Tool bit having a bimetal tip

A tool bit includes a drive portion configured to be selectively coupled to a tool. The drive portion is composed of a first material. The tool bit includes a working end portion having a shape configured to correspond with a recess of a fastener for the working end portion to engage and drive the fastener. The working end portion includes a first segment and a second segment. The first segment is located between the second segment and the drive portion. The first segment is composed of the first material. The second segment is fixed to the first segment at a connection interface. The second segment is composed of a second material different than the first material.

FIELD OF THE DISCLOSURE

The present disclosure relates to tool bits and, more particularly, to tool bits being composed of multiple materials.

SUMMARY

In one aspect, a tool bit includes a drive portion configured to be selectively coupled to a tool. The drive portion is composed of a first material. The tool bit also includes a shank coupled to the drive portion. The shank is composed of the first material. The tool bit includes a working end portion having a first segment and a second segment. The first segment is coupled to the shank and being composed of the first material. The second segment is fixed to the first segment at a connection interface. The second segment is composed of a second material different than the first material. The second segment is configured to engage a fastener for the working end portion to drive the fastener.

In another aspect, a tool bit includes a drive portion configured to be selectively coupled to a tool. The drive portion is composed of a first material. The tool bit includes a working end portion having a shape configured to correspond with a recess of a fastener for the working end portion to engage and drive the fastener. The working end portion includes a first segment and a second segment. The first segment is located between the second segment and the drive portion. The first segment is composed of the first material. The second segment is fixed to the first segment at a connection interface. The second segment is composed of a second material different than the first material.

In yet another aspect, a method of manufacturing a tool bit includes providing a first stock of material composed of a first material, providing a second stock of material composed of a second material different than the first material, fixing the first stock of material and the second stock of material together to form a connection interface, determining a length of the second stock of material extending from the connection interface, shaping the first stock of material to form a first segment of a working end portion, and shaping the second stock of material based on the determined length to form a second segment of the working end portion. The second segment is configured to engage a fastener for the working end portion to drive the fastener.

DETAILED DESCRIPTION

FIGS.1and2illustrate a tool bit10for use with a tool (e.g., a power tool and/or a hand tool). The illustrated tool bit10includes a tool body having an insertion end portion14(e.g., a hexagonal drive portion), a working end portion18, and a connection portion22(e.g., a shank) extending between the working end portion18and the insertion end portion14.

The insertion end portion14is configured to be connected to the tool. More particularly, the insertion end portion14is 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 portion14defines a first end26of the tool body that is opposite the working end portion18. The insertion end portion14is composed of a first material. An outer surface on the insertion end portion14is at least partially defined by a non-circular profile30. In the illustrated embodiment, the non-circular profile30is a hexagonal or hex-shaped profile configured to be received in a hexagonal or hex-shaped bit holder. In other embodiments, the non-circular profile30may 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 portion14not defined by the non-circular profile30is defined by a circular profile34. In other embodiments, the circular profile34may be another profile, such as square, octagonal, star-shaped, irregular, and the like, or the circular profile34may be omitted. The circular profile34is proximate the connection portion22.

The connection portion22is positioned between the working end portion18and the insertion end portion14(e.g., between the working end portion18and the circular profile34). The connection portion22includes a circular cross-sectional shape and defines a maximum radial dimension R3(e.g., a maximum radius;FIG.2) relative to a longitudinal axis of the tool bit10. In additional embodiments, the connection portion22may define a cross-sectional shape that is rectangular, octagonal, star-shaped, and the like. The connection portion22is also composed of the first material.

The working end portion18is configured to engage with a fastener (e.g., a screw). More particularly, the working end portion18is configured to drive the fastener into a workpiece. With reference toFIGS.1and2, the working end portion18includes a first segment38(e.g., a rearward segment) separated from a second segment42(e.g., a forward segment) by a connection interface46. As shown inFIG.2, the connection interface46defines a maximum radial dimension R2(e.g., a maximum radius) relative to the longitudinal axis of the tool bit10. A cross-section of the working end portion18at the maximum radius R2defines a cross. As such, the maximum radius R2is 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 toFIGS.1and2, the illustrated forward segment42is composed of a second material and includes a first portion50and a second portion54. The second portion54includes a second end58(e.g., a tip) of the tool body that is opposite the first end26. The second portion54of the working end portion18is the portion of the tool bit10that is inserted into a recess of the fastener when the tool bit10engages and drives the fastener. As such, the second portion54can be referenced as a fastener engagement portion. In particular, the working end portion18is inserted into the fastener up to a depth measured from the second end58(e.g., the axial distance between the second end58and the interface between the first and second portions50,54). At this depth (e.g., a location at which fastener engagement ceases), an outer surface of the working end portion18defines a maximum radial dimension R1(e.g., a maximum radius;FIG.2) relative to the longitudinal axis of the tool bit10. In the depicted embodiment, a cross-section of the working end portion18at the maximum radius R1also defines a cross. As such, the maximum radius R1is 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 R2is larger than the radius R1. Additionally, the radius R1and the radius R2are both larger than the radius R3. Furthermore, a distance from the second end58to the location of the maximum radius R1is less than a distance from the second end58to the location of the connection interface46.

In the illustrated embodiment, the working end portion18is composed of the first material and the second material. The second material defines the second segment42(e.g., the first and second portions50,54), and the first material defines a remainder of the working end portion18(e.g., the first segment38) 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 segment42is harder than the first segment38. In some embodiments, the hardness of the second material is at least 5% greater than the hardness of the first material. In other embodiments, the hardness of the second material is between 5% and 30% 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 1018. AISI 1018 low carbon steel includes a balance of toughness, strength, and ductility. AISI 1018 low carbon steel includes approximately 0.14% to 0.2% carbon and 0.6% to 0.9% manganese. In other embodiments, the first material may be a high carbon steel, such as AISI 1065. AISI 1065 high carbon steel includes a high tensile strength. AISI high carbon steel includes approximately 0.6% to 0.7% carbon and 0.6% to 0.9% manganese. In additional embodiments, the first material may be an alternative material. The tool steel may have a hardness, for example between about 45 HRC and about 60 HRC. In some embodiments, the tool steel may have a hardness of between about 45 HRC and about 55 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 1.4% carbon, 4% Chromium, 5.65% tungsten, 5.2% molybdenum, and 4% 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 60 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 bit10is minimized while the strength of the tool bit10is maintained. The cost to manufacture the tool bit10is 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.3illustrates a method62of manufacturing the tool bit10. Although the illustrated method62includes 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 method62may also include additional or alternative steps.

The illustrated method62includes providing a first stock of material (step66) composed of the first material and providing a second stock of material (step70) composed of the second material. Step74includes fixing the first stock of material to the second stock of material (e.g., the forward segment42composed of the second material is secured to the rearward segment38composed of the first material). The segments38,42are fixed together at the connection interface46. In the illustrated embodiment, the segments38,42are 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 segments38,42are 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 interface46is determined (step78) as discussed in more detail below. The first stock of material and the second stock of material may then be machined or shaped (steps82,86) to form the tool bit10. Shaping the second stock of material (step86) is based on the determined length (step78) of the second stock of material. The first stock of material forms the first end26to the connection interface46, and the second stock of material forms the second end58to the connection interface46. In other words, the first stock of material is shaped to form the insertion end portion14, the connection portion22, and the rearward portion38. The second stock of material is shaped to form the working end portion18from the second end58to the connection interface46(e.g., the forward segment42). In other embodiments, the method62can 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 interface46(step78), the torsional stress τR1is calculated at the radius R1. The torsional stress τR1is related to an applied torque TR1, the radius R1that the stress is occurring at, and a polar moment of inertia of the cross section JTR1at the radius R1. The torsional stress τR1at the radius R1is expressed in Equation 1.

The torsional stress τR2allowed at the radius R2may then be calculated based on the torsional stress τR1at the radius R1. The torsional stress τR2allowed at the radius R2is a percentage P of the torsional stress τR1at 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 80% the hardness of the second material, the torsional stress τR2allowed at the radius R2would be 80% the torsional stress τR1at the radius R1. The torsional stress τR2allowed at the radius R2is expressed in Equation 2.

In addition to the torsional stress τR2allowed at the radius R2being expressed in Equation 2, the torsional stress τR2allowed at the radius R2may be related to the applied torque TR2, the radius R2, and a polar moment of inertia of the cross section JTR2at the radius R2. The torsional stress τR2allowed at the radius R2is expressed in Equation 3.

Equation 2 may be equated to Equation 3. Since the applied torque is the same through the drill bit, the torque TR1at the radius R1is the same as the torque TR2at the radius R2. This expression is shown in Equation 4.

The connection interface46may be selected such that the ratio of the radius R2to the polar moment of the cross section JTR2at the radius R2is less than or equal to the ratio of the radius R1to the polar moment of the cross section JTR2at the radius R1multiplied by the percentage P difference between the hardnesses of the first material and the second material.

In some embodiments, the tool bit10may have a reduced diameter portion (e.g., the illustrated connection portion22) that allows the tool bit10to twist along its length. If the tool bit10includes this type of reduced diameter portion, the allowed torsional stress at the radius R2is calculated to account for the reduced diameter portion. The radius R3is located within the reduced diameter portion. The allowed torsional stress at the radius R2is illustrated in Equation 5, which is similar to Equation 4.

The connection interface46may be selected in view of both Equation 5 and Equation 4. In other words, the ratio of the radius R2to the polar moment of the cross section JTR2at the radius R2is additionally less than or equal to the ratio of the radius R3to the polar moment of the cross section JTR3at the radius R3multiplied by the percentage P difference between the hardnesses of the first material and the second material.

An axial distance of the connection interface46from the second end58may be determined (step78) based on the ratio of the radius R2to the polar moment of the cross section JTR2at the radius R2. In other words, a radius and a polar moment may be calculated along a length of the working end portion18to determine where the correct ratio occurs. For example, the axial distance of the connection interface46of a square tip tool bit10(e.g., size #2 square bit;FIG.4) is based on the ratio of the radius R2to the polar moment of the cross section JTR2at the radius R2, as depicted in the table below. In this example, the hardness of the first material is 80% of the hardness of the second material, and the engagement distance (i.e., the location of the maximum radius R1) is about 0.08 inches from the second end58. As such, the ratio of the radius R1to the polar moment of the cross section JTR1at the radius R1is 2614.5. Using Equation 4 above, 80% of 2614.5 is 2091.6, which is the target ratio for R2. Based on the table below, the calculated ratio for radius R2to the polar moment of the cross section JTR2at the radius R2is equal to or less than 2091.6 when the distance from the second end58is 0.16 inches. As such, the connection interface46between the first material and the second material for a size #2 square bit should be at about 0.16 inches from the second end58.

Distance from the second end (inches)Polar Moment of Inertia of the cross sectionRadius (inches)R⁢2JTR⁢20.080.000031170.0814962614.5670.10.000033280.0830712496.120.120.000036080.0846462346.0550.140.000040290.086222139.9970.160.000046130.0877951903.214

Determining the axial distance of the connection interface46of the #2 square bit, as described above, can be applied to different sizes and/or types of bits10. The table below provides some examples of different sizes and types of bits10and maintains that the hardness of the first material is 80% of the hardness of the second material. Specifically, the first column in the table below represents the type and size of the bit10(e.g., PH1is a size #1 Phillips-head bit, PZ1is a size #1 Pozidriv-head bit, SQ1is a size #1 square-head bit, and T10is a size #10 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 interface46of a size #1 Phillips-head bit relative to the tip58is about 0.087 inches. Specifically, a typical axial distance between the tip58and the radius R1(e.g., a depth at which a #1 Phillips-head bit is received within a fastener) is about 0.075 inches. At that axial length, the polar moment of the cross section JTR1at radius R1is 0.00000840 and radius R1is 0.058544 inches, such that a ratio of the radius R1to the polar moment of the cross section JTR1at the radius R1is 6969.524. Taking in account for the differential between the hardnesses of the first and second materials, 80% of 6969.524 is about 5575.62, which is the target ratio for R2. As shown in the table below, the calculated ratio for radius R2to the polar moment of the cross section JTR2at the radius R2is equal to or less than 5575.62 when the distance from the second end58is about 0.087 inches. As such, the connection interface46between the first material and the second material for a size #1 Phillips-head bit should be at about 0.087 inches from the second end58. Similar calculations can be performed for the other types of tool bits10within the table below.

Tip TypeDistance between the radius R1 and the second end (inches)Distance between the connection interface and the second end (inches)Polar Moment of Inertia of the cross sectionRadius (inches)R⁢2JTR⁢2PH10.075—0.000008400.0585446969.524—0.0870.000011900.0639005369.748PH20.1180.000048890.0976771997.897—0.1380.000070680.1074801520.661PH30.135—0.000115000.1181101027.043—0.2050.000146100.118110808.419PZ10.07—0.000007290.0574897886.008—0.0830.000009900.0625006313.131PZ20.13—0.000063200.1041941648.639—0.160.000086100.1138701322.532PZ30.15—0.000124000.118110952.500—0.250.000162470.118110726.965SQ10.08—0.000014980.0664874438.385—0.130.000019840.0690003477.823SQ30.09—0.000058470.0951341627.057—0.160.000078180.0991801268.611T100.07—0.000007020.0533577600.712—0.120.000009220.0559706070.499T250.1—0.000047160.0866911838.232—0.160.000061200.0890001454.248T300.12—0.000111000.108388976.468—0.190.000148400.113250763.140T400.13—0.000245600.130452531.156—0.2120.000323400.136861423.194

In other types of tool bits10, a T15bit includes a distance between the connection interface46and the tip58of about 0.12 inches with a fastener engagement depth of about 0.07 inches, a T25bit includes a distance between the connection interface46and the tip58of about 0.16 inches with a fastener engagement depth of about 0.1 inches, and a T27bit includes a distance between the connection interface46and the tip58of about 0.175 inches with a fastener engagement depth of about 0.11 inches.

With reference toFIG.5, welding the first material to the second material may create a heat affect zone90. The heat affect zone90has a lower material strength than a material strength of the second material. A distance at which the heat affect zone90has affected the second material is added to the axial distance of the original connection interface46ato offset a desired connection interface46ban additional amount. For example, if the heat affect zone90is 0.11 inches and the initially calculated axial distance of the connection interface46ais 0.16 inches from the second end58, a revised connection interface46bto account for the heat affect zone90would be 0.27 inches from the second end58.

In some scenarios, the tool bit10may be stress relieved or heat treated after the first material is welded to the second material. In such scenarios, the heat affect zone90may be neglected, and an offset for the connection interface46would not need to be calculated.