METHOD OF TENSILE FLOW FORMING

FIELD OF THE INVENTION

[0001] The invention relates to flow forming, and more particularly, to a method of tensile flow forming.

BACKGROUND OF THE INVENTION

[0002] Flow forming processes for sheet metal are known in the industry for gathering and thickening material to form hubs, pulleys, and similar products. In all of the existing processes the material flows from an outer portion of a rotating round blank inward, namely, from the larger diameter to a smaller diameter. Consequently, the forming process involves compressive stresses and strains. For instance, a large slab or ingot may be rolled in a rolling mill under compressive forces to sub millimeter thickness sheet metal. On the other hand, if the same slab or ingot is pulled through in a tensile direction, it will “neck” i.e. thin out and break. Necking and breaking is the common failure mode for all tensile forming processes. However, there are processes such as wire drawing in the industry that utilize tensile forming. Once a rod has been rolled under compressive forces to a given diameter, it may be drawn to smaller diameters under tensile forming stresses. However, for a tensile forming process to work without failure of the part, the process parameters have to be adjusted and maintain precisely.

[0003] Representative of the art is U.S. Pat. No. 5,987,952 to Kutzscher et al. (1999) which discloses a method for making a hub/pulley by spin forming from a disc forming an annular collar extending radially inward of the hub.

[0004] Also representative of the art is U.S. Pat. No. 6,105,410 to Sauberlich et al. (2000) which discloses forming a hub disc by at least one roller infed and substantially radially moved in, a material flow taking place on the workpiece.

[0005] What is needed is a method of flow forming in a tensile direction. What is needed is a method of flow forming in a tensile direction using thinner blanks. What is needed is a method of flow forming in a tensile direction using a roller moved on a workpiece in a radially outward direction. The present invention meets these needs.

SUMMARY OF THE INVENTION

[0006] The primary aspect of the present invention is to provide a method of flow forming in a tensile direction.

[0007] Another aspect of the invention is to provide a method of flow forming in a tensile direction using thinner blanks.

[0008] Another aspect of the invention is to provide a method of flow forming in a tensile direction using a roller moved on a workpiece in a radially outward direction.

[0009] Other aspects of the invention will be pointed out or made apparent by the following description of the invention and the accompanying drawings.

[0010] The invention comprises a method of flow forming in a tensile direction. More particularly, it comprises flowing the metal on the surface of a sheet (or plate) metal blank from a center radially outwards. A roller is initially engaged near or at the center of a rotating metal blank. The roller is then moved radially outward to the edge of the metal blank, gathering the metal as it moves. An outer mandrel surface may be used to accumulate the gathered metal to form a predetermined shape at the edge of the blank, such as v-belt or multi-ribbed v-belt profile, or gear/sprocket teeth profile.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]
FIG. 1 is a cross-sectional view of a roller engaged with a work piece.

[0012]

FIG. 2

a
is a cross-sectional view of a piece after tensile flow forming.

[0013]

FIG. 2

b
is a cross-sectional view of a finished piece after tensile flow forming.

[0014]

FIG. 2

c
is a cross-sectional view of an outer profile.

[0015]

FIG. 2

d
is a cross-sectional view of an outer profile.

[0016]

FIG. 2

e
is a cross-sectional view of an outer profile.

[0017]

FIG. 2

f
is a cross-sectional view of an outer profile.

[0018] FIGS. 3(a) through 3(h) depict a prior art compressive flow forming process.

[0019]
FIG. 4 is a top perspective view of a roller engaged with a workpiece.

[0020]
FIG. 5 is a top perspective view of a roller engaged with a workpiece.

[0021]
FIG. 6 is a top perspective view of a roller engaged with a workpiece.

[0022]
FIG. 7 is a top perspective view of a roller engaged with a workpiece.

[0023]
FIG. 8 is a top perspective view of a roller engaged with a workpiece.

[0024]
FIG. 9 is a top perspective view of a roller engaged with a workpiece.

DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION

[0025]
FIG. 1 is a cross-sectional view of a roller engaged with a workpiece. Roller R is rotatably mounted to a tool mounting bracket T on bearings B. Workpiece 10 is rotatably mounted in rotating mandrel chuck C and profile tool D. Workpiece 10 is held in place on chuck C by stud S. The point of contact 13 of roller R on workpiece 10 may be anywhere from the center of the workpiece to the edge of the workpiece, depending in part on the volume of metal to be gathered and the required thickness of the finished part.

[0026] The method comprises a first movement M of tool T to bring roller R into contact with workpiece 10. Point of contact 13 is at or near the center of rotation 14 of workpiece 10. Next, tool T moves in direction MR. Direction MR is in a substantially radial direction away from center 14. A movement in direction MR results in tensile stresses being imparted to the workpiece.

[0027] As roller R moves in a radial direction, metal is gathered and formed outwardly toward outer portion 11 of piece 10 until roller R reaches finished position R2. As roller R moves, the workpiece material thins under the tensile load in the radial direction, with some compressive forces in the thickness direction, because the swept area under the roller increases as the radius increases. During the process the metal flows into the steadily increasing swept area. The gathered material is formed in profile tool D into a predetermined shape. A surface 120 of profile tool D may have any profile that may be required for the finished part. The profile may comprise flat, multi-ribbed or toothed. The finished part may comprise without limitation, a pulley, gear, sprocket, cap, closure, piston, or other substantially circular form.

[0028] Once completed, tool T is slightly retracted along path -MR and thereafter disengaged from the workpiece. One can appreciate that a fully completed part is accomplished in a single step using the instant method.

[0029] This instant method comprises flowing or forming the metal in an outward or tensile direction. This results in the ability to spin thick outer portions 11 using a blank having a comparatively smaller diameter than is used in the existing art. The prior art teaches flow forming the metal in a compressive direction beginning at a radially outer surface of a blank. With the inventive method the web portion of the part can be significantly thinner as compared to the prior art. This results in a significant weight savings over other spun-formed products. For example, using the process disclosed in U.S. Pat. No. 5,987,952 the material cannot be flow formed to a very small thickness, i.e., <1 mm. Consequently, some waste is created using the prior art process as the product is finished.

[0030] Once the workpiece has been formed is removed from the chuck. A fastener receiving portion, such as a hole or holes, can then be punched, drilled, cut or pressed in a manner known in the art into the workpiece cooperatively disposed relative to an axis of rotation. A fastener such as a bolt can then be inserted to fasten the finished pulley to a shaft.

[0031] The instant method also provides the ability to create forms and shapes on the outer portion 11 of the workpiece 10 such as multi-ribbed pulley grooves or sprocket teeth, without wasting any materials. Finally the instant method provides the ability to use existing equipment in the industry with relatively minor changes, some as simple as reprogramming an NC machine.

[0032]

FIG. 2

a
is a cross-sectional view of a part after tensile flow forming. Workpiece surface 12 is shown with a multi-ribbed shape. Workpiece surface 12 can be used to engage a belt (not shown). Of course, depending upon the profile formed into surface 12 the workpiece may also be used to engage a sprocket, gear, cylinder or other part.

[0033]

FIG. 2

b
is a cross-sectional view of a finished piece after tensile flow forming. Member 15 has been removed from the workpiece 10 leaving only a ring comprising outer portion 11 and surface 12. Surface 15 may comprise a web in a pulley.

[0034]

FIG. 2

c
is a cross-sectional view of a workpiece profile. This is a detail of a multi-ribbed shaped surface 12 shown engaged with profile tool D.

[0035]

FIG. 2

d
is a cross-sectional view of a workpiece profile. This is a detail of a single groove shape 121 in surface 12. Workpiece 10 is engaged with profile tool D.

[0036]

FIG. 2

e
is a cross-sectional view of a workpiece profile. A toothed shape 1200 is shown in surface 12. See also FIG. 5. A toothed profile may be used to engage gears or synchronous belts known in the industry. In the instant method the toothed profile is fully formed in surface 12 as part of the forming process in profile tool D. Forming a toothed profile in this single step eliminates the need for a separate hobbing step wherein the toothed profile is separately cut into the outer portion 11 of the partially complete pulley workpiece. Further, this method eliminates waste otherwise created by hobbing the teeth since the teeth are formed as part of the spinning process. The inventive method also eliminates residual stresses that may be present in the workpiece and/or teeth as a result of a hobbing step.

[0037]

FIG. 2

f
is a cross-sectional view of a workpiece profile. This is a detail of a flat formed shape 110 for surface 12. Flat surface 12 can be used to engage flat belts.

[0038] It also should be noted that the prior art process of gathering and splitting the metal edge is limited in thickening due to the material buckling limit. FIGS. 3(a) through 3(h) depict a prior art compressive flow forming process. In this process, the material edge is gathered with a “V” or “U” shaped roller. However, only a certain length of material, D1, can extend from the edge of the spin tooling see FIG. 3(a). Length D1 cannot exceed the buckling limit of the material. If length D1 is too long, the material will not gather and thicken, rather, it will buckle, see FIG. 3(h). Length D2 in FIG. 3(h) exceeds the buckling limit length shown in FIG. 3(a) and will buckle if it is worked. As a result, in the prior art several stations each having a differently shaped tool are required to gradually thicken the material at the edge of a blank while staying under the buckling limit, as shown in FIGS. 3(a) through 3(e), giving the result in FIG. 3(f).

[0039]
FIG. 4 is a top perspective view of a roller engaged with a workpiece. Outer portion 11 of workpiece 10 engages profile tool D as roller R moves radially outward as described elsewhere in this specification. The part being formed is a gear having transversely oriented teeth 110. Teeth 110 are created by forming or flowing the metal of outer portion 11 into profile tool D. Pressure from roller R forces the gathered metal into the teeth and grooves of profile tool D.

[0040]
FIG. 5 is a top perspective view of a roller engaged with a workpiece. Workpiece 10 rotates in direction L. Outer roller rotates in direction S. Outer portion 11 of workpiece 10 is simultaneously engaged by roller R and outer roller OR. Roller R exerts a force FR on workpiece 10. Roller OR exerts a force FOR on a workpiece 10. Force FR and force FOR are substantially equal in magnitude and opposite in direction once both are engaged with outer portion 11. Roller R and outer roller OR each turn at a speed sufficient to result in substantially zero relative movement between roller R and outer roller OR at the point of engagement of each, P1 and P2, with outer portion 11. In this way metal that is moved outwardly by movement of roller R is formed into the toothed profile 200 of outer roller OR. This causes the metal to acquire a toothed profile as the workpiece 10 is rotated between roller R and outer roller OR.

[0041]
FIG. 6 is a top perspective view of a roller engaged with a workpiece. This is substantially similar to the forming process shown in FIG. 5 with the exception that outer roller OR has a multi-ribbed profile 300 for forming a multi-ribbed surface 301 on workpiece 10.

[0042]
FIG. 7 is a top perspective view of a roller engaged with a workpiece. This is substantially similar to the forming process shown in FIG. 1 and FIG. 2c. A multi-ribbed profile 12 is formed in workpiece 10.

[0043]
FIG. 8 is a top perspective view of a roller engaged with a workpiece. This is substantially similar to the forming process shown in FIG. 7 with the exception that profile tool D has a flat surface profile 400 for forming a flat surface 401 on workpiece 10.

[0044]
FIG. 9 is a top perspective view of a roller engaged with a workpiece. This is substantially similar to the forming process shown in FIG. 6 with the exception that outer roller OR has a flat surface profile 402 for forming a flat surface 401 on workpiece 10.

[0045] Although a single form of the invention has been described herein, it will be obvious to those skilled in the art that variations may be made in the construction and relation of parts without departing from the spirit and scope of the invention described herein.

METHOD OF TENSILE FLOW FORMING

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