In order to perform effective and accurate bending, press brakes require quality tooling that is suited to the application. By this we mean that the tooling is designed to bend the profiles you require in the material type and thickness you select. We will deal with types of tooling and how to select it in a later article. Today, our goal is to understand how tooling is made, how it is mounted to the machine and how it affects the bending process.
So - how is is press brake tooling made?
First we need to understand the stresses press brake tooling can be subjected to. Many press brakes can cycle up to 3000 times per day, resulting in more than 1000,000 presses per year. Often, the tools are bending various types of material, from aluminium to special, harder materials such as Hardox. Given this environment, tools are made from high quality tool steel, of which types 42CrMo4 and C45 are good examples.
The tools are made to the specification required by the customer. The tool is machined from a billet of steel on large milling machines, planers and grinders up to 0.01 mm precision, and is usually sectioned in 510, 835 or custome lengths, after which it undergoes a hardening process. The tool steel is preferably induction hardened or quenched, to improve its lifespan.
Now we need to fit the tooling to the press brake.
Press brakes will use a top tool (punch) and reciprocal bottom tool (die) to form the desired work piece. Each tool set is mounted in the machine differently. The punch set is usually clamped to the top beam using clamps that features a wedge adjustment and either manual or quick release clamping mechanisms. There are two popular methods of clamping - Promecam type or Axial type. The Promecam type is the most popular and is for use in applications where it's limit of 100ton/m is not reached. The Axial type is used in heavier applications and for the purposes of this article, we will focus on the Promecam type.
The hallmarks of the Promecam system are as such: The connection to the clamp is 30mm in height and 14mm wide. The punch tip is centred to a half of this, allowing the tool to be reversed with a double clamp. The die typically has a base of 60 or 90mm depending on the tool design. The die sections rest in a tool tray, or if it is a single full length die, is set directly on the bed and clamped at either end with front and back clamps allowing for positioning directly under the punch tip.
Great - now I know how to mount the tools. How do they affect bending?
The choice of tooling is intimately linked to the machine tonnage, length of the bed, material type and bending process. Let's discuss the features of the punch and die that will impact your bending outcomes. The first and perhaps most important is the profile. There are literally hundreds of tool profiles available, providing huge flexibility to the bending process. Knife tools, Goosenecks, Radius tools, special purpose tools and more give different outcomes. We will discuss these in more detail in seperate article. For now, we will concentrate on angle, punch tip radius and useful height.
Of the three considerations this is the most important. The angle of the punch and the die, will dictate the minimum angle that can be bent, when the tools "bottom". It also allows for spring back compensation. For example - if you have to bend stainless steel at 90° then opting for an 85° tip and overbending, will compensate for the 5° springback. It also follows that if you have a 90° die and a 85° punch, the minimum angle you can bend is 90°.
2. Punch tip radius
As a rule of thumb, the punch tip radius should be less than the desired internal radius of the profile you wish to bend. A useful ratio to use is the following: radius of punch=internal radius x 2/3. If too small a radius is used the punch will leave obvious mark on the inside of the profile.
3. Useful height
In order to avoid machine and or tooling damage it is critical to understand the useful height metric. Punch useful height is calculated as follows: Total height - Tang height (where the tang is the clamped portion of the punch). Useful die height is simply the total height of the die tool. When you are setting your machine up with your new tools, it is important to check that the machines total opening height exceeds: Punch useful height+Die useful height+material thickness.
There you have it, a brief look at press brake tooling and what to be aware of when starting down the path of buying new tooling or considering a machine for purchase that has tooling in it, that you would like to add to. If you would like advice on what tooling to choose, why not contact us and we would be glad to help by understanding your application and the profiles you wish to bend.