EP2445676A1

EP2445676A1 - Method and device for precision machining of crankshafts or camshafts

Info

Publication number: EP2445676A1
Application number: EP10726441A
Authority: EP
Inventors: Markus Heinloth; Jürgen Bär; Helmut Klein; Ralf KLÖTZER
Original assignee: Kennametal Inc
Current assignee: Kennametal Inc
Priority date: 2009-06-26
Filing date: 2010-06-18
Publication date: 2012-05-02
Also published as: KR20120039516A; WO2010149317A1; US20120076599A1; DE102009030856A1; US8584556B2; CN102413975A; BRPI1009865A2; JP2012530612A; CN102413975B

Abstract

The invention relates to a method and a device for precision machining of crankshafts or camshafts to final dimensional tolerances Rz < 10 µm, preferably less than or equal to 5 µm, and runout tolerances of less than or equal to 30 µm, preferably less than or equal to 6 µm. The crankshafts or camshafts are machined and at least partially hardened. According to the invention, after the first machining and subsequent hardening to 45 to 60 HRC, preferably 50 to 53 HRC, a final machining is performed using CBN or PCD inlet cutter inserts. The device used to this end has cutter inserts (12, 13, 14) populated with CBN or PCD inlets, wherein lateral, radial, and tangentially oriented cutter inserts follow each other alternately.

Description

Method and device for the final dimensional machining of crankshafts or camshafts

The invention relates to a method and apparatus for endmaßgenauauen machining of crankshafts or camshafts to Endmaßtoleranzen R ₂ <10 microns, preferably ≤ 5 microns and concentricity tolerances <30 microns, preferably <6 microns. The crankshafts or camshafts have been machined and at least partially subjected to hardening.

In the machining processes known from the prior art, the crankshafts usually pass through several treatment stages. First of all, the cast or forged shafts are subjected to a machining operation such as turning, turning and turning, internal milling and external milling, in particular at high milling speeds, whereby the allowance provided for casting or forging is removed down to a residual value in the millimeter range.

In order to increase the abrasion resistance of the crankshaft, the shaft is at least partially cured after a further step, for example by inductive hardening, in order to achieve the desired material and microstructure. When curing a delay and a slight dimensional change of the crankshaft or the camshaft can not be excluded, which must be compensated in a later processing step.

Usually, the crankshafts are ground in a third processing step, for example, with a grinding wheel whose axis of rotation moves parallel to the axis of rotation of the rotating crankshaft or camshaft. In most cases, the grinding is carried out with the addition of cooling lubricants in order to avoid excessive heating of the crankshaft during the final grinding cycle. Apart from the fact that the disposal of the resulting grinding sludge, which contains both the ground corrugated particles and the torn off abrasive grains of the grinding wheel, is costly, since grinding sludge as hazardous waste must be treated when grinding neither a high heating of the workpiece completely exclude still unfavorable influences on the workpiece surface, which produce an undesirable surface structure in the microscopic range due to the high processing pressures during grinding.

On this basis, the present invention has the object to provide a method and an apparatus of the type mentioned, with which the disadvantages mentioned are avoided.

According to the invention, the crankshaft or camshaft is first subjected to a first machining operation and a subsequent hardening, for example to values between 45 and 60 HRC, preferably 50 to 53 HRC. This is followed by a final machining operation with CBN or PCD inlets equipped cutting inserts, with which the final gauge shape is made. For this purpose, a device is used, which consists of an internal or external milling cutter, on the periphery of which radially and / or axially adjustable cutting inserts are fastened, each of which is equipped with CBN or PCD inlets, wherein preferably alternately clamped laterally, radially and tangentially Cutting inserts follow each other. However, the number of tangentially clamped cutting inserts, which serve to smooth the lifting or main bearings, be significantly lower than the number of laterally clamped cutting inserts, which are required for the respective cheek processing and undercut.

The replacement of the following grinding on a hardening against machining has not only the advantage that the entire production line dry, ie can be used without the use of cooling lubricant, which in particular eliminates the burden of chips and grinding sludge disposal of the cooling lubricant or its reprocessing, but also the manufacturing accuracy is increased. However, this presupposes that the cutting work is carried out with CBN or PCD cutting edges, which enables a sufficiently accurate final dimension-accurate production while maintaining low tolerances. The mere replacement of a grinding process after hardening with a machining In any case, conventional carbide cutting inserts do not provide the desired final dimensions, which is why fine grinding must still be carried out with such cutting operations, for example by means of abrasive belts. By using the CBN or PCD cutting, a surface structure is created which allows a tolerance in the range R _z <10 μm and a concentricity tolerance below 30 μm, preferably at 6 μm or less, to be maintained.

Is used both before curing and after curing with a defined cutting edge, i. H. worked with a machining, a higher runout can be eliminated in the first stage of machining in the final cutting cycle, since the passive force on the bearing is significantly smaller than when grinding. In a final machining process, one or two milling revolutions are sufficient to eliminate runout, whereas multiple revolutions with the disadvantages described above were required during grinding.

As a further positive effect results in the use of PCD and CBN cutting next to a high surface quality of the workpieces and long service life, whereby the efficiency of the treatment process is increased. The high abrasion resistance of the PCD or CBN cutting edges also ensures high process reliability and high setting accuracy. The resulting increase in the cost of cutting inserts (compared to one-piece carbide cutting inserts) is more than compensated in a shorter cycle time as a result of prolonged stall per blade, so that the crankshaft or camshaft production is also cheaper overall.

The roughness R _z represents the distance between the highest elevation and the deepest depression of a microscopic surface structure within a defined test track, whereby the value thus determined of 5 test sections is determined for the determination of R _z . This will not overrun outliers from the surface profile, namely very high peaks and very deep valleys. The concentricity is determined by circles, which are applied inside and outside to the actual contour of the workpiece. The two circles are arranged concentrically to each other, so that the actual cross-sectional profile of a workpiece lies in the space between these two circles. The present invention is based, in particular, on the finding that cutting processes by means of an external or internal milling cutter guarantee a higher concentricity than excessive grinding, in which the removal of material is relatively low anyway. If the choice of cutting tools and the adjustability on an external or internal milling cutter ensures exact, long life, cutting insert positioning, good results can be achieved despite the lack of grinding, which meet the requirements of claim 1 in terms of Endmaßtoleranzen and concentricity tolerances.

Preferred embodiments of the cutting inserts which are equipped with CBN or PKD inlets are described in the subclaims. Thus, in particular the respective cutting insert for machining the lifting or center bearing of a crank or camshaft is equipped with a roof-shaped cutting edge having two cutting edge portions which enclose an angle of 173 ° to 178 °, preferably 175 ° with each other. The hereby formed two usable cutting the possibilities of use are increased, d. H. that the cutting insert can be used for both right and left cutting work. The respective blades can be reground to increase the life of the cutting insert.

The said cutting edge portion ends go over an edge radius of R = 0.4 mm to 1, 5 mm (depending on the size) in minor cutting, which is inclined relative to a normal to the support surface of the cutting insert by 2 ° to 3 °, preferably 2.5 ° ,

According to a further embodiment of the invention, the laterally clamped cutting inserts for cheek processing on a CBN or PCD inlet, each with two usable cutting edges, which enclose an angle of 80 ° ± 5 °; the two Cutting edges are connected by a cutting edge radius of R = 1 to 1, 5 mm. These blades are regrindable.

Preferably, all cutting inserts disposed on an internal or external milling cutter are mounted in cassettes with an adjustment device that permits precise adjustment of the cutting insert position relative to the tool carrier.

In bearing machining, the crown of the bearing should preferably be between 0 and 4 microns.

Embodiments of the invention are illustrated in the drawings. Show it:

1 is a perspective view of a tool segment with three different cassettes,

2a, b is a detail view of a cassette with laterally laterally disposed cutting insert,

3a, b is an exploded view of the embodiment of FIG. 2a, b,

4a-c three views of a laterally clampable cutting insert and

Fig. 5 is a side view of a tangentially clamped cutting insert.

External milling cutters, which rotate during cutting around their longitudinal axis and which have a disc-shaped tool carrier having circumferentially arranged, each equipped with a cutting insert cartridges on a ring or semi-annular or segment-shaped, releasably either directly on a machine spindle or indirectly via an adapter are fixed to a machine spindle fixed carrier are described for example in DE 10 2007 013 153 A1. FIG. 1 shows a segment-shaped carrier 11 of such an external cutter. In the lower region, this carrier 11 has an open slot-shaped recess 29 which ends blindly and has an attachment point for a screw shank at its end. The axial clamping of this segment-shaped carrier 11 on a spindle, not shown, via clamping wedges. Several segments 11, which are fastened next to each other via suitable clamping pieces, form a complete ring, which is fixed on an existing spindle. Individual segments over a full one-piece annular body have the advantage that a partial replacement for cutting insert change is possible. In Fig. 1, a laterally clamped left cutting insert 12, a laterally clamped right cutting insert 13 and a centrally mounted cutting insert 14 are mounted on the periphery 15. The cutting inserts 12 and 13 are both radially and axially adjustable and with respect to their cutting edge inclination for adjusting the so-called camber, while the cutting insert 14, the axial adjustment is unnecessary.

It can be seen in detail from FIGS. 2 a and 2 b and 3 a and 3 b that the cutting insert 13 is fastened in the insert seat of a cassette 20 by means of a clamping screw, which has a plate seat with a bearing surface 21 and two side surfaces 22 and 23. The cutting insert 13 is fixed by means of a clamping screw 16 having a countersunk head. The clamping screw engages with its shaft, the central bore of the cutting insert 13 and is in a threaded bore 24 (see Fig. 3a, 3b) screwed. The cutting insert has a cutting edge 17 which is part of a CBN inlet, which will be discussed later. The cutting edge 17 is convexly curved towards the outside. The cutting insert 12 is like cutting insert 13 arranged in a cassette, the cassettes for the cutting inserts 12 and 13 are mirror-symmetrical but otherwise the same structure. Also screwed into a cassette is the cutting insert 14, whose width is chosen to be larger, so that the contact surface 23 can be arranged further to the left (see FIG. 1). Uniformly all cassettes are fixed with a clamping body 18 which is actuated by a double-threaded screw 19. The clamping body 18 is angled at its lower end, wherein the selected obtuse angle iden- table is selected with the corresponding corresponding angular contour of the cassette.

For axial adjustment of the cassette 20 is an adjusting body 25 which is displaceable over the double-threaded screw 26. This adjusting body has a wedge surface 251, by the longitudinal displacement of the cassette and thus the cutting insert 13 can be moved axially. For radial adjustment of the adjusting body 27 with a wedge surface 271, which is displaceable by means of the double-threaded screw 28. The cassette 20 has a substantially cuboid shape and has a slot-shaped groove 30 which, as can be seen in particular from FIG. 3 b, extends relatively far through the clamping body 20 as far as its rear wall 31. By spreading the groove 30, the part lying above the groove 30 201 is moved approximately in the direction of the arrow 32, which leads to a corresponding tilting of the cutting edge 17 by a (greatly exaggerated) angle α. In this way, a fine adjustment of the camber of the cutting insert or the cutting edge can be effected. To adjust the gap width is a double-threaded screw which engages existing holes in the parts 201 and 202 and which is designed as a crosshead screw 33, the head rests on a grub screw 34 in the assembled state. In Fig. 3a socket wrench 35 and 36 are shown with which it is demonstrated how these keys are inserted and operated. The operation of the capstan screw is possible via the laterally accessible recess 37 of the cassette (see FIG. 3 a).

For axial, radial and angular adjustment of the cutting insert 12 or 13, the screw 19 must first be actuated to release the clamping body 18 when the tool is mounted. After this, the adjustment screws 26 and 28 can be actuated via inbuse interventions, by means of which the cutting insert can be displaced axially and radially. In addition, by rotation of the crosshead screw 33, the fall of the cutting edge, ie their angular position can be adjusted by an arbitrary angle. This adjustment is of course limited by the selected slot arrangement in that the groove spacing can be changed only limited according to the Kassettenverformbarkeit. After selected setting The cutting inserts are each fixed by tightening the screw 19 via the clamping body 28 each insert. The cutting insert 14 is only radially and with respect to the cutting edge angular position adjustable.

Details about the cutting inserts 13 and 14 used are shown in FIGS. 4 a to c and FIG. 5. The cutting insert 13 has a CBN inlet 131, which is soldered in a carrier body 132, which may consist for example of steel or hard metal.

The CBN inlet 131 has an upper cutting edge 133 and a shorter cutting edge 134 which is tilted at an angle β of 10 ° with respect to the vertical to the cutting edge 133. The cutting edges 133, 134 merge into each other over a radius of for example 1 mm. The inclination of the CBN insert 131 determined by the angle α (see FIG. 4 a) is preferably 6 °. The cutting insert has a countersunk hole 135 formed for an N4 screw.

A side view of a cutting insert 14 is shown in FIG. 5, whose CBN inlet is labeled 141. This inlet has a two-part cutting edge with cutting edge portions 142 and 143 enclosing an angle γ of 175 °. The cutting edges 142 and 143 are endwise over a radius of, for example, 0.4 mm in inclined edges, which is inclined at an angle δ of 2.5 ° (which is exaggerated in the drawing). As seen in Figure 5, the CBN inlet 141 does not have to extend the full height of the cutting insert.

The external cutters equipped with CBN inlet are used in particular for the subsequent machining of a crankshaft or camshaft.

The cast or forged crankshaft or camshaft is first subjected to a first machining operation by means of external cutters, which apply at several points of the crankshaft or camshaft for main and Hublagerausbildung and cheek processing. Already in this first Zerspanungsgang becomes a highest possible surface quality (with R _z <50 μm and concentricity tolerances <100 μm). Subsequently, the crankshaft or camshaft is subjected to inductive hardening, where appropriate, the hardening can be limited to the later heavily loaded bearings. In a final machining cycle, the required final dimension quality with final dimension tolerances R ₂ <10 μm and concentricity tolerances ≤ 30 μm is set using an external or internal milling cutter equipped with CBN inlets. All cutting work is dry, ie without the use of cooling lubricants.

LIST OF REFERENCES

11 segmental carrier

12, 13, 14 cutting inserts

131 CBN inlet

132 carrier body

133, 134 cutting edges

135 lowering

141 CBN Inlet

142, 143 cutting edge sections

15 periphery of the carrier 11

16 clamping screw

17 cutting edge

18 clamping body

19 Double thread screw 0 Cassette 01, 202 upper and lower part of the cassette 1 contact surface of the insert seat 2, 23 side surfaces of the insert seat 4 threaded bore 5 adjusting element for axial adjustment 51 wedge surface 6 double threaded screw 7 adjusting element for radial adjustment 71 wedge surface 8 double threaded screw 9 slotted recess 0 slotted groove of Cassette 20 1 Cassette rear wall 2 Arrow 3 Pivot screw 4 Grub screw Insertion key lateral recess

Claims

claims

1. A method for endmaßgenauauen machining of crankshafts or camshafts to final dimensions R _z <10 microns, preferably ≤ 5 microns and concentricity tolerances <30 microns, preferably ≤ 6 microns, which have been machined and at least partially subjected to curing, characterized that after the first machining and subsequent hardening to 45 to 60 HRC, preferably 50 to 53 HRC, a final machining with CBN or PCD Inlet stocked cutting inserts is performed.

2. The method according to claim 1, characterized in that all machining operations dry, d. H. be carried out without the use of cooling lubricants.

3. The method according to claim 1 or 2, characterized in that the machining by means of an external or internal milling cutter having adjustable, equipped with CBN or PCD inlets cutting inserts, is performed.

4. Apparatus for dimensionally accurate machining of crankshafts or camshafts to final dimension tolerances R ₂ <10 μm, preferably ≤ 5 μm and concentricity tolerances ≤ 30 μm, preferably <6 μm, which have been machined and at least partially subjected to hardening an inner or outer cutter arranged radially or axially adjustable cutting inserts, characterized in that the cutting inserts are fitted with CBN or PCD inlets, wherein alternately follow laterally, radially and tangentially clamped cutting inserts successive.

5. The device according to claim 4, characterized in that the tangentially clamped cutting insert for machining the lifting or center bearing of a crankshaft or camshaft has a roof-shaped cutting edge with two cutting edge sections having an angle of 173 ° to 178 °, preferably 175 ° with each other lock in.

6. The device according to claim 5, characterized in that the cutting edge portion ends over an edge radius of

R = 0.4 mm to R = 1, 5 mm in secondary cutting edges, which are inclined relative to a normal to the support surface by 2 to 3 °, preferably 2.5 °.

7. The device according to claim 4, characterized in that the laterally clamped cutting inserts for cheek processing have a CBN or PKD inlet with two usable blades, which enclose an angle of 80 ° ± 5 ° and over a Schneckenckenradius of R = 1 to 1, 5 mm are interconnected.

8. Device according to one of claims 4 to 7, characterized in that all cutting inserts are mounted in cassettes with a setting device.