AU706778B2

AU706778B2 - Screw driving-in process

Info

Publication number: AU706778B2
Application number: AU43456/96A
Authority: AU
Inventors: Helmut Osterle; Erich Palm
Original assignee: SFS Industrie Holding AG
Current assignee: SFS Industrie Holding AG
Priority date: 1994-12-21
Filing date: 1995-12-18
Publication date: 1999-06-24
Anticipated expiration: 2015-12-18
Also published as: PL320855A1; DK0799113T3; AU4345696A; PL177827B1; EP0799113A1; EP0799113B1; RU2153605C2; DE59504846D1; WO1996019320A1; CA2208700A1; CN1170377A; CZ177797A3; CN1046452C; GR3029398T3; FI114974B; JPH10500364A; ES2129890T3; ATE175612T1; FI972606A; DE4445812A1

Abstract

In a process for driving in a self-boring, self-piercing, thread-shaping or thread-cutting screw (1), an axial percussion effect (6) is added to the rotary drive (7) during the hole boring step. During the thread-shaping step, the axial percussion effect is stopped and only the rotary drive remains.

Description

Screw driving-in process The invention relates to a process for driving in a self-drilling or selfpiercing, thread-shaping or thread-cutting screw, which has a drilling part or a hole-shaping end section and a shaft with a self-shaping or self-cutting thread, in which during a drilling or hole-forming operation an axial percussion effect is applied, generated by percussion drill-like continuous impact movements.

DE-A 14 78 914 describes a process of the aforementioned type. In the known process, the percussion effect consists of a single stroke, which is exerted in order to produce the hole. Then the screw is screwed into the work piece. This known process can be used for thin materials only if a stop is provided on the opposite side, in order to prevent bending of the material when the stroke to produce the hole is exerted. Providing such a stop requires an additional work step, which lengthens the driving-in time, and is ,**-furthermore not always possible. Furthermore, until now, when driving in screws, attention was always paid to ensuring that the drilling process is *°"finished before the thread-shaping process starts, since the advance speed is significantly greater, in accordance with the thread pitch, than the usual 20 drilling advance. In a drilling process, a corresponding axial force and also a corresponding torque must be applied, while after engagement of the first thread turn, practically only a corresponding torque needs to be applied.

From US-A 4,370,906 a process to drive in a self-piercing as well as thread-shaping or thread-cutting screw is known, wherein during the hole- 25 forming process a percussion effect is added, acting in the axial direction.

°..This percussion effect is generated by percussion drill-like continuous impact movements. The percussion effect is completely eliminated during the following thread-forming or thread-cutting operations.

Summary of the Invention The present invention is a process for driving in a self-boring or self hole-forming, and thread-forming or thread-cutting screw which has a drilling part or a hole-forming end section and a shaft with a first selfforming or self-tapping thread, in which during a drilling or hole-forming operation by the screw an axially-acting percussion effect is applied which is induced by constant impact movements produced in the manner of a hammer-drill, characterised in that during the drilling or hole-forming operation, the axially-acting percussion effect is applied with a rotary drive for the screw, and in that during a subsequent thread-forming or cutting operation the percussion effect is maintained or reduced in its intensity, or eliminated entirely.

An advantage of at least some embodiments of the present invention is that a process of the type stated initially is proposed, which may provide optimum shaping and optimum fit in the thread, especially for thin materials, with a shorter driving-in time.

Another advantage of the process according to the invention lies primarily in the possibility of using the process even for thin materials, without having to provide a stop on the opposite side in order to prevent bending. While a percussion screwdriver, i.e. a combination of a percussion drill and percussion screwdriver is known from DE 43 01 610 Al as well as DE 42 36 819 Al, in which the percussion effect can be shut off, these are neither intended nor suitable for a process for driving in self-drilling or selfpiercing as well as thread-shaping or thread-cutting screws.

In the process according to the invention, the fact that an axial percussion effect is added has a positive effect whether a drilling part with a 20 cutting effect or a hole-shaping end section with non-cutting production of a hole is provided on the screw. The drilling time or the time for the formation of the hole is significantly reduced, both for thin work pieces and for correspondingly thicker ones.

It is actually known for the production of drill holes in concrete that 25 the drill bit has an axial percussion effect in addition to a rotary drive, but such a percussion effect has obviously not been viewed as possible, by persons skilled in the art, for implementation when drilling or shaping a hole with a screw, and has therefore never been considered. This is presumably because it would be completely undesirable to have an axial percussion effect with a corresponding intensity during the subsequent thread-shaping or thread-cutting process, since in such a case the thread would be correspondingly widened in the axial direction. Then it would no longer be possible to speak of a good firm fit or a good thread fit between the screw and the work piece.

Therefore the present invention should be specifically recognised for having combined the two operations, namely to add to a rotary drive to an axially acting percussion movement, and then reducing the percussion effect, or eliminating it entirely, during the subsequent thread-shaping or threadcutting process. It should therefore be viewed as particular progress in the field of driving in screws that these different process steps are used consecutively in a single driving-in process.

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With a substratum of wood or wood materials, it is even possible to maintain the percussion effect during the driving-in process. With a substratum made of metal, however, it is necessary to reduce the strength of the percussion effect or to eliminate it entirely.

Advantageous further developments of the invention are defined in the dependent claims.

For example, in one version of the invention, it is possible that the axial percussion effect is added to the rotary drive for the screw during the hole-drilling or hole-shaping process. By means of the rotary drive and the superimposed percussion effect, the hole-drilling or hole-shaping process can be further improved.

In this connection, it is particularly advantageous that the reduction in the strength of the percussion effect or its elimination takes place immediately after complete penetration of a drilling part or a hole-shaping end section of the screw, and even before engagement of the first thread turn into the bore or the hole.

M.:le fit of the screw that has been completely driven in will be all the more precise if the switch or shut-off

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;an take place in a precise and timely manner, since not only has an optimum bore or hole been .produced, but also the mutual thread engagement between the work piece and the shaft with the thread I 000s particularly good.

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n.oi a variant of the process according to the invention, it is provided that the switch from an axial percussion effect to an axial percussion effect reduced in strength or to elimination of the percussion effect is triggered by axial relief immediately after completion of the hole-drilling or hole-shaping process.

Sudden axial relief can occur, for example, when the drilling part or the hole-shaping end section has g4.c'crnpleted the bore or the hole, so that immediate and sudden axial relief takes place because of -:c:mpletion of the drilling process. This axial relief whether it occurs suddenly or more slowly can be used as a mechanical signal or as a trigger for electrical signals, in the process according to the invention, *0 Se "ii'order to reduce or entirely eliminate the axial percussion effect.

Pursuant to another variant, it is proposed that the switch from an axial percussion effect to an axial ~@rcussion effect reduced in strength, or the elimination of the percussion effect, can be triggered by an •:.*afjustable depth stop. This variant of the process according to the invention can also be implemented with a simple design, since an axial percussion effect is only present, for example in the case of piston drills or drill hammers, if a corresponding axial counter-pressure is applied. If this counter-pressure is W096119320 PCT/EP95104993 -4eliminated, on the screw side, after a corresponding depth stop makes contact, the switch or shut-off according to the invention takes place.

The process according to the invention will be explained in greater detail in the specification below, on the basis of a screw to be driven into a work piece. The drawing shows: Fig. 1 a side view of the screw, which has just been set onto a work piece; Fig. 2 this screw after it has shaped a hole and immediately before the beginning of the thread-cutting or thread-shaping process; Fig. 3 an enlarged cross-section through the work piece and the screw, where the mutual thread engagement is particularly evident.

1O The hole-shaping and thread-shaping screw 1 shown here is provided with an end section 2 that ends in a point or a point-like shape, and shapes a hole without cutting. Furthermore, a shaft section 4 provided with a thread 3, and an engagement section 5 for attaching or inserting a tool, are provided.

In the representation, the point of departure is a screw 1 which is structured to be self-hole-shaping as well as self-thread-shaping. In other words, there are a non-cutting hole-shaping end section 2, and a corresponding thread 3. The process described here is applicable, however, to all screws which are selfhole-shaping or thread-shaping in some other way. It is not of essential importance for the present process whether work is carried out in non-cutting or cutting manner during the drilling process or the holeshaping process or the thread-shaping or thread-cutting process. In experiments, it has been shown that the present process can be used with special success even for self-drilling screws that cut. In this connection, it does not matter whether a drill tip produced by forming or a corresponding drill blade is present at the free end of the screw. It has also been shown that with the present process and specifically also with a non-cutting hole-shaping end section, screws which are made entirely of stainless material can be driven in. As a rule, in the case of a screw which is at least partially made of stainless material, an attempt is generally made to make the drill tip, at least, out of a material which can be hardened, in order WO96/19320 PCT/EP95104993 to be able to apply a corresponding drilling force. Therefore expensive welding solutions were always necessary for screws.

By means of the use of the process described here, even screws with a hole-shaping end section 2 or with a different design structure can be used, where the screws can consist entirely of a stainless material.

The process described here accordingly consists of adding a percussion effect, acting in the axial direction 6, to the rotary drive for the screw 1 during the hole-shaping process. The screw is acted on not only by the rotary drive 7 but also the axial percussion effect 6. Therefore a corresponding hole 8 can be formed in the work piece 9 with a significantly shorter working time as compared to before. In the process described here, however, it is certainly possible to carry out the hole-shaping process only by means of 1O the axial percussion effect. A rotary drive would then be added to shape the thread, after hole-shaping was complete.

As soon as the hole 8 has been completed, as can also be seen in Fig. 2, the percussion effect is eliminated according to the further process step;, so that only the rotary drive 7 is in effect. For forming the thread 3 into the hole 8 in the work piece 9, this is the best variant, because this means that no axial percussion or shaking movements occur. The thread formed in the hole wall therefore rests against the surface of the thread 3 of the shaft 4 with an exact fit.

As a rule, or in practically all embodiments and possibilities of use, the percussion effect will be shut off during the subsequent thread-shaping or thread-cutting process. In very special areas of use, however, it would also be possible that a slight percussion effect, in other words one reduced in its strength as 'O0 compared with the drilling process, might be practical. An additional positive effect results from the axial percussion effect, because the hole wall is additionally formed downward during such effect, both during shaping and during drilling of a hole, particularly in the case of thinner work pieces 9, so that a type of collar 10 forms in the region of the hole 8. This results in relatively large axial regions in which the thread 3 of the threaded shaft 4 of the screw 1 can engage, even in the case of relatively thin work pieces 9.

In the present process, it is, however, certainly possible to superimpose a percussion effect acting in the direction of rotation on the axial percussion effect, where the former has practically no significance for the 44) eT 0~ WO96119320 PCTIEP95104993 -6hole-drilling or hole-shaping process, but can result in additional advantages during the subsequent threadshaping or thread-cutting process.

Furthermore, in the method described here, it is practical if elimination of the percussion effect or the switch to a corresponding reduction of the strength of the percussion effect can take place as precisely as possible after complete penetration of a drilling part or a hole-shaping end section 2. The switch or the elimination should therefore take place before engagement of the first turn of the thread 3, if at all possible.

In order to trigger this switch or elimination, there are various possible variants which can advantageously be used. For example, it would be possible to trigger the switch or elimination by a sudden axial relief immediately after completion of the hole-drilling or hole-shaping process. This is also possible, for O example, if a short shaft section 11 without any thread follows the end section 2, as shown on the drawing.

As soon as the end section 2 has completed the hole in the work piece 9, sudden axial relief occurs, since the thread-free shaft section 11 suddenly drops down through the hole 8 as a result of the axial contact pressure which is still being exerted. This sudden relief can be utilized by corresponding mechanical elements or electrical controls, in order to bring about the switch or elimination of the axial percussion N effect. Another mechanical possibility exists if a corresponding adjustable depth stop is present. As soon as the depth stop makes contact with the work piece 9, an axial relief is exerted, which then terminates the axial percussion effect in a normal mechanical way. Of course, any kind of electrical or electronic switching or shut-off can also take place, where the corresponding control values can be derived directly in the region of the rotary drive.

Claims

1. A process for driving in a self-boring or self hole-forming, and thread- forming or thread-cutting screw which has a drilling part or a hole-forming end section and a shaft with a first self-forming or self-tapping thread, in which during a drilling or hole-forming operation by the screw an axially- acting percussion effect is applied which is induced by constant impact movements produced in the manner of a hammer-drill, characterised in that during the drilling or hole-forming operation, the axially-acting percussion effect is applied with a rotary drive for the screw, and in that during a subsequent thread-forming or cutting operation the percussion effect is maintained or reduced in its intensity, or eliminated entirely.

2. A process according to claim 1, characterised in that the reduction in the intensity of the percussion effect or its elimination takes place immediately after full penetration of the drilling part or hole-forming end section of the screw and before the first thread engages into a bore or hole.

3. A process according to either claim 1 or 2, characterised in that a switch from an axial percussion effect to either a percussion effect of reduced intensity or to elimination of the percussion effect is triggered by an axial relieving of load immediately after termination of the drilling operation or 20 hole-forming operation. O gg 0.

4. A process according to any one of claims 1 to 3, characterised in that a switch from an axial percussion effect to either an axial percussion effect of reduced intensity, or to the elimination of the percussion effect, can be triggered by a preadjiustable depth control stop. ego. 25

5. A process for driving in a self-drilling or self hole-forming, thread- forming or thread-cutting screw substantially as hereinbefore described with reference to the accompanying drawings. 00 Dated this Twelfth day of March 1999 SFS INDUSTRIE HOLDING AG Patent Attorneys for the Applicant: F B RICE CO