EP0137859A2

EP0137859A2 - Burring chamfering method

Info

Publication number: EP0137859A2
Application number: EP83108687A
Authority: EP
Inventors: Tamio Takahashi
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 1983-09-02
Filing date: 1983-09-02
Publication date: 1985-04-24
Also published as: EP0137859A3

Abstract

@ A method of burring and chamfering a workpiece (2) employes an apparatus including: a workpiece carrying belt conveyor (3); one or a plurality of elastic grinding wheels (4) obliquely disposed over the belt conveyor (3), the grinding wheels (4) being arranged in parallel to each other in the same direction; and split-type press rollers (5X, 5Y) disposed along both sides of each of the grinding wheels (4). The method comprises the steps of: passing the workpiece (2) under a first grinding wheel (4X) wich has a grinding surface rotating in the direction opposite to the moving direction of the workpiece (2) thereby to effect burring and chamfering; and passing the workpiece (2) under a second grinding wheel (4Y) which is disposed in parallel to the first grinding wheel (4x) and has a grinding surface rotating in the same direction as the moving direction thereby to effect burring and chamfering. The grinding wheels (4X, 4Y) may be rotated while having an angle of about 45 degrees with respect to the moving direction. The moving direction of the belt conveyor (3) may be changed every time a predetermined time elapses. Moreover, the grinding wheels (4X, 4Y) may be vibrated in an axial direction of the grinding wheels.

Description

BACKGROUND OF THE INVENTION

The present invention relates to a method of burring and chamfering a work, and more particularly, to a burring chamfering method suitable for use in uniformly burring and chamfering the surface of a piece of work carried on a conveyor by means of a plurality of grinding wheels.
The manufacture of such sheet metal products as produced through blanking or punching thin sheet materials has been increasing in scale every year. The invention pertains to highly efficient machining techniques for removing burrs produced by such press working and for chamfering machined portions or cut surfaces of work pieces. Throughout the specification, the term "machining is used to mean a machining operation such as blanking or punching.
Burrs are unavoidably produced on cut or machined surfaces in the initial process of sheet metal working. A product with burrs not removed may injure people or cause other problems and therefore is variously harmful. In addition, if a machined portion is left having a 90-degree edge, the removal of only projecting burrs cannot completely eliminate the above-mentioned problems. Therefore, the machined edge portion must be subjected to chamfering (edge smoothing) simultaneously with burring.
By the way, the greater part of products subjected to sheet metal working have shapes as shown in Fig. 1, and are formed by blanking a steel plate having a rectangular outer periphery so as to have square machined portions parallel to the outer peripheral portion and circular machined portions or elliptical machined portions obtained by the combination of round and square machined portions. Such an apparatus as shown in Fig. 2 has been conventionally employed for surface machining operations, such as burring and chamfering, for these workpieces after blanking. This surface machining apparatus 1 is arranged such that a grinding wheel 4 for burring and chamfering the surface of a workpiece 2 is provided over a feed conveyor 3 for carrying the workpiece 2, and press rollers 5 for pressing down and feeding the workpiece 2 are disposed along and close to the front and rear sides of the grinding wheel 4, respectively, and moreover, the grinding wheel 4 is disposed so as to be at right angles to the moving direction of the feed conveyor 3 and is driven by means of a driver 6. In conducting the above-mentioned surface machining operations by employing such a conventional apparatus, although it is possible to machine the sides parallel to the axis of the grinding wheel 4, i.e., sides 2A, 2C, 2a, 2c at right angles to the moving direction of the feed conveyor 3, it is difficult to uniformly machine sides 2B, 2D, 2b, 2d at right angles to the axis of the grinding wheel 4, since these sides are parallel to the tangential direction of the rotation of the grinding wheel 4 and therefore are different in grinding conditions from each other. Accordingly, it is difficult to burr and chamfer the workpiece 2 by one pass by employing the conventional apparatus, and the workpiece 2 must be passed under the grinding wheel 4 one more time after turning the direction of the workpiece 2 through 90° in order to machine the sides 2B, 2D, 2b, 2d properly. Even if the workpiece 2 is passed under the grinding wheel 4 twice, however, there is undesirably a difference in degree of surface machining such as burring and chamfering between the cut sides 2A, 2C and the machined portion sides 2B, 2D, disadvantageously resulting in a non-uniform surface machining.

SUMMARY OF THE INVENTION

Accordingly, it is a primary object of the invention to provide a burring chamfering method which permits even a small workpiece, from short to long in overall dimensions, to be machined and allows all the sides of the workpiece to be uniformly burred and chamfered by moving the workpiece on a conveyor only once for machining as well as to permit the wear of grinding wheels to be kept uniform, thereby overcoming the above-mentioned disadvantages of the prior art.
It is general that the above-mentioned difficulty in machining, i.e., the difference in machining degree between machined portions, is most conspicuous on a square machined portion but inconspicuous on a circular machined portion owing to the shape and a curved change of machining conditions.
Therefore, according to one aspect, the invention provides a burring chamfering method wherein, with a square machined portion taken as an object to be burred and chamfered, the grinding wheel is obliquely disposed while having an angle of about 45 degrees with respect to the square portion, thereby to allow the machining effect of the rotation of the grinding wheel to act on all the four sides of the machined portion under the same conditions, and in addition, split-type rollers are arranged as rollers for pressing down and feeding the workpiece, thereby to permit even a small workpiece, from short to long in overall dimensions, to be machined.
According to another aspect, the invention provides a burring chamfering method wherein, on a belt conveyor for carrying a workpiece, a first grinding wheel which has a grinding surface rotating in the direction opposite to the carrying direction and a second grinding wheel which is disposed in parallel to the first grinding wheel and has a grinding surface rotating in the same direction as the carrying direction are provided, and the workpiece is passed under these grinding wheels so as to be burred and-chamfered.
The above and other objects, features and advantages of the invention will become apparent from the following description taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a front view of an example of a sheet metal product to be worked;
Fig. 2 is a plan view of a conventional surface machining apparatus;
Fig. 3 is a plan view of a surface machining apparatus in accordance with the invention;
Fig. 4 is a front view of the surface machining apparatus shown in Fig. 3; and
Fig. 5 to Figs. 7a and 7b illustrate other embodiments of the invention, in which:
Fig. 5 is a front view of a surface machining apparatus to which one embodiment of the surface machining method in accordance with the invention is applied;
Fig. 6 is a plan view of the surface machining apparatus shown in Fig. 5; and
Figs. 7a and 7b are front views for describing a method for making uniform the wear of grinding wheels of the surface machining apparatus shown in Figs. 5 and 6.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the invention will be described hereinunder with reference to the accompanying drawings.
Referring first to Fig. 3, grinding wheels 4X and 4Y are disposed while having an inclination angle of about 45 degrees with respect to a belt conveyor 3 which carries a workpiece 2 from the inlet side to the outlet side. In addition, split-type free-rotating press rollers 5X and 5Y which rotate in the same direction as the direction of the flow of the conveyor for holding the workpiece from being displaced as well as for feeding the workpiece in accordance with the flow of the conveyor are arranged on the front and rear sides of the grinding wheels 4X and 4Y, respectively.
Moreover, each grinding wheel is adapted to apply to the workpiece a pressure most suitable for machining according to the thickness of the workpiece as well as apply a pressing force to the press rollers required for prevention of displacement of the workpiece due to machining. By rotating in opposite directions, the two grinding wheels can apply burring chamfering actions (e.g., machining forces applied in all direction) to the entire periphery sides (all four sides) of a machined portion to be ground.
More specifically, the workpiece placed on the conveyor closer to the inlet side is subjected to a machining action when passing under the grinding wheels while being carried by the belt and the press rollers. At that time, the workpiece is subjected to a displacing force in the tangential direction of each wheel. Since the pressing forces between the belt and the split-type free rollers 5X and 5Y rotating in the same direction as the flow of the conveyor are larger than the displacing force, the workpiece will not be displaced and passes under the grinding wheels at the same speed as the belt moving speed while being subjected to the machining actions. When passing under the grinding wheel 4X, the side 2c shown in Fig. 3 is subjected to a grinding action from the upper side, i.e., a down-cutting action, while the side 2a is subjected to a grinding action in the opposite direction, i.e., an up-cutting action, therefore, an excellent machining efficiency is obtained. On the other hand, when passing under the grinding wheel 4Y, the sides 2c and 2a are subjected to an up-cutting action and a down-cutting action, respectively. The sides 2b and 2d are also subjected to the cutting action in the same manner. Further, cut sides 2A, 2B, 2C, and 2D are also subjected to machining under the same condition. As a result, the machined portion of the workpiece passing under both the grinding wheels has four sides thereof all subjected to machining under the same conditions.
According to the invention, the split-type free rollers are disposed along the sides of the wheels, hence, even a small workpiece can be machined. In addition, since the grinding wheels act while having an angle of about 45 degrees with respect to the flow of the workpiece, the machined portion passing under the grinding wheel rotating counterclockwise and the grinding wheel rotating clockwise is uniformly burred and chamfered.
In the surface machining apparatus thus constructed, it is possible to obtain a substantially uniform degree of surface machining such as burring and chamfering, since all the cut sides and machined portion sides of the workpiece 2 are subjected to surface machining such as burring and chamfering by means of the rotation of the grinding wheels 4X and 4Y. However, by this surface machining apparatus, some sides are subjected to a down-cutting action by the grinding wheel 4X having a grinding surface rotating in the same direction as the moving direction of the workpiece 2, while the other sides are subjected to an up-cutting action by the grinding wheel 4Y, while countering thereto, which has a grinding surface rotating in the direction opposite to the moving direction. Therefore, there is such a tendency that the latter is inevitably burred and chamfered more effectively than the former.
Referring now to Fig. 4 which practically illustrates the above description, a reference numeral 7 denotes each of conveyor rollers, while 8 represents a conveyor plate. In the Figure, the side 2a of the workpiece 2 is subjected to surface machining such as burring and chamfering by the grinding wheel 4X having the grinding surface rotating in the same direction as the moving direction of the conveyor 3 while moving away from the grinding wheel 4X in the moving direction of the conveyor 3. On the other hand, the side 2c of the workpiece 2 is subjected to surface machining such as burring and chamfering with the grinding wheel 4X while countering thereto by means of the movement of the conveyor 3. In consequence, the side 2c of the workpiece 2 is more burred and chamfered than the side 2a, showing a tendency to cause a non-uniform burring and chamfering between both the sides 2a and 2c of the workpiece 2. The cut sides 2A and 2D of the workpiece 2 also have the above tendency.
In addition, since the grinding wheel 4X first disposed with respect to the moving direction of the workpiece 2 machines a workpiece which has not been machined, while the second grinding wheel 4Y machines the workpiece which has been surface-machined once, the first grinding wheel 4X is larger in wear than the second grinding wheel 4Y. Accordingly, in the case where a multiplicity of grinding wheels 4 are disposed, the grinding wheels tend to become smaller in wear in the disposition order, i.e., they tend to have non-uniform wear.
Figs. 5 and 6 in combination show another example of the surface machining apparatus to which a further improved burring chamfering method in accordance with the invention is applied.
The surface machining apparatus shown in Figs. 5 and 6 differs from the above-described machining apparatus of the invention in that the number of revolutions of the grinding wheel 4X having the grinding surface rotating in the same direction as the moving direction of the conveyor 3 and that of the grinding wheel 4Y having the grinding surface rotating in the direction opposite to the moving direction are selected to be substantially equal to each other in relative to the workpiece 2. More specifically, the number of revolutions of the grinding wheel 4X is set so as to be increased by 2v (where v: the speed of the conveyor), and the number of revolutions of the grinding wheel 4X is selected to be in the vicinity of the set value. In other words, the grinding wheels are rotated so that the speeds (peripheral speeds) V of the grinding surfaces of the respective grinding wheels in machining the workpiece 2 are substantially equal to each other in relation to the workpiece 2. It is to be noted that it is desirable to properly select the above revolution numbers according to the quality of material of the workpiece 2 and the wheels.
The following is the description of the burring chamfering method of the invention attained by the above surface machining apparatus.
First, the number of revolutions of the grinding wheel 4X is made higher than that of the grinding wheel 4Y. More specifically, the speed of the grinding surface of the grinding wheel 4X is set to be faster than that of the grinding wheel 4Y by 2v.
Next, the workpiece 2 passes under the grinding wheel 4X while subjecting its cut side 2C and machined portion side 2a to up-cutting actions, so that these portions are burred and chamfered.
Further, the workpiece 2 passes under the grinding wheel 4Y while subjecting its cut side 2A and machined portion side 2c to up-cutting actions, so that these portions are burred and chamfered.
Thus, since the relative speed of the grinding surface of the grinding wheel 4X is made equal to that of the grinding wheel 4Y with respect to the workpiece 2, it is possible to make uniform the degree of surface machining such as burring and chamfering of the cut sides 2A, 2C which are at right angles to the moving direction of the workpiece 2, and the machined portion sides 2a, 2c which are parallel to the moving direction. (The degree of surface machining of 2B, 2D, 2b, 2c is also just the same as the above-mentioned sides.) Such a burring chamfering method is made more effective by applying axial vibrations to the grinding wheels 4X and 4Y as follows:

If the grinding wheels 4X and 4Y are: vibrated in axial direction as shown by arrows M and N in Fig. 6, the entire peripheries of the cut and machined portions are more effectively burred and chamfered by the up-cutting actions of the grinding wheels 4X and 4Y.

By thus applying axial vibration to the grinding wheels 4X and 4Y, the entire peripheries of the cut and machined portions can be uniformly burred and chamfered advantageously.
Figs. 7a and 7b are front views for explaining a method of making uniform the wear of the grinding wheels 4X and 4Y.
It has already been mentioned that, in the surface machining apparatus employed in this embodiment, the grinding wheel 4X which is first disposed with respect to the moving direction of the workpiece 2 has greater wear than the second grinding wheel 4Y. Therefore, in this apparatus, the belt conveyor is not driven in a fixed moving direction at all times, but the moving direction of the conveyor 3 is changed every time a predetermined time elapses, as shown in Figs. 7a and 7b. By so doing, the wear of the grinding wheels 4 can be made uniform.
Such a method is extremely effective in the case where two or more of the grinding wheels 4 are employed.
As has been described, according to the improved method of the invention, the speed of the grinding surface of the grinding wheel rotating in the same direction as the moving direction of the workpiece and that of the grinding surface of the grinding wheel rotating in the direction opposite to the moving direction are made equal to each other in relation to the workpiece to effect burring and chamfering. Therefore, the workpiece can be uniformly burred and chamfered advantageously.
Although the invention has been described through specific terms, it is to be noted here that the described embodiments are not exclusive and various changes and modifications may be imparted thereto without departing from the scope of the invention which is limited solely by the appended claims.

Claims

1. A method of burring and chamfering a workpiece, characterised by employing an apparatus including: a workpiece carrying belt conveyor (3); a plurality of grinding wheels (4X, 4Y) obliquely disposed to the moving direction of and over said belt conveyor (3), said grinding wheels (4X, 4Y) being arranged in parallel to each other; and split-type press rollers (5X, 5Y) disposed along both sides of each of said grinding wheels (4X, 4Y).

2. The method of claim 1, comprising the steps of: passing said workpiece (2) under a first grinding wheel (4X) which has a grinding surface rotating in the direction opposite to the moving direction of said workpiece (2) thereby to effect burring and chamfering; and passing said workpiece (2) under a second grinding wheel (4Y) which is disposed in parallel to said first grinding wheel (4X) and has a grinding surface rotating in the same direction as said moving direction thereby to effect burring and chamfering.

3. The method of claim 1 or 2, wherein said grinding wheels (4X, 4Y) are rotated while having an angle of about 45 degrees with respect to said moving direction.

4. The method of any of claims 1 to 3, wherein the moving direction of said workpiece carrying belt conveyor (3) is changed every time a predetermined time elapses.

5. The method of any of claims 1 to 4, wherein said grinding wheels (4X, 4Y) are vibrated in their axial direction.