Note: Descriptions are shown in the official language in which they were submitted.
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Screw driving-Tn pr~cess
The invention relates to a process for driving in a self-drilling or self-piercing, 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 an axial percussion effect is added to the rotary drive during the hole-drilling
or hole-shaping step performed by the screw.
DE-A 14 78 914 describes a process of the aforementioned type. In the known process, the percussion
eflect 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 means an addi:ional 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 sigl,irical,lly greater, in accordance with the thread pitch, than the usual 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, p,aclk-'ly only a corresponding torque needs to be applied.
The present invention has now set itself the task of proposing a process of the type stated initially, which
guarantees optimum shaping and optimum fit in the thread, especially for thin materials, with a shorter
driving-in time.
Accordi~ ,9 to the invention, this is accomplished in that the percussion effect is brought about by constant
percussion movements produced in the manner of a drill hammer, and that the percussion effect is
r"~ ,~ ,ed or reduced in strength or ~I ni"~led entirely during the subsequent thread-shaping or thread-
cutting process.
The advantage achieved by the process accordi. ,9 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
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prevent bending. While a percussion screwdriver, i.e. a combination of a percussion drill and percussion
screwdriver is known from DE 43 01 610 A1 as well as DE 42 36 819 A1, in which the percussion effect
can be shut off, these are neither intended nor suitable for a process for driving in self-drilling or self-
piercing 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 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 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 imple",entalion when drilling or shaping a hole with a screw, and has
therefore never been considered. This is presumably because it would be cor"?'ately undesirable to have
an axial percussion effect with a co, I~:spon.li"9 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 recognized for having combined producing the
percussion effect during the hole-drilling or hole-shaping process, by means of con~lal1t percussion
movements in the manner of a drill hammer, and then reducing the percussion effect, or ~'iul;ll~lillg it
entirely, during the subsequent thread-shaping or thread-cutting process. It should therefore be viewed
as particular pru~less in the field of driving in screws that these different process steps are used
consecutively in a single driving-in process.
With the process according to the invention, it has actually become possible to form a hole without any
rotary drive, in other words only with consla"l percussion movements produced in the manner of a drill
hammer, which results in the advantages as indicated above, particularly for thin work pieces.
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With a substratum of wood or wood ll,ale~ ,, it is even possible to maintain the percussion effect during
the driving-in process. With a substratum made of metal, however, it is necessaly to reduce the strength
of the percussion effect or to eliminate it entirely.
Advantageous further dcv~lop",ehl~ of the invention are the objects of the dependent claims.
For exdnl,c'E, 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 2'i~" ,alion takes place i",~"e.li-dlely after cor"Fl~le 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.
The fit of the screw that has been completely driven in will be all the more precise if the switch or shut-off
can 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
is particularly good.
In a variant of the process acco,di ,9 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 l,iyger~d by axial relief immediately after col"plelion 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
completed the bore or the hole, so that immediate and sudden axial relief takes place because of
cor"pl~tion 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 ele~;l,ical signals, in the process according to the invention,
in order to reduce or entirely c' ";"dle the axial percussion effect.
Pursuant to another variant, it is proposed that the switch from an axial percussion effect to an axial
percussion effect reduced in strength, or the ~ dlion of the percussion effect, can be triggered by an
adjustable 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
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eliminated, on the screw side, after a corresponding depth stop makes contact, the switch or shut-off
acGordi"g 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 i",l"ediately before the beginning of the thread-cutting
or thread-shaping process;
Fig. 3 an enla,yed cross-section through the work piece and the screw, where the mutual thread
engagement is particularly evident.
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 engagel"ent 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 desc,ibed here is app'..,ab'e, however, to all screws which are self-
hole-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 hole-
shaping 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 speciric~ 'Iy
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
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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 sle.. ,less material.
The process described here accoldi"gly 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
the axial percussion effect. A rotary drive would then be added to shape the thread, after hole-shaping
was cor",~!ete.
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 possil,:' ~ies 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
co",pared 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
d i~ ~clion of rotation on the axial percussion effect, where the former has pr~;lica"y no significance for the
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hole-drilling or hole-shaping process, but can result in additional advantages during the subsequent thread-
shaping or thread-cutting process.
Furthermore, in the method described here, it is pr~;lical if elimination of the percussion effect or the
switch to a cor,~sponding 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 el Il ,alion, there are various possible variants which can advantageously
be used. For example, it would be possible to trigger the switch or c" "i,,~lion by a sudden axial relief
immediately after co",r'etion of the hole-drilling or hole-shaping process. This is also possible, for
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 cor"~'oted 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 cl ";.,alion of the axial percussion
effect. Another mechanical possil,.'ity 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.
