REFORM will make cutting composite materials more eco-friendly by using abrasive waterjet machining in place of conventional techniques. This means that some research needs to be done to improve the accuracy and repeatability of waterjet machines so they can be used in high-value, high-precision applications.
The technical goals for the waterjet are:
- Reduce the amount of water used by developing a low-maintenance, low-energy water- and abrasive-recycling system;
- Reduce the amount of scrap by 50% by developing intelligent and adaptive monitoring and control systems;
- Reduce energy use and costs by 5%-10% by selecting the most suitable processes and parameters;
- Reduce processing costs by decreasing cutting time by approximately 15%-20%.
Waterjet machines use a precisely controlled stream of
extremely high-pressure water, containing a small amount of abrasive particles,
to rapidly erode metals and other materials, effectively cutting them.
The process is very versatile, being able to mill, drill, turn and create pockets and slots using a single machine. There is minimal
thermal distortion of the cut surfaces and there is no heat-affected zone.
The main damage when cutting composites is delamination.
The damage is due to the shock wave impact of the water stream on the material.
The jet thrust pushes uncut plies which are weakened and can easily
deform. Its also possible for abrasive to be embedded between layers. Because of the cutting jet shape (kerf), the
edges of the work-piece are generally rounded. The base quality of the part is affected by exit burrs, especially in metals. Waterjet machining can produce a tapered surface; this taper
angle can be minimised by reducing traverse speed and increasing the water
New hybrid waterjet machine
Partners in REFORM are developing a multi-tasking hybrid waterjet machine. The AMRC, University of Sheffield have designed a new cutting head and nozzle which will increase the accuracy and cutting power of the machine. This means that less abrasive can be used and that the waterjet can be used in high-value applications. The AMRC are also developing a modular fixturing system to allow only worn sections to be recycled.
TECNALIA is developing a chip extraction system for the milling head which will remove this composite material for recycling.
Water and abrasive recycling unit
NOVA are developing a unit to recycle water and abrasive. Waterjet systems use around 4 gallons of water per minute, all of which is filtered before being sent to the drain. This is wasteful and can preclude waterjet use in areas where water is metered or scarce. NOVA has developed a low-maintenence system which can filter the water so that it is clean enough to be used by the waterjet pump. The system can recover and separate roughly 90%-95% of water and abrasive, and has been optimised for low energy and material consumption.
Waterjet cutting also uses around 0.5 kg of abrasive per minute, which accounts for 60% of the cutting cost. Using recycled abrasive will not only reduce environmental due to mining and transportation but should also halve waterjet cutting costs. Trials comparing new and recycled abrasives are underway to see how the cutting power and material properties are affected.
The prototype machine as developed and tested at Nova's facility in Bergamo. It is currently being installed and tested at USFD.
Optimising processing parameters
During the first 18 months of the project, TECNALIA studied the parameters for different waterjet cutting technologies. They showed that the selection of the appropriate tools and parameters can affect:
- Productivity by 370%
- Cost by 60%
- Abrasive consumption by 70%
- Energy consumption by 65%
Therefore, selecting the best combination of cutting tools and
parameters can significantly reduce energy-use and the amount of
abrasive required, along with the associated mining, processing and
At the same time, Fraunhofer IPT investigated the milling tool parameters to allow them to reduce the reduce the environmental footprint of milling composites. The cutting and coating materials and tool geometry all affect tool-life, and simple tool geometries require less initial machining, so these have been selected for further investigation. Fraunhofer are also working to determine the optimum cutting parameters which will cause the least damage to the part. This will improve part quality and reduce rejection rates. Composite material are difficult to cut because they are not homogenous due to the presence of fibres. Fibre direction needs to be taken into account when machining composites to increase part quality and reduce scrap and rework.
Development of CAD/CAM module
The waterjet requires different cutting strategies to traditional milling. The longer the jet remains at a given location, the more material is removed. Also, due to the jet-shape, the cut tends to be tapered, which means the head needs to be correctly angled and the distance to the workpiece is important. To meet the industrial requirements of the end-users, REFORM will:
- Develop a Technical Model for the Abrasive Waterjet and identify the main error types
- Develop CAD/CAM software which can generate optimized toolpaths for both 3- and 5-axis machines. It will be possible to integrate these modules with commonly-used CAD programs.
- Validate the models.