Method of joining steel work-pieces having different gauge ratios

A method of joining a multiple member work-piece includes providing a first steel work-piece having a first thickness and a second steel work-piece having a second thickness. The first thickness is at least twice the second thickness. A third material is disposed in contact with the second steel work-piece. For example, the third material may be in the form of a rivet, a plurality of pins, or a coating material. The method includes resistance welding the first and second work-pieces together. A bonded assembly includes the first and second steel members and the third material being bonded together, where the thickness of the first member is at least twice the thickness of the second member.

TECHNICAL FIELD

This disclosure relates to joining steel members that have different gauge ratios, and an assembly including the joined members.

INTRODUCTION

Resistance welding has been a common and successful process for joining steel work-pieces together. Resistance welding has largely been successful because the materials being joined generally had similar thicknesses to one another. However, when attempting to resistance weld steel work-pieces together that have large differences in thickness, or gauge, the result has been a lack of weld penetration into the thinner steel work-piece. For example, typically, when one of the steel work-pieces is at least twice as thick as the other steel work-piece, the weld penetration has been inadequate, and the weld joint easily breaks apart.

SUMMARY

The present disclosure provides a method for joining steel work-pieces together that have different thicknesses, or gauges, and a resultant joined assembly. A third material, which may be in the form of a rivet, a plurality of pins, or a coating, by way of example, is used to concentrate the welding heat into the thinner steel work-piece, which results in balanced weld penetration and a good weld joint.

In one form, which may be combined with or separate from the other forms described herein, a method of joining a multiple member work-piece is provided. The method includes providing a first steel work-piece having a first thickness and providing a second steel work-piece having a second thickness, where the first thickness is at least twice the second thickness. The method includes disposing a third material in contact with the second steel work-piece. The method further includes resistance welding the first and second steel work-pieces and the third material together.

In another form, which may be combined with or separate from the other forms disclosed herein, a bonded assembly includes a first member formed of a first steel material having a first thickness and a second member formed of a second steel material having a second thickness. The first thickness is at least twice the second thickness. A third material is disposed in contact with the second member. The first and second members and the third material are bonded together.

Additional optional features may be provided, including but not limited to the following: the first thickness being at least three times or at least four times the second thickness; the first and second steel work-pieces being formed of the same material; and/or the first and second steel work-pieces being formed of different materials.

In some examples, the third material is provided in the form of a rivet that may be pierced into the second steel work-piece. The rivet may be inserted only partially into the second work-piece or completely through the second work-piece and pierced into the first work-piece. The rivet has a head disposed on an outer side of the second work-piece, and the rivet may have a shank inserted into/through the second member. The rivet and a die may be used to create a bulge extending from the second work-piece at a faying interface between the first and second work-pieces. Resistance welding is performed by pressing a first electrode against the head of the rivet and a second electrode against an outer side of the first work-piece and passing a current between the first and second electrodes, through the first and second work-pieces, and through the rivet. The resultant bonded assembly includes the head of the rivet being bonded to the second member. The head of the rivet may have a thickness in the range of less than twice the thickness of the second member and greater than one-fifth the thickness of the second member.

In other examples, the third material may be provided in the form of a plurality of pins disposed in contact with both the first and second work-pieces. In such cases, the method may include adding the plurality of pins to the first work-piece using a cold metal transfer arc welding process.

In yet other examples, the third material may be provided in the form of a coating, such as a thermal spray coating, disposed between the first and second work-pieces or members. The third material may be, for example, nickel, an aluminum silicon alloy, a steel alloy, an adhesive material, or a combination thereof.

The above features and advantages and other features and advantages are readily apparent from the following detailed description when taken in connection with the accompanying drawings.

DESCRIPTION

Referring to the drawings, wherein like reference numbers refer to like components,FIG.1is a block diagram illustrating, at a high level, a method10for joining a multiple member work-piece. Referring toFIGS.2A-2D, along withFIG.1, the method10includes a step12of providing a first steel work-piece14having a first thickness t1and a step16of providing a second steel work-piece18having a second thickness t2. As shown inFIG.2C, the first and second work-pieces14,18are provided in a stack-up20in a resistance welding operation, with the second work-piece18being disposed on the first work-piece14.

The thicknesses t1, t2of each of the respective work-pieces14,18are different from one another, with the thickness t1of the first work-piece14being much greater than then thickness t2of the second work-piece18. For example, the first work-piece14is at least twice as thick as the second work-piece18, such that t1≥2*t2. In some examples, t1is at least three times t2, and in some examples, t1is even at least four times t2.

As explained above, work-pieces in a stack-up with substantial differences in thickness would typically not form a good bond to one another in a resistance spot welding operation because a weld nugget would not normally penetrate well into the thinner work-piece, due to the fact that heat would be concentrated in the thicker work-piece. To provide for a well-penetrated weld joint, the method10includes a step22of disposing a third material in contact with the thinner steel work-piece18.

In the example ofFIGS.2A-2D, the third material is provided as an insert or rivet24that is inserted into the second steel work-piece18. In the illustrated example, the rivet24has a head36and a shank40. In this example, the diameter D of the head36is more than twice the diameter E of the shank40, but other head diameters could alternatively be used without falling beyond the spirit and scope of the present disclosure. Furthermore, the head36has a thickness t3that is preferably in the range of less than twice the thickness t2of the second work-piece18and greater than one-fifth the thickness t2of the second work-piece18. Thus, e.g., 2>t3/t2>0.2.

Referring toFIGS.2A-2B, a punch26and die28are used, along with the rivet24, to form a bulge30or other extension that extends from a faying side32of the second work-piece18. The head36of the rivet24is disposed on an outer side38of the second work-piece18and the shank40is pierced or inserted into the second work-piece18. The rivet24could be a self-piercing rivet or another type of insert or rivet. Thus, the bulge30extends from the second work-piece18at a faying interface44between the first and second work-pieces14,18.

Referring now toFIG.2C, and with continued reference toFIG.1, the method10further includes a step34of resistance welding the first and second work-pieces14,18and the rivet24together. In the example ofFIG.2C, the resistance welding operation is a resistance spot welding operation that is performed by pressing a first electrode46against the head36of the rivet24and a second electrode48against an outer side50of the first work-piece14. A current is passed between the first and second electrodes46,48through the first and second work-pieces14,18and through the rivet24. As the current is passed through the rivet shank40and the bulge30of the second work-piece18, joule heat generation is enhanced at the faying interface44between the first and second work-pieces14,18, which improves the weld penetration into second steel work-piece18(that is, into the thinner of the work-pieces14,18).

Referring now toFIG.2D, a balanced weld nugget52is therefore formed at the faying interface44of the steel work-pieces14,18, where the weld nugget52penetrates well into both of the work-pieces14,18and penetrates the rivet24. For example, the weld nugget52may penetrate into each work-piece14,18by 25-75% of the total mass of the weld nugget52. Thus,FIG.2Cillustrates a bonded assembly54that includes the first member14, the second member18, and the third material (which is the rivet24) bonded together through the weld nugget52.

The first and second work-pieces or members14,18may be formed of the same steel material or different steel materials. For example, the work-pieces14,18may be formed of steel materials such as second-generation high-strength (GEN 2) steels (austenitic stainless steels), third-generation advanced high-strength (GEN 3) steels, transformation-induced plasticity (TRIP) steels, twinning-induced plasticity (TWIP) steels, boron steel alloys (such as PHS 1300), interstitial free (IF) steels or other mild steels, high-strength low alloy steels (such as 340HSLA), dual-phase steels (such as DP590), martensitic steels (such as MS1500), multi-phase steels (such as MP1180 or MP980, or dual-phase steels (such as DP980, DP780, or DP590).

Referring now toFIGS.3A-3D, another example of an application of the method10ofFIG.1is illustrated. In this example, a different type of rivet124is disposed through the second work-piece118and into the first work-piece114in a work-piece stack-up120. The rivet124is a blind rivet having a mandrel56disposed through a shank140. The rivet124has a head136disposed on an outer side138of the second work-piece118. The shank140and mandrel56are pierced or otherwise disposed completely through the second work-piece118and in contact with the first work-piece114. For example, the rivet124may be friction stir driven through (with or without assist-heating) the second work-piece118without pre-drilling the second work-piece118, or the rivet124may be inserted through a pre-drilled hole in the second work-piece118. In some variations, the rivet124may be upset after being inserted through the second work-piece118to create a projection58, and part of the mandrel56, such as a top portion, may be removed (if desired).

All other details of the description and figures regarding the work-piece stack-up20ofFIGS.2A-2Dmay apply toFIGS.3A-3D. For example, the thicknesses t1′, t2′ of the first and second work-pieces114,118vary substantially. Thus, the thicknesses t1′, t2′ of each of the respective work-pieces114,118are different from one another, with the thickness t1′ of the first work-piece114being much greater than then thickness t2′ of the second work-piece118. For example, the first work-piece114is at least twice as thick as the second work-piece118, such that t1′≥2*t2′. In some examples, t1′ is at least three times t2′, and in some examples, is even at least four times t2′.

To provide for a well-penetrated weld joint, the method10includes a step22of disposing a third material in contact with both the first and second steel work-pieces114,118. In the example ofFIG.3B, the third material is provided in the form of the blind rivet124, which is inserted through the second steel work-piece118and contacting the first steel work-piece114to provide for greater heating in the second work-piece118.

Referring now toFIG.3C, a resistance spot welding operation is performed by pressing a first electrode146against the head136of the rivet124and a second electrode148against an outer side150of the first work-piece114. A current is passed between the first and second electrodes146,148through the rivet124and the first and second work-pieces114,118. As the current is passed through the rivet shank140and the work-pieces114,118, joule heat generation is enhanced at the faying interface144between the work-pieces114,118, which improves the weld penetration into the thinner steel work-piece118. The heat generated by the electrodes146,148begins to form a molten weld pool151at the faying interface144.

Referring now toFIG.3D, the electrodes146,148have been removed, and the molten weld pool151has hardened into a balanced weld nugget152at the faying interface144. The weld nugget152penetrates well into both of the work-pieces114,118. For example, the weld nugget152may penetrate into each of the first and second work-pieces114,118by 25-75% of the total of the weld nugget152. Thus,FIG.3Dillustrates a bonded assembly154that includes the first member114, the second member118, and the rivet124bonded together through the weld nugget152.

Referring now toFIGS.4A-4D, yet another example of the application of the method10ofFIG.1is illustrated. In this example, a material is coated onto one of the work-pieces. In one variation, the material is thermally sprayed onto a first work-piece214to form a thermal spray coating64on the first work-piece214. For example, a torch may be used to atomize the material into a powder that forms the coating64on the first work-piece214. In the alternative, the coating64could be formed by another process, such as by hot dipping. A second work-piece218is disposed onto the first work-piece214with the coating64disposed between the two work-pieces214,218to form a work-piece stack-up220. Thus, the coating64is in contact with both work-pieces214,218. In the alternative to forming the coating64on solely the first work-piece214, the coating64could also or alternatively be formed on the second work-piece218.

All other details of the description and figures regarding the work-piece stack-ups20,120ofFIGS.2A-2D and3A-3Dmay apply toFIGS.4A-4D. For example, the thicknesses t1″, t2″ of the first and second work-pieces214,218vary substantially. Thus, the thicknesses t1″, t2″ of each of the respective work-pieces214,218are different from one another, with the thickness t1″ of the first work-piece214being much greater than then thickness t2″ of the second work-piece218. For example, the first work-piece214is at least twice as thick as the second work-piece218, such that t1″>2*t2″. In some examples, t1″ is at least three times t2″, and in some examples, t1″ is even at least four times t2″. A thickness u of the coating64is less than the thicknesses t1″, t2″ of either work-piece114,118. For example, the coating thickness u may be one-fifth or less than the thickness t2″ of the thinner work-piece218.

To provide for a well-penetrated weld joint, the method10includes a step22of disposing a third material in contact with both the first and second steel work-pieces214,218. In the example ofFIG.4B, the third material is provided in the form of a coating64at the faying interface244to provide for greater heating in the second work-piece118.

Referring now toFIG.4C, a resistance spot welding operation is performed by pressing a first electrode246against an outer side238of the second work-piece218and a second electrode248against an outer side250of the first work-piece214. A current is passed between the first and second electrodes246,248through the first and second work-pieces214,218and through the coating64. As the current is passed through the coating64and the work-pieces214,218, the coating64enhances joule heat generation at the faying interface244, which improves the weld penetration into the thinner steel work-piece218.

Referring now toFIG.4D, a balanced weld nugget68is therefore formed at the faying interface244between the first and second steel work-pieces214,218, where the weld nugget68penetrates well into both of the first and second work-pieces214,218. For example, the weld nugget68may penetrate into each of the first and second work-pieces214,218by 25-75% of the total of the weld nugget68. Thus,FIG.4Dillustrates a bonded assembly254that includes the first member214, the second member218, and the coating64bonded together through the weld nugget68.

The coating64is preferably formed of a high resistivity material. In some examples, the coating64could be formed of a boron steel alloy (such as PHS1300), a GEN 3 steel, a multi-phase steel (such as MP1180 or MP980), a dual-phase steel (such as DP980, DP780, or DP590), or a high-strength low alloy steel (such as 340HSLA). The coating64could alternatively be formed of nickel or an aluminum-silicon alloy, or an adhesive material. In some examples, the coating64could be formed of combinations of these materials, such as an adhesive containing steel, nickel, and/or an aluminum-silicon alloy.

Referring now toFIGS.5A-5D, yet another example of an application of the method10ofFIG.1is illustrated. In this example, a plurality of projections or pins74are disposed onto the first work-piece314(and/or the second work-piece318). For example, an arc welding torch75may be used in a cold metal transfer process to form the pins74onto an inner surface76of the first work-piece314. In the alternative, the pins74could be added by another process. A second work-piece318is disposed onto the first work-piece314with the pins74disposed between the two work-pieces314,318to form a work-piece stack-up320. Thus, the pins74are in contact with both work-pieces314,318.

All other details of the description and figures regarding the work-piece stack-ups20,120,220ofFIGS.2A-2D,3A-3D, and4A-4Dmay apply toFIGS.5A-5D. For example, the thicknesses t1′″, t2′″ of the first and second work-pieces314,318vary substantially. Thus, the thicknesses t1′″, t2′″ of each of the respective work-pieces314,318are different from one another, with the thickness t1′″ of the first work-piece314being much greater than then thickness t2′″ of the second work-piece318. For example, the first work-piece314is at least twice as thick as the second work-piece318, such that t1′″≥2*t2′″. In some examples, t1′″ is at least three times t2′″, and in some examples, t1′″ is even at least four times t2′″.

To provide for a well-penetrated weld joint, the method10includes a step22of disposing a third material in contact with both the first and second steel work-pieces314,318. In the example ofFIGS.5A-5D, the third material is provided in the form of a plurality of pins74at the faying interface344to provide for greater heating in the second work-piece318.

Referring now toFIG.5C, a resistance spot welding operation is performed by pressing a first electrode346against an outer side338of the second work-piece318and a second electrode348against an outer side350of the first work-piece314. A current is passed between the first and second electrodes346,348through the first and second work-pieces314,318and through the pins74. As the current is passed through the pins74and the work-pieces314,318, the pins74enhance joule heat generation at the faying interface344, which improves the weld penetration into the thinner steel work-piece318.

Referring now toFIG.5D, a balanced weld nugget80is therefore formed at the faying interface344between the first and second steel work-pieces314,318, where the weld nugget80penetrates well into both of the first and second work-pieces314,318. For example, the weld nugget80may penetrate into each of the first and second work-pieces314,318by 25-75% of the total of the weld nugget80. Thus,FIG.5Dillustrates a bonded assembly354that includes the first member314, the second member318, and the pins74bonded together through the weld nugget80. After the spot-welding operation, the pins74may be substantially or fully subsumed within the weld nugget80, as shown inFIG.5D.

The pins74may be formed of, for example CMT (cold metal transfer) print or CMT pins. The pins74may be formed of a steel material, for example, ER70S-3 or ER70S-6 steels, by way of example. An ER70S-3 steel may contain: 0.06-0.15 weight percent carbon; 0.90-1.40 weight percent manganese; 0.45-0.75 weight percent silicon; a maximum of 0.025 weight percent phosphorus; a maximum of 0.035 weight percent sulfur; a maximum of 0.15 weight percent nickel; a maximum of 0.15 weight percent chromium; a maximum of 0.15 weight percent molybdenum; a maximum of 0.03 weight percent vanadium; a maximum of 0.50 weight percent copper; and the balance iron. An ER70S-6 steel may contain: 0.06-0.15 weight percent carbon; 1.40-1.85 weight percent manganese; 0.80-1.15 weight percent silicon; a maximum of 0.025 weight percent phosphorus; a maximum of 0.035 weight percent sulfur; a maximum of 0.15 weight percent nickel; a maximum of 0.15 weight percent chromium; a maximum of 0.15 weight percent molybdenum; a maximum of 0.03 weight percent vanadium; a maximum of 0.50 weight percent copper; and the balance iron.

Though the multiple work-piece stack-ups20,120,220,320illustrated herein include two work-pieces, additional work-pieces could be included in the stack-ups20,120,220,320without falling beyond the spirit and scope of the present disclosure.