RU2136475C1 - Method of grinding multistep parts - Google Patents

Abstract

FIELD: mechanical engineering. SUBSTANCE: grinding is performed by wheels positioned coaxially. Wheel minimum in diameter has continuous operating surface. The remaining wheels have intermittent operating surface with variable length of cutting projections which decreases from wheel periphery to center. Thickness of removed layer is selected constant in all cross sections of interacting surfaces of wheel and work-piece at any recorded movement of grinding. Length of wheel cutting projection is determined by calculated formula including peripheral velocity of solid wheel, peripheral velocity of part step treated by intermittent wheel, diameter of part step treated by intermittent wheel, intermittent wheel diameter, rotational speed of grinding unit spindle, diameter of part step treated by solid wheel, and solid wheel diameter. EFFECT: enhanced stability of surface quality. 2 dwg, 2 tbl, 1 ex

Description

 The invention relates to the processing of multi-stage parts and may find application, for example, in the processing of treadmills of cones and paws of drill bits.

Known prefabricated grinding tool (A.S. N 872238, B 24 D 5/00, B 24 17/00), comprising a housing on which abrasive wheels with an intermittent working surface formed by alternating protrusions and depressions are installed, the lateral surfaces of the protrusions in a radial direction have a curvilinear shape determined from the relation
l = R ₁ α ₁ = R _i α _i ,
where l is the length of the arc of the working section of the protrusion on R _{i the} radius of the circle;
R ₁ is the initial radius of the grinding wheel;
α ₁ - the Central angle in radians of the arc of the protrusions, corresponding to the initial radius of the grinding wheel;
α _i , R _i - current values, respectively, of the central angle and radius of the grinding wheel.

 The disadvantage of this tool is that during grinding, it does not provide high accuracy of differences in the diameters of the part and stable quality of the surface layer of each machined step, since the peripheral working speeds of each constituent circle of the grinding block are different (the grinding block is composed of a set of circles of different diameters).

 Grinding wheel speeds affect the entire set of processing indicators: layer thickness, removed by one abrasive grain; cutting force developed by one grain; surface roughness; instantaneous temperature in the grain work zone; wear, grinding wheel and other indicators.

 The closest in technical essence is the method of grinding multi-stage parts (a.s. N 795889, B 24 B 1/00, B 24 B 5/12), in which the grinding of all stages of the parts is carried out simultaneously by several coaxially mounted circles having diameters, drops which correspond to the differences of the work steps of the part, with discontinuous working surfaces, while the ratio of the length of the working surface of the grinding wheel to the length of the surface of the work step interacting with it is constant.

 The disadvantage of this method is similar to the disadvantage of the above method of grinding multi-stage parts - it does not take into account the influence of regime processing parameters (wheel speed and part speed in each cross section of the interacting surfaces of the circle and the workpiece) and thus does not provide high accuracy and stability of the surface quality of each step.

 The technical result is to increase the accuracy of the form and the stability of the surface quality along the entire width of each step.

где l_пi - длина режущего выступа круга i-го радиуса;
V_ксi - окружная скорость сплошного круга i-го радиуса;
V_дс - окружная скорость ступени детали, обрабатываемой сплошным кругом;
V_дп - окружная скорость ступени детали, обрабатываемой прерывистым кругом;
d_п - диаметр ступени детали, обрабатываемой прерывистым кругом;
D_пi - i-й диаметр прерывистого круга;
n_ш - частота вращения шпинделя шлифовального блока;
d_с - диаметр ступени детали, обрабатываемой сплошным кругом;
D_сi - i-й диаметр сплошного круга
Отличительными признаками являются:
1. Переменная протяженность режущих выступов выбрана из условия постоянства толщины слоя, снимаемого одним абразивным зерном, в каждом поперечном сечении круга и заготовки в любой фиксируемый момент времени шлифования. Признак обеспечивает постоянство: нагрузки на шлифующее зерно; силы резания, развиваемой одним зерном в каждом сечении; контактной температуры в зоне шлифования и все остальные параметры процесса шлифования. Это приводит к равномерному износу рабочего профиля шлифовального круга, а следовательно, и к повышению точности формы поверхностей (при врезном шлифовании форма профиля круга копируется по форме обрабатываемой поверхности), стабильности качества поверхности вдоль всей ширины каждой ступени.The technical result is achieved by using intermittent circles with a length of cutting protrusions decreasing in the direction from the periphery of the circles to the center, determined from the condition that the thickness of the layer to be removed is constant in all cross sections of the steps of the interacting surfaces of the circle and the part at any fixed grinding time according to the formula:

where l _pi is the length of the cutting protrusion of the circle of the i-th radius;
V _xi is the _peripheral speed of a continuous circle of the i-th radius;
V _ds is the peripheral speed of a step of a workpiece machined in a continuous circle;
V _DP - the peripheral speed of the step of the part processed by an intermittent circle;
d _p - the diameter of the step of the part processed by the intermittent circle;
D _pi - i-th diameter of the dashed circle;
n _w - spindle speed of the grinding block;
d _with - the diameter of the steps of the part processed by a continuous circle;
D _сi - i-th diameter of a continuous circle
Distinctive features are:
1. The variable length of the cutting protrusions is selected from the condition that the thickness of the layer removed by one abrasive grain is constant in each cross section of the circle and the workpiece at any fixed grinding time. The sign provides constancy: load on the grinding grain; cutting forces developed by one grain in each section; contact temperature in the grinding zone and all other parameters of the grinding process. This leads to uniform wear of the working profile of the grinding wheel, and therefore to an increase in the accuracy of the shape of the surfaces (during mortise grinding, the shape of the profile of the circle is copied according to the shape of the surface being machined), and stability of surface quality along the entire width of each step.

где a_Zmax - максимальная толщина слоя, снимаемого шлифующим зерном, мм;
V_дс - скорость детали, м/мин;
V_кс - скорость круга, м/с;
t_ф - поперечная подача, мм/мин;
t_ф = t • n, здесь t - подача на один оборот заготовки (глубина шлифования), n - частота вращения заготовки, об/мин;
l_ф - расстояние между зернами, мм;
D_с, d_с - диаметр круга и детали соответственно, мм;
S - продольная подача, мм/мин;
B - фактическая ширина шлифуемой поверхности, мм;
При шлифовании методом поперечной подачи S = B, тогда отношение S/B = 1.The thickness of the layers (slices), removed by each abrasive grain, taking into account the operating parameters (speed of the wheel, speed of the part and feed), as well as the dimensional parameters of the machined surface and the grinding wheel (diameter of the part, diameter of the grinding wheel and its width) for internal grinding is determined by E.N. Maslov (E.N. Maslov. Theory of metal grinding. M: Engineering, 1974, 320 p.) According to the formula [(62), p. 71]:

where a _Zmax is the maximum thickness of the layer removed by grinding grain, mm;
V _ds is the speed of the part, m / min;
V _cs - circle speed, m / s;
t _f - transverse feed, mm / min;
t _f = t • n, here t is the feed per revolution of the workpiece (grinding depth), n is the speed of rotation of the workpiece, rpm;
l _f - the distance between the grains, mm;
D _with , d _with - the diameter of the circle and details, respectively, mm;
S - longitudinal feed, mm / min;
B is the actual width of the grinding surface, mm;
When grinding by the transverse feed method S = B, then the ratio S / B = 1.

 The plus sign is taken when the circle and part rotate in opposite directions, and the minus sign is when the circle and part rotate in the same direction.

The invention is illustrated in the circuit shown in FIG. 1 and FIG. 2. On the mandrel 1 (Fig. 1) grinding wheels 2 and 3 with diameters D _c and D _p that are in contact with steps 2 'and 3' with diameters d _c and d _{p of} part 4, respectively, are firmly fixed. The working surface of grinding wheel 2 is continuous the working surface, and the circle 3 is intermittent with protrusions 5 and alternating depressions 6 (Fig. 2). The cutting length l on the cutting protrusions 5 of the intermittent wheel 3 decreases in the direction from the periphery to the center (l> l _i > l _n ) due to the reduction of the grinding wheel 2 with a continuous working surface depending on its wear.

A grinding block composed of circles 2 and 3, moving in direction 7 with a transverse feed D _s , grinds the corresponding stepped surfaces 2 'and 3' of part 4. The thickness of the layer removed by one abrasive grain in cross sections II and II-II of the interacting surfaces circle and workpiece 2-2 'and 3-3' constant. The preservation of the constancy of this parameter at each fixed point in time of grinding with the wear of the wheels is ensured by changing the cutting length of the protrusions - l _p discontinuous grinding wheel 3.

 Specifically, the implementation of the proposed method of grinding multi-stage parts will be shown by the example of processing the raceways of the cone of the drill bit.

The initial data for the calculation
Detail:
- the diameter of the large roller track (bd) - d _p = 70.7 mm;
- the diameter of the small roller track (m.r.d.) - d _with = 41.7 mm

Grinding wheels:
- the initial diameter of the dashed circle D _p = 60 mm;
- extremely worn-out diameter of an intermittent circle D _p = 50 mm;
- the initial diameter of the solid circle D _s = 31 mm;
- extremely worn-out diameter of a continuous circle D _c = 21 mm.

Mode parameters:
- the rotation frequency of the grinding block n _W = 14000 rpm;
- frequency of rotation of the part n _d = 30 rpm;
- the largest actual cutting depth with one grinding grain t _f = n • t, where t = 0.1 mm / rev - feed per billet revolution (grinding depth) n _d = 30 rpm - part speed;
t _f = 0.1 • 30 = 3 mm / min.

 Mark of grinding wheels - 24A25SM1K5.

 Let us show how the thicknesses of the layers taken by one abrasive grain differ in sections I-I and II-II (Fig. 1) when processing stepped surfaces by known methods of grinding multi-stage parts for the original, 50% worn and extremely worn circle diameters.

 The calculation results performed according to dependence (2) are given in table. 1 at the end of the description.

 From the table. 1 it can be seen that the thicknesses of the layers (sections) removed by one abrasive grain in sections I-I and II-II at the same fixed grinding time are different. This means that at the same part, steps 2 'and 3' are processed under different grinding conditions so that at the initial moment of grinding from the surface 2 'the layer of metal removed by one abrasive grain is 0.00079 mm, and from the surface 3' - 0,00038 mm. With 50% wear of grinding wheels, the thicknesses of the layers are respectively 0.00124 and 0.00053 mm, and with extremely worn circles the thicknesses of the layers (sections) removed by one abrasive grain are 0.00197 mm - from the surface 2 'and 0.000698 mm - from the surface - 3 '.

To achieve a technical result, it is necessary that the thicknesses of the layers (sections) removed by one abrasive grain at the same fixed time point of grinding be the same i.e. each workpiece has a thickness
a _ZI-I = a _ZII-II = ... = a _Zn-n = c = const,
where II, II-II, ..., nn are the cross sections of the work steps of the part.

To ensure condition (3), it is necessary to use the expression (2) to determine a _Z in sections II and II-II and equate their right-hand sides.

у прерывистого круга выражение πD_п заменить на длину его режущего выступа - l_n и решить это равенство относительно данного (l_n) переменного параметра, т.е.Then in this equality, which is part of the circle speed formula

in an intermittent circle, replace the expression πD _n with the length of its cutting ledge - l _n and solve this equality with respect to a given (l _n ) variable parameter, i.e.

где i - произвольные радиусы кругов от исходных до их предельно изношенных значений
При a_ZI-I = a_ZII-II и πD_п = l_n имеем

В табл. 2 в конце описания приведены расчетные значения суммарных длин режущих выступов сплошного круга - l_с (сечение I-I) и прерывистого круга - l_п (сечение II-II), обеспечивающие постоянство толщины срезаемого слоя a_Z в любой фиксируемый момент времени шлифования, т.е. при обработке каждой отдельной детали.

where i are arbitrary radiuses of the circles from the original to their extremely worn values
For a _ZI-I = a _ZII-II and πD _n = l _n we have

In the table. 2 at the end of the description, the calculated values of the total lengths of the cutting protrusions of the solid circle — l _s (section II) and the discontinuous circle — l _p (section II-II) are provided, ensuring the thickness of the shear layer a _Z is constant at any fixed grinding time, i.e. . when processing each separate detail.

From the table. 2 it follows that condition (3) is satisfied. The thicknesses of the layers removed by one grinding grain in section II and II-II at the same fixed moment of grinding time are constant. So, at the initial moment of grinding, the layer thickness a _Z is 0.00079 mm, and at the final moment a _Z = 0.00197 mm. Thus, the steps 2 'and 3' of the part 4 are machined under the same grinding conditions.

 By ensuring conditions in accordance with expression (3), uniform radial wear of the working profile of the grinding wheel is achieved, and therefore, the accuracy of the shape of the surfaces is increased and is maintained throughout the entire grinding process until the wheel is completely worn.

 Using the proposed method provides a constant thickness of the layers removed by one abrasive grain in each cross section of the circle and the workpiece at any fixed time point of grinding.

This condition is provided by changing the length of the cutting part (l _p ) of the discontinuous circle in section II-II. Achieving high accuracy of the shape of the surfaces of the workpiece by the proposed method is based on a new technological approach, fundamentally different from all previously known technical solutions that take into account the real conditions for the interaction of the surfaces of the circle and the workpiece with the complete removal of the specified allowances in each cross section of the workpiece. Here, the influence of all processing processing parameters is taken into account, which formed the basis for the development of a new method of mortise grinding of multi-stage surfaces.

Claims (1)

A method of grinding multi-stage parts, in which the grinding of steps is carried out by several coaxially mounted grinding wheels, the differences in diameters of which correspond to the differences in the diameters of the work steps of the part, the wheel with a minimum diameter having a continuous working surface, and the rest of the wheels being intermittent, characterized in that they use intermittent wheels with decreasing in the direction from the periphery of the circles to the center by the length of the cutting protrusions, determined from the condition of constant thickness of the removed layer I at all cross sections of stages of the interacting surfaces of the circle and the details at any time fixed by the time of grinding by the formula

where l _ni is the length of the cutting protrusion of the circle of the i-th radius;
V _kci is the _peripheral speed of a continuous circle of the i-th radius;
V _ds is the peripheral speed of a step of a workpiece machined in a continuous circle;
V _DP - the peripheral speed of the step of the part processed by an intermittent circle;
d _n is the diameter of the step of the part processed by the intermittent circle;
D _ni is the i-th diameter of the dashed circle;
n _w - spindle speed of the grinding block;
d _with - the diameter of the steps of the part processed by a continuous circle;
D _ci is the i-th diameter of the solid circle.

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