EP1228856A2

EP1228856A2 - Powder compacting tool

Info

Publication number: EP1228856A2
Application number: EP02445013A
Authority: EP
Inventors: Enrico Cacciorni; Jonas Jerklind
Original assignee: SKF AB
Current assignee: SKF AB
Priority date: 2001-02-06
Filing date: 2002-02-04
Publication date: 2002-08-07
Also published as: SE0100364D0; EP1228856A3; CN1369368A

Abstract

The present invention relates to a method of compacting a powder disposed in a forming chamber by a powder compacting tool having at least two upper punches and two lower punches, the punches being moved different travel distance during compaction in order to create a compacted body having uniform density and different thickness in different parts thereof, whereby the method includes moving the punches in sequence and with the same velocity, and accomplishing the method with a powder compacting tool (1) comprising a matrix (2) having a through-going cavity, at least two upper punches (3,4), which are movable in the axial direction of the cavity, and a at least two lower punches (5,6). According to the invention the upper punches (3,4) have different axial lengths and the tool comprises a single ram (8) for moving the upper punches (3,4) towards the at least two lower punches (5,6) during a compacting operation and means are for holding the at least two lower punches stationary during a compacting operation.

Description

TECHNICAL FIELD

The present invention relates to a method of compacting powder disposed in a matrix having a through-going cavity, at least two lower punches and at least two punches, being moved different lengths in order to create a compacted body having uniform density and different thickness in different parts thereof. The invention also relates to a powder compacting tool for performing the method.

BACKGROUND OF THE INVENTION

The manufacturing of compacted bodies having different thickness in different parts thereof is conventionally made by powder compacting tools in which the punches are moved with a low velocity, typically by velocities less than 1 m/s. Separate upper and lower punches for the parts of different thickness are used. In order to avoid cracks in the compacted body due to flowing of powder particles from areas with higher densities to areas with lower densities or breaking of bonds between particles in areas with different densities, it is essential that the densities in the different parts of the compacted body are the same during every moment in the whole compacting operation. Multi-plate systems to move the separate punches with different velocities are necessary in order to obtain the same density throughout the compacting operation. Such a manufacturing leads to a complicated tool with many components and a rather sophisticated control system.

Powder compacting tools in which the punches are moved with high velocities, typically by velocities higher than 2 m/s, are used to create compacted bodies having higher densities than compacted bodies produced by the conventional low velocity powder compacting tools. However, it is very difficult to control the velocity of the individual punches during the whole compacting operation with such high velocity tools with the precision required for creating the same densities in different parts of a compacted body having parts with different thickness. There is therefore a need for a method of creating compacted bodies having different thickness in different parts thereof that can be easily used for high velocity powder compacting tools and that is simpler than the method known for low velocity powder compacting tools.

The objectives of the present invention are to fulfil this need and also to provide a powder compacting tool for producing bodies having different thickness in different parts thereof which has few components and which can be used in a simple manner during a high velocity compacting operation.

SUMMARY OF THE INVENTION

These objectives are according to the invention obtained by a method of compacting powder disposed in a forming chamber by a powder compacting tool having at least two upper punches and two lower punches, the upper punches being moved different lengths in order to create a compacted body having different thickness in different parts thereof, characterised by moving the punches in sequence and with the same velocity.

In a preferred embodiment the punches are actuated by the same ram unit. Furthermore, the forming chamber is defined by the side wall of a cavity in a matrix of a powder compacting tool and the end walls of at least two lower punches and at least two upper punches having different axial lengths, and the method comprises the following steps;

filling powder into a forming chamber with lower punches in filling position,
transferring the powder by moving the lower and upper punches with slow motion to punching position
moving the other upper punches downwards with the ram unit with high velocity and in sequence defined by the position of the punches wherewith a compact body having a different thickness in different parts thereof is obtained, and
thereafter ejecting the compacted body.

The invention also relates to a powder compacting tool comprising a matrix having a through-going cavity, a first and a second upper punch, which are movable in the axial direction of the cavity, and at least two lower punches, characterised in that the upper punches have different axial lengths and that the tool comprises a single ram for moving the upper punches in sequence towards the at least two lower punches during a compacting operation and means are for holding the at least two lower punches stationary during a compacting operation. During the compacting operation of such a tool it is only the upper punches that are moving, all of the upper punches being moved by the same ram. Thereby, only means for regulating the single ram is needed during the compacting operation and such a tool can be made with a minimum of components.

In a preferred embodiment the tool comprises a first and a second upper and lower punches, the first upper and lower punches and the second upper and lower punches being opposite to each other. The cavity of the matrix is furthermore cylindrical and a core pin is disposed in the cavity and extended along the symmetry axis of the cavity.

BRIEF DESCRIPTION OF THE DRAWING

The invention will now be described with reference to the following Figures, of which;

Fig. 1 schematically shows a sectional view of a powder compacting tool according to a preferred embodiment of the invention in the very beginning of a compacting operation,

Fig. 2 shows in a view similar to Figure 1, the very beginning of the compacting of the thinner part of a work body, and

Fig. 3 shows in a view similar to Figure 1, the end of the compacting operation.

DESCRIPTION OF EMBODIMENTS

In Figures 1-3, a powder compacting tool 1 for the manufacture of annular bodies having a annular flange projecting from the central portion of the outer side thereof is schematically shown in different stages of a compacting operation.

The tool 1 comprises a matrix 2 with a through-going cavity in which a first and second

upper punch

3 and 4, respectively and a first and second

lower punch

5 and 6, respectively are vertically movable by suitable means. As is evident from the Figures the first upper punch 3 is shorter than the second upper punch 4 and the upper ends of the

lower punches

5,6 is axially displaced in relation to each other. The tool also comprises a core pin 7 and a ram 8.

The tool works in the following way.

Before the powder filling, the

upper punches

3 and 4 have been moved out of the cavity in the matrix and the lower punches are moved upwards so that upper end of the second lower punch 6 is disposed nearer the upper side of the matrix than the upper end of the first lower punch 5. Thereafter powder is filled into the space defined by the side walls of the cavity in the matrix 2, the core pin 7 and the second lower punch 6 and the upper end wall of the first lower punch 5. Then the first and second upper punches are moved downwards until they reaches the upper side of the matrix and thereafter are all the punches moved downwards to the positions shown in Figure 1.

In Figure 1 the positions of the punches before the beginning of the compacting operation are shown, the punches and the core pin defining a forming chamber C. In the starting positions the first upper punch 3 is disposed above the second upper punch 4 by a distance d.

The compacting operation starts by actuating the ram 8 to move downwards by a sequence of strokes or by a press force F. In the beginning only the first upper punch 3 is influenced by the ram 8, whereby the compacting of the powder in the forming chamber C begins for the part of the powder that lies between the end surfaces of the first upper and

lower punches

3 and 5. It is to be noted that the

lower punches

5 and 6 are held stationary during the whole compacting operation.

When the first upper punch 3 has been driven downwards the distance d, the ram 8 reaches the level of the upper end of the second upper punch 4 and the second upper punch will also be driven downwards by the ram 8 with the same velocity as the first upper punch 3. This stage in the compacting operation is shown in Figure 2. Thereafter, the first and second upper punch are driven downwards together until the desired thickness of the annular body and its flange is obtained.

Figure 3 shows the positions of the punches in the end of the pressing operation, the compacted body in the forming chamber C having a central annular body with a flange, the thickness of the flange being considerably smaller than the thickness of the central body.

The ejecting of the compacted body is made by moving all of the punches out of the cavity of the matrix by moving the lower punches upwards. Thereafter,

punches

3 and 5 are pushed against the compact body by a small force and the

punches

4 and 6 are retracted. Finally, the compact body is released from the

punches

3 and 5.

The distance d is so chosen that the compacted material in the central body and in the flange has the same density, i.e the powder column between the opposing end surfaces of the first upper punch 3 and the first lower punch 5 has been shortened by the same percentage as the powder column between the opposing end surfaces of the second upper punch 4 and the second lower punch 6.

The tool can of course be used to produce compact bodies having other configuration that the one shown in the Figures, for example a compact body in which the flange is projecting from the lower part of the central body. It is also possible to produce bodies being more thick in the outer part than in the central part by making the inner punch longer than the outer punch, i.e to change the positions of the first and second punches in the described embodiment. If cylindrical bodies are to be produced instead of annular bodies, the core pin is removed. The bodies produced can have other forms than circular, for example square, triangular , U-shape etc. It is also possible, but not preferred, to only use one lower punch having an upper end surface adapted to the configuration of the underside of the compact body to be produced. In such a case the filling operation and the ejecting operation will be more complicated. Furthermore, it is also possible to provide the tool with more than two upper and lower punches if a compact body having more than two portions of different thickness is to be produced and the number of lower punches can be different from the number of upper punches, in dependence of the shape of the compact body to be manufactured.

By the present invention, a tool in which the compacting is accomplished with the activation of only one single ram is provided. This simplifies the compacting operating and the regulating means needed therefore.

By the method and the tool described above flawless compacted bodies having a density of 7,3 g/cm³ have been produced of press-ready powder mixes. It is surprising that such bodies can be produced without cracks by this method, since the densities in different parts of the compacted body differs until the end of the operation. It is believed that these surprising results are due to the fact that the flowing of powder particles from areas with higher densities to areas with lower densities within the compacted body, will not take place due to the short duration of the compacting operation.

Claims

A method of compacting powder disposed in a forming chamber by a powder compacting tool, operating at high velocity and having at least two upper punches and two lower punches, the upper punches being moved different travel distance during compaction in order to create a compacted body having uniform density and different thickness in different parts thereof,
characterized in
moving the upper punches in sequence and with the same high velocity, and thereby directly actuating the upper punches with a common ram unit.
The method according to claim 1, wherein the forming chamber being defined by a side wall of a cavity in a matrix of a powder compacting tool and end walls of the at least two lower punches and the at least two upper punches having different axial lengths, the method comprising the following steps;
filling powder into forming chamber,
characterized in
placing the upper punches in such a way that the upper ends of the upper punches are positioned at different levels,
moving the upper punches in sequence with high velocity and starting with the one having the highest level, with the aid of the ram unit, and
thereafter ejecting the compacted body with the lower punches.
A powder compacting tool (1) comprising a matrix (2) having a through-going cavity, having an axial direction, at least two upper punches (3, 4), and at least two lower punches (5, 6), which are movable in the axial direction of the cavity,
characterized in that the upper punches (3, 4) are of different lengths and that the tool comprises a single ram unit (8) intended to cause a displacement of the upper punches (3,4) in sequence towards the at least two lower punches (5,6) during a compacting operation and thereby during an initial part of the compacting operation entirely keep at least one of the upper punches relieved from pressure, and means for arresting the at least two lower punches (5,6) in a stationary position during a compacting operation.
The tool according to claim 3,
characterized in that the tool (1) comprises a first upper punch (3) and a second upper punch (4) and a first lower punch (5) and a second lower punch (6), whereby the first upper and first lower punch (3, 5) and the second upper and second lower punch (4,6) being opposite to each other.
The tool according to claim 3 or 4,
characterized in that the cavity is cylindrical and that a core pin (7) is disposed in the cavity and extended along the symmetry axis of the cavity.