Threading Technology – Clamping Technology 520

638 Tap Holders Soft- synchro Speed- synchro KSN MQL SFM HF EM Accessories Tech. Info Product Finder Additionally, the computer speed of modern CNC machining centers is not sufficient to handle a higher number of impulses of the rotary pick-up in the range of n = 0 up to the max. spindle speed and to adjust the axis to be synchronized. The example of a CNC machining center with 256 impulses per spindle rotation shows that the axial force working on the tool flanks, increases with growing cutting speed. The following graphs show that the axial force for forming an M10 thread with 500 rpm (about 51.5 SFM / 15.7 m/min) is at about 427 lbf (1900 N); with an increase of the speed to 2000 rpm (about 208 SFM / 62.8 m/min) at over 562 lbf (2500 N). This clearly shows that the arising axial force, caused by the synchronisation fault, depends on the speed. 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 3000 2500 2000 1500 1000 500 0 Speed 500 rpm Roll form tap M10 in material 1045 Axial force [N] Time [s] 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 3000 2500 2000 1500 1000 500 0 Speed 2000 rpm Roll form tap M10 in material 1045 Axial force [N] Time [s] 7.4 Rigid tapping Why synchronous thread production with rigid collet holders will not result in optimum tool lives. When producing a thread on a CNC machine with taps or roll form taps (for simplicity’s sake, we will call them threading tools in the following) the speed of the rotation movement of the machine spindle with the speed of the feed axis must be registered, accounted and synchronized. When accounting the threading tool pitch and the cutting speed – giving the feed speed, faults may occur caused by parameters not being considered during the control. Two main influencing variables are: 1. Influencing factors by the CNC machining center Computer speed, resolution of the axis detection (linear axis, turning axis, C-axis), mechanical condition of the machine. 2. Influencing factors by the threading tool a) Tolerances of the thread pitch acc. to DIN EN 22857 b) Change of thread pitch and length of the threading tool when t Work ≠ t Measurement 1. Influencing factors by the CNC machining center Regarding the formfitting between tool and workpiece, the cutting and forming of threads with synchronous spindles requires permanent µ-exact control and adjusting of the feed axis movement in relation to the rotation movement of the tool spindle. Thus the thread production differs from other known kinds of machining eg drilling, reaming or milling. These processings only require an exact linear movement of the control for positioning purposes, as these tools are not connected formfitting with the workpiece. Consequently, the main emphasis of machine manufacturers is on the control of the linear axis. In practice today simply rotary pick-ups with 256 impulses per spindle rotation (360°) are used to control the rotation axis. This corresponds to an angle and so a control gap of 1.4° per impulse. P Axial forces during thread machining arise caused by control faults or control inaccuracies. Example: Tap M10 Thread pitch 1.5 mm Possible uncontrolled spindle rotation 1.4° P Possible axial position fault of about 5.8 µm between threading tool specified position and machine spindle real position. 0.1 0 1 2 3 4 5 6 7 8 9 0.3 0.5 0.7 0.9 1.1 1.3 1.5 1.7 1.9 Thread pitch P = 1.5 mm possible machine-sided pitch fault Axial fault [µm] Angle fault [Degree] Graph machine spindle turning position fault /axial pitch fault (depends on thread pitch) Effect of machine turning movement fault on the tool