Sheet Metal Bending: Critical Engineering Considerations

Sheet Metal Bending: Critical Engineering Considerations

Known for its precision and reliability, the press brake is one of the oldest types of equipment used on the metal fabrication floor. A complex and versatile tool, it is capable of completing dozens of different bends in materials of varied thicknesses.

Though, that complexity does come with a downside. Even the tiniest mistake in design, programming or operation can lead to distortion, material loss, equipment damage or wasted time if re-engineering is required.  

In this article, we explain the metal bending process, collate design considerations for engineers to avoid costly errors, and illustrate why Badger Sheet Metal Works has the experience, skill and technology to lend a hand (or an entire shop floor!) to your next custom metal fabrication project.

WHAT IS METAL FORMING?

Metal forming involves applying force to reshape a workpiece. The applied force exceeds the material’s yield strength, so the metal plastically deforms and can be reworked to a specified shape.

There are many processes used to form materials in metal fabrication, with bending being among the most common.

WHAT IS METAL BENDING?

Bending is typically used to deform metal into an angular shape, often utilizing a press brake using carefully controlled pressure. The mechanical bending involves clamping a workpiece between a matching punch and die. The punch applies consistent force while the die controls the finished shape or angle of the transformed metal.

Modern press brakes use advanced computer technology to bend sheet metal and other materials with incredible precision, creating straight lines or complex shapes like cylinders, cones and more.

BSMW’S PRESS BRAKE TECHNOLOGY

BSMW has continuously invested in press brake improvements since 2010, and its shop floor now boasts machines with the technological capability to deliver precise metal bending at a variety of tonnage strengths and lengths up to 168.5 inches.

AMADA

  • 1-HDS2204NT: Max Bend Length 168.5″ – 243 TON
  • 1-HDS8025NT: Max Bend Length 101.0″ – 88 TON

CINCINNATI

  • 1-135AF Auto- Form CNC Forming Center, 8″ Stroke
  • 144″ bed, 135 ton
  • 1-230CB Hydraulic 10″ Stroke
  • 144″ bed 230 ton

MAX LENGTH & THICKNESS

  • 7G < 160″ max length
  • .25 < 120″ max length
  • .375 < 75″ max length
  • .500 < 60″ max length

***Mild Steel***

Common metals formed at BSMW include stainless steel, mild steel and aluminum.

COMPLEX PARTS MADE SIMPLE THROUGH OFFLINE PROGRAMMING

With BSMW’s Amada press brakes, bending sequences can be programmed offline, keeping machines running as much as possible while improving accuracy.

Once a part’s flat pattern is finalized, it’s reviewed by the BSMW programming team before being cut. This extra step of quality control allows programmers to evaluate the complexity of the part and whether the press brake operators will require extra support. A more complicated part will be programmed offline with Amada’s Dr ABE bend software.  

“I’ll develop the offline program, save it in a server, and then once the part gets out to the floor, the operator can just look up the part number,” explained Peter Schaap, a BSMW programmer. “It will pull the program off the server and load it onto the screen that’s built into the press brake.”

The offline program provides press brake operators with forming instructions, tooling placements, and gauging positions. If needed, the operators can review the whole forming process through a 3D simulation and make any changes ahead of running the program.

HOW TO PREVENT PRESS BRAKE PROBLEMS AND ENSURE ACCURACY: IMPORTANT CONSIDERATIONS FOR ENGINEERS

Hole Locations (Minimum Feature Distance)

If you don’t closely inspect the location of a part’s features before it’s cut and formed, you run the risk of the features distorting or possibly deforming and ruining the part.

Design tips: Small round features (e.g., holes and the rounded end of slots) can be formed with no distortion with a minimum of two material thickness distance from the edge of the hole to the bend line. Features with an edge parallel to the bend line should be treated as a part edge and will need the minimum flange length to prevent distortion. Any features too close to the bend line can still be formed without distortion using a relief cut on the bend line equal to the features’ distance and welded closed after forming.

Flange Lengths

Designing a flange that’s too short or narrow can cause distortion, overload the press brake and likely require a re-engineered part. Take time to consider the “little extra” length needed so you can send off a design with confidence the bend will be successful on the first attempt.

Design tips: Minimum achievable flange length will depend on the bottom die you will be using to form the part. While it may seem like you should only need to have half of the “V width” for the minimum flange, you will actually need a bit more. This is because the V width is calculated from the virtual intersection points of the die surfaces and does not account for the radius on the shoulder of every V die. Because it can be a bit of a process to work out the actual minimum flange width, it is highly recommended to either get the information from the tooling manufacturer (or draw out the tools if unavailable) and create a reference sheet for future use.

Part Tonnage

To prevent a stalled-out press brake, you must calculate the tonnage needed to bend your part.

Design tips: The tonnage required to form any given part will depend on the bend length, tooling used, tensile strength of the material, and the friction between the part and the dies. Though there are many reference charts and materials available for approximating the tonnage requirements of a given part, these are the two online tonnage calculators we can highly recommend:

For a simple rough estimate:
https://dealersupport.accurpress.com/qry/ht_loadcalc.taf

For a more advanced calculation:
https://www.pacific-press.com/hydraulic-press-and-press-brake-calculators/bending-force-calculator/

If the press brake does not have the tonnage to form a given part, you can either split the flange down to the bend line to bend in stages or use a wider V opening. With a split flange, you will have to weld the pieces and clean them up after forming. For thick plate, this may require some grinding to make sure there is good weld penetration, as well as some time for cleanup. When figuring for a larger V width, it is important to keep in mind that this will affect both the minimum flange size you can have as well as your achieved inside radius.

Is the Part Formable? (Machine Contact)

Avoiding tooling or machine collisions during forming is essential to a successful part design. While all press brakes are designed to withstand large amounts of vertical tonnage, they are not designed for large amounts of sideways pressure. Forming parts that intersect with the machine or tooling as part of their forming process can end up resulting in costly repairs to a press brake’s tool holding systems, deformation to the parts being formed, and if the collision is especially severe or if the part is a thick gauge, pose a safety risk to the press brake operators.

Design tips: To check for this, every tooling manufacturer will have a “bend limits” graph for all the standard profiles they offer. This will allow you to sketch out the final bend of your part quickly to check if they have any intersections. This method can be imprecise, but in most cases, it’s all that’s needed to see that there is plenty of room.

https://www.wilsontool.com/WilsonTool/files/c3/c3ddd678-e4d2-42dd-b28b-b625460fad01.pdf

If you have access to any CAD software, it could be worth your time to make a drawing file with all your standard tool profiles to check parts against. This is a much more precise method, at the cost of being a bit more of a process and requiring some setup.

BSMW’s programming team often checks for part collisions through offline programming. They simulate the entire bend process, flagging any collisions that occur. It’s essential for very complicated bend processes because it allows you to see the whole machine and not just the tooling, as well as check for collisions across the entire part instead of just the bends in the profile you are focusing on.

BSMW’S DESIGN REVIEW SYSTEM

At BSMW, the sales department is the first to analyze a new part design. If a part profile looks complex or possibly problematic, the department passes the design along to the BSMW programming team. Programmers will then compare the design against tool profiles that already exist or even run the design through bend software as a virtual test before quoting out the project.

WHAT SEPARATES BSMW’S BENDING SERVICES FROM OTHER CUSTOM METAL FABRICATORS’?

  • Newer, advanced technology enables programmers and operators to build more complicated parts with increased accuracy and full confidence
  • A dedicated, detail-oriented programming team that always goes above and beyond

“BSMW’s programming department invests far more time than an average custom metal fabrication shop,” said Schaap. “We know when a part gets to the floor that everything will go smoothly and machine operators won’t need to ask many, if any, questions. Any changes that needed to be made to the part have already been made by the time it’s cut. By investing some extra time ahead of a bend, the programming team gets parts prepped so they can be shipped out to the customer after the first run and not need engineering to fix problems after the fact.”


Keeping these tips in mind during the engineering design process will help eliminate costly, time-consuming revisions. If you have bending or design questions that weren’t covered in this article or would like to learn how BSMW’s press brake expertise and services will enhance your next project, contact us today.

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