The dissertation is devoted to the development of the technology of machining of internal threads using the method of non-centroidal bending on CNC milling machines with the use of a non-profile cutting tool. On the basis of the analysis of the advantages and disadvantages of existing methods of machining internal threads with profile cutting tool or comb tool cutters, and multi-pass turning with a non-core cutting tool, the working hypothesis of the dissertation research was formulated. It consisted in justification of the prospects of using the method of non-centroidal bending as a more productive technology of ensuring the accuracy and quality parameters of internal thread. It was justified the area of application of machining method of non-centroidal with a non-core cutting tool for the metric thread- in the range of thread steps from 2 to 3,5 mm and diameters from 16 to 64 mm, trapezoidal threads with thread step - 2 mm and diameters from 16 to 28 mm, inch thread - with all standard sizes of steps and diameters from G3/8 to G3'' and rope thread with a thread step – 12,7 mm and diameters from R22 to 64 mm.
In present research by means of calculating the parameters of the spiral trajectory, the kinematic scheme of combining the rotation of the cutting tool, the movement of the axial feed of the cutting tool, the movement of the circular supply of the workpiece around the axis of the cutting tool, and the number of cutting inserts it was theoretically justified condition of bending of cutting inserts for a new method for machining internal threads. Based on mathematical modeling of force interaction, the efficiency of the proposed design of a cutting tool for the implementation of the method of non-centroidal bending on CNC milling machines was justified. As a result of modal analysis of designed cutting tool for machining of rope, metric and inch threads it was determined proved no resonance when using the developed tool. The value of the first internal frequency of a non-core tool for machining rope thread was 2213 Hz, which didn’t coincide with the natural frequency of machining, which was 63 Hz, at spindle speed ni = 1250 rpm for cutting tool with three cutting inserts. The first internal frequency of a non-core cutting tool for machining metric and inch thread was 1537 Hz, which also did not coincide with the natural frequency of the cutting tool during machining – 50 Hz, which corresponds to the spindle speed ni = 1000 rpm for cutting tool with three cutting inserts.
By means of linear programming and optimization based on the criterion of maximum productivity, with the limitation on the parameters of accuracy and quality of internal thread, the area of optimal cutting parameters was determined. It was established and experimentally confirmed that the proposed manufacturing technology, as well as the design of cutting tools for circular R32 and metric cut M48x3-7N and M48x3-LH-7N, allowed to ensure the accuracy of machining in accordance with the requirements of the relevant standards. The optimal cutting parameters for rope thread R32 was determined for machining of stainless steel 5ХНМ (1.2711, 1.2713, 55NiCrMoV5 in DIN classification): cutting speed – 118 m/min and FPM – mm/min, and for machining steel 40Х (1.7045, 37Cr4 in DIN classification) cutting speed – 144 m/min, and FRM – 210 mm/min. On the basis of calculation of operating time according to the criteria of the direct manufacture time and auxiliary time it was determined that the proposed technological process allowed to reduce direct manufacture time from 2 to 9 times, and the auxiliary time - from 2 to 3 times in comparison with the existing technological process of machining of internal threads.
Implementation of the results of the dissertation research into manufacturing allowed to receive an economic effect, according to the enlarged calculations, for machining bit blank in the amount of 42260 UAH., and when machining double socket – 16550 UAH., with annual output 2000 pcs. of each item. That allowed to reduce the cost of one part by 21,13 UAH. and 8,28 UAH respectively.
