US3189238A

US3189238A - Method of working hard brittle metals

Info

Publication number: US3189238A
Application number: US90420A
Authority: US
Inventors: John F Sherrill
Original assignee: LEMERT ENGINEERING CO Inc
Current assignee: LEMERT ENGINEERING Co Inc
Priority date: 1961-02-20
Filing date: 1961-02-20
Publication date: 1965-06-15
Anticipated expiration: 1982-06-15

Description

June 15, 1965 H L Q 3,189,23&

METHOD OF WORKING HARD BRITTLE METALS Filed Feb. 20. 1961 f?" HMF/AA.

.INV EN TOR.

A 7" TKAQ/VE K United States Patent 3,189,238 METHOD OF WORKING HARD BEETLE METALS John F. Sherrill, Lament Engineering Q0. Inc, Plymouth, Ind. Filed Feb. 20, 1961, Ser. No. 90,4 20 5 Claims. (til. 225-1) This invention relates to a method of working hard brittle metals and is a continuation-in-part of my copending application, Ser. No. 587,687, filed May 28, 1956, now Patent No. 3,001,279, dated September 26, 1961.

Certain metals which possess valuable physical properties, such as great strength, ability to withstand high temperatures, and the like, possess other properties, such as brittleness and frangibility, which make the working thereof difficult, expensive and time-consuming. Examples of such metals are titanium alloys, magnesium alloys, certain aluminum alloys, and stainless steel, each of which is characterized by extreme hardness and brittleness and lack of workability when cold. Thus such metals tend to break when subjected to hard or heavy blows, as in punching and piercing thereof.

As a result of these properties, it has been common heretofore to drill holes to be formed therein, even though the metal is of thin section.

I have found that it is possible to pierce such metals while cold without danger of fracture, weakening or otherwise endangering the desired properties of the metal, and it is the primary object of this invention to overcome the disadvantages of hot working methods and to accomplish effectively, quickly and inexpensively the piercing of hard and brittle metals by a cold working process.

Other objects will be apparent from the following specification.

In the drawing:

The figure is a side view of a piercing method.

My method, broadly stated, entails the piercing of metal by impact at high speed at a limited area of the work piece while continually and progressively changing the location of the tool, so that diiferent areas of the Work piece are struck by successive blows, and wherein the blows are limited to a value less than the physical fatigue limit of the metal.

Referring to the drawing which illustrates the application of my process to the work of piercing sheet metal, the method can be applied to the service of piercing hard metal sheets by an arrangement as illustrated in FIG. 1, wherein a base or anvil 50 has an aperture or punch hole 52 formed therein. The work piece 54 is supported upon the anvil to span the punch hole 52, and a punch member 56 concentric with the punch hole 52 is reciprocated endwise and is rotated. The punch member 56 has a narrow blade 58 extending diagonally thereof and projecting from the end of the punch, which blade 58 has an end surface substantially perpendicular to the axis of the punch. Repeated impacts of the narrow blade 58 at the portion of the sheet 54 which spans the punch opening 52 will serve to pierce the sheet and form a hole therein without inpuring the sheet around the opening.

The hammer member 56 is caused to reciprocate in a direction perpendicular to the work-supporting surface of the member 50 and in coaxial relation with the aperture 52 in the work piece. The rate of reciprocation will be rapid and preferably substantially uniform. Thus the reciprocation may be at a slow rate to apply as few as four or five hundred blows per minute or at higher rates, such as a rate to apply sixteen thousand or more blows per minute. The blows will be of substantially uniform value so as to have a predetermined total pressure or impact value per unit of time. In general, the force of the individual blows will usually be substantially inversely proportional to the number of blows. Thus each 3,189,238 Patented June 15, 1965 blow delivered at the rate of 500 blows per minute could be much heavier than the individual blows delivered at the rate of 16,000 blows per minute. In all cases care must be taken to limit the force of each blow to a value less than that which would injure the work piece, i.e., must be restrained within the physical fatigue limits of the material.

Simultaneously with the reciprocation of the hammer 56 to apply blows rapidly, said hammer is rotated about its axis or otherwise shifted to change the location of successive blows upon the work area. The hammer 56 preferably terminates in a thin longitudinal blade portion 58. As a result of such formation of the hammer head or blade 58, it will be evident that only a small portion of the area of the sheet which is to be pierced is contacted by the blade '53 upon each stroke or hammer blow thereof.

As a result of the rapidity of the hammering operation, heat is generated within the sheet but the amount of heat usually does not greatly exceed 100 degrees F. and is not sufficient to cause heat damage to the work piece or expansion thereof. In cases where magnesium alloys are involved, the heat generated will not be suflicient to cause combustion to occur.

As an example of the process, a vanadium type titanium alloy commonly used for aircraft purposes has a hardness producing a Rockwell A reading in the order of 70. I have found that sheets of this material can be effectively pierced while cold by using a tool having a blade or.

peen thickness of about ,5 of an inch which is oscillated at the rate of between 6500 and 16,000 blows per minute, and preferably approximately 7000 blows per minute, with each blow delivering a force of about one-quarter pound in the lower part of the range and reducing progressively as the frequency of blows is increased, and with the hammer or peen blades being rotated at a speed of approximately 1200 revolutions per minute or more. The ratio between the force of the blows and the frequency of the blows will be such that the total force exerted per unit of time will be substantially the same throughout the full range of speed adjustment.

Another example of successful cold piercing of a brittle alloy used in the aircraft industry and successfully cold pierced by my method is known as S.T. 6 aluminum alloy. This metal has a Rockwell A rating of about 40. In practicing my method on this material, I employ a hammer having a blade one-quarter inch thick which is oscillated at the rate from 1500 to 3500 blows per minute and preferably approximately 2000 blows per minute. Each blow exerts a force of about one pound at the lower end of the range, and less, as one-half pound, at the upper end of the range. The hammer is rotated at 1200 rpm. or faster.

In both examples, the width of the blade is substantially less than the total area of the surface to be pierced, and the rate of speed of rotation is such that successive blows by the blade contact different areas of the work piece within the total area to be pierced. The time required for the performance of the piercing operation in both cases is less than the time which would have been required for piercing the same work piece by the conventional drilling methods.

Any means found suitable for controlling the rate of impact, the force of impact and the rotation of the hammer with respect to the work piece may be employed. One example of such apparatus is illustrated in my Patent No. 2,876,742, dated March 10, 1959, for Variable Speed Fluid Pressure Actuation Impact Device, in which a tool is rotated continuously as it is oscillated. Any other apparatus suitable for the performance of the steps required to rapidly hammer limited portions of an area to be pierced may be used.

amazes While the preferred steps of the nethod have been described, it will be understood that the method is not limited precisely thereto, but that any procedure which falls within the scope of the appended claims is contemplated within the spirit of the invention.

I claim:

1. The method of forming a circular hole in sheet metal characterized by hardness and brittleness when cold and selected from the group consisting of titanium alloys, magnesium alloys, aluminum alloys and stainless steel, consisting of the step of repeatedly and simultaneously oscillating and rotating an impact tool having a blade with a fiat end parallel to the metal sheet to be pierced and of a width equal to the desired diameter of the hole to be formed and a reduced thickness to impart successively and rapidly to different limited portions only of the area of the metal sheet to be pierced, while said sheet is cold and is supported by a member having an opening axially aligned with said tool and of a diameter slightly greater than the width of said tool blade, blows substantially normal to the metal sheet to be pierced and of substantially uniform force and less than the fatigue limit of the metal, the force of each blow and the width of the impact surface of the tool being inversely proportional to the rapidity of the blow and sufficient to pierce the metal, the direction of said blows being substantially perpendicular to the end of the blade and to the metal sheet to be pierced, and the rotation of said tool producing hammering of all of the area registering with said opening.

2. The method of forming a circular hole in sheet metal characterized by hardness and brittleness when cold and selected from the group consisting of titanium alloys, magnesium alloys, aluminum alloys and stainless steel, consisting of the step of repeatedly and simultaneously oscillating substantially perpendicularly to said metal sheet and rotating an impact tool having a flat ended blade of a width equal to the desired diameter of the hole to be formed and a reduced thickness to impart successively and rapidly to different limited portions only of the area of the metal sheet to be pierced, while said sheet is cold and is supported by a member having an opening axially aligned with said tool and of a diameter slightly greater than the width of said tool blade, blows substantially normal to the sheet metal and of substantially uniform force and less than the fatigue limit of the metal, the force of each blow and the width of the impact surface of the tool being inversely proportional to the rapidity of the blow and sulficient to pierce the metal, and the rotation of said tool producing hammering of all of the area registering with said opening, the rate of hammering being in a range between 400 blows per minute and 16,000 blows per minute, the flat end of said blade being substantially parallel to the metal sheet to be pierced.

3. The method of piercing hard frangible sheet metals having a Rockwell A reading in the order of 79 to form a round hole, consisting of the step of repeatedly and simultaneously oscillating perpendicularly to said metal sheet and rotating an impact tool having a flat ended blade of a width equal to the desired diameter of the hole to be formed and a thickness of approximately one-sixteenth inch to impart successively and rapidly to different limited portions only of the area of the metal sheet to be pierced, while said sheet is cold and is supported by a member having an opening axially aligned with said tool and of a diameter slightly greater than the width of said tool blade, blows substantially normal to the metal sheet at a rate in the range between 6590 and 16,000 per minute and with exertion of a force or". approximately one quarter pound per blow in the lower part of said speed range and with exertion of inversely proportional force in the upper part of said speed range, said blows hammering all of the area registering with said opening the fiat end of said blade being substantially parallel to said metal sheet.

4. The method of piercing hard frangible sheet metal having a Rockwell A reading in the order of 40 to form a round hole, consisting of the step of repeatedly and simultaneously oscillating and rotating an impact tool having a ended blade of a width equal to the desired diameter of the hole to be formed and a thickness of approximately one-eighth inch to impart successively and rapidly to different limited portions only of the area of the metal sheet to be pierced, while said sheet is cold and supported by a member having an opening axially alignedwith said tool and of a diameter slightly greater than the width of said tool blade, blows substantially normal to the sheet metal at a rate in the range between 1800 and 3500 per minute each of a force in the range of approximately one pound at low speed in said speed range to one-half pound at high speed in said speed range said fiat tool end being positioned parallel to said metal sheet during application of said blows to said metal sheet.

5. The method of forming a circular hole in sheet metal.

characterized by hardness and brittleness when cold and selected from the group consisting of titanium alloys, magnesium alloys, aluminum alloys and stainless steel, consisting of the step of repeatedly and simultaneously oscillating longitudinally and rotating an impact tool having a blade with a flat end substantially parallel to said metal sheet or" a width equal to the desired diameter of the hole to be formed and a reduced thickness to impart succes sively and rapidly to difierent limited portions only of the area of the metal sheet to be pierced, While said sheet is cold and is supported by a member having an opening axially aligned with said tool and of a diameter slightly greater than the Width of said tool blade, blows substantially normal to the sheet metal and of substantially uniform force and less than the fatigue limit of the metal, the force of each blow and the width of the impact surface of the tool being inversely proportional to the rapidity of the blow and sufiicient to pierce the metal, and the rotation of said tool producing hammering of all of the area registering with said opening, the rapidity and force of the blow and the dimension of the work-engaging portion of the tool being substantially in the order and ratio of the following examples:

ANDREW R. lUHASZ, Primary Examiner.

CARL W. TOMLIN, HUNTER C. BOURNE,

LEON PEAR, Exm'niners.

Claims

1. THE METHOD OF FORMING A CIRCULAR HOLE IN SHEET METAL CHARACTERIZED BY HARDNESS AND BRITTLENESS WHEN COLD AND SELECTED FROM THE GROUP CONSISTING OF TITANIUM ALLOYS, MAGNESIUM ALLOYS, ALUMINUM ALLOYS AND STAINLESS STEEL, CONSISTING OF THE STEP OF REPREATEDLY AND SIMULTANEOUSLY OSCILLATING AND ROTATING AN IMPACT TOOL HAVING A BLADE WITH A FLAT END PARALLEL TO THE METAL SHEET TO BE PIERCED AND OF A WIDTH EQUAL TO THE DESIRED DIAMETER OF THE HOLE TO BE FORMED AND A REDUCED THICKNESS TO IMPART SUCCESSIVELY AND RAPIDLY TO DIFFERENT LIMITED PORTIONS ONLY OF THE AREA OF THE METAL SHEET TO BE PIERCED, WHILE SAID SHEET IS COLD AND IS SUPPORTED BY A MEMBER HAVING AN OPENING AXIALLY ALIGNED WITH SAID TOOL AND OF A DIAMETER SLIGHTLY GREATER THAN THE WIDTH OF SAID TOOL BLADE, BLOWS SUBSTANITALLY NORMAL TO THE METAL SHEET TO BE PIERCED AND OF SUBSTANITALLY UNIFORM FORCE AND LESS THAN THE FATIGUE LIMIT OF THE METAL, THE FORCE OF EACH BLOW AND THE WIDTH OF THE IMPACT SURFACE OF THE TOOL BEING INVERSELY PROPORTIONAL TO THE RAPIDITY OF THE BLOW AND SUFFICIENT TO PIERCE THE METAL, THE DIRECTION OF SAID BLOWS BEING SUBSTANTIALLY PERPENDICULAR TO THE END OF THE BLADE AND TO THE METAL SHEET TO BE PIERCED, AND THE ROTATION OF SAID TOOL PRODUCING HAMMERING OF ALL OF THE AREA REGISTERING WITH SAID OPENING.