Press Brake Hemming Tools Guide: Open, Closed & Teardrop Hems
Press brake hemming tools fold and close a sheet edge to remove a sharp edge, reinforce a part or create a controlled return flange. The operation normally has two stages: form an acute pre-bend, then flatten or planish it into a closed, open or teardrop hem. Correct tooling depends on the material, thickness, bend length, target gap, press-brake style, available opening and required force.
Quick answer
A common hemming workflow uses an acute punch and die to make the first bend, often near 30 degrees, followed by a flattening tool that closes the return flange. A dedicated spring-loaded or combination set can sometimes complete both stages without changing tools. Select the system from the approved material thickness, hem geometry, tooling style, bend length and manufacturer force chart.
Do not use a normal air-bending tonnage estimate for the flattening stage. Closing a hem creates high contact force and lateral movement. Verify every component's load rating and prove the setup with representative material.
How the two-stage hemming process works
- Create the pre-hem. Form the edge to the acute angle specified by the hemming system. The bend radius and flange length established here influence the final gap and teardrop shape.
- Reposition the part safely. Keep the formed edge oriented according to the approved setup. Confirm that the workpiece is supported and cannot eject or slide unpredictably.
- Flatten or planish the hem. Apply controlled stroke with the flattening tool. Stop at the programmed position for an open hem or continue within approved limits for the intended closed profile.
- Inspect the released part. Measure gap, parallelism, length, surface condition and cracking after unloading. Adjust only through the approved setup procedure.
Open hem vs closed hem vs teardrop hem
| Hem style | Finished geometry | Typical reason to use it | Key control |
|---|---|---|---|
| Closed or crushed hem | Return flange pressed against the parent sheet | Remove an exposed edge and increase local stiffness | Closing force, surface marking, trapped coating and cracking at the fold |
| Open or gapped hem | Controlled parallel space remains between layers | Create clearance, receive another component or limit surface compression | Tool gap, stroke repeatability and springback |
| Teardrop hem | Rounded internal profile with the edge returned toward the sheet | Reduce cracking or create a controlled rounded edge | Pre-bend radius, material response and final stroke |
| Rope or special hem | Application-specific rolled or formed edge | Special stiffness, assembly or appearance requirements | Usually needs dedicated or custom tooling and trials |
Mate describes the closing operation as planishing and notes that lateral force can make the sheet try to move out of the die. WILA likewise distinguishes pre-bending from flattening and directs users to application-specific force charts. That is why a hem should be treated as a planned forming operation, not as a last-minute squeeze.
Choose the tooling arrangement
Separate pre-bend and flattening tools
This flexible approach uses an acute punch/die set for stage one and a dedicated flattening set for stage two. It can suit occasional hemming and allows each operation to be optimized, but it adds a tool change or second station and another handling step.
Spring-loaded or combination hemming die
A combination die can use an acute V opening during the pre-bend and then compress through a spring-loaded flattening section. It may reduce tool changes and handling. Each model still has specific maximum material thickness, angle, gap and load limits.
Dedicated gapped or special hemming set
When the drawing calls for a repeatable gap, teardrop geometry, unusual return length or cosmetic surface, a dedicated or custom set can control the final form more reliably than stopping a general flattening tool by eye.
Seven details needed to select hemming tools
| Selection detail | Why it matters | What to send |
|---|---|---|
| Tooling style and clamping | The tang, safety system, holder and overall height must match the press brake | Brake model, holder model, style and photos or drawings of the clamping interface |
| Material grade and temper | Strength, ductility and springback change pre-bend and closing behavior | Exact alloy/grade, temper, coating and grain direction |
| Thickness range | Every hemming system has a rated range; double thickness affects final geometry | Minimum, maximum and most common thickness |
| Hem geometry | Closed, open and teardrop hems need different gap and stroke control | Section drawing with angle, radius, gap and return length |
| Bend length | Force rises with length and must remain within all tooling and machine ratings | Maximum continuous hem length and any staged lengths |
| Surface requirement | Flattening commonly marks sheet or damages protective film | Visible surfaces, finish class, film and acceptable marking |
| Production volume | Frequency determines whether a two-tool process or combination system is more economical | Parts per batch, batches per week and changeover target |
Tonnage and load checks
The first acute bend can be evaluated with the approved air-bending data for its tooling and material. The second flattening stage is different: force depends on the material, thickness, bend length, pre-bend and target closure. Use the force table for the exact hemming tool rather than a general air-bending calculator.
Confirm the lowest allowable load across the press brake, ram, intermediates, clamps, holders, punch, die and any segmented sections. Short tooling segments do not automatically allow the full machine tonnage to be concentrated into a small length. If the required force or load distribution is uncertain, stop and have the application reviewed.
For the first-stage bend, the press brake tonnage chart and tonnage calculator can help with planning. They do not authorize the flattening stage.
Material and surface considerations
- Mild steel: a common baseline, but grade and actual strength still influence force and springback.
- Stainless steel: commonly requires higher force and may show stronger springback and marking.
- Aluminum: alloy and temper are critical; tight acute pre-bends can crack less-ductile material.
- Galvanized or coated sheet: high contact pressure can mark, crack or transfer the coating.
- Protective film: WILA notes that hemming can damage film and leave marks; validate cosmetic parts with production-equivalent samples.
Press brake hemming tooling to evaluate
These are real catalogue products. Compatibility, material limits, tool pairing and force must be confirmed before ordering or use.
1415 LVD-Style Hemming Punch
20-degree hemming punch listed for compatible LVD-style press-brake tooling systems.
View Hemming Punch
3449 LVD-Style Hemming Die
Matching-style 20-degree hemming die with listed V-opening and load specifications.
View Hemming Die
3176 Amada/Promecam Hemming Tool
28-degree hemming-die option for compatible Amada/Promecam-style systems.
View 3176 Hemming ToolHemming setup review checklist
- Confirm the brake, holder and tooling style.
- Review the exact section drawing and identify the target hem type.
- Verify material grade, temper, thickness, grain direction and surface requirement.
- Check the approved pre-bend angle, minimum flange and tool clearance.
- Use the exact hemming-tool force chart for the closing stage.
- Program and prove the setup using representative samples and the facility's safe-work procedure.
- Inspect the released part for cracking, gap, parallelism, markings and dimensional change.
Press brake hemming FAQ
What is a press brake hemming tool?
A press brake hemming or flattening tool closes a previously formed acute flange into a flat, open or teardrop hem. Some systems use separate pre-bending and flattening tools, while spring-loaded or special sets can perform both stages with one tool arrangement.
What angle should be used before hemming?
A 30-degree acute pre-bend is a common starting arrangement, and many dedicated systems use a matching acute punch and die. The approved angle depends on the hemming set, material, target hem and manufacturer instructions; do not assume every tool uses the same value.
What is the difference between an open and closed hem?
A closed or crushed hem presses the return flange against the parent sheet. An open hem intentionally retains a gap, while a teardrop hem retains a rounded internal profile. The tooling, stroke and material response determine the final geometry.
How much tonnage does a sheet-metal hem require?
Flattening force depends on material type, thickness, bend length, pre-bend geometry, hem style and tooling. Use the hemming-tool manufacturer's force chart and the lowest load rating across the brake, holders, punch and die. Do not use a generic air-bending tonnage value for the closing stage.
Can stainless steel or aluminum be hemmed?
Many grades can be hemmed, but alloy, temper, thickness, grain direction, minimum bend radius, surface finish and tooling limits must be reviewed. Stainless generally needs more force than a mild-steel baseline, while some aluminum tempers can crack at tight pre-bends.
Will hemming mark the sheet surface?
Hemming produces high contact pressure and commonly leaves marks or affects protective film. Tool surface, knurling, cleanliness and protective materials can influence the result, but a cosmetic requirement should be proven with representative test pieces.
Technical references
- WILA: Hemming application guidance — hem purpose, material considerations, marking and tonnage references.
- WILA tooling catalog: Flattening tools — pre-bending, flattening and force considerations.
- Mate: Press Brake Hemming Tools — two-stage forming, planishing and lateral-force considerations.
- Wilson Tool: Custom Hemming/Flattening — 30-degree pre-bend and gapped-hem options.
Continue learning: identify the press brake tooling style, choose a V-die opening, or open the Education & Product Guides hub.
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Reviewed By
This guide is reviewed by Kartar Chalotra, who leads sales and operations at Rise Tek Machinery.