GB2098901A - Roll forming a workpiece - Google Patents

Abstract

During forming of a workpiece 2 using profiled rolling tools 3, 4, a parameter of the workpiece, e.g. diameter or depth of profiling, is continuously sensed and is used to control the forming. Apparatus for carrying out out such a method comprises a sensing device (9) having a probe (11, 12) for sensing the workpiece (2) and feeding signals to a control system 18 connected to actuating means (20, 21) for controlling the forming operation. The roll force or speed of forming may be controlled by a feedback loop. <IMAGE>

Description

SPECIFICATION Method and apparatus for forming a workpiece This invention relates to a method and apparatus for forming a workpiece, such as gears, shafts, cylindrical surfaces.

In the manufacture of various articles, especially repetitive articles made in substantial quantities, such as gears or shafts, it is well known to make these from a blank by forming and to carry out the forming process as a socalled cold-rolling princess. The blank which, depending on the type of article to be made, may consist of a plastifiable plastics or a ductile metal is placed between at least one tool or die acting on it and an abutment, the tool being loaded by a rolling force until the shaped profile of the tool is progressively reproduced on the blank or article to be made out of it. The tool and, where applicable, the abutment having the same geometry or shaped profile as the tool, is mounted on a guide and is slidable in the direction of the rolling force acting on the workpiece.Due to this slideability of the tool and, where applicable, also of the abutment where constructed as a tool, the shaped profiles formed on these are progressively imparted to the workpiece.

While the shaped profiles being imparted, an amount of material displaced, which corresponds to the rolling force applied, flows up to contact the shaped profile on the tool. The degree of material up-flow is a function of the ductility of the material, of the amount of rolling force applied and of the length of time it acts upon the workpiece, but these factors are not variable during forming as they act on the workpiece.

A known method for forming workpieces such as gears, splined shafts, etc. and suitable apparatus for this method functions in a manner that a workpiece is placed between, and pulled by, a tool and an abutment into a rolling zone where it is formed by at least the one tool being loaded with a rolling force. The workpiece, which is pulled between the forming elements as a blank or as a pre-processed part, is subjected to a greater or lesser degree of rolling depending on the rolling force selected and is preferably rotated about its axis of rotation so that the shaped profiles of the tools can act upon the full surface of the workpiece.On completion of forming, the workpiece, e.g. the finished article, is ejected from the loading zone and, depending on further processing of the article, is delivered as a finished part or segregated as a reject or subjected to additonal processing, e.g. a heat treatment or other operations.

During this method of forming, it is considered a disadvantage, however, that after appropriate setting of the tool relative to the workpiece to be formed, there is no further control of the forming process. Thus, as a result of different dimensions of the blanks, different dimensions may occur on the finished parts, whereby the reject rate is increased and, in particular, additional processing of such workpieces is affected.

An added disadvantage is that such a method cannot always be applied to cold forming of workpieces, because it is greatly dependent on the quality of the batch of blanks to be formed and the specified tolerances for finishing or finish forming, so that even minor irregularities in the batch, because tolerances are not observed, may cause high reject rates. For these reasons, the suitability of such a method for high-volume production is limited, especially where it is important substantially to reduce or even eliminate the amount of additional processing of the workpieces (cf. German Patent Specification 1204615).

An object of the present invention is to provide a method and apparatus whereby the manufacture of workpieces is possible even to close tolerances and preferably without any, or at least without a great amount of, necessary additional processing, and which method permits the use of the same tools for the manufacture of workpieces of different materials while retaining the configuration of one tool geometry.

The invention provides a method of forming a workpiece, wherein a parameter related to the workpiece and the forming operation is sensed continuously during the operation and the magnitude of this measurement with respect to its variation in time controls the rate of variation of various factors of the forming process, especially in respect of material, tool geometry, rolling force application, peripheral force and speed as long as is required to have the geometry to be impressed on the workpiece of at least one tool exerting the rolling force on the workpiece in a predetermined forming cycle reproduced on said workpiece.

The invention further provides apparatus for carrying out the above-described method comprising at least one tool formed with a shaped profile and at least one abutment acting in opposition to that said tool with at least the tool being capable of sliding on a bearing and capable of being loaded with a rolling force for the forming of a workpiece to be inserted between the tool and the abutment and at least the tool being provided with a profile shape to be transferred to the workpiece in the nature of a tool geometry to be impressed on the workpiece and features a sensing device between the abutment and the tool for measuring the flow of the workpiece, the sensing device being provided with a probe permitting measurements on the workpiece at least while it is flowed and which is connected to a control system accepting inputs supplied by signals derived by the probe from indivi dual parameters of the forming process and which is connected to actuating means initiating functions, in particular to provide timed control of the shaping process.

These features offer the possibility of shaping workpieces which not only afford wide application of these discoveries to a wide range of workpieces and types of materials, but also facilitate implementing the method and designing and operating the proposed apparatus according to readily detectable and controllable parameters in regard to the shaping process. Application of these features has shown that, contrary to other teachings, the behaviour of a material while it is being shaped essentially depends on four parameters or factors, namely, the characteristic property of the material of the workpiece to be shaped, on the geometry of the tool used for shaping, on the parameters of the apparatus employed, such as the possible speed, rolling force etc. and on the concept of the apparatus i.e. whether it is the workpiece and/or the tool that is moved.The features described here also permit combinations ofthese parameters in a simple manner each combination resulting in a specific characteristic time dependency which, according to the disclosures of the invention, can be measured in different ways and the output can be used to control the individual parameters, especially those of the apparatus. Such measurements may involve, for instance, the variation in time of the geometry produced on the workpiece and/or the variation in time of the reaction force produced by the rolling force in the material being shaped relative to th geometry of the specific tool forming the material.

The possibility of detecting these individual variations in time and, consequently, parameters of the shaping process permit exact monitoring of the specific shaping operation, enabling the desired optimum geometry of a workpiece to be obtained with different combinations of the individual parameters of the apparatus for every workpiece consisting of the same type of material, depending on whichever is more suitable.These features offer an advantage in that, after a certain combination of the parameters of the apparatus, and possibly also those of the method, have been determined, for instance for a spcific helical geometry of a workpiece and the material sitable fo this, a charcteristic curve results, on the one hand, from the variation in time of the geometry of the workpiece being produced and, on the other hand, from the variation in time of the reaction force of the material being formed relative to the geometry of the tool forming the material which, in a simple manner, permit feedback information on the condition of the workpiece.

If only deviations occur, e.g. in the highvolume production of screws, from the predetermined optimum curves derived as explained above, then it is easy and quick to decide that either the diameter of the premachined stock was outside an acceptable tolerance or that another material was supplied for processing or shaping.

The optimum cycles of the shaping process may be stored either as a whole in a control device, e.g. a microprocessor or parts of the cycles (e.g. minimum/maximum values) may be entered in the apparatus itself, e.g. in its system applying the rolling force, such as the hydraulic system. This stoage of optimum values offers an advantage in that, in the case of a deviation of the curve shape measured during the shaping from the values stored in the control system and/or apparatus, the workpiece will immediately be detected as a reject and as such promptly segregated or no longer processed in the apparatus. in this manner, it is possible to improve the efficiency of the apparatus and to reduce the rate of deficient workpieces in the completed batch.

An embodiment of the invention will now be described with reference to the accbmpanying drawings in which: Figure 1 is a schematic side view of apparatus according to the invention showing between tools, Figure 2 shows elevational and plan views of the apparatus of Fig. 1 showing only the tools and a workpiece therebetween, Figure 3 is a longitudinal centre section through part of a tool and workpiece with shaped profile already imparted thereto, Figure 4 is an enlarged view of a sensing system for use with the apparatus of Fig. 1, Figure 5 is a graph of feed against penetration time for a characteristic cycle of the penetration paths of tools into workpieces of differing types of materials, the materials being denoted C 15; C 25;C 45 and C 60, Figure 6 is a graph of the outer diameter of a workpiece against forming time over the path/time cycle, indicating permissible tolerance bands, Figure 7 is a graph of the rolling force F in N (Newton) against the forming time in seconds, indicating a permissible tolerance value for the force/time cycle, Figure 8 is a graph of the workpiece diameter in mm against the rolling force F in N as well as the forming time in seconds for force/path/time cycles, Figure 9 shows diagrammatically apparatus and process computers with feed forward and feed-back as well as display screen, control console and magnetic tape inputs, and Figure 10 is a graph of force variation P during forming against forming time t for some materials, indicating a force peak.

In Figs. 1 and 2, apparatus 1 for shaping a workpiece 2, typically of ductile metal such as steel, brass or aluminium, essentially comprises two tools 3, 4 with shaped profiles -the so-called tool geometries to be transferred to the workpiece. At least the tool 4 is arranged on a shaft 7, which is slidable in the advancing direction 6 of the tool onto the workpiece 2. The other tool 3, which serves as an abutment or reaction member, may also be mounted on a shaft 8, which is slidable in the direction 6 or which is non-slidable. The workpiece 2 to be formed is placed between the tools 3, 4 and, depending on the forming operation, moves between the tools or is intermittently stopped, at least during the working of the tools on the workpiece.The shaped profiles 5 on the tools 3, 4 may, depending on their geometry, be formed as teeth or as a smooth cylindrical surface, or as combinations of such profiles.

A measuring or sensing system 9 is arranged above the workpiece 2 and, as can be seen from Fig. 4, is an electro-mechanically operating system. This sensing system 9 comprises at least one rod 10 having a sensing plate 11 attached thereto and a sensing pin 1 2 extending from a plate 1 3. The rod or rods 10 and the sensing pin 10 are slidable plunger-fashion in the plate 1 3. The rod or rods 10 together with the sensing plate 11 preferably form a yoke having a yoke beam formed by the sensing plate 11 against which the sensing pin 1 2 bears.Whereas the ends of the rod or rods 10 slide in the plate 1 3 with low friction, preferably in ball bushes 14, the end of the sensing pin 1 2 slides in an inductive displacement transducer 15, also with low friction.

Thus, the path covered by the sensing pin 1 2 as it moves out of the plate 1 3 and as the sensing plate 11 moves into a shaped profile 1 6 of the workpiece 2 provides a measure of the depth of penetration depth and is fed as a signal to the sensing system 9. Such a signal may be derived before the start of the forming operation, during the operation or on completion of the operation, or it may be determined and fed to the measuring system 9 continuously throughout the clamping and/or forming cycle of the workpiece.

Derivation of this signal is effected particularly during the forming of the workpiece 2, in such a way that the sensing plate 11 attached to the rods 10, and preferably ground, extends into the profile shape 1 6 imparted by the tools 3, 4 to the workpiece 2 and senses the penetration depth ofthe shaped profile continuously.

If, in addition to the depth of the profile 16, the steepness 1 7 of the glanks of, for instance, the toothing to be imparted the workpiece 2 is to be determined, it is possible to use a sensing element 11 which is better matched to th profile, e.g. a wedge. Thus, as the penetration depth increases, the particular parameters of the shaped profile to be imparted to the workpiece 2 can also be determined which result from the flowing-up of the material around the specific shaped profile.

These signals, measured preferably continuously on the workpiece 2, are transmitted via the sensing pin 1 2 and the inductive displacement transducer 1 5 to a control system connected downstream. The control system substantially comprises a process computer 18, a controller 1 9 connected downstream thereof and actuators 20, 21 controlling the tools 3, 4.The computer 18, which may have the optimum desired values of a forming operation fed therein beforehand, will determine any differences between these desired values and the actual values found by the measuring system 9 and, via the controller 19, will initiate any necessary corrections which the controller, in turn, will feed in as variations of the parameters to the apparatus 1, e.g. increase or decrease of the rolling force, variation of the speed etc., to the actuators 20, 21 of the tools 3, 4 and to initiate correcting action as and when required. If the signals obtained reveal a serious defiency in the workpiece 2 and, if this cannot be remedied by varying the parameters within pre-determined tolerance spans, the workpiece will be recognized as a reject and, as such, segreated immediately so that further forming operations on it would be discontinued at an early stage.

In order to enable the workpiece 2 to be given a specific geometry for the desired forming operation, the tools 3, 4 shaping the workpiece are also provided with a corresponding geometry which may, for example, take the form of a toothed profile 5, a cylindrical surface or a combination thereof. If a toothed profile 5 is adopted as shown in Fig.

3, the teeth of this profile are provided on the surface of a wheel of the tools 3, 4 mounted on shaft 7, 8. The workpiece 2, which in its blank state 22, may, for instance, be cylindrical, is inserted between the tools 3, 4 and shaped by working, at least one tool, e.g. tool 4, against it. The rolling force acting on one or both tools 3, 4 causes the profile 5 of each tool to be imparted gradually to the workpiece 2, and during this, the material situated around the shaped profile, i.e. the corresponding tooth, is caused to flow so that a valley, e.g. a gap 23 between teeth, and a rise, e.g.

a tooth flank 30W are produced. The tooth flank 30 is formed out of the material displaced from the valley 23, the height of the blank being greater or smaller depending on the depth of the valley. The penetration depth S from S = O to S = S, of the profile 5 of the tools 3, 4 into the workpiece corresponds to the flank height of the individual teeth of the tools and the rolling force with which these are pressed into the workpiece. The finish of the shaped profile 1 6 formed on the workpiece 2 is so good that even after heat treatment of the workpiece 2 for the purpose of hardening and tempering or stress relieving, there is hardly any need for further addi tional finishing.

As to the tools 3, 4 themselves, these are rotatably supported on the machine base 25 and at least the tool 4 is arranged on a bearing system 26 permitting movement in the working direction 6. Analogous to this arrangement of the tools 3, 4, which, preferably, are constructed as roll-forming dies, the tool 3 being arranged fixedly serves as a socalled abutment whereas the other tool 4 is the moving tool. However, in cases where, say, high speed forming is at a premium, both tools 3, 4 would be arranged so as to be slidable in the working direction on the machine base 25 so that, during the forming operation, they would move against each other and, consequently, act in opposition.

The workpiece 2 situated between the tools 3, 4 may be either connected to a separate drive or it may be caused to move solely as a result of the frictional contact with the tools acting thereon. The direction of rotation 27 of the tools 3, 4 in the case of such frictional contact is clockwise so that the workpiece 2 would rotate in an anti-clockwise direction.

The above-described apparatus operates as follows: As stated earlier, the geometry on the workpiece 2 is obtained as a result of either tool 3, 4 penetrating into it and the material of the workpiece flowing up around the shaped profile penetrating into it. This involves the following measurements with respect to the time dependence of the impressing operation which are coincidental with the changing of shape, namely a) the variation with time of the geometry obtained on the workpiece 2, b) the variation with time of the reaction force of the shaped material of the workpiece 2 against the shaping geometry of the tool 3, 4.

In implementing the method according to the relationship a), it has been found that measurement of the time-dependent generation of the geometry of the workpiece 2 in the apparatus 1 outlined above can be achieved in the simplest form by having the ground sensing plate 11 contacting the still unprocessed blank 33 rp hsa orkpiece. As the blank 33 is shaped, its material will flow up on the flanks of the shaped profile of the tool 3, 4 as explained earlier. As a result, the sensing plate 11 will be displaced radially away from the centre M of the workpiece.The sensor pin 1 2 of the inductive displacement transducer 1 5 arranged on and/or contacting the sensing plate 11 will be deflected and the resultant change in voltage of the inductive transducer will provide an analog signal of the displacement S = O to S = S1 of the penetration depth. Converting this analog signal into digital values produces a curve from the feed motion (S) with respect to the material (f) and the dwell time (t) according to the equation s = f (t). Fig. 5 shows such characteristic displacement/time curves for various materials such as C 15; C 25; C 45; C 60 referred to the penetration path S, in mm of the tools 3, 4 into the workpiece or workpieces 2.

The usefulness of these curves is that, to start with, the diameter of the blank 33 rp hsa orkpiece 2 received can be determined. The complete shape of the curve is characteristic of the working geometry of the tools 3, 4, the material processed and the parameters of the apparatus 1 selected. The maximum value of these curves (outside diameter of finished workpiece 2) is equally included as is the initial diameter of the blank 44Z 0 hus one or several, clearly-defined measured actual values are available for the evaluation of the shaping operation for each phase of the cycle, i.e. before shaping, during shaping and after shaping. The associated desired values may be stored either in a micro-processor of the control system 1 8 or entered via minimum/ maximum value circuits in the apparatus 1 itself.

The comparison of the actual value and the desired value at any arbitrary point of the shaping process, i.e. before, during and after same, provides the criterion for the decision within freely selectable tolerances, on passing or rejecting a workpiece.

In implementing the method on the basis of the relationship b) above, it has been found that the variation with time of the reaction force of the material being shaped can be measured via strain in parts of the machine base 25, strain in the tools 3, 4 via load measuring devices in the tool-holders (e.g.

spindles) and the mechanical or hydraulic element 21 producing the rolling force in the machine. The variation with time of the rolling force measured with respect to feed and time, i.e. F = f(t) for a specific geometry of the tool 3, 4, a specific material of the blank 44 and a setting combination of the parameters of the apparatus 2W such as speed, rolling force, etc., is characteristic of the impressing and/or flowing process. Such a characteristic force/ time curve is shown in Fig. 6.

As described earlier under relationship a), a desired time characteristic of the force variation may be stored in a micro-processor or minimum/maximum values may exist or entered into the apparatus 1 and/or mechanical and/or hydraulic elements 21 of the forming machine 25 itself. The comparison of such desired/actual values again in this case would decide on whether the workpiece is passed or rejected.

The representation of these conditions according to relationship b) for the force/time characteristic is given in Fig. 7 which provides a curve of the material flow as a function of the rolling force indicated in terms of N (Newton) and time s (seconds). From this curve it can also be clearly seen that shaping of the workpiece 2 has been effected within a tolerance band (hatched band) whose maximum and minimum values have not been exceeded.

Analogous to what has been stated above, combinations of the conditions accoding to the relationships a) and b) are possible, such as the combination c) of the measurement of the geometry of the workpiece 2/ tools 3, 4 and the variation of the rolling force applied.

For special shaping processes, it can be useful to measure both the independence of the geometry variation of the material being processed and the resulting time characteristic of the reaction force of the material being processed. Fig. 8 shows such curves for s = f (t) and F = f (t) where (S) is the penetration depth with respect to the material (f) and time (t) and (F) is the rolling force also with respect to the material (f) and time (t).

In such a case, too, the desired curve characteristic s = f (t) and F = f (t) may be incorporated as a whole or as minimum/maximum values in a micro-processor or in simple minimum/maximum circuits in the apparatus 1 itself.

Again, this comparison of desired and actual values provides the decision on the quality of the workpiece 2 and, consequently, on whether the workpiece is passed or rejected.

Analogous to the information provided by the observed curves and/or the criteria provided by S = f (t) and F = f (t) leading to the decision as to whether the workpiece is passed or rejected, further criteria for decisions can be derived from the curves. For instance, information can be obtained on such aspects as:: d) what are the optimum setting data of the machine and/or apparatus 1, e.g. in respect of rolling force or speed for a specific shaping process, i.e. a geometry of the tools 3, 4 or material of the blank 22? e) how should the rolling force and speed of the tools 3, 4 be controlled during shaping in order to prevent load peaks arising in the apparatus 1? In answering the questions raised under d) it has been found that, according to the aforedescribed system of the masurement on workpiece 2 and the measurement of various geometries and materials there is also a large number of curves s = f (t) and F = f (t) for differing combinations of the parameters, specifically of appratus 1, so that it can be deduced from a comparison of these curve shapes which curve and/or which parameters represents the optimum setting data for the specific shaping of a workpiece.If the shaping is carried out, for instance, with a controllable forming machine or apparatus 1, e.g. according to Fig. 1, in conjunction with a process computer 18, then this computer can detect and measure the various curve plots s = f (t) and F = f (t) and compare them with stored curve plots, such as magnetic tapes 28, 29 or with curve shapes computed from the measurements themselves. In simplified terms, it may be stated that, in the case of such a machine/computer combination, for instance, a learning process will take place from test run to test run and, eventually, the optimum setting of the individual parameters will result, such as for the combination of apparatus 1 and the timing of the forming operation.

As disclosed in e), a rigid setting of rolling force and speed with both parameters 6 at constant values will result in a load characteristic 28 of the shaping cycle according to P = f (t) which starts with a load peak 30 in the cycle. Referring to this curve (P) is the power or load of the shaping operation and (F) the type of material and (t) the rolling time.

These load peaks 30 have to be sustained by the tools 3, 4 which calls for very rugged and complex tools. The life of these tools 3, 4, which are also costly, is considerably affected by these load peaks 30. If then, as described under d), apparatus 1 and/or a rolling machine/computer combination according to the invention is used, the computer 1 8 would measure and plot the curves s = d (t), F = f (t) and compare them with stored curves P = f (t) or curves computed from the measurements themselves. Using, for instance, a predetermined load curve P = f (t) without load peaks 30, the computer 1 8 would control the apparatus 1 and, consequently, its rolling force, speed or its other parameters in a manner that no load peaks would occur, see curve 31.

In order to avoid such load peaks, the apparatus 1 according to the invention would use a curve 31 for the shaping process or at least a curve approximately as shown by the broken line in Fig. 10. Such a curve 31 can be applied to different types of materials as indicated in this Figure, for instance, for C-15, C-35, C-45 and C 60.

Claims (11)

1. A method of forming a workpiece by applying to the workpiece a rolling force of at least one tool having a shaped profile to be transferred to the workpiece so that the material of the workpiece is caused to flow in the region of the shaped profile acting upon the workpiece and where at least part of this material, together with other material which is as yet substantially unaffected by the profile, reproduces a degree of the profile shape and, consequently, the tool geometry specific to the forming cycle, on the workpiece, wherein during forming a parameter relating to the workpiece and the forming operation is continuously sensed and the magnitude of the sensed parameter with respect to its variation with time is used to control the rate of variation of parameters of the forming.

2. A method as claimd in claim 1, wherein for each forming operation a magnitude is sensed the variation of which with time is used to control the action in time of parameters of the forming.

3. A method as claimd in claim 1, wherein the variation in time of the forming operation is capable of being influenced by the parameters influencing th forming, the magnitude and length of operation of these parameters on the workpiece being controllable from the continuously determined magnitude of the forming phase completed.

4. A method of forming a workpiece substantially as herein described with reference to any one of the embodiments described and shown in the accompanying drawings.

5. Apparatus for carrying out the method as claimed in any one of claims 1 to 4, comprising at least one tool provided with a shaped profile and at least one abutment acting in opposition to the tool, at least the tool being slidably mounted on a bearing and capable of being loaded with a rolling force for the shaping of a workpiece to be inserted between the tool and abutment, at least the tool being provided with a shaped profile to be transferred to the workpiece, wherein a sensing device is arranged between the abutment and the tool for sensing the forming of the workpiece, the sensing device having a probe permitting measurements on the workpiece at least while it is being formed, the sensing device being connected to a control system capable of receiving the individual signals and/or parameters of the forming determined by the probe, the control system being connected to actuating means control ling the forming.

6. Apparatus as claimed in claim 5, wherein the sensing device is a mechanical sensing device, and the probe is constructed as a sensing plate attached to at least one rod and bearing against a feeler pin, the rod being slidable in a low-friction bush in a plate of the sensing device and the feeler being slidable within an inductive displacement transducer in the plate, the displacement transducer being connected to a console system initiating parameters of the forming operation.

7. Apparatus as in Claim 5, wherein the sensing device is an electric sensing device and the probe for determining the forming is constructed as a photo-electric displacement sensor which is mounted for universal movement on a holder slidable in a low-friction axial drive in a plate of the sensing device, the displacement sensor of the sensing device being connected to the control system initiating the parameters of the forming operation.

8. Apparatus as in claims 6 or 7, wherein the plate of the sensing device is arranged over the workpiece and the probe is arranged in the perpendicular longitudinal centre-plane of the workpiece over the completed profile shape in this workpiece.

9. Apparatus as claimed in claim 5, wherein the abutment is formed by a tool having the same shaped profile as the movable tool and the abutment and/or tool is rotatably supported about an axis.

1 0. Apparatus as in claims 8 and 9, wherein the tool serving as an abutment is slidable on a bearing, and the sensing device is axially slidable on a guide, the sensing device being connected to a drive which is dependent on the moement of at least the one tool for synchronous movement of the sensing device on the guide.

11. Apparatus for forming a workpiece substantially as herein described with reference to any one of the embodiments shown in the accompanying drawings.