How to Adjust the Blades of Hydraulic Pendulum Shears?

1. Introduction

In recent years, with the rapid development of manufacturing industry, the shearing machine is more and more widely used as the main processing equipment of the sheet metal.

Among them, the hydraulic pendulum shearing machine is favored by users because of its simple structure, low failure rate and good cutting quality.

In order to give full play to the good cutting quality of the hydraulic pendulum shearing machine, the users are required to have a deeper understanding of the blade installation and adjustment.

Although the adjustment method of the blade of the hydraulic pendulum shearing machine is given in the general literature, it is difficult to obtain satisfactory results in practice due to the influence of the length and hardness of the blade, as well as the material and thickness of the plate to be cut.

Based on the analysis of the blade position, blade size and installation of the hydraulic pendulum shearing machine, this article puts forward that the blade adjustment of the hydraulic pendulum shearing machine includes not only the adjustment of blade height, but also the adaptation of blade helix.

2. The installation requirements of the blade in the cutting process of the hydraulic pendulum shearing machine

As shown in Fig. 1, the swinging tool carrier rotating around the o-point cuts the sheet metal downward under the action of the hydraulic cylinder.

Fig. 1 The principle of shearing

Fig. 1 The principle of shearing

In order to realize continuous cutting from right to left, the blade installed on the tool rest forms an angle X (i.e. cutting angle) with the worktable.

The main requirements are as follows:

1) Requirements of the front and back angle

In order to ensure the cutting quality, the vertical plane between the blade and the worktable should always be at a γ angle.

In fact, because it is impossible to ensure that the blade is always on the same rotary cylindrical surface of the tool carrier, the front and back angles of the blade would change during the whole cutting process.

If the middle point of the blade’s full length is taken as the starting point, at the beginning of cutting, the front angle is large and the back angle is small because  of the small turning radius (OA ‘) of the tool carrier;

At the end of shearing, the front angle is small and the back angle is large due to the increase of the turret turning radius (OB ‘).

2) In order to prevent serious friction between the front of the blade and the plate to be cut, the front face of the blade must always be within the arc of its motion path during the whole cutting process (from point c to point d).

3) Clearance requirement

In order to obtain a better quality of shear section, it is necessary to ensure that the clearance △ between the blade and the plate to be cut is a fixed value as far as possible (see Fig. 2).

Fig. 2 Shearing clearance

Fig. 2 Shearing clearance

The blade clearance is consistent in the whole length of the blade.

Improper adjustment will aggravate the wear and damage the blade, and even bite the table or overturn the sheet metal.

In order to achieve the above requirements, it is necessary to adjust the front of the blade to a space spiral surface as far as possible, so as to ensure that the front and back angles remain unchanged in the cutting process.

3. General adjustment methods of hydraulic pendulum shearing machine blade

Since it is impossible to adjust the front face of the blade to a space spiral surface in practice, the requirement of space curved surface is generally realized by adjusting the thickness of the adjusting gasket between the blade and the tool carrier, as shown in Figure 3.

Fig. 3 The adjustment of blade

Fig. 3 The adjustment of blade

Although the method of adjusting the gasket thickness is very simple, there are still some problems.

According to the space parallel curves requirements of ideal blade installation, the blade must meet the following requirements:

x=R cosθ
y=R sinθ                                    (1)


  • θ – rotation angle of the tool carrier around the axis
  • Ф – shear angle

The blade is required to be a spatial helix, and the front surface of the blade should be a cylindrical helix.

Using a simple method to adjust the gasket will bring the following two problems.

1) The gap problem.

A simple way to adjust the gasket thickness is to use a straight line to approach the helix along the length direction of the blade, that is, the blade of the blade is a straight line, as shown in Figure 4.

Fig. 4 The blade of the blade is a straight line.

Fig. 4 The blade of the blade is a straight line.

Then, the gap between the blade and the plate to be cut actually becomes △+.

Since λ changes with the swing angle θ of the tool holder, the gap between the blade and the plate to be cut becomes a variable.

The range of change of λ is as follows:

λ=R(1- cosβ)           (2)


  • β – swing angle of tool carrier from the beginning to the end of shearing
  • β = arcsin( btgФ /R)

If QC12Y-6×200 is taken as an example to calculate (R=469mm, Ф =1.5° and b=1600mm), the range of variation is about 1.8mm.

If the 1100mm blade is used to adjust the gasket thickness, the range of variation is 0.88mm, even exceeding the recommended 0.5mm gap when cutting 6mm steel plate.

Obviously, the method of adjusting the gasket thickness is very simple, but it can’t guarantee the clearance between the blade and the sheet metal in the whole shearing process as a fixed value, so it can’t guarantee the shearing quality.

2) The front angle problem

The method of adjusting the gasket thickness ignores the situation that the front of the blade should be a spiral surface, and directly replaces it with a plane perpendicular to the workbench, which can not guarantee the requirement of the front angle (it is generally 1.5° to 2° , which is to ensure the shear quality and blade strength) during shearing.

For the blade with width W, the gap between the upper and lower edges and the ideal helical surface is calculated as follows:

X’=R{1- cos[arcsin(y /R)}                        (3)

By substituting the relevant parameters of QC12Y-6×200 into equation (3), then X ‘= 6.87mm is gotten, and the maximum anterior angle is -arctan (x’/y’)=4.91°.

A negative value indicates a negative front angle.

Obviously, such a large variation range of front angle can not guarantee the shear quality.

4. Solutions

1) Problem of the clearance

The reason for the large shear clearance in the above analysis and calculation is that only two straight lines are used to approximate the spiral line segment of the blade in the whole shear process.

If the multi-line segment approximation is used, the maximum gap will be reduced.

The blade of QC12Y-6×200 is 1100mm, and the spacing between locating holes is 200mm,

If the gasket is used at each positioning hole for adjustment, the shear clearance variation λ = 0.03mm, which is calculated by the formula (2) and it can fully meet the requirements.

As for the thickness of the adjusting gasket, it can be obtained by calculating the height of each straight line segment approaching the arc bow.

In order to meet the requirement of frontangle (γ = 1.5 ° ~ 2.0 °), it is necessary to increase the distance y between the turret rotation axis and the worktable.

y is related to the turret rotation center and plate thickness.

The shorter the turning radius of the turret, the thicker the sheet metal and the larger the y value.

Of course, these must be considered in the design of shear.

In practice, the gap adjustment device is usually used to increase the shear gap. Naturally, this is done at the expense of shear quality.

Figure 5 is the bevel gasket, and the bevel angle n is ground in the direction of the gasket perpendicular to the worktable (1.5 ° is selected in the design, and the swing radius of the tool carrier can be slightly increased when it is small), so as to compensate the error caused by using the plane perpendicular to the worktable to approximate the spiral surface.

Fig. 5 Bevel gasket

Fig. 5 Bevel gasket

In order to better adapt to the requirements of helical surface, when the tool holder is long, the surface contacting with the blade can also be ground with an inclined plane of 1 ° along the length direction of the blade (as shown by the dotted line in Figure 5).

In this case, the longer the turret is, the more significant the effect is.

5. Practice results

The above methods are applied to the blade clearance adjustment of QC12Y—6 × 3200 and Q12Y—12 × 2500 shears, as shown in Table 1.

The following data show that the blade clearance can be reduced without undercut in the actual shearing process by using the inclined gasket and trimming the gasket on each mounting hole, which improves the shearing quality.

It should be noted that the experimental data in Table 1 include the effect of blade shape error on the minimum shear gap.

Table 1 The contrast of minimum shearing clearance between two adjusting methods of the blade / mm

Model General adjusting method Use the inclined gasket and trim the gasket on each mounting hole
QC12Y—6 × 3200 0.62 0.36
Q12Y—12 × 2500 1.0 0.65


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