Production bending on a multi axis press brake?
- Peter Dawber
A modern CNC press brake will often be offered with a multi axis CNC control. What benefits do the different axes bring? Or are they just adding complexity without increasing productivity? What is the minimum you need?
To help with these common questions I have summarised the functions and productivity benefits which the various axes bring. This is in no way intended to be a definitive guide but aims to give some insight into what functions will be required for your production.
At top level there are three main groups of CNC controlled axes on a modern CNC press brake; the control of the bending ram, the control of the back gauge and the control of various productivity options and accessories. Several of these axes have universally denoted letters , however some vary from one manufacturer to another with common axis configurations on new press brakes varying from as little as 2 or 3-axis up to 7-axis and beyond. Some manufacturers offer standard machine configurations e.g. 4-axis or 7-axis press brakes, others such as Morgan Rushworth, allow you to fully configure machines to your application.
So what are the different axes and their functions?
Y axis – Position of the bending ram (upper beam on a down-stroking press brake)
Unlike older mechanical press brakes operating with a flywheel, modern hydraulic machines allow precise control of the bending rams, each ram cylinder often being controlled individually as Y1 + Y2 axes. As well as ensuring that parts are bent equally across the width of the machine, the Y axis can also control the open height of the beam, allowing for either the minimum return height required for the next bend or to return to a higher open height to remove a large flange.
X axis – Position of the back gauge depth (in/out movement)
This is the essential axis for every press brake, controlling the length of the flange to be bent. X axis travel can vary from model to model, however 750mm to 1000mm is common. While on many machines the X axis is fixed across the width of the machine, it can also be specified as X1 + X2 axes with the left and right sides of the back gauge to moving in and out independently, allowing for a non-parallel flange to be bent.
R axis – Position of the back gauge height (up/down movement)
This is commonly used for two applications; firstly when a number of different dies are used with varying heights, the R axis can adjust automatically to the height of the tool. Secondly, when bending a Z flange, the back gauge height can adjust to work with an already bent flange which is now at a different height to the top of the bending die. This is probably the most common axis offered as an option and brings a good ratio of investment to increase in productivity. If a number of tools are set up on the machine with differing die heights, then an R1 + R2 back gauge will allow the back gauge fingers to move to the height of each station as a program is cycled through.
Z1 + Z2 axes – Left and right position of the back gauge fingers (side to side movement)
If bending flanges on all sides of a long narrow blank, this allows the back gauge fingers to move from a narrow setting to a wide setting as required for the individual sides of the part. Commonly however this is associated with a number of tooling set ups on one machine where a number of bends are cycled through and the back gauge fingers move to each tooling station according to the bending program. Machines without the Z1 + Z2 axes can be specified with additional back gauge fingers; this is a cost effective option which reduces the need to manually adjust the finger position from left to right.
Other axes and back gauges options which are controlled by the CNC;
Other back gauge style includes fully independent tower back gauges, where instead of a bar across the width of the machine, the left and right back gauge fingers have individual towers which move in all directions. This is known as an X1 + R1 + Z1 and X2 + R2 + Z2 back gauge. Some other options are not generally considered to be individual axes but are however controlled by the CNC, for example;
- Motorised bottom tool crowning system or anti-deflection table
- Front sheet follower supports
- Laser angle measuring systems which give live feedback to the Y axis allowing precise compensation for the bending angle according to the behaviour of the material
- Pneumatic or hydraulic top and bottom tool clamping systems
Given the large number of options and configurations available I believe it is highly advisable to spend some time reviewing the intended use and production requirements when specifying a new press brake. Some applications may even lend themselves to an alternative machine such as a CNC folding machine. Examples of this are folding small flanges on each edge of large sheets or narrow strips, or when a critical dimension is between two flanges such as when folding a door casing. My earlier article comparing the relative benefits of press brakes and folders can be found here.
Much of the above could be examined in more depth and I would like to expand on this further in future posts. In the meantime I hope this will be of use – please feel free to share with your colleagues who may find this of interest. Thanks for reading.