CC BY
21
SRSTI 55.31.29, 55.19.03
Zh. K. Mussina1, G. T. Itybaeva2, A. Zh. Kasenov3, M. Zh. Abisheva4
1A3Candidate of Technical Sciences, associate professor, Department of «Mechanical Engineering and Standardization», S. Toraighyrov Pavlodar State University, Pavlodar, 140008, Republic of Kazakhstan; 4student, «Standardization and Certification», Department of «Mechanical Engineering and Standardization», S. Toraighyrov Pavlodar State University, Pavlodar, 140008, Republic of Kazakhstan e-mail: '[email protected]; [email protected]; 3 [email protected]; [email protected]
COMPARISON OF TWIST DRILLS SHARPENING METHODS
The majority of sharpening methods differ from each other not only in technological features, but also in a form of back surfaces of a drill. Therefore there is no coincidence on distribution of back angles along the main edges and to geometrical parameters of a cross edge: to face angles, camber, and sometimes tilt angle between drills of different sharpening even at identical values of corners and a.
Keywords: drills, sharpening methods, steel, cross edge, conic of the 1st type, planetary, two-plane, spiral, complicatedly spiral type.
INTRODUCTION
The firmness of a drill substantially depends on symmetric sharpening of both feathers. According to the data of G. V. Bechin asymmetry of gardening especially adversely effects on firmness of the drills working on the conductor where loading cannot be redistributed between feathers at the expense of a drill bend. When processing of steel, possessing high degree of an elastic consequence, opposite, beating of the main edges within 0,2-0,4 mm and the breakdown of a hole arising at the same time reduce friction of ribbons and increase firmness of a drill.
MAIN PART
When drilling the majority of materials with increase in beating of the cutting edges the firmness of a drill (figure 1) decreases.
Cutting edge run-out m the axial direction
The processed material is steel 45. Diameter of the drill is 15, 88 mm. Drilling mode: v=38 of m/min, Soc =0,45mm /cycle, depth of the hole is 30 mm. Figure 1 - Dependence of firmness of a drill on the size of axial beating of the cutting edges
Correctly constructed technology of processing allows reaching equivalent symmetry of back surfaces at all sharpening methods. However at conic and shaped sharpening the improved skills of the worker, higher precision of production of the machine and the complicated operation cycle are required in comparison with planetary, screw and difficult and screw methods for this purpose.
In the conditions of equality of angles 2^ and a and symmetry of the main edges the difference the drills exploited qualities is connected with a different form of back surfaces. Comparison of geometrical parameters of drills demonstrates that increase of back angles from the periphery to the center at all methods of sharpening proceeds practically with an identical speed (table 1).
For all sharpening methods within diameters of the cutting cylinder Dx = (0,35 ^ 1) D the back angle is approximately equal
The main distinction determined by a sharpening method consists in geometrical parameters of a cross edge on which process of deformation of chip scrap represents a complex combination of expression and cutting with negative face angles.
Table 1 - Geometrical parameters of drills with different sharpening 2^=118°, ^=45^50°
Sharpenin g method Back Angles Relative recession of the back surface — D Parameters of the cross edge Remark
On the periphery a in degrees Near the middle of a in c degrees face angles )■'., in degrees relative arrow of cambers f/D before
Conic of the 1st type 10 29 0,1-0,15 -(48-53) 0,01 o = 45°
Planetary 10 30 0,08-0,12 -(50-56) 0,02 o = 30°
Two-plane 10 27 0,15-0,20 -(46-48) 0,02 a2= 40°
Spiral 10 32 0,04-0,06 -(34-38) 0,02 from two eccentrics, with a pointing of the cross edge
Complicatedly spiral 10 26 0,08-0,12 -(46-50) 0,01
About 60 % of axial force and 10 % of torque when drilling are the share of a cross edge. Axial force decreases with reduction of negative face angles on a cross edge, its extent and also lengths of a way of the chip scrap which is formed on it to an exit flutes. That is why sharpening methods in ascending order of axial force when drilling form a row: screw, two-plane, complicatedly spiral, conic and planetary (table 2). Such ratio remains at all sharpening modes (figure 2).
/
y
- i- J
""1 * - y
30 J t to S SO i ! r
Drill with a diameter of 20 mm with core thickness: 1-2,7 mm; 2-2,25 mm; 3-1,9 mm. Angles: 2<p=l 16°, <x=12 Drilling mode: v = 28 —; saf = 0,4—,
ZR171 ' CyC
The processed material is steel 45.
Figure 2 - Dependence of axial force on a tilt angle of a cross edge at conic
sharpening of the 1st type
If the torque minimum is reached at ^=55^60°, then the minimum of axial force for all sharpening methods is in the area of lower angles ^=35^45°.
Change of a tilt angle with 55 to 45° reduces axial force on average by 1,5 times and levels difference between sharpening methods. It is connected first of all with relief of a descent of the chip scrap which is formed on a cross edge in drill flutes, and at some methods also with reduction of angles.
Application of drills with a tilt angle less than 35° not only on increase of axial force, but, the main thing, because of a hole facet is inadmissible.
Table 2 - Comparison of sharpening methods on the axial force and accuracy of drilling
Sharpening method The axial force Breaking of Inaccuracy of
y = 55° ¥ = 45° holes holes form Remark
In kg % In kg % In mm % In mm %
Conic of the 1st type 1480 100 870 100 0,23 100 0,11 100 o = 45°
Planetary 1510 102 930 107 0,17 74 0,09 82 o = 30°
Spiral 930 63 750 86 0,15 69 0,07 67 from two eccentrics
Complicatedly spiral 1180 80 840 97 0,22 96 0,11 100 -
At
Two-plane 1120 76 820 95 0,20 87 0,10 91 if
Increase in a share of the axial force falling on a cross edge is followed by increase of thermal tension of process of cutting on a cross edge and affects temperature of the main cutting edges. A. M. Danielyan and D. V. Kozhevnikov's researches have shown that depending on cutting conditions on a cross edge to temperature of peripheral points of the main edges can change on 30-50° (figure 3). Though with increase in speed of
cutting temperature of the main edges also increases, but the difference of temperatures at drills with different sharpening remains actually invariable.
When drilling with the standard cutting modes when temperature of the main edges is in limits of 300-400°C, its change on 30-50°C cannot significantly affect firmness of drills (table 3).
On the contrary, at the forced modes when temperature on the main edges exceeds the limit of 480-500°C, each additional 30-50°C very sharply influence on the drill firmness very sharply. At speeding up of the processing mode the difference in firmness of drills with two-plane (y=40°) and conic sharpening (y=55°) increases from 1, 4 to 11 times. On the contrary, at the forced modes when temperature on the main edges exceeds the limit of480-500°C, each additional 30-50°C very sharply influence on the drill firmness very sharply. At speeding up of the processing mode the difference in firmness of drills with two-plane (y=40°) and conic sharpening (y=55°) increases from 1, 4 to 11 times. On the contrary, at the forced modes when temperature on the main edges exceeds the limit of480-500°C, each additional 30-50°C very sharply influence on the drill firmness very sharply. At speeding up of the processing mode the difference in firmness of drills with two-plane (y=40°) and conic sharpening (y=55°) increases from 1, 4 to 11 times. On the contrary, at the forced modes when temperature on the main edges exceeds the limit of 480-500°C, each additional 30-50°C very sharply influence on the drill firmness very sharply. At speeding up of the processing mode the difference in firmness of drills with two-plane (y=40°) and conic sharpening (y=55°) increases from 1, 4 to 11 times. On the contrary, at the forced modes when temperature on the main edges exceeds the limit of 480-500°C, each additional 30-50°C very sharply influence on the drill firmness very sharply. At speeding up of the processing mode the difference in firmness of drills with two-plane (y=40 °) and conic sharpening (y=55°) increases from 1, 4 to 11 times. On the contrary, at the forced modes when temperature on the main edges exceeds the limit of480-500°C, each additional 30-50°C very sharply influence on the drill firmness very sharply. At speeding up of the processing mode the difference in firmness of drills with two-plane (y=40°) and conic sharpening (y=55°) increases from 1, 4 to 11 times.
a) b)
H
xa> ta>
SCO an
too
UK SO) u»
№
a) - on the axial force (diameter of a drill is 27,7 mm); b) - temperature of the main edges of a drill (diameter of a drill is 26 mm): 1 - conic sharpening; 2 - screw; 3 - two-plane; 4 - drilling by a drill with screw sharpening on a hole which diameter is equal to length of a cross edge.
The processed material is steel 45 mm, saf is 0,33 mm /eye Figure 3 - Influence of a sharpening method picture
Table 3 - Influence of the processing mode on firmness of a drill
Sharpening method Parameters of a cross edge Firmness of a drill in min at the drilling modes
9 in degrees );■; in degrees u=29 m/min Saf =0,43 mm/cyc u = 29 m/min Saf =0,72 mm/cyc = 29 m/min Saf =0,43 mm/ cyc
Conic of the 1st type 55 -(53-55) 70 5 5,5
Conic of the 1st type 35 -(43-51) Was not researched
Two-plane 40 -43 110 27 60
On the contrary, at the forced modes when temperature on the main edges exceeds the limit of 480-500 °C, each additional 30-50 °C very sharply influence on the drill firmness very sharply. At speeding up of the processing mode the difference in firmness of drills with two-plane (y=40°) and conic sharpening (y=55°) increases from 1, 4 to 11 times. At equal angles ^=35^40° the twofold advantage of two-plane sharpening got at the forced mode will be minimized on the mode standard.
Researches have shown that in the conditions of equality 2^, a and y have shown that at the limiting runout of firmness ribbons of drills with conic, planetary, screw and two-plane sharpening are approximately identical, and the one-plane method because of big back angles gives firmness of drills for 20-25 % lower (table 4).
Table 4 - Firmness of drills with sharpening
Sharpening method Drills diameter 20,6 mm Drills diameter 6 mm Remark
Value of limit runout,in mm
On ribbons 1,3 On back surfaces 0,6 On ribbons 0,5 On back surfaces 0,2
Firmness of drills in quantity
holes in % holes in % holes in % holes in %
Conic of the 1st type 710 100 263 100 435 100 220 100 o = 45°
Planetary 650 92 253 96 430 99 213 97 o = 30°
Spiral 655 93 500 190 425 98 292 132 From two eccentrics
Two-plane 670 95 247 94 449 103 210 95 a2 = 40°
One-plane - - - - 315 72 185 84 -
Cutting mode -
Studying of runout on a back surface has revealed almost twofold advantage of screw sharpening.
Two-plane sharpening of drills with the angle a2 = 40 + 45°is also unsuitable for drilling of high-strength materials as the cutting wedge of the main edges has the
lowered durability and rigidity and also takes away heat badly. The drill firmness decreases because of vibration and the accelerated runout of back surfaces. For drilling of high-strength materials the second plane has to be settled down at an angle a2=25^30°, at the same time advantages of two-plane sharpening in parameters of a cross edge are lost so it is necessary to undermine an edge.
The interrelation of breakdown of a hole and withdrawal of its geometrical axis with beating of the main edges without the shift of a core is expressed when processing became the following empirical formulas offered by A. D. Martynov (figure 4):
xa = 0.0005D 4- 0,04 VZ> + (1,67 4- 0,015Z>) bd;
3 I3 I3
xv =-- 0,00006— + 0,0003 ^r bd,
у D D3 ' D3 d
where xa is an average value of breakdown of a hole in mm;
-v... is an average value of withdrawal of an axis of a hole on 100 mm of length mm;
D is a nominal diameter of a drill in mm;
1 is a length of a working part of a drill mm;
-V; is an axial beating of a drill in average points of the main edges in mm.
a)
b)
Q20 QW a!
%
-5 ш
1 woo
1 am
J.
aim
auoo
1
s am
7
/ /
7 J
—j* )M~—|
Q20 QiO ™>
Ы
a) - is on breakdown of a hole; b) - is a withdrawal of an axis of a hole Figure 4 - Influence of beating of the main edges on the average diameter of a drill
Accuracy of drilling depends on breakdown of a hole, withdrawal of its geometrical axis and a form inaccuracy which are caused by imbalance of forces on feathers and emergence of the resultant radial force bending a drill In turn, the reasons of imbalance of forces on feathers and emergence of the resultant radial force bending a drill are first of all beating of the main edges and shift of a core of a drill.
Drills with more convex cross edge and smaller negative angles on its counteract top shift from the resultant radial force which has arisen on the main edges better and give more exact openings. Therefore in process of decrease in accuracy of processing,
methods of drills sharpening form a row: screw, planetary, two-plane, complicatedly spiral and conic.
The sharpening of a cross edge of a drill is carried out for increase in accuracy of holes and reduction of axial force.
Thus, at a stressed processing mode the sharpening of a cross edge in connection with improvement of conditions of education and removal of chip scrap can increase also firmness of a drill.
The more adverse after sharpening parameters of a cross edge are, the bigger effect is reached by its sharpening. At screw and two-plane a2 = 40 -=- 45,:,a method the sharpening of a cross edge of a drill does not influence the accuracy of drilling and axial force.
Four kinds of a sharpening are applied: with preservation of a cross edge or with its partial replacement with a new edge (figure 5).
a) b) c) d)
a) - with preservation of a cross edge and cutting of an occipital part of a feather;
b) - with preservation of a cross edge without cutting of an occipital part of a feather;
c) - with partial replacement of a cross edge without correction of face angles on the
main edges; d) - with partial replacement of a cross edge and correction of face angles on the main edges Figure 5 - Kinds of sharpening
In the first case improvement of face angles is reached and the descent of the chip scrap which is formed on a cross edge in drill flutes is facilitated. The central site of a cross edge about 0,5 mm length is not undermined. The sharpening shown in the figure 5 is carried out by a grinding wheel of a direct profile. Therefore the advantage of such sharpening is simple editing of a grinding wheel, and disadvantages are its labor input and decrease in rigidity and durability of the cutting wedge. The specified disadvantages are liquidated when using a shaped circle.
On a cross edge by installation of a drill and circle it is possible to receive face angles to +5° that at conic sharpening reduces axial force by 1,5-2 times. The two first kinds of a sharpening can be recommended for drilling of materials of low and average durability, especially on drills with a reinforced core.
At partial replacement of a cross edge improvement of angles Yn and a descent of chip scrap are reached and also some effect of a breaking chip scraps on the main edge. The advantage of a sharpening is the possibility of correction of face angles on the main edges and creations of the breaking chip scraps rapids.
The mandatory requirement imposed to thy cross edge sharpening is symmetry of its performance. This operation should be performed on special or universal and tool-grinding machines where the correct installation of a drill and exact division is provided.
CONCLUSION
Thus, the cross edge needs to be undermined at all drills with core thickness more than 0,18D irrespective of a sharpening method of back surfaces. At the drills with thinner core working on materials of low and average durability after screw or two-plane sharpening it is inexpedient to undermine a cross edge.
It should be mentioned that when forming the occipital surface having the raised back angle it is necessary to reduce a comer <Pо on 7-8°. When sharpening a drill on two cones it is possible to process a diamond wheel not only the main, but also cross edge.
REFERENCES
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4 Ghorbani Siamak, Aguayo Crisostomo, Alejandro Veliz, Rogov, V. A. Experimental and theoretical research on drilling epoxy granite using coated and uncoated carbidespiral drill bits // International Journal of Mechanical Sciences. -Vol. 135. - 2018. - P. 240-252.
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Material received on 15.05.18.
Ж. К. Мусина1, Г. Т. Итыбаева2, А. Ж. Касенов3, М. Ж. Абишева4 Спиральд1 бургылардыц кайрау эдктерш салыстыру
1,2,3,4С. ТораЙFыров атындаFы Павлодар мемлекетлк университет^ Павлодар к., 140008, Казахстан Республикасы.
Материал баспаFа 15.05.18 тYстi.
Ж. К. Мусина1, Г. Т. Итыбаева2, А. Ж. Касенов3, М. Ж. Абишева4 Сопоставление методов заточки спиральных сверл
1,2,3,4Павлодарский государственный университет имени С. Торайгырова,
г. Павлодар, 140008, Республика Казахстан.
Материал поступил в редакцию 15.05.18.
Квпшшк цайрау эдютерт 6ip-6ipiHeH технологиялъщ ерекшелiктерiмен гана емес, бургылардыц артцы бeтiндeгi нысандарымен eрeкшeлeнeдi. Сондъщтан, бургылардыц арасындагы эртYрлi цайрау кезтде, тiптi 2ф жэне а бурыштарыныц бiрдeй мэндертде, артцы бурыштарыныц басты жиeктeрi бойымен жэне квлденец жиегШц геометриялыц парамeтрлeрi аумацтары бойынша бвлу тyшсуi жоц: алдыцгы бурышы, бетШц двцестш, кeйбiр жагдайда квлбеу бурышы болады.
Большинство методов заточки отличаются друг от друга не только технологическими особенностями, но и формой задних поверхностей сверла. Поэтому, между сверлами разной заточки, даже при одинаковых значениях углов 2ф и а, нет совпадения по распределению задних углов вдоль главных кромок и геометрическим параметром поперечной кромки: передним углом, поверхности выпуклости, в некоторых случаях и углом наклона.
