Rotary Swaging Technology Process, Advantages, Possibilities Christine Kienhöfer, Philipp Grupp
Table of contents Introduction... 2 Process Terminology.. 2 Basic principle.. 3 Types of Rotary Swaging.. 4 Process Specific Features Tolerances 5 Surface quality. 6 Work hardening, degree of deformation and grain structure... 7 Forming versatility.. 8 Materials saving and weight optimisation 10 Net-shape manufacture 10 Wall thickness variations dictated by process. 11 Cycle times.. 12 Materials Suitable materials 13 Tube. 13 Solid material and pre-forms..... 14 Machines and Dies Machines.... 14 Dies.... 16 Applications Applications for automobiles.... 19 Other applications.. 23 Component Development and Prototyping... 25 Axial Forming as Supplementary Method.. 26 The Future... 28 Rotary_Swaging_Technology.doc - 1 -
Introduction Although rotary swaging has long been established in industry it is still a relatively little known production technology. There are a number of good reasons for this. Rotary hammering, as rotary swaging was initially known, was invented in America in the 19 th century. At the beginning it was only applied in some very narrow areas, primarily as an auxiliary operation in pipe manufacture, for conification of the leading end to assist in guiding it into At first only for very special the next smaller die. applications The application required neither precision nor short cycle times. The resulting image of an inaccurate, noisy and slow process is still met today. In addition the process was applied in the armaments industry, in the manufacture of gun barrels. Here the use of mandrel technology was of special importance. The application of the technology in the optical industry for spectacle frame manufacture led to wider possibilities, introducing the process to high volume production. Starting with a cut-off from wire, a series of Making spectacle frames led to high volume production forming operations result in a formed component ready for further processes such as embossing. The application makes considerable demands on surface quality and straightness. In addition, very exacting tolerances must be met to prevent material overflow during embossing. Frequently the metal cutting properties of the materials used are poor. The first rotary swaging transfer line was developed in the 1970s to meet the high production volume requirements of the optical industry. Peripheral processes such as cutting to length were integrated from the outset. Soon the process found applications in the automobile industry, to reduce weight of components and of material used, shorten the production chain due to near-net-shape manufacture, and to reduce demands on resources generally (fig. 1). Fig. 1: Rotary swaging installation for automobile drive shafts Rotary swaging is now employed for a wide range of components for automobiles as well as Today an in many other industries. It established method has become an established modern production method. Process Terminology Rotary swaging is a forming process under the general heading of pressure forming. It is applied primarily for the manufacture of workpieces with In the field of pressure forming symmetry of rotation, with a clear centre line or axis, stepped outside diameters and/or complex internal geometries. In the German standard DIN 8583, rotary swaging is defined as a free forming method for altering cross sections on bar and tube of metal using two or more die segments which partially or fully surround the Rotary_Swaging_Technology.doc - 2 -
cross section to be reduced, using a series of simultaneous radial actions. Free forming means that the shape of the workpiece is not strictly tied to the shape of the dies. However, in rotary swaging normally the dies have a geometry in the working area that corresponds to the workpiece to be formed. Deviations from this general rule arise where this will result in improved flow of material. The shaping of the workpiece is the result of the relative movement between the dies and the workpiece. Normally the workpieces are formed at room temperature. Basic Principle In rotary swaging die segments arranged opposite one another are moved radially relative to the axis of the workpiece, applying forming forces in rapid sequence. The forming energy is employed to provide high specific forming forces. The die segments are guided in guiding slots in the end face of the shaft in the swaging unit (fig. 2). The outward movement of the dies is achieved making use of centrifugal force supported, depending on the machine, by spring pressure. 1 2 3 4 5 Using forming energy to provide the forming force Fig. 2: Schematic representation of the rotary swaging unit When the thrust piece is in a position between two pressure rollers, the dies are in the opened up position, and when the highest point of the thrust piece is directly under the roller, the dies are closed. Resulting from the rotation of the swaging shaft, the rollers held in a roller cage (1) act on the cam shape at the head of the thrust piece (2) to impart a continuous oscillating movement. The thrust pieces are of special wear resistance optimised design. The effective cam height on the head of the thrust pieces controls the stroke of the dies, which is normally between 0.25 and 1.5 mm in each case. Since the desired forming process is not achieved in a single working stroke but in a large number of individual steps, rotary swaging can be described as a type of incremental forming process. The rate of oscillation may be between 1,500 and 6,000 strokes per minute depending on the size of machine. Between the die segment (3) and the thrust pieces, compensating plates (4) or wedges are fitted. In feed swaging the compensating plates are Principle components used for precision setting of the dies. For recess swaging wedges are fitted in this position and these are used both for fine adjustment and for changing the effective position of the oscillation stroke for radial positioning of the dies. The outer ring (5), which consists of a retaining ring and a shrunk-in wear ring, takes up the radial forces and is the controlling factor for the rigidity of the machine. The outer ring can be stationary or it can be driven in the opposite direction to the swaging shaft in order to increase the rate of oscillation, which may also be referred to as the swaging frequency. During processing the workpiece must rotate depending on the speed of rotation of the swaging shaft. This may be achieved either by a rotary drive for Rotary_Swaging_Technology.doc - 3 -
the holding chuck or by allowing some slip against the friction of the chuck jaws. Depending on the application, the swaging unit may be fitted with a 2, 3, 4 or 6-segment die system. The twosegment arrangement has some disadvantages for the process and is therefore now rarely used. Types of Rotary Swaging Fundamentally the technology of rotary swaging is divided into two Feed and groups, namely feed recess swaging and recess swaging swaging. Which of these is chosen depends on the geometry of the workpieces to be formed. Feed Swaging Feed swaging is employed for the manufacture of long reduced cross sections at one end of the workpiece. The workpiece is pushed forward in the axial direction into the For the manufacture of long reduced cross sections reciprocating dies and in this way the diameter in the worked zone is reduced as it progresses through in the conical infeed section of the dies. Subsequently the worked zone passes into the sizing section of the die (fig. 3). The angle of the cone of the die which will be copied on the workpiece should not exceed 15 in order to keep the reactive forces within permissible limits and hence minimise wear on the die surface. This version of the process cannot be applied for forming recesses. In feed swaging on solid bar or on tubing on a mandrel, material flow can only With solid bar material flow be in the axial direction. can only be In the case of tubing axial formed without the use of internal tooling to but with prevent this, material tubing radial flow is also flow in the radial possible direction, leading to an increase in wall thickness, is also possible. Recess Swaging Recess swaging is applied where steep angles at changes in diameter are required. The technique makes it possible to achieve For the manufacture of steep angles at changes in diameter localised changes in cross section of the workpiece as well as to form recesses in the middle zone. Unlike the feed swaging process, in the recess swaging method the workpiece (6) is positioned when the dies are opened up. 2 3 6 Fig. 3: Feed swaging 7 Fig. 4: Recess swaging Rotary_Swaging_Technology.doc - 4 -
The oscillating (stroking) zone of the dies is changed during Altering the the forming process. A stroking closing-up and position of the opening-up action of dies the dies is superimposed on the actual working stroke. To achieve this, adjustable wedges (7) are fitted between the thrust head (2) and the die (3) (fig. 4). In recess swaging it is possible to form angles at changes in diameter of generally up to 60. In certain cases steeper angles are possible, but 90 can Axial flow of the material in both directions only be achieved in very exceptional cases. In the process the material flows only axially, in both directions. As in the case of feed swaging, there will be an increase in the wall thickness when working on tube without employing a mandrel. By using a combination of feed and recess swaging, a reduction in the middle zone of workpieces can be realized over a length that can be greater than the length of the dies. Rotary Swaging over a Mandrel If during swaging on the outside diameter of tubing appropriate mandrels (8) are employed, complex internal contours can be formed. This applies both to rotary feed swaging and rotary recess swaging. Depending on the shape required, the mandrel will be fixed in position in the swaging unit or fed forward in the axial direction in unison with the workpiece. Resulting from the forming operation and reduction in diameter on the outside, the inside of the workpiece is shaped in accordance with the shape of the mandrel (fig. 5). In this way it is possible to form cylindrical or stepped internal contours with excellent surface quality and with regular or irregular and high-precision internal splines. Furthermore, rotary swaging can significantly reduce faults in concentricity that arise particularly with seamless tubing. Process Specific Features In the first instance rotary swaging offers all the advantages of cold forming, including excellent grain structure For the manufacture of precision internal contours Advantages and useful work-hardening. Added to this, in comparison with other processes, are the wide variety of geometrical shapes and the high degrees of deformation achievable and the possibilities for weight optimisation. Tolerances 8 Fig. 5: Rotary swaging over a mandrel Rotary swaging can maintain very exacting tolerances so that subsequent machining is, in most cases, not necessary. In considering the tolerances it is necessary to differentiate between feed and rotary swaging. A further major Factors that make up the cycle time factor is the cycle time available for the forming operation in question. The time for the feed movement and the time for Rotary_Swaging_Technology.doc - 5 -
sizing also have to be accommodated in the total cycle time. Table 1: Tolerance classifications For outside diameters the tolerances lie between ± 0.01 mm and ± 0.1 mm. Normally tolerance classifications IT 8 to 9 are achieved (table 1). As in the case of all other processes, in rotary swaging the achievable tolerances expressed in units of dimensions are reduced with reducing diameter. Thus, for example, the diameter of 1.3 mm of the shaft of the valve needle shown in fig. 6 (the second component from the right) can be reliably produced to an accuracy of ± 0.01 mm. depending on the forming speed applied. In general inside diameters formed over a mandrel are formed to be accurate within a tolerance of < 0.03 mm. This corresponds to tolerance classification IT 6. Internal splines formed by rotary swaging over a ground profiled mandrel and measured using the across roller technique show accuracies up to 0.02 mm, lying between tolerance classifications 5 and 7 in the German Standard DIN 3961/62. In certain cases it is necessary to accept some compromises in respect of accuracy, for example where several geometrical shapes are to be formed on a workpiece in a single setting, in order to shorten the process chain. Either by employing appropriately more complex dies or applying NC Assembling several process steps may mean sacrificing some precision technology, several process steps can be combined into one sequence. In general, however, it is not possible in either of these cases to achieve optimum results for all diameters involved so that depending on the individual case there are likely to be some negative effects on the tolerances. Surface quality Fig. 6: Small parts rotary swaged In the bearing zone of the steering shaft the 25 mm diameter formed by recess swaging is produced to within a tolerance of 0.05 mm absolute. The same outside diameter formed by feed swaging would have a tolerance of between ± 0.03 mm and ± 0.1 mm Rotary swaged surfaces feature very low surface roughness and a high load carrying Average surface finish area. In recess swaging 0.1 µm average surface finishes (R a ) up to 0.1 µm are achieved. The surface qualities are therefore comparable with those achieved in grinding and in some cases even in polishing (fig. 7). Rotary_Swaging_Technology.doc - 6 -
Fig. 7: Extract of DIN 4766, part 2, manufacturing processes of roughness of surfaces In feed swaging, due to the superimposed forward feed of the workpiece during the swaging stroke, the surface tends to be more uneven. Resulting from the relative movement of the workpiece and the rotating dies, a series of parallel spiral groove markings are left from the last cycle of the forming process. The feed speed and hence the cycle time affects the unevenness of the surface in a similar way as the achievable diameter tolerances the greater the feed speed, the more pronounced will be the marking. This is a noticeable effect that is typical for feed swaged surfaces and is clearly visible to the eye, but so slight as to be difficult to measure. If the dies are carefully designed and manufactured, very good surface qualities with average surface finishes 1.0 µm are today achievable in spite of this characteristic. When swaging over a mandrel it is possible to achieve an average surface finish of only 0.1 µm. The quality achieved depends also on the surface quality / roughness of the mandrel. Work-hardening, degree of deformation and grain structure As with other cold forming processes, rotary swaging does not lead to an interruption of the grain structure of the workpieces (fig. 8). The mechanical load-carrying capability of the workpiece is increased resulting from the cold forming work-hardening effect on the material Slightly uneven surface Higher yield point and greater tensile strength structure. The yield point, which is normally the decisive factor in the assessment of the mechanical strength of the workpiece, is raised, this effect being more pronounced than the increase in the tensile strength. The homogeneous forming of the full cross section results in an increase in these values throughout the whole working zone. This change in the mechanical properties of the material can be taken into account as a parameter for the component to be produced. Thus reduced wall thicknesses with corresponding reductions in component weight are often made possible. Fig. 8: Grain structure The degree of work hardening is influenced by the change Calculating in shape and depends the change in on the properties of the shape material. The change in shape of the cross section is calculated as follows: Change in shape (ε) = A a A where A is the initial and a the final cross section. With increased change in shape both the tensile strength and the yield point will be higher. Again, as compared with other cold forming methods, rotary swaging enables greater changes in shape to be achieved, without the need for intermediate annealing to avoid material damages. x 100 [%] Changes in shape of more than 90% are possible. Rotary_Swaging_Technology.doc - 7 -
Changes in shape of 90% and more are possible. The reason for this is that, in addition to the fact that the force is applied radially, in rotary swaging the workpiece is formed in increments and friction between the dies and the workpiece is minimal. The radial effect produced by the die segments during each forming increment affects the internal stress in the material in such a way that the plastic forming capability of the material is increased, since the pressure resistance capability of the material is greater than the tensile strength. The range over which the process can be applied is thus extended up to the point of material failure. The material 34 Mn 5 used for the intermediate shaft shown in fig. 9 increases its tensile strength from the initial 550 N/mm2 (52.5 mm diameter, wall thickness 7.5 mm) to approx. 880 N/mm2 (32.0 mm diameter, wall thickness 2.5 mm) after forming. The change in shape corresponds to approx. 70%. The initial blank is 168 mm long and after swaging the length is increased to 430 mm. Fig. 9: Automobile intermediate shaft Increased formability A hollow shock absorber piston made of 22.3 mm diameter tubing was closed pressure-tight using rotary swaging and it serves as a good example of how, even after such a large Further cold amount of forming, forming further cold forming was possibilities possible, in this case forming a thread (see fig. 25, page 21). Furthermore, in some cases for this type of application, the material used has not been annealed after forming into tubing initially, so that it would already have undergone some work hardening. Forming versatility Rotary swaging enables a wide range of shapes to be formed both on the outside and inside of the workpiece. Fig. 10 shows a number of examples of cross sections that can be produced by rotary swaging. It is clear that A wide shape spectrum rotary swaging offers many more forming possibilities compared with other cold forming methods. Not all swaging that is done in this context can strictly speaking be called rotary swaging since Non-circular external forms are possible non-circular external geometries like DD and triangular shapes, squares or hexagons can be formed. (fig. 10, Nos. 9 to 13). In these cases, a stationary swaging shaft is used and there is no relative rotary movement between the die and the workpiece. The working stroke is actuated by using a rotating outer ring. To produce workpieces of circular or non-circular cross section, the initial material can be either round or in the form of profiled material. The possibilities to form recesses have already been mentioned. It is important thickness Increase in wall to point out that recess swaging is by no means bound to cause a weakening of the workpiece since the wall thickness is not necessarily reduced to the contrary, it Rotary_Swaging_Technology.doc - 8 -
Fig. 10: Examples of rotary swaged shapes may be increased (fig. 10, Nos. 3 and 4). It has already been mentioned that workpieces can be closed up pressuretight by the rotary swaging technique (fig. 10, No. 5). Rotary swaging can also be used to fix two workpieces firmly together for the transmission of force or torque, achieving a precision fit (fig. 10, Nos. 14 and 17). The forces which this type of coupling can take without failure are significantly greater than those that would be possible if the parts had been joined by rolling or crimping. Because of the possibilities offered in producing and fitting complex geometries, rotary swaging is often able to replace welding or soldering operations. Of particular importance in the case of tube material is the possibility to form spherical ends (fig. 10, No. 4). Resulting from the excellent Manufacture of spherical workpiece ends surface quality and accuracy in the form of the ball shape, often no further finishing operation is required. By employing appropriate mandrels it is possible to form complex, highprecision internal contours. In this process the swaging action is applied on the outside diameter of the material which is to be formed over the mandrel. It is, for example, possible to size the inside diameter of the tubing or to produce an internal square cross section. For internal profiles, such as serrations or involute splines (fig 10, No. 15) rotary swaging is often a better production method compared with conventional metal cutting, both from the point of view of tool life and reproducibility. The better reproducibility results from the fact that there is no creeping worsening in tolerances since the ground splined mandrels suffer very little wear and mostly fail by breaking. Rotary swaged teeth are generally also superior to tooth forms produced by the drawing process since the rotary swaging technique used does not necessitate the provision of tapered or conical mandrels. Rotary swaging provides the designer with new possibilities for component shapes. For example, internal teeth on workpieces with reducing wall thicknesses or in blind holes can be formed without difficulty and at advantageous costs. Generally the process allows designing workpieces with variations in wall thickness be matched to the requirements of the component. The mandrel technology can be used to produce a cylindrical or varying outside diameter and precise, stepped, inside diameters. Quality standards, as demanded for cylindrical tubing can be met. The ability to internal teeth and tubes with zones with different wall thicknesses manufacture tubular parts with thick and thin wall thicknesses in different zones is extremely useful for reducing weights of components (fig. 10 Nos. 6, 7 and 8). Rotary_Swaging_Technology.doc - 9 -
Material saving and weight optimisation As the distribution of the material within the component during the swaging process replaces Weight of conventional metal material used cutting, with bars and reduced tubes the weight of the material used is reduced. The elimination of swarf or equivalent waste material eliminates also the cost of disposal. The cost of material in tube form is often higher than with bar material and this is not normally compensated completely by the saving in cost of the weight material no longer required. Nevertheless, the application of rotary swaging is worthwhile in a vast number of cases when all the other factors are taken into consideration. The significant advantages include greater flexibility for shape design that the process allows and the savings resulting from the elimination of subsequent finishing processes. Contamination of the environment is considerably reduced and requirements for disposal of swarf or other chippings are very greatly reduced and this also plays a significant part in the overall economics. Of greatest importance, particularly in the automobile industry, is the fact that solid workpieces can be replaced by rotary swaged parts made from tubing. This is possible due to the specific features of the process. With appropriate mandrel designs, controlled wall thickness reductions in different zones of the workpiece are possible whilst at the same time not only meeting the demands of the static and dynamic loading to which the workpiece will be subjected, but also, in some cases, the demand for controlled noise reduction. A wide range of possible internal and external diameter contours can be formed, meeting the widest range of functional requirements, without any need for additional machining operations (fig. 11). Examples in this area show particularly the importance of taking account of the possibilities and the requirements of this new technology at the design stage of the workpiece, to achieve optimum results in respect of economic advantage and process reliability. Besides many other applications, steering columns, drive shafts, propeller shafts, shock absorber piston rods, headrest brackets and gearbox components have become established as rotary swaged components that feature optimum weight distribution. Shafts and axles made of tubing often need to be provided with external splines, of which special account must be taken. Conventional processes such as tooth rolling are often, and particularly with thin-walled components, unsuitable. For such thin-walled shafts and axles, splines may be formed using a combination of rotary swaging and axial forming (see chapter Axial Forming as a Supplementary Process, pages 26 28). Net-shape manufacture Fig. 11: Weight reduction shown on an example of a shock absorber piston Net-shape manufacture means producing components ready for Manufacture of components installation. For this, ready for rotary swaging offers installation great advantages both Rotary_Swaging_Technology.doc - 10 -
due to the wide range of shapes possible and severity of changes in form that can be achieved. However, in spite of the many geometries that are possible by rotary swaging, it is essential to combine the technique with other methods. Since commercially available raw material will show tolerances in diameter, wall thickness, and length, it is necessary, if precision workpieces are to be produced, to include a turning operation to trim off a small amount of material corresponding to the tolerances on these parameters. If the material has been formed by rotary swaging over a mandrel where the inside and the outside dimensions are precisely controlled, the variation in volume in the blank will only result in variations in the length of the finished formed part. Therefore, if an exact length is a requirement, it is in most cases necessary to trim the length of the by combining different forming technologies workpiece at one end. Where a subsequent heat treatment or hardening operation on the rotary swaged components is necessary, it may be possible to include some allowance for distortions resulting from this. If exacting tolerances are demanded the workpiece may require grinding or precision turning after hardening. The general trend is for the distortion arising in hardening on rotary swaged workpieces to be generally less than on parts formed by other methods. This is another result of the more homogeneous material structure that is a characteristic for rotary swaged parts. The effect applies particularly in respect of the straightness of the parts so that subsequent straightening operations are simplified or eliminated. Wall thickness variations dictated by process When external geometry of a hollow part is altered by swaging the internal contour of the workpiece and its wall thickness will change, depending on constraints applied. As previously mentioned, the wall thickness of cylindrical cross sections will be increased in the area where the material has been formed. On the other hand, in zones of conical shape the wall thickness may be reduced. The wall thickness in the cylindrical area is affected in various ways. Most significant is the type of process, i.e. whether feed swaging or recess swaging is used, and the resulting geometry of the dies. For feed swaging, Schulz (Schulz, E.: The manufacture of fishing tackles on rotary swaging machines) introduced the following equation for the geometry shown in fig. 12. It provides the relationship between the parameters that come into play. s 1 s 0 d D s 1 = s 0 x d x 10 0.5 x D - 0.45 d D = Final wall thickness = Initial wall thickness = Final outside diameter = Initial outside diameter Calculation of wall thickness The formula should, however, only be interpreted as providing guidance figures since the increase in wall thickness will in practice by dependent on many parameters, e.g. the angle β of the conical infeed section and the lubrication s (see chapter Dies, page 16). Beyond this the die geometry, and changes in shape, and not just the principle diameters will play a part. Rotary_Swaging_Technology.doc - 11 -
Cycle times Fig. 12: Reductions in wall thickness according to Schulz Furthermore, it has been established that the axial position of the internal changes in diameter will not follow precisely the changes in shape of the external contour. This will affect the wall thickness in the conical area at the change in diameter (fig. 13). Fig. 13: Wall thickness distribution In the case of angles at the change in diameter of less than 40 the wall thickness will be maintained and may even increase whereas with angles greater than Reduced wall 40 the wall thickness thickness with angles greater will normally be than 40 reduced: in the case of steep angles at changes in diameter in the conical range there may be a reduction in wall thickness. The example of an automobile headrest bracket (fig. 14) shows the changes in wall thickness at a 90 change in diameter on the left and a 30 change in diameter on the right. Fig. 14: Internal contour of a headrest bracket The cycle times achievable depend primarily on the workpiece geometry and the selected manufacturing strategy. In the case of feed swaging, axial feed speeds of up Infeed speeds to 60 mm/s. are 15-40 mm/s possible. Where mandrels are used or severe redistributions of material are involved, this may be reduced to between 15 to 40 mm/s and many applications fall within this range. To the times resulting from these speeds must be added the time for the return movement of the swaging feed during which the swaging dies will still be operating. These return speeds are, however, normally higher than the infeed speeds. In recess swaging the cycle time depends primarily on the difference between the starting and finishing diameters in the zones in question. This will be understandable if one considers that the forming operation takes place not during an axial feed movement but is based on changes in the radial position of Diameter reduction 2 4 mm /s the oscillation dies. Diameter reductions from 2 4 mm/s are achievable. To these values must be added the time used for sizing during which there is no superimposed movement on the dies. The time for this sizing can vary between 0.5 and approx. 2 seconds, depending on the tolerance required. Again, as in the case of feed swaging, the use of mandrels or requirements for greater change in material distribution will result in corresponding reductions in the rate of production. To actual processing times as described then have to be added the times needed for loading and unloading or transferring. A few examples of practical cycle times in volume production are given in the chapter on applications (pages 19 25). Rotary_Swaging_Technology.doc - 12 -
Materials Suitable materials Fundamentally all materials that can be formed can be used for rotary swaging. The Many materials can be used greater the initial hardness the less will be the amount of change in shape that the material will allow. Materials with higher elongation before failure allow more forming work to be done. Steel is the most widely used material for rotary swaging. Both mild steels and low and high alloy steels are suitable. Alloys which favour metal cutting operations are generally less suitable for forming. The forming capability of material can be considerably affected by the grain structure. Whilst annealed material is ideal, cold finished material can be formed to a limited extent (see table 2). It is also possible to spheroidize the steel by heating and holding the material just below the critical temperature. Name Bright, hard drawn (cold finished) Bright drawn, soft (light cold finished) Bright drawn and stress relief annealed Annealed Normalized Explanation No heat treatment after the last cold forming operation. The tube has only limited formability. After the last heat treatment a light cold finishing operation is carried out. Limited cold forming possible (e.g bending, expanding). After the last cold forming operation material heat treated. By reducing internal stresses the tube can, if correctly treated, be processed within limits by cold forming and metal cutting. After the last cold forming operation the tube was annealed in inert gas. After the last cold forming operation the tube is annealed in inert gas at temperatures below the critical point. Table 2: Condition of commercially available tubing However, because of the need to hold the temperature for an extended period, it is rarely economical to apply this process material for rotary swaging, but it is sometimes the only solution for cold heading or extruding, if extensive change in shape is required. There is no problem in using materials such as aluminium, copper, brass or bronze and their alloys. Tube As stated in the relevant German Standard DIN 8583, it is possible to rotary Trends towards tube swage tube as well as solid material. Because of the everincreasing demand in the automobile industry to make optimum use of weight, the trend is to make more and more parts from tube. Tube may be either welded or seamless. Welded tube Safety-related automobile parts such as steering gear, drive Applications in train components and safety-related shock absorber piston components rods, some of which may have to withstand high stresses, have for some years been produced from welded tube. Appropriately processed and tested the welded seam does not present any safety risk nor are there any disadvantages experienced in the subsequent manufacturing process, even where there are severe changes in cross section. The precision steel tubing is made from steel strip, either hot or cold rolled. The strip is formed using Starting material is steel strip various methods and then electrically welded under pressure. Depending on the tube quality, the beads that result from the manufacturing process on the outside and on the inside may be removed. Generally tubing to DIN 2393 (see also DIN EN 10305-2) is used. These tubes stand out due to their high Rotary_Swaging_Technology.doc - 13 -
dimensional accuracy and consistency in volume. The tubes provide optimum starting conditions for high-precision rotary swaged parts, especially where extensive material redistribution is involved. On the other hand, tubing to DIN 2394 (see also DIN EN 10305-3) is only rolled to size after welding and not sized to more exacting tolerances. Depending on the particular application such tubing may also be employed successfully in rotary swaging. Seamless tube In contrast to welded tube, seamless tubing is produced hot from rolled or continuously cast material. The material Rolled steel or continuous is heated to between cast bar 1,200 and 1,300 C material and then rolled in a special angled mill with drive rolls in which the central hole is formed using a mandrel positioned between the rolls. Further manufacturing steps of various kinds follow, leading to a final sizing operation. The method of manufacture results in deviations in concentricity between the inner bore and the outside diameter. This variation is generally greater than in the case of welded tube and may in subsequent forming operations involving the redistribution of wall thickness lead to tolerance problems, and affect straightness. It is also to be taken into account that the hot working process results in more surface blemishes. Solid material and pre-forms Two tube qualities Greater concentricity variations Rotary swaged parts may also be manufactured from solid Solid profiled material respectively material and bars of various quality. pre-forms The material may be rolled, drawn, peeled or ground. For maximum economic advantage, preforms are also sometimes processed by rotary swaging. The pre-forms may have been hot or cold formed. Examples are (closed die) forgings, extrusions or (deep) drawn parts. Machines and Dies Machines The highly developed and sophisticated modular machine concept Modular makes it possible to use machine identical modules irrespective of the degree of concept automation to be incorporated with a given machine. Thus, for example, a semi-automatic machine of size 40 fitted up for the manufacture of steering columns may be, to a great extent, identical with a corresponding station in a multi-station transfer line. The basic mechanical components of a rotary swaging machine are (fig. 15): 1 2 3 4 Fig. 15: Basic concept of a rotary swaging machine Base plate (4) with shock absorber mountings and intermediate frame (3). Rotary swaging unit (1) Swage feed unit (7) with clamping gripper (5). (The clamping gripper may either hold 5 6 7 Rotary_Swaging_Technology.doc - 14 -
the workpiece firmly or serve as friction brake during the swaging operation to allow optimum Components of a rotary swaging repositioning machine in the forging die from one forming step to the next. The axial forces arising are taken up by a stop in the clamping gripper.) Depending on the requirements of the forming process, the basic modules of the Supplementary equipment rotary swaging machine can be supplemented by further units. Examples of these are the following, to mention just the most important: Mandrel unit fitted on the swage feed side to form internal contours on the workpiece Mandrels and / or ejectors (2) fitted on the swaging unit side to form internal contours on the workpiece or to guide short workpieces between two counter-supports. Swaging shaft lock on the rear of the rotary swaging unit to stop the rotation of the swaging shaft. This module is applied where non-circular as well as circular external geometries are to be formed. A further vital part of a rotary swaging machine is the noise reducing and safety enclosure. Noise reducing This is an essential and safety part of a machine enclosure required to comply with CE marking directives since the noise level from rotary swaging is generally above 75 db(a), except in the case of some very light work. In respect of automation for rotary swaging machines the following basic alternatives are available: Basic machine A basic machine consists of a machine base and a rotary swaging unit with the necessary control. It may be equipped with a cooling facility. Single-station semi-automatic machine In this case the swaging feed gripper is loaded by hand or by means of a mechanical handling device provided by the customer (for example a gantry type loader or a robot.). The swaging cycle is initiated either from the operator s control panel or an appropriate interface for the automation equipment, after which the operating cycle takes place automatically. The workpiece is clamped in the clamping gripper. The swaging feed brings the workpiece into the swaging unit and extracts it again after forming. The workpiece is taken out of the holding gripper. The machine in this form for manual loading is very flexible, making it ideal for trial purposes or small batch production. Single-station fully automatic machine This machine type is basically similar to the semi-automatic machine previously described with the difference that the machine builder has equipped it with Manual loading, fully automatic processing With automation equipment automation equipment. The automation equipment incorporates an infeed conveyor or bunker magazine on the infeed side and discharge conveyor, a palletising system or a simple discharge chute. A linear feed takes the workpiece through the machine to the clamping gripper of the swaging feed and from there to the outfeed. Rotary_Swaging_Technology.doc - 15 -
The arrangements on the in and outfeed sides can vary considerably. In principle, the degree of automation depends on customers wishes and the relevant production parameters. Single-station automatic machines are applied for high volume production for applications where only a single swaging operation is involved, but the concept of a flexible production cell is desired. Fig. 16 shows a machine built to provide such a flexible concept. The machines can also be operated as a semi-automatic unit. Fig. 16: Flexible production cell Multi-station transfer lines for combinations of metal forming and metal cutting operations Linear transfer technology for applications requiring such combinations was developed at an early stage and allows any desired number of stations to be connected. Such a transfer line is able to meet the wishes of many customers to produce complete workpieces ready for installation. In addition to rotary swaging operations, other forming operations, such as axial forming, thread forming or rolling, can High volume production Integration with other processes be combined with metal cutting operations such as turning, milling, boring or piercing, all within a single transfer line. The automatic handling on the in and outfeed ends is in each case designed to meet customers wishes and the requirements of the specific workpiece. The flexibility of the transfer line is, however, limited by the rigid linear connection between the individual stations and hence a specific process chain. Transfer lines are, therefore, only economical for high volume, large batch production. It is, however, possible to accommodate a family of workpieces provided that allowance is made at the time of preparation of the project. CNC technology CNC technology can, if desired, be incorporated on a single-station machine or a transfer line and increases the flexibility Optional CNC by reducing changeover equipment times. All principle movements can be controlled on CNC axes. For each feed axis control signals appropriately interpolated for the adjustment or movement, increase the forming operations that can be achieved in a single setting. Several geometric shapes can be produced with a single die. Generally speaking some sacrifice in cycle time for some of the operations has to be accepted. The module described in this section enables machine systems to be laid out in such a way that, taking account of the production volumes and company philosophy, an optimum machine concept can be developed. Dies Design The forming dies play a fundamental role for the tolerances and surface qualities achieved with rotary swaging. In general the forming surfaces of the dies correspond closely to Rigid linear interconnection limits flexibility Die design the basis for tolerances and surface quality Rotary_Swaging_Technology.doc - 16 -
the geometry of the workpieces to be produced. Some deviations may be introduced in order to achieve an improvement in the material flow. The final geometry of the workpiece will depend on the relative motion between the dies and the workpiece. Different forming conditions in feed and recess swaging require different die geometries. The forming geometry of the die in rotary feed swaging features a conical infeed section in which the workpiece is reduced in a cylindrical sizing section. The zone where the reducing and sizing areas join is soft, i.e. there is a radius and not a sharp corner, in order to achieve optimum surface quality. The main forming operation is, however, completed in the conical or tapered infeed section using an angle between 3 and 15. The subsequent cylindrical portion of the die is purely for fine calibration. Decisive for the die geometry is how tightly the die is matched to the required relationship between the diameter to which the die has been machined and the finished part diameter. This can be represented by the following equation: Matching ratio (s) = Finished part diameter Die diameter Generally a ratio of between 0.94 and 0.99 is appropriate. With this value particularly good Optimum match surface results are ratio between achieved and damage 0.94 and 0.99 to the material is avoided. A limit is set when the finished part diameter is equal to the die diameter. In this case, the value of s is 1 (fig 17). With values s > 1 material will enter into the gap between die segments, resulting in a damaged workpiece surface. Match ratio < 1 Match ratio = 1 Fig. 17: Shape matching for feed swaging dies In rotary recess swaging the closing-up action onto the workpiece is achieved by radial closing up of the oscillating dies, in contrast to feed swaging. The part is therefore formed making use of the full area of the forming surfaces of the die, causing the material to be pressed radially and flow axially. The surface must be so designed that at no point material will flow into the gaps between the dies. To initiate the recessing operation when the workpiece diameter is larger, it is therefore necessary that the ratio of the diameters is less than 1. When the workpiece diameter has been reduced by recess swaging to a value close to the die diameter, attempting further swaging would result in swaging outside the limiting matching ratio value for optimum results. For this reason, recess swaging dies are designed with different geometries compared with feed swaging dies. In the zone of the gap between the dies the effect is taken care of by making the contact surface tangentially longer (fig. 18). Fig. 18: Superimposed closing-up movement of recess dies This then enables matching ratios to be used with values between 0.94 and 0.99 as in the case of feed swaging dies. D d Alternative design 2α Rotary_Swaging_Technology.doc - 17 -
The angle α for the sector outside which the radius is cut away tangentially depends on the diameter ratio δ of the initial diameter D relative to the final diameter d (fig. 19). The limits for the process are generally reached when δ is less then 2. Process limitation with δ > 2 The forming operation then has to be divided between 2 stages as otherwise the resulting poor surface quality and possible material damage will not be acceptable. The reason for this is that the angle of the sector α would be excessively reduced. The part of the die that is of the desired inside diameter will be excessively shortened. Fig. 19: Sector angle α in relation to diameter ratio δ for recess dies The die design may be very complex if several diameters are to be produced in one operation since the design considerations that have been described have to be applied separately for each diameter zone. In addition to this, in the area where the cylindrical zones join the conical zones on recess tool dies, a soft transition is required (i.e. no hard corner) for better material flow whilst the oscillating zone of the dies is moved further inward. With CAD-assisted die design of rotary swaging dies, the following procedure is followed (fig. 20): Fig. 20: Die design using 3D CAD The process sequence for the forming work is established on the basis of the workpiece drawing (A). Next the forming CAD supported requirement on the die design cross section is entered into the CAD system and this is transformed into a 3D image of the required body by rotation around the centre line (D, C). The tangential enlargements and matching requirements are taken into account in this process. The design is then applied to the die blank and this results in the image for the individual die segments (D, E). Manufacture Rotary swaging dies have a hardness of 60 HRC or more. For this reason until recently these could only be produced using eroding technology. To produce complex forms necessitated several electrodes and erosion operations. However, with more recently developed hard milling technology it is now possible to mill rotary swaging dies in tool steel with a hardness of approx. 60 HRC in a Erosion is replaced by hard milling single clamping. Surface damage as experienced with the erosion does not arise. The milled surface is of good quality and subsequent manual Rotary_Swaging_Technology.doc - 18 -
polishing is not required. Even complex contours can be machined. Reproducibility within one die set and between sister die sets is significantly increased. To make the dies, the data generated in the CAD process is entered directly via a CAD-CAM interface. If high-strength materials are to be formed or the operation involves dies particularly prone to wear, carbide dies are required. In this case the erosion method continues to be applied. Applications Applications for automobiles Fig. 21 gives an overview of applications in the automobile industry. 1. Interior: seat adjustment shafts, headrest brackets, rotor shafts for electric motors 2. Chassis / running gear: hollow shock absorber piston rod, shock absorber outer tube, stabiliser, push rod for braking system, track rod, ball journal 3. Drive train: propeller shafts, intermediate shafts, drive shafts, shaft journal 4. Gearbox: gearbox shafts 5. Motor: expansion bolt, glow tube, glow pin, injection pipes, guide tube of oil dipper rod, pipe connections, starter shaft, starter bush, air conditioning tube, balance shaft 6. Steering system: steering shaft, steering rack, piston on steering rack, steering sleeve, servo valve, steering pinion 7. Passenger safety: belt tensioning cylinder tube, air bag container tube Fig. 21: Applications of rotary swaged parts in automobiles. The process is clearly useful for a wide range of components, Wide range of in the areas of the applications steering gear, the motor, the transmission and drive train as well as for safety and protection equipment. Steering shaft Very high demands are made on automobile steering parts. These parts Greatest demands applied to safetyrelated parts are safety-related components which must not fail under any circumstances. Furthermore, in the event of an accident movement of the steering column into the passenger compartment of the vehicle must be prevented to avoid injury. Other features must meet the increasing demands for driver comfort. Steering wheel height and length adjustments are now considered standard features and theft prevention is essential. Fig. 22 illustrates a steering shaft that provides steering column length adjustment through the use of a system of Combination of external and internal splines appropriate internal and external splines. These splines allow collapse of the steering column in the axial direction, to prevent movement of the steering wheel in the direction of the driver in the event of an impact. Rotary_Swaging_Technology.doc - 19 -
Fig. 22: Steering shaft with internal splines The section with external splines is pushed into the section with internal splines. Since, additionally, the column must allow for the essential function of transmitting torque, if possible without any kind of play, the accuracies demanded of the rotary swaged splines are very severe. The bearing area and the location for the steering wheel lock are finished to a tolerance of 0.05 mm. The external spline for the fixing of the steering wheel itself Eight operating is formed by the axial stages are forming method. required Chipless forming is also used for the M14 x 1.5 mm thread for fixing the steering wheel. To produce the steering column shown requires 8 operations. Cycle times for the manufacture of steering columns are generally between 12 and 17 seconds. Drive shafts made from tube Drive shafts are made by rotary swaging, starting either with solid material or tubing. Hollow drive shafts have become more and more established over recent years for several reasons. There is a clear saving in weight. This is Hollow drive shafts are becoming established becoming even more important since, in the interest of reducing noise and vibration, manufacturers and system suppliers need to work with larger and larger diameters in the middle zone of the shaft. Rotary swaging has been found a valuable alternative to produce such hollow shafts, which would otherwise be made in three sections welded together. The shafts must be designed and tested to stand up to severe static and dynamic loads and to meet established standards in respect of oscillations and maintain the desired properties on a long-term basis. The uninterrupted grain structure and the avoidance of stress concentrations at changes in geometry, as well as the specific load taking capability at the swaged surface, all contribute to make the rotary swaging technology ideal for these applications. The hollow automobile drive shaft shown in fig. 23 shows that the wall thickness in the middle Wall thickness zone can be reduced reduction in the to a minimum when, in middle zone order to save material and weight, rotary swaging is applied. Fig. 23: Hollow drive shaft The maximum wall thickness can be left unaltered at the ends of the shaft. These areas which are usually splined, are of particular importance for longterm strength of the component since here torque is to be transmitted. A further requirement is accurate balance (concentricity) in view of the high speeds of rotation of the drive shaft. Reduced eccentricity Rotary swaging is able to reduce concentricity errors by up to 50 % compared with the initial condition of the tube employed. Using suitable transfer lines drive shafts can be formed to the required net shape requiring only subsequent hardening. In addition to rotary swaging, the transfer line incorporates stations for surfacing / chamfering respectively turning of the groove, Rotary_Swaging_Technology.doc - 20 -
pressing the spline and rolling the groove for the bellows. The drive shaft shown is produced at a rate of 4.5 workpieces per minute. Propeller shaft For similar reasons as those applying to the drive shafts rotary swaging has also become successfully established for the manufacture of propeller shafts (with universal joint) (see fig. 24). Piston rod The main reason for changing to tubing in the manufacture of shock absorber piston rods is the saving in weight which can be achieved. Alongside the other advantages that rotary swaging offers, the application demonstrates an additional feature of the process: workpieces can be sealed Pressure-tight closing pressure-tight (fig. 25). The piston side (on the left of the illustration) are partially swage formed with a plus tolerance. The necessary steep shoulders are turned. To fix the piston a M8 x 1.25 thread is formed. At this end the workpiece must be closed pressure-tight for the shock absorber to function. Fig. 24: Universal joint shaft Cylindrical tubing has been in use to make these components for some time. Safety requirements led to the development of the so-called crash tubes and features for Reduction in noise reduction are a diameter further requirement. Starting with a larger diameter, the middle zone (for example 80 mm, wall thickness 1.5 mm) is formed with precisely specific changes in diameter and corner radii, with unchanged wall thickness to form the smaller diameter ends (e.g. 60 mm). In this the wall thickness at the ends has to be maintained or at least accurately sized over a mandrel in order to meet the necessary precondition for friction welding. Propeller shafts may be up to 1,000 mm long and must meet exacting tolerances in concentricity. For example, a tolerance of 0.2 mm may be specified over a total length of 750 mm. Fig. 25: Shock absorber piston rod At the fixing end an internal hexagon shape is formed and all external fitting surfaces are formed by rotary swaging. Since this side protrudes into the engine space, ingress of water is prevented Ball prevents ingress of water by pressing a ball into the piston rod. Afterwards the external thread M14 x 15 is formed. The cycle time is approx. 12 seconds. Gearbox shaft With the increasing demand from the market for automatic gearboxes and, the manufacturers ongoing search to reduce weight, the trend is to make more and more of the parts in the form of hollow workpieces. As a result this has become another area of interest for rotary swaging. Some shafts in any Rotary_Swaging_Technology.doc - 21 -
case have to have a through hole for their function in the gearbox and may also require steps or internal splines, often to very close fitting tolerances. To form such parts by metal cutting is very costly. By employing rotary swaging over a mandrel as already described, the required bearing areas with high quality surface as well as the internal splines can be formed to exacting tolerances. A subsequent finishing operation on the rotary swaged outside diameter, either before or after hardening, can however generally not be avoided. This is due to the need for steep shoulders and the recesses that are required. The example in fig. 26 shows different manufacturing strategies for such a workpiece. Fig. 26: Gearbox shaft Forming demanding internal contours In fig. 27 the process is shown diagrammatically. It is divided into 5 set-up stages on a transfer line for high volume production. The semi-finished part, already provided with the flange, is entered at the infeed end and is then swage formed in Transfer line: cycle time 15 three operations, seconds followed by an axial swaging operation to form the external splines, and turning to length. The cycle time is approximately 15 seconds. Alternatively, an identical shaft could be produced in one clamping in a singlestation rotary swaging machine if this machine is equipped with NC technology. In this case the die is designed in such a way that several diameters can be formed using the same die. The cycle time for rotary swaging is approximately 40 seconds in this case since the operation has to be divided into several stages. On a further separate machine the external splines are pressed on and the end is trimmed by metal cutting. The decision as to which concept is the most appropriate depends on production volumes and batch sizes and the desired flexibility. Fig. 28 shows the prototype for a gearbox shaft on which rotary swaging is applied after pre-forming. The part is subsequently finished by metal cutting operation on the outside. The advantage in this case is a significant reduction in Rotary swaging machine: cycle time 40 seconds Small allowance the allowance needed as compared for example a forged blank which would also require deep-hole drilling in order to get near to the low weight. Fig. 27: Operation sequence for a gearbox shaft on a transfer line Fig. 28: Gearbox shaft Rotary_Swaging_Technology.doc - 22 -
Headrest bracket The new generation of headrest brackets produced by rotary swaging achieve optimum wall thickness reduction to minimise weight. Full advantage is taken of the resulting work hardening. Fig. 29 shows the manufacturing sequence for the components of a 3-part headrest bracket. The weight is approx. 60 g; Weight saving 75% made from solid the weight would be 240 g. Drill holder Employing well-designed combinations of processes, efficient production sequences can be devised. An example is the manufacture of the tool holder for a drilling machine (fig. 30). The pre-form is produced Manufacture of the external contour in one operation by metal cutting and the internal contour with two grooves is then formed by rotary swaging over a profiled mandrel. The complex internal contour is completed in one operation. No subsequent finishing operation is required. Fig. 29: Headrest holding rod The total process chain is significantly simplified. An additional contribution was the use of stainless steel which has environmental advantages by eliminating a chromium plating operation. The cycle time for the manufacture of headrest bracket rods on a 6-station transfer line is approx. 8.5 seconds. Other Applications Although the main applications have up to now been in the automobile industry, there are a large number of applications in other industries where rotary swaging can be employed economically. These include manufacturers of optical, medical, electrical, domestic, heating and air conditioning equipment and the makers of handheld and other machines. In the following a few examples have been selected. Fig. 30: Drill holder Fitting sleeve onto wire rope As already stated in the chapter Forming Versatility see pages 8 9, rotary swaging can be used for strong and tight fixing together of two components. Whereas in the case of rotary swaging over a mandrel the die must be made in such a way that the workpiece can easily be released, the opposite applies in this case. The internal part is firmly attached to the external part (fig. 31). Rotary_Swaging_Technology.doc - 23 -
Fig. 31: Steel sleeve fitted on wire rope In the wire rope shown, the material of the sleeve is pressed into the gaps between the individual wires. The method of fixing is so far superior in reliability over other Proven, strong fixing methods that rotary swaging is the most frequently used method for such purposes in the aviation industry. Depending on the axial or radial loading involved, the inside of the rod or tube can be knurled or provided with a groove to give a firm hold. Expansion bolts Although in the previous examples many advantages of using tubing have been described, rotary swaging can also be very advantageous for solid components. required is thus significantly reduced. If the shape were to be produced by metal cutting a significant loss of material in the form of swarf would arise. In the case of this highly stressed component, resistance to fatigue (due to the continuously changing applied load) is of decisive importance. Rotary swaging offers considerable advantages for this. As previously mentioned, excellent surface quality is achieved and stress concentrations are reduced. In addition to this, the grain structure is Improved fatigue resistance not interrupted by the forming method and in fatigue resistance is improved. Bone nail There are also a number of examples in the manufacture of products for medical applications where rotary swaging can be applied economically. The quantities are generally relatively small so that the versatility of the machine technology is of particular importance. For example, in the case of bone nails a very wide range of lengths is needed, but of each length only a few hundred are required each year. Fig. 32: Expansion bolt Fig. 32 shows an expansion bolt that has been rotary swaged. In the forming operation the length of the part is greatly increased and the weight of material Reduced weight of material Fig. 33: Bone nail In a typical case, bone nails are produced from a 278 mm blank which are reduced by feed swaging over a mandrel fixed in position underneath the swaging dies. In the process the length of the workpiece is increased to Rotary_Swaging_Technology.doc - 24 -
480 mm. The tensile strength of the stainless steel 1.4441 that is used is increased in the rotary swaging operation from High tensile strength, 600 ± 50 N/mm² to 860 to straightness, 1100 N/mm². After smooth swaging the 3 grooves in surface the length direction are rolled into the previously reduced zone (fig. 33). Straightness and surface quality are the important parameters for this component. Saw blade carrier A carrier for saw blades is shown in fig. 34. It is a good example of a part on which an internal form is produced that would be impossible to make by any other method. Fig. 34: Saw blade carrier On the one hand there is a local thickening of the wall in which later a thread is to be provided, whilst in another zone two grooves and two V- shaped pockets are formed for guiding and fixing the saw blade into position. In this case rotary swaging replaces making the component in two parts. Additionally, the work hardening effect makes it possible to use a less costly material for the component. Component Development and Prototyping Since knowledge of the possibilities and limitations of rotary swaging as they apply Integrating a to the design specialist possibilities for particular components is generally only available to a limited extent, successful development requires early integration of a specialist into the design team. By working together in this way, the product manufacturing process can be worked out jointly at the appropriate stage, leading to optimum conditions for subsequent manufacture. The following aspects need to be taken into consideration: Operations to precede and to follow the process chain What aspects are essential and what details can be varied Material used, taking account of each of the steps in the process chain and (of course) the function of the workpiece into the early phases of product development Essential points All technical specifications relating to the function of the workpiece, method of assembly of the workpiece and the resulting restrictions on the design Rotary swaged parts are often intended to replace conventionally produced parts. Alternatively they may be required for newly developed systems. In either case, possibilities for full simulation of the effect of a particular design are strictly limited. Making prototypes is therefore very desirable if not essential. (See also chapter The Future, pages 28 29). Rotary_Swaging_Technology.doc - 25 -
Even though larger swaging machines are often able to form workpieces which are on the lower limit of or outside the size range for which the machine is primarily intended, sample components should be produced on a machine of the size that is intended for volume production. Only in this way will it be possible to produce valid information in respect of tolerances achievable, localised workpiece hardening and meaningful details of the material flow. Last but not least, the machine size selected also affects the cycle times achievable. Only if sampling is done on a machine of the correct Producing samples on a suitable machine The right machine size is of decisive importance size will the result give reliable information on what is likely to be achieved in volume production. Unlike dies for other forming methods, rotary swaging dies closely resembling those used in volume production can today be produced quickly and at advantageous prices. A factor that can affect the speed of prototype manufacture is, in many cases, the time needed to obtain the raw material of the selected specification (diameter, wall thickness, analysis). This applies particularly in the case of tubing. Axial Forming as a Supplementary Method In the automobile industry, as well as in other industries, components are often required which need to transmit torque using a system of splines. In the automobile industry such parts are in the first instance the shafts in the drive train and the steering gear, but there are also examples of such parts used in many other areas. Whilst for solid parts (fig. 35), in principle, a range of metal cutting and forming processes are readily available, the forming of splines on hollow shafts (fig. 36) makes special demands. In the first instance, it is desirable to avoid the need to increase the wall thickness in order to be able to form the splines by the method selected. Moreover, the splines must be produced reliably to a high quality standard. Fig. 35: Gearbox components with external spline Fig. 36: Gearbox shaft These requirements are met by the axial forming process for external splines and profiles. The method is equally suitable for tubular and solid components. In axial For the forming of external splines and profiles forming the die is moved onto the firmly clamped workpiece or vice versa (fig. 37). Since a one-piece die is employed, relatively high tolerances on the diameter on which the splines are to be Rotary_Swaging_Technology.doc - 26 -
formed can be accommodated. The high tolerances will have no effect on the pitch error nor will tolerances in the quality of the material itself, between different batches, have any harmful effect. Workpiece Mandrel Fig. 38: Displacement time diagram for axial forming Clamping jaw Fig. 37: Principle components of an axial forming set-up The tolerance of the pre-spline diameter and variations in the strength of the material can, however, affect the filling of the tooth form, i.e. the major diameter of the splines. The outside diameters should be selected such that there will be no overflow of material since this would result in an unnecessary rise in press force and early wear in the die. In conventional axial forming the die is moved at a constant speed. There is a high axial pressure load on the workpiece in the area between the die and Die High axial pressure load the clamping equipment because of the high friction and forming forces. If the cross section of the workpiece is not sufficient, this can cause upsetting of the workpiece. In order to avoid this limitation to forming external teeth on weightoptimised thin-walled workpieces, a method is required to minimise these forces. In frequency modulated axial forming, which is a patented further development of conventional axial forming, the feed movement is superimposed by an axial oscillation (fig. 38). The result is that the force needed is significantly reduced. As compared with the conventional Frequency modulated axial forming reduces axial force required. method, it may be reduced by up to 50%. This is explained by the fact that material flow conditions are different and that the lubrication film can constantly be renewed (fig. 39). It is important in this context that the die is actually lifted off the workpiece at each return oscillation since this not only releases the stress but also allows the lubricant film to be replenished. force [KN] 300 250 200 150 100 50 0-50 -100-150 "norm al" axial form ing frequency modulated time Fig. 39: Comparison of force behaviour in normal and frequency modulated axial forming As in the case of conventional axial forming, the forming die for frequency modulated axial forming consists of a die which represents a negative image of the workpiece to be formed. The die Rotary_Swaging_Technology.doc - 27 -
is contained in a housing. The die core is normally made of coated carbide. Fig. 40: Single-station axial forming machine in 2-pillar construction For external spline forming applications or other operations such as expanding, reducing or stretching, specially developed, generally horizontal machines are applied (fig. 40). Axial forming equipment can be in the form of a production cell, a Horizontal... multi-station transfer line or installed in conjunction with rotary swaging in combined chipless forming and. or vertical axial forming machines metal cutting transfer lines. For short workpieces vertical automatic axial forming machines are employed (fig. 41). The Future Fig 41: Automatic vertical axial forming machine in 4-pillar construction The housing is generally prestressed in the form of a steel ring shrunk onto the die core. In spite of this, it can happen that in the pressing process the die will expand so that diameter-related dimensions of the spline will be subject to variation. Therefore, if high levels of deformation are involved or when very exacting tolerances are demanded, resistance to deflection can be further increased by applying a reinforcing strap arrangement. Since the automobile industry is the main user of rotary swaged components, the ongoing development in rotary swaging has to follow primarily the demands made on this industry. The aim is to further improve the economic advantages by reducing cycle times and increasing machine and flexibility availability. Flexibility must be increased at the same time as reducing the time needed for changeovers, to accommodate both reduced batch sizes and shorter delivery periods. A great challenge is presented by the fact that rotary swaging has up to now only been the subject of scientific research in relatively few fields of interest. To a great extent rotary Improvement of economic advantage Hardly scientific knowledge swaging still depends on empirically established experience. Over the last 10 years, more and more scientific work has been done on the subject, but conclusions have only been reached in a few isolated areas. Only a few rules in the normal sense have so far been established and there is, in general, no Rotary_Swaging_Technology.doc - 28 -
research result for the way in which the various parameters interact with one another. The companies offering rotary swaging do, however, have a great deal of know-how at their disposal so that in many cases they are able to offer a reliable assessment of the ability to produce a part, the tolerances and cycle times achievable and the machine size required. Some parameters important for the design of workpieces such as work-hardening due to the flow forming operation of the material, can currently only be established by trials. Even trials, however, do not give complete information in respect of stresses and strains that will arise in the production workpiece. Compared with other forming processes, rotary swaging has the advantage that dies close to those that would be used in practice can today be produced for test purposes quickly and at relatively advantageous price. Particularly in the automobile industry the ever-decreasing times allowed for development mean that component modifications often result in a whole series of further trials being needed when revision becomes necessary. This is the reason for the desire, both by those offering the Manufacturers know-how and experience Desire for a theoretical model equipment and their customers, for theoretical models that will give an accurate prediction of what the process will achieve. Fig. 42: 3-dimensional simulation of recess swaging Investigations with select geometries at the Institute for Production Technology and Forming Machines at the University of Darmstadt have shown that 3D finite element analysis may also offer a useful solution for the future Finite element analysis suggests a possible solution of rotary swaging (fig. 42). A plan has therefore been established for further research involving manufacturers of machines and other industrial partners for establishing the fundamental understanding of the effects of the different process parameters on material flow, stress, elongation, and the necessary forming forces. The aim is to achieve meaningful numerical simulation of the process based on known parameters that can be entered. FELSS GmbH Maschinenfabrik Dieselstrasse 2 D-75203 Koenigsbach-Stein Phone +49(0)7232/402-0 Fax +49(0)7232/402-122 www.felss.de * info@felss.de Rotary_Swaging_Technology.doc - 29 -