DE102020109815A1 - Process for creating a workpiece tapped hole - Google Patents

Abstract

The invention relates to a method for producing a threaded workpiece hole (2) with a pre-drilling process step in which a thread-free pre-hole (31) is produced with a drilling tool, the bottom of the hole (3) of which lies _{at a target drilling depth (t B),} and with a threading process step in which a thread-generating tool generates an internal thread (9) in the pilot hole (31) in a thread stroke (G) with a thread-generating feed rate (vf) and a thread-generating speed (n) synchronized therewith. According to the invention, the thread generating tool has at least one cutting edge (19) at the bottom of the hole facing the bottom of the hole (3).

Description

The invention relates to a method for producing a workpiece threaded hole according to the preamble of claim 1, a thread producing tool according to claim 8 and a workpiece threaded hole according to claim 9.

The crankshaft flange of a crankshaft of an internal combustion engine has a number of circumferentially distributed threaded bores into which screw bolts can be screwed in order to connect a flange on the transmission side to the crankshaft flange by means of a screw connection. The threaded bores of the crankshaft flange can be implemented as blind holes, which prevents oil from passing through the threaded bores. In this case, the target drilling depth of the respective threaded hole corresponds to the flange thickness of the crankshaft flange minus a sufficiently large remaining base thickness at the bottom of the threaded hole.

With such a flange geometry, the challenge is to enable a sufficiently high screw strength of the screw connection despite the reduced nominal drilling depth.

In a generic method for producing a threaded workpiece hole, there is initially a pre-drilling process step in which a thread-free pre-drilling is produced. This is followed by a threading process step in which a thread generation tool generates an internal thread in a thread stroke with a thread generation feed rate and a thread generation speed synchronized with it. Such a method is exemplified from EP 1 497 067 B1 known, which discloses a method for producing threads. From the DE 38 10 884 C1 a device for producing internal threads without pre-drilling is known. From the EP 3 484 647 B1 a method for producing a threaded hole is known. Further methods for creating a threaded hole are from the DE 10 2012 105 183 A1 , from the DE 38 76 820 T2 and from the DE 36 27 798 C2 known.

The object of the invention is to provide a method for producing a workpiece threaded hole in which the threaded hole enables a sufficiently high screw strength despite the reduced nominal drilling depth.

The object is achieved by the features of claim 1, claim 8 or claim 9. Preferred developments of the invention are disclosed in the subclaims.

The invention is based on the fact that in the prior art the thread generating tool is axially spaced apart from the bottom of the bore via a tool clearance at the end of the thread generation. In the prior art, the tool clearance is dimensioned sufficiently large along the bore axis so that the tool tip of the thread generating tool can protrude without stress, i.e. without contact with the base of the bore. In this case, the target thread depth results from the target drilling depth minus the comparatively large tool clearance. As a departure from the process control known from the prior art, the provision of such a tool clearance at the bottom of the bore is dispensed with according to the invention. Rather, according to the characterizing part of claim 1, the thread-generating tool has at least one cutting edge at the bottom of the tool at its tool tip facing the bottom of the hole. In the threading process step, the thread generating tool is brought up to the stop with the bottom of the hole, so that the cutting edge of the bottom of the hole can remove a small amount of material from the bottom of the hole. At the same time, the internal thread is created right up to the bottom of the hole. In this way, the screw bolt can be screwed almost to the bottom of the hole. As a result, a sufficiently large usable nominal thread depth can be achieved despite the reduced nominal drilling depth.

In the method according to the invention, the pre-drilling process step is carried out with a separate drilling tool which creates a thread-free pre-drilling in the workpiece, the bottom of which lies on the target drilling depth, which can still be subject to tolerances. Tolerance compensation for the target drilling depth is carried out in the tapping process: In the tapping process, the cutting edge of the hole bottom of the thread generating tool can remove material from the bottom of the hole, whereby any tolerance allowance that may still be on the bottom of the hole can be removed.

It is preferred if, in the thread drilling process step, the thread generating tool inserted into the pilot bore is aligned with its tool rotation axis coaxially to the bore axis. Alternatively - depending on the tool design - the thread generating tool can also be guided axially parallel to the bore axis.

In a preferred embodiment variant, the cutting edge of the bottom of the hole can have a transverse cutting edge that runs at right angles to the tool axis of rotation and that can be brought into chip engagement with the bottom of the hole of the pilot hole. In this way, a flat or planar bore bottom can be generated, which with regard to a larger usable nominal drilling depth is preferred (compared to a conical bottom of the drilling).

The thread generating tool has at least one thread profiling tooth on its outer circumference. Its radially outer tooth tip can move on a circular path the size of a diameter when the tool rotates. In contrast, the thread-generating tool can have an outer circumference of reduced diameter, diametrically opposite to the thread-profiling tooth, with respect to its tool rotation axis. This can move on a circular path with a small diameter when the tool rotates. In this case, there is a radial clearance between the small-diameter circular path and the large-diameter circular path. In the threading process, the tool can therefore be controlled radially by a radial offset (with partial use of the radial clearance) in order to disengage from the internal thread produced. The thread-generating tool can then be guided out of the threaded hole without intervention.

In a preferred process control, the thread-generating tool can be moved into the pilot hole in the thread stroke, to be precise with the generation of the internal thread. In this case, the thread-generating tool is not subjected to tension during thread generation, but rather to compression. At the end of the thread stroke, the thread generating tool comes into contact with the bottom of the hole and a free cut groove is generated. During the free cut groove generation, the feed rate and the speed of the thread generating tool are no longer synchronized with one another. Accordingly, the free cut groove has no thread pitch. The internal thread is thus fully formed up to the free cut groove on the thread base and can be used for a screwing process.

With its lower groove flank, the free cut groove merges directly into the bottom of the hole, to be precise without the formation of an additional tool clearance, which is present in the prior art between the internal thread and the bottom of the hole.

After the free cut groove has been created, a reversing stroke takes place. To prepare for the reversing stroke, the thread generating tool is moved clear of the cutout groove by a radial offset. In the subsequent reversing stroke, the thread generating tool can therefore be guided out of the workpiece threaded hole without thread engagement.

An exemplary embodiment of the invention is described below with reference to the accompanying figures.

• 1 in einer Seitenschnittdarstellung ein in einem Kurbelwellenflansch ausgebildete Gewindesackloch-Bohrung;
• 2 und 3 unterschiedliche Ansichten eines Gewindeerzeugungs-Werkzeugs;
• 4 bis 7 jeweils Ansichten, die der in der 1 gezeigten Gewindesackloch-Bohrung in einer Prozessabfolge veranschaulichen.

Show it:

• 1 in a sectional side view, a threaded blind hole formed in a crankshaft flange;
• 2 and 3 different views of a threading tool;
• 4th until 7th each views that of the 1 illustrate tapped blind hole drilling shown in a process sequence.

In the 1 is a crankshaft flange 1 with a threaded blind hole 2 shown of a flange thickness f having. The hole 2 is with its hole bottom 3 up to a target drilling depth t _B in the crankshaft flange 1 incorporated in a process sequence that is later based on the 4th until 7th is explained. The threaded hole 2 has a circumferential thread countersink at its bore opening 7th on, which in the further course down into an internal thread 9 transforms. The internal thread 9 extends along the axis of the bore B. up to a usable target thread depth t _G . The thread of the internal thread 9 opens into a ring-shaped circumferential free cut groove 13th , whose lower groove flank 14th ( 5c ) directly, ie without an interposed smooth cylindrical pilot hole wall, merges into the bottom of the hole 3, which has a residual bottom thickness d having.

That in the 1 shown internal thread 9 is made using one of the following using the 2 and 3 described threading tool produced. Accordingly, the threading tool in FIG 2 a clamping shaft 15th on which a thread generating body 17th connects. The thread generating body points at the tool tip 17th a hole bottom cutting edge 19th on. This is with a transverse cutting edge 21 formed at right angles to the tool axis of rotation W. runs. On the outer circumference of the thread generating body 17th are a total of three machining teeth, namely one pre-machining tooth 23 , an intermediate tooth 24 and a finishing tooth 25th educated. The teeth 23 , 24 , 25th are in the 3 arranged one behind the other in the tool circumferential direction and positioned approximately at the same height in the axial direction.

As from the 3 As can be seen further, are the three machining teeth 23 , 24 , 25th Grouped in a tool circle sector, that is, not evenly distributed around the circumference, but arranged asymmetrically. With reference to the tool rotation axis W. diametrically opposite to the profiling teeth 23 , 24 , 25th is in the 3 a diameter-reduced outer circumference 27 formed, which moves on a small-diameter circular path when the tool rotates. In contrast, the profiling teeth move 23 , 24 , 25th on a circular path with the size of a diameter 26th . This results in a radial clearance 29 ( 3 ), which is described later in a free travel step F. ( 6th ) is required.

The following is based on the 4th until 7th the process chain for creating the workpiece tapped hole 2 Described: First, a thread-free pilot hole is made in a separate pre-drilling process step with a drilling tool (not shown) 31 ( 4th ) is generated, the bottom of the hole 3 approximately at a target drilling depth t _B lies. Then the thread generating tool is in one thread stroke G coaxial to the bore axis B. into the pilot hole 31 retracted with a threading feed v _f as well as a synchronized thread generation speed n . This is how the internal thread becomes 9 generated. At the end of the thread stroke, the thread generating tool is brought up to the stop with the bottom of the hole 3, where the cutting edge of the bottom of the hole is 19th carries out a material removal. At the same time, a free cut groove is created at the end of the thread stroke, during which the feed v _f and the speed n of the thread generating tool are no longer synchronized with each other. In this way, the attached to the internal thread 9 subsequent circumferential free cut groove 13th generated. The internal thread is up to the free cut groove 19th completely fully formed and usable for a screwing process.

After the free cut groove has been produced, the thread production tool is released in one step F. ( 6th ) by a radial offset Δr from the cutout groove 13th cleared. In this way, in the subsequent reversing stroke R. ( 7th ) the thread generating tool without thread engagement from the workpiece tapped hole 2 be led out. In free travel F. becomes the radial clearance 29 of the threading tool is at least partially used up.

List of reference symbols

1

Crankshaft flange

2

Threaded hole

7th

Thread countersink

9

inner thread

13th

Free cut groove

14th

Groove flank

15th

Clamping shank

17th

Thread generating body

19th

Hole bottom cutting edge

21

Cross cutting edge

23, 24, 25

Thread profiling tooth

26th

Circular path

27

diameter-reduced outer circumference

29

Radial clearance

31

Pilot hole

B.

Hole axis

W.

Tool rotation axis

tG

Target thread depth

tB

Target drilling depth

d

Remaining floor thickness

vf

Feed

n

rotational speed

G

Thread stroke

R.

Reversing stroke

F.

Free cut step

f

Flange thickness

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• EP 1497067 B1 [0004]
• DE 3810884 C1 [0004]
• EP 3484647 B1 [0004]
• DE 102012105183 A1 [0004]
• DE 3876820 T2 [0004]
• DE 3627798 C2 [0004]

Claims (9)

Method for producing a workpiece threaded hole (2) with a pre-drilling process step in which a thread-free pre-hole (31) is produced with a drilling tool, the hole bottom (3 _{) of which lies at a target drilling depth (t B} ), and with a thread Process step in which a thread generating tool generates an internal thread (9) in the pilot hole (31) in a thread stroke (G) with a thread generation feed rate (vf) and a thread generation speed (n) synchronized with it, characterized in that the thread-generating tool has at least one cutting edge (19) on its tool tip facing the bottom of the hole (3), and that in the threading process step the thread-generating tool can be brought up to the stop with the bottom of the hole (3), so that by means of the bottom of the hole -Cutting edge (19), material is removed from the bottom of the hole (3). Procedure according to Claim 1 , characterized in that in the threading process step the thread generating tool entering the pilot bore (31) is coaxial with its axis of rotation (W) to the bore axis (B), and / or that in particular the bore base cutting edge (19) has a transverse cutting edge (21) which preferably runs at right angles to the tool axis of rotation (W) and which can be brought into chip engagement with the bottom of the hole (3) of the pilot hole (31). Procedure according to Claim 2 , characterized in that the thread-generating tool has at least one thread-profiling tooth (23, 24, 25), the radially outer tooth tip of which moves on a circular path (26) of large diameter when the tool rotates, and that the thread-profiling tooth (23 , 24, 25) of the thread-generating tool with respect to the tool rotation axis (W) is diametrically opposite to an outer circumference (27) of reduced diameter which, when the tool is rotated around a radial clearance (29) within the circular path (26 ) lies. Method according to one of the Claims 1 , 2 or 3 , characterized in that in the thread stroke (G) the thread generating tool is retracted into the pilot hole (31) while generating the internal thread (9), and in particular at the end of the thread stroke a free cut groove is generated, during which the feed (vf) and the speed (n) of the thread generating tool are no longer synchronized with one another, so that a circumferential free cut groove (13) adjoining the internal thread (9) is generated without thread pitch. Procedure according to Claim 4 , characterized in that during the free cut groove generation, the hole base cutting edge (19) is in chip engagement with the hole base (3), and that in particular a groove flank (14) of the free cut groove (13) merges directly into the hole base (3), and / or that the free cut groove (13) is positioned directly between the internal thread end and the bottom of the bore (3). Procedure according to Claim 4 or 5 , characterized in that a reversing stroke (R) takes place after the free cut groove is generated, and that in preparation for the reversing stroke (R) the thread generating tool is moved away from the free cut groove (13) by a radial offset (Δr), so that in the reversing stroke ( R) the thread generating tool can be guided out of the workpiece threaded bore (2) without thread engagement, and that in particular the radial clearance (29) of the thread generating tool is at least partially used up when moving free in the radial direction. Procedure according to Claim 4 , characterized in that at the end of the thread stroke the thread generating tool is moved away from the internal thread (9) by a radial offset (Δr) without generating a free cut groove, so that a thread run-out is formed at the internal thread end, the thread profile height of which extends in the direction of the Bore bottom (3) reduced. Thread generating tool for a method for generating a workpiece threaded hole (2) according to one of the preceding claims. Workpiece threaded bore, in particular in a crankshaft flange (1), which is produced in a method according to one of the preceding claims.

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