Design and Fabrication of Hydraulic Rod Bending Machine

What is it all about?

All hydraulic machines use the system with two or more cylinders connected to a single pipe containing the oil, and the pistons that cause moving of the fluids inside the cylinders. Their work is based on the principles of hydraulics, which practically mean that the greater force should be produced, by introducing less force, in other words the force is multiplied.

The Pascal's law states that when there is an increase in pressure at any point in a confined fluid, there is an equal increase at every other point in the container. Considering the vessels have two surfaces with the areas A1 and A2 respectively, and F1 and F2 to be the forces acting on surfaces A1 and A2, the pressure acting on surface 1 is given by:

                                                                                 P1 = F1 / A1
                                                                                 P2 = F2 / A2

As the pressure is same in all directions, the smaller piston receives smaller force and a large piston receives large force. Therefore, a large force can be generated with smaller force input by using hydraulic systems.
                                                                                     P1 = P2
                                                                              F1 / A1= F2 / A2

Fluid does not absorb any kind of supplied energy and it is capable of moving much greater load's and providing much higher forces due to the incompressibility.

The rods in various dimensions and made of different materials, are widely used in the industries and construction, and there are different machines used for bending it.

When bending, the outer portion of the work piece is stretched and its inner portion is compressed. If the tension is too great the farthest distance from the neutral axis becomes the danger zone, particularly if the tensile strength of the material is exceeded when it is being pressed. Through the stretching on the outer radius, a crack will develop, or in the inner radius, a wrinkle will be formed on the pipe.

Hydraulic rod bending machines utilize hydraulic cylinder, which can be driven by hand or by electric pump. The inserts with different radiuses can be attached to the piston of the cylinder, and it pushes the rod which is fixed at the frame.

Rod bending as a process starts with loading a rod into a bender and clamping it into place between two dies, the clamping block and the forming die. The rod is also loosely held by two other dies, the wiper die and the pressure die. The process of rod bending involves using mechanical force to push the rod against a die, forcing the rod to conform to the shape of the die. Often, rod is held firmly in place while the end is rotated and rolled around the die.

A wiper die is usually made of a softer alloy i.e. aluminum or brass to avoid scratching or damaging the material being bent. Much of the tooling is made of hardened steel or tooled steel to maintain and prolong the tools life. However wherever there is a concern of scratching or gouging the work piece, a softer material such as aluminum or bronze is utilized.

Why is this important?

The most important characteristic of hydraulic rod bending machines is that small manual or electrical force should be involved in order to produce large output force. This way, even the larger diameter rods can be bent, by using only human strength.
If hydraulic rod bending machine is automated or electrically operated, the rate of processing can be increased.

How it was before?

  In the past and also today, manual rod benders have been widely used. Usually it consists of a lever, frame and several dies that one can swap out to get different radius bends.

This process requires physical strength, especially when it is repetitive, in case a large number of rods have to be bent. Also, only small diameter rods can be bent this way.

Advantages of this technology

  Hydraulic systems possess numerous advantages over other systems of power operation. They are light in weight; they are simple and extremely reliable, requiring a minimum of attention and maintenance. Hydraulic controls are sensitive, and afford precise controllability.

How to build it?

  Here is presented an example of how to build hydraulic rod bending machine.
The main part of this machine is Hydraulic jack, which consists of a hydraulic cylinder, ram, oil tank, plunger, release valve lever and handle. Other parts of the machine are: moving die, die holder, spring, and frame stand.

Bending process:
Hydraulic jack’s reciprocating handle moves up and down continuously, that way building the oil pressure in the cylinder, so that the compressed oil exerts pressure to the jack’s piston. The moving die is fixed to the end of the plunger. The compressed oil pushes the hydraulic jack’s plunger forward, and it pushes  the rod to be bended, which is already fixed in between revolving die and moving die. The die is supported by the die holders. By changing the die in the hydraulic rod bending machine, we are able to produce different shape and radius of curve, such as “V” type, “L” type etc. The ram (moving die) pushes the rod forcefully, so that the rod is bended according to the shape of the die in the die holder.

Construction details of rod bending machine:

In the constructional part, a base frame structure is fabricated using mild steel bars.

- Frame:
A platform is formed on the top of this base structure. On this platform the two mounting points are fixed. These mounting points are kept very robust as they have to withstand huge lateral forces during the work of the machine. Set of pulley pairs of various diameters should be fabricated or machined, so that the rods could be bended with different radiuses.

- Supporting Pulley:
The peripheral cross section area of pulley pairs, in any set, should have the same shape, either semi rounded or half square, depending on the rod cross section to be bent. Rods with different cross section shape can also be bent, but special pulleys would have to be made in that case.

- Hydraulic Jack:
Hydraulic jack has half of the pulley attached to the top of its plunger, and is fixed on the frame, between and below the two pulleys. It should be positioned in such a way, so as to be able to achieve different shapes of the curvature.

- Springs:
Quick retraction springs are attached to the moving die (half pulley attached to the top the plunger), for easy and fast retraction of the plunger. Springs should be chosen and set in such a way, so that they do not impede the movement of the plunger.

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