Friction welding

What is friction welding? There are several different types of welding and many different ways of friction welding. In this post we will tell you the main principle of friction welding process. Also, we will explain how it differs from traditional welding. Friction welding is process known as solid state welding process.

Solid state welding is a welding process that does not use external heat. Like in traditional welding, where the welding is conducted with external heat. In solid state welding, external pressure is applied to a stationary matter – such as a cylinder rod – to form the weld. In friction welding, the two pieces that need to be joined are welded together with rotating movement. The rotation with hard force against each other creates friction. The friction then heats the materials at the contact surfaces.

Friction welding is also used in cylinder manufacturing at Hydroline. It is actually said to be the most cost-effective method of producing high integrity piston rod assemblies in high quantities. The friction welding project has been ongoing at Hydroline since 2012 and the first machine was acquired in 2015.  It has yet not reached its full capacity as certain forms and elements are not usable for friction welding. However, it is extremely suitable for very demanding objects, such as boom cylinders and steering cylinder as well as safety critical cylinders.

So how does it work actually? In friction welding, two components are rubber together at a controlled rotational speed. Although the term welding is used to define the process, it actually has no resemblance to conventional welding as there is not filler material involved. The other component stays on place and the other one is rotated as the components are brought together. When pressing the components together, this creates the fiction and the heat that allows both components to reach a plastic state and be forged together. Rotation is stopped and after that, some extra pressure is applied to the joint. With friction welding, a 100% welded, forged quality bond is achieved. As a final step, the machine removes the extra flash by lathing.

friction welding process hydraulics hydraulic cylinder

Friction welding at Hydroline

At Hydroline, we are using friction welding in about 20 of our products at the moment (2019). The method is extremely reliable and definite process as the component is welded completely through; when welding with wire in conventional welding, the structure cannot be welded all the way through. At the moment, there are about 15 000 pieces around the world with friction welding manufactured by Hydroline and none of them has not been complained because of the welding. In case a customer wants their cylinder with friction welding, it needs to be taken into account in design as the component shortens a little bit with this method because of the material length loss that occurs in the process. By using our design department, the customer can be sure that the proper calculations have been made and the final product with friction welding is made according to the customer’s needs and fits the measurements.

Usually, when new materials or size classes are used in the process, certain quality control researches are performed; metallurgical integrity and such. The researches are done in outside labs where the welded component is opened, and the connecting surface is investigated. Depending on the welded piece’s geography, also bending and tensile tests might be done.

What are the benefits of friction welding?

The benefits of friction welding are the material and production efficiency as the method creates a stronger connecting surface than conventional welding process. Friction welding also requires less raw materials, post-weld machining and preparation. As the method creates 100% bonds, it allows high strength join with superior, forged quality and small heat-affected zones on the components. The result in friction welding is also melt-free. The machine-controlled friction welding process is consistent and eliminates the human error; the parameters are easily controlled, repeatable and monitored all the way through. The process allows the joint of dissimilar materials which then allows the design of bimetallic parts. This provides flexibility in design. Friction welding also requires a smaller area for heat control as the heat-affected zone is smaller than in traditional welding.

The process itself is also much faster than conventional welding and only minimal post-weld machining needs make the component almost immediately ready for the next step in the overall manufacturing process. The process is also ecological as it is energy efficient and uses no gases, flux or filler materials. Material waste in the process is minimal and it creates no weld splatters. Therefore, friction welding is also an eco-friendly process because it does not create smoke or release harmful toxins.