FR2713123A1 - Method of lapping the surface of a workpiece and lapping rod for implementing this method. - Google Patents

Abstract

The present invention relates to a method of lapping the surface of a part and to an expansion type lapping bar for its implementation. The method of the invention consists in particular in calibrating a first cylindrical part (14a) of the external abrasive surface of the lapping rod by bringing it into contact with a reference zone of the surface to be lapped (15a), in gradually eliminating a protuberance ( 16a) by bringing it into contact with a second frustoconical part (14b) of said external abrasive surface, and in calibrating the zone whose protuberance has been eliminated by bringing it into contact with said first cylindrical part previously calibrated. The invention applies in particular to the lapping of cylindrical barrels comprising a hard metal coating obtained by electrolytic deposition.

Description

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  The present invention relates to a lapping method of the surface of a workpiece, in particular the internal surface of a cylindrical bore formed therein, and a lapping machine for example of the expansion type for the implementation of this method. Some parts, such as valves, gears, cams and combustion engine cylinders, are intended to undergo repeated movements and

  at high speed by rubbing contact.

  In order to minimize the friction and wear of the parts, it is necessary to calibrate them very precisely by performing a running-in of their surface, that is to say a final machining, to selectively remove the excess material,

  such as asperities, which remains on their surface.

  Sometimes, the above-mentioned excess material is in the form of thicker protuberance, located especially in the end zones of the part, especially when this part has on its surface a hard metal coating, such as chromium or nickel- silicon, obtained

by electrolytic deposition.

  In order to break-in the surface of a part, in particular the surface of a bore, it is known to use expansion-type grinders, which comprise a pin capable of being rotated about its longitudinal axis, a mandrel retained by one of its ends by the spindle, a guide sleeve in which the mandrel can slide axially and an external abrasive surface adapted to be spaced radially relative to said longitudinal axis under the effect of the thrust of the mandrel when

last is moved axially.

  However, conventional lapping techniques do not allow precise calibration of the parts that have the above-mentioned protuberance located on their surface, since the elimination of this protrusion causes excessive and local wear of the abrasive surface of the honers

  and thus generates a geometric defect of it.

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  The present invention aims to eliminate the aforementioned drawbacks and to provide a lapping method for removing the protuberances from the surface of the workpiece without excessive wear of abrasive materials and to perform a reliable and accurate calibration of that -this. The subject of the present invention is a method for lapping the surface of a workpiece, in particular the internal surface of a bore formed therein, consisting in driving a tool forming a stirrer in rotation about its longitudinal axis, to bring the external abrasive surface of the lapping rod in contact with the surface opposite the lapping piece and moving the lapping rod axially along this surface so as to lapping an area with a protuberance thereof, characterized in that it consists in calibrating a first cylindrical part of said abrasive surface bringing it into contact with a reference zone of the surface to be honed, to gradually eliminate said protuberance by bringing it into contact with a second part, preferably frustoconical, of the external abrasive surface , and to calibrate the zone whose protuberance is eliminated by bringing it into contact with said

  first cylindrical part previously calibrated.

  According to a particularly advantageous characteristic of the invention, the method consists in calibrating the first cylindrical part, progressively eliminating the protuberance of the area to be honed from the end of the smaller outer diameter of the second part, and calibrating this zone. lapped in single pass of the lapel on the

surface to be honed.

  According to another characteristic of the invention, the method advantageously consists in adjusting the difference between the external diameter of the two longitudinal ends of the second part to a value greater than twice the

  the thickness of the protuberance to be eliminated.

  The subject of the present invention is also an expansion type grinder for implementing the aforementioned method, comprising a pin capable of being rotated about its longitudinal axis, a body forming

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  particular mandrel retained by one of its ends by the spindle, a guide sleeve in which said body can slide axially, and an external abrasive surface adapted to be displaced radially relative to said longitudinal axis under the effect of the thrust of said body when the latter is moved axially, characterized in that the external abrasive surface comprises a first cylindrical portion for calibrating the surface of a workpiece, a second portion whose outer diameter varies along the longitudinal direction of the honing rod, preferably in the manner of a truncated cone, intended to eliminate the protuberance of the surface to be lapped, the proximal ends of said parts

having the same external diameter.

  Advantageously, the proximal ends of said portions are adjacent, so as to form a one-piece body. According to a particular embodiment of the invention, the external abrasive surface of the lapper is defined by the outer surface of a plurality of platelets forming cylinder portions movable radially by bearing means and subjected to a restoring force towards the lug. spindle axis by elastic means, said support means being housed in openings in the guide sleeve. According to another particular embodiment of the invention, the external abrasive surface of the lapper is defined by the external surface of a deformable sleeve of

  thin and with longitudinal slits.

  The invention will be better understood and other purposes, features, details and advantages thereof

  will become clearer during the description

  following explanatory of several particular embodiments currently preferred of the invention, given solely by way of illustrative and nonlimiting examples, with reference to the appended schematic drawing, in which:

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  - Figure 1 is a partial longitudinal sectional view of the lap according to a first embodiment of the invention; - Figure 2 is a quarter sectional view of the grinder of Figure 1, along the line II-II; - Figure 3 is a partial longitudinal sectional view of the lap according to another embodiment of the invention; and - Figure 4 is a graph illustrating the

  different stages of the lapping method according to the invention.

  Figures 1 and 2 show an expansion type grinder according to a first embodiment of the invention. This lapper comprises a pin 1 adapted to be rotated about its longitudinal axis 2 by a shaft of

  transmission (not shown in the drawing).

  A mandrel 3 is retained by one of its ends 3a by the pin i and has at its opposite end two

  frustoconical bearing surfaces 4a and 4b forming a bearing surface.

  The smaller diameter end of the first frustoconical bearing surface 4a is connected by a cylindrical section 5 to the larger diameter end of the second bearing

frustoconical 4b.

  The mandrel 3 can slide axially in a cylindrical guide sleeve 6 which is connected by its end

  upper by a nut 7 to the frame of the bead 8.

  A screw 9 is radially projecting from the outer surface of the central portion of the mandrel 3 and is housed in a longitudinal blind recess 6a formed in the wall

internal sleeve 6.

  In FIG. 1, when mandrel 3 slides axially downwards, support pieces 10 are

  radially spaced with respect to the axis 2.

  Each support piece 10 has two end portions 10a separated by a central portion lob, said end portions 10a having a portion of

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  notched surface 10c of shape corresponding to the surfaces

  external frustoconical spans 4a and 4b.

  These end portions 10a are arranged circularly around the frustoconical bearing surfaces 4a and 4b, respectively. The number of support pieces 10 is generally understood

between 3 and 12.

  The bearing pieces 10 are housed in longitudinal openings formed in the lower part of the sleeve 6. These openings serve as axial stops for the bearing parts 10 which are forced to move radially under

the thrust of the mandrel 3.

  An upper sheath 11 is fitted on the upper part of the sleeve 6 and fixed thereto by a nut 12 and a counter-nut 13. A lower sheath 11a is fitted on the lower part of the sleeve 6, and provides the plating of an elastic washer 22 on the latter, the washer 22 ensuring the maintenance of the plates 14 resting on the upper sheath 11. The lower sheath 11a is fixed by

  a nut 12a and a counter nut 13a.

  Longitudinal through holes 6b, radially formed in the sleeve 6, are able to receive

  platelets 14 forming cylinder portions.

  The plates 14 may be radially spaced apart by the bearing parts 10 and are subjected to a restoring force towards the longitudinal axis 2 by elastic means (not

represented on the drawing).

  The wafers 14 have an abrasive outer coating (shown in the drawing by dotted lines), such as diamond grit or lapping stone, for honing the surface of a workpiece, for example the inner surface

  has a bore 15 formed in a cylinder 16.

  The plates 14 are circularly separated by smooth cylindrical portions of the sleeve 6, which has the consequence that the grinder has an abrasive surface

  external discontinuous (see Figure 2).

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  The outer surface of the plates 14 comprises a first cylindrical portion 14a and a second frustoconical portion 14b (separated in FIGS. 1 and 3 by a mixed line), said portions 14a and 14b being adjacent by their end of larger diameter, so that form a

monobloc body.

  FIG. 3 represents a variant embodiment of

grinder of the invention.

  This lapper comprises a mandrel 3 'consisting of a rod 17 which is extended by a portion 18 whose outer surface

is substantially frustoconical.

  The mandrel 3 'is able to slide axially in a cylindrical guide sleeve 6' which is secured by its lower end with a metal deformable sleeve 19 of small thickness provided with longitudinal slots 19a. These longitudinal slots 19a allow a slight expansion of the sleeve 19 under the thrust of the frustoconical portion 18

  when it is moved axially downwards.

  The deformable sleeve 19 has an internal surface of shape corresponding to the external surface of the part

frustoconical 18.

  The outer surface of the deformable sleeve 19 comprises an abrasive coating and has a first cylindrical portion 20 and a second frustoconical portion 21, to

  like the bead shown in Figures 1 and 2.

  The second frustoconical portion 14b, 21 of the external abrasive surface of the lapper has a slope relative to the axis of the lapper preferably between 2% and 10% and the ratio between the length of the cylindrical portion and the total length of the part abrasive is advantageously

between / 5 and 13.

  Of course, the second portion 14b, 21 is not limited to a frustoconical shape and may have a convex or concave outer surface, from the moment when its outer diameter decreases along the longitudinal direction of the lap between one end more great

  diameter and one end of smaller diameter.

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  We will now describe the operation of the lapel of

  the invention with reference to FIG.

  It is assumed here that the bead is arranged vertically, but of course it can be arranged horizontally or in an inclined position. FIG. 4 represents the main steps of the lapping method of the invention as a function of their respective duration. Step "a" is to lower the lap in a bore in a cylinder until the outer abrasive surface of the lap is next to

the inner surface of the bore.

  Step "b" consists of radially spreading the external abrasive surface of the lapper by moving axially towards the

down the mandrel of the lapper.

  Step "c" is to contact the external abrasive surface of the bead with a reference area on the inner surface of the bore, so as to calibrate the

first cylindrical part.

  Step "d" consists in vertically raising the lap after having locked the mandrel in the frame of the lap, to come gradually lapping an annular bead which is radially projecting from the upper end of the bore and, once the bead eliminated, come calibrate this area

previously protruding.

  Step "e" is to stop the rotation of the lapper once it has come out of the bore and to relax the

  abrasive outer surface of the prong apart.

  This relaxation is obtained by a vertical upward movement of the mandrel within its guide sleeve, which causes a return of the external abrasive surface towards the longitudinal axis of the lap by the elastic means. Step "f" consists in rotating the stirrer about its longitudinal axis during steps "a" to "d".

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  Although the invention has been described in connection with several particular embodiments, it is obvious that it is in no way limited and that it can bring many variations and modifications without departing from its scope and of his mind. One can imagine a hollow burr with an abrasive surface directed inwards to come

  for example, honing the outer peripheral surface of a shaft or any cylindrical zone of a part of revolution.

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Claims (7)

  1. Method of breaking in the surface of a part,   in particular the internal surface of a bore formed in that   Here, consisting of driving a spindle tool in rotation about its longitudinal axis, and bringing the external abrasive surface of the honer into contact with the surface facing the workpiece and axially moving the honing rod along this surface so as to to grind an area & protuberance thereof, characterized in that it consists in calibrating a first cylindrical portion (14a, 20) of said abrasive surface by bringing it into contact with a reference area of the surface (15a) to grind, to gradually eliminate said protuberance (16a) by bringing it in contact with a second portion (14b, 21), preferably frustoconical, of the external abrasive surface, and to calibrate the zone whose protuberance (16a) has been removed by bringing it into contact with said first cylindrical portion (14a, 20) previously calibrated.   2. Method according to claim 1, characterized in that it consists in calibrating the first cylindrical portion (14a, 20), to gradually eliminate the protuberance (16a) of the area to be honed from the end of smaller diameter outer portion of said second portion (14b, 21) and calibrating said lapped zone (16a) in a single pass of the lapel on the surface (15a) to be honed.   3. Method according to claim 1 or 2, characterized in that it consists in adjusting the difference between the outer diameter of the two longitudinal ends of said second portion (14b, 21) to a value greater than twice the   the thickness of the protuberance (16a) to be eliminated.   4. Expansion type reamer for the implementation of the   process according to any one of claims 1 to 3,   having a pin adapted to be rotated about its longitudinal axis, a body forming in particular a mandrel retained by one of its ends by the spindle, a 2713123   guide sleeve in which said body can slide axially and an external abrasive surface adapted to be displaced radially with respect to said longitudinal axis under the effect of the thrust of said body when said body is moved axially, characterized in that the external abrasive surface comprises a first cylindrical portion (14a, 20) for calibrating the surface (15a) of a lapping part (16) and a second part (14b, 21) whose outside diameter varies along said longitudinal axis (2), preferably in the manner of a truncated cone, for progressively removing the protuberances (16a) from the surface (15a) to be lapped, the proximal ends of said portions (14a, 14b;   21) having the same external diameter.   The rasp of claim 4, characterized in that said proximal ends of said portions (14a, 14b; 20, 21) are adjacent to form a monobloc body.   6. Rasp according to claim 4 or 5, characterized in that its outer abrasive surface is defined by the outer surface of a plurality of platelets (14) forming cylinder portions movable radially by means of support (10) and subject a restoring force towards the spindle axis (2) by elastic means, said bearing means (10) being housed in openings (6b) formed in said guide sleeve (6).   7. Rasp according to claim 4 or 5, characterized in that its external abrasive surface is defined by the outer surface of a deformable sleeve (19) of small thickness and to longitudinal slots (19a).