks.
- Flatness and production requirements
Agree the measurement method, inspection stage, throughput, and handling conditions.
Use representative full-width parts where practical. A narrow sample can help with an initial assessment, but it cannot by itself validate full-width performance. Likewise, solid sheet is not a substitute for the actual perforated pattern.
Record the material identity, configuration, trial sequence, and before-and-after inspection results. Where the production range varies substantially, more than one representative condition may need testing. Acceptance should rest on those agreed results rather than on a general product-range figure.
- Define the finished-part requirementAgree the measurement stage, free or fixtured condition, inspected faces, and unacceptable surface defects.
- Match the configuration to the partReview material condition, width, thickness, hole pattern, roller geometry, and support arrangement together.
- Qualify the result and production fitRecord the trial sequence and inspect flatness and surface finish. Assess handling and throughput before accepting the configuration.
07 / QUICK ANSWERS
Frequently asked questions
Does 6-Hi mean six leveling rollers?
No. It normally describes three roll layers on each side of the material: work rolls, intermediate rolls, and backup rolls. The number of work rolls along the feed path is a separate specification; confirm both on the machine drawing.
Will a 6-Hi leveler prevent every roller mark?
No. Intermediate rolls can help address a particular contact-pattern risk, but the finish also depends on roller condition, cleanliness, material surface, processing conditions, and handling. Verify the required finish using representative parts.
Can the same machine process perforated steel and aluminum mesh?
Possibly, but matching thickness alone is insufficient. Material condition, width, pattern, surface requirements, and the machine's specific capability must all be reviewed and tested.
CONTINUE YOUR RESEARCH
Related equipment and application guides
FROM REQUIREMENTS TO A TRIAL
Discuss your perforated-part leveling requirement
Send HENLI your part drawing, material condition, photographs, and acceptance requirements. The next step is to identify a suitable configuration and agree a trial that checks both flatness and surface quality.
