Full-factor matrix model of accuracy of dimensions performed on CNC multipurpose machines

OBRABOTKAMETALLOV Том 23 № 4 2021 TECHNOLOGY In fi g. 2 shown the in fl uence of technological and design factors on plane-parallel displacements and angular displacements around the base points of the technological system at the value of the diametric dimension performed on the longitudinal carriage during multi-tool double-carriage machining equal to the scattering fi eld. The base variant is the same as in fi g. 1 and shows the changes for another option. Here, taking a two-fold value of the ratio of the length of the workpiece to its diameter ( X 0 = 149.8 mm, Y 0 = 74.9 mm, X 0 / Y 0 = 2), as a base variant (Fig. 2, a ), shown the percentage quantitative expression of plane- parallel displacements and angular displacements around the base points at the values of the diametrical dimension formed on the longitudinal carriage, equal to the scattering fi eld during the increase in the length of the part by 6 times. And here 3 pivot points (links) are highlighted on the graphs: ● – t 1 = 2 mm, t 2 = 2 mm; ▲ – t 1 = 3 mm, t 2 = 2 mm and ■ – t 1 = 1 mm, t 2 = 2 mm. In the base variant (Fig. 2, a ), for each pivot point it is shown on which of the graph branches it is located. In fi g. 2, a , if we pay attention to the base variant, we will see that for this variant, the percentage quantitative expression of angular displacements around the base points at the pivot points is – for ● 10 % (respectively, linear displacements 90 %), for ▲ 15 % (respectively, linear displacements 85 %) and for ■ – 125 % (respectively, linear displacements 225 %). Fig. 2 . In fl uence of technological and design factors of angular displacements around base points and plane- parallel displacements of the technological system at the value of the diametric size being performed on the longitudinal support with multi-tool two-carriage processing equal to the scattering fi eld: a – X 0 = 149.8 mm (base variant); b – X 0 = 898.8 mm a b Since for the case ■ linear displacements and angular displacements occur in different directions, in its total value its quantitative expression as a percentage is obtained inverse to each other. In this case, the ratio of linear movements to angular movements is 0.56. However, this ratio changes in other variants. Studies show that with an increase in the ratio of the length of the workpiece to its diameter by 1.5 times, 2.5 times, 5 times, the value of the scattering fi eld of the diametrical dimension performed on the longitudinal carriage changes accordingly at the base points from a decrease of –312 % to an increase of 12.5 %, from a decrease of –684 % to an increase of 67 %, from a decrease of –14,424 % to an increase of 384 %. And here such a change in the error is explained by possible angular displacements associated with the turning moments of the technological system. The increase in negative percentages is explained by the increase in angular displacements in the total displacement. Figure 1 shows the effect of the depth of cut on the machining error, however, during design, other parameters are more bene fi cial for control – feed on the longitudinal carriage and the transverse carriage. The in fl uence of these factors is shown in Fig. 3.