US3745803A - Method of extruding tubular products - Google Patents

Abstract

A method is provided for extruding a tubular product wherein a billet is loaded into a container in a press, the billet is restrained in the container by crushing it between a ram and a die block, the die block is moved with respect to the billet so that the end of the billet toward the die block is substantially unrestricted, the billet is pierced with a mandrel, and the pierced billet is extruded over the mandrel and through the extrusion die.

Description

United States Patent Livelsberger July 17, 1973 [54] METHOD OF EXTRUDING TUBULAR 2,798,286 7/1957 Anderson 72/266 O CT 3,408,846 ll/l968 Schofield 72/267 [75] inventor: Bert V. Llvelsberger, Mulberry, ind. Primary fixaminerncharles w Lanham [73] Assignee: Aluminum Company of America, istant Exam erR0bert M. Rogers v Pittsburgh, Pa, Attorney-David W. Brownlee 22 F1 d: A .25, 1971 l 1 57 ABSTRACT [21] Appl. N0.: 174,880 A method is provided for extruding a tubular product wherein a billet is loaded into a container in a press, the [52] US. Cl. 72/265 billet is restrained in the container by crushing it be- [51] Int. Cl. B2lc 23/20 tween a m and a die block, the die block is m ved [58] Field of Search 72/264, 254, 255, with pec t t e b e o that the end of the billet t0- 72/256, 266, 265 ward the die block is substantially unrestricted, the bi]- let is pierced with a mandrel, and the pierced billet is [56] References Cited extruded over the mandrel and through the extrusion k UNITED STATES PATENTS l,948,242 2/ 1934 Schubarth 72/266 6 Claims, 5 Drawing Figures 1 METHOD OF EXTRUDING TUBULAR PRODUCTS BACKGROUND OF THE INVENTION In extruding tubular products over a mandrel, it has been common practice to pierce a billet with the mandrel with the billet restrained against an open extrusion die. In so piercing a billet, a slug of metal in the form of an extruded rod is pushed through the open die by the piercing mandrel. In addition to the metal lost as a pierced plug, the'plug adheres to the tube that is subsequently extruded and prevents air from entering the tube as it is being extruded. The vacuum that is produced may cause collapse of the extruded tube and can result in scrapping of the collapsed tube. To avoid such collapse, the end of the extruded tube has sometimes been punctured or cut in order to permit air to enter the end of the tube.

Accordingly, a method of extruding a tubular product is desired which will not produce an extruded plug of material-on the endof the extruded tubular member.

SUMMARY OF THE INVENTION This invention provides a method of extruding a billet over a mandrel and through an extrusion die to form a tubular product in whichduring piercing with the mandrel, the billet is restrained in a container in the press without substantially restricting deformation of the material atthe die end of the billet. The billet is pierced against lateral restraint only whereby the forward end of the billet can be formed around the nose of the mandrel during penetration without producing a slug of metal. According to the invention, the lateral restraint of the billet in its container may be provided by crushing the billet between a die block and a ram so that the billet is locked in the container by frictional and shear forces atthebillet/container interface. The die block can then'be moved with respect to the billet so that the forward end of the billet is substantially unrestrained during piercing. v

Accordingly, an object of the invention is to provide an improved method of extruding a tubular product.

Another object of the invention is to provide a methodof extruding a tubular product over a mandrel in an extrusion die wherein, during piercing, a billet is laterally restrained in-its container without substantially'restricting the die end of the billet with tools.

A further object of the invention is to provide a method of extruding a tubular product in which a billet is crushed in its container in a press between a die block and a ram whereafter the die block is spaced from the forward end of the billet during piercing so that the mandrel can pierce the billet without extruding a slug of materialthrough the die aperture.

A further object of the invention is to provide a method of extruding a tubular product in which less force is required to pierce a billet than is required by conventional methods.

BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects and advantages of the invention will be more fully understood and appreciated with reference to the following description and the drawings appended thereto wherein:

FIG. 1 is a fragmentary cross-sectional view of extrusion apparatus with a billet therein;

FIG. 2 is a fragmentary cross-sectional view similar to FIG. I with the billet crushed in its container;

FIG. 3 is a fragmentary cross-sectional view similar to FIGS. 1 and 2 showing the extrusion die spaced with respect to the billet;

FIG. 4 is a fragmentary cross-sectional view similar to FIGS. 1 3' showing piercing of the billet; and

FIG. 5 is a fragmentary cross-sectional view similar to FIGS. 1 4 showing extrusion of a tubular product over the mandrel and through the die aperture in the die.

DESCRIPTION OF A PREFERRED MODE Referring to the Figs, extrusion apparatus is shown which may be employed'in either direct or indirect (inverted) extrusion processes depending onthe press arrangement. The difference between direct and indirect extrusion is primarily a matter of whether there is relative movement between the container and ram (direct) or between the container and the die (indirect), and both include the same basic apparatus. With respect to the invention, it is equally well suited to use in either direct or indirect extrusion presses.

The apparatus which has been selected for illustration has been designed for the extrusion of aluminum or an alloy thereof, but the invention can be employed in the extrusion of many other materials such as lead, copper, brass, steel, or the like which are commonly extruded in tubular form. A preferred mode of the invention will be described with respect to. the extrusion of aluminum as being exemplary of the practice of the invention.

FIG. 1 illustrates a typical press arrangement for extruding a tubular product including an extrusion die 10, an extrusion container 12, a pressure ram 14 and a mandrel 16 with a nose or piercer l8 thereon. As will be explained, piercer 18 preferably has a low angle tip or needle nose thereon but may also have a blunt nose of various configurations as is well known for conventional extrusion processes. Extrusion die 10 has a die aperture 20 therein which has dimensions approximating the outer dimensions of the tubular products to be extruded, and mandrel 16 has an extruding surface 22 which approximates the inside dimensions of the product to be extruded. In the apparatus selected for illustration, mandrel 16 does not move with respect to die aperture 20 during extrusion, although the mandrel may also be advanced through the die aperture in the extrusion die during extrusion as is well known in conventional extrusion processes. It will also be obvious to those skilled in the art that a mandrel can be provided which has a plurality of extrusion surfaces of different diameters, and which can be sequentially advanced and/or retracted with respect to the die aperture to extrude tubular products having differing wall thicknesses. In the apparatus selected for illustration, the end of mandrel I6 is advanced into die aperture 20 and locked in position so that the product which is extruded thereover will have a substantially uniform wall thickness.

FIG. I further shows a billet 24 to be extruded, loosely positioned in container 12 as is conventional. Billet 24 may be'a cast ingot or may be formed from plate or other stock material. In extruding an aluminum billet, the billet is preferably pre-heated to a temperature in the range of 600 F to l,000 F so that the aluminum can be extruded more easily.

After a billet has been loaded into a container, it must be pierced by a mandrel so that the nose of the mandrel can be positioned in the die aperture for extruding a tubular product thereover. According to prior practices, billets have usually been restrained against either an open die or a dummy die block during piercing. When a billet is pierced against an open die, a slug of metal may be forced through the die aperture by the mandrel as it displaces metal during piercing. When pierced against a dummy die block which prevents the formation of a slug, substantially more power is required to force the mandrel through the billet, and the mandrel cannot completely pierce the billet.

It is a feature of this invention that billet 24 is restrained in container 12 during piercing without substantially restricting the end of the billet with an open die or dummy die block. According to this invention, billet 24 is crushed or upset between die and pressure ram 14, to lock the billet in the container, and the die is then moved away from the billet to pennit piercing without tool restraint against the end of the billet. It will be obvious to one skilled in the art that a dummy die block, not shown, could be substituted for die 10 for crushing billet 24 against ram 14. Crushing billet 24 between die 10 and ram 14 effects radial expansion of the billet against the inner walls of container 12 and thereby locks the billet in the container. This locking effect is produced by the pressure of the billet against the inner wall of the container and will hold the billet against the piercing force as will be described. Depending on whether the extrusion apparatus is designed for direct or indirect extrusion, crushing may be effected by moving either the ram 14 or the die 10 with respect to container 12. For example, in an indirect extrusion operation, the container 12 and ram 14 may be moved toward die 10 which is stationary to compress billet 24 between the die and the ram. In a direct extrusion operation, the container and die may be stationary and the ram is usually moved with respect to container and toward the die to squeeze a billet between the die and the ram.

After billet 24 is crushed in container 12, die 10 is moved with respect to billet 24 to provide a space therebetween so that the face of the billet is substantially unrestricted by tools. In indirect extrusion apparatus, this space may be provided by moving container 12 and ram 14 rearward away from die 10. If a dummy die block is used for the crushing operation, the block may be completely removed from the press for the piercing operation. It is important that adequate space be provided adjacent the forward face of the billet for it to be deformed outwardly as the billet is pierced by mandrel l6. Depending upon the size of the billet, the size of the mandrel and the material being pierced among other factors, the amount of defonnation may vary substantially. As an example, an eleven inch diameter billet which is 14 inches long and which is pierced by a 3 and inch diameter piercer mandrel should have approximately 4 to 6 inches of clearance between its face and die 10 for deformation of the billet.

Although not essential to the practice of the invention, a space may also be provided between the rear face of billet 24 and pressure ram 14 during piercing to provide room for back flow of the material in the billet during piercing. This clearance can be provided by restraining container 12 and retracting ram 14 to provide an inch or more of space between the billet and the end of ram 14.

FIG. 4 shows billet 24 as it is being pierced by mandrel 16 and piercer 18 on the end of the mandrel to produce a hemispherical dome on the forward face of the billet with a hole through the end of the dome. As illustrated, the piercing stroke is completed with the tip of piercer 18 having penetrated the end of billet 24. If a hole is not formed in the face of billet 24, the end of the tubular product which is subsequently extruded may also not have a hole in it. In the absence of a hole in the end of the tubular product, a vacuum could be produced in the product during extrusion and such a vacuum could cause collapse of the product. Depending upon the shape of the piercer nose, the diameter of the piercer, the material, the temperature of the billet, and billet shape among other factors, the hemispherical dome may be of various shapes and sizes. With some piercers, particularly blunt nose piercers, a ring of material may be separated from the face of the billet and may result in scrap material. Accordingly, a needle nosed piercer may be preferred for the practice of the invention for some applications because such a piercer may facilitate forming a hole in the end of a billet with a minimum of deformation of the billet.

It has been found that a piercer with a nose which is slightly longer than the radius of the dome which is formed on the billet works well in the practice of the invention. If the nose is substantially longer than the radius of the dome on the billet, the nose may be weak and may be broken or may be too flexible to form a concentric hole in the billet and extrude a product with a uniform wall thickness. If the length of the nose is less than the radius of the dome on the billet, the larger diameter base of the mandrel must be forced further through the billet in order to completely pierce the billet. This increases deformation of the billet and may cause separation of a ring or ball of material from the face of the billet. It has been found that a piercer nose with a length in the range of approximately 1.25 to l .75 times the radius of the piercer mandrel, depending on the material, temperature, and tube sizes, among other factors, works well in the practice of the invention, although is not limiting of the invention.

The hemispherical dome is a result of flow of material in the billet outward and forward ahead of the piercer nose. Since the face of the billet 24 is unrestrained by tools, there is no external resistance to such deformation. Further, since die 10 is spaced from the forward face of billet 24, no material is forced through the open die aperture 20 and no slug of scrap material is formed on the end of the tubular product which is subsequently extruded. Moreover, since there is no external resistance to such deformation, the force required to pierce a billet by the method of the invention is substantially less than the force which is required for piercing a billet against an open die or a dummy die block. It has been found that the invention reduces the force required for piercing a billet by as much as 50% or more from the force required for piercing a billet by conventional methods.

After billet 24 has been pierced, it is again compressed or crushed between die 10 and pressure ram 14, and material from the billet is extruded through die aperture 20 around piercer 18 on mandrel 16 to form a tubular product. Although recrushing billet 24 and the extrusion of material through the die aperture is usually one continuous operation, recrushing of the billet between die 10 and ram 14 is sometimes considered to be a separate step in the extrusion process prior to actual extrusion of material. To effect extrusion of a tubular product, it may also be necessary to either ad vance or withdraw mandrel l6 and piercer 18 so that extrusion surface 22 on the piercer is properly located in die aperture. This positioning of the extrusion surface 22 may be done prior to, concurrently with, or subsequent to the recrushing of billet 24 after the piercing operation and is not critical to the invention.

Upon extrusion of material through die aperture 20, the first portion of the tubular products 26 may include a small length of scrap 28 as shown in FIG. 5. Scrap portion'28 will usually be relatively small, however, and will have an open end or hole 30 therein so that air can enter the tube and therefore avoids collapse of the tube due to a vacuum in the tube.

It is therefore seen that a method has been illustrated and described for extruding a tubular product which does not produce a slug of metal on the end of the product which must be scrapped and which can cause collapse of the tubular product. The method involves piercing of a billet without substantially restraining the die end of the billet whereby material from the billet can flow outward and forward ahead of the piercing mandrel without resistance from the tools. Although a preferred mode has been described, it will be obvious to those skilled in the art that numerous variations can be made in the method without departing from the invention. Included in such variations are the provision of various shapes for the piercer on the mandrel, the use of direct or indirect extrusion apparatus and variations in the means for restraining a billet in a container.

What is claimed is:

1. In a method of extruding a tubular product over a mandrel and through an extrusion die, the improvement comprising the steps of:

crushing a billet in a container in a press between an extrusion die and a pressure ram to lock the billet in the container;

moving the die with respect to the billet to provide a space therebetween for deformation of the forward end of the billet during piercing;

piercing the billet with a mandrel; and

extruding a tubular product over the mandrel in the extrusion die.

2. A method as set forth in claim 1 in which, after crushing, the pressure ram is moved with respect to the billet to provide a space therebetween for back flow of material in the billet during piercing.

3. A method as set forth in claim 1 in which an aluminum alloy billet which has been heated to a temperature in the range of 600 F 900 F is extruded.

4. A method as set forth in claim 1 in which the billet is recrushed between the die and the ram after it has been pierced.

5. A method as set forth in claim 1 in which the billet is pierced with a mandrel with a needle nose piercer thereon.

6. A method as set forth in claim 5 in which said needle nose has a length in the range of 1.25 to 1.75 times the radius of the mandrel.

Claims (6)

1. In a method of extruding a tubular product over a mandrel and through an extrusion die, the improvement comprising the steps of: crushing a billet in a container in a press between an extrusion die and a pressure ram to lock the billet in the container; moving the die with respect to the billet to provide a space therebetween for deformation of the forward end of the billet during piercing; piercing the billet with a mandrel; and extruding a tubular product over the mandrel in the extrusion die.

2. A method as set forth in claim 1 in which, after crushing, the pressure ram is moved with respect to the billet to provide a space therebetween for back flow of material in the billet during piercing.

3. A method as set forth in claim 1 in which an aluminum alloy billet which has been heated to a temperature in the range of 600* F - 900* F is extruded.

4. A method as set forth in claim 1 in which the billet is recrushed between the die and the ram after it has been pierced.

5. A method as set forth in claim 1 in which the billet is pierced with a mandrel with a needle nose piercer thereon.

6. A method as set forth in claim 5 in which said needle nose has a length in the range of 1.25 to 1.75 times the radius of the mandrel.

Images