A sheet can come out of the laser completely cut and then end up as a poor finished part a mere 10 minutes later.
The holes could be correct. The exterior shape might be accurate. However, following the bending, one flange is too short, a hole does not match the required shape anymore, or a long panel is already welded but has an imprecise geometry.
Therefore, a press brake for sheet metal fabrication shouldn’t just be referred to as a bending machine.
The press brake is located between flat part preparation and downstream welding, fastening or assembly in a fabrication shop in reality. APEX’s current press brake series features a combination of rigid constructions, synchronized control and programmable backgauges and CNC functions for a variety of sheet metal workloads.
However, the pertinent question is not just, “Can this machine bend our sheet?”
It is:
Can it make our cut blanks into parts which the next operation can use without correction?
The best bend begins prior to the part hitting the brake.
Sometimes, bending issues can start upstream.
| Incoming Blank Item | What to Confirm Before Bending | Risk if Missed |
| Material | Grade and batch | Wrong bending response |
| Thickness | Actual vs. drawing | Angle / force variation |
| Blank Size | Critical outside dimensions | Finished size error |
| Holes / Slots | Position from bend reference | Assembly misalignment |
| Surface | Visible side / protective film | Cosmetic damage |
| Bend Reference | Correct gauge edge | Wrong flange position |
| Part Orientation | Front / back and bend direction | Reversed component |
Operators must be aware before loading the blank: Material type, actual thickness, bend direction, critical flange size and the features that will be the bending references.
The basic forming procedure is simple: the sheet is placed between a punch and a die and the punch is moved in a controlled fashion to induce deformation in the sheet. However, before programming a production part, it is important to have an understanding of how a press brake works in terms of die opening and punch penetration which affect the radius and force and final angle.
The best cut blank won’t save wrong bending assumptions.
Drawing data and bending data should depict the same part before production starts.
If the previous bend is OK, then the final bend must be OK.
A bend is not the end of the line for fabrication.
The component can then be welded into a frame, attached to another panel, wrapped around an electrical assembly or assembled with a number of other bent components.
That alters the definition of “accurate.
A 90° angle is satisfactory and the part fails due to:
a hole move off the edge;
the flange is not long enough;
The bend line was moved;
the long edge is not straight;
two mating panels no longer are parallel.
APEX’s press brake bending accuracy guidance thus distinguishes between angle accuracy and straightness, parallelism, flange dimension and position as well as part to part repeatability.
Those dimensions should be verified based on the requirement for the next process for the fabrication shops.
The V-Die Selection is Not Just a Bend Radius Selection!
A V-die is more than just a block of support beneath the sheet.
When it’s opening changes it changes a number of conditions simultaneously.
APEX’s Press Brake for Sheet Metal Fabrication guide notes that V-opening affects the following: forming force, natural inside radius, minimum flange support, surface marking and tooling load. A smaller opening tends to increase the forces and allow for more restricted geometry, while a larger opening will reduce the forming force, but will need more support for the flange and will result in a larger radius.
That introduces realistic compromises in the actual manufacture.
Short flanges and surface quality may be of interest to a cabinet manufacturer. A thicker material and tonnage may be more of a concern for the structural fabricator. A part might be dimensionally OK but still be rejected by the architectural shop if the surface that is visible has heavy die marks.
This means that the right die is dependent on the finished piece and not just thickness.
The ease and awkwardness of a complex part depends on the bends used in a sequence.
A flat blank will not remain flat for long.
A new flange is found after the first bend. The operator may be limited in the positioning of the part after the second. At the fourth bend, geometry created in prior bends can interfere with the punch, tooling or machine.
That is why the sequence of bends should be decided prior to the first stroke of production.
In case of multi-bend parts, see:
which flange to start with;
which side can still be used as a reference side;
if flanges are formed, whether or not there is tool interference;
When it is necessary to rotate or flip the sheet; and
If the backgauge will be able to get to each reference needed.
If a sequence is not well planned, there can be too many awkward handlings, or a close to completion product can be left unfinishable.
The backgauge is used to conclude the drawing to the real part.
When there is a wrong angle operators tend to think about the ram.
Errors found with flanges typically necessitate further investigation.
The backgauge is used to determine the position of the sheet with respect to the tooling. Even when the sheet reference is poor, or the gauge position is wrong, the angle may be perfect but the bend line may be in the wrong place.
With workpieces that require multiple reference points, varying flange depths or asymmetric positioning, multi-axis systems come into play. Servo controlled and multi-axis backgauge options are available on appropriate configurations on APEX’s press brake platform.
It should NOT be a buying question, like:
“How many axes can we place an order for?”
It should be:
“What parts of our unit have to be repositioned and remeasured manually by the operator?”
The cost of First-Part Approval is less than Batch correction.
First bend is NOT production approval.
The first full part should be tested prior to the beginning of the batch.
APEX’s press brake setup guide is followed in this order: Look at the drawing, choose tooling, set up and align tooling, test bend a part, measure test bend and approve the first part made.
When working with sheet metal, check the entire piece:
angle, flange, critical hole relation and surface condition, overall geometry.
It will take about a minute or two.
It takes longer to locate the same fault in 40 completed parts.
Measure the Fabrication Throughput at Finished-Part End
Rapid movement of the ram appears to be productive.
But the press brake could be waiting for many hours for the parts to be positioned, rotated, measured or corrected.
Take entire bending operation measurement:
blank arrives, set up, load, position, bend, re-position, inspect, release downstream.
It is more productive a productivity number than a stroke speed.
Consider backgauge capability if positioning is a problem. If it is set up; Improve stored programs and tooling organization. If the long parts have to be corrected again, check for the reason, which may be due to process instability and/or crowning.
Machine specification should reflect the actual “bottleneck”.
Make the Press Brake Specification Based on the Fabrication Mix
Do not ask for a machine quotation based on one easy drawing – gather representative parts.
Add the longest regular bend, the shortest flange, the most frequently used material, the thickest recurring sheet, a multi-bend enclosure and an assembly critical downstream bend size.
Then, write down the usual number of batches and how often it changes jobs.
This provides the supplier with sufficient detail to converse with the supplier about tonnage, working length, tooling, backgauge configuration and CNC functions while discussing actual fabrication work.
The correct press brake for sheet metal fabrication should do more than just perform a bend.
It should help to take the component from flat blank to subsequent manufacturing process in a less surprising manner.
| Typical Fabrication Work | Machine Capability to Evaluate |
| Long enclosure panels | Working length + crowning |
| Repeated brackets | Program recall + repeatability |
| Multi-bend boxes | Tool clearance + bend sequencing |
| Different flange depths | Backgauge flexibility |
| Mixed material thickness | Tonnage + tooling range |
| Cosmetic panels | Surface-friendly tooling setup |
| Frequent job changes | CNC programming + setup efficiency |
FAQ
Q1. What is the function of a press brake in sheet metal working?
A press brake is a piece of machinery that uses a punch and die to bend flat sheet into angles, channels, boxes, brackets and other bent profiles. It is typically used in between cutting and downstream welding or assembly.
Q2. So, what is the selection criteria for choosing a press brake to use in sheet metal fabrication?
With real materials, thickness, max bend length, flange geometry, tolerance, and typical part complexity. The machine tonnage and working length should be in accordance with the production requirements.
Q3. Why is it important to have V-die opening?
The opening has an impact on the forming force, minimum flange support and surface marking, as well as the natural bend radius. Therefore, it must be chosen in conjunction with the material, thickness and geometry of the finished part.
Q4. Does CNC backgauge increase sheet metal fabrication?
It can enhance repeatable bend-line positioning, as well as minimize manual measuring, especially with parts that have multiple flange sizes. The more axes become valuable the more often the geometry of the work piece really demands positioning freedom.
Q5. Which of the following should be checked on the first bent part?
Check the bend angle, flange dimensions, bend position, critical holes, straightness and visible surface condition. The part should also be checked for requirements of the next fabrication or assembly process.