JPH0340499Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a drill for drilling deep holes in which a cemented carbide head is brazed to the tip of a steel shank.

[Conventional technology and its issues]

Drills with a cemented carbide head brazed to the tip of a steel shank are well known in order to improve drilling efficiency and extend the life of the drill.

By the way, in deep hole cutting where the depth of the machined hole is three times or more the diameter of the drill, when a twist drill is used, chips are likely to become clogged, and smooth discharge of chips cannot be expected.

Therefore, the poor chip evacuation is usually compensated for by lowering the operating conditions of the drill (rotation speed, feed rate) or applying step feed several times during machining, but this does not improve cutting efficiency. I can't.

The chip evacuation performance improves as the helical groove becomes deeper, that is, the core thickness (web thickness) becomes thinner, but since carbide drills are more brittle and break easily than steel drills, attempts are made to reduce the core thickness. If so, it becomes necessary to lower the cutting power as a condition. In order to reduce this cutting power, a method of thinning the tip of the drill is used to reduce the thickness of the tip.

However, in the generally widely used method of thinning the core thickness of the drill tip using only thinning treatment (for example, the method shown in Fig. 2 or 3 of JP-A-56-82105), the following A problem arises.

That is, let's assume that in order to reduce the thrust force, we would perform a thinning process as shown in Figure 6 based on the general concept of cutting edge construction (the shaded area in the figure is the thinning groove) to reduce the tip core thickness. In this case, the axial rake angle (β in Fig. 7) of the cutting edge 6 in the part along the thinning groove becomes a negative rake angle (generally, the angle is about -25°), and the cutting form in that part However, it approaches the same plastic working form as the chisel blade 11. For this reason, even if the length of the negative angle cutting edge along the thinning groove is suppressed to about half of the total length, the cutting power (torque/thrust) will be extremely large, and the reduction in cutting power due to the thinning of the core thickness will result. is killed. Therefore, extra strength (torsional and bending rigidity) is required.

In addition, the extra strength must be secured by increasing the core thickness, but as the center rise amount W _1/2 of the cutting edge increases, the negative radial rake angle -γ increases, which causes the chip The force of A flowing outward increases and it is pressed against the inner surface of the cut hole, and it also becomes easier to enter between the outer periphery of the drill and the hole surface, so the torque further increases. For this reason, conventional carbide drills have had to have a core thickness that is somewhat thick, and it has been impossible to improve chip evacuation.

In addition, when cutting oil is supplied externally as is conventionally done when cutting deep holes, the oil does not reach the cutting edge sufficiently and the cutting heat is trapped inside the hole. In such drills, the heat and chip clogging combine to easily cause the carbide head to fall off.

[Means to solve the problem]

In order to solve the above-mentioned problems, the present invention has a cemented carbide head 3 having a length of 1.0D to 2.5D (D = drill diameter) joined to the tip of a steel body 2 by brazing.
In a single-blade twist drill, the core thickness W ₁ of the part excluding the tip of the head 3 is approximately 0.35D to 0.45D,
The tip of the head 3 has a constant axial rake angle β in the range of 0 to 15° over the entire straight section of the cutting edge 6.
In addition, a flat rake face 7 with a tip core thickness W ₂ of 0.15D to 0.25D and a corner rising from the inner end of this rake face 7 and tilted in the twisting direction of the helical groove on the center side of the drill are created. The width _W3 of the breaker wall 8 and the chisel blade 11 located near the center of rotation is 0.05D~
A thinning groove 10 with a diameter of 0.10D is provided, and the width of the rake face 7 in the drill axis direction gradually becomes narrower from the inner end of the cutting blade 6 toward the outer end, and the width a becomes 0.05 at the outer end of the cutting blade. D to 0.10D, and oil supply holes 5 are provided inside the main body 2 and the head 3 to branch within the head 3 and exit symmetrically on the flank 9, each having two branch holes 5a. The diameter of the hole before branching is 0.2D or less, and the diameter after branching is 0.15D or less.

[Effect]

By providing a flat rake face (7 in Fig. 8) at the tip of the head to reduce the helix angle of the helical groove over the entire groove width, the cutting edge angle of the cutting edge 6 can be prevented from becoming extremely blunt. The rake angle β in the axial direction of the straight part of the cutting edge (Figs. 5 and 10) is 0 to 15° over the entire area.
The core thickness of the drill tip is kept constant within the range shown in Figure 6.
It can be reduced from W ₁ to W ₂ in FIG. From this state, change the width of the chisel blade 11 as shown in Figure 8.
The thinning groove 10 for reducing W to ₃ may have a shallow depth, and since the shallow thinning groove 10 is provided near the inner end of the cutting edge 6, the area where the cutting edge becomes a negative angle is reduced by the thinning groove. (Even if the groove is shallow, if it spreads toward the outer end of the cutting edge 6, the blunted area of the cutting edge will increase.) Therefore, compared to conventional thinning treatment, there is less deterioration in cutting quality and the cutting power is reduced. .

In addition, the amount of center rise of the cutting blade 6 shown in Fig. 8 is also W ₂ /
2, and the radial rake angle -γ' becomes -γ'<-γ, which not only weakens the force with which the chips A are pressed against the inner surface of the hole but also makes it difficult for them to enter the outer periphery of the drill. In addition, the rake face 7 widens the space for discharging chips at the tip of the drill, and the breaker wall 8 works to change the flow direction of chips toward the center of the drill so that they flow smoothly into the groove 4. do. In addition, since cutting oil is supplied from the oil supply hole 5 (Fig. 5) inside the main body to the side of the flank 9, the chips are forcibly discharged by the return oil, and therefore the flow of chips is also safe, which makes it possible to increase the torque. becomes even smaller. In this way, since the drill of this invention has the rake face 7 and the breaker wall ₈ , the increase in cutting power is minimized. ) can improve chip evacuation. In addition, since the cutting power is small and chips are smoothly discharged, the head does not fall off due to cutting heat and chip clogging.

If the length of the head (l ₀ in FIG. 2) is too short, cutting heat will easily be transferred to the brazed joint with the main body, and the longer the head, the greater the core thickness is required from the viewpoint of strength. On the other hand, if the core thickness _W1 is too thin, the bending rigidity of the head (if it is low, so-called chatter will occur and the cutting edge is likely to chip) and torsional rigidity will be insufficient, and if it is too thick, the chip evacuation will be poor. Therefore, considering these factors, the head length l ₀ is 1D to 2.5D, and the core thickness W ₁
was defined as approximately 0.35D to 0.45D.

Also, the rake face 7 has a helix angle α of the helical groove 4.
(Fig. 5) The larger the return, the thicker the tip of head 3.
W ₂ becomes smaller and the thrust is reduced, but W ₂
If it is made too small, the tip of the head will be unnecessarily thinned, resulting in insufficient strength, and the axial rake angle β of the cutting edge 6 will decrease.
(Figure 5) also becomes dull and loses its sharpness. The cutting edge 6 exhibits good cutting quality if β is 0 to 15 degrees, so taking this into consideration, the axial rake angle β of the cutting blade is set to 0 to 15 degrees,
The tip core thickness _W2 of the head was set at 0.15 to 0.25D.

Furthermore, the upper limit of the width W ₃ of the chisel blade 11 was set to 0.1D in order to reduce the thrust force, and the lower limit was selected to be 0.05D in consideration of maintaining the function of the chisel blade.

In addition, the drill axial width a at the drill outer circumference of the rake face 7 is limited to 0.05D to 0.10D in order to keep the properties of the cutting edge 6 constant over almost the entire area (the straight part of the cutting edge excluding the thinning part). This is to avoid unnecessary cutting of the head, which would be disadvantageous in terms of strength.

Note that no matter how large the core thickness W ₁ is, if the diameter of the oil supply hole 5 increases, the drill cross-sectional area will decrease, and the torsional and bending rigidity of the main body will decrease, so the diameter d ₁ of the hole 5 before branching ( Figure 4) sets the upper limit to 0.2D. It is desirable to keep the lower limit at around 0.1D to avoid a shortage of cutting oil supply. For the same reason, the diameter _d2 of the branch hole 5a at the tip of the hole 5 is set to about 0.1 to 0.5D.

〔Example〕

Hereinafter, one embodiment of the drill of the present invention will be described based on the attached drawings.

Reference numeral 1 in FIGS. 1, 2, and 4 indicates the drill of the present invention. This drill 1 is constructed by brazing and joining a cemented carbide head 3 to the tip of a steel body 2 (14 is the joint). Two twisted grooves 4 are formed on the outer peripheries of the main body 2 and the head 3, and furthermore,
As can be seen from FIG. 4, supply holes 5 are provided inside the main body and head, which are branched within the head 3 and each branch hole 5a passes through the flank 9 of the drill.

In addition, the tip of the head 3, that is, each helical groove 4
The tip of the helical groove 4 has a helix angle α (see Fig. 5), and the axial rake angle of the cutting edge 6 is β=0 to
A flat rake face 7 that is reduced to a value of 15°, a breaker wall 8 rising from the inner end of this face, and a thinning groove 10 for adjusting the chisel thickness (width) are formed.

The length l ₀ of the head 3 of this drill (Fig. 2) is:
It is 1 to 2.5 times the drill diameter D, and the core thickness W ₁ (Fig. 3) of the part of the drill excluding the head tip is set to 0.35 to 0.45 D to ensure the required torsional and bending rigidity. The core thickness W ₂ of the tip of the head excluding the center of rotation and the width W ₃ of the chisel blade 11 are W ₂ = 0.15D ~
0.25D, W ₃ =0.05D to 0.1D.

Further, the axial width a of the rake face 7 at the outer periphery of the drill is set to 0.05D to 0.1D, and the extending direction of the breaker wall 8 is inclined toward the twisting direction of the twisting groove 4.

Furthermore, the oil supply hole 5 has a diameter d ₁ (fourth diameter) before branching.
(Fig.) is 0.1D to 0.2D, and the diameter _d2 of the branch hole 5a is also 0.1D.
It is set to ~0.15D.

This drill now has a core thickness of
When W ₂ is limited, the inner end position Q of the cutting edge 6 is determined,
The outer end position S of the cutting edge 6 is determined by the width a of the outer end of the rake face 7 and the axial rake angle β of the cutting edge 6, and thereby the overall position of the cutting edge 6 is determined.

Furthermore, once the above a and β are determined, the rear end edge of the rake face 7 intersects with the helical groove 4, so the overall width and shape of the rake face 7 is also determined. Naturally, the width becomes wider toward the inner end of the cutting edge 6, but the width at the inner end is affected by the helix angle of the groove 4, the size of the corner radius of the groove, etc.
Even if and β are the same, they may change.

Furthermore, the axial rake angle β of the cutting edge 6 is also constant throughout the straight portion. If the rake face 7 is a twisted surface as shown by the chain line in FIG. 10, the value of β will change at each part of the cutting edge, but since the face 7 is flat, such a change does not occur.

Note that the opening position of the branch hole 5a on the flank 9 shown in FIG. 3 changes as it approaches the cutting edge 6 and the drill center.
The angle θ to the reference line (the line passing through the center of the two cutting edges) should be 30 to 40 degrees, and the pitch P of both holes should be 0.6 to 0.6 to prevent the oil flow from worsening due to a decrease in the distance between the two holes.
It is best to install it at a location that is 0.8D.

In addition, the branching part of the hole 5 should be formed at a position where the distance l ₁ (Fig. 4) from the joint surface of the head 3 is about 1 to 5 mm to prevent the hole from being clogged by the solder material during soldering. Good.

Furthermore, the intersection line 6a (Fig. 3) where the blade formed by the intersection line of the thinning groove 10 and the flank face 9 connects to the straight part of the cutting edge 6 is rounded with a small arc to strengthen it. It's good to keep it. The effect of this circular arc treatment on preventing chipping of the cutting edge is well known. Further, as is also well known, by rounding the heel portion 12 with an R surface 13 of approximately 0.2D, chip evacuation performance can be further improved.

In addition, in FIGS. 3 and 8, the twisted groove 4 is not twisted in order to make it easier to understand the relationship between the core thicknesses, and therefore the rake face 7 is shown in the figures, but in reality In the end view shown in FIG. 2, the rake face 7 completely overlaps the cutting edge 6 when β is 0. Furthermore, when β becomes a positive value, the rake face 7 is hidden by the flank face 9 and cannot be seen at all.

The exemplary drill configured as described above can have a core thickness _W1 smaller than that of the conventional drill due to the effect described in the previous section, so that chip clogging does not occur even when drilling deep holes.

Also, chips do not get clogged. Cutting power decreases. Internal oil supply suppresses heat generation. As a result, there is no accident of the carbide head falling off, and in addition to stabilizing the cutting torque, the drill core thickness W ₁ has also been reduced.
Torsional and bending rigidity is sufficiently ensured in parts where rigidity is required, and the rake face 7 at the tip of the helical groove 4 increases the cutting edge angle of the cutting edge 6 to increase the strength of the cutting edge, and the cutting power is conversely reduced. This prevents chipping of the cutting edge, and these effects enable stable cutting even in deep hole machining.

FIG. 9 shows a comparison graph of the results of a cutting test conducted using the conventional drill shown in FIG. 6 and the drill shown in FIG. 8 which satisfies the structural requirements of the present invention. The test conditions are as follows.

Drill diameter: 12 Machine used: 6.5 machining center Work material: FCD45 Cutting conditions: V (rotational speed) = 40 m/min f (feed) = 0.3 mm/rev As you can see from this graph, the drill of this invention has a torque of 100 kg・The cm thrust was 175Kg, but with the conventional drill, both torque and thrust increased rapidly immediately after cutting started, and the machine used stopped due to excessive power. Although the shape of the thinning groove 10 in the drill shown in FIG. 8 is somewhat different from that in FIG. It is no different from the drill in Figure 1.

〔effect〕

The drill of the present invention described above has a flat rake face 7 at the tip of the helical groove that reduces the helix angle of the groove, so that the axial rake angle β of the straight portion of the cutting edge 6 is
First, the thickness of the tip of the head 3 is reduced from W ₁ to W ₂ while keeping it at a constant value in the range of 0 to 15 degrees over the entire area, and then a small area at the center of rotation is thinned to thin the chisel blade 11. Since the width has been changed from W ₂ to W ₃ , unlike conventional drills that reduce the core thickness from W ₁ to W ₃ all at once, there is very little area where the cutting edge loses sharpness due to thinning, and cutting power can be reduced. Therefore, the required torsional and bending rigidity can be achieved with a core thickness that is better than before.
W ₁ can be made thinner and secured, and by providing the breaker wall 8 and adding the oil supply hole 5 to adopt an internal oil supply system, it is possible to satisfy the chip discharge performance.

In addition, the head is prevented from falling off because it does not become clogged with chips, the cutting power is reduced, and heat generation is suppressed by internal oil supply. Additionally, the flat rake face strengthens the cutting edge, making it possible to efficiently machine deep holes with high precision. For example, it is possible to drill deep holes with high efficiency by rotating at a cutting speed of about 80 m, which is about four times faster than conventional drills.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an example of the drill of the present invention;
Fig. 2 shows the device, Fig. 3 is a front view (this figure shows the grooves without twisting to make it easier to understand the relationship between the core thicknesses), Fig. 4 is a longitudinal side view, and Fig. 5 The figure is a cross-sectional view taken along the line X-X in Figure 2.
Figure 6 is a front view of a conventional drill whose tip core thickness has been reduced by thinning treatment, Figure 7 is a cross-sectional view along the Y-Y line, and Figure 8 is a front view of the drill of this invention used for cutting tests. (The same representation as in Fig. 3), Fig. 9 is a graph comparing the cutting test results, and Fig. 10 explains that the axial rake angle of the straight part of the cutting edge is constant over the entire area. FIG. 11 is a diagram for explaining the reason why the position of the cutting edge, the size, shape, etc. of the flat rake face are determined. 1...Drill, 2...Steel body, 3...Cemented carbide head, 4...Twisted groove, 5...Oil supply hole,
5a... Branch hole, 6... Cutting edge, 7... Rake face,
8... Breaker wall, 9... Flank surface, 10... Thinning groove, 11... Chisel blade, 12... Heel portion, 13... R surface, 14... Joint portion.

Claims (1)

[Scope of utility model registration request] In a two-blade twist drill 1, in which a cemented carbide head 3 with a length of 1.0D to 2.5D (D = drill diameter) is brazed to the tip of a steel body 2, the tip of the head 3 is The core thickness W ₁ of the excluded part is approximately 0.35D ~
0.45D, and at the tip of the head 3, the axial rake angle β of the entire straight section of the cutting edge 6 is constant in the range of 0 to 15 degrees, and the tip core thickness W ₂ is set to 0.15D to 0.25D. a flat rake face 7, a breaker wall 8 that rises from the inner end of the rake face 7 and creates a corner inclined in the torsional direction of the helical groove 4 toward the center of the drill; Position chisel blade 11
Thinning groove 10 that changes the width _W3 from 0.05D to 0.10D
The width of the rake face 7 in the axial direction of the drill gradually becomes narrower from the inner end to the outer end of the cutting blade 6, and the width a is 0.05D to 0.10D at the outer end of the cutting blade 6. Furthermore, inside the main body 2 and the head 3, oil supply holes 5 are provided which branch within the head 3 and extend symmetrically to the flanks 9, each having two branch holes 5a.
The diameter of the hole before branching is 0.2D or less, and the diameter after branching is 0.2D or less.
A brazing joint drill for deep hole drilling configured with a diameter of 0.15D or less.