Some features of using a spiral drill with a stepped blade for processing holes in elastic-viscous materials

Размещено на http://www.allbest.ru/

Some features of using a spiral drill with a stepped blade for processing holes in elastic-viscous materials

Introduction. In recent decades, the use of elastic-viscous polymer composite materials (PCM), which due to the combination of their high mechanical, physical and chemical properties, have become widespread in aviation, automotive, ship and rocket engineering and other areas of industry, are constantly in the focus of researchers. Among such materials also include bone tissue, in which holes are processed for various surgical operations.

PCM is a combination of high-strength fibers with a matrix that provides a monolithic composite and gives the part the necessary shape and mutual arrangement of its working surfaces [1]. Well- known studies [1-4] have established that the mechanism of cutting with a PCM blade tool differs significantly from cutting of metal materials, since when processing metal alloys, the process is the result of plastic deformations, in the case of PCM, only elastic deformations take place [1-4].

In the process of manufacturing PCM parts, very serious problems are detected when drilling holes, which is associated with ensuring the quality of the treated surface and dimensional accuracy.

The main defects of the PCM surface when processing them with a blade tool are uneven roughness, large undulations, breakouts and chipping at the ends, fiber stratification, hairiness, cracks and scratches, deviation of the shape and mutual arrangement of surfaces [5].

It is known that when cutting PCM with reinforcing fibers characterized by low plasticity, micro cracks in the form of incisions are systematically formed on the treated surface, directed approximately perpendicular to the cut line [6].

The reason for the formation of these defects is the force effect of the cutting tool on the material being processed, and therefore the search for ways to reduce the overall force load of the material cutting process is one of the main ways to improve the efficiency of hole processing in PCM.

On the basis of researches of force loading of the manufacturing system at cutting multiblade tool [7], and the application of the cutter with multi-blade [8, 9], it was found that the overall loading of the cutting materials can be adjusted by the number of simultaneously cutting teeth [7] or the number of cutting steps of the cutting tool [8,9] that allows to two or more times to reduce the total cutting force.

It is known [10] that the most used method for connecting parts from PCM is bolt or rivet connections, which require processing holes in PCM, which are mainly carried out with spiral drills.

In this regard, the development of new ways of making twist drills, including twist drill bits with multi-blade, and the establishment of its optimal geometry, to improve the hole quality and productivity [5] is an important task of machine building engineering.

Purpose of work.The purpose of this work is to improve the quality and performance of processing of elastic-viscous materials, such as PCM and bone tissue, by developing new methods for manufacturing spiral drills and establishing the optimal geometry of their blades.

Spiral drill with multi-stage blade. Spiral drills with a multi-stage blade include the well-known spiral drill [11], which is used in medicine for processing materials with different viscosities, in particular, for processing bone tissue, in traumatology and orthopedics for performing through and blind holes (Fig. 1).

This drill contains a rod 1 with a blade 2, on which the main cutting edges 3 are made, screw chip grooves 4 and additional chip grooves 5 on the back of the feather 2, on which the chamfers 6 are made, forming an additional cutting edge. Therod 1 passesin to the shank 7.

On one of the main cutting edges 3 of the blade 2, cutting wedges 8 are made (Fig. 1), and the main cutting edges 3 are made at the working ends of the blades 2 at an angle a to the axis of the tool, which can be 45-60° of the viscosity of the processed material [11].

Additional cutting edges (chamfers 6) are made at an angle p=30-60^o to the tangent of the forming surface, and on one of the main cutting edges 3 along its entire length, cutting wedges 8 are made to a depth of 0.5-1.0 mm, and the angle between the cutting wedges 8 is not less than the cutting angle of the main cutting edge 3.

Fig. 1. Spiral drill for processing holes in materials with different viscosities [11]

When cutting bone tissue with such a drill, the material to be removed is crushed, the transport of which is accompanied without increasing the temperature of the cutting elements of the drill and the material to be processed, which allows processing without the use of a coolant, increasing the processing speed and, consequently, reducing the time of surgical operation.

The main disadvantage of such a spiral drill is that the second main cutting blade in comparison with the first one works in more severe cutting conditions. This is due to the fact that the second blade cuts off the remaining part after cutting the first blade notches on the surface of the hole.

The length of contact of the second blade with the materials being processed is equal to its width, which leads to increasing treatment temperature and reduction of the durability of drill bits. Thus, the blades of such twist drills are working in various conditions, they are subject to various lateral forces, thereby increasing the magnitude of slip of the drill and a corresponding decrease in processing accuracy of the hole. Note also that sharpening such a drill requires the use of special equipment, although this does not cause certain difficulties.

For drilling holes in elastic viscous and elastic-plastic materials are also used twist drill that includes the pen 1 with dividing chip groove 2 and the pen 3 without chip separation grooves, and the cutting edge 4 of the pen 3 stands relative to the cutting edge 5 of the pen 1 by an amount equal to the depth of the groove formed by the intersection of a plane passing through the rear surface of the pen 1 and the bottom of the groove 2 (Fig.2) [12]. A special feature of this drill is that the cutting steps are formed after sharpening the drill with traditional methods.

Fig. 2. Spiral drill with chip separation groove [12]

In this case, the cutting blades of the drill, as in the previous case, also work in different cutting conditions, which contributes to the appearance of significant transverse forces acting on the top of the drill, which increases the amount of removal of the drill, which leads to a corresponding decrease in the accuracy of the hole processing. It should be noted that the need to ensure the protrusion of one cutting edge of the drill relative to the other by a certain amount requires the use of a special complex sharpening device.

To eliminate these shortcomings, the National Polytechnic University of Armenia (NTUA) has developed a new design of a spiral drill with a multi-stage blade, shown in Fig. 3 [13].

Visible (Fig. 3) that the spiral drill has conventional lines of cutting edges 1 and 2, which are the tops of the cutting steps, made on the front surfaces of these edges along the surface of the spiral chip- removing grooves 7 and 8 spiral chip-separating grooves 3 and 4, the back surfaces 5 and 6 and the jumper 11. In this case, the closest sides of 9 and 10 spiral chip-separating grooves of triangular crosssection to the drill axis are made at an angle of 3 ... 50 in the direction of the drill axis (Fig. 3). Moreover, made in two spiral chip grooves, the spiral chip separation grooves along the main cutting edges are offset relative to each other by half the width b of the spiral chip separation grooves (Fig. 3).

The specialty of such a spiral drill is that the jumper 11 together with the adjacent chip-separating grooves is a small centering drill and during the cutting process performs centering and drilling. The tops of the remaining cutting stages perform the process of boring holes obtained by previous cutting stages, which is a less loaded cutting process compared to drilling. This makes it possible to reduce the overall load by up to 1.5 times and reduce the average temperature of the process to drilling.

Due to this, small chips are formed during processing, which, even if they stick together, are easily removed from the processing zone along the chip-removing grooves of the drill without the use of lubricants. At the same time, both cutting edges of the drill work under almost identical conditions, due to which the components of the cutting force in the transverse direction differ slightly, which contributes to improving the quality of processing and the durability of the drill. Sharpening such a drill after it is blunted can be carried out using traditional classical technologies and standard devices.

Conclusions. A new spiral drill with a multi-stage blade has developed. It is established that the bridge together with the adjacent grooves of the steps is a small centering drill and during the cutting process performs centering and drilling, and the tops of the other cutting steps carry out the process of boring holes obtained by the previous cutting steps. In the process of processing holes with a spiral drill with a multi-stage blade, small chips are formed, which are easily removed from the processing zone along the chip-removing grooves of the drill without the use of lubricants. To determine the rational geometry of a tool with a multistage blade, additional theoretical and experimental complex studies are required.

The work was completed out with the financial support of the Committee on science under the Ministry of education, science, sports and culture of the Republic of Armenia within the framework of the research base laboratory "Machine-Building technologies" of the NPUA.

1. Bazhenov S.L. Polymer composite materials / S.L. Bazhenov, A.A. Berlin, A.A. Kulkov, V.G. Oshmyan. Dolgoprudny: Intellect, 2010. 352 p. (in Russian).

2. Ivanov Yu.N. Experimental study of the influence of thermal expansion of processed materials during dry drilling of holes in packages of the structure "polymer composite material-titanium alloy" / Yu.N. Ivanov, E.Ya. Kaverzin, A.P. Chapyshev // Bulletin of the Irkutsk state technical University, 2013. № 10 (81) (in Russian).

3. Alexandrov I.A. Study of the influence of deformation properties of binders on the processes of destruction of carbon fiber / I.A. Alexandrov, A.N. Muranov, G.V. Malysheva // All materials. Encyclopedic reference book, 2012. № 7. Pp. 40-45 (in Russian).

4. Andreeva A.V. Fundamentals of physics and chemistry of composite technology: textbook. in the expedient / by A.V. Andreev. Moscow: IPRZHR, 2001. 192 p. (in Russian).

5. Makarov V.F., Meshkas A.E., Shirinkin V.V. Research of problems of mechanical processing of modern high-strength composite materials used for the production of parts of aviation and rocket and space technology / Bulletin of PNRPU. Vol. 17. № 2-2015. Pp. 30-41 (in Russian).

6. Polymer composite material. Strength and technology / S.L. Bazhenov [et al.]. Moscow: Intellect, 2009. 352 p. (in Russian).

7. Balasanyan B.S. Theoretical and technological bases of increasing the stability of processing systems using ultrasound: autoref. dis. ... Doct. Techn. science: 05.03.02 / State engineering. UN-t of Armenia. Yerevan, 2003. 35 c. (in Russian).

8. Garayan A.V. Increasing the stability of the multi-blade processing process by regulating the number of simultaneously working blades: autoref. dis. ... Cand. Techn. science: 05.03.02 / State engineering. UN-t of Armenia. Yerevan, 2008. 22 c. (in Russian).

9. Hurmuzan D.G. Improving the efficiency of processing of metals by use of a cutter with multiblade: author. dis. ... Cand. Techn. science: 05.03.02 / State engineering. UN-t of Armenia. Yerevan, 2010. 23 m. (in Russian).

10. Dudarev A.S. Improving the efficiency and quality of hole processing based on the stabilization of the drilling process of products made of polymer composite materials: Dis. ...Cand. Techn. science: 05.02.08 / PSTU. Perm, 2009. 21 c. (in Russian).

11. Beklemishev I.B., Sychev M.I. Twist drill bit. Russian patent N 2198608, A61B17 / 16, B 23 b 51/02, 2003 (in Armenian).

12. Kuzovenko E.G., Shlyakhtin N.N., Kuzovenko I.E. Spiral drill. AS USSR N 1812003, IN 23 IN 51/02, 1993 (in Russian).

13. Balasanyan M.A., Balasanyan B.A., Arshakian A.L. and others. Spiral drill. RA patent № 3292 A2, B23B51/02, A61B17/1, 2019 (in Armenian).

Размещено на Allbest.ru