5-axis focus [18/08/2009] Machining prismatic components on machine tools having 3, 4 or 5 axes is possible. Hardinge's Mukund Patel explains the benefits of 5-axis machining by reference to some examples A 3-axis machining centre has three linear axes – X, Y and Z. These are mutually perpendicular, where, on a vertical spindle machining centre, Z is vertical up-and-down movement; X is side-to-side movement; Y is back and forth. A 4-axis vertical machine has an additional rotary axis, typically rotating in A (about X-axis), B (rotating about Y-axis), or C-axis (rotating about the Z-axis). A 5-axis vertical spindle machine tool adds another, so that in addition to X, Y and Z linear, there are two additional axes, once again, a combination of A,B and C. Some or all axes will move to cut a part – movement of more than one axis at a time to do so is termed simultaneous movement. (Horizontal spindle 3, 4 and 5-axis machines also exist, but are less commonly used than are verticals.) Some components, like a propeller, are efficiently machined by the 5-axis route; for while it is possible to machine a propeller using simultaneous 3-axis operation, there will be an increase in machining time, while a large number of set-ups for orientating and presenting the component in suitable manner will also be required. There will also be a need to blend in a number of surfaces generated in various set-ups to achieve the desired shape. Image: Click here The machining of such curved surfaces here and on other components, such as turbine blades or impellers, is typically now undertaken with 5-axis simultaneous machines, where the tool is able to be continuously inclined so as to gain access and present the tool at the best cutting angle. There are components, typically termed prismatic parts, which on first impression look as if they would not benefit from using a 5-axis machine tool. To machine the prismatic type component shown top right would require six set-ups (one per face) assuming that all the features are a perpendicular to the spindle axis. Each face of the component would have to be presented perpendicular to the spindle axis machining. In this case, the component benefits from 5-axis positioning – in other words cutting is not undertaken in five axes simultaneously, as with the propeller, but instead the extra axes are used to position the tool in the appropriate position to 'attack' each face. You will notice that there is a feature on the component that is not perpendicular to any one face, so this feature would require an additional operation to achieve all the specified features on a 3-axis machine. Image: Click here However, a case can be made that a machine with 4-axis capability could also produce all the features required on the above prismatic component using two set-ups and therefore there is no need to use a 5-axis machine. In this case, the part would simple be rotated below the vertical spindle, presenting faces in turn to the cutter. Elsewhere there are parts that look like they fall between 3-axis and 5-axis machining. The aerospace component, bottom left, is highly suitable for machining using a 5-axis machine. There are features, such as the pocketing, that can be generated via 3-axis machining; however, there are a lot of features that blend in three planes. This component was machined in two operations on 5-axis machine, while on a 3-axis machine a minimum of seven set-ups would be required. Image: Click here Three-axis set-up times are around 1.5 hours, while for a 5-axis machine the set-up time would be 2.5 hours. But in addition to reducing set-up times, machining time is improved, due to optimised tool-to-surface conditions, giving better cutting conditions and allowing for the use of shorter tools (less overhang equals higher rigidity equals less vibration equals better surface finish). Image: Click here The key benefits of 5-axis machining therefore, are: reduced number of setups; simpler fixturing; reduced errors, due to relocation of component; better cutting conditions; shorter cutting tool; machining on the flank or bottom of tool; more accurate component – machined in one set-up; better blending of surfaces, due to appropriate cutting strategies. Image: Click here There are a number of configurations available to choose from for a 5-axis machine. In the case of a small component that fits, say, inside a150 mm cube, a machine having the two rotary axis positioning on the machine table (top, left) would be appropriate. However, for a larger part, such as an aircraft wing spar typically a metre or more in length, this probably see a machine used that has the two rotary axis on the spindle (bottom, right). There is of course the third combination where one rotary axis is applied for the positioning of the component and the other rotary axis built into the spindle. First published in Engineering Apprentice, Summer 2009 Related Companies: Hardinge Machine Tools Ltd