Microstructured metal surface

Abstract

Microstructures optimise the sliding and frictional behaviour of surfaces. For metal workpieces, current methods use special machines, which disadvantageously cost money and additional machine time. The present invention overcomes this disadvantage for the first time by successfully using now accessible, more precise machines in combination with measures for vibration damping. Surprisingly, for the first time during thread whirling, a microstructure was able to be provided on the side flanks of a threaded spindle in a reproducible manner which, during operation, permanently had a coefficient of friction which was up to 30% lower. As a result, spindle drives have a longer life, run more smoothly and are more efficient in the end application.

Description

[0001] Micro-structured metal surface

[0002] SCIENTIFIC AREA

[0003] The present invention can be assigned to the field of running, sliding and bearing properties of microstructured metal surfaces. Microstructuring which is intended to improve the friction and bearing behavior of metallic components of moving parts has been researched for some time. Documents such as JP 03265575 A, JP 09078102 A, JP 11230364 A or JP 11287329 A disclose structures and methods for their production which can improve the friction and running properties in combination with a lubricant. EP 1 111 225 A1 also discloses microstructures in the range 1 to 600 micrometers; the targeted creation and tuning of fine structures in order to optimize piston lubrication is described there. Microstructures are therefore known as suitable optimization structures and lubricant pockets.

[0004] GENERAL BACKGROUND

[0005] The present invention relates to microstructured metal surfaces according to the preamble of the independent claims. Metal surfaces which are frictionally slidably operated in assemblies are frequently obtained by metal-forming methods such as milling, pressing, rolling, or the like. In this case, the whirling of metallic workpieces forms the starting point of the present invention. The whirling of workpieces can be assigned to the field of machining and has been known for some time.For example, DE 2 151 315 A discloses a method for whirling multi-start threads; US 3 776 655 A discloses various cutting tools for the iterative milling of threads; DE 24 44 208 A additionally discloses methods for producing suitable tools; DE 25 51 250 A explains various work steps when using a whirling machine and DE 87 05 365 explains advantageous tool holders of a whirling machine.

[0006] DESCRIPTION OF THE STATE OF THE ART

[0007] DE 10 2004 009 088 A1 discloses a whirling machine with multiple tool holders. This allows for the targeted milling / smoothing / finishing of structures such as thread flanks or flanks of a whirled groove or thread groove through the alignment and positioning of the various cutting edges.

[0008] The inventors assume that vibration damping and uniform tempering during thread cutting have not yet been sufficient to enable fine structuring during machining.

[0009] Accordingly, the basic idea of ​​flank structuring disclosed in 10 2009 043 909 Al does not lead to any protective right: It seems that no concrete processes could be named which could have brought a commercial benefit in the sense of a sufficiently regular microstructure within the scope of the usual manufacturing processes for a thread.

[0010] Instead, corresponding protective rights such as US 8,512,097 B2, for example, focus on transverse vibrations of +- 50 micrometers that are disadvantageously superimposed with additional components in order to provide an additional structure.

[0011] Against this background, the question arose as to whether, using vibration damping measures that have since been developed and established, it is possible to create a useful microstructure directly during workpiece production using current, precisely controlled metal processing methods such as whirling. Inquiries to manufacturers of suitable machines regularly resulted in the response that the environmental influences on site cannot be sufficiently predicted or controlled to ensure a sensible and effective microstructure. The object of the present invention was therefore to overcome the established prejudices and disadvantages of the prior art and to provide a method that is able to create a microstructure directly as part of the known manufacturing process - in this case whirling.

[0012] The present invention proposes, for the first time, the controlled, technically effective, and commercially viable provision of a fine structure in the micrometer range within the framework of established whirling with now established vibration dampers. Surprisingly, this was directly successful with a simple vibration dampening device—in this case, a solid, vibration-damping foundation.

[0013] The solution is provided according to the features of the independent claims. Advantageous embodiments emerge from the dependent claims and the following description.

[0014] SUMMARY OF THE INVENTION

[0015] According to the invention, the microstructured metal surface is obtained by using a vibration-damped vortex device.

[0016] DESCRIPTION OF THE INVENTION AND ADVANTAGEOUS FEATURES

[0017] The metal surface according to the invention is microstructured; 'micro' refers to structures in the range from 1 micrometer to hundreds of micrometers. From 1,000 micrometers onwards we speak of millimeters. A microstructured metal surface therefore has structures from 1 to 999 micrometers. This is achieved by using a vibration-damped whirling device. Vibration-damped here means that an available whirling machine as known from the prior art is used in combination with at least one established measure from the field of vibration damping - e.g. placing it on a decoupling foundation area. By specifying the travel paths and positions of the workpiece and cutting edge to be whirled, the surfaces to be whirled can be precisely defined.

[0018] Typically, whirled surfaces exhibit concave side flanks; when aligned adjacent to one another in cross-section, a profile can advantageously be produced during whirling, as illustrated in EP 1 111 225 A1 in Figure 6A as a separately produced profile. This essentially results in ridges aligned transversely to the machining direction with concave valleys located between them, directly during the aligned manufacturing process.

[0019] Preferably, the metal surface is at least a portion of the surface of an external thread. Thread whirling often involves the targeted reworking of sub-segments to prevent excessive roughness. With appropriately predefined positioning, partial surfaces of a thread can be specifically provided with microstructures during the thread whirling process.

[0020] Preferably, the metal surface is arranged on the side flanks of the external thread of a threaded spindle. Threaded spindles intended to move assemblies or materials under pressure or against counterforce can be better adjusted to their intended use by microstructuring their friction-sliding behavior.

[0021] The external thread is preferably a trapezoidal thread. Trapezoidal threads are thicker and can typically transmit higher forces; improved sliding and friction properties are particularly advantageous in this case.

[0022] The threaded spindle is preferably made of an iron-based alloy, is equipped with a thixotropic lubricating grease in the thread, and is combined with a spindle race made of a softer, preferably copper-based, alloy that engages the thread. This allows a harder, lubricated surface with an optimized microstructure to slide over a softer spindle race that smooths itself over the structures during operation.

[0023] Preferably, the grease and material of the spindle bearing group are matched to one another so that any resulting abrasion can be carried by the lubricating grease and, if necessary, with the help of single-part additives such as amorphous silica or nanoscale hard materials, can even be helpfully crushed and / or carried. Adjusting and auxiliary measures for lubricating greases can be found, for example, in the documents EP 0 318 642A, US 2008 / 0132433 A and the documents cited therein. A thixotropic lubricating grease is characterized by the fact that it solidifies quickly when the machine is at a standstill and is no longer able to flow; slight movement leads to it liquefying again; this means that the lubricating grease, which is liquid during operation, remains securely in the thread even after longer downtimes and is reliably available for the next operation.

[0024] The structure preferably consists of a sequence of peaks and valleys. The number of peaks can be increased or decreased in proportion to the expected counterforce or pressure load, thus providing a reduced, friction-reduced contact area with predominantly elastic deformation of the structures even before operation. Abrasion and friction can thus be controlled in advance.

[0025] The height of the peaks is preferably 1 to 10 micrometers. Structures in this size range consistently resulted in a full-surface, uniform distribution of the grease for thixotropic, temperature-resistant greases for high to extremely high pressures / forces.

[0026] The distance between the peaks is preferably 1 to 10 millimeters. With a continuously concave valley profile between two peaks, a reduction in friction with minimal abrasion of the peaks was achieved during initial operation.

[0027] Preferably, the height to distance ratio is in the range 1 to 250 to 1 to 4000, preferably 1 to 500 to 1 to 2000, particularly preferably 1 to 800 to 1 to 1600.

[0028] The swirling device preferably comprises at least one thermostat. A thermostat monitors a temperature for constancy and activates a cooling or heating circuit accordingly in the event of deviations. In this case, a temperature such as the temperature of the ambient air, the temperature of the machine, the temperature of the workpiece, the temperature of the cutting tool, the temperature of the cutting oil, the temperature of the removed chips, the temperature of the surfaces exposed by machining can be measured and controlled individually or in combination.

[0029] The whirling device preferably includes optically adjustable tool positioning. Digital cameras enable the detection and spatial determination of the tool position. Continuous detection of the exact position allows for early detection of errors caused by thermal distortion, wear, uneven heating, or inadequate fixation and compensation by readjusting the positioning. This increases product quality and advantageously reduces the amount of scrap.

[0030] The whirling device preferably comprises cutting tools with a structured cutting edge. Useful structures are known, for example, from documents DE 79 22 542 U, DD 210 625 A, DE 691 31 231 T2, DE 298 10 969 U, DE 197 25 341 A1, or DE 102 16 408 A. They are designed for targeted chip guidance, chip cooling, and reliable chip breakage.

[0031] The structured cutting edge preferably comprises a plurality of cutting segments arranged in a line and spaced apart from one another. This creates a plurality of parallel, smaller chips during whirling. The corresponding surface can be provided with additional, unmachined areas within the chip removal. Advantageously, several blunter mountain structures are thus simultaneously produced with only one whirling process.

[0032] Further advantages emerge from the exemplary embodiments. The features and advantages described above and the following exemplary embodiments are not to be understood as exhaustive combinations of features, unless explicitly described as such. Additional, advantageous features and additional combinations of features, as explained in the description, disclosed in the cited documents and the prior art explained therein, and established in the scientific field, can be implemented in the claimed subject matter both individually and in different combinations as an addition within the scope of the independent claims, without departing from the scope of the invention.

[0033] DETAILED EXPLANATION OF THE INVENTION USING EXEMPLARY EMBODIMENTS

[0034] A whirling machine of the type disclosed in DE 10 2004 009 088 A1 was built on a particularly solid, vibration-damping base plate. A program for thread whirling a trapezoidal thread was then programmed so that the whirling surfaces on the side flanks of the thread only slightly overlap. A steel spindle blank was clamped and machined. Checking the surface morphology revealed surprisingly clear and clean structures: Continuously adjacent, flat, concave valley structures with a valley width between 1 mm and 4 mm, combined with a valley depth / peak height between 2 and 5 micrometers, could be replicated.Toughness, wettability and chip behavior of the workpiece on the one hand and chip depth, angle, speed and sequence of the cutting tools and cutting edge geometries on the other hand are the key parameters that had to be tested on a blank in a test run in order to be able to reliably outline the suitable operating parameters and producible structures. In comparison, threaded spindles produced on a non-damped machine showed a significantly higher roughness, which no longer allowed the set and desired structures to be recognized. For a trapezoidal thread with a microstructure with a peak height in the micrometer range and a peak spacing in the millimeter range, preferably around 3 to 7 micrometers in height and 3 to 5 millimeters spacing, tribological tests for a steel spindle with a softer, copper-based traveling nut showed a friction coefficient that was up to 30% consistently lower over 40,000 operating hours.The friction and sliding behavior was significantly and consistently improved compared to a non-structured threaded spindle.

[0035] INDUSTRIAL APPLICABILITY

[0036] Microstructures optimize surfaces in terms of their sliding and friction behavior. Current approaches for metal workpieces require dedicated machines, which disadvantageously cost money and require additional machine time.

[0037] The present invention overcomes this disadvantage for the first time through the successful application of now available, more precise machines in combination with vibration damping measures. Surprisingly, this is the first time that thread whirling has made it possible to repeatedly produce a microstructure on the side flanks of a threaded spindle that exhibits a friction coefficient up to 30% lower during operation.

[0038] This makes spindle drives more durable, smoother running and more efficient in the end application.

Claims

CLAIMS 1 . Microstructured metal surface , characterized in that it was obtained by using a vibration-damped vortex device .

2. Metal surface according to the preceding claim, characterized in that the metal surface is at least part of a surface of an external thread.

3. Metal surface according to the preceding claim, characterized in that the metal surface is arranged on side flanks of the external thread of a threaded spindle.

4. Metal surface according to the preceding claim, characterized in that the external thread is a trapezoidal thread.

5. Metal surface according to one of the two preceding claims, characterized in that the threaded spindle consists of an iron-based alloy, is equipped with a thixotropic lubricating grease in the thread and is combined with a spindle race group engaging in the thread and made of a softer, preferably copper-based, alloy. 6 . Metal surface according to one of the preceding claims, characterized in that the structure consists of a sequence of mountains and valleys.

7. Metal surface according to the preceding claim, characterized in that the height of the mountains is 1 to 10 micrometers. 8 . Metal surface according to one of the two preceding claims, characterized in that the distance between the peaks is 1 to 10 millimeters.

9. Metal surface according to the preceding claim, characterized in that the height to distance ratio is in the range 1 to 250 to 1 to 4000, preferably 1 to 500 to 1 to 2000, particularly preferably 1 to 800 to 1 to 1600.

10. Metal surface according to one of the preceding claims, characterized in that the vortex device comprises at least one thermostat.

11. Metal surface according to one of the preceding claims, characterized in that the vortex device comprises an optically adjustable tool positioning.

12. Metal surface according to one of the preceding claims, characterized in that the whirling device comprises cutting tools with a structured cutting edge.

13. Metal surface according to the preceding claim, characterized in that the structured cutting edge has a plurality of cutting segments arranged in a line and spaced from one another.