EP0297324B1

EP0297324B1 - Knife for blanking in sheet

Info

Publication number: EP0297324B1
Application number: EP19880109208
Authority: EP
Inventors: Chuji Yanagimoto
Original assignee: Laserck Corp
Current assignee: Laserck Corp
Priority date: 1987-06-10
Filing date: 1988-06-09
Publication date: 1990-10-03
Also published as: EP0297324A1; DE3860739D1; JPH0558878B2; JPS63312099A

Description

Field of the Invention

The present invention relates to a knife for blanking sheet, which is utilized to punch a specifically shaped hole in a sheet of paper, plastic, or corrugated paper board by press blanking.

Description of the Prior Art

A prior art knife (FR-A 2 512 704) is shown in Figs. 5 and 6. This knife A is made of thin strip material (of a thickness ranging from 0.4 to 1.0 mm) and has two bevelled surfaces at its blade portion so as to form a blade edge 1. It has a wedge-like shape in in cross-section. A knife A is fixedly fitted, for use, in a knife fitting groove 3 arranged in a knife holding base 2 made of wood. The knife fitting groove 3 is preliminarily formed into a determined configuration (according to the shape of a blank) with the use of a jig saw or by means of laser cutting.ln case the knife fitting groove 3 is cut by a laser cutting operation which has widely been employed recently, the widthwise measurements of the inner region of the knife fitting groove 3 may be found unequal although cutting into an intricate configuration is possible. if the knife A is fitted into the knife fitting groove 3 under such a condition, the knife holding base 2 is deformed. Thus, the knife fitting groove 3 should be finished appropriately with the use of a router. The knife holding base 2 securely equipped with the knife A is then attached to a blanking press (not shown) together with athin ferrous plate 11, a paper sheet 10, and a back plate 4. Particularly, while the knife A is fitted into the knife fitting groove 3, its height halters to a very slight degree at the comer portions 5 of the knife A and thus, should appropriately be adjusted by the operator prior to the blanking operation. At the same time, an inherent error in the height h of the knife A is also corrected.
During a trial blanking operation, this adjustment is made by adhesively mounting a sheet of height adjusting paper, such as a strip of tape 7, between the thin ferrous plate 11 and the back plate 4 in an area where the height h of the knife A is rather low (see Fig. 6). The error in the height h of knife A likewise may be eliminated by deflecting the thin ferrous plate 11 throughout the respective area. However, the afore-said adjustment requires a highly experienced skill and particularly has the disadvantage that it is troublesome to carry out.
A knife of the type shown in Fig. 7 likewise is known (FR-A 2 512 704 and GB-A1 366 757). This knife B has a tapered back portion 8 the material thickness of which is less than that of the main portion of the knife. The thinner back portion can easily be deformed under pressure. Knife B also is fitted into a knife fitting groove 3 formed in a knife holding base 2. Then, the knife holding base 2 is attached to a blanking press together with a thin ferrous plate 11, a paper sheet 10, and a back plate 4. During a test blanking operation, the back portion 8 is yieldingly compressed by forcefully pushing the thin ferrous plate 11. Consequently, the knife Bis partially automatically adjusted so that its height h can be uniform. However, in this case the back portion 8 is tapered and thinner than the knife main portion. This may cause the knife holding base 2 to be deflected when the knife B is inserted under pressure into the knife fitting groove 3. As a result, a problem may arise such that during press blanking operation, a sheet, such as a corrugated paper board 12 transported on a chain conveyor not shown, is not transferred smoothly; rather its leading end may strike the blade edge 1 of the knife B attached to the knife holding base 2 (see Fig. 8). This problem is likely to become particularly troublesome when the distance H between the blade edge 1 of the knife B and the top of the corrugated paper board 12 is adjusted to a small value (e.g. 4 to 5 mm) to speed-up the press blanking operation. Another problem is that the holding force of the knife holding base 2 for holding the knife B is lessened as the area in which knife B contacts the side wall of the knife fitting groove 3 is decreased in view of the thinner back portion 8.

SUMMARY OF THE INVENTION

The knife of the present invention is designed in view of the above-mentioned aspects.
In conformity with the present invention a knife for blanking sheet having a blade portion, a main portion and a back portion, the material thickness of the back portion being less than that of the main portion, the back portion and a part of the main portion being fitted in a knife fitting groove arranged in a knife holding base, is characterized in that consecutive sections along the length of the back portion are deformed in alternate transverse directions in such a manner that the overall thickness of the back portion is equivalent to that of the main portion.
This configuration of the back portion of the knife provides for an extended area of contact thereof with the side wall of the knife fitting groove. Accordingly the holding force of the knife holding base for holding the knife is increased. Additionally, the pressing forces on the side wall of the knife fitting groove become uniform, whereby the deflection of the knife holding base will be minimized.
Furthermore, the height of the knife is automatically adjusted to be uniform because higher ends of the back portion thereof are yieldingly compressed upon forcefully striking the usually employed thin ferrous plate. Thus, an operator who is less experienced in the adjustment can carry out the operation of adjustment with ease.
Moreover, when the knife is fitted into the knife fitting groove in the knife holding base, the back portion thereof will deflect according to the width of the knife fitting groove or else, the contacting are of the side wall of the knife fitting groove to the back portion will partially yield to pressure under the stresses exerted thereon. Accordingly, the work of finishing the knife fitting groove with a router may be omitted.

BRIEF DESCRIPTION OF THE DRAWINGS

Figs. 1 (a), 1 (b) and 1 (c) illustrate one embodiment of the knife of the present invention, in which:

Fig. 1 (a) is a perspective view;
Fig. 1 (b) is a plan view taken from the direction of arrow E of Fig. 1 (a); and
Fig. 1 (c) is a cross-sectional view taken along the line F-F' of Fig. 1 (a);
Fig. 2 is a cross-sectional side view showing that the knife is fixedly fitted in a knife fitting groove arranged in a knife holding base while the height of the knife has been adjusted;
Fig. 3 is a perspective view showing another embodiment of the knife of the present invention;
Fig. 4 is a view similar to Fig. 1 (c), showing a further embodiment of the knife of the present invention;
Fig. 5 is a perspective view showing the knife prior to installation to a knife holding base explanatorily in respect of the background art of the present invention;
Fig. 6 is a view similar to Fig. 2, showing a prior art knife;
Fig. 7 is a view similar to Fig. 2, showing another prior art knife;
Fig. 8 is an explanatory view showing an operation of press blanking.

DETAILED DESCRIPTION OF THE PREFERRED

EMBODIMENTS

Similar elements including such as those of the prior art knifes A and B shown in Figs. 6 and 7 are represented by similar numerals in this description.
In the primary embodiment shown in Figs. 1 (a), 1 (b), and 1 (c) the back portion 8' of a knife C is tapered and has a material thickness which is less than that of the main portion of the knife. Consecutive sections along the length of back portion 8', are deformed in alternate transverse directions such that a wave-shaped configuration is obtained. The wave-shaped portion is formed by a pressing operation in such a manner that the overall thickness (represented by t in Fig. 1 (b)) of the back portion is equivalent to that of the main portion of the knife C. The knife C also has two bevelled surfaces so as to form a blade edge 1.
When knife C is fitted into a knife fitting groove 3 formed in a knife holding base 2, the convex sides of the back portion 8', arranged in wave-shaped configuration come in contact with the side walls of the knife fitting groove 3. Thus, the areas of contact of the knife C with the side walls of the knife fitting groove 3 are positively maintained with help of the spring action resulting from the wave form thereof. As a result, the holding force of the knife holding base 2 for holding the knife C will be increased.
Additionally, for the reason that the spring action is effected by the back portion 8' of the knife C, the knife C can be fitted into the knife fitting groove 3 as its back portion 8' deflects throughout the knife fitting groove 3 or as the contacting area of the side wall of the knife fitting groove 3 with the back portion 8', partially deflects due to a stress intensively exerted thereon, even in case that the knife fitting groove 3 is not uniform in width after having been cut e.g. by a laser cutting operation. Therefore, a finishing work with the use of a router after laser cutting operation may be omitted.
The knife holding base 2 having the knife C fixedly fitted in the knife fitting groove 3 therein is then attached to a blanking press (not shown) together with a thin ferrous plate 11, a sheet 10, and a back plate 4. For adjustment of the height h of the knife C, a region of the back portion 8' where the height h of the knife C becomes greatest is yieldingly compressed by the thin ferrous plate 11 under the pressure exerted during the test blanking operation (see Fig. 2). This allows the height h of become automatically uniformly adjusted.
Accordingly, when the adjustment of the height h of the knife C is carried out by the operator, it requires no advanced technique and thus with be accomplished with ease.
In another embodiment shown in Fig. 3, a knife G is arranged in such a way that its back portion 8' is formed into a plurality of tongues 9 flexed in alternate transverse directions.
In a further embodiment shown in Fig. 4, a knife D has a single bevelled surface so as to form a blade edge 1'.

Claims

1. A knife (C, D, G) for blanking sheet having a blade portion, a main portion and a back portion (8'), the material thickness of the back portion being less than that of the main portion, the back portion (8') and a part of the main portion being fitted in a knife fitting groove (3) arranged in a knife holding base (2), characterized in that consecutive sections along the length of the back portion (8') are deformed in alternate transverse directions in such a manner that the overall thickness (t) of the back portion (8') is equivalent to that of the main portion.

2. A knife (C) for blanking sheet as defined in claim 1 wherein the back portion (8') is wave-shaped.

3. A knife (G) for blanking sheet as defined in claim 1 wherein the back portion (8') comprises a plurality of tongues (9) flexed in alternate directions.

4. A knife (C, G) for blanking sheet as defined in claims 1, 2 or 3 wherein its blade portion has two bevelled surfaces so as to form a blade edge (1).

5. A knife (D) for blanking sheet as defined in claims 1, 2 or 3 wherein its blade portion has one bevelled surface so as to form a blade edge (1').