GB2065026A

GB2065026A - Methods and apparatus for preventing or minimizing vibrations and noises in machine tools such as bandsaw machines

Info

Publication number: GB2065026A
Application number: GB8035140A
Authority: GB
Original assignee: Amada Co Ltd
Current assignee: Amada Co Ltd
Priority date: 1979-10-31
Filing date: 1980-10-31
Publication date: 1981-06-24
Also published as: AU538221B2; IT1129359B; AT383759B; FR2468795B1; DE3040829A1; FR2468795A1; JPS5669022A; SE8007652L; ATA532280A; GB2065026B; JPS5852767B2; AU6385380A; IT8068672A0; SE445718B

Abstract

Noise from bandsaw machines has been a problem in the past, for which no real solution has been available. It has now been surprisingly found that the vibration (and thus the noise) of an elongate flexible member can be prevented or reduced, by periodically changing the length thereof, by periodically changing the tension thereof, by periodically changing the Young's Modulus (E) and/or by periodically changing the density thereof. The driven or driving wheel of a bandsaw blade may be provided with axially extending peripheral grooves.

Description

SPECIFICATION Methods and apparatus for preventing or minimizing vibrations and noises in machine tools such as bandsaw machines The present invention relates generally to machine tools such as a bandsaw machine having an elongate flexible bandsaw blade entrained around a plurality of wheels or pulleys and, more particularly, to methods and apparatus for preventing or minimizing vibrations of and noise from an elongate flexible member such as a bandsaw blade in machine tools such as a bandsaw machine.

Although the present invention is described herein in connection with bandsaw machines by way of example, the present invention is not only limited in application to bandsaw machines but also to other machine tools.

As is well known, a bandsaw machine comprises a flexible endless bandsaw blade and a plurality (usually a pair) of wheels or pulleys around which the bandsaw blade is entrained. The wheels or pulleys for the bandsaw blade are mounted for rotation on spaced substantially parallel axes and one of the wheels or pulleys is power driven to drive the bandsaw blade, through frictional engagement of the power driven wheel or pulley with one flat side of the bandsaw blade. Also, in order adequately to tension the bandsaw blade, one of the wheels or pulleys is biased, together with the shaft on which it is mounted, in a radial direction away from the other wheel(s) or pulley(s).Furthermore, one of the lengths of the bandsaw blade between the wheels or pulleys is slidably guided and held by a pair of guide means with the flat sides of the blade perpendicular to workpiece(s) to be cut, so as to act as the cutting length in cutting operations. In a horizontal bandsaw machine, the wheels or pulleys holding the bandsaw blade are mounted on a saw head assembly which is so arranged as to be lowered toward the workpieces in cutting operations, to enable the bandsaw blade to cut into the workpiece(s). In a vertical bandsaw machine, the wheels or pulleys holding the bandsaw blade are vertically spaced from each other to hold the cutting length of the bandsaw blade vertically so that the workpiece(s) to be cut may be horizontally fed into the bandsaw blade.

One of the embarrassing problems with the conventional bandsaw machines is the fact that the bandsaw blade will suffer from vibration and this often produces a very keen, screeching noise when effecting cutting operations. Of course, the keen, screeching noise from the bandsaw blade is very offensive to the ear and also can be harmful to the health of operators of bandsaw machines. Furthermore, the noise is apt to become an issue as a noise pollution, especially because the bandsaw machines are very widely used even in small factories and shops in non-industrial areas.

The vibration of the bandsaw blade causing the keen, screeching noise occurs primarily because the bandsaw blade will be vibrated inherently, due to the flexible nature thereof, not only sideways or laterally but also depthwise or vertically when making cutting operations. Also, the vibration of the bandsaw blade has a tendency to be increased or amplified because of the fact that there is a larger tensile stress in a length of the bandsaw blade which has cuttingly passed through a workpiece to be cut than in a length about to cut into the workpiece. This is because the bandsaw blade is pulled by the driving bandsaw wheel or pulley under a strong tension.Although the undesirable vibration of the bandsaw blade is reduced by the sawblade guide means for slidably guiding the bandsaw blade, the fact is that the vibration is generally too severe to be satisfactorily reduced merely by the guide means and, consequently, the bandsaw blade will often continue to vibrate whilst travelling around the bandsaw wheels or pulleys.

Unfortunately, the vibration of the bandsaw blade will not only cause the keen, screeching noise, but will also adversely influence the cutting rate and accuracy of the bandsaw blade, as well as the life of the bandsaw blade. Furthermore, it will cause the cutting lubricant to be sprayed of the bandsaw blade. For instance, the vibration of the bandsaw blade will result in a poor surface roughness of a cut workpiece, and also it will make the initial part of the kerf wider than a subsequent part.of the kerf and, therefore, an accurately straight cut cannot be obtaibed. Because the bandsaw blade is apt to be floating, the cutting rate will be decreased considerably. Also, the bandsaw blade will have a tendency to be worn uselessly without cutting.Furthermore, since the vibration bandsaw blade will spray the cutting lubricant like a mist, the lubricant is lost out of the bandsaw machine without being recovered and splashes the operation and the work area in the vicinity of the bandsaw machine.

With regard to bandsaw machines, another fundamental vexing problem is the fact that the bandsaw blade is apt to slip on the wheels or pulleys when travelling thereover to make cutting operations. Such slippage results from the fact that the bandsaw blade is always flooded or bathed with cutting lubricant during cutting operations and such lubricant is carried onto the peripheral surfaces of the bandsaw wheels by the bandsaw blade. Consequently, a film of the lubricant will be formed between the bandsaw blade and the peripheral surfaces of the wheels or pulleys. The slippage of the bandsaw blade on the bandsaw wheels or pulleys will result in the bandsaw blade being damaged to some extent, because, on slipping, the blade is forced into the workpiece to be cut without performing cutting.Although the slippage of the bandsaw blade can be overcome to some extent by increasing the tension of the bandsaw blade between the bandsaw wheels or pulleys, too much tension can cause early wear or breakage of the bandsaw blade.

It is an object of the present invention to provide a method of and apparatus for preventing or minimizing the noise from an elongate flexible member, such as a bandsaw blade, in a machine tool, such as bandsaw machine.

It is, therefore, another object of the present invention to provide a method of and apparatus for preventing or minimizing the vibration causing noise from the elongate flexible member such as the bandsaw blade in a machine tool such as a bandsaw machine.

According to the first aspect of the present invention there is provided a method of preventing or reducing vibration of an elongate flexible member, which comprises periodically changing the length thereof, by periodically changing the tension thereof, by periodically changing the Young's Modulus (E) and/or by periodically changing the density thereof.

According to the second aspect of the present invention there is provided an apparatus for preventing or reducing vibration of an elongate flexible member, which comprises means for periodically changing the length thereof or means for periodically changing the tension thereof.

Thus, the objects of the present invention are accomplished by preventing or obviating a standing wave from occurring from a compound of a progressive wave and a reflected wave of a longitudinal-wave vibration, which has been found to be a major cause of the noise occurring in bandsaw machines in operation. According to the present invention, the standing wave of the longitudinal-wave vibration is prevented from occurring (or occurrence thereof is mitigated) by periodically disturbing the reflected wave by periodically changing the length or the tension of the elongate flexible member, such as the bandsaw blade, in operation between holding members, such as the bandsaw wheels or pulleys, by which the elongate flexible member is held.

The present invention also provides a method of and apparatus for changing the length and the tension of an elongate flexible member, such as a bandsaw blade, to prevent or minimize the noise and the vibration in a machine tool such as a bandsaw machine in operation.

Accordingly, use of the present invention can increase the working accuracy, the work rate and the tool life of a machine tool, such as a bandsaw machine, by preventing or minimizing the vibration of an elongate flexible member, such as the bandsaw blade.

It is a further object of a subsidiary aspect of the present invention to provide a bandsaw machine in which the bandsaw blade will not slip on the bandsaw wheels or pulleys.

For a better understanding of the present invention and to show how the same may be put into effect, reference will now be made, by way of example, to the accompanying drawings, in which :- Figure 1 shows a front elevational view of a horizontal bandsaw machine in which the principles of the present invention can be embodied, Figures 2a, 2b and 2c show graphs of the changes in noise with changes in speed of a bandsaw blade in a horizontal bandsaw machine, Figures 3a and 3b show graphs of the changes in noise with changes in span or distance between the guide means for a bandsaw blade in a horizontal bandsaw machine, Figure 4 shows a front elevational view of a bandsaw wheel for a bandsaw machine, such as shown in Figure 1, which has embodied therein the principles of the present invention, Figure 5 shows a side elevational view of the bandsaw wheel of Figure 4, and Figure 6 shows a graph of changes in length of a bandsaw blade during a cutting operation in a bandsaw machine having the bandsawwheel of Figures 5 and 6.

Referring now to the accompanying drawings, the present invention will be described by way of example with regard to a horizontal bandsaw machine which is shown in Figure 1 and is generally designated by the numeral 1. However, it should be initially noted that the present invention is not limited in application to this particular type of bandsaw machine but it is applicable not only to any suitable known type of bandsaw machines but also to other machine tools than bandsaw machines.

As is conventional, the horizontal bandsaw machine 1 comprises an oblong box-like base 3 on which a work-table 5 and a vise assembly 7 are mounted to hold a workpiece W to be cut and a saw head assembly 9 which has spaced husing sections 11 and 13 and is movable up and down toward and away from the base 3.

The saw head assembly 5 may be pivotally connected to the base 3 by means of a hinge pin 15 and may be so arranged as to be raised away from and lowered toward the base 3 by a suitable means such as a hydraulic motor 17 of a cylinder type. In the saw head assembly 5, a flexible endless bandsaw blade 19 is trained around a driving wheel 21 and a driven wheel 23 which are mounted for rotation on spaced parallel shafts 25 and 27, respectively, in the housing sections 11 and 13, respectively. The driving wheel 21 is power driven together with the shaft 25 to drive and impart orbital motion to the bandsaw blade 19, and the driven wheel 23 is kept drawn or biased away from the driving wheel 21 by a suitable means so as to adequately tension the bandsaw blade 19.The bandsaw blade 19 at the cutting zone of the horizontal bandsaw machine 1 is slidably held or guided with its cutting edges faced vertically downwardly by a pair of guide assemblies 29 and 31 so that the cutting stretch may be provided therebetween. The guide assemblies 29 and 31, which are usually so designed as to supply the bandsaw blade 19 with cutting lubricant, are detachably fixed at or integrally provided at lower ends of supporting arm members 33 and 35, respectively, which are held by a beam member 37 fixed at any upper portion of the saw head assembly 9. Also, either or both of the supporting arm members 33 and 35 can be adjustably moved along the beam member 37 so as to adjust the span or distance between the guide assemblies 29 and 31 according to the cross-sectional length of the cut to be made on the workpiece W. Thus, when the saw head assembly 9 is swung down around the hinge pin 15 from its raised position, the bandsaw blade 19 rotating around the driving wheel 21 and the driven wheel 23 in the saw head assembly 9 will be fed to cut the workpiece W held by the vise assembly 7 on the work-table 5.

In the horizontal bandsaw machine 1 as described in the above, it has been conventionally seriously disadvantageous that the bandsaw blade 19 will suffer from vibration and produce a very keen and screechy noise because of such vibration and also is apt to slip on the driving and driven wheels 21 and 23 when making a cutting action. The vibration causing the noise of the bandsaw blade 19 will have a tendency to be increased or amplified since there is a larger tensile stress in the stretch of the bandsaw blade 19 between the workpiece W and the driving wheel 21 than in that between the workpiece W and the driven wheel 23.

Although the guide assemblies 29 and 31 are effective to reduce the vibration of the bandsaw blade 19, the fact has been that the vibration is too severe to be reduced only by them and the bandsaw blade 19 will remain severely vibrating to produce the keen and screechy noise.

Heretofore, however, it has not been made clear how the keen and screechy noise will be produced from the vibration of the bandsaw blade 19 during a cutting operation in bandsaw machines. Such being the case, -the inventor made several experiments to analyze the frequency of the vibration and noise of the bandsaw blade 19 especially with a view to investigate the type of wave of the vibration causing the keen and screechy noise. In the experiments, the inventor cut a stainless steel bar (Japanese Industrial Standard (JIS): SUS 300) of 200mm diameter at a fixed cutting rate with a feeding pressure of 13kg/cm2 with use of a horizontal bandsaw machine (Model HA-404 of Amada Company, Ltd.) and a bandsaw blade (GLB-3M of the same company).

Firstly, in order to find the changes in noise with changes in speed of a bandsaw blade, the inventor made experiments in cutting with the span or distance between the guide assemblies set approximately to 200 mm and with the various bandsaw blade speeds of 30m/min., 40m/min. and 60m/min. As the result of the experiments, the noise changed with the changes in frequency as shown in the graphs of Figures 2a, 2b and 2c. It will be seen that the fundamentals with the bandsaw blade speeds of 30m/min., 40m/min. and 60m/min. were 1400 Hz, 1425 Hz and 1425 Hz, respectively, as shown in Figures 2a, 2b and 2c, respectively.

Thus, it has been found from the experiments that the frequency with 1400 Hz taken as fundamental is not correlated with the speed of the bandsaw blade so much. Consequently, the result of the experiments seems to mean that an inherent resonance of the bandsaw blade and the body of the horizontal bandsaw machine will have an influence on the noise.

Nextiy, in order to find the changes in noise with changes in distance between the guide assemblies for the bandsaw blade, the inventor made experiments in cutting at a bandsaw blade speed of 30m/min. with the distance between the guide assemblies variously set to 200mm and 300mm. As the result, the frequencies with 1400 Hz taken as fundamental were not changed whether the distance between the guide assemblies was set to 200 mm or 300 mm as shown in the graphs of Figures 3a and 3b. Thus, it has been found from the experiments that the noise will occur mainly from the longitudinal wave of the vibration of the bandsaw blade in the horizontal bandsaw machine.

Furthermore, as a result of experimentally hammering various portions of the horizontal bandsaw machine, it has been found that the body of the horizontal bandsaw machine including the saw head assembly and the guide assemblies for the bandsaw blade will produce no resonance with the bandsaw blade. More particularly, it has been found that the bandsaw blade forms an independent system of vibration together with the driving and driven wheels while the body of the horizontal bandsaw machine forms another independent system of vibration.

As has been described above, it has been found from the experiments that the noise in the horizontal bandsaw machine will occur mainly from the longitudinal-wave vibration which is independent of the body of the horizontal bandsaw machine. This result of the experiments is made reasonable by mathematically computing the inherent vibration of the horizontal bandsaw machine which has been used in the experiments.

The differential equation of a longitudinal wave of a flexible member is expressed as follows:

where: C2 = E p p = density E = Young's modulus With regard to the bandsaw blade, the equation (1) can be transformed as follows:

where: u = displacement of the bandsaw blade t = time x = coordinates A = sectional area of the bandsaw blade IJ = moment of inertia of the driven wheel r = radius of the driving and driven wheels When a longitudinal wave of the vibration occurs in the bandsaw blade in the bandsaw machine, the conditions of the boundary between the bandsaw blade and both of the driving and driven wheels are expressed as follows:

where:: IK = moment of inertia of the driving wheel The above equations, however, are not sufficient to solve the equation (1), and also the moments IK and IJ of inertia of the driving and driven wheels are very large. Accordingly, assuming that both ends of the stretch of the bandsaw blade between the driving and driven wheels are fixed, the following equations are obtained: u = 0 when x = L u = 0 when x = 0 (2) The equation (1) is transformed as follows:

u=QX Q = Asin vt + B cosvt x=Csinex+ D cos c x (3) where: v = inherent vibrations (rad/sec) A,B,C,D = constants By substituting the equations (2) for the equations (3), the inherent vibrations are expressed as follows:

By using the equation (4), the inherent vibrations of the bandsaw blade in the cutting experiments can be obtained as follows:

= n1891.2(Hz) (n=1,2,3,4..... ) where: L= 1358 mm = 135.8cm E = 2.1 x 104 kg/mm2 = 2.1 x 109 g/cm2 = 7.8 g/cm2 Thus, the result of the above equation is approximate to the fundamental 1400 Hz, and therefore it is concluded that the experiments are reasonable.

Generally, a longitudinal-wave vibration occurring on an elongate flexible member which is fixed at its end will go or be transmitted along such an elongate flexible member as a progressive to the fixed end and is then reflected by the fixed end and return as a reflected wave. In such transmission of the longitudinal-wave vibration, the progressive wave and the reflected wave will lag in phase by a half cycle from each other, and the progressive wave and the reflected wave will be compounded to produce a standing wave causing the noise. Also, it is understood that the standing wave of the longitudinal-wave vibration is prevented from occurring by periodically disturbing the reflected wave.

According to the present invention, the standing wave of the longitudinal-wave vibration of an elongate flexible member such as the bandsaw blade is prevented from occurring by periodically disturbing the reflected wave by periodically changing the length or the tension of the elongate flexible member.

Referring to Figures 4 and 5, there is shown a bandsaw wheel 21(23) which can be mounted on the horizontal bandsaw machine 1 shown in Figure 1 as either or both of the driving wheel 21 and the driven wheel 23 so that the bandsaw blade 19 may be trained therearound. The bandsaw wheel 21 (23) shown in Figures 4 and 5 is provided at its periphery with grooves 39 so as to change the length or the tension of the bandsaw blade 19 during a cutting operation. The grooves 39 are formed at the periphery of the bandsaw wheel 21(23) in parallel with the shafts 25 (27) thereof at suitable intervals so as to periodically change the length or the tension of the bandsaw blade to disturb the reflected wave of the longitudinal-wave vibration.

However, instead of the grooves 39, elongate projections may be formed or integrally fixed around the periphery of the bandsaw wheel 21 (23) so as to change the length or tension of the bandsaw blade 19 when the bandsaw wheel 21 (23) is rotated.

By providing either of the driving and driven wheels 21 and 23 with the grooves 39, the length L of the bandsaw blade 19 between the driving and driven wheels 21 and 23 will be periodically changed between L + P/2 and L - P/2 as shown in Figure 6. More particularly, the stretch of the bandsaw blade 19 between the driving and the driven wheels 21 and 23 is periodically changed in length L between L + P/2 and L - P/2 as shown in Figure 6 since the end of the stretch of the bandsaw blade 19 being in contact with the bandsaw wheel 21 (23) is changed in position between both edges of each of the grooves 39.

In this connection, the grooves 39 or the elongate projections formed at the periphery of the bandsaw wheel 21(23) will act not only to prevent the vibration and the noise as has been described in the above but also to prevent the bandsaw blade 19 from slipping on the bandsaw wheel 21 (23) during cutting operations.

It will be understood that the bandsaw blade 19 will be prevented from slipping since the cutting lubricant carried onto the periphery of the bandsaw wheel 21 (23) by the bandsaw blade 19 is forced into the grooves 39 without becoming a film between the bandsaw blade 19 and the periphery of the bandsaw wheel 21 (23).

Furthermore, it will be understood that the bandsaw blade 19 will be also prevented from slipping by the elongate projections formed on the periphery of the bandsaw wheel 21(23) since the pressure applied to the bandsaw blade 19 to tension the same is localized on the projections during cutting operations.

In order to prevent the noise of the bandsaw blade 19, the standing wave of the longitudinal-wave vibration can be also prevented from occurring by periodically changing the tension, the Young's modulus (E) or the density of the bandsaw blade 19. Also, the length and the tension of the bandsaw blade 19 can be changed by periodically moving either of the driving and driven wheels 21 and 23 toward and away from the other by a suitable means such as a hydraulic motor to prevent the standing wave from occurring.

Furthermore, the tension of the bandsaw blade 19 can be changed by a tension roller which is provided between the driving and driven wheels 21 and 23 so as to periodically press the bandsaw blade 19.

In the above, the present invention has been described with regard to the horizontal bandsaw machine and the bandsaw blade by way of example, but it will be understood to those skilled in the art that the present invention can be applied to any elongate flexible member other than the bandsaw blade to prevent the vibration and the noise.

Although a preferred form of the present invention has been illustrated and described, it should be understood that the device is capable of modification by one skilled in the art without departing from the principles of the invention. Accordingly, the scope of the invention is to be limited only by the claims appended hereto.

Claims

1. A method of preventing or reducing vibration of an elongate flexible member, which comprises periodically changing the length thereof, by periodically changing the tension thereof, by periodically changing the Young's Modulus (E) and/or by periodically changing the density thereof.

2. A method according to Claim 1, which comprises periodically changing the length thereof.

3. A method according to Claim 2, wherein the elongate flexible member is a bandsaw blade and wherein the length thereof is periodically changed by moving either a driven wheel therefor or a driving wheel therefor toward or away from the other thereof.

4. A method according to Claim 2, wherein the elongate flexible member is a bandsaw blade and wherein the length thereof between a driven wheel therefor and a driving wheel therefor is periodically changed by one or both of the wheels having axially oriented grooves or projections on the surface of which the bandsaw blade is to be entrained.

5. A method according to Claim 1, which comprises periodically changing the tension thereof.

6. A method according to Claim 5, wherein the elongate flexible member is a bandsaw blade and wherein the tension thereof is periodically changed by a tension roller being periodically pressed against the bandsaw blade.

7. An apparatus for preventing or reducing vibration of an elongate flexible member, which comprises means for periodically changing the length thereof or means for periodically changing the tension thereof.

8. An apparatus according to Claim 7, wherein the elongate flexible member comprises a bandsaw blade and wherein the means comprises a wheel, being either the driven wheel or the driving wheel of a bandsaw, having axially oriented grooves or projections on the surface of which the bandsaw blade is to be entrained.

9. A bandsaw machine comprising an apparatus in accordance with Claim 7 or 8.

10. A method according to Claim 1, substantially as hereinbefore described with reference to the accompanying drawings.

11. An apparatus according to Claim 7, substantially as herein before described with reference to the accompanying drawings.

12. A bandsaw machine substantially as hereinbeforre described with reference to the accompanying drawings.

13. Any novel feature or combination of features described herein.