RU2183546C2 - Method of additive grinding - Google Patents

Abstract

FIELD: machining by diamond abrasive tools with bound grain; machining narrow-tape high-precision surfaces, such as microtome knives. SUBSTANCE: in the course of machining, stage-by-stage additive removal of surplus by set of sectional grinding closed abrasive contours is effected. Part is moved through center of tool and is positioned at angle relative to discrete cutting plane. Machining is started by inner abrasive contour whose cutting speed is lesser than clamping force by 1.3 to 2.0 times and clamping force exceeds these parameters of outer abrasive contour by 1.2 to 1.6 times. At all stages similar magnitudes of functions estimating the contact dynamic interaction of tool with work are maintained. Quantitatively, they are calculated by formulae and are compared at varying technological parameters to obtain equality of functions at all stages of machining. Sharpening the microtome knives by the additive grinding pattern makes it possible to avoid subsequent finishing operations. High-quality surface if obtained for 10 to 18 s; geometry of this surface Ra is better than 0.16 mkm. EFFECT: enhanced efficiency. 1 dwg

Description

 The invention relates to the field of machining with a diamond-abrasive tool with bound grain and can be used in various fields, in particular, in the processing of narrow-band high-precision surfaces such as microtome knife blades.

 There is a method of abrasive processing based on additive-adaptive removal of allowance with a set of prefabricated end tools in several stages [1], when the total allowance is divided into discrete allowances, the values of which are assigned depending on the clamping force of the tools. However, this method is intended for grinding parts whose size is comparable to or a multiple of the size of the working surface of the abrasive tool. Therefore, the method is ineffective when grinding long parts.

 The invention is aimed at improving the quality of polished surfaces.

This is achieved by the fact that a gradual additive removal of the allowance is carried out by a set of prefabricated grinding closed abrasive contours, for which the part moving through the center of the tool is positioned at an angle of 1-7 ^o to the discrete cutting plane, and the treatment is started with an internal abrasive contour, the cutting speed of which is 1 , 3-2.0 times less, and the clamping force is 1.2-1.6 times more than these parameters of the external abrasive circuit, and at all stages they maintain the same values of functions that evaluate the conditions of contact dynamic the interaction of the tool with the part, and quantitatively they are calculated by the formulas (1), compared and, varying the technological parameters, achieve equal functions at all stages of processing.

The figure 1 shows a diagram of the relationship between the part and the tool when removing stock. Designated: VRK and NRK - respectively, the abrasive internal and external working circuit, and the corresponding stages are I and II. The cutting speed in stages: I is V ₁ ^VRK and II - V ₂ ^NRK . Clamping forces: total F ₀ , on the contours, respectively: I - F ₁ and II - F ₂ . Part feed speed S _P The total grinding depth is -t. B ₁ and B ₂ - the width of the abrasive contours of the WRC and NRC. The angle between the part and the working surface of the tool is φ. Diameters of closed loops: BPK-D ₁ , NRK-D ₂ .

Justification of the grinding method and an example of its implementation. The processing process is controlled by varying the characteristics of the tool and the elements of the cutting mode [2]. Particularly effective is a tool made of movable abrasive inserts, the elasticity of the base of which is interconnected with the grain size of the abrasive grains [3]. However, due to the chaotic removal of the allowance, this processing method (and the tool) cannot be used for sharpening narrow-band surfaces, but the idea should be used. Therefore, in multi-stage processing using various abrasive contours, the following is proposed. At the first stage, abrasives with grain sizes d ₃ = 160/125 μm or 125/100 μm, or 80/60 μm, etc. are used in the NQF loop. Moreover, these grains are located in a “soft” bond, for example, softer than a metal bond on a copper-tin base, which is used in an abrasive circuit for the second processing step. At stage II, the grain sizes of the abrasives are d ₃ = 60/40 μm, 40/28 μm or 20/14 μm, etc.

 An indispensable condition for a stable quality of processing on the entire surface of the part is the identity of the dynamic conditions of any abrasive contour, i.e. the contact conditions of the part and tool at any stage of processing should be the same or close.

You can control the conditions of contact interaction using the technological parameters of the grinding process. These include: the cutting speed V _p , the pressing force F _{o of the} part to the tool, B is the width of the abrasive layer, S _n is the feed speed of the part, t is the grinding depth, the angle of inclination of the part and the cutting plane of the tool, as well as the characteristics of the abrasive layer ( d ₃ , the type of bundle, the nature of the macroscopic topology of the working surface (RP) of the tool, i.e., solid or intermittent (PRP), which can be taken into account by entering the coefficient K _n ) and the physicomechanical properties of the material M _{CB of} the workpiece, for example, microhardness and t .P.

 Between themselves, the above parameters have complex relationships that are difficult to describe. A known set of indicators called material processability grinding [2]. This is a combination of properties, such as material removal per minute, grinding force and temperature, specific wheel consumption, etc. However, they are difficult to tie together.

 There is a universal comprehensive indicator of the contact interaction of objects of the technical system part-tool-environment, called the indicator of contact machinability by grinding [4]. However, in a known form, it does not take into account the kinematics of the grinding process and the role of abrasive space. But its modification and the introduced adjustments reflecting the consideration of the kinematic processing scheme are acceptable for describing grinding processes in a generalized form.

Технологические параметры, входящие в первый сомножитель формулы, можно варьировать, тем самым достигать для контуров ВРК и НРК одинаковых численных значений f_офвор. При этом суммарные условия динамического воздействия инструмента и процесса обработки будут равны, хотя их составляющие (скорость резания V_p, усилия прижима F_о, аддитивные значения t, номинальные для НРК и ВРК) несколько отличаются на каждом из этапов. Коэффициент К_n учитывает соотношение жесткости абразивных контуров с зернистостью абразивов и видом связки. Ширина рабочей части замкнутого абразивного контура стандартная (5, 10, 15, 20 мм), поэтому следует исходить из этих значений, но если они различны, то это сказывается на первом сомножителе. Хотя в процессе обработки все параметры не меняют своих значений. Их выбирают, когда сравнивают между собой f_офвор, вычисленные по формуле для ВРК и НРК, и достигают равенства варьированием параметров первого сомножителя, т.е. в итоге имеем:

Диапазоны варьирования таковы. Скорость резания V₁ и V₂ взаимосвязаны между собой условиями динамического воздействия и конструктивными условиями. Стандартные шлифовальные круги имеют размеры от φ50 до φ250мм. Оптимальное соотношение между V₁ и V₂ при таких конструкциях составляет 1,3...2,0 раза. Это целесообразно также с позиции необходимости соблюдения на ВРК и НРК баланса температурно-силовых параметров, что достигается при различии скоростей резания порядка 50% [2].If we group the properties of the workpiece, as well as the speed and the removal scheme of the discrete allowance, taking into account the work being done, we can obtain an estimated function of the conditions of contact interaction of the part and the tool, which we will call f _off . Its values, taking into account the above notation, are calculated by the following formula:

The technological parameters included in the first factor of the formula can be varied, thereby achieving the same numerical values of f _off for the circuits of the _{RCS and the RCS} . In this case, the total conditions of the dynamic impact of the tool and the machining process will be equal, although their components (cutting speed V _p , pressing forces F _о , additive values of t, nominal for NRK and VKR) are slightly different at each stage. The coefficient K _n takes into account the ratio of the rigidity of the abrasive contours with the granularity of the abrasives and the type of bond. The width of the working part of the closed abrasive contour is standard (5, 10, 15, 20 mm), so you should proceed from these values, but if they are different, then this affects the first factor. Although during processing, all parameters do not change their values. They are selected when f _offor , calculated by the formula for the WRC and _NQF , is compared with each other, and they reach equality by varying the parameters of the first factor, i.e. in the end we have:

The ranges of variation are as follows. The cutting speed V ₁ and V _{2 are} interconnected by dynamic impact conditions and design conditions. Standard grinding wheels have sizes from φ50 to φ250mm. The optimal ratio between V ₁ and V ₂ with such designs is 1.3 ... 2.0 times. It is also advisable from the point of view of the need to observe the balance of temperature and power parameters at the air-tight water heater and air-tight air heater, which is achieved with a difference in cutting speeds of the order of 50% [2].

The clamping forces F _{o are} determined based on the conditions of stable destruction (removal, deformation) of the structure of the material of the part, as well as taking into account the design of the part and the magnitude of the temperature and force parameters in the contact zone of the part and tool. It was experimentally established that for high-strength steels the range of clamping forces is 5-500N, but the most acceptable range is 10-300N.

The values of the angle φ of the tilt of the part to the discrete cutting plane of the tool are limited by the following factors. On standard equipment, the accuracy of the angle is 1 ^o ± (20 '... 30'). In this case, the removed allowance is determined by the width of the narrow tape surface (this is 0.5-2.0 mm or more). The amount of removal is up to 0.6-0.25 mm. When the angle ϕ = 6–8 ^{°, the} resulting surface exceeds the size of the narrow strip, moreover, the process becomes difficult, since the proportions of the nominal depths at the stages are violated. Usually it is: at stage I t _n ^I ≈ (0.6-0.8) t, at stage II t _n ^II ≈ (0.4-0.2) t.

 The remaining parameters are set experimentally or use literature data.

The principle of the method. A workpiece moving at a speed of S _p located at an angle φ to HRK and WRC is set so that its total allowance t is divided into t _n ^I and t _n ^II . A constant force F _о acts on the part, pressing it to the assembly tool. Having come into contact with the WRC, at stage I, the clamping force F _{1 is} set in the system. Coarse-grained abrasives working according to a rigid-elastic removal pattern remove up to 80% of the total allowance. In stage II, the rest of the stock is removed. Due to the lower stiffness of the part-tool system, but the greater “hardness” of the NRF contour (since the microhardness of the binder is higher and the abrasive is less granular), the scheme of rigid-elastic stock removal is saved in the system. However, at this stage, the action of the NQF is likened to the smoothing and nursing effects carried out with increased cutting speeds. Due to this, the microgeometry of the treated surface and its waviness are reduced, and the flatness of the narrow tape surface is improved.

Comparative tests showed the advantages of the proposed grinding method. So, sharpening special microtome knives according to the additive grinding scheme allows you to abandon subsequent finishing operations. At the same time, in 10-18 seconds (depending on the length of the knife), a high-quality surface is obtained whose microgeometry is R _a = 0.6-1.0 μm. Traditional sharpening methods require 35-40 s of time and provide only R _a = 0.8-1.25 microns. By varying the processing regimes and characteristics of the tool using the criterion f _{ofovor, the} microgeometry of the knife surface is guaranteed to reach no worse than R _a = 0.16 μm. The additive grinding method is simple to implement. You can use standard circle tools in your work; only some modernization requires equipment.

Sources used
1. Patent of the Russian Federation, 2118248 V 24 V 7/04, 1998. Starov V.N. Bull. 24.

 2. SU. a.c. 1077771 B 24 D 5/06, 1984. Starov V.N. et al. Bull. 9.

 3. Maslov E.N. Theory of grinding materials. - M.: Mechanical Engineering, 1974. - 320 p.

 4. Starov V. N. Features of the finishing processing of non-metals and indicators of contact machinability of materials by grinding. - M .: Dep. in VINITI, 1996. - 14 p. 1013-B 96.

Claims (1)

The method of additive grinding by phased removal of the workpiece material with a set of end-use prefabricated tools consisting of external and internal abrasive contours, in which the total allowance is divided into discrete allowances depending on the pressure of the tool, and the part is moved through the middle of the abrasive contours, characterized in that the part is placed under 1-7 ^o angle to a discrete plane of the tool, and its processing is started abrasive inner contour cutting speed which at 1.3-2.0 times less effort and Presser and 1.2-1.6 times greater than those parameters of the outer contour of the abrasive, and maintained at all stages of the same conditions of contact interaction tool with the workpiece, which is calculated by the formula:

where f _OFVOR - the estimated function of the conditions of contact interaction;
K _n - coefficient taking into account the characteristics of the tool;
t is the grinding depth;
B is the width of the abrasive layer;
F _o - the pressure of the parts to the tool;
V _p - cutting speed;
φ is the angle of inclination of the part to the cutting plane of the tool;
S _p - the feed speed of the part;
M _St. - the properties of the material details
compare them and, varying the technological parameters K _n , t, B, F _o and V _p , achieve the equality of the values of f _OFVOR at the processing stages.