KR100676248B1 - A method of turning a rotating metallic work piece - Google Patents

Abstract

The present invention relates to a method of turning a rotating metal workpiece having a hardness in the range of 45 to 65 HRC. A turning tool 10 comprising a cutting insert holder 11 and a cutting insert 12 mounted therein is engaged with a workpiece that rotates with respect to the turning tool. The cutting insert has cutting edges 14 and 14 'made of square boron nitride that is harder than cemented carbide and has a cutting edge length. The cutting insert is conveyed in the direction F by a predetermined distance to the rotating workpiece, which distance is shorter than the cutting edge lengths L1; L1 'to provide _a surface finish Ra of up to 0.2 μm. The end of the active cutting edge 14 is located outside the contact area with the workpiece 13.

Description

A METHOD OF TURNING A ROTATING METALLIC WORK PIECE

The present invention relates to a method of turning a rotating metal workpiece in accordance with the preamble of the independent claim.

Square polycrystalline boron nitride (PCBN) is comparable to diamond, the hardest material. In contrast to diamond, PCBN is stable at high temperatures, which means it is also possible to turn hardened steel (45-65 HRC) with economically favorable cutting data. It is used in today's modern machining industry by turning hardened parts that were previously ground. Efficient CNC lathes enable fast and flexible machining at the same quality as grinding in surface roughness and tolerances, but at low cost and short machining times. As with residual strains in the machined surface during grinding and hard turning, so-called martensite transformations, called white layers, can occur. This phenomenon depends on the generation of heat in the cutting process and the mechanical strain and is influenced not only by the selection of the tool path but also by the cutting data and the tool shape.

Hard material turning methods currently used in machining attempt to minimize the contact between the cutting insert and the workpiece surface in order to meet the quality requirements of the finished part. This means that the machining is done with a small cutting depth and feed and a relatively sharp cutting corner. The cutting corner with small engagement is brought from the beginning to the end of the machining surface using typical cutting data of cutting depth ap = 0.1 mm, feed f = 0.1 mm / r and cutting speed 150 m / min.

It is an object of the present invention to provide a hard turning method comprising the advantages of the prior art.

Another object of the present invention is to provide a hard material turning method for remarkably reducing processing time during fine turning of hardened parts.

Another object of the present invention is to provide a hard turning method for improving the surface quality when finishing hardened parts.

Another object of the present invention is to provide a hard turning method for minimizing the presence of white layers and residual strain in the machined surface.

These and other objects are achieved by a hard turning method as defined in the following claims with reference to the drawings.

1 and 1a are cross-sectional views of a bite gear before engaging a tool.

2 and 2a are cross-sectional views of the ball bearing rings before engaging the tool.

1 and 1 a, the turning tool 10 is shown to include a cutting insert holder 11 and a cutting insert 12 mounted thereto. Cutting inserts are made of harder materials than cemented carbides with hardness greater than 1500 HV1 (Vickers hardness with the load 1 kg). "Carbide alloy" means here WC, TiC, TaC, NbC, etc., which are combined with a binder metal such as, for example, Co or Ni. The cutting insert of FIGS. 1 and 1 a has a basic triangular shape with three cutting edges 14. Each cutting edge 14 is located between two adjacent cutting corners of the insert and has a cutting edge length L1 defined by the maximum available insert blade length. By inserting the PCBN insert into the same profile as the guide surface 15 of the finished part 13, machining takes place faster because all cutting edge profiles are engaged at the same time and the feed occurs in the opposite direction to the feed in the prior art. to be. The cutting insert is consequently provided only in a single direction F at a distance shorter than the cutting edge length L1. The finished surface 15 of the finished part 13 has a length L2. The cutting edge length L1 is always longer than the length L2 of the contact region, such that the end of the active cutting edge 14 is outside the contact region with the workpiece 13 during turning. Therefore, the surface roughness (R _a) is obtained with a maximum 0.2㎛.
Test results show that the process according to the invention can reduce machining time by one tenth of the time taken by conventional hard material turning methods. Surprisingly, the presence of white layers was reduced and the level of tension appeared to be reduced.

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Example 1.

Machining of the outer guide surface 15 of the bleed gear 13 with a 59 HRC hardness for the gearbox according to FIGS. 1 and 1a.

Conventional method:

a. Rough turning by neutral octagonal cutting inserts with vc = 130 m / min, f = 0.16 mm / r, ap = 0.1 mm, where vc is the cutting speed, f is the feed rate and ap Cutting depth.

b. Finishing according to this method, except that f = 0.06 mm / r, ap = 0.05 mm, provided _a surface finish (R _a ) of 0.3 μm with typical surface quality by conventional turning and 0.06 on the resulting surface. It had a spiral ridge, clearly distinguished by mm.

Method according to the invention:

Machining by the triangular cutting insert 12 where vc = 200 m / min, f = 0.05 mm / r and the cutting insert is engaged at 80% (the parameter "cutting depth" is omitted) is the rotation axis CL of the workpiece. A surface finish of R _a 0.2 μm was provided during transfer in the vertical direction (F) only. By "missing" it is meant that the cutting depth is not a parameter in the method of the invention. The time saved compared to conventional turning is about 60% and the turning provided a completely shiny production surface.

An alternative embodiment of the turning tool 10 'includes a cutting insert holder 11' and a profile insert 12 'mounted therein and shown in FIGS. 2 and 2a. The hardness of the cutting insert 12 'relative to the hardness of the workpiece 13' is the same as described above in connection with FIGS. 1 and 1A. The cutting insert 12 'has a basic triangular shape except that it has at least one convex cutting edge. The cutting edge length L1 ', which is defined as the maximum available insert edge 14' length, is always longer than the length L2 'of the contact area, so that the end of the active cutting edge 14' at the end of the workpiece 13 ' It is outside the contact area with.

Example 2.

Machining of the inner bearing race 15 'of the ball bearing ring 13' with 58 HRC hardness according to FIGS. 2 and 2A.

Conventional method:

a. Roughing by cutting inserts of positive triangle type with vc = 150 m / min, f = 0.1 mm / r, ap = 0.15 mm.

b. Finishing according to the above method, except that vc = 180 m / min, ap = 0.05 mm, provided _a surface finish (R _a ) of 0.3 μm with typical surface quality by conventional turning, 0.1 on the resulting surface. Clearly visible screw-shaped bumps, separated by mm.

Method according to the invention:

The creation of the machined surface by the profile insert 12 'with vc = 400 m / min, f = 0.02 mm / r (parameter "cutting depth" omitted) is perpendicular to the axis of rotation (CL) of the workpiece. When provided only as a surface finish of R _a 0.2 μm was provided. The time saved compared to conventional turning was 50% to 90% depending on the size of the part. The inner bearing race 15 ′ of the ball bearing ring 13 ′ has obtained a fully shiny production surface by the method according to the invention, which improves the fatigue strength of the bearing race and reduces the resistance to rolling in the bearings. .

By means of the method according to the invention, subsequent honing and polishing operations can be avoided in most cases.

As a result, the present invention relates to a method of turning a rotating metal workpiece with reduced depth of cut, in which the machining time at the finishing of the hardened part is significantly reduced and the presence of white layers and tension at the finished surface is also reduced.

Claims (3)

The turning tool 10; 10 ′ comprising a cutting insert holder 11; 11 ′ and a cutting insert 12; 12 ′ mounted therein engages a workpiece that rotates with respect to the turning tool, the cutting insert being more than carbide. In a method of turning a rotating metal workpiece having a hardness in the range of 45 to 65 HRC, having a cutting edge 14; 14 'made of square boron nitride having a harder and cutting edge length L1; L1'. The cutting edge is conveyed into the workpiece rotating a predetermined distance shorter than the cutting edge length L1; L1 'to provide _a surface finish Ra of up to 0.2 μm, where the active cutting edges 14 and 14'. The end of which is positioned outside the contact area with the workpiece (13; 13 '). The method of claim 1, A turning method characterized in that a substantial part of the available cutting edges (14; 14 '), preferably at least 80%, is temporarily engaged with the workpiece. The method of claim 1, The cutting edge (12; 12 ') is characterized in that the feed only in a single direction (F) relative to the rotating workpiece.

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