Part 1: Determine the Material to Be Bent
When a fabrication shop is trying to decide what will be the right press brake for their needs, the critical thing to look at is the metal bending projects they will be doing and what they will be trying to accomplish with their new brake.
The first question the metal fabricator needs to ask is, “What type of material will I be bending?” They need to know not only the type of metal, but also if it has any special characteristics that have to be factored in when calculating a bend, such as increased tensile strength (which they can find out from their metal service center).
The fabricator also needs to determine the thickness and length of their material, as well as what flange lengths are required. All specifications of the metal and the finished part are needed to choose the right press brake.
Once they know their specific metal and its characteristics, they then need to look at V-dies and tonnage. For example, if a customer calls me and says, “I need a press brake that can bend 10 feet of 1/4″ mild steel,” the first thing I do is consult our air-bending tonnage chart and determine that the standard for bending 1/4″ is a 2″ V-die, so we start there. It also tells me that it’s going to take 15.5 tons per foot to bend it. Taking that 15.5 and multiplying it by 10 gives me 155 tons, which means they will need at least a 155-ton press brake with a minimum of 10′ of bed length for their metal bending job.
I will then ask the customer what their flange lengths are, as that will determine if the standard 2″ V-die will work for their project. If they tell me that they want to bend a 1″ flange length in their metal, then a V-die that is 2″ across won’t work, as the flange will fall into the die. If I change to a 1-1/2″ V-die to accommodate the flange length, then the tonnage has to dramatically increase in order to make the bend (the smaller the flange, the higher the tonnage). In this case, going from 15.5 to 22.8 tons per foot, the press brake buyer will now need a minimum of a 228-ton brake bend their job.
The flange length can also affect the required length of the press brake as well as the tonnage. If someone has a long flange length, say 3′ long, then they will be bending that 3′ of material back into the press brake. If the width of the metal is 10′ then a 10′ wide brake won’t be wide enough to allow for that size of flange, as the distance between the side frames is always less than the length of the bed. The side frames on a 10′ press brake are around 8′ apart and would prevent a 3′ flange on 10′ material from being bent back inside of the machine. So the customer would actually need at least a 12′ press brake (with 10′ between the frames) to bend that length of flange.
Open Height Is a Factor
The “open height” (also called “daylight”) of the machine also needs to be looked at when determining the right brake for your needs. While standard open height will work for most people, the customer may want to consider purchasing a brake that has a larger open height depending on the metal bending jobs they are doing, what tooling they are running, and what stroke they will need for their operation. If the customer is bending large flanges they may find that they can’t easily remove the part from a press brake with standard open height.
Press brakes with larger open height (and longer stroke) can be ordered. These machines are completely adjustable as they operate, so they can maintain a smaller stroke while running, but then can open up to allow the operator to remove the bent metal or otherwise provide for the requirements of the job.
Knowing all aspects of the metal that is to be bent is essential in sizing the machine, but that is only the starting point in choosing the right press brake.
Other articles in this series:
Part 3: Determine the Correct Control [Forthcoming]
Part 4: Determine the Tooling and Accessories [Forthcoming]
Part 5: Determine the Power Usage and Other Factors [Forthcoming]
Also by Jared Peterson: