WO1985003896A1

WO1985003896A1 - Method for removing particles generated during a form grinding operation and which adhere in the grinding gap

Info

Publication number: WO1985003896A1
Application number: PCT/CH1985/000021
Authority: WO
Inventors: Werner Ullmann; Harry Neumann; Ulrich Hans Seuser
Original assignee: Werner Ullmann
Priority date: 1984-03-05
Filing date: 1985-02-07
Publication date: 1985-09-12
Also published as: CH664727A5; EP0174316A1

Abstract

During a grinding operation, particles form undesirable layers in the gap (2) delimited by the form grinding tool (5) and the work-piece (9). This is prevented during the grinding operation by means of medium (14) which increases the molecule interval of the particles and/or by a suppression of the potential to which the tool (5) is charged.

Description

Process for removing particles that arise during a molding / grinding process and become lodged in the grinding gap.

The invention relates to a method for removing particles during the grinding process, which particles arise during the grinding of a workpiece by means of a machine-driven and preferably program-controlled tool and which adhere to the surface of the tool containing the electrically insulating materials.

The invention is a method that was developed especially for machine tools that grind complicated, three-dimensional workpieces. The so-called mold grinding tool has the shape that the tool should have after the grinding process. For this reason, the form grinding tool is made of easily formable and hardenable material such as polycondensates, polymers and addition polymers. The grinding wheels made of hard material such as corundum, silicon carbide, cubic boron nitride, diamond etc. are inserted in the grinding surface. The workpiece, for example made of graphite, is clamped on a machine table and is ground from the full piece to its final shape. Here, the form grinding tool, which is arranged in the tool head of the machine tool, is moved by a feed in the direction and by a special drive in a planetary movement to the feed axis to the workpiece. During the grinding, the ground surface particles of the workpiece attach themselves to the tool and form layers at some points on the grinding surface. Since these layers form at seemingly arbitrary points on the grinding surface and grow slowly and arbitrarily, the precision and the abrasion control of the grinding become worse without external indications. These layers can accumulate so strongly that the grinding surface is ineffective. This phenomenon leads to poor quality of work and destruction of the tool or workpiece.

The object of the invention is to eliminate these disadvantages. In preparation for the invention, intensive studies were carried out, which came to the unexpected result that the ground parts or particles from the material of the workpiece become attached to the grinding surface of the mold grinding tool due to electrical charges. These electrical charges are created on the tool by e.g. the sharpening of the grinding surface, by wind or dust during storage of the tool or by clearing itself. As is known, the tool is sharpened before the grinding process.

The grinding tools are often built from casting resins, the surface of which contains abrasive grains. After molding, the surface is smooth because the abrasive grains are completely embedded in the plastic. By blasting, for example with sand or glass powder, a thin layer of plastic is loosened between the abrasive grains, so that the grains remain embedded, but the tips in the Surface are exposed. This process is called sharpening the grinding tool. Because of the friction of the sand or glass grains on the poorly or not at all conductive surface, this is particularly strongly electrostatically charged.

Even during the actual closing of the process, friction always creates local electrostatic charges. As is known, grinding tools made of metal or with a metallic bond are also occasionally used. Due to the high contact resistance (grease, lubricated bearings, etc.), the charges can only flow off when the potential reaches a certain voltage. Then there are spark jumps or electrolytic conduction, which can damage the machine tool.

It was also found that the forces between the molecules of the cut open particles help to build up a crystal lattice characteristic of the cut material. These forces are the well-known van der Waals forces.

The object of the invention is achieved by the method defined in claim 1. The invention is explained in more detail with reference to the grinding devices shown in the drawings. Show it:

Figure 1 shows a known form grinding machine to which the invention is applied;

Figure 2 is a sectional view of a form grinding tool and a workpiece to explain the invention.

REPLACEMENT LEAF Figure 1 shows the hydraulic cylinder 1 in which the plunger or quill 3 is movably arranged. On the plunger 3, the plunger plate 4 is fastened, which is guided by means of four columns 8 and the guides 6. Only two of the columns are shown. The three-dimensional shape grinding tool 5 is fastened on the lower side of the ram plate 4. The form grinding tool has the three-dimensional shape that the workpiece 9 is to have after machining. In the present example, the workpiece 9 consists of the material graphite and is fastened in block form as a blank on the work table 10. The workpiece 9 can also consist of another material, such as metals or their alloys, or of an insulating material such as wood. The work table 10 is connected to two eccentric drives 11 which bring the work table and the workpiece 9 into the planetary or orbital or circular movement. The movement takes place in the X and Y coordination, which are perpendicular to the feed direction of the tool 5. The control panel 7 contains a large number of operating elements. The operator can use these organs to operate the electronic NC control 12, the unit 13 and the drive motors arranged in the machine base 15. It should be pointed out that the operator intervenes in the work process only in very rare cases. Processing is usually fully automatic.

The work process begins with the electronic NC control 12 lowering the ram plate 4 with the form grinding tool 5 in the direction of the workpiece 9 via an electrical or hydraulic system likewise provided in the machine frame 15. At the same time, the two ^* eccentric drives 11 are put into operation by the NC controller 12.

REPLACEMENT LEAF puts. They drive the work table 10 and the workpiece 9 in a circular motion. The amount of eccentricity is determined by the NC control. The workpiece 9 is given the desired spatial shape by this movement to the form grinding tool 5. In the course of machining, the tool 5 moves more and more into the workpiece 9 at a certain feed rate. An abrasive ensures the correct process. The abrasive is worked into the surface of the tool 5.

During the entire work process, a medium 14 is processed in the unit 13 and transported to the work table 10 via hoses. The workpiece 9, which was provided with at least one but preferably a plurality of rinsing channels 93 before the grinding process, is fastened to the work table 10 in such a way that the medium 14 supplied by the unit 13 reaches the gap 2. Tool 5 and / or workpiece 9 can optionally be provided with rinsing channels.

In Figure 1, the tool 5 is shown very simply as a blank before grinding. This is for general illustration only. In reality, the surfaces or the spatial shape are much more complicated.

This is shown in FIG. 2, which shows a tool 9 that is about to end the cutting process. The tool 5, which is attached to the plunger plate 4, soon gave the workpiece 9 its final shape. The rinsing channels 93 are visible in the workpiece 9. The medium 14 according to the invention is conveyed through the feed 92, which is connected to the unit 13, into a chamber which is provided in the base plate 91 and passes from

REPLACEMENT LEAF there into the individual flushing channels 93, which distribute the medium evenly in the gap 2. In the gap 2, the medium 14 ensures that the particles formed by the grinding do not form any undesirable layers and can hinder the grinding process or make it impossible. The mechanism of this mode of action is not completely clear. You can think of him as follows. As a result of the special composition of the medium 14, it shifts, so to speak, between the molecules of the particles which have arisen from the grinding, and thus increases the distances between these molecules, so that they are unable to support themselves by the van der Waat_scheπ forces Kristal lattice to combine and so the unwanted layers, eg. B. to form on the Schleiffl surface of the tool 5.

Three examples of the composition of the medium 14 are described below:

1st example

Water is mixed with alcohol in a certain ratio. Monohydric alcohols have proven particularly good. Isopropyl alcohols have given the best result. The mixing ratios depend on the type of alcohol used and are in the range from 10: 1 to 1: 1 water / alcohol. The mixture is added to the unit 13 in FIG. 1.

2nd example

The wetting agent P3-T 5130 from Henkel & Cie is added to the water with 0.5 vol% to 10 vol% and into the Aggregate 13 of Figure 1 poured.

3rd example

The neutral cleaner P3-T 5125 from Henkel & Cie. with 0.5 vol% to 10 vol% added to the water and added to the aggregate 13 of FIG. 1.

In addition to the prevention of the undesired layers by the medium 14 during the grinding process, there is also the possibility of reducing the electrical potential that builds up on the grinding surface of the mold grinding tool 5 ′, specifically to a value of the machine table 10 on which the workpiece 9 is clamped is. The inventors found that such a potential favored the formation of the undesirable layers. The potential degradation takes place in that good electrical connections are made between the tool 5, ram plate 4, guides 6, columns 8, machine table 10, base plate 91 and workpiece 9. Particularly in the case of moving parts such as guides 6 and Columns 8, which are also kept sliding well by electrically non-conductive lubricants, the electrical connections must be kept in good condition. These electrical connections can be strands that are braided from copper wires, for example, and are commercially available. Such a strand 16 is shown in FIG. 2 between the tappet plate 4 and the machine table 10. This strand follows all the movements that occur during the movement between the tool 5 and the workpiece 9, such as feed and retraction as well as planetary movements. A further possibility of reducing the potential difference between tool 5 and workpiece 9 can be accomplished in that the medium 14 has good electrical conductivity. This is done by means of additives which are added to the medium 14 or which are already present in the medium. Here, a substance is colloidally dissolved. This colloidal solution forms 2 electrically conductive bridges in the gap to reduce the potential.

The inventors were able to establish that during the grinding process the tool 5 charges up to a potential of a predetermined polarity and an approximately predetermined amount. This can be prevented by the tool 5 being charged to a potential with reversed polarity and the amount to be expected before the grinding operation. In this case, the medium 14 must not have any electrical conductivity and the electrical connections on the machine frame must not be present.

The potential degradation and the particularly composed medium 14 can either be used as individual measures or in combination to prevent the undesired layers. This arises from case to case.

Claims

P A T E N T A N S P R U E C H E

Process for removing particles during the grinding process, which particles arise when a workpiece is ground using a machine-driven and preferably program-controlled tool and are attached to the grinding surface of the tool containing electrically insulating materials, characterized in that the molecules of the particles are embedded in a medium (14) that increases the molecular distance and, if appropriate, an electrical potential that builds up on the grinding surface of the tool (5) in the direction of the workpiece (9) and on the value of a machine table (10) carrying the workpiece is built.

Method according to claim 1, characterized in that the medium (14) which increases the molecular distance is a mixture of water and alcohol, preferably monohydric alcohol, in particular isopropyl alcohol, and has a mixing ratio which is in the range from 10: 1 to 1: 1 water / alcohol.

3. The method according to claim 1, dadurchge ¬ indicates that the mol ekül ver distance * enlarging medium (14) of water and a wetting agent is mixed, which wetting agent with 0.5 vol.% to 10 vol.% is added to the water.

3. The method according to claim 1, characterized in that the medium-increasing medium (14) is mixed with water and a nitrite-free neutral cleaner, which neutral cleaner is added to the water with 0.5 vol.% To 10 vol .

4. The method as claimed in claim 1, so that the workpiece (9) is given a potential which is high and opposite to the potential of the tool (5).

5. The method according to claims 1 and 4, so that the tool (5) and / or the workpiece (9) is conductively connected to the machine table (10).

6. The method according to claim 1, so that the tool (5) and / or the workpiece (9) are grounded to the machine table.

7. The method as claimed in claim 1, so that an electrically conductive medium (14) is placed in the gap (2) between the tool (5) and the workpiece (9).

8. The method according to claim 1, characterized in that the tool (5) and / or the workpiece (9) before the grinding operation in each case individually to the same or the opposite to the natural process Potential is brought.

9. The method according to claim 1, so that the tool (5) is sharpened before being clamped onto the impact plate (4) and is irradiated with a liquid that is electrically 1-sided.