US2952767A - Thermo stretch forming of metal - Google Patents

Description

Sept. 13, 1960 B. M. MALONEY THERMO STRETCH FORMING OF METAL Filed May 6, 1957 United States Patent G i THERMO STRETCH FORMING OF METAL Bartley M. Maloney, Torrance, Calif., assignor to Northrop Corporation, Hawthorne, Calif., a corporation of 'California Filed May 6, 1957, Ser. No. 657,341

1 Claim. (Cl. 2`19149) This invention has to do with the forming of metal .and more particularly with the forming of metal in a stretch vpress and using thermal units to heat certain essential structure.

Historically metal, both eX'trusions and sheet, annealed and hardened, has been formed on stretch presses for a good many years. However, in most instances the metal has been formed cold or at room temperature. The result of such procedure was that the inherent qualities of the metal resisted forming to accurate tolerances. Hardened metal, whether it is extruded or in sheet form has created therein, due to stretch forming, certain internal stresses and a certain resilience that results in a spring bac when formed in the cold state. The die, when the metal was formed cold, had to exaggerate the configuration desired in order to compensate for the spring back or resilience in the metal. This procedure of course could not be applied accurately for the reason that the spring back was extremely diiicult to predict and calculate. Therefore, it was necessary to perform hand forming or hammering operations, following the stretch forming, in order that the metal could be placed in a usable condition. This additional hand forming or hammering operation was particularly costly for the reason that each piece had to be done by hand and the time consumed was a decided cost elevating factor. Additionally, there was a definite number of pieces that had to be rejected because no amount of hammering or hand forming could place them in a usable condition.

An object of this invention is to provide structure that may be incorporated into a stretch press whereby hardened sheet metal or extrusions of metal may be heated to a predetermined temperature and at the same time the die, of the stretch press, may also be heated to the same temperature to provide a formed piece of metal that will be well within acceptable tolerances.

Another object of this invention is to provide structure for the thermal stretching of metal and at the same time provide structure for stopping the forming of metal at a predetermined moment in order that the formed piece will be well within acceptable tolerances.

A yet further object of this invention is to provide structure for the thermal forming of metal that is economical, easily installed on existing equipment and readily operated with a minimum of effort and a maximum benecial result.

Briefly the invention comprises a die having a controlled heating element or elements thereon; the metal to be formed has controlled heat applied to it; and a switch or switches are provided to stop the forming of the metal at the proper moment. This enumerated structure is applied to a conventional stretch press and related equipment.

Figure 1 is a perspective View illustrating certain structure schematically.

Figure 2 is a fragmentary, cross-sectional view taken on line 2 2 of Figure l.

P24,952,767 Patented Sept. 13, 1960 Figure 3 is a cross-sectional view similar to Figure 2, but illustrating another form of the invention.

Referring to the drawings for a more detailed description of the present invention 10` designates a stretch press die having a conventional configuration. The die is placed upon the bed or table 12 of the press and a captive holddown bolt or stud 14 is firmly applied to the die to prevent movement thereof during the forming operation.

Each conventional stretch press is provided with a pair of movable metal holding jaws 16, each of which may move in the manner and direction indicated by the arrows. It may be seen that the jaws may stretch and wrap the metal, to be formed, about the die.

Referring to Figures 1 and 2, the die 10 may have a plurality of holes therein into each of which, with one exception, is removably inserted a heater 18. The holes and the heaters are adjacent the working surface 20 of the die. Instead of there being a heater in one hole there is a heat sensing element 21 that is connected to a thermostat 22. Obviously each heater 18` is also connected to the same thermostat through leads 24. Power is supplied the thermostat through a generator 26.

The effect of the described structure is that the die 10 may be heated to a predetermined temperature and this temperature may be maintained through the entire operation.

The jaws 16 have inserted therein a strip of hardened metal or an extrusion 28 that is to be formed about the working surface 20 of the die 10. Over the metal material adjacent each end or each jaw' is a heater electrode 30. Power is supplied to the electrode by a resistance heater 32, having a thermostatic control.

The metal material 28 should be heated to the same temperature as that of the die 10.

Attention is directed to the fact that the die 10 and the material 28 are made of the same material and as a result there is the same identical heat of expansion.

The generator 26 may provide 110 volts and the resistance heater 32 may provide 440y volts. This feature is not to be considered a limitation for the reason that other generators and resistance heaters having a different potential may also be used.

Attention is directed to the well known fact that each hardened metal and metal alloy has a characteristic that permits the metal to be heated to a predetermined temperature which results in certain strains or internal stresses being eliminated when the metal is formed in a stretch press and the hardened condition retained. As a result the metal material may be stretched and wrapped and the metal will not spring back, but will assume and maintain the conguration to which it was formed.

Referring again to Figure l, a switch 34 is suitably located in relationship to each jaw 16. The switches are connected to the main power source, not shown, to provide a shut off of the stretch press when the jaws have reached a predetermined stretch and wrap position. As illustrated, two switches are shown, but obviously one switch would also be applicable.

Figure 3 illustrates a modified form of the heater systern. A groove 36 is provided in the die 10 adjacent the working surface 2l)` and an elongated strip-type conventional heater 38 is placed in the groove. In all other respects that form of the invention illustrated in Figure 3 is identical to that shown in Figures 1 and 2.

Attention is directed to the fact that the jaws and stretch press proper all are suitable and adequately insulated as at 40 and 42 respectively.

The operation of the invention is as follows: The hardened material 28 is inserted in the jaws 16. The electrodes 30 are placed over the material and the heaters 18 or heater 38 are properly located in the die 10. Heat is then applied to the material untila predetermined temperature is obtained that corresponds to the previously established and maintained temperature of the die. When this temperature vis reached the jaws are caused to be moved through'ther path of travel until the switch or switches 34 are actuated to de-energize the stretch press. The material 28 is then removed from the jaws 16 in the final form. There is absolutely no spring back as the result of this dened operation and forming procedure.

necessary.

While in order to comply with the statute, the invention has been described in language more or less specific as to structural features, it is to be understood that the invention is not limited to the specific features shown, but that the means and construction herein `disclosed comprise a preferred form of putting the invention into eifect, and the invention is therefore claimed in any of its forms or modifications Within the legitimate and valid scope of the appended claim.

What is claimed is:

In a stretch press having a die and a pair of movable,

No further hand forming or hammering is l spaced apart jaws that receive metal materials to be formed into predetermined shapes, the invention of which comprises a plurality of heaters removably received in openings in the die adjacent the periphery thereof; a controlled resistance heater removably attached to each end of said material; means for de-energizing said stretch press when said jaws have moved a predetermined distance; and electrical and heat insulating means on said 0 jaws and stretch press.

References Cited in the file of this patent UNITED STATES PATENTS 2,325,481 Crawford July 27, 1943 2,443,336 Waldie lune 15, 1948 2,493,679 Markey Jan. 3, 1950 2,513,739 ONeill July 4, 1950 2,676,229 Knight Apr. 20, 1954 2,783,363 Gunther et al Feb. 26, 1957 2,791,674 Westin May 7, 1957 2,808,501 Kilpatrick et al. L.-- Oct. vl, 1957

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