CNC Sheet Metal Bending for Steel and Aluminium Parts

What is CNC press brake bending?

CNC bending is the forming of sheet metal on a press brake, in which the punch (upper tool) presses the sheet into the die (lower tool) at a precisely controlled angle. Numerical control manages the position of the punch, backgauge and the sequence of bends – the operator prepares the program and the machine maintains the angle of successive parts within the agreed tolerance.

Unlike cutting or milling, the process does not remove material – it reforms it. The sheet remains in one piece, while the bend line produces an edge with a controlled internal radius and precise angle.

7 control axes on the AMADA HFE-M2-5012 EVO press brake – what they mean in practice

The press brake in the ANBI-TECH machine park has seven controlled axes that support the positioning of the beam and backgauges. The arrangement helps to set the bend line, height and backgauge position accurately for simple, asymmetric and multi-bend parts.

The control system automatically sets the programmed axis positions, while the operator handles, turns and repositions the part between successive bends and checks the process result.

Bend allowance and springback – why the programmed angle differs from the angle after release

After pressure is released, every material partly returns to its previous geometry. This phenomenon is called springback (springback). Its value depends on the material, sheet thickness and bend radius.

• Stainless steel has greater springback than carbon steel.
• Aluminium has greater springback than steel of the same thickness.
• The larger the bend radius, the greater the springback.

The second parameter – bend allowance (bend allowance) – is the developed length of sheet required for the bent part to have the designed external dimensions. It results from the neutral axis of the sheet not lying exactly halfway through its thickness.

The process engineer sets the bend allowance and springback compensation in the program according to the material grade and thickness, radius and trial-bend result. The control system executes the programmed positions, while the operator verifies the result and makes the necessary corrections.

Materials and minimum bend radius

The bend radius depends on the ductility of the material. The less ductile the material is (harder steel or a high-strength alloy), the greater the minimum radius needed to prevent cracking on the tensile side. Typical values for the most frequently bent materials (r = internal radius, t = sheet thickness):

The maximum declared sheet thickness is 8 mm. Actual feasibility depends on the material, geometry, bend length and required operation.

For parts requiring a smaller radius (for example r < 0.5×t in stainless steel), sharp-radius bending is possible, but the risk of cracking on the tensile side increases. In that case, we require prior process consultation and a trial part.

Angular and dimensional tolerances in CNC bending

There is no single bending tolerance that applies to every part. The accuracy of the angle and flange length depends on the grade and thickness of the sheet, die width, bent-edge length and how far the bend is from the edge. We therefore agree the tolerance for a specific drawing rather than applying one value to every order.

What actually affects sheet-metal bending accuracy

• Material springback – after unloading, the sheet partly returns. Stainless steel and aluminium exhibit noticeably more springback than carbon steel, so the angle set in the program must be smaller than the target angle.
• Die width – a wider die gives a larger internal radius and requires less force, but changes the developed length of the part. Selecting a die is a trade-off between force, radius and edge appearance.
• Internal radius – in practice, it is assumed that it should not be smaller than the sheet thickness. For galvanised sheet, this rule also protects the zinc coating from cracking at the bend.
• Rolling direction – bending across the grain is safer than bending along it, especially with small radii and higher-strength grades.
• Distance of the bend from the edge – an excessively short flange will not rest correctly on the die, and the angle will vary across the batch.

How to prepare an enquiry: the greatest time saving comes from stating on the drawing which dimensions are critical and what angular deviation is acceptable. For parts with a tight angle or a bend close to the edge, we make a trial bend and adjust the program before starting the batch.

Press brake vs folding machine – when to choose which

The two technologies are often confused, but they produce different results:

• Press brake (our AMADA) – bends along a straight line in one punch stroke. It is suitable for parts with complex geometry, multiple independent bends at different angles and bends in different locations on the part.
• Folding machine (panel bending) – bends along the whole edge of a panel by rotating a side arm. It is more efficient for large, flat parts with simple perimeter bends (for example cabinet enclosures and worktops).

In practice: a part with 4-6 bends at different angles and tight dimensional tolerance – press brake. A flat 600×400 mm enclosure with four perimeter flanges – folding machine.

Bending as part of comprehensive CNC machining at ANBI-TECH

Most parts that we bend undergo other processes at our facility first:

• CNC cutting – preparing the sheet-metal outline to the cutting-line tolerance.
• CNC milling – making holes, pockets and threads before bending (after bending, tool access is often impossible).
• CNC turning – producing bushes, pins and knobs fitted to the bent enclosure.
• Press brake bending – final forming of the sheet metal.

Completing the whole route at one facility shortens the production cycle and eliminates coordination between several subcontractors. Every stage follows the same inspection documentation and is covered by the ISO 9001:2015 system.

How much does CNC sheet-metal bending cost?

Bending prices are set using one of three models:

• Per bend – a unit rate for a single punch stroke. This works well for parts with 1-2 simple bends in long production runs.
• Per press-brake hour – a quotation based on machine and operator time. This is standard for complex parts (4+ bends, non-standard tooling or trial bends).
• Per complete part – a price covering the full route: preliminary cutting, bending and inspection. This is standard for orders involving several technologies.

The unit cost in production runs is affected by the type and thickness of sheet metal, number of bends, set-up time (punch and die selection), quantity and dimensional-inspection requirements. We quote every order individually from a DXF/STEP drawing.