Familiarising yourself with this sheet metal bending machine and others like it.
A press brake is a machine tool designed to bend sheet metal. Press brakes come in many shapes and sizes whether hydraulic press brakes or mechanical press brakes, and various configurations in terms of frame, stroke, bend force delivery etc. In this post we will discuss at a high level some of the differences, quirks, advantages and disadvantages of these machines.
But first an over view. The press brake consists of 6 main components:
- Top beam
- Bottom table
- Hydraulic, mechanical or electro mechanical drive system
These 6 components come together in a system (often with many more accessories) that provides the means by which sheet metal plates of varying lengths can be formed with varying angles and flange lengths. Advanced techniques can result in tube forming, box bending, multi-station bending and even cone bending.
Types of press brake.
At its most basic a press brake delivers force through a longitudinal top beam in a downward stroke, towards a fixed parallel bottom beam. A variation of this of is an upward stroking machine, whereby the bottom table delivers the pressure to form the sheet metal in an upward motion, such as the Promecam system. Developed by the French, this system had numerous advantages including a perfectly balanced delivery of pressure across the length of the table and longer service life because the main wear points are bearings rather than slides. It does however require that bending is done from the centre of the machine, careful calibration of the balancing system to bend evenly and in larger capacities a specially designed foundation. The up stroker can, if maintained and used correctly, give many years of excellent service.
A downward stroking press brake, offers the advantage of a lower cost of purchase relative to an upstroker, easier material handling when it comes to thick material and whilst bending is always recommended in the centre of the table on any press brake, bending in-capacity material off centre should not risk the parallelism of the top beam (unless of course the the machine is misused). The top beam does not require the complex balancing arrangement of an upstroker, rather it uses a torsion bar, or synchronised hydraulic cylinders to maintain parallelism with the bottom beam. Larger capacities also require a foundation. Once again, correct maintenance and use of the machine will result in years of accurate bending.
Press brakes also adopt different types of frame configurations - with the most popular being the C frame. A C frame hydraulic press brake can be either upstroking or downstroking and offers the advantage of rigidity, strength and a self contained unit with all parts connected to the frame. The disadvantage is that the full length of the bed can only accommodate full length bending depths to the depth of the throat of the machine. To bend deeper, a sacrifice must be made in bending width, so the material can pass the frames. A second frame configuration is the H Frame which has a distinct advantage of offering the complete bend length capacity at any depth of bend, but a consideration is that large box bends are not possible, since a large flange can’t be ‘outside’ of the machine, something that is possible on a C frame.
Bend force delivery - hydraulic, mechanical, electro-mechanical.
Finally, press brakes can be configured with three different methods of delivering bending pressure. The first and oldest method is via mechanical means - with the beam being driven by an eccentric system in much the same way as a standard eccentric press. Various clutch types can be used. These machines provide a greater speed, but lack accuracy and set-up times can be long and involved. One particularly important quirk is that coining is not advisable on a mechanical machine, as it causes the machine to ‘jam’ in the down position resulting in a difficult and invasive process to disengage. In addition they wear tools significantly faster, are very noisy and energy inefficient and pose a safety risk as the machine's entire stroke cycle must complete with each activation and cannot be stopped quickly to avoid injury.
The most common method of delivering the bending pressure is by means of a hydraulic system consisting of an oil tank, pump, motor to drive the pump, a hydraulic valve block and hydraulic cylinders. Hydraulic press brakes are slower than mechanical press brakes, but significant improvements in speed have been made and some machines are very fast. Different bending techniques can be performed, including air bending, coining and bottoming. In addition, the cylinders can be controlled independently to allow or compensate for deflection if the bend requires this. Hydraulic press brakes are more energy efficient and the latest systems idle or shutdown motors whilst not in use.
The last and latest method of delivering bending pressure is electro-mechanical - using the latest advances in high torque servo motor technology and multi pulley systems, an electro brake can deliver a significant amount of force quietly, evenly, quickly and very efficiently. These machines offer the significant advantages of speed and accurate bending without crowning compensation, since force is evenly delivered across the top beam. The disadvantage is one of cost, as these machines are relatively new and complex, requiring advanced electronics to deliver their best performance.
This brings to a close our first article on press brakes and bending and we hope you found it informative. If you would like to use the article, please do link to the page rather than copying the material as it is original and is protected by copyright law. In any case, we will return the favour with a link to your website, if you let us know.
In our next article we will discuss tooling, top and bottom, types and tips and tricks. Till then, cheers and happy bending.
-The MTO Team