Machining large parts is considered challenging because the parts are too bulky or heavy to be handled by one person especially when it comes to moving them over to a different location. Some parts are also too large that they are hard to fit into the work zone of commonly used China cnc machining tools. The large parts unfortunately apply to carious industries including power generation, oil drilling, construction and aircraft and they are therefore very important and need to be machined anyway.
Most challenges with the large part machining lies with the performance of in a single setup. 5 axis machining is usually required for the machining center to be able to achieve as many part features as possible in single setup. There is also need to locate parts prior to the machining and this means having on-machine probing. It is no doubt that large part machining is different and requires professionalism and precision to achieve the desired results. But what exactly are the major difficulties and what can be done about them?
Temperature and machining accuracy – Temperature is very significant when machining large parts. Even the smallest temperature change can violate the tolerance band. This means that in most cases the parts need to sit and wait until they stabilize to the right temperatures before they become ready for machining. The metal expanding effect can be reversed by ensuring that the working space remains at constant temperatures so the parts remain cool and ready to be machined appropriately.
Material stress – Large parts bring in material stress challenges for the process to be effective enough especially with large castings. The roughing amount needs to find a balance between light enough for sufficient stock finishing and deep enough for unlocking distortions that are stress related and could affect the finishing accuracy.
Machining tools challenges – In essence the machining tools used for large parts should be good enough to make milling easy and to also improve effective and quick delivery drilling. The machine’s spindle matters a lot in this with machines with spindles that pivot more than 90° being better in reaching drilled holes on the part surfaces including those on the flanges, opposite flange and middle section all in single setup. A 5 axis machine would make a better choice to achieve this.
Speed and accuracy – Machining large parts requires plenty of tolerance band especially for castings. This means, therefore that the best method needs to be found to achieve this kind of tolerance with the large parts. To achieve tighter tolerance that is important on the large scale feature, it is necessary to take semi finish passes and measure before taking the appropriate finishing passes. It is an important machining step that determines the accuracy of the finished product and the speed at which the finished product is reached.