In the world of machining, there are increasing demands on sustainability requirements and pressures for components to be made faster, greener and cheaper whilst maintaining the same standard of quality. Increasing the rate of production involves following the example of the automotive industry by way of switching to a degree of automation of manual tasks. At a past AMRC Forum event called ‘Unconventional Machining’, the presenters revealed what their company’s were doing to propel their machining practices into the 21st century and beyond.
Chris Dance explained that BAE Systems, in collaboration with the AMRC, has developed new cutting tools to deliver reductions in machining times. In a separate project, the company integrated its offline process for large bore reaming into the CNC machining of components, which also contributed to significantly reducing machine times. Further research has involved replacing cutting tools with carbide alternatives for high removal rates. This too has resulted in considerable time savings which can translate into cost savings and higher productivity.
The success of the research was partly attributed to thoroughly understanding the dynamic characteristics of the material. For improvements to be made to the processing of the material, understanding how it behaves (vibrates etc) will ensure that the correct parameters are manipulated.
Richard Ward (WARDJet) opened by sharing how water jet machining, which was previously deemed a lower quality process, has grown extensively over the years. The tungsten carbide nozzles would only last for a short period of time and as such it was uneconomical to build a higher tolerance machine when the wear of the internal diameter was the limiting factor. Now it is possible to get 100-120 hours of use from a nozzle. In addition, the machine can achieve considerably higher tolerances.
The company’s latest offering is a GCM-series 5-axis water jet and milling machine is one of the largest in the UK, and arguably the most capable. It has a cutting envelope of 4 x 8 metres and 1.5 metres in height. The 5-axis milling head is suitable for machining composites at spindle speeds up to 24,000 rpm.
Unique to this machine is the ability of the water jet head to rotate infinitely around the vertical axis without needing to unwind. Coupled with its ability to cut virtually any material, the opportunities to its users are numerous.
Going forward, they are looking to incorporate height sensors (take in external input and spontaneously rewrite the program) and use metrology, probes and lasers to map the actual part and compare it to a 3D model prior to cutting. In this way, variances can be found and rectified before the material is cut which in turn will reduce materials wastage and save money.
In addition, there has been an increase in the use of multiple heads and controls as it is now possible to put nine 5-axis mechanisms on a single crossbeam. This equates to 32 axes of motion, which opens up new opportunities for water jet applications. Robots can also be mounted on gantries to exploit the benefit of the gantry’s ability to cover a large area and the robots ability to reach obscure places.
WARDJet has also successfully developed an air hockey style table which pumps air out to float the material across the bed. After it lines up with the sensors, the table is reversed into a vacuum to lock it into place. This is extremely useful for very heavy materials and incorporates a degree of automation as materials can be rolled on the bed, cut, and rolled off again in a continuous cycle. Hence up time is critical.
BAE Systems also use water jet milling at its Samlesbury facility-chemical milling in particular. Here, it is used to cut complex shapes that are difficult to machine using conventional routes. “It is versatile and effective, and it can cope with the thickness variations from superplastic formed materials,” said Chris Dance.
The company has also conducted trials to observe pocketing in aluminium and its ability to remove the oxide layer (alpha case) formed during the superplastic forming of titanium. Proximity to the work piece, pressure, speed and tool path are critical factors to be considered in this process. Grit from the abrasive is often embedded in the surface of the material. This is undesirable as it could cause the material to fail whilst in operation. Therefore, soluble abrasives are being investigated. This will help BAE Systems maintain competitiveness in the market by creating high value manufacturing technologies for future aircraft.
Electric Discharge Machining (EDM)
Mitsubishi has been using EDM for materials that are difficult to machine, with poor conductivity properties, explained Scott Elsmere. EDM is not just for finishing; it can also do one shop drilling that provides a good surface finish, high accuracy and repeatability for the lifetime of the tool. Using micro EDM, small parts for the tool and die market can be machined.
In a new trend, an increasing amount of companies are investing in wire EDM to allow the machine to run on 4-10 parts unmanned. The parts are rough wired, which eliminates the need for roughing work in subsequent milling or turning applications. In comparison to broaching, it requires low man power as 4-5 machines can be run by one operator. It is also less labour intensive and the material can be recycled.
This change results from developments in CAM systems software. The programming, handling software and servo amplifiers are more sophisticated meaning that applications that are not normally associated with EDM wire cut can be explored. For example, high speed rotation for small medical parts was challenging task as the servo amplifiers were not available and processes had to be carried out at a fixed speed.