DE3045054A1 - METHOD FOR PRODUCING CUTTING TOOLS BASED ON SI (DOWN ARROW) 3 (DOWN ARROW) N (DOWN ARROW) 4 (DOWN ARROW) - Google Patents

Description

The invention relates to a method for manufacturing cutting tools based on SiN ..

3 4

Cutting tools based on Si N are known; albeit the known cutting tools have a high hardness and great stability, so have the known or previously proposed materials still inadequate chemical stability of the secondary phase. Furthermore, the cutting tools have a coefficient of friction that is still too high when used as intended as a cutting tool on.

1 300A0 / 0931

Seat of the company: Cologne - Cologne registry court. HRB 84 · Chairman of the Supervisory Board: Robert A. Lutz

Board of Directors: Peter Weiher, Chairman Hermann Dederichs - Waldemar Ebers Hans Wilhelm Gab Paul A. Guckel - Wilhelm Inden

Alfred Langer - Hans-Joachim Lehmann ■ Dieter Ullsperger

Fo3? D / ub '= il £ 9 / 2Ci ₀ Novembe

It is therefore the task of the invention to provide a process for the production of a Silir.eiäv / ei.'l'SQiiges ^ osauscMagen, bsi dem. as a result of driving Vss · check a ScäseM ⁷ v7erl'ssm.g results ,, the work the advantages of known cutting senge j näsmlieh high hardness raid large impact resistance at high Tempsi'ateea ₃ retains but better chemical stability and also having reduced coefficient of friction has siaea .

The task of the Surfindssg \ 7 is through the application of the main message gekennseicMGSes. Process steps reached 5 angular Refinements ssr Erfasdaag result from the application of the The procedural steps not identified in the sub-aspects.

It has emerged ₃ that when the process steps according to the present day are applied, the five-part properties of cutting tools of known origins are retained or improved . The sack dessi erfiiaciGmgsgemäßea Verfahrea prepared Sdcmeiav / e ^ aiiicli hzsuge Ins = special besitsea a Hoh <s therssiisehe conductivity ,, a low "iiTärjsiesHisdeiinusigskoeffizienten VNA good properties with respect to the ErzEiMung bsi high TeEaperaturesa. Prepared The ¹ points beyond the SEN according to the erfiiadaags gem & Verfahreil Cutting tool hardly ever broke deformation when used as a tool at high temperatures. As a result, the method according to the invention improves the chemical stability and the coefficient of friction of the tool is reduced higher temperatures than with known tools.

130040/0931

F © rd / US = ino / 2§ ₀ November 3L9SO

S045054

The use of the Scfe.aeife / es.'kaecgs according to the invention is particularly advantageous when it is being machined in cast iron doodling, milling, turning or drilling. A dureligeheadei " or a w & fcGvhsQckeztsz- incision can be made ",

The erfindungsgeniäüe method will be described again in detail:

The cutting tool according to the? Erfisadiaag ψήζά so produced, that first a mixture of Si ₅ N ₇ , - Fuder ν, ηά HfO .. = powder is divided into fine grains ; then at holier Tempsffata? The Misclimig is exposed to pressure until approximately the theoretically impossible one hundred percent compression is reached . In order to achieve this compression, the pressure applied must be maintained for a certain period of time. The resulting part is then machined until it has assumed the desired shape of a cutting tool. In this method, HfO_ acts as a flux; its presence in the mixture is limited to 4 to 12 % by weight of the mixture. As a base material, silicon nitride powder can preferably be used, which has an SiO _? - Has coating (usually 0.75 to 1.5 %) and which contains at least 85% ALPHA silicon nitride. Of impurities should not be present as the following amounts: 0, 5% by weight iron, 0, 01% by weight calcium; 0.4 % by weight aluminum, 2 % by weight oxygen and 1.5 % by weight free silicone. Accordingly, the total proportion of impurities should be less than 1%, with the exception of the free silicone. It is desirable to use a powder that has an average particle size of 2 to 2.5 microns for the silicon nitride powder. It is also advantageous to use a stabilized hafnium oxide powder which has a purity of 99.9 % and which is commercially available with a particle size of less than 325 mesh

130040 / 093.1

Ford / US-1119/20. November

fi

(corresponds to a clear mesh size of 0.046 millimeters according to DIN 1171). 88 % HfQ and 12% YO are used as stabilized HfO _51.

The powders used can be mixed using a ball mill, which also produces the required particle size. The balls in the ball mill can contain Ύί, WC, Al ₃ O and SiC. The Kugelmühlverfahren can persist for several days and is ausse = suggest that a particle size of the powder is achieved from about I ₈ 5 micron. In this occurs typiscl ■> wear of the balls or of the other elements of the ball mill is a _s about 1 75 to 2, 5% by weight of the final mixture. This proportion represents the impurities that are present in the sadvaligea mixture of powder.

The hot pressing of the powder mixture takes place at a pressure between

/ 2/2

281 and 492 kgf / cm, preferably at a pressure of 422 kg / cm at a temperature between 1,680 and 1,750 Celsius, preferably at a temperature of 1,700 Celsius. The exposure time of the The temperatures of the pressure can be 2 to 8 hours, preferably 6 hours.

The hot pressing is preferably carried out in a graphite mold, with the graphite serving as a protective environment for the workpiece serves. However, it is also possible to carry out the pressing process in a nitrogen atmosphere perform. If the workpiece is treated in a graphite mold, it is beneficial to use the powder mixture first

. 2
a pressure of 35 kp / cm. Then a pressing

2
at a pressure of 422 kgf / cm, an increase to this value being made so that the pressure increases about 70 kgf / cm per minute. The increase in temperature can

/ take place when the workpiece already has a pressure of 35 kp / cm:

130040/0031

ill 9/20, November

has been exposed. From this point on, the temperature can rise to a temperature of 1 70 ° Celsius. The hot pressing is to be carried out with this Tesapeira & js · imd feeisi maämalen pressure until the Yerdiclitmig has seen at least 99%, preferably 99.3% of the theoretically possible diameter. Οϊΐΐ to be safe _; that this value en? © eight is'i _c kasm de ^ Hub des ¹ '^ re £ "7OrrichU" iag are observed. -/earth.

ϊ'ατ το produced object kaasi da; si brought to the known form £ fe sin iSsftseidwes'kzei'.g v / erdes _s etv / a dsrcii Aaweadaag from Dia-Siuxnt2shlei £ er :, Das so srssugte WeÄseag ordered from sodireaa • L ^ piRiär-Matris · = phase voasilikonnifi ^ M aiii; siaer iiatergraaularen SokuiT.äcirphass-s dä-3 as a binder for 03.-3 matrix dieat uad from Si H., SiO, -ana HfO ,. besiaht This Sekuadüi'phase promotes chemical stability for that! "eramisehen Gegesastaad USSD feat aiicli sur consequence that a smaller Rsibisigskoeffiaient £ bi ^s the Werkssug v / hile vorhaades its use as -Schneidwerkzeug. is »The ultimate modulus of tear for a material produced in this way is between 4,218 and 6,327 kp / cm at room temperature. Des ⁵ ■ coefficient of thermal expansion

0
is not greater than 1.056 per Celsius iasd the thermal conductivity

not greater than U ₀ 372 kcal / mh ° Celsius (3.0 BTü / krin ° F). The hardness of the tool is at least 86 Rockwell 45-N, where

3 the density is about 3.25 to 3.5 grams per one.

The cutting tool obtained by the process can be used, in particular, for machining _{cast iron 9} , especially gray cast iron, with good results. Here the cutting tool achieves very long service lives. The invention is not

130040/0931

Ford / üS-1119/20 "November 1980

only with regard to the cutting speed and the machining performance comparable with the ceramic materials, which were manufactured on the basis of silicon nitride after the addition of Y ^ O. The tools according to the. ' In contrast to known tools, however, the invention has increased chemical stability and a lower coefficient of friction. However, great chemical stability is also important, since when the tools are used for the intended purpose, the temperature in the cutting area is very high. The high temperature in this area essentially influences the chemical behavior, which in turn causes a large amount of ice to wear out on the plate in the cutting tool. Various theories have been developed to explain the interaction in the area of the charge level between the workpiece and the metal plate. At . Action of forces and high temperatures in the Verbiaduagsbereich, beisn tool enters VersclileiiS ata £ ₅ triggered by Adhäseion and abrasion.

However, it may also, in certain circumstances the Werkseuges lead to a diffusion of the components with the processed material, as well as to a mutual solubility ,, Diffusion and solubility are controlled and influenced VOA the temperature at the top of the hard metal plate raxd ₅ which is very important is the chemical stability of the tool material. According to the invention it has been found that the resistance to wear of the tool is qualitatively dependent on the free energy of the material of the tool in accordance with the chemical stability. It has been found that the properties, as they result from the periodic system of the elements, as well as the free energy of the material produced by the method according to the invention is smaller than that of aluminum oxide, titanium oxide or the other carbides

130040/0931

11 1 9/2 & _o I ^ O "/ esabsr 190 §

or nitrides in connection with AlBsaisfeESj, Titea _s Teagstea silicone. The free energy of Ή & ίηΐηχΓίΟΐιψά vajriie ^ t; s «yissfeea about 125 kcal per gram at" cn. o. at 3L§ © "C eis ims to eirsa. 07 kcal _o per gram at 2,000 Celsius.

However, the knowledge that Kafniumoxyd increases the chemical stability and the coefficient of friction in eisesa material on Silikoaaiteid · = ■ Basic reduces, not enough to even before susehen _s that the other important physical Eigenscliaftea are present in iron material, which it as material for eia cutting tool. According to the invention, however erkanafe _s that are promoted by the use of 2 ™ most of the desired properties eiaes = cutting substance. For example, by using hafnium oxide, it is possible to influence the mechanical strength, the coefficient of thermal expansion and the thermal conductivity so favorably that the properties can be achieved in the same way as when other additives are used in the event of thermal shock and stress at high temperature Silicon nitride base.

Example 1;

A number of small bars were pressed in the laboratory made on the basis of Si N, each several centimeters long and about 50 to 15 millimeters in diameter. The ingots were made by hot pressing silicon nitride powder with an addition of 8%

2 ^De i a pressure of 422 kp / cm and a temperature of 1700 .Celsius generated, the exposure time being 6 hours. The material thus produced was then machined so that it could serve as a cutting tool. The test results for the application in turning and milling of gray cast iron are shown in Table 1. When turning, speeds of 305 m / min to

130040/0931

-.he-

610 m / min, achieved, the use time being 10 minutes . In this case, the wear was no greater than 0254 mm O _5, and no thermally induced cracks or deformations occurred. Furthermore, when the tool was used for milling work at a cutting speed of 1,829 m / min and a cutting performance of 163.9 cm / min. Wear of no more than 0.0762 millimeters was found over a period of OK meows. Even over a period of 67 minutes, the wear was no greater than 0.4572 millimeters.

In known tools based on aluminum oxide, the wear is O ₅ 254 millimeters at a cutting speed of 305 to 610 m / min, during a period of 10 meows of use. Known tools of this type, however, cannot be used up to a cutting speed of 1,829 m / min without difficulties. It is clear from the foregoing that the cutting tool produced by the method according to the invention, especially when used for machining cast iron, has unexpectedly long service lives at high cutting speeds and good cutting performance.

Example 2;

The material produced according to Example 1 was converted into a standard Cutting tool used and subjected to a test, as it corresponds to the normal production process in a large company. It was machined a difficult part for use in a transmission for a motor vehicle. The part to be machined was designed so that it was not interrupted Alternate cutting areas with interrupted cutting areas on other surfaces. The tool was made for that long

130040/0931

Ford / US-II19 / 20. November 198C

Machining of many workpieces used ₉ until it failed. The number of parts produced with a tool \ waTÜe sedasia festhaltea,

Id the given test could be done with the tool as per the. Process according to the invention was produced, 620 parts are pi'oduziert. The test was then repeated using a known tool which consisted of alvismasium osside coated with tungsten carbide. With this "who could manufacture 50 parts. From this comparison it is clear what increase in service life can be achieved by using the material according to the method according to the invention."

130040/0931

Table 1

Laboratory Test Results Type of cutting feed cutting Machining speed (mm / revolution) depth

(m / min.) or (mm)

(mm / tooth)

Cut machining line time (cm / min) (min.)

Wear remarks (mm)

O C? O

Turn

Milling

610 0.2794 305 0.5588 1 829 0.0914 1 829 0.5334

2.54 432.6 10

2.54 432.6 10

2.54 426.1 67

2.54 2 474.4 10.4

0.0152 0.0279

0. 4547 0.0762

no heat cracks and deformations

no heat cracks and deformations

cn O cn

4 >>

Claims (6)

Claims 1. Method of making cutting tools on the base of Si "N, characterized by the following process steps : a) A uniform mixture of Si N powder, which has a coating of SiO_ and 4 to 12 % by weight of HfO powder, is produced; b) the mixture is subjected to a pressure and heat treatment for a period of time that a almost complete compaction of the material is achieved; c) the result is brought into the desired shape of a cutting tool by mechanical processing. 2. The method according to claim 1, characterized in that the mixture additionally has up to 3.5 % by weight of impurities resulting from the grinding process of the powder mixture. 3. The method according to claim 2, characterized in that the impurities consist of W, WC, Al ₂ ⁰ O u ™ ^{1 SiC} . 4. The method according to claim 1 to 3, characterized in that that the powder of the mixture are prepared in a ball mill, the ball mill running until a particle size of about 1.5 microns is achieved. 130040/0931 Ford / US-1119/20. November 1980 5. The method according to claim 1 to 4, characterized in that / 2 that the powder mixture to a pressure of 281, 2 kp / cm / ² ο 457 kp / cm at a temperature of 1680 to 1740 Celsius exposed for a period of 1 to 8 hours. 6. The method according to claim 1 to 5, characterized in that that the HfO- powder has a purity of 99.9% or more and a particle size of less than 325 mesh (0.046 mm clear Mesh size according to DII '"1171) au £% veisted. 130040/0931