WO1992007686A1

WO1992007686A1 - High frequency honing

Info

Publication number: WO1992007686A1
Application number: PCT/EP1990/001822
Authority: WO
Inventors: Oswald Kopp
Original assignee: Kadia-Diamant Maschinen- Und Werkzeugfabrik O. Kopp Gmbh & Co.
Priority date: 1990-10-31
Filing date: 1990-10-31
Publication date: 1992-05-14
Also published as: JP2571322B2; WO1992007687A1; DE59102385D1; EP0555285B1; EP0555285A1; JPH06506157A

Abstract

According to a process for machining bores in workpieces, a honing tool provided with an abrasive coating and radially pressed against the wall of the bore carries out simultaneously a rotary and a reciprocal movement. In addition to the reciprocal and rotary movements (2, 3) the honing tool (1, 100) carries out a high frequency, short-hub oscillating movement (31, 32).

Description

Title: High frequency honing (2)

DESCRIPTION

The invention relates to a method for machining bores in workpieces, in which a honing tool coated with an abrasive material and pressed radially against the wall of the bore executes a rotary movement and a stroke movement at the same time. This is the well-known honing.

The invention is based on the object of further improving the honing in such a way that greater material removal can be achieved. At the moment it is, for example, with the "Dorn-'Ηonen, in which with a slight excess in just one Double stroke is worked, only possible to work off an addition of 4 μ. A higher addition should be possible without higher axial forces and torques occurring. At the same time, a bore should be formed which, if possible, no longer has a burr and which is also characterized by the highest possible contact area.

According to the invention, this object is achieved in that the honing tool performs a high-frequency, short-stroke oscillation in addition to the lifting and rotating movements.

A particularly advantageous embodiment of the invention provides that the short-stroke, high-frequency oscillation of the honing tool takes place in the ultrasonic range with a frequency of 20 to 40 kHz and an amplitude of up to 15 μm and in the axial direction of the bore, so that the machining takes place in just one double stroke , and that the honing tool has a conical cutting zone whose diameter, which is larger in the rear in the direction of the axial lifting movement, has an oversize of more than 4 μm compared to the diameter of the unmachined bore.

In particular, the new process enables high machining allowances with relatively fine grain sizes with fine machining surfaces. With the achievable surface qualities, the previous quality limits of conventional honing are exceeded. So far, values have been around 0.6 m R _z as limit for hardened steel. This surface quality could be significantly improved with the method according to the invention. High frequency honing in accordance with the invention results in relatively low machining forces. The result of this is only an extremely small amount of burr formation. A new surface structure is created with a particularly high contact area. Depending on the kinematics, a periodic surface pattern with regular "troughs" or "pockets" is created, which are particularly suitable for accommodating lubricant.

An embodiment of the invention and its advantageous developments are described in more detail below with reference to the accompanying drawings. They represent:

Figure 1 is a scheme for explanation;

FIG. 2 shows a control scheme for machining a bore using the method according to the invention;

Figure 3 shows the waveform of a

abrasive grain on the wall of a hole;

FIG. 4 shows a scheme for explaining the grain coverage;

Figure 5 shows a device for carrying out the method according to the invention;

Figure 6 shows a first embodiment of a

Honing tool for carrying out the method according to the invention;

FIG. 7 shows the contour of the abrasive coating 40 in

Tool 1 according to Figure 6;

Figure 8 shows a second embodiment of a

Honing tool for carrying out the method according to the invention;

FIG. 9 shows a surface photograph of a bore machined using the method according to the invention;

FIG. 10 shows a scheme for explaining the honing allowances that can be achieved with the method according to the invention.

Figure l shows a honing tool 1. The usual honing movement, which results in the cross-section image, is the sum of a rotary movement (corresponding to arrow 2) and a lifting movement, according to arrow 3. According to the invention, these two movement components now have a third movement, namely one short-stroke oscillation in the axial direction, as indicated by the Arrows 32 and 33 illustrated, superimposed. In one exemplary embodiment, this oscillation takes place at a frequency of 21.7 kHz with an amplitude that could be set to a maximum of 15 μm.

The workpiece 4 has a bore 5 that is to be machined. The honing tool is provided with a conical cutting zone 6, whose - in the direction of the axial stroke - (cf. the arrow drawn) rear larger diameter Oχ is larger than the smallest diameter of the honing tool l not yet machined bore 5. The front smaller diameter D ₂ allows the introduction of the tool 1. With the stroke in the direction of the arrow, the conical cutting zone 6 moves into the bore 5 and works off the material corresponding to a bore diameter of less than D 1 . Following the conical cutting zone 6, the honing tool 1 is cylindrical, so that it is then guided into the part of the bore that has already been machined. Machining takes place with an axial double stroke. This process corresponds - unless a high-frequency oscillation of the lifting and rotating movement is also superimposed according to the invention - to the known "mandrel honing ^11. If the honing tool 1 is additionally excited with a high-frequency, short-stroke ultrasonic vibration in the axial direction, the unexpected effect results that much more material can be removed and thus corrected more than since form errors of the hole. FIG. 2 shows the control diagram of the lifting movement at (a), the rotary movement at (b), and the high-frequency vibration at (c) in their association with one another and as a function of time. The broader line at (c) indicates the amplitude of the high-frequency oscillation. The dwell time dt at (a) is adjustable. Points A, B, C, D can also be set, ie the beginning and end of the rotary movement and the high-frequency vibration. A machine for carrying out the method according to the invention, taking into account the control diagram according to FIG. 2, was experimentally designed with the following data:

Stroke length: 400mm

Lift drive 0.4 kW

Lifting speed: less than 650mm/min

Rotary drive: 0.4 kW

Speed: less than 5,000 1/revolution

Dwell time at the bottom of the hole: less than 10 s

amplitude: roax. 15 microns

Frequency: 20-24kH

Sound power of the generator: up to 2.4 kW

The trajectory of a tip of an abrasive grain 7 as a function of time is shown in FIG. 2 in a range from 0 to 300 μs. The upper and lower boundary lines, each of which represents a rising track, correspond to the sloping course of the grooves in conventional honing.

If one imagines that along this high-frequency oscillation path the individual abrasive grains 7 have a specific area on the surface to be machined rest, one of the two situations that is shown in FIG. With (a), i.e. with relatively "narrow" vibration in relation to the contact surface of the cutting medium grains 7, the result is that an abrasive grain 7 sweeps over a certain surface during a first ultrasonic stroke, which is also partly sweeped over again during the next ultrasonic stroke taking place in the opposite direction becomes. This means: Depending on the choice of these parameters, the same surface is practically processed several times, resulting in a "fire out" effect. By choosing these parameters differently, as in (b), one can achieve that this effect is limited to areas near the vibration peaks. In general, it is more advantageous to choose the parameters so that the curve according to (a) results.

FIG. 5 shows a device for carrying out the method.

The honing tool 1 ground to fixed dimensions and contour is accommodated in the tool receiving cone 8 . This is located in a sound transmission body 9. The

Sound transmission body 9 has two flanges 10, 11, which are provided with grooves at points 10', 11' in the offset type shown, so that thin points 10', 11' form, which practically have the effect of a joint, so that an axial high-frequency vibration, which the sound transmission body 9 performs, is not transmitted to the housing 12 in which the sound transmission body 9 is clamped in the manner shown. The sound transmission body is made of titanium so that the thin areas can withstand this. The housing 12 consists of the cylindrical part 13, the lower cover 14 and the upper cover 15. The upper cover 15 has a bore 16 provided with an internal thread in the middle, into which the threaded pin 17 protrudes, which is fixed to the receiving hub 18 connected is. The housing cover 15 and receiving hub 18 are thus firmly screwed together, with the disk 19 being clamped between them. In this way, the housing 12 rotates with the receiving hub 18, which in turn is driven via the toothed belt wheel 20 and the toothed belt 21 in the direction of rotation. The entire unit, as shown in Figure 5, including a motor (not shown), can be moved up and down for the purpose of generating the lifting movement, as is known per se from conventional honing machines, so that a more detailed description of this constructive Details can be omitted in the present context.

The actual ultrasonic vibration exciter 25, which is formed in the exemplary embodiment by two piezoelectric elements (quartz crystals) 26 and 27, sits on top of the sound transmission body 9, with above the Ultrasonic vibration exciter 25 is still arranged to tune the oscillating system, a disk 28 representing an oscillating mass. The entire arrangement is tightly clamped by the clamping screw 29 which is screwed into the sound transmission body 9 . The centering takes place by means of a centering sleeve 29'. A coolant channel 30 passes through the sound transmission body 9 and the clamping screw 29 . A cooling medium can be supplied to the interior of the housing via the line 31 and the openings in the disk 19 and in the cover 15 .

The supply of electrical energy to the

Ultrasonic vibration exciter 25 takes place in the manner shown by means of slip rings 35 arranged on cover 15 and slip rings 36 attached to a part of said unit that does not rotate. Figure 6 shows the simplest form of a honing tool 1, which is designed as a fixed mandrel, i.e. mandrel with fixed, non-adjustable external dimensions . The cutting layer has the contour 40 as shown in detail in FIG. 8, namely an introduction zone 37 over less than 10% of its length, followed by the already mentioned cutting zone 6, which extends over somewhat less than half of the entire length length of

The cutting means coating extends, as does the cylindrical guide zone 38 adjoining it. Although such a tool is functional in principle, it has the disadvantage that it cannot be readjusted when the cutting means coating 40 is worn. The usual radial opening, as is known from honing tools, causes certain difficulties in the present case, since there is a risk that individual mutually adjustable parts that are not in a vibration node rub against each other with the high frequency, so that excessive heating occurs. In addition, it must be ensured that no parts come loose despite the high-frequency vibration. In this respect, specially designed honing tools are advantageous. Such a honing tool 100 is shown in FIG. The cutting layer 40, which has the contour according to FIG. This is the case, for example, when the recess 103 in the shank 101 on the one hand and the widening piece 102 on the other hand are conical, so that axial displacement of the widening piece results in an elastic widening of the shank in the radial direction, which, however, is a solid body without grooves and without Slots is designed to ensure extra stability. The elastic radial expansions required here can also be achieved in this way. In the axial direction following the expansion piece 102 there is a pressure piece 104 which is used in the recess 103 in an exchangeable manner. Its right end rests against the pressure surface 105 of the receiving part 106 , which in turn is then inserted with the right end into the tool receiving cone 8 of the sound transmission body 9 . So you can use the cutting tool coating 40 expand elastically by using pressure pieces 104 of different lengths. The longer the pressure piece 104, the more the shank 101 is radially expanded.

FIG. 9 now shows the surface that can be achieved with the method according to the invention as a photograph—since it cannot be represented otherwise—whereby, in order to clarify the scale, a distance that corresponds to 30 μm in reality is drawn in under the photograph. Surprisingly, it turns out that along the mutually sloping grooves that result in the cross-hatch pattern during classic honing, the superimposed high-frequency vibration causes troughs or pockets to form in the surface at short intervals, which are practically "hammered in" or "chiseled in", whereby - as shown in readily apparent from this photograph - burr-free planar supporting areas are formed which can support bearing parts, and that the pockets or troughs are formed in between and are ideally suited in practice as an oil reservoir for lubricant. The material is removed evenly and a surface pattern that is periodic according to the kinematics is created. It is of course strongly dependent on the set parameters. At a low speed, for example, the cutting marks generated by the high-frequency oscillation are very close together. At high speeds, these cut marks are correspondingly stretched and result in a somewhat less favorable contact area. The wearing percentage was one Test series in approx. 0.2 μm cutting depth at approx. 30%.

In this way, a new surface is created, which results in an extreme improvement in the carrying properties. If, for example, a certain bore is machined in two processing stages with grain sizes D46 and D15 (according to the FEPA definition), values below 0.5 μm can be achieved with regard to the bore geometry (straightness, roundness). This was done experimentally with workpieces that had been conventionally pre-honed to a diameter of 6.955 to 6.965 mm and were finish-machined in two further machining steps using the method according to the invention. The surface roughness was initially 0.7 μm R _z and could be improved to below 0.4 μm R _z as the number of pieces increased.

The machining forces that occur are of particular importance for the application of the method according to the invention. An axial force of 1.0 N and a torque of 1.120 Ncm were determined with an addition of 10 μm (difference in the diameter of the unmachined bore compared to the final dimension aimed for by machining) using the fixed mandrel with grain size D46. A direct comparison with processing in which the same tool would have been used without high-frequency exposure was not possible, since an addition of more than 4 μm cannot be achieved without high-frequency oscillation. If you want to remove more material with one stroke without HF oscillation, do this the tool seizes. But even with an addition of 4 μm without high-frequency oscillation, i.e. with an addition reduced by more than 50%, the axial force was still 2.4 N and the torque was 1.3 Ncm. It can therefore be assumed that with the method according to the invention, 2 to 3 times the addition can be removed in a double stroke, and the axial force and torque are even lower than with conventional methods.

It also follows from this that only a very small amount of burr formation is caused with the method described here. As can be clearly seen from FIG. 9, no burr formation was observed at all on experimentally machined workpieces.

Finally, FIG. 10 shows the honing allowance dz (in microns) as a function of the grit k (according to the FEPA definition) in comparison between the - known - mandrel honing (lower bar slightly increasing from a grit D15 to D181) in comparison to high-frequency honing ( black filled area). The workpiece was hardened steel with a hardness of more than 60 HRc.

Claims

PATENT CLAIMS

1. Method for machining bores in workpieces, in which a honing tool covered with an abrasive coating and pressed radially against the wall of the bore executes a rotary movement and a lifting movement at the same time, characterized in that the honing tool, in addition to the lifting and rotary movement (2 ,3) performs a high-frequency, short-stroke oscillation (31,32).

2. The method according to claim 1, characterized in that the short-stroke, high-frequency oscillation of the honing tool (1,100) takes place in the ultrasonic range with a frequency of 20 to 40 kHz and an amplitude of up to 15 μm and in the axial direction of the bore, that the machining takes place in takes place in only one double stroke, and that the honing tool (1,100) has a conical cutting zone (6) whose larger rear diameter (Di) in the direction of the axial stroke movement has an oversize of more than 4 μm compared to the diameter of the unmachined bore.

3. The method according to claim 2, characterized in that the high-frequency oscillation has a frequency of 20 - 24 kHz.

4. The method according to claim 1, characterized in that the An abrasive agent (lapping agent) in suspension is added to the coolant used.

5. The method according to claim 2, characterized in that to achieve a spark-out effect, the rotational speed of the honing tool, the feed of the honing tool in the axial direction (stroke speed), and the amplitude and frequency of the ultrasonic vibration of the honing tool are determined in such a way that the abrasive grains at a Ultrasσhallhub swept surfaces are swept over again to a part at the respective following opposite Ultrasσhallhub.

6. Device for carrying out the method according to Claim 1 or one of the following claims, characterized in that the honing tool (1,100) is accommodated in the lower end (8) of a sound transmission body (9) on which an ultrasonic vibration exciter (25) acts from above, and that the sound transmission body is suspended in a housing (12) at least in a plane which lies in the nodal area of the ultrasonic vibration by means of restraining means (10', 11') in such a way that it (9) can carry out the ultrasonic vibration relative to the housing (12), while the housing does not carry out the vibration, that the housing (12) is driven in rotation (20,21), and that the housing (12), sound transmission body (9), honing tool (1.100) and Rotary drive (20,21) formed unit for generating the axial lifting movement in a conventional manner is adjustable in height.

7. The device according to claim 5, characterized in that the supply of electrical energy to the ultrasonic vibration exciter (25) via slip rings (35,36).

8. The device according to claim 6, characterized in that the ultrasonic vibration exciter (25) is formed by oscillating crystals (26,27) which are clamped onto the upper end of the sound transmission body (9) by a clamping screw (29).

9. Honing tool for use in a device according to claim 5, characterized in that the cutting coating (40) is applied to a shank (101), that the shank can be expanded elastically by an expanding piece (102) which is in a recess (103) can be inserted in the shank (101), that an exchangeable pressure piece (104) is also accommodated in the recess (103), and that the shank is screwed to a receiving part (106) in such a way that a pressure surface (105) of the receiving part supports the pressure piece and firmly presses the expander against the inner surface of the shank in a position which, depending on the length of the pressure piece, produces the desired expansion of the shaft results.

10. Honing tool according to claim 9, characterized in that the screw connection of the receiving part to the shank takes place in the region of a vibration node.

11. Honing tool according to claim 8, characterized in that the shank is an unslotted solid body.