RU2176179C2 - Method of grinding screws with unifilar grinding wheel - Google Patents

Abstract

FIELD: mechanical engineering, machine-tool industry and manufacturing engineering, finishing abrasive treatment of spiral surfaces of accurate screws, mostly, having great helix angle and made from difficult to machine materials. SUBSTANCE: disk unifilar grinding wheel is set to an α_в helix angle of machined screw. Independent rotary motion and longitudinal feed equal to the lead of the helix is imparted to the wheel. Rotary motion and translation motion cinematically connected to the longitudinal feed of the wheel is imparted to the workpiece. The grinding wheel is of medium soft and fine-grained and its height is equal to the half of helix lead of the machined screw. The grinding wheel is inclined at an acute angle α_АРС to the surface which is perpendicular to the rotation axis of the wheel to provide axially shifted cutting layers. The angle α_АРС is determined from a given relation. EFFECT: enhanced efficiency, quality, and reduced consumption of abrasive and heat density of the process. 1 ex, 3 dwg

Description

 The invention relates to mechanical engineering, to the fields of machine tool engineering and mechanical engineering technology, can be used in the finishing abrasive treatment of screw surfaces of precision screws, mainly with a large angle of elevation, from difficult to process materials.

 There is a method of final grinding of spindles on thread grinding machines of type 5D822B, MB 140, machine tools of the company Matrix (United Kingdom) and other circles of elbor and other abrasive material when installing parts in centers with supporting lunettes and heavy cooling [1].

 The disadvantage of the grinding method with single strand wheels is the great complexity of the abrasive processing process, which requires special equipment, and low productivity, which is associated with the low dimensional stability of the wheels, leading to a decrease in accuracy and a quick loss of cutting properties.

 The closest in technical essence and the achieved result is the method of final grinding of the spindles on thread grinding machines such as 5D822V, MB 140, machines of the company Matrix (Great Britain) and other circles made of elbor and other abrasive material when the part is installed in centers with supporting lunches and heavy cooling [2].

 Final grinding is carried out with single-thread grinding wheels. The grinding wheel is installed at an angle equal to the angle of the thread and rotates in the same direction as the product for external threads and in the opposite direction for internal threads. The longitudinal feed is carried out by the translational movement of the product along the grindable thread relative to the grinding wheel. Cross feed of a circle to the grinding depth is made on the course of the table.

 The disadvantage of the grinding method with single strand wheels is the great complexity of the abrasive processing process, which requires special equipment, and low productivity, which is associated with the low dimensional stability of the wheels, leading to a decrease in accuracy and a quick loss of cutting properties.

 The method requires special machines with a short kinematic chain, with mechanisms to eliminate gaps during changes in the direction of rotation and grinding in both directions, and this increases the cost of processing.

 In addition, the method does not allow to intensify the cutting conditions, since the fine-grained circles recommended to obtain the minimum roughness give intensive burns during intensive modes.

 A wheel that is too hard with the traditional grinding method is quickly salted, too soft is quickly worn out, which affects the accuracy of the screw.

 The objective of the invention is to improve the quality, productivity and accuracy of processing through the use of a harder and less granular disk single-thread grinding wheel with an axially offset cutting layer, i.e., inclined at an acute angle to a plane perpendicular to the axis of rotation of the wheel.

The problem is solved by the proposed method of grinding screws with a single-disc disk grinding wheel, including setting the wheel at an angle α _{in the} elevation of the turn of the machined screw and informing it of independent rotational movement and longitudinal feed, and the part - rotation and translational movement kinematically associated with the longitudinal feed of the wheel equal to the pitch the machined screw, using a medium-soft fine-grained circle with a height equal to half the pitch of the machined screw, and additionally tilt it one acute angle α _APC to the plane perpendicular to the axis of rotation of the circle, to create an axially offset cutting layer, which is determined by the formula
α _APC = arctg [(t • cosα _at -0.5t) / D ^and ],
where α _in = arctan [t / (2D)] is the angle of elevation of the turn of the screw being machined, deg;
t is the pitch of the screw, mm;
D is the pitch diameter of the screw, mm;
D ^and - the outer diameter of the grinding wheel, mm

 The essence of the method is illustrated by drawings.

In FIG. 1 shows a processing diagram of the proposed method with the installation of the part — screw pump screw in the cartridge and in the rear center, top view; in FIG. 2 is a view along A in FIG. 1, front view with a new maximum outer diameter D _max ^and grinding wheel; in FIG. 3 is a view along A in FIG. 1, front view with the most worn out outer diameter D _min ^and grinding wheel.

At the final finish abrasive treatment of screws 1 (for example, screws of screw pumps ЭВН5-25-1500, having the profile and dimensions D, D ₁ , t, e, e ₁ shown in the drawings) according to the proposed method, carry out a single-disc disk grinding wheel 2. Grinding the circle 2 is set at an angle equal to the angle of the thread, and rotates in the opposite direction with the product. The longitudinal feed equal to the pitch of the screw is carried out by the translational movement of the grinding wheel along the grinding screw. Cross feed of a circle to the grinding depth is made on the course of the table.

 The workpiece to be machined - screw 1 - is fixed in the chuck 3 of the spindle 4 of the headstock 5, for example, a lathe with a grinding head with an individual drive on the support (not shown), and the center 6 of the tailstock 7 is pressed.

On the spindle 8 (Fig. 2), rotated relative to the axis of the workpiece by an angle α _{in the} inclination of the turn of the screw being machined, a grinding head (not shown) using oblique washers 9, two pieces installed at each end, is fixed at an acute angle α _APC to the plane perpendicular to the axis of rotation of the wheel disk single thread grinding wheel 2.

The height of the circle is taken equal to half the step t of the machined screw 1. The angle α _{APC of the} installation of the circle 2 on the spindle 8 is determined from the condition
α _APC = arctg [(t • cosα _at -0.5t) / D ^and ],
where α _in = arctan [t / (2D)] is the angle of elevation of the turn of the screw being machined, deg;
t is the pitch of the screw, mm;
D is the pitch diameter of the screw, mm;
D ^and - the outer diameter of the grinding wheel, mm

Due to the rotation of the circle by an additional angle α _{APC, the} peripheral cutting surface will oscillate, capturing the cutting zone B ₀ = t, two times larger than the height of the circle B _k = t / 2. Moreover, the oscillating cutting zone, leaving a sinusoidal mark on the surface to be treated, allows you to interrupt cutting for some cross sections of the workpiece, making it possible to reduce the heat stress of the cutting process. Thus, the method allows you to take advantage of intermittent cutting during continuous grinding.

 The proposed method positively affects the choice of the characteristics of the circle. If, during traditional grinding, small threads are usually cut in circles with a smaller grain size than coarse threads, since fine-grained circles produce a less rough surface of the thread, but they are less productive than coarse-grained, and under intense cutting conditions can cause burns, then using the proposed method, due to the oscillation of the axially displaced cutting layer of the wheel, it becomes possible to use fine-grained wheels for grinding screws with a large step in intensive cutting conditions I guarantee besprizhogovost grinding, less rough surface and high performance.

 In the traditional grinding of screws with single-thread circles, too hard circles are quickly greased, too soft - quickly wear out, which negatively affects the accuracy of the manufacture of screws.

 The proposed method of grinding with an axially offset cutting layer promotes tool self-sharpening, a longer resistance period between regrindings, increases the accuracy, quality and productivity of manufacturing screws.

As the wheel wears and straightens, its outer diameter decreases and will not capture the required grinding width B ₀ = t; therefore, it is necessary to increase its tilt angle α _APC with respect to a plane perpendicular to the axis of rotation with each grinding and dressing of the wheel. This increase can be carried out using two oblique washers 9, which are installed from each end of the circle, by their mutual rotation relative to each other at a certain angle.

Example. The left screw H41.1016.01.001 of the screw pump EVN5-25-1500 was processed, which has the following dimensions: total length -1282 mm, length of the screw part - 1208 mm, screw cross-section diameter 27 ^-0.05 mm, eccentricity e ₁ = 1 , 65 mm, e = 3.3 mm, pitch t = 28 ^{± 0.01} mm, roughness R _a = 0.4 μm; single-helical screw surface, left direction; material - steel 18HGT GOST 4543-74, hardness HB 207-228, weight - 5.8 kg. Side allowance - 0.25 mm. The processing was carried out on a modernized mod screw-cutting lathe. 16K20 with a tool grinding head mounted on a support, with an abrasive one-strand disc taken one degree of hardness higher and one grain number less than with traditional grinding, type PP 200x16x32 44A25NSM110K GOST 2424-83 (instead of 44A 8-16 M1-M2 8-12K - according to the basic version), when editing, the circle height was brought to В _к = 14 mm, head speed V _и = 31.42 m / s, n _и = 3000 rpm, peripheral workpiece speed - Vд = 15.1 m / min, n _d = 160 rpm, longitudinal feed S _ol = 28 mm / r, the angle of inclination of the coil of the screw surface α _in = 24 ^° 48 ′ _, additional angle the slope of the new circle α _APC = 3 ^° 16 ′ maximally worn (up to a diameter of 70 mm) - α _APC = 9 ^° 5 ′, the required roughness and accuracy of the screw surface was achieved after T _m = 7.6 min (against T _m ^bases = 16 , 5 minutes according to the basic version with traditional grinding on a modernized lathe 1K62 with a grinding head on a support at JSC Livhydromash). The control was carried out by an indicator bracket with an indicator ICh 10 B cells. 1 GOST 577-68. The cumulative error between any non-adjacent steps was not more than 0.1 mm, the clearance during the control by the straightedge of the protrusions forming in diameter was not more than 0.07 mm, which is permissible according to the technical specifications.

 Thanks to the application of the proposed method for abrasive processing of screw surfaces of screws with a single-grinding grinding wheel, the quality has improved, the processing productivity has increased due to the use of a wheel with an axially offset cutting layer, less granular, harder and reduced consumption of abrasive.

Sources of information
1. Technology of mechanical engineering (special part): A textbook for engineering specialties of universities / A.A. Gusev, E.R. Kovalchuk, I.M. Kolosov and others. - M .: Mechanical Engineering, 1986. With 317-320.

 2. Reference technologist-machine builder. In 2 vols. T.1 / Ed. A.G. Kosilova and R.K. Meshcheryakova. - 4th ed., Revised. and add. - M.: Mechanical Engineering, 1986. S. 372-373-prototype.

Claims (1)

A method of grinding screws with a single-thread disk grinding wheel, including setting the wheel at an angle α _{in the} elevation of the turn of the workpiece and telling it an independent rotational movement and longitudinal feed, and the part to rotate and translate kinematically associated with the longitudinal feed of the wheel equal to the pitch of the work screw, this uses a medium soft fine-grained circle with a height equal to half the pitch of the machined screw, and additionally tilt it at an acute angle α _APC to the plane, perpendicular the bright axis of rotation of the circle, to create an axially offset cutting layer, which is determined by the formula
α _ARC = arctan [(t • cosα _B -0.5t) / D ^and ],
where α _B = [t / (2D)] is the angle of elevation of the turn of the screw being machined, deg;
t is the pitch of the screw, mm;
D is the pitch diameter of the screw, mm;
D ^and - the outer diameter of the grinding wheel, mm

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