JPH0351053Y2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a tapered handle structure of a tool holder.

<Prior Art> A connecting portion between a tool holder 1 for holding a rotary tool equipped with an automatic tool changer in a machining center and a main shaft 2 of a machine tool is constructed as shown in FIG. That is, the main shaft 2 has a bearing 4 in the quill 3.
The main shaft 2 is provided with a main shaft nose 6 having a main shaft hole 5, a clamp rod 8 having a ball 7, and the like. The holder 1 has a tapered handle 9 that can be fitted into and removed from the main shaft hole 5, and a pull stud bolt 10 is screwed into the tip of the small end of the taper handle 9. The pull stud bolt 10 has a bolt head 11, and when the bolt head 11 is inserted into the clamp rod 8 and the clamp rod 8 is retracted, the ball 7 engages with the bolt head 11 and the holder 1 can be fixed. It's becoming like that.

By the way, it is desired that the machining ability of the machine tool is such that the cutting ability of the main spindle 2 is adapted to the size (maximum machining size) of the main body. That is, the size of the main shaft hole 5 corresponds to the output (motor rotational force) of the main shaft 2, and the size of the main shaft hole 5
The cutting power transmission performance of the joint with the holder 1 that fits into the holder 1 limits the machining capacity of the machine. The main shaft hole 5 is generally standardized as a tapered shank. The tapered surface connecting the holder 1 and the spindle hole 5 maintains a rigid force corresponding to the cutting resistance force, and at the same time maintains concentric precision so that the axis line of the holder 1 and the axis line of the spindle 2 coincide as much as possible. It is in charge of maintenance functions. The cutting resistance force is applied in two directions: the force in the rotational direction of the rotary tool and the cutting resistance force due to the bending stress applied to the tip of the tool, and in the case of a rotational force that cannot cope with the frictional force of the tapered surface, The cutting force that accompanies bending is transmitted between the main shaft end and the side surface of the holder metal fitting via the drive key 12, etc., and on the other hand, the cutting force that accompanies bending is held by the tapered surface. Therefore, it is desirable that the tapered surface of the spindle hole 5 and the tapered surface of the tapered handle portion 9 on the side of the holder 1 be in close contact with each other as much as possible over the entire surface, and a reduction in the contact area is a serious factor in deteriorating the machining ability of the machine.

With the spread of machining centers, machine manufacturers are striving to achieve the same taper accuracy for the spindle hole 5, and holding tool manufacturers are striving to improve the accuracy of each holder 1. Both of them are attached to the pull stud bolt 1 in the screw hole at the small end of the holder 1.
When screwed in, the automatic tool changer automatically attaches and detaches the tool.

When the pull stud bolt 10 is screwed into the holder 1, which has a tapered surface that matches the taper of the main shaft hole 5, since the wall thickness of the small tapered end of the threaded portion 13 of the bolt is thin, the screw must be tightened as shown in FIG. Due to the force, the tapered surface (small end outer circumferential surface) expands slightly to form an increased diameter portion 14. Pull stud bolt 1
Even if the taper contact with the main shaft hole 5 is normal when the pull stud bolt 10 is not screwed in, the taper contact will be at the small end after screwing in the pull stud bolt 10, and there will be a slight gap at the large end of the taper handle 9. When the tool holder enters a holding state, the holding force decreases due to a decrease in the runout accuracy and bending rigidity of the tip of the tool holder, and a decrease in precision such as a decrease in machined surface accuracy and a decrease in tool edge life due to the occurrence of chatter vibration during cutting is unavoidable. In order to avoid this effect as much as possible, each equity stake is devised, but each measure has its own drawbacks.

For example, there is one shown in FIG. 6 or 7. That is, FIG. 6 shows the pull stud bolt 10.
The axial length B of the spindle hole 5 is tapered so that the diameter-increasing portion A that increases when screwed into the small end side of the tapered handle 9 of the holder 1 does not touch the tapered surface of the spindle hole 5. It is made shorter than the length of the handle 9.

FIG. 7 shows that while the taper angle on the main shaft hole 5 side is a regular angle, when processing the taper surface of the taper handle 9, the expansion due to screwing of the pull stud bolt 10 is taken into account in advance to create a taper surface on the small end side. The diameter is made small so that the increased diameter part 14 of the pull stud bolt 10 after screwing in hits the tapered surface of the main shaft hole 5.
This prevents the tip of the holder 1 from wobbling.

<Problems to be solved by the invention> However, in the former case shown in FIG. There is a problem in that as the hole 5 becomes shorter, the rigidity is definitely lowered by the length of the hole 5, and the maximum cutting capacity is lowered.

Furthermore, in the case of the latter shown in FIG. 7, even if the tightening force for screwing in the pull stud bolt 10 is constant, the increased diameter portion 14 does not necessarily increase in diameter by a constant amount, but there is variation, so the individual There is a drawback that the accuracy is not stable, and there is also a drawback that the taper contact at the center of the tapered handle portion 9 is weak, and the rigidity is correspondingly weak.

<Means for Solving the Problems> The present invention is intended to solve these conventional problems. A tool holder consisting of a pull stud bolt screwed into the small end of the tool holder, in which a crowning part is provided on the small end of the tapered handle with a diameter reduced by the same amount as the diameter increase due to screwing in the pull stud bolt. be.

<Function> Since the small end of the tapered handle 9 of the holder 1 is previously crowned to have a small diameter, the increased diameter portion after the pull stud bolt 10 is screwed in will not cause a decrease in runout accuracy. In addition, in response to bending stress due to cutting resistance applied to the tip of the holder 1, the crowning portion 15 is pressed and bears the load over the entire tapered surface.

<Example> Hereinafter, the present invention will be described in detail with reference to the illustrated example.As shown in FIG. The axial width of the part that increases in diameter by screwing in the pull stud bolt 10 at the small end of the taper handle 9 (approximately 5 to 20 mm) is the normal taper angle.
) is removed in a crowning manner by an amount of expansion corresponding to the amount of diameter increase (approximately 0.03 to 0.05 mm) to form a crowning portion 15. This crowning part 15
The tapered handle 9 may have a tapered shape with a reduced diameter having the same taper angle as the other parts of the tapered handle 9 as shown in Fig. 2, or it may have a larger taper angle than other parts as shown in Fig. 3. But it's okay.

This holder 1 is connected to a main shaft hole 5 having a regular taper angle and length. Then, since the tapered surface of the holder 1 excluding the crowning part 15 has a regular taper angle, it maintains an optimal contact surface with the taper contact surface with the main shaft hole 5, and therefore, optimal runout accuracy can be obtained for the runout of the tip of the holder. . in this case,
Since the contact surface of the crowning part 15 is weak, the length of the taper contact between the two is shortened accordingly, and the rigidity is lower than that in the case of full contact.

However, this stiffness force is as follows when compared with the cases of FIGS. 6 and 7.

In the case of the present invention, since the taper angle is normal, the runout accuracy of the tip of the holder is equivalent to that shown in FIG. 6. However, in the case of FIG. 7, it decreases.

In other words, the rigidity of the joint against the bending stress applied to the holder tip increases as the cutting force increases from light cutting to medium cutting, and the bending stress reaches its maximum near the maximum mechanical output. The rigidity is also the highest. Therefore, the relationship between machining content and run-out and bending rigidity is such that the holder tip is No great force is applied to the
High-precision machining with small tip runout is performed. Therefore, in this case, the present invention and the one shown in FIG. 6 have good run-out accuracy and rigidity, but the one shown in FIG. 7 is inferior because the run-out is reduced.

Next, in the case of heavy cutting, the bending stress applied to the tip of the holder increases, and as the cutting force approaches the maximum, the machined surface becomes considerably distorted due to the accumulation of deformations of the holder, cutting tool, and spindle. Therefore, the main focus is on rough machining, and the comparison of rigidity and force is more about cutting amount than machining accuracy.

In the case of the present invention, when a certain level of cutting force is applied to the tip of the holder, the crowning part 15 then moves to the main shaft hole 5.
It begins to come into close contact with the tapered surface of the main shaft hole 5, and corresponds to the bending stress over the entire taper of the spindle hole 5, and its rigidity exerts the maximum capacity of the machine. but,
The one in Figure 7 has a tapered handle part 9 for both light cutting and heavy cutting.
It is held only at both large and small ends, and is advantageous in that it has a longer taper than the one shown in FIG. 6, but it poses a problem during finishing.

In addition, the one in Figure 7 receives bending stress by holding the tapered surface only at both ends during light cutting force machining.
As the cutting force increases, the uncontacted part at the center of the taper gradually responds to the stress and comes into close contact.
It is possible to obtain rigidity proportional to the contact area.

In light finishing cutting, run-out accuracy is important due to dynamic balance due to vibrations caused by high-speed rotation, etc.
In this regard, the present invention is as optimal as the one shown in FIG. However, in the case of the one shown in FIG. 7, the variation in runout accuracy is large.

In addition, in rough machining and heavy cutting, since heavy cutting generally tends to rotate at low speeds, bending rigidity due to cutting resistance is sufficient to output the maximum output (cutting waste amount) of the cutting tool used as much as possible due to the influence of runout accuracy. A durable tapered joint structure is desired.

<Effects of the invention> According to the invention, a crowning part is provided on the small end side of the tapered handle, the diameter of which is reduced by the same amount as the diameter increase due to screwing in the pull stud bolt. Screw in the pull stud bolt and
The crowning portion increases in diameter and comes into contact with the tapered surface of the spindle hole over the entire length of the tapered surface, thereby improving rigidity and runout accuracy.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing one embodiment of the present invention;
3 and 3 are front views showing modifications of the same essential parts, FIG. 4 is a cross-sectional view showing the conventional example, FIG. 5 is a front view for explaining the conventional example, and FIGS. 6 and 7 are separate. FIG. 2 is a sectional view showing a conventional example. 1... Tool holder, 2... Spindle, 5... Spindle hole, 9... Tapered handle, 10... Pull stud bolt, 15... Crowning part.

Claims (1)

[Scope of utility model registration request] In a tool holder consisting of a pull stud bolt screwed into the small end of a tapered handle that is connected to the spindle hole of a machine tool, the small end of the taper handle has a
A tapered handle structure of a tool holder characterized by having a crowning part whose diameter is reduced by the same amount as the diameter increase due to screwing of a pull stud bolt.