HK40117455A - Tool holder comprising a plurality of tool-holder spindles and numerically controlled machine tool comprising such a tool holder - Google Patents

Description

Includes multiple tool holders for holding the tool spindle and a CNC machine tool including the tool holder.

Technical Field

This invention relates to the field of CNC machine tools for machining parts, preferably micro-mechanical parts, and to the field of equipment for such machine tools.

More specifically, the present invention relates to a tool holder comprising a plurality of spindles for holding a tool, and a CNC machine tool comprising such a tool holder.

Background Technology

CNC machine tools are used for the mass production of parts, particularly by machining according to instructions from a computer program. These machine tools include a tool mounted on a spindle for holding the tool and are typically equipped with a tool changer for replacing the tool held by the spindle to adapt it to machining operations performed on parts held in a fixture.

When changing tools, the machine tool ceases production, meaning the machining operation is interrupted. Therefore, the goal is to minimize tool change time. To this end, tool changers have been developed to operate within the shielded time as much as possible and to minimize machine tool downtime, thereby improving its productivity.

For example, a multi-axis tool post is known to include a head with several spindles arranged on it, one of which is in operation and the others are in a resting state. Specifically, the working spindle is engaged with a drive mechanism via a coupling system. Therefore, between two machining operations, the tool can be changed by disengaging the working spindle (i.e., the spindle carrying the tool to be changed), rotating the head to present the next spindle, and coupling that spindle to the drive mechanism.

However, this solution is not entirely satisfactory because while it reduces tool change time, it does not completely eliminate it. In fact, for this type of multi-axis tool turret, the tool to be changed must be braked before each tool change, and the next tool must be accelerated after it is engaged with the drive mechanism until it reaches its machining speed. These multi-axis tool turrets also require time to disengage the tool to be changed, rotate the head, and position the next tool to align with the coupling system before engagement. This solution is also particularly complex and expensive due to the coupling system.

There are also multi-axis tool holders that solve the problems of spindle acceleration and braking, in which all tools are driven to rotate synchronously. Therefore, when changing tools, the next tool is already driven at its machining speed and can begin machining the part. However, these multi-axis tool holders require a large amount of energy to rotate all tools simultaneously. In addition, due to the motion transmission power chain, the maximum rotational speed of the tools they support is relatively limited.

Overall, existing multi-axis tool holders are very large, whether the tools they carry rotate individually or simultaneously. This generates a large moment of inertia and increases the risk of collision between the fixture and the tools carried by the tool holder.

In addition to the drawbacks mentioned above, these solutions are not suitable for machining micro-mechanical parts.

Summary of the Invention

This invention addresses the aforementioned drawbacks by providing a solution that allows for complete shielding of tool changeover time, particularly by shielding the tool acceleration and deceleration phases. Another objective of this invention is to maximize the compactness of the machine tool and reduce the number of moving masses.

Therefore, the present invention relates to a tool holder comprising a body extending along an axis A-A, the body including a base at one end for fastening to a CNC machine tool, and a rotatably movable head at the other end. The head includes at least two spindles for holding tools, each spindle being configured to receive a cutting tool in an engaged manner. Depending on the angular position of the head, the spindles occupy a working position or a standby position; in the working position, they are used to perform machining operations on a workpiece held in place in a fixture; in the standby position, they are retracted from the workpiece. Each spindle is configured to be controlled independently of the other spindles to either fix its carried cutting tool stationary or drive it to rotate, regardless of its position.

Because the spindle is independently servo-controlled, it can be accelerated and decelerated during the shielding time. Therefore, this invention allows for tool changes within the dead time, reducing the dead time to only the duration from head rotation to the next tool contact with the workpiece. Due to the features of this invention, the tool change time (total tool change time) can be estimated in the range of a few tenths of a second.

The present invention also has the advantage of being applicable to any existing machine tool.

Furthermore, thanks to this invention, the spindle can achieve relatively high rotational speeds, for example, in the range of 60,000 to 80,000 revolutions per minute.

In specific embodiments, the present invention may also include one or more of the following features, which may be considered individually or in any technically feasible combination.

In a specific embodiment, the rotation axis of the head coincides with axis A-A.

In a specific embodiment, the base is configured such that axis A-A forms an angle between 35 degrees and 55 degrees relative to the vertical axis.

These features help to maximize the compactness of the device.

In a specific embodiment, these spindles are distributed around the rotation axis of the head, preferably evenly distributed, and each spindle is arranged such that its axes B-B, B-B' and B-B” form an angle between 35 degrees and 55 degrees with respect to the axis A-A, and their axes B-B, B-B' and B-B” do not intersect.

On the one hand, this feature makes it easier to clean the tool when it is at rest, thus avoiding or limiting the risk of collision with the fixture; on the other hand, it enables all spindles to maintain the same working position, thereby helping to ensure that machining tolerances are met.

In a specific embodiment, these principal axes are arranged relative to each other such that the projections of their longitudinal axes B-B, B-B', and B-B'' onto a plane P orthogonal to axis A-A form a regular n-gon centered on axis A-A, where n is the number of principal axes.

In a specific embodiment, these spindles are arranged such that the distance between their longitudinal axes B-B, B-B' and B-B” and axis A-A is greater than the radius of the spindle.

This feature also helps to clear tools that are at rest, in order to avoid or limit the risk of collision with the fixture.

In a specific embodiment, each spindle includes its own motor for rotating or fixing the cutting tool it carries.

This feature allows for reduced energy consumption of the tool post, as spindles not performing machining operations do not rotate around their respective longitudinal axes.

In a specific embodiment, at least one spindle is adapted to occupy at least two different working positions, each working position being defined by a predetermined angular position of the tool holder head.

In a specific embodiment, at least one spindle is adapted to continuously occupy the working position as the head of the tool holder rotates. This arrangement also involves continuous movement of the fixture.

According to another objective, the present invention relates to a CNC machine tool preferably used for machining micro-mechanical parts, comprising at least one tool post as described above, the tool post being directly fastened to a frame or a carrier capable of translational movement in a vertical plane via a base, such that axis A-A forms an angle between 35 degrees and 55 degrees with respect to a vertical axis, the machine tool further comprising a fixture for holding the part to be machined in place.

In a specific embodiment, the machine tool includes two tool holders arranged on both sides of the fixture.

In a specific embodiment, the machine tool includes a protective wall to prevent chips and cutting fluid from splashing, and the body of the tool holder or each tool post is liquid-tightly engaged in a corresponding opening in the protective wall.

Another aspect of the present invention relates to a method for replacing the cutting tool of a machine tool as described above, wherein:

- A first cutting tool engaged in the spindle in the working position performs the first machining stage, and a second cutting tool engaged in the spindle in the standby position is intended to perform the second machining stage and is prevented from rotating;

- Before the end of the first machining stage, the second cutting tool rotates about its axis B-B' until it reaches the speed characteristic of the second machining stage;

- Once the first machining stage is completed, the head is pivoted about axis A-A to drive the spindle carrying the second cutting tool into the working position, so that the second cutting tool can start the second machining stage, and drive the spindle carrying the first cutting tool into the standby position. Once the spindle carrying the first cutting tool reaches its standby position, the rotation of the first cutting tool is stopped.

Attached Figure Description

Other features and advantages of the invention will become apparent after reading the following detailed description, given as a non-limiting example, with reference to the accompanying drawings, in which:

Figure 1 shows a perspective view of a multi-spindle tool post according to a preferred embodiment of the present invention;

Figure 2 shows a view of the tool holder of Figure 1 oriented along the longitudinal axis of the tool holder body;

Figure 3 shows a side view of the tool holder of Figure 1;

Figure 4 shows a perspective view of two tool holders arranged on both sides of the workpiece fixture.

It should be noted that, for clarity, the accompanying drawings are not necessarily drawn to scale.

Detailed Implementation

Figure 1 illustrates a tool holder 10 for machining parts, preferably micro-mechanical parts. The tool holder 10 includes a body 11 extending along a longitudinal axis indicated by "axis A-A". In embodiments of the invention, the body 11 includes a base 12 at one end and a head 13 at the other end. The base 12 is for fastening to a CNC machine tool 20, and the head 13 is rotatable about an axis coinciding with axis A-A. The head 13 has at least two spindles 14, 14', or 14" for holding tools, each spindle for receiving cutting tools 15, 15', or 15" in an engaged manner. Depending on the angular position of the head 13, each spindle 14, 14', and 14" occupies a working position or a standby position, in which it performs machining operations on a workpiece held in place in a fixture 21, and in which it is withdrawn from the workpiece.

It should be noted that the tool holder 10 can be driven by translation, for example, in the case where the base 12 is fastened to the machine tool 20 with a carrier (not shown) that can move along at least one translational degree of freedom, the carrier preferably moves along three translational degrees of freedom in the reference XYZ directions.

Alternatively, the tool holder 10 may remain stationary, for example, in the case where the base 12 is directly fastened to the frame 22 of the machine tool 20.

Advantageously, spindles 14, 14', and 14" are configured to be controlled independently of each other so as to rotate or hold stationary the cutting tools 15, 15', or 15" they carry. This feature is particularly advantageous when changing tools. Preferably, spindles 14, 14', and 14" are motorized spindles, also known as "electric spindles," and each spindle includes its own motor for rotating or holding stationary the cutting tools 15, 15', or 15" it carries.

In particular, in order to replace the first cutting tool 15 for performing the first machining stage with the second cutting tool 15' for performing the second machining stage, the second cutting tool 15' is rotated before the end of the first machining stage until it reaches the rotational speed specific to the second machining stage.

The first cutting tool 15 is engaged in the spindle 14 in the working position, and the second cutting tool 15' is engaged in the spindle 14' in the standby position.

Once the first machining stage is completed, the head 13 is pivoted to drive the spindle 14 in the working position to the standby position, and to drive the spindle 14' in the standby position to the working position. Since the second cutting tool 15' has reached its machining speed when the spindle 14' in which it is engaged is in the standby position, the second machining stage begins immediately. The spindle 14 carrying the first cutting tool 15 is now in the standby position, and the first cutting tool 15 is stationary.

Therefore, since the second cutting tool 15' rotates and the first cutting tool 15 stops rotating during the hidden time, the cutting tool is replaced with a dead time that is reduced to only the duration of the head rotation.

Each spindle 14, 14', and 14" extends along a longitudinal axis indicated by "axis B-B", "axis B-B'", and "axis B-B"", respectively. These longitudinal axes also form their axes of rotation, which are shown only on spindle 14 in the working position in Figures 1 and 3. As shown in these figures, in the working position, spindle 14 is oriented such that its axis B-B is parallel to the vertical axis. However, in another working position, spindle 14 can also be oriented such that its axis B-B is parallel to the horizontal axis. Spindle 14 can also occupy a dynamic working position, i.e., the head 13 can rotate during machining operations. In this case, fixture 21 can move and move according to instructions associated with the machining program, and/or tool holder 10 can move via its base 12 and move according to instructions associated with the machining program.

In a preferred embodiment of the invention, as shown in the figure, the tool holder 10 includes three spindles 14, 14', and 14"". In Figure 2, which specifically illustrates the distribution of spindles 14, 14', and 14" on the head 13 of the tool holder 10, the spindles 14, 14', and 14" are uniformly distributed about the axis of rotation of the head 13, that is, in an embodiment of the invention, the spindles 14, 14', and 14" are uniformly distributed about axis A-A. The spindles 14, 14', and 14" are arranged relative to each other such that the projections of their axes B-B, B-B', and B-B" onto a plane P orthogonal to axis A-A form a regular n-gon centered at axis A-A, where n is the number of spindles. In the example shown in Figure 2, the longitudinal axes of the spindles 14, 14', and 14" form an equilateral triangle.

Furthermore, in a preferred embodiment of the invention, spindles 14, 14', and 14" are arranged such that the distance between their axes B-B, B-B', and B-B" and axis A-A is greater than the radius of spindle 14, 14', or 14"—for example, at least corresponding to the diameter of spindle 14, 14', or 14". This arrangement allows for maximizing the clearance between the cutting tools 15' or 15" in the ready position and spindles 14' and 14" to avoid the risk of these cutting tools 15' and 15" colliding with the fixture 21 or the workpiece. It should be noted that, generally, the more spindles the head includes, the greater the distance between axis A-A and the spindle axes B-B, B-B', and B-B".

Furthermore, as shown in Figure 3, the tool holder 10 is configured such that, due to the structure of the base 12, the axis A-A forms an angle between 35 and 55 degrees, preferably 45 degrees, relative to the vertical axis. Therefore, the spindles 14, 14', and 14" are arranged on the head 13 such that their axes B-B, B-B', and B-B" are inclined relative to the axis A-A at an angle between 35 and 55 degrees, preferably 45 degrees, so that in their working position, they are parallel to the vertical axis, as described above.

In general, it can be inferred from the foregoing and the accompanying drawings that the main axes 14, 14' and 14” are arranged symmetrically about axis A-A, and the axes B-B, B-B' and B-B” of the main axes 14, 14' and 14” do not intersect each other.

Furthermore, the specific arrangement of the spindles 14, 14', and 14" relative to the head 13 of the tool holder 10 reduces force circulation. In fact, the spindles 14, 14', and 14" are fastened as close as possible to the connecting element, which is formed, for example, by a ball bearing, so that the head 13 can pivot relative to the body 11 of the tool holder 10.

Furthermore, the machine tool 20 may include two tool holders 10 arranged on both sides of the fixture 21, as shown in Figure 4. As shown in the figure, because there are two tool holders 10, two machining operations can be performed on the same workpiece simultaneously. Advantageously, in the working position, the rotation axes of the spindles 14 of each tool holder 10 may coincide.

The fixture 21 can take the form of a worktable designed to hold the workpiece in place and have varying degrees of translational and rotational mobility.

As shown in Figure 4, the machine tool 20 may have a protective wall 23 to prevent chip and cutting fluid splashing. Specifically, the protective wall 23 is arranged in a liquid-tight manner around the body 11 of the tool holder 10 or each tool holder 10, and includes an opening through which the body 11 engages. The opening may include an oil-scraping seal arranged abutting against the body 11 around its periphery. Furthermore, the protective wall 23 may advantageously include a corrugated portion. The oil-scraping seal and the corrugated portion allow liquid tightness to be maintained during movement of the tool holder in the XYZ directions.

The protective wall 23 is fastened to the frame 22 of the machine tool 20 through its perimeter.

Furthermore, each protective wall 23 advantageously extends in a plane orthogonal to the axis A-A, i.e., in a plane inclined relative to the horizontal axis, which allows for the flow of cutting fluid and chips. This arrangement also makes it easier for the operator to access the clamp 21 and the spindle 14, 14' or 14".

More generally, it should be noted that the implementation schemes and manufacturing methods considered above have been described as non-limiting examples, and other variations are therefore conceivable.