EP0348608B2 - Method of deposing silicon crystals - Google Patents

Description

The invention relates to a method for exposing Silicon crystals on the surfaces of finely machined, preferably honed workpieces in which the silicon crystals are embedded in a much softer matrix.

Such methods are e.g. used to the cylindrical piston raceways of the engine blocks from To edit motor vehicle engines. By exposing it raised compared to the recessed aluminum matrix Silicon crystals form the wear-resistant surface which the pistons or piston rings run while that through the Resetting of the aluminum matrix released volumes between the silicon crystals to absorb lubricating oil serves. A frequently used light metal material is the hypereutectic aluminum-silicon alloy Al Si 17 Cu 4 Mg. It is cast using the low pressure process and forms at Solidification of highly wear-resistant silicon crystals of a size 30-80 µm. Finishing is done by drilling and honing. The crystals are then exposed.

In known method of the above type (JP-A 62,173,164) said the exposure is performed by electrochemical or electroless chemical etching (ECM E lektro C hemical M achining). However, etching requires a high level of engineering support in series production, since satisfactory work results can only be achieved by carefully monitoring the process. The asset value is extremely high. There are also problems with the disposal of the used etching and cleaning liquids. This results in very high operating costs. The act time is up to four minutes. The processes are automated only with great effort.

It is also known (EP-A-1-0247572; VDI journal volume 128 (1986) Number 11 - June (I), pp. 439-442), the inner surfaces of Gray cast iron cylinder liners or coated light metal cylinders to brush after honing. This postprocessing of the Ready-to-use surfaces serve the so-called Eliminate sheet metal jacket and - with gray cast iron - thus also Expose graphite flakes. By eliminating the The running-in time is shortened. Through the Exposure of the graphite lamella results in favorable Emergency running properties. However, the known method takes place an already operational surface instead and does not serve individual areas of the workpiece surface reset and thus space for lubricants create.

It is an object of the present invention, a method of type mentioned in such a way that an easy automatable simplified procedure of the beginning to create the mentioned type with considerable cost reduction.

According to the invention this object is achieved in that the Surface of the workpiece after finishing is brushed. Advantageous developments of the invention are defined in the subclaims.

In contrast to the known one, the invention thus creates chemical etching a cutting process. Doing so you look at the very different localities in the material Hardening the silicon crystals on the one hand and the Aluminum matrix on the other hand, as well as the associated different machining properties of both materials advantage. Through the use of a brushing tool Area of the matrix, i.e. the softer material, material worn away. Due to the twenty times greater hardness of the Silicon crystals are processed Silicon crystals do not take place. This procedure is extraordinarily easy, because well-known honing machines are also included can be used. The cycle time drops to less than a minute.

Brushing is done with a relatively simple brushing tool without handling corrosive liquids.

Figur 1a schematisch die Lage von Silizium-Kristallen

und Ib in einer Aluminium-Matrix vor und nach dem Bürsten;

Figur 2 ein Bürstwerkzeug zur Ausführung des Verfahrens;

Figur 3 einen Schnitt entlang der Linie III-III in Fig. 2;

Figur 4 eine fotografische Aufnahme einer bei einem Bürstwerkzeug gemäß Fig. 2 und 3 eingesetzten Borste;

Figur 5 (a), (b),
(c) Funktionsdiagramme des Bearbeitungsablaufs;

Figur 6 eine fotografische Aufnahme der durch das Bürsten bearbeiteten Oberfläche.

The invention and its advantageous developments are described below with reference to the accompanying drawings. They represent:

Figure 1a schematically shows the position of silicon crystals

and Ib in an aluminum matrix before and after brushing;

FIG. 2 shows a brushing tool for carrying out the method;

3 shows a section along the line III-III in Fig. 2;

FIG. 4 shows a photograph of a bristle used in a brushing tool according to FIGS. 2 and 3;

Figure 5 (a), (b),
(c) functional diagrams of the machining process;

Figure 6 is a photograph of the surface processed by brushing.

Figure 1a shows the surface of a
Silicon-aluminum alloy after fine machining, for example after honing, silicon crystals 1 being embedded in an aluminum matrix 2. FIG. 1b shows the desired state in which the aluminum matrix 2 after processing has been set back by an amount h compared to the contact surface formed by the silicon crystals. Such a surface can be, for example, cylindrical piston raceways in an engine block. The brushing tool 3 shown in FIGS. 2 and 3 is suitable for this application.

The brush tool 3 has brush strips 4, which by a in cross-section T-shaped carrier 5 and a There are a large number of bristles 6 mounted thereon. The vertical standing bars 7 of the T-shape of the cross section of the beams 5 have an axially parallel edge 7 'and an oblique to it running edge 7 ''. Has a brush strip 4 or a carrier 5 in the axial direction two such beams 7. The edges 7 'and 7' ' interact with an expansion body 8, the two conical Has areas 9, in each of which grooves 10 are provided are that receive the beams 7 of the carrier 5 and cause the oblique edges 7 'of the beam 7 on the bottom of the grooves 10 slide. The radial expansion of the brush strips 4 takes place by axial displacement of the expansion body 8. Die Brush strips 4 are radial by springs 11 and 12 Direction held together. They are from a cuff 13 surrounded on the front with a lid 14 is screwed and has slots 15 through which the ends of the bristles of the brush strips extend. The Sleeve 13 encompasses a flange 16 of tool body 17 and is screwed to it. The tool body is by means of Bolt 18 firmly connected to the sleeve 19. In the tool body 17 is a disk 21 by means of a Seegerrring 20 arranged. Furthermore, the expansion body 8 is fixed to the rod-shaped cylindrical extension 22 connected to the also carries a circlip 23. Between the disc 21 and the circlip 23, a spring 24 is effective, the Extension 22 and with it the expansion body 8 to the left in the Location that pulls the least radial expansion Brush strips 4 corresponds. An expansion takes place when the Expanding body 8 is pushed to the right. This is done by a pressure pin 25 which is displaceable in the sleeve 19 is recorded and at the same time over a transversely arranged Bolt 26, which is through slots 27 in the sleeve 19th extends through, is connected to a threaded sleeve 28. This sits on the outside of the sleeve 19 by means of a thread 29. A rotation of the threaded sleeve 28 on the thread 29 on the sleeve 19th causes an axial displacement of the pressure pin 25 and thus via extension 22, expansion body 8 and a radial Displacement of the brush strips 4. With the sleeve 19 is a Clamping shaft 30 connected to the clamping in the rotary driven and according to a certain feed in Axially displaceable spindle of a machine unit serves.

In the brushing tool shown, the Strips in the radial direction manually, i.e. by twisting the Threaded sleeve. For series production you will be accordingly take differently trained tools that are not manual a threaded sleeve, but by means of an inside of the Clamping shaft 30 extending an operating rod Stepper motor are adjustable in steps. A closer one Description of such a device is however in existing relationships are not necessary, because such Infeed devices are for radial honing machines Widening of honing tools known to the person skilled in the art. That applies in Principle for tools of the type described, albeit the conicity of the expansion body 8 in the present case very much is much larger than with conventional honing tools because the Wear of the bristles happens faster and accordingly larger delivery routes are required. Since brushing with much higher peripheral speeds are used, the tool body is balanced.

FIG. 4 shows a greatly enlarged image of an individual bristle 6. Cutting grains are embedded in a carrier material made of polyamide. The cutting grains 31 can consist, for example, of diamond, corundum, silicon carbide, boron carbide or CBN (cubic drilling nitride). The grain sizes range from 60 to 800 mesh. The diameter of a single bristle should be designed so that it is not greater than the average distance between the silicon crystals on the surface to be processed. In the case of the above-mentioned material Al Si 17 Cu 4 Mg there are, for example, about 14,000 silicon crystals with a grain size of 30 to 50 µm and about 3,100 crystals with a grain size of 40 to 80 µm on 1 cm ² . The resulting minimum crystal spacing on the surface is approximately 0.030 to 0.050 mm. The bristle diameter should therefore be chosen correspondingly smaller, but depends on the distance between the crystals. It is important that the bristles reach the areas of the matrix between the silicon crystals directly and can remove material there.

To adjust the cutting ability is careful Selection of the lubricant necessary, also for it Fat content, which is the friction between the bristle ends and the Matrix and thus the cutting behavior of the bristles Cutting grains determined on the bristles. In practice it has a water-soluble coolant with a low fat content proven. The friction of the cutting grain and material can be set so that exactly the required Material removal from 1 to 1.5 µm in the area of the matrix 2 results.

The also has an important influence on the work result Preloading the brushes. The tool is only in the Drilled hole, the inner surface of which is to be brushed. When a constant expansion dimension is reached, the Rotary motion on. To expand the tool, Use of a tool according to FIGS. 2 and 3 - one Defined adjustment of the threaded sleeve 28 in the Series production - as described - using a stepper motor driven delivery system is replaced. It definitely has to be sure that the tool is on every cycle is expanded to the same expansion diameter and thus works with constant bristle pretension. To one Wear on the bristles and fill material compensate, is used in series production empirically the number of pieces to be determined, the tool by a certain amount, that corresponds to the wear, expanded more. This is done when using step control additional delivery impulses.

It has been found that the bristle pretension expediently between 0.5 and 2 mm in diameter is, i.e. that the bristles have a diameter of Bristle end to be expanded to the bristle end without Concern about a hole is larger by the amount mentioned than the diameter of the hole.

5 shows the functional diagram for the machining process. 5 (a), the axial position 1 of the tool is plotted against time t. 1 _H is the stroke length. Point a denotes the upper end position. 5 (b) shows the infeed movement dr as a function of time. From this it can be seen that the expansion of the tool takes place after the retraction and that the brush strips are retracted again in the radial direction before the extension of the tool. 5 (c) shows the course of the rotary movement n over time. It can be seen from a comparison with FIGS. 5 (a) and 5 (b) that the rotary movement only begins after the tool has been retracted and expanded. The direction of rotation is reversed after half the machining time so that the silicon crystals are cut from both sides. It is preferably carried out at a peripheral speed of 250 to 450 m / min and with an axial feed of 5 to 15 m / min. The processing time can be 10 to 40 seconds. That gives 10 to 20 double strokes.

Figure 6 shows a photograph of a processed Surface. You can clearly see how that Silicon-crystalline 1 protrude from the aluminum matrix 2, so that the desired picture results. These are around a scanning electron microscope image of a honed one Surface of a light alloy engine block. The uniform Cutting level at which the aluminum matrix and the flat silicon crystal is clearly recognizable. Different roughnesses are also visible due to the partial hardness differences between the two Materials - silicon and aluminum - result.

Claims (3)

1. Method for exposing silicon crystals at the surface of finely machined, preferably honed workpieces, with which the silicon crystals (1) have a grain size of at least 30 to 80 µ and a minimum distance of 30 to 50 µ and are embedded into a considerably softer aluminum matrix (2), and with which the volume set free by setting back the matrix (2) by 1 to 2 µ serves to receive lubricating oil, characterized in that the surface of the workpiece subsequent to the fine machining is brushed with bristles (6), in the surface of which cutting grains (31) are incorporated, in which the diameter of the bristles is determined such that it is not larger than the medium distance of the silicon crystals.
2. Method in accordance to claim 1, characterized in that, when brushing boring surfaces, the diameter of the brush (4) used for carrying out the method, is by 0.5 to 2 mm larger than the diameter of the bore.
3. Method in accordance to claim 1 or 2, characterized in that the direction of rotation of the brush tool (3) is reversed after half the required machining time.

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