US3583191A

US3583191A - Compressive straightener

Info

Publication number: US3583191A
Application number: US798908A
Authority: US
Inventors: Raymond E Colonius; George L Andersen; John E Nohren Jr
Original assignee: Cargill Detroit Corp
Current assignee: Cargill Detroit Corp
Priority date: 1969-02-13
Filing date: 1969-02-13
Publication date: 1971-06-08
Anticipated expiration: 1988-06-08
Also published as: DE2006728B2; DE2006728A1; GB1270883A; FR2031400B1; DE2006728C3; FR2031400A1

Abstract

The invention pertains to the cold straightening of long slender parts made of brittle and hard materials such as grey cast iron camshafts. Beam loading in a straightening machine will ordinarily cause tensile failure of such a part if straightening is attempted. The invention provides for compressive column loading of the part so that the neutral axis of the part is moved towards the opposite outermost fibers as the beam loading is applied. Thus, the tensile stress may be minimized or eliminated while the compressive stress in the outermost fibers of the side towards the beam loading increases beyond the compressive yield strength and plastic strain occurs. The part will be plastically deformed and possess a statistically balanced internal residual stress distribution when the loading is released. The invention provides for rotation of the part as the beam loading is released resulting in cyclic plastic deformation and relaxation for all the outermost fibers about the desired axis. A brittle material such as grey cast iron that has a significantly larger plastic range in compression than in tension may be successfully straightened in this manner.

Description

United States Patent [72] inventors Raymond E. Colonlus Bloomfield Hills, Mich.; George L. Andersen, Columbus, Ohio; John E. Nohren, J r., Birmingham, Mich. [211 Appl. No. 798,908 [22] Filed Feb. 13, 1969 [45] Patented June 8,1971 [73] Assignee Cargill Detroit Corporation [54] COMPRESSIVE STRAIGHTENER 30 Claims, 14 Drawing Figs.

[52] US. Cl. 72/110, 72/80, 72/1 11, 72/383 [51] Int. Cl. 821d 3/02 [50] Field of Search 72/80, 94, 110, 111,381,383

{56] Reierenees Cited UNITED STATES PATENTS 624,019 5/1899 Harrington 72/381 3,113,608 12/1963 Puyear 72/110 3,213,659 10/1965 Armstrong 72/80 Primary Examiner-Lowell A. Larson AttorneyFarley, Forster and Farley ABSTRACT: The invention pertains to the cold straightening of long slender parts made of brittle and hard materials such as grey cast iron camshafts. Beam loading in a straightening machine will ordinarily cause tensile failure of such a part if straightening is attempted. The invention provides for compressive column loading of the part so that the neutral axis of the part is moved towards the opposite outermost fibers as the beam loading is applied. Thus, the tensile stress may be minimized or eliminated while the compressive stress in the outermost fibers of the side towards the beam loading increases beyond the compressive yield strength and plastic strain occurs. The part will be plastically deformed and possess a statistically balanced internal residual stress distribution when the loading is released. The invention provides for rotation of the part as the beam loading is released resulting in cyclic plastic deformation and relaxation for all the outermost fibers about the desired axis. A brittle material such as grey cast iron that has a significantly larger plastic range in compression than in tension may be successfully straightened in this manner.

PATENTED Jun 8 ml SHEET 1 [IF 6 INVENTORS [I PAWO/VO COIO/V/US R Mr M W A T TORNEVS sum 2 or 6 PATENTEU Jun 8 m A T TORNEYS PATENTEU JUN awn 3583191 sum 3 or 6 SOL 50L. |F

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Ls chm L5 71 L5 EHHfi-Ls 7 INVENTORs u /Maw;

A 7'7'ORNEVS STRESS PATENIEDJUN am i FIG.9

1Z0 STEEL STRESS SHIET 5 UF 6 F i G '7 .36 5'- i a 1.9 X g r I I I lll GRAY IRON STRAIN STRAIN INVENTORJ RAY/"0N0 1 C01 O/V/US ATTORNEYS PATENTEDJUN 8i97l SHEET 8 OF 6 COMFRESSIVE STRAIGEITENER BACKGROUND OF THE INVENTION Relatively long and slender parts made of ductile materials are easily straightened because their tensile strength and compressive strength are usually about equal and well above the stress necessary to cause permanent deformation of the material. Simple beam loading may be used to straighten such a part since high tensile stresses in the plastic range may be tolerated. Rotation of the part as the beam loading is released will eliminate the need for determining the proper rotational orientation necessary for straightening.

As applied to a rotating ductile shaft the beam loading will result in a cyclic plastic deformation in tension and in compression as the shaft turns. The shaft will be straightened if sufficient beam loading is applied to stress the outermost fibers into the plastic strain region and gradually released as the shaft continues to turn. However, in the case of a brittle or hard material sufficient beam loading to cause plastic strain in the outermost fibers will often result in tensile failure of the shaft. With most brittle and hard materials only a very slight plastic strain in tension may be accommodated. Therefore, only a slight amount of straightening is possible. Some brittle materials may be hot straightened to a greater extent than cold straightening allows. However, parts that require more extensive straightening than the above methods will allow usually must be scrapped.

SUMMARY OF THE INVENTION The invention is an improvement that may be incorporated into a basic straightening machine for straightening ductile parts by rotating them and applying a beam loading that is gradually released as the part rotates. In one form of straightening machine the part rests on rollers near each end and the part is driven by a chuck at one end that is free to accommodate changes in the deflection angle of the longitudinal axis of the part at that end. Near the center of the part a ram with rollers applies a bending load to the part as the part revolves. The load initially is sufficient to cause plastic deformation in the outer fibers of the part cyclically as the part revolves. The ram is then gradually retracted resulting in a relaxation of the cyclic loading. The initial loading preferably is sufficient to cause a deflection in the part from its nominal neutral axis equal or greater than the plastic yield point of a straight part.

The invention replaces the supporting rollers near each end with compression thrust bearings at each end of the part. The bearings are free to accommodate changes in the deflection angle of the longitudinal axis of the part at each end. The bearings will accommodate both transverse loads and longitudinal loads. A framework connects the stationary portions of the bearings and incorporates an hydraulic cylinder to apply a force to one of the bearings such that the part can be compressively loaded as a column between the bearings. The other end bearing incorporates a through shaft in the moving part of the bearing to rotate the part. A universal joint connects the through shaft to an hydraulic motor. The part is loaded to an amount just below theoretical column failure. In addition, pairs of rollers are provided along the part and resiliently supported by an amount sufficient to prevent buckling of the part. Just before the column loading is applied the ram is also positioned close to the shaft to prevent buckling. With the column loading applied and the shaft rotating the ram now moves and applies a load sufficient to cause a deflection in the shaft from its nominal neutral axis equal or slightly greater than the plastic yield point of a straight shaft. The ram then retracts gradually as above.

A combination of column and bending loading shifts the neutral axis of the stress distribution in the same direction as the deflection. Therefore, the proper chosen values of bending and compressive column loading will eliminate or minimize tensile stress in the shaft. Thus a shaft, such as a camshaft made of grey cast iron may be plastically strained in compression without subjecting the shaft to tensile stresses. As the shaft turns, the outermost fibers will cycle through a maximum compressive stress resulting in plastic strain and as the ram retracts this maximum compressive stress will reduce, the cycling strain will tend to reduce and the part will tend to relax into a straightened position with an internal statistically balanced stress distribution. The stiffness of the resiliently loaded rollers along the shaft must be sufficient to prevent buckling but flexible enough to allow the necessary deflection caused by the ram. The part to be straightened need only be cylindrical in cross section at the locations where the rollers touch the part. Therefore, in the case of a camshaft, the camshaft bearing locations may be used and in the case of a part that does not have any cylindrical cross sections, cylindrical collars may be fitted over the part such that they are concentric with the axis of rotation desired. The invention may also be usefully employed for straightening notched parts where a tensile stress at the base of the notch would result in failure.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view of a straightening machine fitted and adapted for compressive column loading of a part;

FIG. 2 is a fragment cross section taken along the lines 2-2 of FIG. 1;

FIG. 3 shows the bearing assemblies at each end of the part loaded in the machine;

FIG. 4 shows the centering and driving means applied to the driven end of the rotating part;

FIG. 5 is a schematic of the hydraulic and pneumatic circuits for the machine;

FIG. 6 is a schematic of the electrical control circuit for the machine; 4

FIG. 7 shows a modification utilizing a cylindrical collar around a noncylindrical part;

FIG. 8 is taken along the line 8-8 of FIG. 7;

FIG. 9 is a representation of a typical tensile stress-strain diagram for three engineering materials;

FIG. 10 is a representation of a tensile and compressive stress-strain diagram for two engineering materials that may utilize the present invention to advantage;

FIG. I! is a schematic of a part showing the cross-sectional orientation of the stress distributions shown in FIGS. 12-14;

FIGS. 12a-12j are idealized stress distributions under a combination of specified loading for a material with a definite yield strength.

FIGS. l3a-l3j are idealized stress distributions under a different combination of specified loading for a material with a definite yield strength; and

FIGS. 14d14j are idealized stress distributions under a combination of specified loading for a material with virtually no elastic range.

FIGS. l4d-Mj are idealized stress distributions under a combination of specified loading for a material with virtually no elastic range.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. I a machine frame 11 supports an overhead member 12 which in turn supports the ram assembly 13. The ram assembly 13 is actuated by the ram 14 of an hydraulic cylinder 15. The ram assembly 13 is kept in proper alignment by the guide cylinders 16 sliding in guides 17. Attached to the ram assembly are one or more roller assemblies 18 and rollers 19. The rollers 19 contact the cylindrical portions 20 of the part to be straightened 21. Just below the part to be straightened 21 are rollers 22 that are mounted on one or more air cylinders 24. The part 21 is held between bearing and spindle assemblies 26 and 27 and rotated by a motor and gear box 25 through a flexible coupling at 28. Each bearing and spindle assembly 26 and 27 is mounted on the bed of the machine 29 and kept in proper alignment by tie rods 30. An hydraulic cylinder 31 for applying an axial load to the part 21 is fastened to the rods 30 and the rods 30 are fastened to the bearing and spindle assembly 26 so as to provide the proper reaction force at the other end of the part 21.

ln FIG. 2 a roller assembly 18 mounted on the ram is shown with paired rollers 19 in contact with a cylindrical portion 20 of a part 21. Below the part 21 is another pair of rollers 22 mounted on an air cylinder 24. The rollers 22 are also in contact with a cylindrical portion 20 of the part 21. Alignment guides and stops 32 are also provided for the rollers 22.

In FIG. 3 the left-hand bearing and spindle assembly 26 and the right-hand bearing and spindle assembly 27 are shown in cutaway detail. The left-hand spindle 35 is driven by a coupling at 28 and revolves in the roller bearing 36. In the right-hand bearing and spindle assembly 27 the spindle 37 rotates in a similar bearing 38. Since the part 21 is squeezed between the spindles 35 and 37 and loaded by the ram through the rollers 19, the bearings 36 and 37 and loaded by the ram through the rollers 19, the

bearings

36 and 38 are specially made to accept both the axial loading, the transverse loading and the slight angular deflection of each spindle 35 and 37 due to the beamwise deflection of the part 21. The hydraulic cylinder 31 by means of the piston 39 and cylindrical yoke 40 acting against the bearing holder 41 provides for the axial loading to the part 21. The spindle 37 is fastened to a retainer 42 by means of a bolt 43. The retainer 42 is guided by the spherically shaped back surface 48 of the bearing holder 41. Similarly, the left-hand spindle 35 is held in place by a retainer 44 and collar 45. The collar 45 is held in place by means of a setscrew 46 and the retainer 44 slides on a spherical back surface 49 of the bearing holder 47.

The configuration of the spindles 35 and 37 depends upon the means used to attach the part 21 and the means used depends upon the configuration of the part 21. Illustrated here the part 21 is a camshaft. The cylindrical right-hand end 50 of the camshaft fits into a socket 51 of the spindle 37. The spindle 35 transmits rotational torque to the left end 52 of the part 21. More particularly, in H6. 4 a live center 53 actuated by a spring 54 is incorporated into the spindle 35. Surrounding the live center 53 and attached to the spindle 35 is a hardened disc 55 having a toothed edge 56 attached. Upon application of the axial force to the part 21 the toothed edge 56 will be driven into the left-hand end of the part 52 sufficient to transmit the necessary rotational torque to the part 21.

in FIG. a constant speed electric motor 60 drives two pressure-controlled variable flow

hydraulic pumps

61 and 62. The hydraulic pump 61 provides hydraulic power for the spindle drive 25 by means of a fluid motor control circuit 63 and three-position solenoid control valve 64. The hydraulic pump 62 supplies hydraulic power for the axial compression cylinder 31 and ram cylinder 15. The movement and location of the piston 39 in the axial compression cylinder 31 is determined by the solenoid operated three-position valve 65 in a low-pressure circuit controlled by the pressure valve 66. The high pressure circuit 67 supplies hydraulic power to the ram cylinder and ram 14. The three-position solenoid-operated valve 68 controls the rapid up and rapid down motion of the ram assembly when the ram assembly is not in contact with the part. The motion of the ram assembly when the ram assembly is in contact with and applying a load to a part is controlled by the three-position solenoid-operated valve 69. The flow rate of hydraulic fluid is controlled by the reversible, variable restrictions 70. Limit switches 71 actuated by the ram 14 control the operation, through the electric circuitry shown in FIG. 6, of the various control valves in the hydraulic circuit. Returning to FIG. 5 the control 72 releases pressure in the high-pressure circuit 67 when the ram 14 is in its uppermost position. Lastly, the air cylinder 24 is supplied with compressed air through the circuit 73 including a pressure control 74. The pressure setting in the pressure control 74 is sufficient to apply a load to the part 21 to prevent buckling when the part is under compressive loading and provides a resilient air spring action when the ram assembly 13 is applied to the part 21 as shown in FIG. 1.

In FIG. 6 the power circuit provides electrical power for the hydraulic pump motor 60 and the transformer 81. The transformer 81 provides electrical power for the secondary control circuit 82. In the following description of the secondary control circuit the sequential operation of the various parts of the compressive straightener will become apparent. Closure of the starting switch 83 completes the subcircuit 84 thus energizing the relays l-M and CRM. Relay 1-M completes the circuit through the hydraulic pump motor 60 and relay CRM completes the control circuit to the rest of the subcircuits. Closure of the switch 85 completes the subcircuit 86 energizing the relay 1 CR. The relay 1 CR completes the subcircuit through the solenoid valve 64 thus turning on the spindle drive. Closure of the switch 87 completes the subcircuit 38 energizing the relay 2 CR which in turn will allow the automatic cycle to begin. Subcircuit 89 is now energized; therefore, relay 3 CR will energize subcircuit 101. Subcircuit 101 will energize the solenoid valve 68 and the ram will lower rapidly to a positionjust above the part. At this point the limit switch 2 LS will open the subcircuit 89 deenergizing the solenoid valve 68 to stop the ram and close the subcircuit 90 thus energizing relay 4 CR. Relay 4 CR will close the subcircuit 102 and energize the solenoid valve 65 thus compressing the part 21 under column loading. When the hydraulic pressure in the compression circuit reaches a predetermined amount, the pressure switch 1 PS will close thus completing the subcircuit 91 and energizing the relay 5 CR. The relay 5 CR thereupon completes the subcircuit 103 through the solenoid valve 69 and the ram feeds downward a predetermined amount to apply the proper beam load to the part. The limit switch 3 LS will close at this full depth point and complete the subcircuit 92 energizing the relay 6 CR. Subcircuit 91 will thus be opened and subcircuit 93 will be closed energizing relay 7 CR. Relay 7 CR will energize the subcircuit 104 and reverse the solenoid valve 69 thus allowing the ram to raise slowly at a predetermined rate. The feed rate as the ram withdraws will be such that all portions of the part undergo cyclic stress several times as the part revolves. Limit switch 4 LS which is open during ram feed closes as the ram just clearsthe part and completes subcircuit 94 energizing timed relay 1 TR which thereupon breaks circuit 93 stopping the ram. The timed relay 1 TR also completes the subcircuit 105 through the solenoid valve 65 which allows the column loading to be released. Upon release of the column loading, the timed relay 1 TR completes the subcircuit 95 energizing relay 8 CR. Relay 8 CR then energizes the subcircuit 106 thus energizing the solenoid valve 68 and the ram raises rapidly back up to its beginning position. At this point the limit switch 1 LS is reopened and the subcircuit 88 is broken. With the subcircuit 88 broken the relay 2 CR is deenergized and the subcircuits 89 through 95 are opened again. Since subcircuit 92 is now opened relay 6 CR is deenergized and subcircuit 88 is now in its initial condition such that a closure of switch 87 will again start the cycle all over for the next part. Where automatic loading and unloading of the compressive straightening machine is provided in a conventional manner the switch 87 may be automatically closed when the next part is placed in the machine. In such an installation the spindle drive may continue during the load and unload cycles by utilizing spindles conventional in the art that will completely release the part when the compression is released.

FIGS. 7 and 8 illustrate a modification for a long slender part that is noncylindrical in cross section. Shown here is an 1- section 21a. Modified spindles 35a and 37a are provided for gripping the ends of the l-section. One or more collars 110 having a cylindrical outer surface 200 and a suitable configuration 20b for gripping the surface of the l-section 21a may be provided and locked into place by the setscrew 111 prior to loading in the compressive straightening machine. Thus, an irregular shape may be rotated in the compressive straightening machine with the air cylinder rollers 22 and ram rollers 19 utilized.

In FIG. 9 three typical tensile test results for metals are illustrated. Curve 1211 is a typical result for a low-carbon steel with definite elastic and plastic regions. Curve 1121 illustrates a smooth blending of the elastic and plastic regions for a ductile iron. Likewise, curve 123 for grey cast iron indicates a smooth blending of plastic and elastic regions. However, in the case of grey cast iron, the elastic region is only very limited and the ultimate strength in tension for grey cast iron is relatively much less than in the case of steel or ductile iron. Therefore, plastic deformation of grey cast iron in tension is greatly limited and the straightening of a grey iron bar with a simple bending load is usually impracticable. Most ductile materials exhibit curves similar to 120 or 121 both in tension and in compression. Therefore, simple beam loading will straighten a bar made ofa ductile material. The present invention takes advantage of the fact that some engineering materials such as grey cast iron exhibit a much higher strength in compression than they do in tension. Such materials may be deformed to a greater extent under compression loading with a higher compression stress.

In FIG. 10 typical curves for engineering materials that may successfully utilize the present invention to advantage are shown. Curves 125, 1126 and 127 illustrate a material that has an ultimate strength in compression significantly greater than the ultimate strength in tension and a significantly large elastic region 127. Most important, however, to the usefulness of the present invention as applied to this material is the fact that the plastic region in compression given by 125 is much larger than the plastic region in tension shown by 126. Thus, a bar under compressive stress only, may be deformed or straightened to a much greater extent than if a portion of the bar is under a severe tensile stress. Simple beam loading would provide essentially the same compressive stress in the outer fibers of the bar as tensile stress. The present invention overcomes this problem by allowing an increase in the compressive stress and at the same time providing a decrease or elimination of the tensile stress in the bar. Thus the bar may be deformed to an extent that would be impossible without tensile failure if simple beam loading were used. Curves 128, I29 and 130 illustrate a material having a very limited elastic range 130 but again an ultimate strength in compression significantly greater than the ultimate strength in tension and a plastic region in compression 128 significantly greater than the plastic region in tension 129. The selection of compressive load and bending load to straighten a bar will depend upon the material and the configuration of the bar. The compressive load applied to the ends of the bar will subject the bar to column loading; therefore, the possibility of elastic buckling due to the column loading must be considered. Where elastic column failure is likely to occur at a compressive loading value insufficient to provide sufficient compressive stress to allow the straightening operation to be performed, the present invention provides for lateral support along the column. In FIG. I the air cylinders 24 provide lateral support through rollers 22 to the part 21 and the positioning of the ram assembly 13 with the rollers 19 just contacting the part 21 also provides lateral support when the compression load is applied. The material and the slendemess ratio of the part 21! will determine how many of the roller assemblies l8 and air cylinders 2 will be necessary to prevent column buckling of the part 21. With column buckling thus prevented sufficient compressive load can be applied to the part such that the compressive yield strength may be as closely approached as desired. Since the slope of the stressstrain curve is much less in the plastic region as shown by curves 125 and 128 in FIG. 10, the bending load necessary to provide a sufficiently large deformation in the part is much less than would be necessary if the compression loading was not used. An additional factor in the reduction of the necessary bending load is caused by the release of compressive elastic energy in the portion of the part where the compressive column stress is reduced by the application of the bending load. This release of energy tends to offset the compressive energy necessarily added to the portion of the part where the compressive stress is increased by the bending load. A significant reduction in the necessary bending load has been found in the case of grey cast tron.

The idealized stress distributions shown in FIGS. 12, 13 and 14 pertain to the cross section shown in FIG. 11. The bending load 139 is shown imposed at this cross section. The compression load is distributed evenly over the cross-sectional area. FIG. 12a depicts the stress distribution due to column loading alone that may be found along the line 145. In this case the stress due to compression is assumed to be about three-fourths of the yield strength in compression. FIG. 12b depicts the normal stress distribution along the line 145 due to the bending load 139 alone. The maximum is assumed here to be approximately one-half of the yield strength in compression. The resultant normal stress for a perfectly elastic material is depicted in FIG. 120. However, for a material, such as that shown in curves -127 of FIG. 10, the resultant normal stress distribution along the line 145 will be more nearly that shown in FIG. 12d. If the bending load is now removed the stress distribution along the line 145 will be that shown in FIG. 12]. Removal of the compression load now will result in an internal residual stress distribution as shown in FIG. 12c. Since the bar has been plastically deformed in the upper portion only with the maximum deformation occurring at the point 140 the bar will have been bent along its length without any tensile loading having been applied at any cross section of the bar. Thus, a curved bar may be straightened in this manner. However, the initial curvature with respect to circumferential location must be known so as to position the bar properly prior to straightening. In the present invention, however, the bar may be rotated so that the initial curvature of the bar does not need to be determined prior to straightening. After both the compression and bending loads are applied and the stress distribution approximates that shown in FIG. 12d, the bar continues to rotate in the direction 144 and as it rotates 90 such that the line 145 coincides with the line 146, the stress distribution shown in FIG. 12f will occur along this line. Since this distribution is now along the neutral axis of the bar, it is under compression loading only, but the normal stress distribution shows the effect of the plastic deformation previously. A further rotation of 90 in the direction 144 will result in a normal stress distribution as shown in FIG. 123 along the line 145. This stress distribution is the result of the summation of the bending stress distribution and the stress distribution as shown in FIG. 12f reversed since the bar is now from its original starting position. A further 90 rotation in the direction 144 of FIG. 11 brings the line 145 again into the position of line 146 but in the opposite direction along the neutral axis and the normal stress distribution is that as shown in FIG. 12):. Finally, after one full revolution, the normal stress distribution will be that as shown in FIG. 121' and the bar will have undergone plastic deformation throughout the cross section. In the case of a bar that was curved along its axis prior to the loading and rotation, the plastic deformation in the fibers of the bar having the greatest radius of curvature will be more extensive than the plastic deformation in the outer fibers of the bar having the least radius of curvature. Therefore, the bar will be straightened by this method. In the practice of this invention the rotation of the bar continues as the bending load is gradually removed, thus the cyclic plastic deformation will diminish with each cycle and when the bending load is finally removed the bar will be substantially straight and will have an internal stress distribution approximately that shown in FIG. l2j when the compression loading is released. The residual stress distribution will be skewed toward the portion of the bar whose fibers initially have the largest radius of curvature prior to the straightening of the bar.

with a sharp division between the elastic and plastic regions at the yield strength, the normal stress distribution will be more like that shown in FIG. ll ld. FIG. 13f indicates the normal stress distribution with release of the bending load and FIG. 13c shows the residual stress distribution with the release of the compression load. If the bar is again rotated under the combined loading in direction 144 as shown in FIG. 11 to the 90 point such that line M coincides with line 146, the stress distribution along the normal axis will also be that shown in FIG. 13f. A further rotation of 90 will result in the stress distribution shown in FIG. 13g. Similarly, in FIG. 13h the line 145 will coincide with the line I46 but in the opposite direction and the stress distribution along the neutral axis will be that as shown. Finally, after one full rotation, the normal stress distribution along the line M5 will be that as shown in FIG. l3i'. As the bar continues to rotate and the bending load is gradually removed, the final stress distribution will be ap proximately that shown in FIG. l3] after release of the compression loading. Again, the residual stress distribution will be skewed toward the portion of the bar whose fibers initially have the largest radius of curvature prior to the straightening of the bar.

In the case of material such as grey cast iron, having the stress-strain curves of l28-l30 as shown in FIG. 10, the resultant stress distribution along the line M5 will be that shown in FIG. 14d. The normal stress distribution will be curved since the stress-strain curve for grey cast iron is nonlinear throughout almost its entire range. Some plastic deformation will therefore occur throughout the cross section of the bar at all times. This plastic deformation in the case of grey cast iron is commonly termed set" and with the elimination of the tensile stresses much higher compressive stresses may be applied to the grey cast iron bar thus allowing larger deformation to occur. FIG. Mf indicates the stress distribution inside the bar after the bending load is released and FIG. Me indicates the residual stress distribution if the compressive loading is released after the bending load is released. However, again, if the bar is rotated 90 under the combined loading, FIG. 14f indicatesthe normal stress distribution along the line 145 which now coincides with the line 146 in FIG. II. A further rotation of 90 in the direction 1144 will result in the stress distribution as shown in FIG. Mg for the line 145. The plastic deformation again takes place along the full length of the line 145 because of the almost totally nonlinear character of the stress-strain curve for cast iron in compression. Again, in FIG. 14h the stress distribution after 270 of rotation is shown and finally the stress distribution after 360 of rotation is shown in FIG. Mi. Subsequent rotation of the cast iron bar as the bending load is gradually removed will result in a residual stress distribution across the bar as shown in FIG. ldj for all diameters of the cross section. This final stress distribution will be skewed as before in the direction of those external fibers that have the greatest radius of curvature for the cast iron hair before the bar was straightened.

In the case of a 1 inch nominal diameter and inch long grey cast iron camshaft the present invention has allowed straightening to within 0.015 inch of the theoretical true axis where the center of the shaft was up to 0.400 inch off the theoretical true axis for a straight camshaft. Previously, without the compressive loading cold straightening was limited to those shafts with an axis that was less than 0.075 inch off from the theoretical true axis at the center. Attempts to cold straighten such shafts without compressive loading that were more than 0.075 inch off resulted intensile failure of the camshaft due to the bending load which caused severe tensile stresses in the outer fibers of the camshaft. I-lot straightening has allowed the straightening of camshafts up to 0.200 inch off the theoretical true axis. However, all shafts with a greater curvature have had to be scrapped until the present invention.

As an example of a typical run of production parts 40 l-inch diameter 20-inch long grey cast iron camshafts which had bowed conditions at two spaced bearings averaging 0.0685

inch and 0.0835 inch off true axis respectively were straightened by the apparatus and method disclosed herein to an average of within 0.067 inch and 0.0088 inch of the true nominal axis respectively.

We claim:

1. A part-straightening machine comprising means for applying a longitudinal compressive load on a part and means for simultaneously applying a transverse bending load on said part.

2. A. part-straightening machine as set forth in claim 1 including means for changing the effective plane of bending while said part remains under said compressive load and said transverse load.

3. A part-straightening machine as set forth in claim 1 including support means substantially at each end of a part.

4. A part-straightening machine as set forth in claim 3 including end support means adapted to accommodate part axis deflection.

5. A part-straightening machine as set forth in claim 3 wherein at least one of said end support means can move axially with respect to the other.

6. A part-straightening machine as set forth in claim 4 including intermediate support means adapted to resist buckling from the compressive loading.

7. A part-straightening machine as set forth in claim 6 wherein said intermediate support means includes resiliently supported means adapted to contact deflected portions of a part.

8. A part-straightening machine as set forth in claim 7 wherein said resilient means includes rollers grouped in pair with each roller of a given pair in substantially the same axial location with respect to a part.

9. A part-straightening machine as set forth in claim 7 wherein said resilient supports include air springs.

10. A part-straightening machine as set forth in claim 6 wherein said transverse load means is applied at the longitudinal position of said intermediate support means.

ll. A part-straightening machine as set forth in claim I incorporating means to rotate a part simultaneously with the application of said transverse and said compressive loads.

12. A part-straightening machine as set forth in claim 11 wherein said transverse load means incorporates a ram as sembly and one or more rollers mounted on said ram assembly arranged to contact cylindrical portions of a part upon extension of the ram assembly.

l3. A part-straightening machine as set forth in claim 12 wherein said rollers are grouped in pairs with each roller ofa given pair in substantially the same axial location with respect to a part.

Ml. A part-straightening machine as set forth in claim 11 including and support means, spindle bearings in said end support means. spindles rotatably mounted in said spindle bearings and concentrically contacting each end of a part.

15. A part-straightening machine as set forth in claim 14 wherein said spindle bearings are adapted to transmit said compressive load.

16. A part-straightening machine as set forth in claim 15 wherein each spindle bearing is adapted to accommodate a changeable deflection angle in the axis of a part.

17. A part-straightening machine as set forth in claim 14 wherein at least one spindle includes means to transmit rotational torque to a part.

18. A part-straightening machine as set forth in claim 14 wherein at least one spindle includes means to center a part.

19. A part-straightening machine as set forth in claim 11 wherein said rotational means includes cylindrical collar means concentric with the axis of a part cross section.

20. A part-straightening machine as set forth in claim 1 wherein said means to apply a compressive load includes a fluid pressure actuated cylinder.

21. A part-straightening machine as set forth in claim 1 incorporating control means to establish a predetermined transverse and compressive load application and release sequence such that the neutral axis of the stress distribution will shift in substantially the same direction as the deflection and the maximum compressivestress will cause plastic deformation in a part.

22. A method for bending parts composed of material with a greater range of compressive than tensile plastic deformation and comprising the steps of: applying a longitudinal compressive load which per se produces a compressive stress which does not exceed the elastic limit of the material; applying a transverse bending load, said bending load in combination with said compressive load providing a maximum compressive stress exceeding the elastic limit of the material while restricting the maximum tensile stress to a relatively lower value than said maximum compressive stress; and releasing said compressive and bending loads.

23. A method for straightening parts comprising the steps of: applying a longitudinal compressive load which per se produces a compressivestress which does not exceed the elastic limit of the material; applying a transverse bending load, said bending load in combination with said compressive load providing a maximum compressive stress exceeding the elastic limit of the material; and releasing said compressive and bending loads.

24. The method of claim 23 applied to parts having a greater range of compressive than tensile plastic deformation.

25. The method as set forth in claim 24 applied to cast iron.

26. The method as set forth in claim 23 applied to relatively long slender parts.

27. The method as set forth in claim 26 including the provision of sufficient lateral support to prevent buckling failure of said parts under said compressive load.

28. The method as set forth in claim 23 applied to notched parts.

29. The method as set forth in claim 23 including the rotation of said parts a sufficient number of revolutions during the application of said bending load and release of said bending load to insure sufficient permanent deformation and relaxation around the circumference of said parts to straighten said parts.

30. The method as set forth in claim 23 wherein the level of compressive load applied is sufficient to prevent tensile stresses above the elastic range in any outer fibers of said parts.

Claims

2. A part-straightening machine as set forth in claim 1 including means for changing the effective plane of bending while said part remains under said compressive load and said transverse load.

11. A part-straightening machine as set forth in claim 1 incorporating means to rotate a part simultaneously with the application of said transverse and said compressive loads.

12. A part-straightening machine as set forth in claim 11 wherein said transverse load means incorporates a ram assembly and one or more rollers mounted on said ram assembly arranged to contact cylindrical portions of a part upon extension of the ram assembly.

13. A part-straightening machine as set forth in claim 12 wherein said rollers are grouped in pairs with each roller of a given pair in substantially the same axial location with respect to a part.

14. A part-straightening machine as set forth in claim 11 including end support means, spindle bearings in said end support means, spindles rotatably mounted in said spindle bearings and concentrically contacting each end of a part.

21. A part-straightening machine as set forth in claim 1 incorporAting control means to establish a predetermined transverse and compressive load application and release sequence such that the neutral axis of the stress distribution will shift in substantially the same direction as the deflection and the maximum compressive stress will cause plastic deformation in a part.

23. A method for straightening parts comprising the steps of: applying a longitudinal compressive load which per se produces a compressive stress which does not exceed the elastic limit of the material; applying a transverse bending load, said bending load in combination with said compressive load providing a maximum compressive stress exceeding the elastic limit of the material; and releasing said compressive and bending loads.

25. The method as set forth in claim 24 applied to cast iron.

28. The method as set forth in claim 23 applied to notched parts.