EP3259098B1 - Honing method and processing machine for form honing - Google Patents

Description

The invention relates to a honing method for machining the inner surface of a bore in a workpiece using at least one honing operation according to the preamble of claim 1, and to a machine tool configured to carry out the honing method according to the preamble of claim 14. A preferred area of application is the honing of cylinder running surfaces in the Manufacture of cylinder blocks or cylinder liners for reciprocating engines.

The cylinder running surfaces in cylinder blocks (cylinder crankcases) or cylinder liners of internal combustion engines or other reciprocating machines are exposed to strong tribological stress during operation. Therefore, when manufacturing cylinder blocks or cylinder liners, it is important to machine these cylinder running surfaces in such a way that later, under all operating conditions, sufficient lubrication is ensured by a film of lubricant and the frictional resistance between parts that move relative to one another is kept as low as possible.

The quality-determining finishing of such tribologically stressable inner surfaces is usually carried out with suitable honing processes, which typically include several consecutive honing operations. Honing is a machining process with geometrically undefined cutting edges. In a honing operation, an expandable honing tool is moved back and forth within the bore to be machined to generate a stroke movement in the axial direction of the bore at a stroke frequency and at the same time rotated at a predeterminable speed to generate a rotary movement superimposed on the stroke movement. To widen the honing tool, the cutting material bodies attached to the honing tool are fed via a feed system with a feed force and/or feed speed acting radially to the tool axis and pressed against the inner surface to be machined. During honing, a cross-hatch pattern typical of honing occurs on the inner surface with crossing traces of processing, which are also referred to as "honing marks".

With increasing demands on the economy and environmental friendliness of engines, the optimization of the tribological system of pistons/piston rings/cylinder running surface is of particular importance in order to achieve low friction, low wear and low oil consumption.

The friction component of the piston group can be as high as 35%, so a reduction in friction in this area is desirable.

A technology that is becoming more and more important for reducing friction and wear is the avoidance or reduction of cylinder distortions or deformations of the engine block (cylinder crankcase) during assembly and/or during operation. After conventional honing, a cylinder bore should typically have a bore shape that deviates as little as possible, e.g. a maximum of a few micrometers, from an ideal circular cylinder shape. However, during the assembly and/or operation of the motor, significant form defects (distortions) can occur, which can amount to several hundredths of a millimeter and reduce the performance of the motor. The causes of delays or deformations are different. These can be static or quasi-static thermal and/or mechanical loads or dynamic loads. The construction and design of cylinder blocks also have an impact on the tendency to deform. The sealing function of the piston ring pack is typically impaired by such hard-to-control deformations, which can increase blow-by, oil consumption and friction.

The so-called form honing, also referred to as free-form honing, is a technology which is intended to ensure or approximate the creation of an ideal form after assembly or in the operating state of the engine by inverting the cylinder distortions (creating a negative form of the error) during processing. Honing is used to create a bore shape that deviates from the circular-cylindrical shape on the unclamped workpiece. Borehole shapes of this type are generally asymmetrical in the axial direction and/or in the circumferential direction, because the deformations of the cylinder block are also generally not symmetrical. In the operating state, the ideal circular cylinder shape should result so that the piston ring pack can seal well over the entire circumference of the bore.

Various variants of form honing, which make it possible to produce non-rotationally symmetrical bore shapes with a systematic deviation from a 2-fold rotational symmetry, are described in the EP 1 790 435 B1 described.

In the WO 2014/146919 A1 a honing method for form honing is described in which a bottle-shaped bore that is rotationally symmetrical with respect to the bore axis is produced, which is narrower in the vicinity of the bore entry than further away from the bore entry. In a variant of the method, a honing tool with axially relatively long honing stones is used. To generate an axially varying material removal in a stroke change phase Stroke length and / or the stroke position of the lifting movement changed. As a result, an axial contour can be generated or changed. The application also describes honing tools that have at least one ring-shaped cutting group with cutting material bodies that are designed as honing segments that are wide in the circumferential direction and narrow in the axial direction. When using such honing tools, bore shapes with axial contours can be machined particularly precisely and economically.

TASK AND SOLUTION

It is an object of the invention to provide a honing method of the type mentioned at the outset that allows bores that are to have an axial contour in the finished state to produce the desired contour over the entire relevant bore length with sufficient precision. Another object is to provide a machine tool configured to perform the honing process.

This object is achieved by a honing method having the features of claim 1. The object is also achieved by a processing machine having the features of claim 14. Advantageous developments are specified in the dependent claims. The wording of all claims is incorporated into the description by reference.

Extensive honing tests (contour honing) with different cutting tool specifications, cutting tool dimensions, cutting tool arrangements (number of segments/bars) as well as ring tool designs and conventional tools (with relatively long honing bars with lengths in the range of approx. 1/3 to 2/3 of the bore length)) have shown that geometric deviations from the target shape can occur in the area of the bore section with the relatively largest diameter. For this purpose, the course of the torque as a function of the stroke length and stroke displacement, the spindle speed and the expansion speed was documented. A tendency was found that the spindle torque can drop significantly when the stroke length is shortened during contour generation. This indicates that the cutting conditions in the contact zone between the body of the cutting material and the inner wall of the bore can change so significantly (reduction in tool stabilization in the process) that material removal is no longer achieved to the intended extent and/or the shape, especially in the end area of the bore far from the entrance, is unfavorable shows deviations.

If the torque transmitted via the spindle to the honing tool is controlled in such a way that the torque during the stroke change phase is essentially remains constant, such shape deviations can be avoided or reduced to non-critical values. In particular, a relatively constant torque can be achieved over the entire bore length to be honed. This results in more consistent cutting forces throughout the honing process. Free cutting of the honing tool can be prevented.

The desired "constancy" of the torque cannot be understood mathematically exactly. Slight fluctuations in torque over time and/or over stroke position within a relatively narrow torque window around a torque setpoint are permissible. For the purposes of this application, a torque is considered to be "substantially constant" when a deviation of the torque averaged over a stroke from a torque setpoint is less than 15%, in particular less than 10% or less than 5%.

For this purpose, the processing machine or its control device can comprise a device for setting a torque setpoint and a torque window around the torque setpoint. For example, the torque limits (lower and upper limit of the torque permissible for the process or minimum and maximum torque) can be entered into the controller using two separate parameters. It would also be possible to enter a torque setpoint and a window width as parameters.

There are different ways to keep the torque essentially constant during machining.

In some embodiments, in order to control the torque in at least one speed change phase, a change in the speed of the honing tool that is dependent on the stroke length is generated in such a way that the speed is reduced when the stroke length is reduced. The honing operation is therefore carried out at least in phases with a variable speed. This variant can also be referred to as form honing with process-integrated speed control. If the speed is reduced in line with the decreasing stroke length, relatively uniform engagement conditions between the body of cutting material and the inner wall of the bore can be maintained, so that the desired axially varying material removal can be achieved.

The speed can be changed as a function of the stroke according to a predetermined speed change function. If for the honing process the desired change in stroke has been defined via the honing operation, the adapted speed curve or the corresponding Speed change function entered by the operator before the honing operation and then carried out automatically by the processing machine by means of a feed-forward control. For example, if the stroke length is continuously reduced in equal steps during a stroke change phase, the speed can also be reduced continuously or in steps. More complicated relationships between stroke length and speed can also be preset if required.

It is possible to store empirically or theoretically certain relationships between stroke length and speed for certain combinations of tool types and workpiece types in a memory of the control device in the form of suitable data sets and to access this data when programming the control for a honing process.

In many cases it has turned out to be particularly advantageous if a change in the speed is also controlled as a function of the stroke length. Among other things, it has been shown that with an increasingly reduced stroke length, a significant drop in torque can be observed. It can therefore make sense, with a gradually decreasing stroke length, to lower the speed at least if the stroke length corresponds to less than 150%, in particular less than 100%, of the axial length of the cutting material body. A corresponding module of the control program can map this relationship, if necessary on the basis of component-specific preliminary tests.

In some embodiments, the torque of a spindle drive provided for rotating the spindle is regulated. A feedback path is set up for this regulation, in which the variable (torque) to be influenced is recorded directly or indirectly and the honing operation is controlled based on the values of the recording in such a way that the torque remains essentially constant or is within a definable, relatively narrow range torque window holds.

In some variants, the torque is regulated in that the torque signal representing the current torque of the spindle drive is detected on the spindle drive and compared with a setpoint value of the setpoint signal representing the torque to determine a setpoint deviation, and the control of the torque of the spindle drive in Dependence on the setpoint deviation takes place. The torque signal can be generated, for example, via the electrical power consumption of a servo drive or another electrical drive. Force measurements on or in the honing tool are also possible.

In some embodiments, it is provided that a target profile of the target value of the torque is specified for a honing operation and a speed of the spindle is controlled in accordance with the target profile. As a result, relatively even cutting forces can be achieved throughout the entire honing process. For example, a target torque window can be defined by specifying a minimum and a maximum permissible torque. If there are deviations in the torque recorded during the honing phase, the speed can then be increased or reduced in such a way that the torque remains within the specified torque window. In particular, the speed can be reduced when the target torque is not reached and the speed can be increased when the target torque is exceeded. The speed can vary between programmable minimum values and maximum values for the speed.

A further possibility to influence the honing result lies in a targeted control of the displacement of the stroke. In some embodiments it is provided that to change the stroke length and/or the stroke position during the stroke change phase, a position of an upper reversal point and/or a position of a lower reversal point of a stroke movement is changed according to a presetting. In this way, the stroke length, i.e. the axial length between the upper and lower reversal point, can be varied. In particular, it can be the case that both the position of the upper reversal point and the position of the lower reversal point are changed between successive strokes at least over one phase. This may result in an improvement in the constancy of the torque compared to a variant in which, for example, only the upper reversal point is changed. In particular, it can be the case that cutting free of the honing tool in the bore end region far from the entry point is reduced and/or minimized in comparison to other method procedures.

Particularly in the case of an axial contour that has a non-linear change in shape or a non-linear surface line in the non-cylindrical area, such as a trumpet-shaped or bell-shaped bore, this shape variant can be produced or introduced by a stroke-dependent, variable infeed.

This can be done in particular in such a way that an infeed force and/or an infeed speed of cutting material bodies of the honing tool are controlled as a function of the stroke position of the honing tool. In this way, variable force/displacement control can be used or contribute to contour design. For example, a trumpet shape or a bell shape or bottle shape or a cone shape of a bore can be produced particularly well with this variant. Generating the desired contour using only Stroke displacement may not be sufficient in such cases. If, on the other hand, the infeed force or the infeed speed is varied as a function of the stroke position, ideally both in the downstroke and in the upstroke, even more complex bore shapes can be easily produced. The variable force/path control can be combined with stroke displacement. In order to produce special shapes, such as a trumpet shape, it can be useful if several lifting positions with different expansion forces can be programmed or specified. For example, it is possible to create a trumpet shape by using smaller distances between the stroke positions (number and position preferably freely selectable) and constant force/displacement control.

The honing process can be carried out with differently designed honing tools. An expandable honing tool is preferably used during machining, which has an expandable, ring-shaped cutting group with a plurality of cutting material bodies distributed around the circumference of the tool body in an end region of a tool body remote from the spindle, with an axial length of the cutting material body being smaller than the effective outer diameter of the ring-shaped cutting group when completely withdrawn cutting material bodies. Such a honing tool is also referred to as a "ring tool" in the context of this application. Examples of suitable honing tools with one or two ring-shaped cutting groups and with a single widening or double widening are in WO 2014/146919 A1 specified. The revelation of the WO 2014/146919 A1 is made to this extent by reference to the content of this description. Alternatively, for example, piezoelectrically controlled honing tools can also be used.

The invention also relates to a processing machine configured to carry out the honing process. This can be a specialized honing machine or another machine tool that offers the functionalities required here.

BRIEF DESCRIPTION OF THE DRAWINGS

• Fig. 1 schematisch die Vorderansicht einer Honmaschine, die zur Durchführung verschiedener Varianten des Honverfahrens genutzt werden kann;
• Fig. 2 in Fig. 2A einen Längsschnitt und in Fig. 2B eine axiale Ansicht eines Honwerkzeugs, das zur Durchführung verschiedener Varianten des Honverfahrens genutzt werden kann;
• Fig. 3 einen schematischen Längsschnitt durch ein Ausführungsbeispiel einer zylindrischkonischen Bohrung mit axialem Konturverlauf;
• Fig. 4 ein Diagramm, in welchem für eine Referenz-Honoperation die Hubposition des Honwerkzeugs, die Drehzahl der Spindel und das Drehmoment des Spindelantriebs aufgetragen sind;
• Fig. 5 ein Messdiagramm einer gehonten Bohrung mit Formabweichungen am breiten Bohrungsende;
• Fig. 6 ein Diagramm einer Verfahrensvariante mit einer linearen Drehzahlreduzierung während der Hubveränderungsphase;
• Fig. 7 ein Diagramm einer Verfahrensvariante, bei der das Drehmoment die Drehzahl regelt; und
• Fig. 8 ein Diagramm einer Verfahrensvariante mit einer unabhängigen Hubverlagerung am oberen Umsteuerpunkt und am unteren Umsteuerpunkt.

Further advantages and aspects of the invention result from the claims and from the following description of preferred exemplary embodiments of the invention, which are explained below with reference to the figures. show:

• 1 schematically shows the front view of a honing machine that can be used to carry out different variants of the honing process;
• 2 in Figure 2A a longitudinal section and in Figure 2B an axial view of a honing tool that can be used to carry out different variants of the honing process;
• 3 a schematic longitudinal section through an embodiment of a cylindrically conical bore with an axial contour;
• 4 a diagram in which the stroke position of the honing tool, the speed of the spindle and the torque of the spindle drive are plotted for a reference honing operation;
• figure 5 a measurement diagram of a honed hole with shape deviations at the wide end of the hole;
• 6 a diagram of a method variant with a linear speed reduction during the stroke change phase;
• 7 a diagram of a method variant in which the torque controls the speed; and
• 8 a diagram of a variant of the method with an independent stroke displacement at the upper reversal point and at the lower reversal point.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

In 1 is a schematic front view of a honing machine 100, which can be used as a processing machine within the scope of various embodiments of methods according to the invention for processing inner surfaces of bores in workpieces, on the one hand in order to carry out one or more honing operations on the workpiece in a conventional manner and on the other hand also on the same workpiece Carry out embodiments of the invention honing.

A clamping plate 104 is fastened to the machine bed 102 of the honing machine and carries a workpiece 106 clamped thereon, which in the example is an engine block (cylinder crankcase) of a multi-cylinder internal combustion engine. A plurality of cylinder bores are formed in the engine block with their cylinder axes oriented generally vertically. The cylinder running surfaces formed by the inner surfaces of the cylinder bores are subjected to a quality-determining finishing process on the honing machine both the macro-shape of the cylinder running surfaces and their surface topography are produced by suitable honing operations.

In the honing machine 100, two essentially identically constructed honing units 110, 112 are fastened to a portal-like support structure 108, which can be used alternately or simultaneously when machining the workpiece. Its structure is explained in more detail using the honing unit 110 . The honing unit comprises a headstock 114 fastened to the support structure, which guides the honing spindle 116 serving as the tool spindle of the processing machine. The honing spindle can be rotated about its longitudinal axis (spindle axis) with the aid of a spindle drive 118 attached to the headstock. The spindle drive has a servo motor, which can be controlled, among other things, with regard to its speed and the torque generated.

Attached to the lower end of the honing spindle is an articulated rod 120, to the lower, free end of which the honing tool 200 serving as the machining tool is mechanically coupled with limited mobility, e.g. via a bayonet connection. In other embodiments, other solutions are possible. For example, a different type of drive rod, e.g. a flexible rod, can be selected instead of the articulated rod. As an alternative to a mechanical coupling with limited mobility, a rigid coupling of the honing tool is also possible.

A lifting drive 124 mounted on the headstock 114 causes the vertical movement of the honing spindle when the tool is inserted into the workpiece or when it is pulled out of the workpiece and is controlled during the honing process in such a way that the honing tool moves in a vertical direction parallel to the spindle axis within the bore of the workpiece - and performs her movement. Stroke length and stroke position can be set by input.

The honing machine is equipped with an infeed system 140 which comprises two infeed devices which can be actuated independently of one another and which can be assigned to different sets of working elements on the honing tool. A hydraulically actuable second infeed device comprises a hydraulic cylinder in which sits a piston that can be subjected to hydraulic pressure on both sides and that is fastened to one end of a push rod 152 . This can accordingly be moved in a controlled manner parallel to its longitudinal axis in both directions by controlling the hydraulic pressure within the hydraulic cylinder. This widening can also be provided with a servo motor - force-controlled or path-controlled. The solid push rod 152 is disposed within a hollow push rod 162 coaxially therewith and movably relative thereto. The hollow push rod belongs to an electromechanical first delivery system, the drive of which is formed by an electric stepper motor acts through a gear on the outer, hollow push rod 162 to move it up and down parallel to the common axis of the push rods. This widening can also be provided with a servo motor - force-controlled or path-controlled.

The spindle drive 118, the lifting drive 124 and the drives of the infeed system 140 are connected to a control device 180, which is a functional component of the machine control and can be operated via an operating device 190. The following process parameters, among others, can be set via the operating device:
Position of the upper reversal point and the lower reversal point of lifting movements. This means that the stroke length and the stroke position can be defined. Stroke Intervals and Stroke Increments. As a result, time-varying strokes can be programmed. Speed, speed increment, minimum speed and maximum speed of a speed window. Delivery speed, lifting speed. Beginning of a honing phase, beginning of one or more further honing phases. Target torque and torque window and/or minimum and maximum allowable torque during a stroke change phase.

2 shows in 2A a longitudinal section and in 2B an axial view of the honing tool 200. The honing tool 200 has a single cutting group attached to the tool body in a ring shape with cutting material bodies distributed around the circumference of the tool body, which can be advanced or retracted in the radial direction by means of an associated cutting material body infeed device . The cutting material bodies are designed as honing segments, the width of which in the circumferential direction is significantly greater than their length in the axial direction. The bodies of cutting material responsible for removing material from the workpiece are concentrated in an axially relatively narrow zone (a ring of the cutting group) and occupy a relatively large proportion of the circumference of the honing tool. Bore shapes in which bore sections of different diameters adjoin one another in the axial direction can thereby be produced with a relatively high material removal rate. Due to the ring-shaped arrangement of the cutting material bodies, the honing tool is also referred to as a "ring tool" in this application.

The honing tool 200 has a tool body 210 that defines a tool axis 212, which is also the axis of rotation of the honing tool during honing. At the spindle end of the honing tool (in Figure 2A above) there is a coupling structure, not shown in detail, for coupling the honing tool to a drive rod of a honing machine or another processing machine which has a spindle which can be rotated around the spindle axis and oscillating back and forth parallel to the spindle axis.

In the example shown, the honing tool is coupled in an articulated manner to the honing spindle or to an articulated rod in order to permit limited mobility of the honing tool in relation to the honing spindle. For this purpose, a multi-axis joint, e.g. a cardan joint or a ball joint, is formed at the end of the honing tool on the spindle side.

At the non-spindle end of the tool body (in Figure 2A bottom) is the ring-shaped cutting group 220, which has several (in the example three) cutting material bodies 220-1, 220-2, 220-3 evenly distributed over the circumference of the tool body, which are infed radially to the tool axis 212 outwards with the aid of the cutting material body infeed device can be used to press the abrasively acting outer sides of the cutting material body with a defined pressing force or pressing force against the inner surface of a bore to be machined. Each of the three arcuately curved cutting material bodies is designed as a honing segment that is very wide in the circumferential direction but narrow in the axial direction and covers a circumferential angle range of between 90° and 110°. The honing segments are decoupled from the tool body and can be displaced radially relative to the tool axis 212 . The ring formed by the honing segments ends almost flush or flush with the tool body on the side facing away from the spindle. The ring sits entirely within the non-spindle quarters of the tool body at the non-spindle end of the ring tool. The axial length of the cutting material body defines the axial length of the cutting area here.

The axial length LHS of the honing segments is less than 35%, in particular less than 15% of the bore length. The honing segments are approx. 5 mm to 90 mm, in particular approx. 10 mm to 70 mm high (in the axial direction), which in the example is between 5% and 50%, in particular between 10% and 20% or 30% of the effective outer diameter of the cutting group (with fully retracted tool bodies). The axial length LHS corresponds here at the same time to the axial length of the entire cutting area of the honing tool.

Each body of cutting material is fastened by brazing to an outer side of an associated steel support strip 224-1, 224-2. Alternatively, the cutting material body can also be attached by gluing or by means of screws, which makes it easier to replace. In the example, each support bar carries only one cutting material body designed like a segment of a circle. Several individual cutting strips can also be attached to a support strip. Each support strip has an inclined surface on its inside which interacts with a conical outer surface of an axially displaceable, tubular or internally hollow infeed cone 232 in such a way that the support strips with the cutting material bodies carried by them are infed radially outwards when the infeed cone is moved by means of a machine-side Advance device against the force of (not shown) return springs in the direction of the end facing away from the spindle of the ring tool is pressed. With the opposite infeed movement, the support rails with the honing segments are brought back radially inward with the aid of circulating return springs. As a result, the radial position of the cutting material body is controlled without play via the axial position of the infeed cone 232 .

Exemplary embodiments of honing methods are described below, which can be used within the scope of embodiments of the invention in order to produce rotationally symmetrical bores with an axial contour profile.

3 shows a schematic longitudinal section through an embodiment of such a bore 310 in a workpiece 300 in the form of an engine block (cylinder crankcase) for an internal combustion engine. The target shape of the bore is rotationally symmetrical with respect to its bore axis 312 and extends over a bore length L from a bore inlet 314 facing the cylinder head in the installed state to the bore outlet 316 at the opposite end. The bore can be divided into several adjacent sections with different functions, which merge smoothly, ie without the formation of steps or edges.

A first bore portion 320 at the upstream end has a first diameter D1 and a first length L1. The first diameter is present over the entire first length L1, so that the first bore section has a circular-cylindrical shape. The first bore section transitions steplessly into an axially narrow transition section 325 with a transition radius R1 into a second bore section 330, which extends from the transition section to the outlet-side end of the bore. The second bore portion 330 is generally conical or frusto-conical in shape and extends a second length L2. The second bore portion has an inner diameter (second diameter) D2 throughout that is greater than the first diameter D1, with the second diameter increasing linearly continuously from the transition portion (approximately of the first diameter) toward the end of the bore. The cone angle α (angle between the bore axis and a surface line of the second bore section running in an axial plane) can be, for example, in the range of less than 5°, also less than 1°, possibly also 0.2° or less.

The first length L1 can be between 10% and 60% of the bore length L, for example. The second length L2 is typically greater than the first length and is often between 30% and 80% of the bore length L. The transition section is very short compared to the adjacent bore sections. Deviations from these geometric conditions are also possible.

The difference in diameter between the first diameter D1 and the second diameter D2 in parts further away from the inlet is well outside the tolerances typical of honing, which for a cylindrical shape are on the order of a maximum of 10 μm (based on the diameter). With an absolute value of the internal diameter of the order of magnitude between 50 mm and 500 mm (the latter e.g. in ship engines), the maximum difference in diameter can be between 20 µm and 500 µm, for example.

The lengths of the outer bore sections and the radius of the transition section can be optimized in such a way that low blow-by, low oil consumption and low wear of the piston rings result in typical engine operating conditions.

The shape of the bore means that the bore is comparatively narrow in the region near the inlet, so that the piston rings of the piston running in the bore are pressed against the inner surface 318 of the bore under high ring stress. As a result, a reliable seal is achieved where combustion mainly occurs and high pressures occur, and the oil film is scraped off on the downstroke. The piston, which is accelerated by the combustion, then moves in the direction of the bore outlet, with the piston rings first passing through the transition section and then through the conical second bore section with the continuously expanding inner diameter. From the transition section, the piston rings can gradually relax, with the seal remaining adequate because the pressure difference across the piston rings decreases. At the end of the second bore section remote from the entry, the ring pack reaches its lowest stress. Then, on the upstroke, the ring tension gradually increases again until the piston rings reach the transition section and traverse it towards the first bore section. Furthermore, it is taken into account that an expansion of the cylinder liner caused by thermal influences is greater in the upper, cylindrical part of the bore than in the conical area. In the fired state, this results in a largely cylindrical or significantly less conical bore shape than in the cold state.

An extensive series of honing tests with different cutting tool specifications, cutting tool dimensions, cutting tool arrangements and tool types (e.g. ring tool designs and conventional honing tools with relatively long honing stones) were carried out in order to develop optimized honing strategies to achieve a desired bore shape with an axial contour. Process variants in which the stroke length and/or the stroke position of the stroke movement are changed according to a specific scheme in order to produce an axially varying removal of material in a stroke change phase are promising. The term "hub position" refers to the position of the hub to a machine-fixed (or in the case of a clamped workpiece also fixed to the workpiece) coordinate system. All of the honing operations documented here are based on a circular-cylindrical bore shape that was previously produced, for example, by long-stroke honing with relatively long honing stones.

During the tests, the course of the torque of the spindle drive as a function of the stroke length of the stroke movement and its displacement, the speed and the expansion speed was recorded using a system for diagnosing machine parameters, and the results were evaluated.

4 shows an example of a diagram resulting from this, in which the honing time t _H (in seconds) of a honing operation is plotted on the x-axis and the stroke position HP of the honing tool, the speed DZ of the spindle and the torque DM of the spindle are plotted together on the y-axis or the spindle drive are applied.

In the reference honing operation (REF) shown, the speed DZ was ramped up to a target value in a start-up phase and then remained constant throughout the entire honing operation. The stroke control was adjusted in such a way that in an initial first honing phase PH1 the stroke length was so great that the honing tool machined the entire bore length, i.e. both the first bore section and the second bore section, using the ring-shaped cutting group using two complete double strokes. A subsequent second honing phase PH2 was programmed as a stroke change phase, in which the stroke position of the honing tool changes from stroke to stroke. The term "stroke position" refers to the area between the upper reversal point UO of a stroke movement (near the bore entry) and the lower reversal point UU of the stroke movement closer to the end of the bore far from the entry, based on a machine-based coordinate system. Each shift of a reversal point thus also changes the stroke position. In the example of 4 the lower reversal point UU was kept constant, while the upper reversal point UO was changed incrementally (adjustable stroke increment) by the controller in the direction of the lower reversal point, so that the stroke length was gradually reduced from stroke to stroke. In this way, the section farther from the entry is processed with more strokes than the section near the entry. During the reference honing operation, a constant expansion, i.e. a constant feed rate, was used.

The torque DM averaged over the stroke fluctuated only relatively slightly within a narrow torque window (in the example between approx. 60% and approx. 70% of a reference value) over more than 2/3 of the second honing phase HP2, which was run with a variable lift.

In this case, the reference value 100% corresponds to the nominal torque of the spindle drive. This fluctuation by a maximum of 15 percentage points or by ±5% to 7.5% around the mean value of 65% is within the scope of what is referred to as “substantially constant” in the context of this application. In the last section of the second honing phase, however, a significant drop in torque to a range well below the specified torque range was discernible (see arrow). In general, it could be stated that the spindle torque decreases as the stroke length is reduced during contour generation. Especially in the last phase, when the stroke length corresponds approximately to the axial length of the cutting material body or even falls below it, a significant drop in torque can be seen. The result of this is that the cutting material bodies can cut free in this area, and under certain circumstances undesirable deviations in shape can occur in the lower area of the conical section of the bore.

figure 5 shows an example of a measurement diagram of a bore honed in this way (bore length approx. 100 - 150 mm) with a target geometry 3 . In the area facing away from the inlet, i.e. in the area of the largest diameter of the conical second bore section, a shape abnormality FA can be seen, which extends to a length of about 10 mm to 15 mm and is attributed to the mentioned effects of free cutting and the reduction in tool stabilization.

Significant improvements in terms of the resulting bore shape were achieved with a process in which, in the stroke change phase (second honing phase PH2), the speed of the spindle motor (spindle drive 118) linearly from a starting speed DZ1 at the beginning of the second honing phase to a final speed DZ2 simultaneously with the gradual reduction of the stroke length was reduced at the end of the second honing phase (cf. 6 ). The stroke length was related in the same way as with the 4 explained reference honing operation is incrementally reduced within the second honing phase PH2 with the lower dead center held constant. It can be seen that a substantially constant spindle torque DM can be achieved by a constant speed reduction. Undesirable free cutting of the honing tool is prevented over the entire length of the bore, especially in the critical phase discussed above towards the end of the honing operation, in which the area far from the entrance is machined with relatively small strokes. The speed can be changed incrementally from stroke to stroke. The speed increment DZI can be calculated or specified according to DZI=(DZ1−DZ2)/HI from the ratio between the difference between the starting speed DZ1 and the final speed DZ2 divided by the stroke intervals HI. Exactly as with the reference honing operation, constant expansion, i.e. constant infeed speed, is also used here.

Another way of optimizing the honing operation can be achieved through in-process torque control. The processing machine was set up in such a way that the spindle speed could be controlled by a freely programmable target torque over the entire bore length to be honed. A corresponding diagram for the time dependence of the stroke position HP, the speed DZ and the average spindle torque DM is in 7 shown. The control system is programmed in such a way that if the torque changes as a result of the process, the speed is automatically changed so that the torque controls the speed. If the actual torque falls below a lower limit of a torque window DMF, the speed DZ is also reduced, so that the actual speed is less than the setpoint speed. Conversely, the actual speed is raised above the value of the setpoint speed when the current actual torque exceeds the setpoint torque by more than a permissible amount and migrates upwards out of the torque window DMF. In this way too, undesired free cutting of the tool over the entire length of the bore can be prevented. This control then has the effect that in phases without a change in torque, the speed also remains constant, while if the torque drops too much, the speed is also reduced and if the torque increases too much, the speed is increased. As a result, the torque remains “essentially constant” since it remains within the permitted torque window DMF (apart from the short time intervals before the control intervention).

A further possibility for positively influencing a form honing operation for generating an axial contour progression consists in allowing or specifying an independent stroke displacement at the upper reversal point UO and at the lower reversal point UU. For example, the axial position of the bottom dead center could remain constant over the entire stroke change phase (second honing phase PH2), while the top dead center incrementally approaches the bottom dead center, so that the stroke length is reduced from stroke to stroke while the position of the bottom dead center remains unchanged (e.g. similar as in the procedure in 6 or 7 ). This can be sufficient in many cases.

Additional degrees of freedom result from a variant of the method in which both the position of the upper reversal point UO and the position of the lower reversal point UU are changed in a targeted manner as a function of time or as a function of the stroke. In the example honing operation off 8 the honing operation begins with a first honing phase PH1, in which, as in the other examples, the honing tool machines the entire length of the bore with a correspondingly large stroke. Then a switch is made to the second honing phase PH2. During the second honing phase, the upper reversal point UO is shifted incrementally from stroke to stroke in the direction of the end remote from the bore. The lower reversal point UU is immediately after the end of the first honing phase PH1 is raised above its desired value at the end of the second honing phase (horizontal dashed line) so that the stroke length is shorter than in a comparable case without changing the bottom dead center position. Then the position of the bottom dead center is lowered incrementally from stroke to stroke until the bottom dead center reaches its desired position at the end of the second honing phase. The lower stroke position can, for example, be lowered by approx. 0.1 mm/stroke increment. It has been shown that in some cases the course of the torque can be improved as a result of better consistency compared to an unchanged lower reversal point.

In many cases, the macro-shape of the hole and the microstructure of the inner surface of the hole after the stroke modification phase are so good within the given specification that the honing can be completed with the stroke modification phase and the workpiece is then finished. In this case, the stroke change phase can be the last phase of the honing process. However, it is also possible to add at least one additional honing phase with specific honing parameters.

For example, there may be cases in which the form honing to be produced is not smooth or fine honing. In these cases, a honing angle to be generated is usually defined for the finished bore, e.g. a honing angle in the range of 40° to 60° with conventional plateau honing. Due to the stroke displacement during contour generation, it is possible that honing angles other than the desired ones arise in this area, e.g. honing angles of less than 15°. In some cases, this can no longer be corrected in the subsequent honing operation. It is also possible that a "stepped profile" is created on the inner surface of the bore when the contour is generated by the displacement of the stroke. In the event of unfavorable cutting behavior in the subsequent honing phases, this may no longer be sufficiently equalized. It is also possible that there is no specific way of rounding the transition from the cylindrical to the conical bore area. Furthermore, it can happen that it is difficult to achieve consistently good form and roundness values in local problem areas of individual components. For example, there may be sections of weak cylinder barrel attachment where it may be difficult to achieve the required roundness.

In such cases in particular, an additional further honing phase (third honing phase) with a freely selectable stroke position, stroke speed, speed, expansion force, expansion speed and operating mode (expansion: force/displacement) can be provided.

For example, the honing parameters can be set in such a way that after the contour has been created, practically any honing angle can be created. Another set of honing parameters can be set in order to equalize any "step profile" that may exist after the contour has been created and/or to "round off" transitions. Alternatively or additionally, a third honing phase can be programmed as position-related sparking out in order to positively influence the roundness in local problem areas of individual components (e.g. weak cylinder tube connection). It has been shown that process-reliable roundness values can also be achieved on unstable connected cylinder tubes.

Claims (15)

1. Honing method for machining the internal face (318) of a bore in a workpiece (106) with the aid of at least one honing operation, in particular for honing cylinder running faces in the production of cylinder blocks or cylinder liners for reciprocating piston engines, wherein

   during a honing operation a flaring-capable honing tool (200) that is coupled to a spindle (116) is moved back and forth within the bore for generating a reciprocating movement in the axial direction of the bore, and is simultaneously rotated for generating a rotating movement superimposed to the reciprocating movement with a torque transmitted by way of the spindle (116),

   a bore shape having an axial contour profile, which is rotationally symmetrical in relation to a bore axis (312) and deviates from the circular cylindrical shape, is generated, and for generating an axially variable material removal in at least one stroke modification phase (PH2) a stroke length and/or a stroke orientation of the reciprocating movement is modified,

   characterized by

   controlling the torque (DM) transmitted by way of the spindle (116) to the honing tool (200) in such a manner that the torque remains substantially constant during the stroke modification phase such that a deviation of the torque, averaged across a stroke, from a torque nominal value is less than 15%.
2. Honing method according to claim 1, characterized in that for controlling the torque (DM) in at least one rotating speed modification phase a variation of the rotating speed (DZ) of the honing tool (200) is generated as a function of the stroke length in such a manner that the rotating speed is reduced upon reducing of the stroke length.
3. Honing method according to claim 2, characterized in that the variation of the rotating speed (DZ) is made according to a predefined rotating speed variation function.
4. Honing method according to any of claims 2 or 3, characterized in that a variation of the rotating speed (DZ) is controlled as a function of the stroke length in such a manner that the rotating speed is reduced in any case when the stroke length corresponds to less than 150%, in particular less than 100%, of the axial length of cutting material members (220-1, 220-2, 220-3) of the honing tool.
5. Honing method according to any of the preceding claims, characterized in that empirically or theoretically determined interrelations between stroke length and rotating speed for certain combinations of tool and workpiece types are recorded in a memory of a controller device (180) of a processing machine (100) in the form of appropriate data sets and said data are accessed during programming of the controller for a honing process.
6. Honing method according to any of the preceding claims, characterized by regulation of the torque (DM) of a spindle drive (118) provided for rotating the spindle.
7. Honing method according to claim 6, characterized in that, on the spindle drive (118), a torque signal representing the current torque of the spindle drive is detected and compared to a nominal value signal representing a nominal value of the torque for evaluation of a nominal value deviation and controlling the torque of the spindle drive is made as a function of the nominal value deviation.
8. Honing method according to any of the preceding claims, characterized in that a nominal contour profile of the nominal value of the torque for a honing operation is predefined and a rotating speed is controlled according to the nominal contour profile.
9. Honing method according to any of the preceding claims, characterized in that for variation of the stroke length and/or the stroke orientation during the stroke modification phase (PH2) a position of an upper reversal point (UO) and/or a position of a lower reversal point (UU) of a stroke movement is varied according to a predefined setting.
10. Honing method according to claim 9, characterized in that at least across a phase the position of an upper reversal point (UO) and the position of a lower reversal point (UU) between successive strokes is varied.
11. Honing method according to any of the preceding claims, characterized in that a honing tool (200) is used which has at least one of the following properties:

    (i) on the annular cutting group (220) more than 60% of the circumference are equipped with cutting means, in particular more than 70% or more than 80% of the circumference of the cutting group;

    (ii) the axial length (LHS) of the cutting material members is less than 50% of the effective external diameter of the cutting group, in particular between 10% and 30% of said external diameter;

    (iii) the axial length (LHS) of the cutting material members is in a range from 5 mm to 90 mm;

    (iv) the axial length (LHS) of the cutting material members is less than 35% of the bore length of the bore.
12. Honing method according to claim 11, characterized in that the cutting material members are configured as honing segments (220-1, 220-2, 220-3) that are wide in the circumferential direction and narrow in the axial direction, wherein an axial length (LHS) of the honing segments measured in the axial direction is smaller than the width measured in the circumferential direction.
13. Honing method according to claim 11 or 12, characterized in that the cutting group includes at least three honing segments (220-1, 220-2, 220-3), wherein preferably three, four, five or six honing segments having the same or different circumferential widths are provided.
14. Processing machine (100) for fine machining an internal face of a bore in a workpiece (106) with the aid of at least one honing operation, in particular for honing cylinder running faces in the production of cylinder blocks or cylinder liners for reciprocating piston engines, comprising at least one spindle (116) for moving a honing tool (200) coupled to the spindle within the bore such that, by means of at least one cutting material member (220-1, 220-2, 220-3) attached to the honing tool, machining of the internal face (318) is performed, characterized in that the processing machine is configured to carry out a honing method according to any of claims 1 to 13 on the workpiece.
15. Processing machine according to claim 14, characterized in that a controller device (180) of the processing machine has a device for adjusting a torque nominal value and a torque frame about the torque nominal value.

Images