The What, Why, and How of Metal Brakes(bending)

Most metal bending is done with a brake, but do you know how and why that is?

Bending is a process in manufacturing that can create a variety of shapes – channel, U or V-shaped. A brake is a metalworking machine that welders use to bend the sheet metal. There are multiple sizes and styles of brakes that can bend the metal, each with its own advantages and disadvantages. Operators should always be aware of the tolerances, tooling types, and other important considerations before using a brake.

Let’s start with more information about what brakes are, before getting into terminology, calculations, and special considerations for their use.

Exactly What is a Brake?

A metalworking machine that allows welders to bend sheet metal is a brake. Brakes are also known as a bending brake or just simply a bending machine. In Britain, brakes are referred to as a folder or sheet metal folder There are multiple types of brakes in use. In general, they are either hydraulic, pneumatic, or electronic.

  • Cornice brake – bends the metal in simple creases and bends
  • Leaf brake – bends the metal upward using an upward swing leaf
  • Box/pan/finger brake – allows the metal to form pan and box shapes.
  • Bar folder – This is the most simple version of a brake. It is smaller than the other types of brakes as well. A bar folder allows for welders to use the machine with a single hand. The end result has much less depth than the other machines.
  • Press brake –  a more complex machine that clamps the metal between a die and a matching punch. It bends the metal on predetermined bends. 

Most machines can bend metal to any angle (up to around 120 degrees).

For the majority of this article, we’ll be discussing press brakes.

What Can Be Made With a Brake?

The applications of a brake for metal bending are nearly endless. They are in use in a variety of different industries like transportation, automotive, aviation, and agricultural. Here is just a small sample of the potential items that are made with different brake types.

  • Gutters
  • Drip edges
  • Soffits (vents)
  • Fascia boards
  • HVAC ducts
  • Custom metal flashing

Parts of a Brake

The brake has just a few major parts. First of all, there is a flat surface that the sheet metal sits on. Above that is a clamping bar, which comes down to hold the material in place while it is being bent. The clamping bar is operated in one of three ways – by a foot pedal, manually, or automatically. For narrow enough areas, the clamping bar helps to make a sharper edge. The front of the brake, the plate, operates similar to a gate. It is a hinge that forces the metal over the edge of the machine, which is straight. This is how the physical act of the bending happens.

There are additional parts of a brake depending on the style of the brake.

  • With box/pan/finger brakes, the clamping bar has several removable blocks. These blocks can be rearranged to allow for the bending of otherwise restricted areas of sheet metal. This also works with partially formed pieces. After the bending is done, a screw, soldering process, weld, rivet, or alternative process completes the job by fixing the metal in place. 

Most machines have an emergency stop button or switch. Be aware of its location prior to using the machine.

Brake Sizes

Brakes also come in a variety of sizes. Some machines are suitable for small boxes made of brass or light aluminum. Most of the smaller brakes are bent by hand. Other, industrial-sized hydraulic machines bend large sheets of heavier metal like steel. These machines have the potential to be enormous and take up large amounts of space.

The Three Types of Metal Bending

One of the fundamentals of metal bending to understand is that there are three common different types available. Those types are air bending, coining, and bottom bending. 

  • Air bending – With this style of bending, the sheet metal is only touched at three points – the die shoulders and the punch tip. This means that the angle becomes unimportant to the process, as the punch decides the angle of the bend. The further into the sheet metal the punch descends, the more acute the angle is. This makes air bending useful for many different angles. It is not for use in older machines.
  • Coining – This type of metal bending takes its name from the way pennies are made. It takes a significant amount of tonnage to both create the angle and thin the metal. It is a very accurate type of metal bending.
  • Bottom bending – With bottom bending, both the punch and the die come together. This creates contact between the sheet metal, the punch tip, and the v-opening’s sidewalls. Springback is fairly likely to happy with bottom bending.

The Bending Process

When using a press brake, the workpiece sits on top of the die block. When in operation, the die block is what presses the metal sheet into the desired shape. During the bending process, there are two types of stresses to overcome – compressive and tensile. After that process is over, residual stress causes it to “spring” back to its starting position. To counteract that, the sheet metal has to be overbent to that the final bend angle is accurate. Part of this calculation is knowing the bend deduction and the bend radius so they can be accounted for ahead of time. 

The bend deduction is the amount of excess material that needs to be cut from the flanges to make a flat product.

The bend radius is how far a pipe (or another similar object) can be bent before it breaks or kinks.

Special Considerations To Know Before Operating a Brake

Many welders state that there are four major areas anyone operating a brake needs to be aware of before operating. These are absolutely non-negotiable when it comes to getting a correct, defect-free result.

  • Operator role – Most importantly are the people operating the brake. Everyone using a brake should have proper training with frequent updates and sign-offs. A good brake operator should know how to make great parts in the shortest amount of time possible. They should also know how to safely reduce set-up times.
  • The machine itself – Obviously, all operators should be very familiar with the machine. This needs to include how it works, any limitations, and necessary maintenance. Don’t guess, ask or seek training.
  • Tooling – Any brake operator should also be familiar with air bending, bottom bending, and coining. They should also know which tooling is good for what specific types of bends. We’ll discuss this below.
  • Drawing – All necessary information for the part being bent needs to be present on the drawing. This needs to include dimensions, bend angle, blank size, and inside radius. It should also include any acceptable tolerances and should be specifically based around the brake. 

Tonnage – What Is It?

Being aware of the appropriate amount of tonnage for your project can make or break a successful bend. Using too much tonnage can cause damage to the brake or even to the operator.

Tonnage relates to a few different factors – material thickness, type, length, the method of bending, and the tooling selection. While this number can be calculated by hand, there are many useful charts and calculators out there to make it easier. 

The “basic” formula is as follows, however : { [575 x (the thickness of the material)² ] / the width of the die} / 12. This calculates the tonnage per inch for a baseline material like steel.

To get the forming tonnage, take that number and multiply it by the length of the bend. Multiply again by the material factor, then by the method factor, and finally by the multiple bend tooling factor.

For reference :

  • The material factor is its tensile strength in PSI and then divided by 60,000.
  • The method factor is 5.0+ when using bottom bending, 10.0+ with coining, and 1.0 with air bending.
  • The multiple bend tooling factor is 5.0 with offset bending (10.0 when using thick materials) and hat tools. It drops to 4.0 with bending tools and stays at 1.0 with conventional tooling.

See how much easier it is to use a pre-set calculator? The math is extremely difficult, and the dangers of getting it wrong are serious.  

How To Use A Brake

While the process for bending metal with a brake varies depending on the style, the basic process is the same. However, before using the brake, make sure to prepare appropriately and read the manual. A good rule of thumb is to “measure twice, bend once.” Make all necessary cuts before bending, as well. 

  • Insert the sheet metal underneath the clamping bar.
  • Adjust the clamping handle cam to accommodate for the metal’s thickness.
  • Measure and then position the edge of the sheet metal parallel to the clamping bar at the correct distance.
  • Pull the clamping handles down at each end to hold the sheet metal into place.
  • Stop the bend apron at the correct angle (generally 90 degrees) with the stop rod.
  • Lift the two handles, which are under the apron, until it stops. Bend your knees instead of using your back. 
  • Slowly release the apron to bring it back down, then release the clamping handles.

The Importance of Tooling and Tooling Tolerances

Tooling is one of the most important parts of operating a brake but it can also be the most confusing. Tooling tolerance is a measurement that is specific down to a fraction of an inch. This measurement specifies the amount that each feature can deviate from what it “should” be. The reason that is an important number to know is that anything outside of that range can lead to a dysfunctional part. Processing methods and materials play strongly into the tooling tolerance measurement. 

This also has financial implications. The “tighter” the tolerance, the more work it takes to create and the more expensive it is to produce. Creating a product with a larger tolerance, if possible, can be helpful.

Knowing the exact tooling tolerance for any part is often not taken seriously enough, especially by new operators.

Common Die Types

Be aware of the different die types, as well as what types of shapes and angles they create. This will ensure you use the correct type the first time and reduce the amount of time and money you spend. Each type of die is slightly different.

  • Offset – creates a Z shape with two angles
  • Rocker-Type – move both up and down as well as side to side
  • Gooseneck – clear flanges (rims protruding from the workpiece)
  • Curling – coils and curls edges
  • V – creates bends in a V shape
  • Multiple-bend – can make several different bends in a single motion for custom shapes
  • Acute-Angle – as well as acute, can also make right and obtuse angles
  • Seaming – makes seems in tubes and sheets

Potential Brake Hazards

There are specific hazards that can happen with brake usage. This is especially true for negligent operators or those without training. Being aware of those hazards can significantly lessen the risk. So can appropriate training before operating a brake. Both are strongly encouraged.

  • Electrical – Although far more of a risk with a brake that is not in good operating condition, electrical hazards can still happen. These hazards include electrocution, burns, and electric shock. Check all plugs, switches, and wires prior to use.
  • Hearing loss/damage – While not generally a problem with infrequent use, hearing loss and damage is possible with longer-term noise exposure. Ear protection needs to always be on during all brake operation.
  • Cuts/lacerations – Objects coming off of the brake can be very sharp. This can lead to a wide variety of cuts and laceration injuries to the hands and fingers.
  • Foot injuries – Feet injuries can come in many different forms. For instance, objects can fall onto the feet. Feet have the potential for injury on or under press brake pedals. Proper foot protection is non-negotiable with brake use.
  • Stuck body parts – There is always a possibility of a body part that gets stuck inside the brake. This makes it very important to always be aware of your body placement when operating the machine.
  • Slips/falls – Most likely to happen around hydraulic press brake machines, due to the leaking of hydraulic fluid. Always wear non-slip shoes and use safety mats to reduce the risk.
  • Back injuries – These can occur due to strain with attempting to pick up heavy objects inappropriately. Use team lifting when possible, and always bend at the knees without using your back.

In Conclusion…

While brakes are an incredibly useful piece of machinery for bending metal, they also have a learning curve. Being aware of exactly how they work and what to look out for before attempting to operate one is the best place to start. 

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