The On-Machine Verification version of Delcam’s PowerINSPECT inspection software provides “an invaluable tool” according to Process Application Engineer, Stewart Seedhouse, from the Makino-NCMT Grinding Division. The technology saves both Makino-NCMT and its customers considerable amounts of time and money.
PowerINSPECT OMV uses probing equipment on the machine tool to allow initial checking of parts to be carried out in situ on the machine rather than having to transfer them to coordinate-measuring machines for inspection.
NCMT has represented the complete Makino range of machining centres in the UK for many years. In 2006, in recognition of the company’s leadership in the application of VIPER grinding, the Makino-NCMT Grinding Division was set up in Coventry to market the technology throughout Europe.
VIPER grinding employs small, vitrified aluminium oxide wheels in creep-feed grinding mode on Makino machining centres, in place of conventional, plated cubic boron nitride wheels. It is mainly used in the production of components from nickel-based alloys, principally in the aerospace and power generation industries but also in the motorsport and medical sectors.
The technology is not only up to eight times faster than the conventional process but also reduces the cost of consumable significantly. Furthermore, the Makino range is the first to combine creep-feed grinding with milling, drilling and turning in a multi-processing environment, reducing the number of separate operations and, therefore, the set-up times.
Even so, the process remains extremely challenging due to the use of difficult-to-machine materials, such as Inconel, the complexity of the shapes that need to be produced and the high levels of accuracy that are required. In addition, many of the components are produced from forgings or castings, which can be both expensive and in very limited supply.
“In a typical project, our customer might be required to produce at least 30 conforming parts from 32 high-value castings,” explained Mr. Seedhouse. “Anything that can make the process more reliable and more accurate is hugely valuable.”
The first stage of most projects uses the PowerINSPECT software to check the machine kinematics by taking measurements from a standard sphere in a known position on the machine. This takes one to two hours but is essential to ensure that the accuracy of future measurements can be trusted.
The next stage is to inspect the datum locations of all the fixtures to be use in the process and, in some cases, their clearances. This is necessary, said Mr. Seedhouse because “although we expect to receive the fixtures in the correct state, being able to ensure they are correct to what we expect at this stage can save a whole lot of time and effort trying to find a problem later on.”
Following these checks, the first part is loaded and OMV is used to measure the amount of stock to be removed. If necessary, the position of the part can be adjusted or a modification made to the datum being used in the machine-tool control to give a more even distribution of stock around the required final shape. The complex shapes found in many of the components would be difficult to check with physical measurement but are easy to measure with PowerINSPECT OMV.
“With new parts and possibly multiple casting suppliers, we often check the amount of stock on the component prior to machining,” explained Mr. Seedhouse. “Too much stock on the component can lead to metallurgical problems such as cracking and burning, or wheel breakdown leading to geometrical problems, and, in extreme cases, even damage to the machine. Once you know that there is more stock than expected, it is easy to add in an extra cut to remove this excess material safely.”
Another potential problem is that residual stress within a forging or casting can be released during machining and change the shape of the part. “If we think this might happen, we carry out an initial cut with extra material left on to release the stress,” said Mr. Seedhouse. “We can then check if any movement within the part has occurred with OMV and so allow the finish machining to be performed accurately.”
OMV is also used to check fixture and part positions after any heavy cuts that might have moved the part or if any problems have occurred during machining.
“PowerINSPECT OMV is an invaluable tool when making any new component or installing a new machine,” claimed Mr. Seedhouse. “It gives you a high degree of confidence almost immediately because it is very, very quick to provide basic measurements on the key points of the part.”
“It can save weeks of time that might be spent waiting for a CMM to be available and for a metrologist to analyse the results,” he added. “OMV even gives us the confidence to ask the customer to check the CMM if the measurements show any errors. In my experience, if the part gives the correct results with OMV, there is not going to be much wrong with it.” This faster commissioning benefits customers because initial test batches can be produced more quickly with high confidence that the parts will be to the required standard.
