JPH02218522A - Coated cemented carbide tools - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field 1] The present invention relates to a coated cemented carbide tool, which is particularly used for bin milling for machining the bin and journal portions of crankshafts of gasoline engines, diesel engines, etc. The present invention relates to a method for manufacturing coated cemented carbide tools with high strength and long life.

[Conventional technology] The pin and journal portions of crankshafts are often ultimately subjected to grinding, but as a pre-processing process,
Cutting is generally done using a pin mirror machine that performs processing similar to a milling machine, or a bin race machine that performs turning. In particular, bottle milling has extremely high productivity per machine, so it is the mainstream cutting method for crankshaft bottles and journals.

Since the cutting process used for this bottle milling is an extremely severe interrupted process, a tough cemented carbide of P-30 grade according to the ISO standard was used. However, in recent years, there has been a strong demand in the industrial world for improving machining efficiency and extending tool life.
c, Ti (CN), TiN, 'A court 20. One or more layers of ceramic thin film, totaling 2μm.
Since then, coated cemented carbide tools with a coating of about 4 μm have come into use.

Coated cemented carbide tools provide a significant life extension when compared to P-30 grade cemented carbide tools.

[Problems to be Solved by the Invention] However, when a ceramic coating layer is formed in order to extend the tool life, the cutting edge surface of the tool is coated with a coating that is harder and more brittle than the base material, which causes the cutting edge to deteriorate. The toughness of the blade decreases. This decrease in toughness becomes more pronounced as the thickness of the coating layer increases.

Therefore, depending on the thickness of the coating, chipping is likely to occur on the cutting edge of the tool, and there is a risk that the tool will be severely damaged. As a result, not only the crankshaft, which is the work material, was damaged, but also the bin mirror was damaged.
Furthermore, there is a problem that the bin mirror machine itself may malfunction, which may lead to a major accident.

In order to solve the above-mentioned problems, the present invention aims to provide a coated cemented carbide tool that extends the tool life and improves the cutting edge strength of the tool.

[Means for Solving the Problems] The coated cemented carbide tool according to the present invention uses cemented carbide as a base material, and has one or more thin films of one or more types of ceramics on the surface thereof, with a total thickness of 0.5 μm or more and 4 μm. It is coated with the following film thickness. In addition, the cutting edge of this coated cemented carbide tool has
0.01mm or more from the cutting edge to the rake face side 0.12
Chamfering by honing is applied to the portions of mm or less. Furthermore, the minimum value of the coating thickness on the chamfered portion is 60% or less of the coating thickness on other portions.

[Function] By chamfering the cutting edge of a coated cemented carbide tool by honing to nine-honing or chamfer-honing in a portion of 0.01 mm or more and 0.12 mm or less on the rake face side from the cutting edge, stress at the cutting edge can be reduced. Concentration decreases and strength increases. If the chamfer size is less than 0.01 mm from the cutting edge to the rake face side, the effect of reducing stress concentration will not be sufficient, and if it exceeds 0.12 mm, the cutting quality will deteriorate and friction with the workpiece will increase. Abrasion resistance is adversely affected.

In addition, by setting the minimum thickness of the coating on the chamfered part of the cutting edge to 60% or less of the coating thickness on other parts, the chamfering of the cutting edge can be done without reducing the wear resistance of the entire cutting edge. The strength of the part can be increased. The reason why there is no decrease in the wear resistance of the entire cutting edge is because although the chamfered part of the cutting edge receives a large impact force when it collides with the workpiece, it does not come into contact with the workpiece during cutting. This is because the amount of wear on the chamfered portion is relatively small compared to the rake face etc. that come into contact with the powder. Furthermore, the reason why the strength of the part with a smaller coating layer is higher is because the toughness of the cutting edge decreases due to coating with a material that is harder and more brittle than the base material of the tool. This is because this toughness deterioration becomes noticeable and can be suppressed by making the coating layer thinner.

[Example] An example of the present invention will be described below with reference to FIG.

A double carbide consisting of Tic, TaC and WC is 1Qv
A cemented carbide base material 4, which is a formed bite for bottle milling, is prepared using a cemented carbide consisting of O1%, Co 12VO1%, and WC, and the cutting edge has a radius of curvature r as shown in Fig. 1. A chamfered portion 3 of the cutting edge was formed by round honing with a diameter of 0.08 mm. Then, using the CVD method, T
iC at 0.5am, Tl (CN) at O-5am
+A Q-203 0.8μm, TiN 0.2am
were sequentially coated to form a coating layer 5 having a total thickness of 2 μm. This coated cemented carbide tool is an internal type bin mirror (
The diameter of the tool mounting part is 250mm, and the number of teeth is 48.

The number of effective teeth actually involved in cutting is 24), and 548
Cutting speed 135 for the crankshaft bottle part consisting of C.
m/min, machining allowance 3 to 4 mm on one side.

When cutting with a feed rate of 0.12 to 0.31mm/blade,
On average, 2000 pins could be machined per cutting edge.

The results of machining a bottle under exactly the same conditions with various coating thicknesses until the minimum coating thickness δ of the chamfered part 3 of the cutting edge reached 0.8 μm are shown in the table below. show. The table shows the minimum value δ1 of the coating film thickness and the corresponding number of pins that could be processed.

As can be seen from the results of the examples in the table above, when the minimum value δ1 of the coating film thickness on the chamfered part of the cutting edge is 1.2 μm or less, that is, 60% or less of the coating film thickness (2.0 μm) on other parts. The number of bottles that have been processed has increased rapidly and now exceeds 3,000.

The reason why the effects of this example can be obtained by chamfering the cutting edge and adjusting the coating thickness at that portion will be explained below.

When a cemented carbide is used as a base material and its surface is coated with a ceramic thin film of several micrometers, its strength decreases to about 60 to 80% of that of the uncoated base material. This is because the cutting edge of the tool is coated with a coating that is harder and more brittle than the base material, thereby reducing the toughness of the cutting edge. This decrease in toughness becomes more pronounced as the thickness of the coating layer increases. Therefore, stress is concentrated on the cutting edge of the tool, which has a particularly sharp shape, during cutting, and depending on the thickness of the coating, damage such as chipping is likely to occur. In order to prevent this, the cutting edge of the coated cemented carbide tool is chamfered to relieve stress concentration on the cutting edge. The larger this chamfer, the more
Since the stress concentration is greatly reduced, the strength of the cutting edge is increased, but the wear resistance is significantly reduced. This is because chamfering causes the cutting edge to lose its sharpness, resulting in poor sharpness and increased friction with the workpiece. Therefore, in order to increase strength without impairing wear resistance, it is necessary to chamfer an appropriate size. Normally, the radius of curvature shown in Figure 1 is 0.
．． 03~0.10mm round honing or second
a shown in the figure is 0.08 mm to 0.20 mm, β is 1
0' to 20" chamfer honing is common. However, chamfer honing is not limited to these shapes, and chamfer honing is at least 0.0" from the edge of the cutting edge to the rake face 6 side.
It has been experimentally confirmed that if chamfering is performed by honing on a portion of 1 mm or more and 0.12 mm or less, the wear resistance and strength required in normal milling processing etc. can be obtained.

However, under extremely severe cutting conditions such as pin milling, in the case of coated cemented carbide tools with a ceramic thin film of several micrometers formed on the base material surface, such chamfering of the cutting edge alone is insufficient to provide cutting edge strength. , chipping of the cutting edge occurs frequently.

Therefore, in addition to chamfering the cutting edge, it is necessary to take measures to further increase the strength of the cutting edge. As a countermeasure to this problem, it was devised to reduce only the coating thickness of the chamfered portion of the cutting edge, which is a feature of the present invention. The reason why a coated cemented carbide tool having wear resistance and strength that can withstand pin milling etc. can be obtained by this measure is explained as follows from consideration of cutting phenomena.

In normal cutting processing, as shown in Fig. 4, the rake face 2 comes into contact with the chips 12 during cutting, so the chamfered part 3 of the cutting edge
does not come into contact with the work material 11 or the chips 12. That is, the chamfered portion 3 of the cutting edge prevents the coated cemented carbide tool 1 from idling to the workpiece 11.
collides with the workpiece 11 at the time of so-called biting when it comes into contact with the
At this time, the workpiece material 1 receives a large impact force during cutting.
No contact with 1. Therefore, the chamfered portion 3 of the cutting edge suffers less wear than other portions. However, in milling processes such as bottle milling, the cutting edge constantly and intermittently bites in response to the rotation of the tool. Therefore, the chamfered portion 3 of the cutting edge whose strength has been reduced by the coating is susceptible to fatigue failure, which further leads to chipping and large fractures.

Therefore, in this embodiment, the thickness of the coating as a whole is not reduced (only the coating on the chamfered portion 3 of the cutting edge is adjusted by honing, etc., and the minimum thickness of the coating film at that portion is δ). , is 6096 times or less than the coating thickness of other parts.This suppresses the deterioration of the toughness of the chamfered part of the cutting edge due to the coating, and provides a long-life coating that maintains wear resistance and does not reduce strength. A cemented carbide tool can be obtained.

The coating film is generally one or more thin films of one or more ceramics selected from the group consisting of Tic, TiN, A-20, and HfN.

It goes without saying that the effect remains the same even if a film of ZrN or the like is used. If the total thickness of this coating film is less than 0.5 μm, the effect of the coating, that is, the effect of improving wear resistance, will not be recognized, and if it is more than 4 μm, the strength will decrease due to the coating, making it unsuitable for pin milling or the like.

Also, if the chamfer of the cutting edge is not round honing as shown in Fig. 1, but chamfer honing as shown in Fig. 2,
In particular, the minimum value δ2 of the coating film thickness on the 6 parts on the flank side of the chamfered part
It has been experimentally confirmed that a similar effect can be observed if the amount is 60% or less of that of other parts.

As a method for adjusting the thickness of the coating film on the chamfered portion 3 of the cutting blade, after coating with a thin ceramic film, only the chamfered portion 3 of the cutting blade is honed with a barrel or the like, or honed with a brush grindstone. .

The effects of the present invention are not limited to tools for pin milling.
Needless to say, it is also effective for milling processes that are exposed to similar extremely harsh environments, such as edge milling.

[Effects of the Invention] As explained above, according to the present invention, a cutting edge is chamfered in a predetermined manner, and the minimum value of the coating thickness of the chamfered portion is set to 60% or less of the coating thickness of other portions. This achieves high strength that can withstand repeated impact loads without reducing wear resistance. As a result, a coated cemented carbide tool that can be used for cutting operations under severe conditions such as pin milling with a long life can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a cross section near the cutting edge of a coated cemented carbide tool in an embodiment of the present invention (corresponding to the A-A cross section in FIG. 3);
FIG. 2 is a diagram showing a cross section near the cutting edge (corresponding to the AA cross section in FIG. 3) of a coated cemented carbide tool in another embodiment of the present invention. Fig. 3 is a perspective view schematically showing the appearance of the area near the cutting edge of the coated cemented carbide tool, and Fig. 4 schematically shows the appearance of the area near the cutting edge during cutting of a workpiece with the coated cemented carbide tool. It is an explanatory diagram. In the figure, 1 is a coated cemented carbide tool, 2 is a rake face, and 3 is a coated cemented carbide tool.
4 is the chamfered portion of the cutting edge, 4 is the cemented carbide base material, and 5 is the coating layer. Note that the same numbers in each figure indicate the same or equivalent elements. 1st compilation 2 days

Claims (1)

[Scope of Claims] A coated cemented carbide tool whose surface is coated with a ceramic thin film with a total thickness of 0.5 μm or more and 4 μm or less, wherein the base material is made of cemented carbide. The blade part is chamfered by honing at a portion of 0.01 mm or more and 0.12 mm or less from the cutting edge on the rake face side, and the minimum value of the coating thickness of this chamfered portion is the same as that of other parts. A coated cemented carbide tool characterized by having a coating thickness of 60% or less.