US3426635A - Arrangement in sheet metal working machines,particularly nibbling machines - Google Patents

Description

FebQll. 1969 s. NICKLASSON 3,426,635 ARRANGEMENT IN SHEET METAL WORKING MACHINES, PARTICULARLY NIBBLING MACHINES Filed Aug. 29. 1966 Sheet of 5 FIG] INVENTOR. f V MCA UlSSO/V BY 0,

Feb. 11. 1969 ARRANGEMENT IN SHEET S. NICKLASSON METAL WORKING NIBBLING MACHINES 9 MACHINES PARTICULARLY Sheet 2 of 5 Fig.3 j

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s. NICKLASSON 3,426, ARRANGEMENT IN SHEET METAL WORKING MACHINES, PARTICULARLY NIBBLING MACHINES Filed Aug. 29, 1966 Sheet 3 of 'FIG.5

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t LL] l m T2 /2 T1/2 a c1=1D0mrn R=mm INVENTOR. l A /V MMMSSOA/ I BY 3,426,635 PARTICULARLY Feb. 11. 1969 s. NICKLASSON ARRANGEMENT IN SHEET METAL WORK ING MACHINES NIBBLING MACHINES Sheet Filed Aug. 29, 1966 mom S 3 I d d 8 i x A m E E m 1 5E 09 u Q 8" Q2 8 8 8 A Q Feb. 11. 1969 SVNICKLASSON ARRANGEMENT IN SHEET METAL WORKING MACHINES PARTICULARLY NIBBLING MACHINES Filed Aug. 29. 1966 Sheet 5 of 5 United States Patent 11,237/ 65 US. Cl. 83-530 Int. Cl. B26d 5/18; Flfih 21/26 5 Claims ABSTRACT OF THE DISCLOSURE A toggle arrangement for sheet metal Working machines wherein a toggle mechanism imparts a reciprocating movement to a tool. The toggle mechanism includes a pair of toggle levers pivotally connected adjacent one end thereof. The other end of one of the toggle levers is connected to the tool holder and the other end of the other toggle lever is connected to the machine frame by means of an adjustment device for permitting the position of the toggle pin tobe adjusted. The toggle mechanism is moved by a drive means which causes the working stroke to occur when the remote ends of the toggle levers approach each other.

When working sheet metal and other material in sheet form one method adopted for this purpose is the so-called short stroke technique. This means that the material is worked between tools of which one, preferably the lower, is stationary and the upper moves in a direction towards the lower at relatively short amplitude and high frequency. The short stroke technique can be used for, e.g. cutting, shaping or other methods of plastic deformation of material. One of the main applications of the short stroke technique is cutting; knives being used that have relatively short cutting edges and that are so designed that curved as Well as straight cuts can be made. Other applications are shaping, such as beading, creasing, joggling, or edge folding. Nibbling constitutes a special application, Le. a form of continuous punching.

Various types of link movements are used to impart the required reciprocating movement to the upper tool in a short-stroke machine. Requirements are thus that the amplitude of the impact movement can be adjusted and that it is possible to switch the entire impact movement between a working position and a neutral position. One example of link motion is the normal crank movement, the upper tool being connected, via a connecting rod, to a rotating crank. The amplitude can thus be adjusted by providing the rotating crank shaft with an adjustable double eccentric, whereby the crank radius can be varied. Adjustment into neutral can be effected by moving the crank shaft vertically by means of some suitable device, for instance by mounting the crank shaft eccentrically in a rotatable bushing.

The impact movement can also be caused by means of a toggle-joint link system as disclosed in Swedish Patent 127,977 and Swedish Patent No. 186,016, which corresponds to US. Patent No. 2,986,947. In these cases the amplitude of the moveable tool is adjusted by causing the pivoting center points of the link system, in their end positions, to adopt different side positions relative to a plane parallel with the direction of movement of the upper tool. The tool is put into neutral by adjusting its upper, stationary pivot point to various height positions. Thus, in a working position the bottom position of the tool is always the same, independent of amplitude.

The above link system is well suited for convential cutting and shaping operations. In the case of the first mentioned, simple crank movement the movement graph of the upper tool, as a function of the time, appears substantially as a sine curve, as also does the movement graph obtained with the toggle-joint movement. This geometry of movement is suitable with respect to the forces which develop when cutting or shaping. At the beginning of the working stroke when the tool meets the work piece, the force exterted on the driving, rotating crank shaft, when movement is constant, is relatively less and the velocity of the tool relatively greater compared. with the ratio at the end of the working stroke. This corresponds rather Well to the force development which ought to arise when carrying out each separate working stroke during clipping or shaping respectively.

However, a special relationship exists in so-called hibbling. With nibbling, a series of holes are punched out of the Work piece; the holes overlapping each other. The nibbling tool comprises, for instance, a circular-cylindrical punch, generally with a fiat end surface, which cooperates with a die having a corresponding circular opening. At every stage a chip is punched out which has the shape of a quarter moon. The punch usually travels down until its end surface meets the upper, flat working surface of the die. When the punch has completed its cutting action it returns to the upper working position and the plate is advanced one step; whereafter the operation is repeated. The distance through which the plate is advanced constitutes approximately 25 to 30% of the diameter of the punch. In nibbling, the force graph is enacted differently than in the case, for instance, when cutting or shaping. When nibbling the maximum force shall be developed when the punch meets the Work piece, which force successively decreases while cutting is being effected so that the requisite force at the end of the stroke is zero. It is also desirable that the speed of the punch is relatively low at the beginning, to avoid damaging impact forces and hammering on the work piece and, further, the punch speed should be increased towards the end of the stroke so that the cut chip is more easily knocked out through the die.

At the same time a particular demand, when nibbling, is made in connection with advancing the work piece in the working direction. For each nibbling stroke it is necessary that the object be advanced through an accurately determined distance (this requirement is not so important when cutting or shaping where the various working strokes engage each other more successively and variation in advancement of the workpiece for each step is not so important with respect to carrying out the working sequence). To enable this accurate advance of the work piece it is necessary, with respect to its acceleration, that a certain period of time is left at disposal. This period must not be too short since diificulties will arise in advancing and retarding a heavy work piece, which can demand troublesome, large forces and corresponding complicated devices to ensure the exact degree of advancement of the work piece. It is naturally conceivable to provide for a desirable period of time between each working stroke by merely causing the amplitude of the punch to be sufiiciently great and by utilizing a small portion of the amplitude for the nibbling process proper. However, this solution is less favorable owing to the fact that the dimensions of the machine used thereby increase to an unnecessarily high degree and the construction becomes more expensive. Neither is the required geometry of motion according to the above obtained when the motion of the crank or toggle joint is amplified.

The present invention provides a solution tothe problem, by means of a link movement of favorably adapted dimensions causing the movement of the punch to be such that it:

(a) Engages the work piece at relatively low speed which successively increases during the clipping action, to stop rapidly in the bottom position,

(b) Develops relatively large forces when shearing begins, said forces successively decreasing during the shearing sequence and,

(c) Leaves an adapted, adjustable, suitable period of time between each working stroke for advancing said work piece.

The invention comprises an arrangement in sheet-metal working machines, particularly for nibbling and punching, in which the tool is imparted a reciprocating movement by means of a toggle lever provided with a link pin, the position of which can be adjusted, and a link pin connected with a tool, tool holder or the like, the toggle lever pin being arranged to obtain a reciprocating movement, and the tool holder being adapted to carry out the working stroke during the moment of movement at which the two first mentioned link pins approach each other.

The present invention will now be more closely described with reference to the accompanying drawings in which FIGS. 1 and 2 diagrammatically show the arrangement according to the invention in various working posi tions and FIGS. 37 show various graphs of stroke movements, as a function of the time.

As can be seen, the arrangement is substantially constructed along the same lines as those disclosed in the said Swedish patents. However, in this case the function and working principle of the arrangement is inverted. The arrangement comprises a crank 11 rotatable about a crank shaft axis 1 and having a pivoting radius R, and adapted to rotate in the direction indicated by the arrow. The crank 11 is laterally adjustable to stationary positions. Two positions of the revolution of rotation are indicated by the reference numerals 2 and 3 respectively. A connecting rod V is pivotally connected with two link arms A and B. The link arm B is pivotally connected at its other end to the frame of the machine, at point 6 which can be made adjustable to stationary positions. The link arm A is connected at its other end with a tool holder RA at point 8. The tool holder RA is guided for vertical movements and encloses completely the link arms, besides which it is connected at the bottom with a tool in the form of a nibbling punch N. On rotation of the crank 11 the link arms A and B, as a result of the movements of the connecting rod, move at the point where they are connected with the connecting rod between positions 4 and 5, the end of the link arm A moving between the points 7 and 8. In position 7 the links form a straight line and the tool lies in an unchan-geable, upper working posi tion. When the intermediate linkage point is swung to one side, to point 5, the punch is drawn downwards. The geometry of motion is then such as that the tool moves according to the graph shown in FIG. 3, at a relatively low speed at the beginning but which increases during the stroke. The tool turns rapidly at point 2. Of the total length of stroke S1 obtained only a certain portion e.g. portion S is utilized. Consequently a relatively long period of time during which the work piece can be advanced is at disposal, outside the portion S As illustrated in FIGURE 1, the rotatable crank 11 can be mounted relative to the machine frame by means of an adjustment device so as to permit the position of the crank shaft axis 1 to be varied as desired. The connecting rod V is pivotally connected to a crank pin mounted on crank 11 so as to be adjustable to positions 2 and 3 as illustrated in FIGURE 1. The crank 11, which is rotatable about the crank shaft axis 1, is eccentrically mounted on an adjustment member 12 rotatable about an axis 113 parallel to the crank shaft axis 1. By rotating the member 12 about the axis 13, the crank 11 may be adjusted into a number of fixable positions having different distances from the line of movement of the punch N. Such adjustment structure is shown merely for purposes of illustra- 4 tion and is old and well known, being illustrated in U.S. Patent No. 2,986,947.

The function can be further improved by means of the adjustment according to FIG. 2. The end positions of the intermediate point of the link system are thus displaced relative to the plane through the tool holder, e.g. by moving the position of the rotating crank shaft axis from 1 to 1'. The intermediate point of the link system thereby rotates between the positions 4' and 5'. The motion graph of the tool thus obtains the form shown in FIG. 4, which puts additional time at disposal for advancing the work piece at a certain length of stroke S2. A small intermediate length of stroke S3 is obtained. In general the characteristic of the motion geometry during the effective length of stroke is similar to that according to FIG. 3.

By suitably displacing laterally the end positions for 4' and 5' of the intermediate point of the link system, for example in the manner described in the previous paragraph, the motion graph of the tool can be made to take, within wide limits, such a form that a period of time, suitably adapted for each case, between each out can be placed at disposal (see FIG. 4). The lateral displacement of the center of the crank shaft can also be combined with such lateral adjustment of the stationary linkage point 6 as mentioned in Swedish Patent 127,977 or 186,016.

To adjust the stroke movement from working position to neutral the stationary linkage point 6 is lifted by means of some suitable device. This can be effected for instance, by mounting the link pin 6 eccentrically on an adjustment member 14 having an axle .15 rotatably mounted relative to the machine frame whereby the adjustment member 14 can be rotated so as to adjust and fixedly secure the link point 6 in a pluarity of various positions having diflferent heights. The arrangement can be designed, for instance, as shown in Swedish Patent 127,977.

Three practical cases with respect to the geometry of motion of the punching tool are illustrated in FIGS. 5-7. The following designations are used in conjunction herewith:

T=the time for one revolution of the crank shaft (a completed movement period).

T =time during which the punch is engaged (the length of time during which the punch moves within the plate).

T =the time for moving the plate at each feed step.

R=crank radius.

a=the length of the toggle link (the link arms A and B).

X:lateral displacement of the center of the crank shaft (see FIG. 2).

In the case shown in FIG. 5 (1:100 mm., R=20 mm., and X=0 mm. The length of the stroke in this case reached 16.7 mm., the thickness of the plate being assumed to be approximately 60% of the stroke and thus supposed to be 10 mm., S is thus 10 mm. According the curve, the ratio T /T :1.46 is obtained for half the stroke period during the downward movement of the punch. The effective punch interval T /2 extends between approximately and of the rotation revolution of the crank shaft. Thus an advancing interval is obtained which extends during a time period corresponding to approximately 210 of the rotation revolution of the crank shaft.

FIG. 6 illustrates the stroke movement for the same linkage system with the crank shaft laterally displaced (see FIG. 2) through a distance of X=4.68 mm. The latenal displacement is such that the links A and B assume a straight line when the crank shaft is rotated through 40. The length of stroke in this case is 12.9 mm. With a plate thickness corresponding to approximately 60% of the stroke, thus 8 mm., S is equal to 8 mm. and the ratio T /T :1.57. With such lateral displacement of the crank shaft a longer advancing interval T is obtained than in the case with adjustment according to FIG. 5. The ratio T /T :l.57, by reasons of symmetry,

is the same if a full period is calculated. The ratio T2/T1 is even more favorable according to FIG. 6 if the thickness of the plate and, therefore S constitutes a still larger fraction of the total length of stroke.

FIG. 7 shows the corresponding ratio T /T in a pure sine movement (S=R (1-Cos oc)). Similar lateral movement is obtained, for instance, if the punch is con nected direct to a crank shaft without an intermediate linkage system, as in FIG. 1 and 2. If it is assumed that S as previously, constitutes approximately 60% of the total strokes the ratio T /T becomes merely 1.78, which is considerably less than that which is obtained in an arrangement according to the present invention.

The embodiment of the present invention has only been shown diagrammatically so as not to complicate unnecessarily the figures and to enable the working sequences to be illustrated more easily. In practice the arrangement can naturally be designed in many ways. For example it is not necessary to arrange a tool holder RA around the link arms A and B, but that the end of the link arm A can be connected direct to the nibbling punch N by means of some suitable connection.

What is claimed is:

1. A sheet metal working machine, particularly for nibbling and punching, comprising:

a machine frame;

a tool holder carrying a tool and mounted on said machine frame for reciprocating rectilinear movement;

toggle means including a pair of toggle levers connected between said machine frame and said tool holder for causing said tool holder to canny out its working stroke as said pair of toggle levers pivotally move toward one another, the adjacent and of said pair of toggle levers being pivotally connected at a first link point and the remote end of one of said toggle levers being pivotally connected to said machine frame at a second link point and the remote end of the other toggle lever being pivotally connected to said tool holder at a third link point;

adjustment means connected between said machine frame and the remote end of said one toggle lever for permitting the position of said second link point to be aldjusted relative to said frame; and

drive means connected to said toggle means for causing movement thereof relative to said frame whereby said toggle means causes said tool holder to movably carry out its working stroke as said second and third link points approach each other.

2. A sheet metal working machine according to claim 1, wherein the tool holder is in its maximum retracted position when the three toggle link points are positioned on a straight line.

3. A sheet metal working machine according to claim 2, wherein the tool holder comprises a frame-like member which encloses the pair of toggle levers and the adjustment means connecting the second link point to the machine frame.

4. A sheet metal working machine according to claim 2, wherein said drive means includes a rotatable crank member and a connecting rod pivotally coupled at opposite ends thereof to the rotatable crank member and to the toggle means at the first link point, and further including adjusting means connecting said rotatable crank member to said machine frame for permitting the rotational axis of said crank member to be fixedly secured in a plurality of different positions in order to vary the distance between the rotational axis of the crank member and the center line of the reciprocal tool holder.

5. A sheet metal working machine according to claim 4, wherein the adjusting means permits the rotational axis of the crank member to be adjusted such that the first link point will execute pivoting movements on both sides of a line connecting the second and third link points as the crank mem'ber undergoes a single revolution.

References Cited UNITED STATES PATENTS 304,673 9/1884 Skinner 74-520 X 2,494,413 1/1950 Slettengren 74-38 2,986,947 6/ 1961 Slettengren 74-38 JAMES M. MEISTER, Primary Examiner.

US. Cl. X.R.

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