Endmills and method of making the same

Abstract

An endmill having a body formed from a single piece of material and having length greater than 1.6 inches and a method for forming such an endmill are provided. The method includes sintering a blank with an ultra hard material while in a heater having a length of at least 1.6 inches.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims priority on U.S. Provisional Application No. 60/666,860, filed on Mar. 30, 2005, the contents of which are fully incorporated herein by reference.

BACKGROUND OF THE INVENTION

An endmill typically is used for machining a surface, edges, grooves, pockets and slots. It can be made of high speed steel, or solid cemented carbide, but it can also consist of a steel tool body with cemented carbide inserts as cutting means. For certain applications, endmills having cutting edges formed of a superhard material, such as PCD, are usually used for the machining of non-ferrous alloys such as aluminum, brass, magnesium, composites, and the like, whereas endmills with cutting edges formed of a superhard abrasive, such as PcBN, are usually used for the machining of ferrous materials such as cast iron and hardened steel and the like.

There are several types of PCD or PcBN endmills on the market today. One method of making an endmill includes sintering at high temperature and high pressure (HPHT) diamond or cBN powder into veins in a solid cylindrical carbide body, i.e., a blank which is then brazed onto a shank and finished into an endmill. When the shank is attached to the endmill blank via brazing or other methods forming a joint, it results in tool with an inherent weakness at the joint. End milling applications under normal conditions exert a complex tensile and shear loads on the endmill that can lead to failure of the endmill at the joint. Consequently, an endmill is desired that does not have this inherent weakness. A method for forming such an endmill is also desired.

SUMMARY OF THE INVENTION

A method is provided allowing for the formation of an ultra hard material, such as a polycrystalline diamond (PCD) or polycrystalline cubic boron nitride (PCBN), endmill from a single solid blank without requiring brazing of the blank onto a shank. In an exemplary embodiment, the method provides for the formation of endmills from blanks having a length of at least 1.6 inches. In a further exemplary embodiment, the method provides for the formation of endmills from blanks having a length of at least 1.7 inches. In another exemplary embodiment, the method provides for the formation of endmills from blanks having a length of at least 1.75 inches. In yet a further exemplary embodiment, the method provides for the formation of endmills from blanks having a length not less than 2 inches. In yet a further exemplary embodiment, the method provides for using longer enclosures in a conventional sintering press, such as a belt press or a piston-cylinder press. In one exemplary embodiment, the method allows for the use of longer sintering enclosures and longer heaters which do not incorporate end heating units by alleviating the use of end heaters.

In another exemplary embodiment a method for forming an endmill having polycrystalline ultra hard material is provided. The method includes providing a blank having a groove, placing an ultra hard material in the groove, placing the blank in a refractory metal enclosure, placing the enclosure in a heater which has a length greater than 1.6 inches, and pressing the heater with the enclosure and blank in a press while heating using the heater for sintering the ultra hard material in the groove forming an polycrystalline ultra hard material. In another exemplary embodiment, the heater has a length of about 2.5 inches. In one exemplary embodiment, the blank has a length of at least 1.6 inches. In yet another exemplary embodiment, the heater has a length greater than 1.7 inches and the blank has a length greater 1.7 inches. In yet a further exemplary embodiment, the heater has a length greater than 1.75 inches and the blank has a length greater 1.75 inches. In another exemplary embodiment, the heater has a length of about 2 inches and the blank has a length not less than 2 inches.

In another exemplary embodiment, a method is provided for forming an end mill having polycrystalline ultra hard material. The method includes providing a blank having a length greater than 1.6 inches and a groove, placing an ultra hard material in the groove, placing the blank in a refractory metal enclosure, placing the enclosure in a heater, and pressing the heater with the enclosures and blank in a press while heating using the heater for sintering the ultra hard material in the groove forming a polycrystalline ultra hard material in the groove. In one exemplary embodiment, the blank may have a length greater than 1.7 inches. In a further exemplary embodiment, the blank may have a length greater than 1.75 inches. In another exemplary embodiment, the blank may have a length of about 2 inches.

In either of the aforementioned exemplary embodiment methods, the blank may be provided in solid or in powder form. Furthermore either of the aforementioned exemplary embodiment methods may include machining the blank to form a flute having a cutting edge defined by the polycrystalline ultra hard material. In an exemplary embodiment, in either of the aforementioned exemplary embodiments the heater does not include end heating units at opposite ends thereof. Furthermore, the presses used may in an exemplary embodiment be a belt press or a piston-cylinder press.

In yet a further exemplary embodiment, an endmill is provided having a body having a length of at least 1.6 inches including a grip portion and being formed from a single piece of material. Polycrystalline ultra hard material is bonded to the body. In another exemplary embodiment, the body has a length of at least 1.7 inches. In a further exemplary embodiment, the body has a length of at least 1.75 inches. In yet another exemplary embodiment, the body has a length of not less than 2 inches. In a further exemplary embodiment, the polycrystalline ultra hard material does not extend to the grip portion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a conventional endmill blank having veins of sintered ultra hard material.

FIG. 2 is a side view of a conventional endmill blank brazed onto a shank.

FIG. 3 is a perspective view of a conventional endmill blank finished into an endmill.

FIG. 4 is a partial cross-sectional view of a conventional heater for use in a sintering process.

FIG. 5 is a cross-sectional view of an exemplary embodiment longer heater for use in an exemplary embodiment sintering process.

FIG. 6 is a side view of an exemplary embodiment endmill blank of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

This invention relates to a helical endmill with polycrystalline cubic boron nitride (PcBN) or polycrystalline diamond (PCD) cutting edges and to a method of making the same. There are several types of PCD or PcBN endmills on the market today. One method of making an endmill includes sintering at high temperature and high pressure (HPHT) diamond or cBN powder into veins in a solid cylindrical carbide body, i.e., a blank which is then brazed onto a shank and finished into an endmill. Exemplary endmills and methods of making the same are described in U.S. Pat. Nos. 4,991,467; 5,031,484; 5,115,697; and 5,685,671, the contents of which are fully incorporated herein by reference.

An endmill is typically formed from a cylindrical tungsten carbide blank 10 having helical grooves or veins 12 formed longitudinally on its outer surface, as for example shown in FIG. 1, which are packed with either diamond or cubic boron nitride and a binder. The blank with the packed grooves is then HPHT sintered in a refractory metal enclosure, typically referred to as a “can”, such as a can made of Niobium or Tantalum. The sintering takes place in a press such as a cubic press. During sintering, the diamond or cBN form polycrystalline diamond (PCD) or polycrystalline cubic boron nitride (PcBN), respectively and simultaneously bond to the tungsten carbide blank.

With current endmills, the length the of the blank is very short, typically less than 1.5 inch. To accommodate for the short length of the blank and to provide a means for holding the tool, i.e., the endmill, the blank is brazed onto a shank 16 as for example shown in FIG. 2. The blank with the polycrystalline ultra hard material and shank combination is then machined to form flutes 15 thereby forming the endmill having ultra hard material cutting edges 17 as for example shown in FIG. 3.

When sintering the blank to form conventional endmills, the blank with grooves packed with diamond or cubic boron nitride is placed in a refractory metal enclosure 11 which is then surrounded by salt 13 and placed in a cylindrical heater 20. Current rings (not shown) and end disks 26 are coupled to the heater which provide current to the heater which in turn heats the enclosure with the blank by resistive heating. The resistive heating is radial heating (as shown by arrows 22 in FIG. 4) through the circumferential outer surface of the heater, when the enclosure is supplied with current through current rings (not shown). The end disks provide for axial heating as shown by arrows 24. The end disks 26 are typically resistive type of heaters. The heater with the enclosure is then placed within the press workspace where it is subjected to pressure. The temperature provided by the heater and the pressure provided by the press for sintering are at levels where diamond and CBN are thermodynamically stable.

Conventional cubic sintering presses cannot accommodate a longer heater with end heaters thus limiting the length of the blank being sintered. A typical cubic press typically has a working space having a length of 2.5 inches and can accommodate a conventional heater which has a length of about 1.60 inches, along with two end disks 26. A conventional refractory metal enclosure has a length of about 1.50 inches. The entire heater length is taken up by the refractory metal enclosure and the salt. Consequently, the length of endmill blanks produced by conventional cubic sintering presses and heaters are limited to a length of about 1.50 inches.

In attempting to overcome these limitations, applicants have discovered that they can sufficiently heat the blank for sintering using only radial heating without using end heating under sufficient pressure supplied by a high pressure apparatus. In this regard, the end disks 26 that are usually used for end heating are not required allowing more length within the press working space to accommodate a longer heater 32 (FIG. 5) and thus, a longer blank. For example, in one exemplary embodiment, applicants were able to use a heater having a length of 2.528 inches. This size heater can be accommodated in a belt press or a piston-cylinder press. With this heater, applicants were able to use a longer refractory metal enclosure to form the endmill blank. With the longer heaters applicants have been able to form endmill blanks having a length of 2 inches or greater. By forming of a longer blank, the need to braze a shank to the blank is alleviated.

In an exemplary embodiment, a blank 40, such as a cylindrical tungsten carbide substrate is provided with longitudinally extending helical grooves 42 which are packed with the appropriate powder, e.g., diamond or cBN powder. The blank with grooves may be formed using any known method. For example the cylindrical blank may be formed using conventional methods and then machined to form the grooves. Alternatively, the blank may be molded with the grooves in place. In another exemplary embodiment, the blank may be provided is powder form such that it is solidified during the sintering process. In yet another exemplary embodiment, the blank may be provided in a powder form bound together with a binder.

With the exemplary embodiment shown in FIG. 6, the helical grooves 42 do not extend along the entire length 44 of the blank body 40. In this regard, when the blank is formed, it is formed with a portion 46 not having any ultra hard material. The blank portion including the ultra hard material is then machined to the appropriate shape without being brazed to a shank. Consequently, an endmill is formed where the portion 46 defines a grip portion. The grip portion is used to mount the endmill in different apparatuses, such as machine collets or holding apparatuses. For example, the end portion of the endmill may be shrink fitted in a shrink fit holder which is then mounted onto a tool used for endmilling purposes. In an alternate exemplary embodiment, a longer blank is formed having longitudinal helical grooves extending along the entire length of the blank. In yet a further exemplary embodiment, the blanks may be formed with only a single groove for receiving the appropriate ultra hard material.

Whereas typical endmills require that they be brazed onto a shank because they have a length less than 1.5 inches, the present invention provides for forming endmill blanks having a length greater than 1.6 inches and more preferably greater than 1.7 inches, thus, providing a grip portion and not requiring brazing to an shank. In an exemplary embodiment, an endmill blank is formed having a length greater than 1.75 inches. In another exemplary embodiment, an endmill blank is formed having a length greater than 1.7 inches and up to 2 inches. In another exemplary embodiment, an endmill blank is formed which has a length of at least 2 inches.

Although the present invention has been described and illustrated to respect to multiple embodiments thereof, it is to be understood that it is not to be so limited, since changes and modifications may be made therein which are within the full intended scope of this invention as hereinafter claimed.

Claims

1. A method for forming an end mill having polycrystalline ultra hard material comprising:

providing a blank having a groove;

placing an ultra hard material in the groove;

placing the blank in a refractory metal enclosure;

placing the enclosure in a heater, said heater having a length greater than 1.6 inch; and

pressing the heater with blank in a press while heating using said heater for sintering the ultra hard material in the groove forming a polycrystalline ultra hard material in the groove.

2. The method as recited in claim 1 wherein the heater has a length of about 2.5 inches.

3. The method as recited in claim 1 wherein providing a blank comprises providing a blank having a length of at least 1.6 inches.

4. The method as recited in claim 1 wherein the heater has a length greater than 1.7 inches wherein providing a blank comprises providing a blank having a length greater 1.7 inches.

5. The method as recited in claim 1 wherein the heater has a length greater than 1.75 inches wherein providing a blank comprises providing a blank having a length greater 1.75 inches.

6. The method as recited in claim 1 wherein the heater has a length of about 2 inches wherein providing a blank comprises providing a blank having a length no less than about 2 inches.

7. The method as recited in claim 1 wherein the blank is provided in powder form.

8. The method as recited in claim 1 further comprising machining the blank to form a flute having a cutting edge defined by the polycrystalline ultra hard material.

9. The method as recited in claim 1 wherein the press is selected from the group or presses consisting of belt presses and piston-cylinder presses.

10. The method as recited in claim 1 wherein the heater does not include end heating units at opposite ends thereof.

11. A method for forming an end mill having polycrystalline ultra hard material comprising:

providing a blank having a length greater than 1.6 inches and a groove;

placing an ultra hard material in the groove;

placing the blank in a refractory metal enclosure;

placing the enclosure in a heater; and

pressing the heater in a press while heating using said heater for sintering the ultra hard material in the groove forming a polycrystalline ultra hard material in the groove.

12. The method as recited in claim 11 wherein providing a blank comprises providing a blank having a length greater than 1.7 inches.

13. The method as recited in claim 11 wherein providing a blank comprises providing a blank having a length greater than 1.75 inches.

14. The method as recited in claim 11 wherein providing a blank comprises providing a blank having a length of about 2 inches.

15. The method as recited in claim 11 further comprising machining the blank to form a flute having a cutting edge defined by the polycrystalline ultra hard material.

16. The method as recited in claim 11 wherein the press is selected from the group or presses consisting of belt presses and piston-cylinder presses.

17. The method as recited in claim 11 wherein the heater is elongate and does not include end heating units at opposite ends thereof.

18. An endmill comprising:

a body having a length of at least 1.6 inches and comprising a grip portion, said body being formed from a single piece of material; and

polycrystalline ultra hard material bonded to the body.

19. The endmill as recited in claim 18 wherein the body comprises a length of at least 1.7 inches.

20. The endmill as recited in claim 18 wherein the body comprises a length of at least 1.75 inches.

21. The endmill as recited in claim 18 wherein the body comprises a length not less than 2 inches.

22. The endmill as recited in claim 18 wherein the polycrystalline ultra hard material does not extend to the grip portion.