Patent Description:
The present disclosure relates to tool bits and, more particularly, to tool bits being composed of multiple materials. <CIT> discloses a tool bit according to the preamble of claims <NUM>, <NUM> and <NUM>.

In one aspect, a tool bit is disclosed according to claim <NUM>.

In another aspect, a tool bit is disclosed according to claim <NUM>.

In yet another aspect, a method of manufacturing a tool bit is disclosed according to claim <NUM>.

Before any embodiments of the disclosure are explained in detail, it is to be understood that the disclosure is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The disclosure is capable of supporting other embodiments and being practiced or being carried out in various ways. Terms of degree, such as "substantially," "about," "approximately," etc. are understood by those of ordinary skill to refer to reasonable ranges outside of the given value, for example, general tolerances associated with manufacturing, assembly, and use of the described embodiments.

<FIG> and <FIG> illustrate a tool bit <NUM> for use with a tool (e.g., a power tool and/or a hand tool). The illustrated tool bit <NUM> includes a tool body having an insertion end portion <NUM> (e.g., a hexagonal drive portion), a working end portion <NUM>, and a connection portion <NUM> (e.g., a shank) extending between the working end portion <NUM> and the insertion end portion <NUM>.

The insertion end portion <NUM> is configured to be connected to the tool. More particularly, the insertion end portion <NUM> is configured to be inserted into and received by a bit holder, chuck, or other structure coupled to or part of the tool. For ease of discussion, all of these types of structures will be referred to as bit holders herein. The insertion end portion <NUM> defines a first end <NUM> of the tool body that is opposite the working end portion <NUM>. The insertion end portion <NUM> is composed of a first material. An outer surface on the insertion end portion <NUM> is at least partially defined by a non-circular profile <NUM>. In the illustrated embodiment, the non-circular profile <NUM> is a hexagonal or hex-shaped profile configured to be received in a hexagonal or hex-shaped bit holder. In other embodiments, the non-circular profile <NUM> may be other suitable profiles, such as D-shaped, flattened, oblong, triangular, square, octagonal, star-shaped, irregular, and the like. A portion of the outer surface on the insertion end portion <NUM> not defined by the non-circular profile <NUM> is defined by a circular profile <NUM>. In other embodiments, the circular profile <NUM> may be another profile, such as square, octagonal, star-shaped, irregular, and the like, or the circular profile <NUM> may be omitted. The circular profile <NUM> is proximate the connection portion <NUM>.

The connection portion <NUM> is positioned between the working end portion <NUM> and the insertion end portion <NUM> (e.g., between the working end portion <NUM> and the circular profile <NUM>). The connection portion <NUM> includes a circular cross-sectional shape and defines a maximum radial dimension R3 (e.g., a maximum radius; <FIG>) relative to a longitudinal axis of the tool bit <NUM>. In additional embodiments, the connection portion <NUM> may define a cross-sectional shape that is rectangular, octagonal, star-shaped, and the like. The connection portion <NUM> is also composed of the first material.

The working end portion <NUM> is configured to engage with a fastener (e.g., a screw). More particularly, the working end portion <NUM> is configured to drive the fastener into a workpiece. With reference to <FIG> and <FIG>, the working end portion <NUM> includes a first segment <NUM> (e.g., a rearward segment) separated from a second segment <NUM> (e.g., a forward segment) by a connection interface <NUM>. As shown in <FIG>, the connection interface <NUM> defines a maximum radial dimension R2 (e.g., a maximum radius) relative to the longitudinal axis of the tool bit <NUM>. A cross-section of the working end portion <NUM> at the maximum radius R2 defines a cross. As such, the maximum radius R2 is measured relative to a circle circumscribed by the cross. In additional embodiments, the cross-section may define a rectangle, an oval, a star, and the like.

With continued reference to <FIG> and <FIG>, the illustrated forward segment <NUM> is composed of a second material and includes a first portion <NUM> and a second portion <NUM>. The second portion <NUM> includes a second end <NUM> (e.g., a tip) of the tool body that is opposite the first end <NUM>. The second portion <NUM> of the working end portion <NUM> is the portion of the tool bit <NUM> that is inserted into a recess of the fastener when the tool bit <NUM> engages and drives the fastener. As such, the second portion <NUM> can be referenced as a fastener engagement portion. In particular, the working end portion <NUM> is inserted into the fastener up to a depth measured from the second end <NUM> (e.g., the axial distance between the second end <NUM> and the interface between the first and second portions <NUM>, <NUM>). At this depth (e.g., a location at which fastener engagement ceases), an outer surface of the working end portion <NUM> defines a maximum radial dimension R1 (e.g., a maximum radius; <FIG>) relative to the longitudinal axis of the tool bit <NUM>. In the depicted embodiment, a cross-section of the working end portion <NUM> at the maximum radius R1 also defines a cross. As such, the maximum radius R1 is measured relative to a circle circumscribed by the cross. In additional embodiments, the cross-section may define a rectangle, an oval, a star, and the like. In the depicted embodiment, the radius R2 is larger than the radius R1. Additionally, the radius R1 and the radius R2 are both larger than the radius R3. Furthermore, a distance from the second end <NUM> to the location of the maximum radius R1 is less than a distance from the second end <NUM> to the location of the connection interface <NUM>.

In the illustrated embodiment, the working end portion <NUM> is composed of the first material and the second material. The second material defines the second segment <NUM> (e.g., the first and second portions <NUM>, <NUM>), and the first material defines a remainder of the working end portion <NUM> (e.g., the first segment <NUM>) not defined by the second material. In the depicted embodiment, the second material has a hardness that is greater than a hardness of the first material. In other words, the second segment <NUM> is harder than the first segment <NUM>. In some embodiments, the hardness of the second material is at least <NUM>% greater than the hardness of the first material. In other embodiments, the hardness of the second material is between <NUM>% and <NUM>% greater than the hardness of the first material.

In the depicted embodiment, the first material is a tool steel. In some embodiments, the first material may be a low carbon steel, such as AISI <NUM>. AISI <NUM> low carbon steel includes a balance of toughness, strength, and ductility. AISI <NUM> low carbon steel includes approximately <NUM>% to <NUM>% carbon and <NUM>% to <NUM>% manganese. In other embodiments, the first material may be a high carbon steel, such as AISI <NUM>. AISI <NUM> high carbon steel includes a high tensile strength. AISI high carbon steel includes approximately <NUM>% to <NUM>% carbon and <NUM>% to <NUM>% manganese. In additional embodiments, the first material may be an alternative material. The tool steel may have a hardness, for example between about <NUM> HRC and about <NUM> HRC. In some embodiments, the tool steel may have a hardness of between about <NUM> HRC and about <NUM> HRC.

In the depicted embodiment, the second material is a high speed steel (HSS), such as PM M4. PM M4 high speed steel includes a fine grain size, small carbides, and a high steel cleanliness, which together provide high wear-resistance, high impact toughness, and high bend strength. PM M4 high speed steel includes approximately <NUM>% carbon, <NUM>% Chromium, <NUM>% tungsten, <NUM>% molybdenum, and <NUM>% vanadium. In additional embodiments, the second material may be an alternative material (e.g., carbide). The high speed steel may have a hardness, for example, of <NUM> HRC or greater.

By using the high or low carbon steel as the first material and the PM M4 high speed steel as the second material, the cost to manufacture the tool bit <NUM> is minimized while the strength of the tool bit <NUM> is maintained. The cost to manufacture the tool bit <NUM> is minimized due to the material being used for the first material generally being inexpensive. The second material compensates for a lower strength of the first material.

<FIG> illustrates a method <NUM> of manufacturing the tool bit <NUM>. Although the illustrated method <NUM> includes specific steps, not all of the steps need to be performed. In addition, the depicted steps do not need to be performed in the order presented. The method <NUM> may also include additional or alternative steps.

The illustrated method <NUM> includes providing a first stock of material (step <NUM>) composed of the first material and providing a second stock of material (step <NUM>) composed of the second material. Step <NUM> includes fixing the first stock of material to the second stock of material (e.g., the forward segment <NUM> composed of the second material is secured to the rearward segment <NUM> composed of the first material). The segments <NUM>, <NUM> are fixed together at the connection interface <NUM>. In the illustrated embodiment, the segments <NUM>, <NUM> are fixed together by a welding process. The first and second stocks of material may be welded via spin welding, resistance welding, laser welding, friction welding, and the like. In other embodiments, the segments <NUM>, <NUM> are fixed together by a different process (e.g., a brazing process or the like). In the depicted embodiment, the first stock of material is a hex-shaped blank and the second stock of material is a cylinder-shaped blank. In additional embodiments, the first and second stocks of material may differ in shape.

An axial length of the second stock of material extending from the connection interface <NUM> is determined (step <NUM>) as discussed in more detail below. The first stock of material and the second stock of material may then be machined or shaped (steps <NUM>, <NUM>) to form the tool bit <NUM>. Shaping the second stock of material (step <NUM>) is based on the determined length (step <NUM>) of the second stock of material. The first stock of material forms the first end <NUM> to the connection interface <NUM>, and the second stock of material forms the second end <NUM> to the connection interface <NUM>. In other words, the first stock of material is shaped to form the insertion end portion <NUM>, the connection portion <NUM>, and the rearward portion <NUM>. The second stock of material is shaped to form the working end portion <NUM> from the second end <NUM> to the connection interface <NUM> (e.g., the forward segment <NUM>). In other embodiments, the method <NUM> can be different (e.g., the axial length of the second stock can be determined before the first and second stock of material are fixed together).

To determine a location of the connection interface <NUM> (step <NUM>), the torsional stress τR<NUM> is calculated at the radius R1. The torsional stress τR<NUM> is related to an applied torque TR<NUM>, the radius R1 that the stress is occurring at, and a polar moment of inertia of the cross section JTR<NUM> at the radius R1. The torsional stress τR<NUM> at the radius R1 is expressed in Equation <NUM>.

The torsional stress τR<NUM> allowed at the radius R2 may then be calculated based on the torsional stress τR<NUM> at the radius R1. The torsional stress τR<NUM> allowed at the radius R2 is a percentage P of the torsional stress τR<NUM> at the radius R1. The percentage P is based on the difference in hardness between the first material and the second material. For example, if the first material was <NUM>% the hardness of the second material, the torsional stress τR<NUM> allowed at the radius R2 would be <NUM>% the torsional stress τR<NUM> at the radius R1. The torsional stress τR<NUM> allowed at the radius R2 is expressed in Equation <NUM>.

In addition to the torsional stress τR<NUM> allowed at the radius R2 being expressed in Equation <NUM>, the torsional stress τR<NUM> allowed at the radius R2 may be related to the applied torque TR<NUM>, the radius R2, and a polar moment of inertia of the cross section JTR<NUM> at the radius R2. The torsional stress τR<NUM> allowed at the radius R2 is expressed in Equation <NUM>.

Equation <NUM> may be equated to Equation <NUM>. Since the applied torque is the same through the drill bit, the torque TR<NUM> at the radius R1 is the same as the torque TR<NUM> at the radius R2. This expression is shown in Equation <NUM>.

The connection interface <NUM> may be selected such that the ratio of the radius R2 to the polar moment of the cross section JTR<NUM> at the radius R2 is less than or equal to the ratio of the radius R1 to the polar moment of the cross section JTR<NUM> at the radius R1 multiplied by the percentage P difference between the hardnesses of the first material and the second material.

In some embodiments, the tool bit <NUM> may have a reduced diameter portion (e.g., the illustrated connection portion <NUM>) that allows the tool bit <NUM> to twist along its length. If the tool bit <NUM> includes this type of reduced diameter portion, the allowed torsional stress at the radius R2 is calculated to account for the reduced diameter portion. The radius R3 is located within the reduced diameter portion. The allowed torsional stress at the radius R2 is illustrated in Equation <NUM>, which is similar to Equation <NUM>.

The connection interface <NUM> may be selected in view of both Equation <NUM> and Equation <NUM>. In other words, the ratio of the radius R2 to the polar moment of the cross section JTR<NUM> at the radius R2 is additionally less than or equal to the ratio of the radius R3 to the polar moment of the cross section JTR<NUM> at the radius R3 multiplied by the percentage P difference between the hardnesses of the first material and the second material.

An axial distance of the connection interface <NUM> from the second end <NUM> may be determined (step <NUM>) based on the ratio of the radius R2 to the polar moment of the cross section JTR<NUM> at the radius R2. In other words, a radius and a polar moment may be calculated along a length of the working end portion <NUM> to determine where the correct ratio occurs. For example, the axial distance of the connection interface <NUM> of a square tip tool bit <NUM> (e.g., size #<NUM> square bit; <FIG>) is based on the ratio of the radius R2 to the polar moment of the cross section JTR<NUM> at the radius R2, as depicted in the table below. In this example, the hardness of the first material is <NUM>% of the hardness of the second material, and the engagement distance (i.e., the location of the maximum radius R1) is about <NUM> inches from the second end <NUM>. As such, the ratio of the radius R1 to the polar moment of the cross section JTR<NUM> at the radius R1 is <NUM>. Using Equation <NUM> above, <NUM>% of <NUM> is <NUM>, which is the target ratio for R2. Based on the table below, the calculated ratio for radius R2 to the polar moment of the cross section JTR<NUM> at the radius R2 is equal to or less than <NUM> when the distance from the second end <NUM> is <NUM> inches. As such, the connection interface <NUM> between the first material and the second material for a size #<NUM> square bit should be at about <NUM> inches from the second end <NUM>.

Determining the axial distance of the connection interface <NUM> of the #<NUM> square bit, as described above, can be applied to different sizes and/or types of bits <NUM>. The table below provides some examples of different sizes and types of bits <NUM> and maintains that the hardness of the first material is <NUM>% of the hardness of the second material. Specifically, the first column in the table below represents the type and size of the bit <NUM> (e.g., PH1 is a size #<NUM> Phillips-head bit, PZ1 is a size #<NUM> Pozidriv-head bit, SQ1 is a size #<NUM> square-head bit, and T10 is a size #<NUM> Torx-head bit). In other words, the number associated with the type/geometry of the bit represents the standard size of the bit head. The table below shows, for example, the axial distance of the connection interface <NUM> of a size #<NUM> Phillips-head bit relative to the tip <NUM> is about <NUM> inches. Specifically, a typical axial distance between the tip <NUM> and the radius R1 (e.g., a depth at which a #<NUM> Phillips-head bit is received within a fastener) is about <NUM> inches. At that axial length, the polar moment of the cross section JTR1 at radius R1 is <NUM> and radius R1 is <NUM> inches, such that a ratio of the radius R1 to the polar moment of the cross section JTR<NUM> at the radius R1 is <NUM>. Taking in account for the differential between the hardnesses of the first and second materials, <NUM>% of <NUM> is about <NUM>, which is the target ratio for R2. As shown in the table below, the calculated ratio for radius R2 to the polar moment of the cross section JTR<NUM> at the radius R2 is equal to or less than <NUM> when the distance from the second end <NUM> is about <NUM> inches. As such, the connection interface <NUM> between the first material and the second material for a size #<NUM> Phillips-head bit should be at about <NUM> inches from the second end <NUM>. Similar calculations can be performed for the other types of tool bits <NUM> within the table below.

In other types of tool bits <NUM>, a T15 bit includes a distance between the connection interface <NUM> and the tip <NUM> of about <NUM> inches with a fastener engagement depth of about <NUM> inches, a T25 bit includes a distance between the connection interface <NUM> and the tip <NUM> of about <NUM> inches with a fastener engagement depth of about <NUM> inches, and a T27 bit includes a distance between the connection interface <NUM> and the tip <NUM> of about <NUM> inches with a fastener engagement depth of about <NUM> inches.

With reference to <FIG>, welding the first material to the second material may create a heat affect zone <NUM>. The heat affect zone <NUM> has a lower material strength than a material strength of the second material. A distance at which the heat affect zone <NUM> has affected the second material is added to the axial distance of the original connection interface 46a to offset a desired connection interface 46b an additional amount. For example, if the heat affect zone <NUM> is <NUM> inches and the initially calculated axial distance of the connection interface 46a is <NUM> inches from the second end <NUM>, a revised connection interface 46b to account for the heat affect zone <NUM> would be <NUM> inches from the second end <NUM>.

In some scenarios, the tool bit <NUM> may be stress relieved or heat treated after the first material is welded to the second material. In such scenarios, the heat affect zone <NUM> may be neglected, and an offset for the connection interface <NUM> would not need to be calculated.

Claim 1:
A tool bit (<NUM>) comprising:
a drive portion (<NUM>) configured to be selectively coupled to a tool, the drive portion (<NUM>) being composed of a first material;
a shank (<NUM>) coupled to the drive portion (<NUM>), the shank (<NUM>) being composed of the first material; and
a working end portion (<NUM>) including a first segment (<NUM>) and a second segment (<NUM>), the first segment (<NUM>) coupled to the shank (<NUM>) and being composed of the first material, the second segment (<NUM>) fixed to the first segment (<NUM>) at a connection interface (<NUM>), the second segment (<NUM>) being composed of a second material different than the first material, characterised by the second segment (<NUM>) being configured to engage a fastener for the working end portion (<NUM>) to drive the fastener,
wherein a distance between the connection interface (<NUM>) and a tip (<NUM>) of the second segment (<NUM>) is based on a first ratio of a maximum radial dimension (R1, R2, R3) at a location along the tool bit (<NUM>) to a polar moment at the location, and wherein the first ratio is multiplied by a percentage (P) difference between hardnesses of the first material and the second material.