image: This was piece milled by waterjet. view more
Credit: CIC marGUNE
Research work coordinated by CIC marGUNE is developing waterjet milling technology which promises highly competitive costs compared to current machining systems. The conventional milling of materials that are difficult to machine, such as aeronautic materials, uses costly and wear-prone cutting tools. Research workers from the Industrial Systems Unit at Tecnalia and from the University of the Basque Country are participating in this project.
Conventional milling basically involves starting with the material using a rotary tool with several blades. It is a technology that is highly optimised for materials such as aluminium, "but, nevertheless, is difficult when used with materials such as titanium and Inconel", explained Ms Amaia Alberdi, researcher at Tecnalia. They are materials of low machinability and cause great wear and tear on the blades of the mill. "This is where the water jet milling process has its niche", stated fellow Tecnalia researcher, Alfredo Suárez.
Despite water jet milling being a technology that is not yet well developed, the same cannot be said for water jet cutting processes. Actually, "water jet cutting process is a mature technology and has been shown to be much more efficient than other technologies for applications where great precision is not required", commented Ms Alberdi.
Limitations of water jet cutting machines
The starting point was a commercial machine for water jet cutting, and the aim is to develop a prediction model for adapting these tools to the milling and machining of parts. "The difference between water jet cutting and milling is marked by the exposure time of the jet on the material. This is why we are developing a model to predict, depending on a series of variables, to what extent is it able to machine the jet", explained Mr Suárez.
The machine used by the Tecnalia researchers and, in general, all water jet cutting machines, enable modification of these parameters, but solely at the beginning of the process. While machining, they cannot be changed. "In the end, they are machines designed to be used by anyone, to be very easy to use and intuitive", stated Mr Suárez.
For the research in hand, however, the researchers pointed out that they would need to vary the parameters at any moment. "In order to be able to do this, nevertheless, we would have to have a manufacturer of these machines to be interested in the project and would let us have a machine that was open in order to implement the developed model, stated Ms Alberdi.
Strategy, look for different paths
Conscious of the limitations of the machine under study, Ms Alberdi developed a prediction model of the different stages. "The first thing we did was to model a straight cut, a single slot in order to see what shape it took, what imprint the jet stream left depending on the parameters we introduced. Then we cut a number of slots, one beside the other and again examined the behaviour of the water jet. Finally, we studied different paths for the jet, in order to examine which one amongst them enabled the most homogeneous depth possible to be obtained with the machining", explained Ms Alberdi.
"In order to machine a part and to achieve, for example, an ashtray, you can aim the water jet in parallel straight lines, or in a spiral or in zig-zag, etc.," continued the research worker, "The difference between one path and another is in the direction changes; the more time it takes to decelerate, turn, and once more accelerate, the greater will be the erosion produced by the jet at these points".
Once the model has been developed, "it can be predicted what is going to happen without any need to invest in material or human resources", stated Ms Alberdi. This model can be tested with different materials, and be easily calibrated for each one of the materials.
The researchers are convinced that machining technology with water "has great potential, above all in materials for aeronautics applications. The advantage is that it will be able to carry out a first roughing at a very economical cost compared to the current one, given that in conventional milling expensive cutting tools are used which suffer great wear and tear", concluded Mr Suárez.