Method of making an end connection to a fluid power cylinder and product

A method of making an end connection to a fluid power cylinder and product wherein a hollow metallic cylindrical tubing is deformed into a step shape to conform to a channel shaped recess provided in the shank of the end cap.

BACKGROUND AND SUMMARY OF INVENTION 
This invention relates to a method of making an end connection to a fluid 
power cylinder and the product resulting therefrom and, more particularly, 
to a permanent connection wherein the component parts are integrated in 
such a fashion as to resist substantial shock forces tending to destroy 
the connection. 
This invention relates to that type of fluid power cylinder which has come 
to be designated "non-repairable". As such, the various components of the 
cylinder are permanently ingtegrated at the time of manufacture so that 
the resulting cylinders are relatively inexpensive and can be readily 
replaced -- as contrasted to being repaired. Although the cost of repair 
labor is high, it is still necessary to provide a relatively inexpensive 
cylinder unit which can be discarded after it has worn out, or otherwise 
failed. Since these cylinders often are in installations where they 
encounter impact loads at very high rates of cycling, it is of real 
importance to have the parts well integrated, particularly the end caps 
and the cylinder casing. Failure of this joint or connection could release 
the piston rod, for example, like a projectile with the capability of 
significant damage and possible injury to the persons in the vicinity. 
Thus, those in this art faced a dilemma; the parts had to be inexpensive 
and readily integrated on the one hand yet, on the other hand, the 
connection had to be rugged and strong enough to withstand the impact 
load. 
For many years the art has employed a simple technique of deforming (as by 
rolling) the end portion of the casing into a sloping-sided trough 
provided in the end cap, and thereafter peening (again as by rolling) a 
portion of the end cap over the rolled portion of the casing. This has 
been deemed inadequate by the workers in this art to withstand the severe 
and repetitive shock loads. For example, the well known construction 
referred to above was augmented by a clamping ring in U. S. Pat. No. 
3,811,367. Even this construction was deemed less than satisfactory 
because in a subsequent patent (U. S. Pat. No. 3,848,325) the encircling 
band was further rigidified through the use of annular ribs. 
I have discovered that the problem of satisfactory connection between the 
tubing and end cap can be advantageously solved through the use of a 
differently contoured trough -- more particularly an annular recess 
provided in the shank which has a channel shape so as to develop a 
pronounced right angled step in the casing end portion so as to provide 
the desired locking securement. According to the method of the invention, 
the aforementioned right angled step is developed through metal 
deformation (again as by rolling) but with the imposition of axial force 
on the tubing which results in the advantageous cold working and flow of 
metal from the casing into the area of the desired joint. 
Other advantages and objects of the invention may be seen in the details 
set down in the ensuing specification.

In the illustration given and with reference first to FIG. 1, the numeral 
10 designates generally a fluid power cylinder. The cylinder 10 includes a 
hollow metallic cylindrical tubing 11 which is open at the ends thereof. 
Slidably mounted within the tubing 11 is a piston 12 and extending to the 
right therefrom (in the illustration given) is a piston rod 13. 
The work end of the cylinder 10 is closed by an end cap 14 and the power 
end of the cylinder is closed by an end cap 15. Inasmuch as the 
connections between the end caps 14 and 15 in the tubing 11 are the same, 
only the connection between the end cap 15 and the tubing 11 will be 
described. However, it will be appreciated that for a cylinder to suitably 
withstand the severe cyclic shock loads, both ends must be equipped with 
connections of equal strength. 
Reference is now made to FIG. 2. There the end cap 15 is depicted only in 
fragmentary form -- as would be seen in a radial section through the axis 
common to the end cap 15 and the tubing 11. The end cap 15 is seen to be 
partially inserted into or received by the tubing 11 and the portion 
received or shank is designated by the numeral 16. The remainder of the 
cap (to the left in FIG. 2) is designated by the numeral 17. The shank 16 
has a diameter reduced relative to the portion 17 and therefore defines 
therewith a shoulder 18. The shank 16, immediately adjacent the shoulder 
18, is equipped with a channel-shaped, annular, inwardly-extending recess 
19. From a consideration of FIG. 2, it will be seen that the shank 16 has 
been positioned within the tubing 11 so that the end portion of the tubing 
11 overlies the recess 19 and abuts the shoulder 18. 
After this step of installation has been performed, the portion of the 
tubing 11 overlying the channel 19 is subjected to a deforming force 20 -- 
see FIG. 3. This is advantageously performed by suitable rolling apparatus 
of conventional design but I have found it further advantageous to arrange 
the apparatus so as to apply the force 20 at a minor acute angle 
relative to a radial line 21. Preferably, the angle is of the order of 
about 1.degree.. 
Inasmuch as the recess 19 is channel-shaped, i.e., characterized by 
substantially right angles, the deformation of the tubing 11 develops a 
similar configuration or right-angle step. This development, according to 
the invention, is accompanied by an axial force 22 simultaneously applied 
to the tubing 11 (again see FIG. 3). 
The simultaneous forcing of the tubing 11 against the shoulder 18 while 
inwardly deforming the tubing 11 into the recess 19 not only causes cold 
working of the metal of the tubing 11 but metal flow as well so that there 
is a substantial amount of metal in the right angled step 23. 
The final step in the formation of the joint or connection between the end 
cap 15 and the tubing 11 is illustrated in FIG. 4. There the numeral 24 
designates a rolling-type tool which develps a cut in the portion 17 of 
the end cap 15 -- and relatively close to the shoulder 18. This results in 
a tongue or lip-like integral projection 25 which overlies the right- 
angle step portion 23 and clamps the same to the shank 16. More 
particularly, the tongue 25 overlies the horizontal leg 26 of the right 
angle step 23 and firmly abuts the vertical portion 27 of the step 23. 
In the practice of the invention, the end caps 14 and 15 are advantageously 
provided of a suitable metal such as brass or anodized aluminum. The 
diameter of the end caps varies according to the size of the cylindrical 
tubing 11 and normally this will be available in a variety of sizes 
ranging from 1/4inches to 2-1/2inches in diameter of bore. The end caps 14 
and 15 are suitably machined to provide the reduced diameter shank 16 and 
the recess 19. 
The tubing 11 is advantageously constructed of suitable tubing materials, 
for example, type 304 stainless steel, and best results are obtained when 
this is in the 1/4 to 3/8 hard condition. Utilizing a harder stainless 
steel, as is achieved through a greater number of passes of the tubing 
through the drawing dies, can result in embrittlement and possible 
cracking in the area of the right-angle step 23. It has been found 
advantageous to preserve a degree of ductility in the stainless steel 
tubing 11 by limiting the hardness within the range of about 1/4 to about 
3/8 hard condition. 
Although the mechanism by which the invention works is imperfectly 
understood, it is believed that the simultaneous application of radial and 
axial forces to the end portion of the somewhat ductile tubing 11 results 
in an advantageous cold working and metal flow to develop a conforming 
step in the tubing end portion which has substantial strength in resisting 
the destructive shocks encountered in the use of the cylinder 10. Further, 
the pronounced step provides a dual anchor for the tongue 25 in both 
overlying and clamping the horizontal leg 26 and by abuting and clamping 
the vertical leg 27.