A METHOD AND GRINDING MACHINE FOR THE INTERNAL GRINDING OF BORES

Abstract: In the process of internally grinding bores with the aid of a slightly conical grinding wheel (15) in a computer controlled manner, the rotational axis (14) of the grinding wheel is adjusted to a small angle ( alpha ) in relation to the rotational axis (3a) of the workpiece (5). The grinding wheel is sharpened along a generatrice which lies opposite the generatrice of the wheel when the wheel is in rough grinding engagement with the bore. The rough grinding operation is carried out at a feed pressure such that twice this angle (i.e. 2( alpha ) is levelled-out or eliminated and the respective generatrices of the wheel and the bore will substantially coincide. The fine grinding phase of the grinding operation is carried out with substantially coinciding bore and grinding-wheel generatrices along an opposite bore generatrice in relation to the rough grinding engagement location. The invention also relates to a grinding machine for carrying out the method.

Description: A Method and Grinding Machinα' for the Internal Grindincr of Bores Technical Field The present invention relates to a method for the computer-controlled internal grinding of bores, and more specifically, although not exclusively, to a method of the kind set forth in the preamble of Claim 1. The invention also relates to an internal grinding machine. When using known computer techniques to effect internal grinding processes, it is possible to control highly complicated and optimized grinding processes with the aid of a programmable computer, when sensors are used to deliver signals relating to grinding forces, feed speeds, vibrations, grinding positions, prevailing bore diameters, etc. to the computer. The program required herefore, i.e. the software, is designed by the in¬ dividual programmer. The grinding process can be con¬ trolled by various combinations of sensor signals, τime variations of such sensor signals can also be used to improve the straightness or trueness of the bores, for instance. Background Art US,A,3.274.738 teaches a method of controlling an internal grinding process which utilizes a principle known as the "controlled force method". US,A,3.774.349 (Uhtenvoldt et al) describes an internal grinding machine equipped with a conical, outwardly tapering grinding wheel. GB,A,519.146 (Aero-Mecanigues) describes a bore and seating grinding process which is effected with the aid of a cylindrical grinding wheel having a conical end part. US,A,3.197.921 (Hohler et al), US,A,3.534.509, US,A,3.426.483 (Droitcour) and US,A,3.694.969 (Hahn et al) describe other known methods, among them methods in which the aforesaid principle is combined with other principles. The Objects of the Invention The present invention assumes the use of a programmable computer for controlling an internal grinding process. The invention is also based on the assumption that in each phase of a bore grinding process, there occurs optimal outward deflection or bending of the spindle or spindle extension carrying a grinding wheel in the feed direction and that there is an optimal angular deflec- tion between the generatrice of the ground bore and the generatrice of the grinding wheel at the location of grinding engagement. For instance, in many cases, it is desired that the angle between the generatrice of the bore and the cutting edge of the grinding wheel is as small as possible, i.e. an angular deflection of close to 0°, both in the rough grinding phase and the ine or finishing grinding phase. These grinding procedures will normally involve reciprocating relative axial movement between grinding wheel and workpiece, which results in deviations in the straightness of the bore being ground, due tc angular twisting of the grinding wheel. This is particularly the case at the ends of the bore, where only a part of the full length of the grinding wheel is located within the bore. A relatively large constant outward deflection of the spindle carrying the grinding wheel is therewith assumed in the rough grinding phase. This results in a substantially constant grinding force, which is dis¬ tributed substantially evenly over the cutting side or generatrice of the grinding wheel. On the other hand, a relatively small linear deflection in the feed direction is assumed in the fine grinding phase, although a grinding force which is essentially evenly distributed over the cutting side or generatrice of the grinding wheel shall also be generated in this case. It is known that the aforesaid desired optimum condi¬ tions can be achieved with a grinding spindle which is mounted on a slide system that can be rotated and moved linearly in the feed direction - and also linearly in a further direction - with the aid of a control system which includes a computer and the requisite sensors and transducers, as described above. It is also known that when using such slide systems, each other combination of outward deflection or bending desired for each phase of the grinding process can be programmed in the computer. A system of this kind, however, is essentially general and includes many parameters and degrees of freedom which influence the end result, and is therewith highly complicated. Object of the Invention The present invention is also based on the aforesaid assumptions or conditions, and the object of the inven- tion is to provide the possibility of effecting a grinding process with desired linear outward deflection or bending of the spindle axle and therewith with a grinding force of desired magnitude in the feed direc¬ tion while maintaining, at the same time, a small angle, i.e. an angle of about 0°, between the genera¬ trice of the grinding wheel at the location of grinding engagement and the generatrice of the bore, during both the rough grinding process and the fine grinding pro¬ cess, without the use of a slide system which can be pivoted continuously during the grinding process. Another object is to provide a method of the aforesaid kind which does not require the use of excessively complicated computer programming and which will never- theless provide a grinding result of good quality with a short cycle time for the grinding operation as a whole. Another object of the invention is to provide a grind- ing method which can be applied readily to different types of existing grinding machines without requiring the provision of additional equipment, and also to provide a method which can be applied readily to satis¬ fy different requirements on grinding accuracy and to make possible effective grinding engagement during the rough grinding phase and which will fulfil high ac¬ curacy demands placed on the fine grinding or finishing process. Still a further object of the invention is to provide an internal grinding machine which will enable an optimum balance to be made between the rough grinding and fine grinding operations without requiring compli- cated additional equipment herefor, and which will also enable adjustments to be made between the rough grind¬ ing and fine grinding processes without requiring long tool feed paths. Another object is to provide a grind¬ ing machine with shorter cycle times and a machine which will fulfil the highest pos-sible demands on the straightness and surface tolerances of the ground bore. A Brief Disclosure of the Invention These and other objects are fulfilled by a method of the aforedescribed kind having the characteristic features set forth in the characterizing clause of Claim 1. This setting of the rotational axis of the grinding wheel at a small angle relative to the rotational axis of the workpiece, in combination with the feature of selecting the feed pressure during the rough grinding phase such that twice this angle is levelled-out or eliminated, means that the generatrice of the grinding wheel and the generatrice of the bore will essentially coincide at the grinding engagement location. Thus, substantially the whole of the axial length of the grinding wheel will be in active grinding engagement with the workpiece, which enables the rough grinding phase to be carried out with the greatest possible efficiency from a technical aspect and, because the- generatrice of the grinding wheel is parallel with the generatrice of the desired bore along the whole of its length, the bore produced during the rough grinding process will be as straight or as true as possible. When the grinding wheel is applied to the diametrically opposite side of the bore, in order to finely grind the bore surfaces, the generatrice of the grinding wheel will also coincide with the generatrice of the bore, therewith enabling the fine grinding phase to be effected with the greatest possible efficiency. It is not necessary to adjust the position of the spindle axis between these two grinding phases; the levelling- out of the setting angle of the spindle extension resulting from the feed pressure generated during the rough grinding phase will ensure that the generatrice of the grinding wheel at the location of grinding engagement will be substantially parallel with the axial extension of the bore, i.e. desired bore straightness or trueness is already ensured in the rough grinding phase. Neither is it necessary to compensate for feed pressure when the grinding wheel engages the substantially diametrically opposite side of the bore in conjunction with a fine grinding operation. The generatrice of the grinding wheel at the location of grinding engagement will be parallel with the bore axis even when the feed pressure exerted during the fine grinding phase is very low, such low pressures being desired. It is also ensured in this case that engagement of the grinding wheel with the bore is effected essentially along the whole of the axial length of the grinding wheel. It will be evident from the aforegoing that the fine grinding phase is effected with the same grinding wheel as that used in the rough grinding phase, which is preferred in practice as a rule. The advantages gained hereby are obvious. One important advantage is that the grinding wheel need only be moved along a very short path between the rough grinding and fine grinding phases. In practice, the distance of this path cor- responds to the bore diameter minus the diameter of the grinding wheel at its centre point. However, it lies within the scope of the present inven¬ tion to carry out the fine grinding phase with a sepa- rate grinding wheel. In this case, the grinding wheel used in the fine grinding phase will preferably be made of a softer material than the rough grinding wheel, and the rough grinding and fine grinding wheels will be adjusted to mutually different angles in relation to the rotational axis of the workpiece. Irrespective of whether one and the same grinding wheel or different grinding wheels is/are used for the rough grinding and fine grinding phases respectively, it lies within the purview of the invention to vary the angle of the rotational axis of the grind wheel during the grinding phase, in order to vary the feed pressure during respective rough grinding and/or fine grinding phase or phases. This variation may be desirable, for instance, in order to increase the feed pressure and therewith render the rough grinding process more effective, for instance. Subsequent to effecting such a change in the predeter¬ mined conditions, for instance so as to increase the amount of material removed over a short period of time, it is possible, in accordance with the invention, to return to current standard conditions in order to achieve the aforesaid elimination or levelling-out of the predetermined angular setting of the spindle axle extension, i.e. so that standard conditions prevail at the time of completing the rough grinding operation and also when commencing thereafter the fine grinding operation on the opposite side of the bore. It has been stated in the aforegoing that the angle between the grinding wheel generatrice and the bore generatrice is preferably equal substantially to 0° at the location of grinding engagement. It is possible, however, within the scope of the present invention to vary this angle slightly, if so desired. This can be achieved, for instance, by pivoting or rotating the grinding spindle through a given (small) angle when sharpening the grinding wheel, and by then turning the grinding spindle back to its starting position when sharpening of the grinding wheel is completed. As before mentioned, when different grinding wheels are used for rough grinding and fine grinding purposes, the grinding wheels can be set to mutually different angles in relation to the rotational axis of the workpiece. In this case, the fine grinding wheel will be set to a smaller angle than the rough grinding wheel. The invention also relates to a grinding machine having the characteristic features set forth in Claim 8. The aforegoing and the following text include such phrases as the "opposite sides" of the grinding wheel and the bore respectively, "the grinding wheel genera¬ trice and the bore generatrice at the location of grinding engagement", etc. It should be borne in mind in this respect that both the grinding wheel and the workpiece, together with the bore formed therein, rotate during a grinding operation. Consequently, both the grinding wheel and the bore will constantly change position. The aforesaid phrases shall therefore be interpreted in this light, i.e. the expressions shall not always be taken literally but instead shall be interpreted as signifying a state in which the grinding wheel and the workpiece can be considered to be sta¬ tionary at a given moment in time. The invention will now be described in more detail with reference to exemplifying embodiments thereof illus¬ trated in the accompanying schematic drawings. The inclined settings of the grinding spindle or spindles and outward deflection or bending of the grinding wheel has been greatly exagerated in all Figures, in order to illustrate the fundamental principles of the invention more clearly. In reality, these deflections and in¬ clined settings are so small as to be unnoticeable to the naked eye. Brief Description of the Drawings Figure 1 is a perspective view of essential parts of a grinding machine with which the inventive method can be applied. Figure 2 is a partially sectioned top view which il¬ lustrates engagement of the grinding wheel with the workpiece during a rough grinding phase. Figure 3 is a partially sectioned top view, correspond¬ ing to Figure 2, showing engagement of the grinding wheel with the opposite side of the bore during the fine grinding or finishing phase. Figures 4 and 5 are schematic illustrations of a rough grinding and fine grinding operation respectively while using two different spindles and associated grinding wheels, the respective spindle axle extensions being adjusted to different angles during the rough and fine grinding phases respectively. Figure 6 illustrates, finally, the formation of an undesired bore configuration obtained when employing bore grinding methods normally applied. Description of Preferred Embodiments In Figure 1, the reference numeral 1 identifies essen- tial components of a grinding machine not shown in detail, namely a feed slide 2, a chuck spindle 3, a chuck 4 mounted for rotation on the spindle 3, a work¬ piece 5 supported in the chuck, and a bore 6 to be ground. The chuck 4 is driven by a motor 7 via a drive belt 8. The feed slide can move transversely in mutu¬ ally opposite directions. Mounted adjacent the feed slide is a table slide 11 which is movable towards and away from the chuck per- pendicular to the direction of movement of the feed slide. When grinding long bores, the table slide 11 is moved backwards and forwards so that the grinding wheel, which is shorter than the bore, will grind the bore as straight or as true as possible. The table slide 11 carries a grinding spindle holder 12 which can be pivoted to different angular positions in relation to the chuck spindle axis and locked therein, with the aid of an adjusting and locking device 10. The holder 12 supports a grinding spindle 13 which is provided with a grinding spindle extension 14 which carries a grinding wheel 15 on one end thereof. The grinding wheel is shaped, i.e. sharpened, with the aid of means intended herefor, e.g. a diamond tool 22, so as to be slightly conical. The diamond sharpening tool 22 is carried by a bracket plate 20 supported on the feed slide 2, such that said tool will lie on the same level as the centre line of the rotational shaft of the chuck spindle 3. Figure 2 illustrates engagement of the grinding wheel 15 with the bore 6 in the workpiece 5 during the rough grinding phase. The geometric axis 13a of the spindle 13 forms an angle α with the geometric axis 3a of the chuck spindle 3. For the sake of clarity, this angle is greatly exagerated in Figures 2 and 3, and in practice will be scarcely noticeable. The feed direction of the workpiece is indicated by arrows PI and P2 in Figures 2 and 3. The feed pressure resulting from grinding engagement of the grinding wheel 15 with the periphery 6a of the bore in the workpiece 5 as the grinding wheel is advanced results in linear and angle deflection of the grinding wheel in relation to the grinding spindle, as illustrated in Figure 2. The rough grinding phase is carried out at a feed pressure such that the given angle 2α will be essen¬ tially levelled-out or eliminated, i.e. the generatrice of the grinding wheel 15 and the generatrice of the bore 6 will substantially coincide, as shown in Figure 2. Before coming into engagement with the workpiece in the rough grinding phase, the grinding wheel 15 will have been sharpened by means of the diamond tool 22 along a generatrice which lies opposite to the generatrice of the grinding wheel that is in rough grinding engagement with the bore 6. The whole of the axial length of the grinding wheel 15 will be active in the rough grinding phase and when grinding the workpiece the table slide 13 is moved backwards and forwards towards and away from the work¬ piece, so as to enable the full axial length of the bore 6 to be ground along the whole of its axial length. Figure 3 illustrates the subsequent fine grinding or finishing operation, which is carried out with substan¬ tially coinciding bore and grinding-wheel generatrices along a bore generatrice which is essentially opposite the rough grinding engagement location. The feed pressure is very slight when effecting the fine grinding phase in accordance with Figure 3, and consequently the spindle extension 14 will not have been deflected or bent outwards to any great extent, and the angle preset in relation to the chuck spindle axis 3a will prevail along the whole of the length of said spindle extension. Thus, full abutment between the generatrices of the grinding wheel 15 and the bore 6 will be obtained along substantially the full axial length of the grinding wheel 15 during the fine grinding phase of the grinding cycle. The arrow P2 in Figure 3 indicates the feed direction of the workpiece during the fine grinding phase. As before mentioned, the grinding wheel can be set to numerically smaller positive or negative angles. This can be effected, for instance, when sharpening the grinding wheel, by pivoting or swinging the grinding spindle through a given small angle and returning the spindle 15 to its starting position when sharpening of the wheel is completed. The angle α can also be re-set, for instance during the rough grinding phase, by means of the setting and locking device 13, without necessarily using the afore- mentioned general computer-controlled arrangement for effecting pivotal movement during the grinding process. Such adjustments to the angle can be made, for in¬ stance, to generate a greater feed force during part of the rough grinding phase, for instance. The feed force may also be reduced, by simply pivoting the grinding wheel in the opposite direction. Figures 4 and 5 illustrate an embodiment in which two mutually different grinding wheels IS' and 15" are used in the rough grinding and fine grinding phases. The spindle setting and sharpening of the wheel correspond to the aforedescribed with reference to the rough grinding method illustrated in Figure 2. Figure 4, however, shows the grinding wheel in the position taken by the wheel upon completion of a sharpening operation, in which position the generatrice of the sharpened wheel is parallel with the chuck spindle axis 3a, this generatrice being opposite to the generatrice along which the rough grinding engagement takes place in a subsequent grinding moment. Similarly, in Figure 5 the grinding spindle 13 and its extension 14 form an angle . with the chuck spindle axis 3a. Subsequent to applying feed pressure, by moving the chuck spindle in the direction of the arrow PI, the grinding spindle extension 14 will be deflected or bent in the same manner as that shown in Figure 2, such that the rough grinding engagement takes place along a generatrice which is opposite to the generatrice along which the grinding wheel 14 was sharpened by the diamond tool 22. Figure 5 illustrates a subsequent fine grinding opera¬ tion with the aid of another grinding wheel 15", which is carried by a grinding spindle extension 14" and driven by a grinding spindle 13". This spindle 13" has been set to an angle α- relative to the chuck spindle axis 3a. The angle α 2 is smaller than the angle α 1 which ensures parallelity with the chuck spindle 3a even during the fine grinding phase, which is effected at very small feed pressure. In contrast to the grinding procedure effected in accordance with the invention in the manner illustrated in Figures 1-5, Figure 6 illustrates a known, often used bore grinding method with which bores of undesir¬ able shapes are generated. The grinding process effected according to the known state of the art in¬ volves a relatively long reciprocating movement between grinding wheel and workpiece, which results in an untrue or crooked bore due to erroneous pivoting of the grinding wheel. As illustrated in Figure 6, this is particularly manifest at the ends of the bore, where only a part of the length of the grinding wheel is located within the bore. In Figure 6, which thus represents an earlier known grinding method, the work¬ piece is referenced 105, the grinding wheel is refer¬ enced 115 and the reciprocatingly movable table slide is referenced 111. In the case of the inventive embodiments illustrated in Figures 1-5, both the rough grinding phase and the fine grinding phase of a grinding cycle are carried out with substantially full abutment between the generatrice of the grinding wheel and the generatrice of the bore at the grinding engagement location, therewith ensuring the greatest possible effectiveness of a grinding operation. The ground bore will also be extremely straight. The grinding operation can be carried out with the aid of simple means, i.e. without needing to program a control computer with complicated software. Instead, all that is needed is adjustment of the presetting of the grinding spindle to the desired feed pressure. The movement path travelled by the grinding wheel between the rough grinding and fine grinding locations is minimum. It will be understood that the angular positions to which the aforesaid settings are made can be modified in a manner to render the grinding process effective, without departing from the basic concept of the inven- tion. Furthermore, the rough grinding and fine grinding phases can be carried out with one and the same grind¬ ing spindle or with different grinding spindles without unduly complicating or influencing the grinding opera¬ tion as a whole.

Claims: Claims 1. A method for the computer-controlled internal grinding of bores with the aid of a conical grinding wheel carried on the free end of a grinding spindle extension with substantially full abutment between the respective generatrices of the grinding wheel and the bore both during the rough grinding phase and the fine grinding phase of a bore grinding operation, c h a r a c t e r i z e d by a) positioning the rotational axis of the conical grinding wheel to the bore at a small angle (α) rela¬ tive to the rotational axis of the workpiece, said conical grinding wheel having an inwardly tapering conicity from the free end of the spindle extension; b) sharpening the grinding wheel along a generatrice which is opposite the generatrice along which the grinding wheel engages the bore; and c) carrying out the rough grinding phase at a feed pressure such that twice said angle (i.e. 2α) is levelled-out and the generatrice of the grinding wheel coincides substantially with the generatrice of the bore. 2. A method according to Claim 2, c h a r a c ¬ t e r i z e d by carrying out the fine grinding phase with the same grinding wheel as the rough grinding phase and with substantially coinciding bore and grinding-wheel generatrices along a bore generatrice which is substantially opposite relative to the loca¬ tion of rough grinding engagement (Figure 3) . 3. A method according to Claim 1 or 2, c h a r ¬ a c t e r i z e d by varying the setting angle of the rotational axis of the grinding wheel during the grind¬ ing process such as to vary the feed pressure during the rough grinding and/or fine grinding phase or phases of said grinding operation. 4. A method according to Claim 1, c h a r a c ¬ t e r i z e d by carrying out the fine grinding phase with a separate grinding wheel, preferably a wheel made of softer material than the rough grinding wheel, and by adjusting the rough and fine grinding wheels to different angles in relation to the rotational axis of the workpiece. 5. A method according to Claim 4, c h a r a c ¬ t e r i z e d by adjusting the fine grinding wheel to a smaller angle than the rough grinding wheel. 6. A method according to any one of Claims 1-5, c h a r a c t e r i z e d by pivoting the spindle axis of the grinding wheel through a given small angle when sharpening said wheel, and pivoting said spindle axis back to its starting position when sharpening is completed. 7. A grinding machine for the internal grinding of bores with full abutment between the generatrice of the grinding wheel and the generatrice of the bore both in the rough grinding and the fine grinding phases, said grinding machine (1) including: a) a chuck spindle (3) which is preferably mounted on a feed slide (2) and which is intended to support a workpiece (5) having a bore (6) formed therein; b) a table slide (11) provided with a grinding spin¬ dle holder (12) provided with a grinding spindle exten¬ sion (14), and a conical grinding wheel (15) mounted on the free end of said extension; c) means (13) for positionally adjusting and detach- ably fixating the grinding spindle holder (12) such that the rotational axis of the grinding spindle will define a predetermined angle (α) in relation to the rotational axis (3a) of the workpiece; d) means for adjustable regulation of the grinding wheel feed in relation to the workpiece (or vice versa) in a manner to vary the feed pressure during the grind¬ ing operation; e) a grinding wheel sharpening device, preferably a diamond tool (22); f) a computer for controlling the grinding process, c h a r a c t e r i z e d in that g) the conical grinding wheel (15) tapers conically inwards from the free end of the grinding spindle extension (14); h) the sharpening tool (22) is intended to engage the grinding wheel (15) along a generatrice which is sub¬ stantially opposite the grinding wheel generatrice when said wheel is in rough grinding engagement with the bore (6); and i) in that rough grinding engagement is intended to take place at such feed pressure that twice the preset angle (i.e. 2a) between the respective rotational axis of the grinding wheel (15) and the workpiece (5) is levelled-out and such that the bore generatrice and the grinding wheel generatrice will substantially coincide at the engagement location. 8. A grinding machine according to Claim 7, in which one and the same grinding wheel (15) is used to effect both the rough and the fine grinding phases, c h a r a c t e r i z e d in that the fine grinding location between grinding wheel (15) and bore (6) is located along a bore generatrice which is essentially opposite the generatrice at the rough grinding location. 9. A grinding machine according to Claim 7, in which different grinding wheels (15 / , 15") are used for the rough grinding phase and the fine grinding phase res¬ pectively, c h a r a c t e r i z e d in that the rough grinding wheel and the fine grinding wheel (15'; 15") are set to different angles (α. and a- respectively) in relation to the rotational axis of the workpiece, the setting angle (α 2 ) of the fine grinding wheel, preferably being smaller than the setting angle of the rough grinding wheel (α.,). 10. A grinding machine according to any one of Claims 7-9, c h a r a c t e r i z e d in that the sharpening tool, preferably a diamond tool (22), is mounted on a bracket (20) which projects out from the feed slide, and engages the grinding wheel (15) sub¬ stantially on a level with the rotational axis (3a) of the chuck spindle.

Inventors: SIGGELIN LARS, SIGGELIN, LARS
Applicants: UVA AB, AB UVA
Application year: 1991
Main classification: B24B49
IPC codes: B24B1, B24B5, B24B49