Jointly sponsored and organised by Heidenhain (GB) and Geo Kingsbury, sole agent for Hermle machines in the UK and Ireland, the event was also supported by CAD/CAM specialist Delcam, tooling supplier Seco and workholding firm, Schunk.
Heidenhain and Hermle head offices and factories are located in southern Germany and the companies have had a close working relationship for many years. Evidence of this was the agreement between the control producer and the machining centre manufacturer whereby Hermle had one year's exclusivity on fitting the TNC 640 to machining centres that incorporate integral turning. Hermle had a marketing advantage for that period, while Heidenhain benefitted from the machine manufacturer's knowledge and expertise. They enabled the capabilities of the CNC system to be refined, particularly with regard to conversational programming and kinematic control of turning functions.
The fruits of the collaboration were communicated to attendees at the NAMRC over the two days. The programme included classroom presentations and computer simulations of various machining cycles followed by live demonstrations on a Hermle 5-axis C 60 U MT. It is an agile machining centre with 50 m/min rapids and 6 m/s2 acceleration in the linear axes, and can produce parts up to 1,200 mm diameter by 900 mm high. The MT suffix signifies that the machine incorporates a torque motor-driven table on the trunnion for in-cycle turning.
A 1.6-tonne EN8 billet measuring 815 mm in diameter underwent a complex series of machining operations at the seminars, while cameras placed within the machine transmitted videos to enable visitors to appreciate the nuances of what they were seeing. Most demonstrations involved cutting dry to assist observation; only deep-hole drilling was executed with 150-bar through-spindle coolant.
Three features of the combination of machine and control that were presented are worthy of special mention. One was A-axis turning, which allows the trunnion to be continuously positioned at any angle while the component on the table is rotated for turning using a fixed tool in the spindle. This simultaneous interpolation improves cutter access and allows shorter turning tools to be used for more stable machining.
Another attribute demonstrated was programmeable Adaptive Feed Control within the TNC 640, which continuously adjusts the feed rate to keep the spindle load constant as the milling cutter moves into different parts of a cycle. So when particularly heavy metal removal is in progress, the infeed slows, whereas during periods when the spindle load is low, such as when the tool is changing direction, the feed rate is raised. In the example given at the seminar, a 17 % reduction of feed times was recorded.
A further function in the TNC 640 is trochoidal milling, whereby a tool spirals in to take a cut wider than the diameter of the mill. Spindle load is reduced when metal is removed in this way, so the full depth of the cutter flutes can be used rather than just the bottom few millimetres, leading to faster metal removal and longer tool life. A demonstration in titanium alloy (Ti64) using a 16 mm diameter solid carbide end mill showed that trochoidal milling increased metal removal rate by one-third, while if AFC was applied as well, the increase was nearly two-thirds.
The third highlight was Active Chatter Control, a feature that allows depth of cut to be increased by up to 20% when roughing without inducing vibration. ACC is achieved not by altering the cutting data, but by varying the output of the feed drives. Apart from enhancing productivity, benefits include less tool wear, reduced machine loading and higher process reliability. Unfortunately, it proved impossible to generate any chatter on the 30-tonne Hermle C 60 U MT, so it was possible only to simulate the feature.
Some 50 production engineers attended the event, for which, Richard Kingsbury, managing director of Geo Kingsbury thanked hosts Nuclear AMRC, fellow sponsor Heidenhain (GB) and equipment suppliers, and Hermle key account manager Martin Wener who travelled over from the company's headquarters in Gosheim. "It really was a team effort."
