US3723698A

US3723698A - Stud welding apparatus

Info

Publication number: US3723698A
Application number: US00213294A
Authority: US
Inventors: L Logan; D Sandoval
Original assignee: TREE FIT PROD CORP
Current assignee: TREE FIT PROD CORP
Priority date: 1971-12-29
Filing date: 1971-12-29
Publication date: 1973-03-27
Anticipated expiration: 1990-03-27

Abstract

The present invention relates to stud welding apparatus and involves such an apparatus with means which will accommodate inaccuracies in the manufactured length of studs which are to be welded to provide the accurate lift required to appropriately melt the end of the studs and the portion of the beam to which the studs are to be subsequently attached. The present apparatus also provides means whereby the plunge distance of the stud can be varied and adjusted as desired in the event, for example, the stud is to be joined to a beam where thin metal decking is provided over the beam. The apparatus includes a housing which has first and second end portions and a coil is carried in the housing and is movable axially relative to the housing between first and second positions. An armature is positioned within the coil and is movable with the coil between the aforementioned first and second positions and is also movable axially relative to the coil what is commonly referred to as a lift distance. A first spring acts between the coil and the armature and normally keeps these two mentioned parts axially spaced from each other the aforementioned lift distance. A stud chuck adapted to carry the stud to be welded, is connected to the armature and is movable therewith. Wall means are provided which act between the coil and the armature and prevent the two from becoming axially spaced from each other more than the aforementioned lift distance. A second spring is provided which acts upon the armature urging the same toward the first mentioned position. First electro magnetic means which include the coil are provided for fixedly securing the coil to the housing and prevent axial movement of the same relative to the housing after the coil has been moved from its first position to its second position. Second electro magnetic means are provided which also include the coil for attracting the armature and moving the same axially toward the coil the aforementioned lift distance. Means are also provided for energizing the coil to cause the aforementioned functions. The inertia of the first electro magnetic means is less than the inertia of the second electro magnetic means so that upon energization of the coil, the coil is first fixedly secured to the housing by means of the first electro magnetic means prior to the armature moving axially toward the coil the lift distance by the action of the second electro magnetic means. Movement of the armature toward the coil causes the stud to be lifted from the surface with which it is engaged and then of course during this operation the conventional arc is established between the tip of the stud and the member to which it is engaged and thereafter heavy welding current is passed between the tip of the stud and the beam which causes melting of the end of the stud and also melting of that portion of the beam which is adjacent the end of the stud and to which the stud is to be attached.

Description

United States Patent [1 1 Logan et a1.

[ s] Mar. 27, 1973 [54] STUD WELDING APPARATUS [75] Inventors: Lewis J. Logan, Lakewood; Dante J.

Sandoval, Cleveland, both of Ohio [73] Assignee: Tree-Fit Products Corporation [22] Filed: Dec. 29, 1971 [21] Appl. No.: 213,294

[52] U.S. Cl. ..2l9/98 [51] Int. Cl. ..B23k 9/20 [58] Field of Search ..2l9/98 [56] References Cited UNITED STATES PATENTS 2,640,133 5/1953 Ainsworth et a1. ..2l9/98 3,346,715 10/1967 Jenkins ..2l9/98 Primary Examiner-R. F. Staubly Attorney-George V. Woodling et al.

[57] ABSTRACT The present invention relates to stud welding apparatus and involves such an apparatus with means which will accommodate inaccuracies in the manufactured length of studs which are to be welded to provide the accurate lift required to appropriately melt the end of the studs and the portion of the beam to which the studs are to be subsequently attached. The present apparatus also provides means whereby the plunge distance of the stud can -be varied and adjusted as desired in the event, for example, the stud is to be joined to a beam where thin metal decking is provided over the beam. The apparatus includes a housing which has first and second end portions and a coil is carried in the housing and is movable axially relative to thehousing between first and second positions. An armature is positioned within the coil and is movable with the coil between the aforementioned first and second positions and is also movable axially relative to the coil what is commonly referred to as a lift distance. A first spring acts between the coil and the armature and normally keeps these two mentioned parts axially spaced from each other the aforementioned lift distance. A stud chuck adapted to carry the stud to be welded, is connected to the armature and is movable therewith. Wall means are provided which act between the coil and the armature and prevent the two from becoming axially spaced from each other more than the aforementioned lift distance. A second spring is provided which acts upon the armature urging the same toward the first mentioned position. First electro magnetic means which include the coil are provided for fixedly securing the coil to the housing and prevent axial movement of the same relative to the housing after the coil has been moved from its first position to its second position. Second electro magnetic means are provided which also include the coil for attracting the armature and moving the same axially toward the coil the aforementioned lift distance. Means are also provided for energizing the coil to cause the aforementioned functions. The inertia of the first electro magnetic means is less than the inertia of the second electro magnetic means so that upon energlzatlon of the 0011, the CO1] 15 first fixedly secured to the housing by means of the first electro magnetic means prior to the armature moving axially toward the coil the lift distance by the action of the second electro magnetic means. Movement of the armature toward the' coil causes the stud to be lifted from the surface with which it is engaged and then of course during this operation the conventional arc is established between the tip of the stud and the member to which it is engaged and thereafter heavy welding current ispassed between the tip of the stud and the beam which causes melting of the end of the stud and also melting of that portion of the beam which is adjacent the end of the stud and to which the stud is to be' attached.

l1 Claims, 9 Drawing Figures PATENTEDHARZYISB 3,723,698

sum 2 [1F 6 FIG. 2

INVENTORS LEW/S Il- LOGAN BY DANTE J. SANDOVAL PATENTEUHARZYIQTZE SHEET 3 OF 6 INVENTORS LEW/S J. LOGAN BY DA/VTE J. SANDOVAL -y (digs.

hm mm km vv mm PATENTEUIMRNIQH 3 7 3,59

sum 5 OF 6 INVENTORS LE WIS J. LOGAN BY DA/VTE J. SANDOVAL 4), ALL m 1 STUD WELDING APPARATUS In the stud welding industry, one of the important factors in obtaining consistent and good welds between the end of a stud and a beam to which it is attached is to maintain the proper spacing between a coil and an armature at all stages so that the appropriate amount of lift occurs upon energization of the coil. This has been accomplished by various means in the past and one of the reasons this particular problem is encountered in stud welding is because of inaccuracies in the manufactured length of a stud. Those skilled in the art will appreciate that ifa stud, for the sake of example, is manufactured longer than it is intended to be, that in many stud welding mechanisms, the placing of the stud into engagement with the beam to which it is to be welded and causing the stud and the armature with which it is connected to move axially until the stud reaches the bottom edge of the welding ferrule, will cause the armature to move closer than normal to the uppermost stop in the coil. As a result when the coil is energized the armature will travel a shorter distance thereby lifting the tip of the stud from the beam a shorter distance and providing too short an arc gap for the welding current to pass across resulting in a faulty weld. By the same token if the stud is manufactured too short then the lift will be too great resulting in a faulty weld.

It has also become prevalent in the industry to use the stud welding operation to stud weld studs to metal beams used, for example, in the construction of multistory commercial buildings. It is common in these constructions to have thin metal decking overlying the main metal beams. In these constructions it is desired that the studs be welded to the beams and so it is necessary to burn through the thin metal decking and then have the mechanism plunge the stud the distance necessary to reach the beam.

The present invention enables one to always have the desired lift to provide for handling inaccuracies in the manufactured lengths of welding studs so that consistent welds are obtained time after time. The apparatus also provides that an extended plunge distance can be obtained without throwing out of balance the desired lift as aforementioned. Various other advantages and features are found in the present apparatus and which will be understood by those skilled in the art upon review of the specification.

Other objects and a fuller understanding of this invention may be had by referring to the following description and claims, taken in conjunction with the accompanying drawings, in which:

FIG. 1 is an elevational view in section of the stud welding apparatus of the present invention and this apparatus is shown in the form of astud welding gun;

FIG. 2 is a fragmentary view similar to that shown in FIG. 1 but showing the parts in a different position from that shown in FIG. 1;

FIG. 3 is a fragmentary view similar to that shown in FIG. 2 but with the parts in a still different position;

FIG. 4 is a fragmentary view similar to FIGS. 2 and 3 but with the parts in a still different position;

FIG. 5 is a view taken generally along the line 5-5 of FIG. 2;

FIG. 6 is a view taken generally along the line 6--6 of FIG. 1;

FIG. 7 is a view taken generally along the line 77 of FIG. 2;

FIG. 8 is a view taken along the line 88 of FIG. I; and

FIG. 9 is an enlarged view ofa portion of FIG. 3.

The stud welding apparatus of the present invention has been indicated generally in the drawings by the reference numeral 20 and as will be noted, includes in combination a housing 22 which has first and second end portions indicated generally by the

reference numerals

24 and 25, respectively. Attached to and formed as part of the housing is a pistol grip 27 which serves to provide for the entrance of electrical wiring into the housing and accommodates a trigger type switch 29 which serves to initiate the stud welding operation and function as is well appreciated by those skilled in the art. The electrical timing mechanism through which all of the electrical conductors extend, to time and sequentially actuate the various electrical functions forms no specific part of the present invention and is basically well known to those skilled in the art. Such mechanism might be such as that disclosed in US. Pat. No. 3,346,715 issued Oct. 10, 1967.

The housing 22 is provided with what will be referred to hereinafter as an axial bore and the parts which are provided within this bore will be described in detail hereinafter. A first wall 32 is provided in the axial bore of the housing and is secured in position by means of a set screw 35 as shown and a second wall 33 is also provided in the axial bore of the housing and is located a spaced distance from wall 32 more toward the second end portion 25 of the housing. Both of the first and

second walls

32 and 33 are provided with axial openings which extend therethrough.

A coil 38 is positioned within the axial bore of the housing 22 and this coil comprises a bobbin 40 (See FIG. 9) about which is wound conventional electrical windings 41 and first and

second end plates

43 and 44 are provided at either axial end of the windings. The I coil also comprises a member 46 which has formed on one end thereof what will be referred to as a stop surface 47 which is a surface complementary to a surface on an armature which will be discussed hereinafter and serves to limit the movement of the armature relative to the coil. A set-screw 49 secures the second plate 44 to the member 46. The member 46 is also provided with a surface 51 on an end opposite the stop surface 47 which is for a purpose which will be described'in more detail hereinafter. The coil 38 is capable of axial movement within the housing between what has been referred to hereinafter as first and second positions, simply for ease in describing the operation of the present apparatus. For the sake of illustration only, the first position of the coil will be indicated as shown in FIG. 1 with the first plate 43 in engagement with the first insulated wall 32 and the second position will be that which is shown in FIGS. 2, 3 and 4 of the drawings.

An armature 54 is provided and is positioned at least partially within the coil 38 and is capable of movement with the coil 38 between the aforementioned first and second positions. The armature 54 is also movable axially relative to the coil through what will be referred to as a lift distance. A surface 56 is provided on the armature which surface 56 will be seen from FIG. 9 to be spaced from the stop surface 47 on member 46. The amount of travel between these two surfaces describes the aforementioned lift distance. A spring 58 is positioned in a counter bore within member 46 and engages reference numeral 60 by means of being threadably connected as shown to an insulated member 62 which member 62 is in turn threadably connected to a screwtype connection 64 which connection 64 is also threadably engaged with an insulated portion of the chuck 60. The chuck 60 has a stop member 66 which limits the extension of a stud 68 into the chuck. The

stud 68 shown is a shear connector with an enlarged head 69 and an opposite end 71 which is adapted to be ultimately welded to a metal member.

A second spring 73 is positioned within the axial bore of the housing and at one end engages the first insulated wall 32 and at the other end engages a shoulder on the insulated member 62 which construction insures that the armature is always biased or urged in the direction of the first end portion 24 of the housing, or in other words, in the direction of the chuck 60. Also shown in the drawings is the conventional leg 75 which is adjustably supported at a first end 76 by the housing 22 in a conventional manner and at the opposite or second end 77 is adapted to hold a ferrule chuck 78 which is adapted to hold a ferrule 79 about the end of the stud 68 which is to be welded. This construction is conventional.

The interior of the second end portion 25 of housing 22 is formed into what will generally be referred to as a cylinder and piston construction. The cylinder is indicated by the reference numeral 82 and may be rotated for a purpose which will be described in more detail hereinafter. A piston 85 as shown is mounted within the cylinder and is adapted to move back and forth therein in accordance with the movement of the armature 54. The end 25 of the housing is closed by a cap 83.

It will be seen from the drawing that a shaft 87 is secured to the armature 54 and extends axially through an opening in member 46 and is threadably secured to another axially extending member 90 and as a result,

shaft

87 and 90 move together as a unit. Member 90 is provided with a surface 91 which is opposite and com-' plementary to surface 51 on member 46. Member 90 is physically secured to the piston 85 and as a result, piston 85 must move with member 90. A slot 93 is provided in the axial end of member 90 and is for the purpose of being able to axially adjust the member 90 with respect to the shaft 87 as desired. An opening 95 is provided in a wall 89 which surrounds cylinder 82 and depending upon the rotational position of the cylinder 82, this opening may be completely closed, may be completely open or may be partially open between the two extremes. This is because of a cam shaped end 88 oncylinder 82. The reason for this construction is to enable one to regulate the exit of air from the cylinder which movement of air is caused by the axial to and fro movement of the piston 85 within the cylinder. This enables the movement of the armature to be dampened or slowed so that in plunging the stud into the molten pool of metal splashing of the metal will not result.

A first electro magnetic means is provided for fixedly securing or locating the coil 38 relative to the housing and the position for the purpose of explaining this invention will be referred to as the second position. The first electro magnetic means includes in this particular embodiment several parts and components. However, it will be understood by those skilled in the art that the function to be performed by this first electro magnetic means is to provide an electro magnetic means for physically and securely holding the coil in a desired axial position within the housing. It will also be understood by those skilled in the art that while in this disclosure the first electro magnetic means includes in part the coil 38, that it might also include a separate and entirely different coil or mechanism for magnetically attaching and securing the coil in position. With this in mind, the first electro magnetic means includes a mounting tube 99 located within the housing between the axial opening of the housing and the pistol grip 27 as best seen in FIG. 5 of the drawings. As part of this means there is provided a U-shaped mounting member 101 which is capable of movement in what will be referred to as a generally radial direction with respect to the housing 22 and this U-shaped mounting member 101 is normally biased away from the axial opening in the housing by means of a spring 102. A magnetically attractable member 104 is secured to the ends of the legs of the U-shaped member 101 on a side opposite the mounting tube 99 from spring 102 and this member 104 is provided with a plurality of teeth 106 along the surface of its axial length. These teeth are preferably triangular in shape with the surface of the teeth being disposed at approximately a angle. Complementary teeth 108 are provided on the first and

second plates

43 and 44 at the position on the plates opposite the teeth on the magnetically attractable member 104 so that the two will properly intermesh and hold against axial slippage once engaged. The magnetically attractable member 104 is caused to move from the positions shown in FIGS. 1, 2 and 5 to the positions shown in FIGS. 3 and 4 by means of electrical energization of the coil 38. Upon the coil 38 being energized, the magnetic flux lines produced are caused to flow in the conventional pattern with'respect to the windings 41 of the coil and this flux path is aided by means of the permeability of

plates

43 and 44 and also the magnetic permeability of the material of construction of member 104. The member 104 is attracted by this means, causing it to move radially with respect to the axial opening in the housing 22 against the urging of springs 102 and the teeth 106 and 108 'are engaged preventing any axial movement of the coil 38.

For the purpose of description in this specification, second electro magnetic means are provided for the purpose of moving the armature 54 relative to the coil 38 against the biasing of spring 58. It will be seen in this embodiment that both the first and the second electro magnetic means include the coil 38 as a portion thereof. However, as mentioned hereinbefore, it will be readily understood that separate or different electro magnetic means might be incorporated into a given apparatus. It is also necessary for a proper operation of the presently disclosed apparatus that the coil 38 be fixedly secured to the housing 22 and prevented from axial movement prior to the armature 54 being moved the given lift distance relative to the coil 38. This is insured in the present device because the inertia of the first electro magnetic means is less than the inertia of the second electro magnetic means whereby upon energization of the coil 38 the coil is first fixedly secured to the housing and the armature then moves axially toward the coil the given lift distance. The inertia of the first electro magnetic means includes many factors. However, comprised within this definition is the magnetic flux path and the speed at which the member 104 is magnetically attracted and moved so that teeth 106 are engaged with teeth 108 and of course includes the mass of the U-shaped mounting member 101 and the strength of the spring 102. Also included is the mass of member 104. The inertia of the second electro magnetic means includes the magnetic flux path necessary to magnetically attract the armature toward the coil the given lift distance, the mass of the armature itself and the strength of the spring 58.

The following will be a brief description of the operation of the present device. With the apparatus in the position shown in FIG. 1, a stud 68 is inserted into the chuck 60 in the manner shown and a ferrule 79 is held by the ferrule chuck 78 about the extreme end of the stud as shown. The stud welding gun is moved into position and the extreme end of the stud is engaged upon or with a beam (FIG. 3) to which the stud is to be subsequently welded. This action physically moves the armature and the coil to the positions shown in FIG. 2. This action is accomplished against the biasing of spring 73 which always tends to move the assembly in the opposite direction. The spring 58 is strong enough to overcome any frictional drag in this movement so as to always maintain the armature and coil spaced from each other the given lift distance. The next step involved is for an operator of the stud welding apparatus to press the trigger switch 29 which through means of an electrically controlled stud welding circuit mechanism such as for the sake as that shown in aforementioned U.S. Pat. No. 3,346,715 causes basically the following sequence of operations to occur. The first thing that happens is that the coil is energized (by way of conductors 97) and because the inertia of the first electro magnetic means is less than the inertia of the second electro magnetic means, the magnetically attractable member 104 moves into engagement with the coil so that

teeth

106 and 108 are intermeshed and the coil is prevented from any axial movement. This is shown in FIG. 3. The second electro magnetic means then causes the armature to be moved axially so as to engage the surface 47 with the surface 56 which causes the stud to be lifted from the metal beam. See FIG. 4.

As the armature lifts or moves toward the coil as aforementioned, the electrical control mechanism previously referred to'causes a pilot arc to bedrawn between the extreme tip of the stud 68 and the beam to which it is to be welded and when the armature reaches it, uppermost position, full welding current is impressed between the end of the stud and the beam causing the end of the stud and that portion of the beam to be melted. All of the parts while in this position are illustrated in FIG. 4. In this position it will be noted that surface 51 on the backside of member 46 is spaced from the surface 91 on member 90. When the welding current has been stopped and the coil 38 de-energized, the magnetically attractable member separates from the coil and the armature moves away from the coil the given lift distance. The spring 73 then plunges the molten end of the stud into the molten pool on that portion of the beam which has been melted and upon cooling of the metal are integrally secured together. Engagement of surfaces 51 and 91 assures that the coil returns to the position of FIG. 1. However, assuming there is very little frictional drag and the apparatus is held in the correct position the coil would return by the action of gravity. The piston 85 and cylinder 82 arrangement assures that the plunge movement is not too rapid.

It will therefore be seen in view of the described structure and operation that regardless of the length of the stud (of course within limits) which may result because of manufacturing tolerances or for other reasons, that the proper lift is always obtained because of the ability of the coil and armature to move together before locking of the coil to the housing. This thereby automatically adjusts for any variance in length of the stud due to manufacturing tolerances. It will be appreciated that this particular mechanism also accomplishes the other desired feature of the invention, that is, providing enough plunge distance for example, when welding through thin metal decking onto a beam underneath the decking. The desired plunge is arranged for by the appropriate extension of the stud below the lower edge of the welding ferrule so that the mechanism is projected far enough into the gun in the step shown in FIG. 2 that after the burning operation takes place, sufficient length of the stud will be projected to reach the molten pool. It will therefore be seen that the desired objects of the present invention are economically and conveniently carried out with the ultimate advantage to the user of the device as well as to the manufacturer of the studs.

.each other said lift distance, a second means acting on i said armature urging same to said first position, electro magnetic means for fixedly securing said coil to said housing and preventing movement of the same relative theretowith said coil at said second position, means for energizing said coil, energization of said coil attracting said armature and moving the same axially toward said coil said lift distance.

2. Apparatus as claimed in claim 1 wherein means are provided which act between said coil and said armature to prevent the two from becoming spaced more than said lift distance.

3. Apparatus as claimed in claim 1 wherein said electro magnetic means includes a magnetizable member carried by-said housing and engageable with said coil to prevent movement of said coil.

4. Apparatus as claimed in claim 3 wherein piston and cylinder means are operably connected to said armature to control movement of same between said first and second positions.

5. Apparatus for stud welding including in combination a housing, a coil carried in said housing and movable axially relative to said housing between first and second positions, an armature positioned within said coil and movable with said coil between said first and second positions and also movable axially relative thereto a lift distance, a first spring acting between said coil and said armature and normally keeping the two axially spaced from each other said lift distance, a stud chuck connected to said armature and movable therewith, wall means acting between said coil and said armature preventing the two from becoming axially spaced from each other more than said lift distance, a second spring acting on said armature urging same to said first position, first electro magnetic means including said coil for fixedly securing said coil to said housing and preventing axial movement of the same relative thereto with said coil at said second position, second electro magnetic means including said coil for attracting said armature and moving the same axially toward said coil said lift distance, means for energizing said coil, the inertia of said first electro magnetic means being less than the inertia of said second electro magnetic means whereby upon energization of said coil said coil is fixedly secured to said housing prior to said armature moving axially toward said coil said lift distance.

'6. Apparatus as claimed in claim 5 wherein said wall means comprises a rod connected to said armature which extends through an axial opening in said coil for relative movement with respect to said coil which rod has a portion larger than said axial opening which portion is adopted to engage said coil.

7. Apparatus as claimed in claim 5 wherein said first electro magnetic means also comprises a magnetically attractable member carried by said housing and adapted for generally radial movement with respect to said housing but not adapted for axial movement, energization of said coil causing said magnetically attractable member to be attracted to said coil and preventing further axial movement of said coil.

8. Apparatus as claimed in claim 7 wherein said first electro magnetic means also comprises annular end plates on either end of said coil which plates are constructed of magnetically permeable material and these end plates are engaged by said magnetically attractable member when said coil is energized.

9. Apparatus as claimed in claim 8 wherein the portions of said end plates and said magnetically attractable member which engage are provided with mating teeth which assist in preventing axial slippage.

10. Apparatus as claimed in claim 5 wherein piston means operable in a cylinder are secured to said armature to control movement of the same from said second to said first position.

1]. Stud welding apparatus including in combination a housing, a leg secured to said housing and adapted to engage a metal support to which a stud is to be welded or pass through when welded to an adjacent metal support, an electrical coil located within said housing and adapted to move axially therein between flI St and second positions, an armature positioned within said coil and adapted to move axially with said coil between said first and second positions and also with respect to said coil a liftdistance, a first spring acting between said coil and said armature and normally keeping the two spaced apart' said lift distance, a stud chuck secured to said armature and adapted to move therewith and carry a stud the end of which is adapted to extend through a ferrule carried by the lower end of said leg, a second spring acting on said armature and constantly urging said armature in the direction of said stud chuck, a magnetizable holding member carried by said housing and located in close proximity to said coil, means for magnetizing said holding member and thereby securing the same to said coil which prevents said coil from further axial movement relative to said housing, means for energizing said coil to cause movement of said armature said lift distance relative to said coil and against 'the urging of said first spring, and means connected to said armature to retard movement of same from said second to said first position.

Claims

1. Apparatus for stud welding including in combination a housing, a coil carried in said housing and movable relative to said housing between first and second positions, an armature positioned within said coil and movable with said coil between said first and second positions and also movable relative to said coil a lift distance, a first means acting between said coil and said armature and normally keeping the two spaced from each other said lift distance, a second means acting on said armature urging same to said first position, electro magnetic means for fixedly securing said coil to said housing and preventing movement of the same relative thereto with said coil at said second position, means for energizing said coil, energization of said coil attracting said armature and moving the same axially toward said coil said lift distance.

3. Apparatus as claimed in claim 1 wherein said electro magnetic means includes a magnetizable member carried by said housing and engageable with said coil to prevent movement of said coil.

6. Apparatus as claimed in claim 5 wherein said wall means comprises a rod connected to said armature which extends through an axial opening in said coil for relative movement with respect to said coil which rod has a portion larger than said axial opening which portion is adopted to engage said coil.

11. Stud welding apparatus including in combination a housing, a leg secured to said housing and adapted to engage a metal support to which a stud is to be welded or pass through when welded to an adjacent metal support, an electrical coil located within said housing and adapted to move axially therein between first and second positions, an armature positioned within said coil and adapted to move axially with said coil between said first and second positions and also with respect to said coil a lift distance, a first spring acting between said coil and said armature and normally keeping the two spaced apart said lift distance, a stud chuck secured to said armature and adapted to move therewith and carry a stud the end of which is adapted to extend through a ferrule carried by the lower end of said leg, a second spring acting on said armature and constantly urging said armature in the direction of said stud chuck, a magnetizable holding member carried by said housing and located in close proximity to said coil, means for magnetizing said holding member and thereby securing the same to said coil which prevents said coil from further axial movement relative to said housing, means for energizing said coil to cause movement of said armature said lift distance relative to said coil and against the urging of said first spring, and means connected to said armature to retard movement of same from said second to said first position.