Patent Application
20140328640
The present disclosure relates to a drill bit having a cutting end made of high speed steel and a shank end made of a softer steel.
This section provides background information related to the present disclosure which is not necessarily prior art.
Wood drill bits such as disclosed in U.S. Pat. No. 1,887,372 have been previously known to include a tip that is attached to a body, wherein the tip is formed of a hard metal alloy and the body is made from alloy steel, high-speed steel, high carbon steel, tool steel or the like. The separate elements are formed by casting, sintering molding, or grinding and then they are secured together in working relation by brazing or welding. The bimetal cutting tool is known to take advantage of attaching the hard metal alloys to a softer metal body so as to reduce the cost associated with using hard metal alloys to form the entire tool. Although the general technology of bimetal drill bits is known, it is desirable in the art to provide an improved drill bit design and method of assembly that provides improved drilling and lifespan characteristics. In addition, it is desirable to provide a bimetal drill bit that is readily recognizable to a user as a metal drill bit having improved metal cutting capabilities as well as a longer life span.
This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.
The present disclosure provides a bi-metal drill bit including a body defining a cutting end and a shank end. At least a portion of the cutting end is formed of a first metal section and at least a portion of the shank end is formed of a second metal section that is welded to the first metal section. The first metal section has a first metal having a material hardness that is higher than a second material hardness of the second metal section. One of the first and second metal sections is treated either by coating or heat treating so as to have a recognizable different appearance than the other of the first and second metal sections. This treatment allows a user to readily recognize that the drill bit is a bi-metal drill bit having improved cutting characteristics due to the hardened cutting end and improved lifespan due to the softer metal body.
The bi-metal drill bit is designed for drilling through sheet-metal and the first metal section is formed from a high-speed steel, e.g., M42 (8% cobalt), M35 (5% cobalt), or M2. The first metal section preferably has an HRc hardness of at least approximately 65 HRc, for example an HRc in the high 60s. This type of steal is more expensive, more brittle, and has a higher electrical resistance than ordinary steel. The second metal section is made from ordinary tool steel, such as 65 Mn steel. This is a softer material with an HRc hardness between approximately 40-50 HRc. This steel is less expensive and more electrically conductive than the high-speed steel used in the first metal section. The length to diameter ratio of the first metal section has been optimized to provide good cutting action for sheet-metal having a thickness of ¼ inch or less. The lengths of the first metal section and the second metal section have been optimized: (1) to allow the first metal section to be able to be held by a welding machine during welding; (2) to allow passage of sufficient current through the first metal section for good electrical resistance welding; (3) to provide better life of the drill bit; (4) to provide better bending toughness in the second metal portion after the first metal section breaks through the sheet-metal; and (5) to minimize the cost of the components of the drill bit.
Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.
The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure.
Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.
Example embodiments will now be described more fully with reference to the accompanying drawings.
Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail.
The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed.
When an element or layer is referred to as being “on,” “engaged to,” “connected to,” or “coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to,” “directly connected to,” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.
Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments.
With reference to
The first metal section 16 is formed from a high-speed steel, e.g. M42 (8% cobalt), M35 (5% cobalt), or M2. The first metal section 16 is a hard material that is good at cutting metal, with an HRc hardness in the high 60s (e.g., at least 65 HRc). This type of steel is more expensive, more brittle, and has a higher electrical resistance than ordinary tool steel.
The second metal section 18 is made from an ordinary tool steel such as 65 Mn steel. This is a softer material with an HRc hardness in the 40s to low 50s (e.g., approximately 40 HRc to approximately 56 HRc). It is less expensive and more electrically conductive than the high-speed steel used for the first metal section 16.
With reference to
The threads 28 have a length that extends along the length of the first metal section 16 and along a portion of the second metal section 18. Preferably, the threads 28 extend along the second metal section 18 a distance that is greater than a length of the first metal section 16.
The tip 30 has cutting edges, and can have a number of possible configurations, e.g., a self-centering tip (pilot point), as illustrated in
As shown in
The primary benefits of the bi-metal drill bit 10 include lowering the cost while increasing the drilling performance and drilling life of the drill bit. The drill bit 10 is designed to extend the drilling life, reduce the cost and improve the manufacturability. The high speed steel tip improves the drilling life while the fluted/threaded region improves the durability to resist breaking within the shank and fluted region.
Premium drill bits tend to be composed of hard metal alloys, such as a high-speed steel (HSS) material. The hard metal alloy material is harder and provides faster and cleaner cutting at the cutting edges at the tip, than less expensive drill bits that are made of ordinary steel. A drawback of hard metal alloy drill bits is its relatively low toughness as compared with ordinary steel, particularly in the fluted region behind the front cutting edges. Toughness is defined as the ability of a material to absorb energy without failure. Current hard metal alloy drill bits are susceptible to failure in the fluted region when submitted to an impact load because the material also tends to be quite brittle. A typical case of impact loading happens during drilling a relatively thin material (such as ¼″ or less steel plate or sheet metal 40); at the moment when the drill bit 10 breaks through the plate 40, there is the potential of a sudden side load if the bit 10 is not perfectly perpendicular to the plate 40 (see
The proposed bi-metal drill bit 10 as described above addresses the weakness of a drill bit composed solely of a hard metal alloy by replacing much of the fluted region with a much tougher and less expensive material. This material 18 has properties that are compatible for welding to the hard metal alloy tip 16, but additionally must have good toughness properties.
The length to diameter ratio of the first hard metal alloy section 16 has been optimized to provide good cutting action in sheet-metal having a thickness of ¼ inch or less, while allowing passage of sufficient current through the front section 16 for good electric resistance welding, and also being short enough to minimize cost and provide better overall strength and life in the fluted rear section 18 after the cutting tip breaks through the sheet-metal. To minimize cost, the volume of hard metal alloy being used has been minimized. For optimizing manufacturability of the first metal section 16 and life of the drill bit, one key factor is the length/diameter ratio (L/D) of the first metal section 16. For example, a typical propulsion method to move material in an automated feed device used in high speed (e.g., about one weld every five seconds) mass production is to use a vibration feed machine to supply the first rod-shaped blank 22 to the resistance weld machine. It has been discovered that an L/D ratio of at least 0.7 is desired for vibratory systems to be able to properly orient the first rod-shaped blank 22 for the welding machine.
Other factors that impact the final length of the first rod-shaped blank 22 also include: the tip design (e.g., self-centering, split point, etc.), the size of heat affected zone (HAZ) due to electric resistance welding, the size of the degradation zone at electrode contact area during resistance welding, and the minimum length of high speed steel material between HAZ and the cutting edge (also known as edge thickness).
Table 1 shows the entire drilling range and the minimum first metal section (TIP) 16 lengths required for self-centering type bi-metal drill bits. Table 1 also shows the upper limit of the first metal section (TIP) 16 length to confidently build production equipment that meets the fast cycle times required for such a high volume product. As can be seen from the table, a minimum to maximum length to diameter ratio (L/D) of the first rod-shaped blank 22 (referred to as TIP) can range from 0.7 to 3.0 while the specific range is detailed in Table 1 for each size of bi-metal drill bit. By way of example, for a 3/16″ drill bit, the minimum to maximum L/D ratio is from 1.3 to 3; for a ¼″ drill bit, the minimum to maximum L/D ratio is from 1.0 to 2.3; and for a ½″ drill bit, the minimum to maximum L/D ratio is from 0.7 to 1.5. Although Table 1 ranges from 3/16″ to ½″ drill bits, other larger and smaller bi-metal drill bits can also be used.
Table 2 is similar to Table 1 but includes data for a split point-type (SP) bi-metal drill bit as compared to the self-centering bi-metal drill bit in Table 1.
The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.
This application claims the benefit of U.S. Provisional Application No. 61/860987, filed on Aug. 1, 2013, and is a Continuation-in-Part of U.S. Design Pat. Application No. 29/449538, filed on Mar. 15, 2013 and a Continuation-in-Part of U.S. Design Pat. Application No. 29/468347, filed on Sep. 30, 2013. The entire disclosures of the above applications are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61860987 | Aug 2013 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 29449538 | Mar 2013 | US |
| Child | 14205577 | US | |
| Parent | 29468347 | Sep 2013 | US |
| Child | 29449538 | US |
