US2719443A

US2719443A - Drop hammer

Info

Publication number: US2719443A
Application number: US342523A
Authority: US
Inventors: Derbyshire Charles Frederick
Original assignee: Rohr Aircraft Corp
Current assignee: Rohr Inc
Priority date: 1953-03-16
Filing date: 1953-03-16
Publication date: 1955-10-04
Anticipated expiration: 1972-10-04

Description

Oct. 4, 1955 c. F. DERBYSHIRE DROP HAMMER 2 Sheets-Sheet 1 Filed March 16, 1953 INVENTOR C. F. DERBYSHWJE Oct. 4, 1 955 c. F. DERBYSHIRE DROP HAMMER 2 Sheets-Sheet 2 Filed March 16, 1953 INVENTOR. C. F. DERBYSHIRE .QZL V W United States Patent DROP HAMlVIER Charles Frederick Derbyshire, Chula Vista, Califi, as-

signor to Rohr Aircraft Corporation, Chula Vista, Calif., a corporation of California Application March 16,.1953, Serial No. 342,523

Claims. (Cl. 78-25) This invention relates to drop forging and more especially to the construction of the ram which supports the movable die of a drop forging machine.

The rams of such machines are usually made massive to deliver a powerful blow when dropped from a height and are provided with a generally rectangular shaped base having a fiat bottom face to which the movable die is bolted. This base is usually made thick and con nected to the upper portion of the ram by a plurality of spaced apart, parallel ribs which merge into the base near its longitudinal edges, the top faces of each rib sloping in toward the center of the ram. It has been the practice to make such supporting ribs and the hammer base all in one piece as an iron casting and to make the ribs relatively thick to add mass to the ram.

This construction provides a heavy ram capable of delivering a powerful blow to the workpiece struck by the die carried by the ram but in practical use it has been found than tensile stresses are developed in the rams which cause them to crack and even break apart after a short period of use. This is especially true when adie of substantially less size than the base of the ram is used, the upper die and the portion of the ram directly over it being stopped almost instantaneously by the workpiece and lower die but the momentum of the edge portion of the ram which projects beyond the upper die keeps this portion moving for a brief period after the main body portion of the ram has come to rest. This momentum sets up tensile stresses within the ram casting which oppose the further movement of its edge portion and finally bring the edge portion to rest. Cast iron is relatively weak in tension and relatively strong in compression. It has been found that these tensile forces cause cracks to develop in one rib after another near where the ribs join the flat base of the ram. After repeated use of the hammer these cracks gradually spread through the ram and cause it to break in two or more pieces, rendering the hammer useless.

It is a purposeof this invention to distribute the metal in the ram of the press in such a way that. internal ten-- sile stresses in the ram casting are minimized or avoided altogether.

Another object of the invention is to provide adjustable members composed of material of high tensile strength and means for tightening such members in order to prestress the ram casting by compressing any portions of it which might otherwise be put in tension upon the impact of the ram with the workpiece.

A further object is to prevent cracks in or breakage of the base of the ram by means of spaced apart members, such as bolts, of high tensile strength connected to the ram base near its edge and arranged to prevent the setting up of tensile forces therein upon impact.

Further objects will become apparent as the descriptionof the drop hammer proceeds. For a better understanding of the invention reference is made to the accompanying drawings, in which:

Figure 1 is a perspective view showing portions of a drop hammer embodying the invention;

Figure 2 is a perspective view showing a modified form of the invention and,

Figure 3 is a sectional view showing a detail of the press ram on an enlarged scale.

Referring to Figure 1, the drop hammer illustrated comprises a base or anvil 10 supporting anvil cap 11 to which is firmly bolted female die 12 whose curved die face 13 is smoothly finished tothe shape of the object to be formed. A male die 14 is bolted to the base 15 of a massive ram 16 and has a curved die face 17 which registers with die face 13 to form' a flat sheet of aluminum, steel or other flexible metal laid on die 12' into a finished shape, in a known manner. Ram 16 isusually made of one piece of metal in the form of an iron or steel casting, the base 15 being of generally rectangular shape. The base is connected by a central longitudinally extending web 18 with a beam 19' having a central portion 20' parallel to base 15 and upstanding outwardly directed end portions 21, 22'. Each end portion is provided with a pair of semi-cylindrical vertical bearing faces 23 which are slidable along four vertical cylindrical guides 24 whose lower ends are firmly se-' cured to anvil 10 and cap 11. The ends 21, 22 of beam 19 are connected to the ends of base 15 by a pair of thick outwardly

flaring ribs

25, 26 and thinner ribs 27' connect the center portion 20 of the beam with base 15.-

Ribs

25, 26 near base 15 are provided with projecting lugs 28 which have semi-cylindrical bearing faces 29 which engage and slide along the guides 24.

The drop hammer as above described is of known construction and ram 16 may be raised by a pair of flexible cables 30 or other known means and when allowed to drop, is guided by vertical guides 24- so that die 14' strikes the workpiece and conforms it to the desired shape.

After a ram of the type described has been used repeatedly, especially with dies which are smaller than basev 15, it has been found that one or more cracks 31 develop in the regions indicated across the top of beam 19" and also that cracks develop in the ribs 27 near the lowerends thereof as indicated at 32. After once started these cracks progress and spread further into the casting upon continued use of the hammer until finally the ram breaks into two or more pieces and becomes unfit for' use. A careful analysis of the internal stresses set up in the ram by the sudden impact, indicated that tensile stresses of considerable magnitude were developed in the casting in the regions where the cracks occur. As cast iron or cast steel does not have much strength in tension, it was concluded that the high internal tensile stresses caused the casting to crack. When the ram 16 is dropped, the die 14 and the region of the ram directly above it is suddently stopped but the momentum of. the end portions of base 15,

ribs

25 and 26 and lugs 28 keeps these" portions of the casting moving down for an instant thereby causing the casting to bend a very small amount and tensile forces are set up lengthwise in the top portion of beam 19' to resist this bending. A purpose of my invention is to prevent such tensile forces from being developed in the beam and for this purpose holesare bored in the center of members 21, 22 to receive the threaded ends of a massive steel bolt 33 of high tensile strength. A pair of

nuts

34, 35 are screwed onto the ends of the bolt and brought against the outer faces of members 21', 22. One of the nuts is then further tightened to put bolt 33 in considerable tension and the beam 19 is such a high state of compression that no tensile stress is developed in the beam due to the impact. This prestressing the upper portion of the casting-in compression has been found to prevent the crack- Patented Oct. 4, 1955 ing of the upper portion of the casting in the manner described.

My analysis also shows that the momentum of the side portions of base 15,

ribs

25, 26 and 27 which extend beyond the sides of die 14causes tensile stresses to be set up in the base and in these ribs immediately after the center portion of base has been brought to a stop by die 12. These tensile forces are believed to be the cause of the cracks 32 and a further feature of my invention is the provision of means for preventing such internal tensile forces from being set up in the casting. These means comprise four spaced apart metal supports 36 which are welded to the top of beam 19, each support being bored to snugly receive bolt 33 and the top of each support having an arcuate groove to receive the central portion 37 of a V shaped bolt 38 made of steel of high tensile strength. The ends 39 of each bolt are threaded to receive a generally cylindrical shaped nut 40 which is received in an inclined bort 41 (see Fig. 3) cut in base 15 near the side edge thereof. Each bore 41 has a counterbore thereby providing an annular shoulder 42 against which the enlarged head 43 of the nut seats. When the two nuts 40 at the end ,of a bolt are tightened, the bolt can be put under tension which places the

ribs

25, 26 and 27 under compression and this compression may be increased to such extent that, although it may be reduced considerably at the moment of impact, nevertheless the ribs are not subjected to internal tensile forces. It has been found that this method of prestressing the ram prevents the formation of cracks in the casting and very gently increases its useful life. The supports 36 serve to absorb the momentum of the center portion of heavy bolt 33 at the moment of impact and prevent the setting up of high internal tensile stresses resulting from bending loads'therein such as might arise from vibrations of the bolt caused by the impact. The head of the drop hammer to which the extended upper ends of vertical guides 24 attach and which supports the mechanism for raising the ram is not shown as this is not necessary to an understanding of my invention.

Figure 2 shows a drop hammer of the same general type as that shown in Figure 1 and corresponding parts are designated by the same reference numerals. The ram 16 however is of improved design and the metal thereof is distributed in a manner to minimize the formation of internal tensile stresses and give it a long life. For this purpose base 15 is made much thicker along its longitudinal center than at its sides 44, the bottom face being kept plane for the securement of die 14. The longitudinal center web 18 extends much higher than in the species of Fig. l and terminates at the top in a heavy arch 45 of much greater thickness than the web. Near its ends the arch has integral projecting lugs 46 in which the semi-cylindrical bearing faces 23 are cut, to guide the ram on guides 24. These lugs also have upstanding portions 47 disposed in a vertical plane through the longitudinal center of base 15 and which are bored for attachmentof the ends of lifting cables 30. Web 18 also has projecting from both side faces symmetrically arranged vertical ribs 48 and horizontal ribs 49 which, together with arch 45 add considerable mass to the ram. From each side of central web 18 also extend vertical supporting ribs 50. whose lower ends merge into base 15 at points 51 which are remote from the side edges 44 of the base. The tensioning bolts 38 and their nuts 40 are the same as above described but two of them have their center portions disposed in holes 52 formed in web 18 and in engagement with the curved upper faces of lugs 53 integral with the web. Figure 2 shows two nuts 54 engaging the upper ends of two bolts which pass through base 15 and serve with a corresponding pair (not shown) on the far side of web 18 to secure die 14 to the ram base. It will be noted that in this embodiment of the invention a much greater portion of the metal of the ram is distributed close to a vertical plane through its longitudinal center line so that a minimum weight of metal extends beyond the marginal edges of die 14 to tend to produce tensile stresses within the ram. The pretensioning of bolts 38 maintains the reinforcing ribs 50 in compression continually and prevents the formation of cracks therein such as form in the usual type of ram. The upward pull along the sides 44 of base 15 may be regulated to cause the base to bend up a small amount so that if its lower face were initially flat, it would be slightly convex after the prestressing.

This invention may be embodied in other forms or carried out in other ways without departing from the spirit or essential characteristics thereof. The present embodiment of the invention is therefore to be considered as in all respects illustrative and not restrictive, the scope of the invention being indicated by the appended claims, and all changes which come within the meaning and range of equivalency of the claims are intended to be embraced therein.

Having thus described my invention, what I claim as new and useful and desire to secure by Letters Patent is:

1. A drop hammer ram comprising a metal block having a substantially rectangular shaped solid horizontalbase of large area, the thickness of said base increasing progressively from its sides to the longitudinal center thereof; a thick web integral with said base and extending for a substantial distance above the base in a vertical plane through said longitudinal center, said web terminating at its top in an arch which is substantially thicker than the body of the web and said web having a plurality of vertical ribs projecting from each face thereof and a plurality of horizontal ribs projecting from each face thereof and connecting with said vertical ribs; and a plurality of vertical reinforcing ribs extending from each of the opposite faces of said web and connecting said web and base, said reinforcing ribs increasing in width progressively as they approach the base and having their outer ends spaced a substantial distance away from the sides of the base.

2. A drop hammer ram as claimed in claim 1, in which said base is provided near each of its sides with a plurality of spaced apart nut-receiving openings; a plurality of spaced apart nut-receiving openings; a plurality of V- shaped bolts having their center portions seated against said web and threaded ends disposed in said openings; and nuts in said openings on said threaded ends pressing against said base to maintain said bolts continuously under tension.

3. A drop hammer ram comprising a metal block having a substantially rectangular shaped solid horizontal base of large area; a thick web integral with said base and extending for a substantial distance above the base in a vertical plane through the longitudinal center of the base, said web terminating at its top in an arch which is substantially thicker than the body of the Web; projecting lugs on the ends of the arch, each of said lugs having a pair of vertical semi-cylindrical bearing faces adapted to guide the ram along a pair of vertical cylindrical guide members; and a pair of lugs integral with the base and projecting from the ends thereof each of said last named lugs having a pair of semi-cylindrical bearing faces in vertical alignment with said first named bearing faces.

4. A drop hammer ram as claimed in claim 3, in which said lugs on the ends of the arch are provided with upwardly projecting vertical portions having apertures therethrough adapted to receive the ends of a lifting cable.

5. A drop hammer ram comprising a metal block having a substantially rectangular shaped solid horizontal base of large area, a thick web integral with said base and ex tending in a vertical plane through the longitudinl center of the base for a substantial distance above the base; vertically aligned bearing faces on each end of the ram adapted to engage stationary posts and guide the ram towards a stationary die; a movable die secured to the bottom of said base near the center thereof, the marginal edges of said movable die being spaced from the sides and ends of said base by a substantial distance; a plurality of vertical reinforcing ribs extending from each of the opposite faces of said web and connecting said web and base, said ribs increasing in width progressively as they approach the base; and a plurality of pretensioned members having their ends engaging said base at spaced apart regions near the sides thereof and having center portions engaging the upper portion of said web, said pretensioned members lying in parallel vertical planes substantially nor- {nal to the plane of said web; and adjustable means asgociated with each of said pretensioned members for increasing the tension therein to a degree suificient to prevent the development of tensile stresses in said reinforcing ribs due to the inertia of the portion of said base lying outside of the marginal edges of said movable die imme- 5 6 diately after said movable die has struck a workpiece o the stationary die.

References Cited in the file of this patent UNITED STATES PATENTS 442,898 Kennedy Dec. 16, 1890 1,067,616 Matteson July 15, 1913 1,194,653 Montstream Aug. 15, 1916 1,473,364 Voelker Nov. 6, 1923 1,852,534 Moore Apr. 5, 1932 1,964,024 Ballard June 26, 1934 2,133,477 Schade Oct. 18, 1938 2,618,148 Reed Nov. 18, 1952