EP2221131A1

EP2221131A1 - Methods of producing a powder compact and a sintered composite body

Info

Publication number: EP2221131A1
Application number: EP09161550A
Authority: EP
Inventors: Gustaf Wandebäck
Original assignee: Sandvik Intellectual Property AB
Current assignee: Sandvik Intellectual Property AB
Priority date: 2009-05-29
Filing date: 2009-05-29
Publication date: 2010-08-25

Abstract

The invention relates to a method of producing a powder compact comprising: in a press tool comprising a die, at least two bottom punches and a top punch, encapsulating a powder B within one or more powders A, the encapsulated powder B and the one or more powders A having different compositions, the encapsulation being made by stepwise positioning, an inner bottom punch and an outer bottom punch surrounding the inner bottom punch, so that a filling space within the die is provided above a punch after each positioning step, one of the powders A or B are introduced into each filling space provided so that powder B is encapsulated within the one or more powders A, and, pressing the combination of powders between the bottom punches and the top punch thereby forming a compact. An additional sintering step provides a sintered body. The invention further relates to a powder compact comprising a pressed powder B encapsulated within one or more pressed powders A, the powders having different compositions. The invention further relates to a sintered body comprising a first sintered material encapsulated within at least one further sintered material, the first and further materials differ in at least one characteristic.

Description

The present invention relates to methods of producing a powder compact and a sintered composite body. It also relates to a powder compact and a sintered composite body.

Introduction

Cutting inserts for metal machining are commonly made by powder metallurgical methods comprising compaction of a powder into a body which is subsequently sintered to consolidate the body. Common materials used for cutting inserts are cemented carbide, cermets, ceramics, and cubic boron nitride. Raw material powder is generally compacted by using a press tool wherein the powder is disposed by a feed shoe into a mould of a desired size and shape and pressed together by two punches, thereby giving a compact of a desired geometrical shape.
Depending on the end-application of a powder metallurgical article the desired properties in terms of, e.g., toughness, hardness, chemical resistance varies. By choosing the proper material composition for the end-application and, hence, the proper raw material powder composition, a great number of requirements can be met.
However, the use of a single raw material powder may not be sufficient in order to achieve the desired properties of the sintered body. Therefore, attempts have been made to use different powders for different parts of the body:

US 2007/0042217 A1 discloses a method of producing a composite article comprising consolidating a first and further powdered metal grades to form a compact.
US 6,086,980 discloses a cemented carbide drill comprising a core of one cemented carbide grade and a surrounding tube of another cemented carbide grade.

Further composite sintered articles where first and further powders are combined to form composite articles are known from US 6,511,265 B1 , US 5,776,593 , US 2008/0145686 A1 , US 5,697,046 , US 5,543,235 , and US 6,685,880 B2 .
However, there are properties of a sintered compact which still cannot be provided by known methods of manufacture or by state of the art products. There is therefore a need for providing a sintered body, and a method of its manufacture, which provides further possibilities and flexibility in tailoring and designing a cutting insert.
The object of the invention is therefore to provide a method for producing a powder compact wherein two or more raw material powders can be combined in order to finally provide a sintered composite body.

Summary of the invention

The object of the invention is achieved by a method of producing a powder compact comprising: in a press tool comprising a die, at least two bottom punches and a top punch, - encapsulating a powder B within one or more further powders A, the encapsulated powder B and the one or more powders A having different compositions, the encapsulation being made by stepwise positioning, an inner bottom punch and an outer bottom punch surrounding the inner bottom punch, so that a filling space is provided above a punch after each positioning step, one of the powders A or B are introduced into each filling space provided so that powder B is encapsulated within the one or more powders A, and, pressing the combination of powders between the bottom punches and the top punch thereby forming a compact.
The present invention further relates to a powder compact obtainable by the method comprising a pressed powder B encapsulated within one or more pressed powders A, powder B and the one or more powders A having different compositions.
The invention further comprises a powder compact comprising a pressed powder B encapsulated within one or more pressed powders A, powders B and the one or more powders A having different compositions.
The invention further comprises a method of producing a sintered body comprising the addition of a step of sintering to the method of producing a powder compact.
The present invention further relates to a sintered body obtainable by the method comprising a first sintered material encapsulated within at least one further sintered material, the first and further sintered materials differs in at least one characteristic.
The invention further comprises a sintered body comprising a first sintered material encapsulated within at least one further sintered material, the first and further sintered materials differs in at least one characteristic.
The invention further comprises a cutting tool comprising the sintered body.

Brief description of the drawings

Figures 1-10 show one embodiment of the method according to the invention and figure 11 shows a further embodiment of a press tool set up.
Fig. 1a shows a top view of a part of a press tool and fig. 1b a view of the section C-C in fig. 1 a. The press tool comprises a die (1), an inner bottom punch (2) and an outer bottom punch (3). In this embodiment the punches as seen from a top view are square shaped.
Fig. 2 shows a position of the bottom punches prior to any introduction of powder. A top punch (4) of the press tool and feed shoes F_A (5) and F_B (6) for introducing powder A and powder B respectively are shown. Filling spaces (7) and (8) above the inner bottom punch and outer bottom punch respectively are shown.
Fig. 3 shows the press tool when introduction of powder A from feed shoe F_A has been made. After completion of introducing powder A the feed shoe F_A is retracted to a resting position.
Fig. 4 shows the press tool after the inner bottom punch has been lowered providing a filling space (9). Feed shoe F_B is moved to the filling position.
Fig. 5 shows the press tool when introduction of powder B from feed shoe F_B has been made. After completion the feed shoe F_B is retracted to a resting position.
Fig. 6 shows the press tool after the inner bottom punch and the outer bottom punch both have been lowered providing a filling space. Feed shoe F_A is moved to the filling position.
Fig. 7 shows the press tool when introduction of powder A from feed shoe F_A has been made. Powder B has thereby been encapsulated within powder A. After completion the feed shoe F_A is retracted to a resting position.
Fig. 8 shows the press tool when the top punch has been lowered and the bottom and top punches are pressed together.
Fig. 9 shows the press tool after pressing has been completed and the formed compact (10) is pushed upwards.
Fig. 10 shows the press tool when the compact can be taken out of the press tool.
Fig. 11 shows a press tool set up wherein a further bottom punch (11) is present situated between the inner and outer bottom punches.

Detailed description of embodiments of the invention

The method of producing a powder compact suitably comprises:

providing at least one filling space above the outer bottom punch, the at least one filling space is introduced with one or more powders A,
providing a filling space directly above the inner bottom punch, the filling space is introduced with one or more powders A,
providing a filling space above previously introduced one or more powders A above the inner bottom punch, the filling space is introduced with powder B,
providing a filling space above previously introduced powder B above the inner bottom punch, the filling space is introduced with one or more powders A.

In the method of producing a powder compact, the stepwise positioning suitably comprises, in the following order, a sequence of steps (a), (b) and (c), wherein:

step (a) comprises positioning the inner bottom punch to provide a filling space within the die above the inner bottom punch, followed by introducing one or more powders A into the filling space,
step (b) comprises positioning the inner bottom punch to provide a filling space within the die above already introduced one or more powders A, followed by introducing powder B in the filling space,
step (c) comprises positioning the inner bottom punch to provide a filling space within the die above already introduced powder B, followed by introducing one or more powders A into the filling space,
the method further comprises at least one step (d) comprising positioning the outer bottom punch to provide a filling space within the die above the outer bottom punch, followed by introducing one or more powders A into the filling space, wherein a step (d) is made:
- before or after the sequence of steps (a), (b), and (c),
- inbetween any of steps (a), (b) and (c), or,
- by positioning the outer bottom punch in step (d) and the inner bottom punch in step (a) or (c) and simultaneously introducing one or more powders A into the filling space provided in step (d) and the filling space provided in step (a) or (c).

The positioning of the inner bottom punch and the outer bottom punch, and subsequent introduction of one or more powders A or powder B into filling spaces can be exemplied by the following embodiments, wherein the term "simultaneously" refers to simultaneous introduction of powder as described above:

In one embodiment, the sequence of steps (a), (b), (c) and (d) is made in the order (d)-(a)- (b)- (c).
In one embodiment, the sequence of steps (a), (b), (c) and (d) is made in the order (a)-(b)- (c)- (d).
In one embodiment, the sequence of steps (a), (b), (c) and (d) is made in the order (a)-(d)- (b)- (c).
In one embodiment, the sequence of steps (a), (b), (c) and (d) is made in the order (a)-(b)- (d)- (c).
In one embodiment, the sequence of steps (a), (b), (c) and (d) is made in the order simultaneously (a) and (d)- (b)- (c).
In one embodiment, the sequence of steps (a), (b), (c) and (d) is made in the order (a)-(b)- simultaneously (c) and (d).
In one embodiment, the sequence of steps (a), (b), (c) and (d) is made in the order simultaneously (a) and (d)- (b)- simultaneously (c) and (d).
In one embodiment one or both of the bottom punches are moved upwards after at least one introduction of powder has been made and the feed shoe is still positioned above the introduced powder. By this, the introduced powder is given an increased density which increases its mechanical stability and reduces the risk mixing of different powders or that introduced powder falls down disrupting its physical shape.

The introductions of the one or more powders A and powder B are suitably made by using different feed shoes.
The horisontal cross section of the inner and outer bottom punches may be of any geometrical shape, for example circular, square-shaped, rectangular, triangular, oval etc. Fig. 1a shows an embodiment wherein the horisontal cross section is square shaped for both bottom punches. The outer bottom punch and inner bottom punch may also have different horisontal cross sectional shapes, for example, the inner bottom punch may be square shaped whereas the outer bottom punch is circular, or any other combinations such as triangular-circular, circular-square shaped etc.
The different compositions of the powders are suitably different chemical composition and/or different particle size.
The powders suitably comprises hard material constituents and one or more binder materials. More specifically, the powders may comprise hard particles comprising a carbide, nitride, carbonitride, boride, silicide, oxide or mixtures thereof. The hard particles preferably comprise one or more metal carbides, carbonitrides, borides, silicides, or oxides, wherein the metal may be tungsten, titanium, chromium, tanatalum, vanadium, zirconium, hafnium and niobium. The binder materials are suitably selected from the group of cobalt, nickel, and iron.
The powder compact suitably comprises at least one parting line. The at least one parting line results from the bottom punches used in the method.
The ratio of the thickness of the at least one pressed powder A of the powder compact to the thickness of the encapsulated pressed powder B at a cross section is suitably from about 0.1 to about 10, preferably from about 0.15 to about 8, more preferably from about 0.15 to about 4, even more preferably from about 0.2 to about 2, most preferably from about 0.2 to about 1.
The different characteristic of the first and further sintered materials are suitably at least one of chemical composition, grain size, elastic modulus, hardness, wear resistance, fracture toughness, tensile strength, corrosion resistance, coefficient of thermal expansion and coefficient of thermal conductivity.
The first and further sintered materials suitably comprise grains of hard material constituents in a binder phase. The hard material grains suitably comprise a carbide, nitride, carbonitride, boride, silicide, oxide or mixtures thereof. The hard material grains preferably comprise one or more metal carbides, carbonitrides, borides, silicides, or oxides, wherein the metal may be one or more of tungsten, titanium, chromium, tanatalum, vanadium, zirconium, hafnium and niobium. The binder phase suitably comprises a metal selected from the group of cobalt, nickel, and iron.
The grain size of the hard material constituents in the sintered materials is suitably from about 0.1 to about 20 µm, preferably from about 0.5 to about 10 µm.
In one embodiment the ratio of the grain size of the hard material constituents in the encapsulated first sintered material to the grain size of the hard material constituents in at least one of the further sintered materials is ≥ 0.1 but < 1, or ≥ 0.5 but < 1, or ≥ 0.7 but < 1.
In one embodiment the ratio of the grain size of the hard material constituents in the encapsulated first sintered material to the grain size of the hard material constituents in at least one of the further sintered materials is > 1 but ≤ 10, or > 1 but ≤ 5, or > 1 but ≤ 3.
In one embodiment the ratio of the grain size of the hard material constituents in the encapsulated first sintered material to the grain size of the hard material constituents in at least one of the further sintered materials is 1.
The sintered body suitably comprises at least one parting line. The at least one parting line results from the bottom punches used in the method.
For the sintered body, the ratio of the thickness of the at least one further sintered material of the sintered body to the thickness of the encapsulated first sintered material at a cross section is suitably from about 0.1 to about 10, preferably from about 0.15 to about 8, more preferably from about 0.15 to about 4, even more preferably from about 0.2 to about 2, most preferably from about 0.2 to about 1.
The ratio of the degree of shrinking at sintering for the encapsulated pressed powder B of the powder compact to the degree of shrinking at sintering for the pressed one or more powders A is suitably from about 0.8 to about 1.2.
In one embodiment of the invention, the ratio of the degree of shrinking at sintering for the encapsulated pressed powder B of the powder compact to the degree of shrinking at sintering for the pressed one or more powders A is from about 0.9 to about 1.1, preferably from about 0.95 to about 1.05, more preferably 0.98-1.02, most preferably essentially 1.
In one embodiment of the invention, the ratio of the degree of shrinking at sintering for the encapsulated pressed powder B of the powder compact to the degree of shrinking at sintering for the pressed one or more powders A is from about 0.8 to about 0.99, preferably from about 0.9 to about 0.98, more preferably from about 0.95 to about 0.97.
In one embodiment the at least one further sintered material enclosing the sintered first material suitably has a residual stress being a net positive tensile stress.
In one embodiment the at least one further sintered material enclosing the sintered first material suitably has a residual stress being a net positive compressive stress.
In one embodiment, in addition to the inner and outer bottom punches, further bottom punches may be present situated between the inner and outer bottom punches (see fig. 11).
In a further embodiment of the method more than two different powders A are used.
In one example of this embodiment, at least one of steps (a), (c) and (d) comprises introducing a further powder A onto an already introduced powder A into a filling space, i.e. a filling space is partly filled with a first powder and partly filled with one or more further powders A.
The method of the present invention may further comprise the following features:

core pin, i.e. the method comprises the presence of a core rod parallel to the top and bottom punches that creates a hole in the pressed geometry;
cross-hole pressing, i.e. the method comprises the presence of a core rod perpendicular to the top and bottom punches that creates a hole in the pressed geometry;
divided top punch, i.e. the method comprises the presence of more than one top punch that, e.g., provides height differences on the top side of the pressed geometry;
side axis pressing, i.e. the method comprises the presence of one or more punches perpendicular to the top and bottom punches that provides side geometries.

The powder compact according to the invention is preferably shaped as a cutting tool insert, such as a turning insert, milling insert, drilling insert etc.
The sintered body according to the invention is preferably a cutting tool insert, such as a turning insert, milling insert, drilling insert etc.

Claims

Method of producing a powder compact comprising: in a press tool comprising a die, at least two bottom punches and a top punch,
encapsulating a powder B within one or more powders A, the encapsulated powder B and the one or more powders A having different compositions, the encapsulation being made by stepwise positioning, an inner bottom punch and an outer bottom punch surrounding the inner bottom punch, so that a filling space within the die is provided above a punch after each positioning step, one of the powders A or B are introduced into each filling space provided so that powder B is encapsulated within the one or more further powders A, and, pressing the combination of powders between the bottom punches and the top punch thereby forming a compact.
Method according to claim 1, comprising:
- providing at least one filling space above the outer bottom punch, the at least one filling space is introduced with one or more powders A,

- providing a filling space directly above the inner bottom punch, the filling space is introduced with one or more powders A,

- providing a filling space above previously introduced one or more powders A above the inner bottom punch, the filling space is introduced with powder B,

- providing a filling space above previously introduced powder B above the inner bottom punch, the filling space is introduced with one or more powders A.
Method of producing a powder compact according to any one of claims 1-2, wherein the stepwise positioning comprises, in the following order, a sequence of steps (a), (b) and (c), wherein:
step (a) comprises positioning the inner bottom punch to provide a filling space within the die above the inner bottom punch, followed by introducing one or more powders A into the filling space,

step (b) comprises positioning the inner bottom punch to provide a filling space within the die above already introduced one or more powders A, followed by introducing powder B into the filling space,

step (c) comprises positioning the inner bottom punch to provide a filling space within the die above already introduced powder B, followed by introducing one or more powders A into the filling space,

the method further comprises at least one step (d) comprising positioning the outer bottom punch to provide a filling space within the die above the outer bottom punch, followed by introducing one or more powders A in the filling space, wherein a step (d) is made:
- before or after the sequence of steps (a), (b), and (c),

- inbetween any of steps (a), (b) and (c), or,

- by positioning the outer bottom punch in step (d) and the inner bottom punch in step (a) or (c) and simultaneously introducing one or more powders A into the filling space provided in step (d) and the filling space provided in step (a) or (c).
Method of producing a powder compact according to any one of claims 1-3, wherein one or both of the bottom punches are moved upwards after at least one introduction of powder has been made and the feed shoe is still positioned above the introduced powder.
Method of producing a powder compact according to any one of claims 1-4, wherein the different compositions of the one or more powders A and powder B comprise different chemical composition and/or different particle size.
A powder compact obtainable by the method according to any one of claims 1-5, comprising a pressed powder B encapsulated within one or more pressed powders A, powder B and the one or more powders A having different compositions.
A powder compact comprising a pressed powder B encapsulated within one or more pressed powders A, powder B and the one or more powders A having different compositions.
A powder compact according to any one of claims 6-7, wherein the different compositions of the one or more powders A and powder B comprise different chemical composition and/or different particle size.
A powder compact according to any one of claims 6-8, wherein the ratio of the thickness of the at least one pressed powder A of the powder compact to the thickness of the encapsulated pressed powder B at a cross section is from about 0.15 to about 8.
Method of producing a sintered body comprising the method according to any one of claims 1-5 with the addition of the step of sintering the powder compact.
A sintered body obtainable by the method according to claim 10, comprising a first sintered material encapsulated within at least one further sintered material, the first and further materials differ in at least one characteristic.
A sintered body comprising a first sintered material encapsulated within at least one further sintered material, the first and further materials differ in at least one characteristic.
A sintered body according to any one of claims 11-12, wherein the ratio of the thickness of the at least one further sintered material of the sintered body to the thickness of the encapsulated first sintered material at a cross section is from about 0.15 to about 8.
A cutting tool comprising a sintered body according to any one of claims 11-13.