On the Problem of Spiralling in BTA Deep-Hole Machining

Abstract

The phenomenon of spiralling or helical multi-lobe formation in holes, produced by the BTA (Boring and Trepanning Association) machining, is experimentally investigated for the solid boring tool. The causes leading to spiralling are deduced from this investigation. The experimental approach pursued in exploring the problem involved the running of the machine, at analytically predicted critical speeds and observing the reoccurrence of the phenomenon. It has been established that sprialling is caused by defectiveness of the tool (radial oversize of the circle-land with respect to the leading pad around the circumference) and the coincidence of the lateral natural frequency of the boring bar-tool asssembly, with five cycles per revoution of the tool, relative to the workpiece. It has also been established that spiralling occurs only in five lobes for the commercially available BTA-solid tool and is a consequence of the standard position of the circle-land, relative to the leading pad. The trials are repeated a number of times with various workpiece materials, to assert validity of the observations.

A Nonlinear Dynamic Finite Element Analysis of Drilling Shaft including Multispan Auxiliary Supports in Deep-Hole Machining

“…Figure 4 shows the influence of variable shaft length on the whirling trajectories of drilling shaft, while taking the diameter of drilling hole as 36 mm, inner diameter as 26 mm, external diameter as 34 mm, drilling depth as = 520 mm, the location of auxiliary supports as = = ( − )/3, the transverse displacement of drilling shaft inside hole due to mass eccentricities as = = 1.3 m, and an other point outside the hole as = = 2.2 m. It is shown in Figure 4 that the shorter shafts yield the smaller whirl diameter, and these responses to drilling shaft generate quasiperiodic motion. The smaller whirling diameter and quasiperiodic motion of drilling tool indicate that the cutting thickness under the hole surface instantaneous changes and the the wave formation can be obtained directly [11]. Additionally, it can be seen from Figure 4 that the longer shafts yield the bigger whirl diameter, and the periodicity of its dynamic response is poorer than that of the shorter shafts.…”

“…It is just at this time that, owing to higher rotational speed of drilling shaft, the cutting tool whirling magnitudes will be enlarged and contain lots of vibration energy. The research results by Deng and Chen and Gessesse et al indicate [10,11] that the cutting tool vibration energy increases, thus leading to the obvious decrease in the hole machining accurateness so as to be easy to form the asymmetric-waviness intersection holes as shown in Figure 9.…”

Varying bending eigenfrequencies in BTA deep hole drilling: mechanical modeling using statistical parameter estimation

“…They may also be interpreted as resonance effects at constant eigenfrequencies. The x-shaped pattern in the spectrogram from sensor B, on the other hand, closely resembles the patterns of changing bending-eigenfrequencies which were calculated for BTA deep hole drilling by Gessesse et al [6,7].…”

“…For drilling without a Lanchester-damper, Gessesse et al [6,7] modeled the time varying structural dynamics of the components relevant for the drilling process using a finite element model. During drilling tests they observed the reproducible occurrence of spiralling when the slowly varying bending eigenfrequencies of the tool intersect with uneven multiples of the rotational frequency of the tool-or workpiece-spindle.…”

Simulation of the BTA deep-hole drilling process

“…If the bore diameter is larger than 20 mm, the BTA (Boring and Trepanning Association) deep-hole drilling process is usually employed [1]. This method creates holes with good surface finish and straightness, but the process is susceptible to dynamic disturbances like chatter [2] and spiralling [3].…”