U.S. patent application number 10/502623 was filed with the patent office on 2006-01-12 for method and an apparatus for producing multi-level components by shock compression of powdered material.
Invention is credited to Kent Olsson.
Application Number | 20060008376 10/502623 |
Document ID | / |
Family ID | 27354793 |
Filed Date | 2006-01-12 |
United States Patent
Application |
20060008376 |
Kind Code |
A1 |
Olsson; Kent |
January 12, 2006 |
Method and an apparatus for producing multi-level components by
shock compression of powdered material
Abstract
The invention refers to a method and an apparatus for producing
multi-level components with conform target density from powdered
material. The powdered material is filled into a mould die, which
includes a multiple of lower and upper relatively movable punches,
and the filling height of the column over each punch is associated
to the geometrical levels of the final component. The material is
optionally pre-compacted by individual static pressure acting on
each punch and is compressed by at least one shock or impact device
from at least one direction. Compensating adjustments for powder
flow between columns and for density gradients are made during the
pre-compression and shock compression.
Inventors: |
Olsson; Kent; (Stockholm,
SE) |
Correspondence
Address: |
YOUNG & THOMPSON
745 SOUTH 23RD STREET
2ND FLOOR
ARLINGTON
VA
22202
US
|
Family ID: |
27354793 |
Appl. No.: |
10/502623 |
Filed: |
January 27, 2003 |
PCT Filed: |
January 27, 2003 |
PCT NO: |
PCT/SE03/00130 |
371 Date: |
August 12, 2005 |
Current U.S.
Class: |
419/66 |
Current CPC
Class: |
B22F 2003/033 20130101;
B30B 11/027 20130101; B22F 3/087 20130101 |
Class at
Publication: |
419/066 |
International
Class: |
B22F 3/02 20060101
B22F003/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 25, 2002 |
SE |
0200230-1 |
Jul 25, 2002 |
SE |
0202324-0 |
Nov 25, 2002 |
SE |
0203475-9 |
Claims
1. A method for producing stepped or multi-level components from
powdered material by filling a moulding die cavity with the
material, compressing the material between one, two or more
relatively movable lower punches inserted in the same, and at least
one or more relatively movable upper punches inserted in the
moulding die, characterised in that the compression is performed by
means of a shock or impact compression device, emitting kinetic
energy from one, two or more directions, with adjustments for
density variations and gradients by different means, to form a
multi-level material body of higher and homogeneous density.
2. A method according to claim 1, characterised in that a
single-level component can be produced between one, two or more
lower punches and one, two or more upper punches.
3. A method according to claim 1 characterised in that during
pre-compaction and/or shock compression, the powder density is
compensated for, such that the desired step heights and target
density of respective associated steps of the final body produced
are reached.
4. A method according to claim 1 characterised in that each punch
may be subjected to an additional and individually controlled
static pressure-applied during the shock compression, enhancing the
acceleration displacement of the punch.
5. A method according to claim 1 characterised in that a static
pressure may be applied prior to and/or retained after the shock
compression.
6. A method according to claim 1 characterised in that the static
pressure on any of the punches may act in a counter-acting
direction to the direction of shock compression, braking the punch
motion relative to any other punch, so that the braked punch
transfers less compression energy to the powder column. Braking may
not necessarily be performed by a counter-acting static
pressure.
7. A method according to claim 1 characterised in that the mass of
the punches may be adjusted relatively to each other such that the
density compensation may be performed during the shock compression
operation.
8. A method according to claim 1 characterised in pre-compacting
the powder material with a press device, where the individual
powder columns between each corresponding lower punch press surface
and the corresponding upper punch press surface associated with the
steps of the final component, to such a density that each powder
column has a column height-density ratio relation to each other,
such that during a parallel and equidistant displacement of all the
lower punches, and, a counter-acting equidistant and parallel
displacement of all upper punches, the final predetermined target
density is obtained in each of the associated component steps.
9. A method according to claim 1 characterised in that the
pre-compaction speed of each of the punches is adapted in such a
way, that the punches reach their respective final press position
at the same time as before filling level correction of the former
press cycle.
10. A method according to claim 1 characterised in that the
pre-compaction press speed of the punches are adapted in such a way
that possible powder flow between the powder columns is compensated
for.
11. A method according to claim 1 characterised in that the final
stage of the pre-compaction is performed with an equidistant motion
of all upper punches in a downwards direction and/or an equidistant
motion of all lower punches in an upward direction to ensure
mechanical contact between all punches and static rams.
12. A method according to claim 1 characterised by individually
adjusting the filling height of the powder columns above each of
the corresponding lower punches, being the distance of the press
surface of the lower punches to the moulding die top surface, such
that the ratios of the adjusted filling height correspond to the
ratios of desired heights and target densities of the respective
associated step of the final body produced.
13. A method according to claim 1 characterised in that the filling
height, of the individual powder columns above the corresponding
lower punch press surface, associated with the steps of the final
component, are compensated for, by individual relative
displacements of the lower punches, possible powder flow between
the powder columns and possible powder density gradients that may
occur in the powder columns during filling and during
compaction.
14. A method according to claim 1 characterised in that the press
force and punch position of the individual upper and lower punches
are measured and compared with desired and predetermined values,
and wherein upon detection of a deviation of any of the punches
from these values, the filling level is adjusted.
15. A method according to claim 1 characterised in that the filling
level and the pre-compaction compensations may be performed
iteratively over any number of process cycles.
16. A method according to claim 1 characterised in that the
pre-compacted powder columns are compressed by at least one shock
or impact stroke, where a striking unit emits enough kinetic energy
to form the body, when striking the material inserted in the
moulding die with a striking means, causing higher density of the
material, where all lower punches performs a parallel and
equidistant displacement relative to all upper punches, which
performs a parallel and equidistant, not necessarily of the same
distance as for the lower punches, counter-acting displacement,
during which the material reaches its target density.
17. A method according to claim 1 characterised in that the shock
or impact stroke can be performed without pre-compaction.
18. A machine for producing multi-level components characterised in
that it comprises a moulding die with a moulding die cavity, a
filling device for filling the moulding die cavity with the
powdered material, at least one upper punch and at least one lower
punch, with at least one relatively movable to the other (s), and a
shock or impact compressing device, from one, two or more
directions, that creates kinetic energy through an impact pulse to
the material, that generates a material body of higher density.
19. A machine according to claim 18 characterised in that a
single-level component can be produced.
20. A machine according to claim 18 characterised in that it may
include a press device that controls each punch individually in a
static press motion which may include control from one, two or more
directions.
21. A machine according to claim 18 characterised in that the
static pressure on all individual punches from the press device is
retained and may be individually controlled in position and in
press force.
22. A machine according to claims 18 to 21, claim 18 characterised
in that the press device performs the pre-compaction and
compensation operations of the powder columns between the upper and
lower punches.
23. A machine according to claim 18 characterised in that a shock
or impact compressing operation may be performed with or without a
press device.
24. A machine according to claim 18, characterised in that a system
monitors the individual punch positions, a control system operating
in response to monitored values, to individually adjust the filling
volumes by individual adjustment of the corresponding lower punch
positions to a die cavity volume, such that the ratios of the
adjusted filling volume correspond to the ratios of the desired
heights and densities of the respective associated steps of the
final body produced.
25. A machine according to claim 18 characterised in that the
monitoring system comprises an apparatus for separately monitoring
the press force and position of each individual lower punch and for
each individual upper punch, and passing the monitored data to the
control system, which compares it with correspondingly desired and
predetermined values, and wherein the electronic control system is
arranged such that, when the monitoring data deviates from the
desired values, the filling volume of the individual powder column
above each corresponding lower punch, is corrected
appropriately.
26. A machine according to claim 18, characterised in that the
control system individually adjusts the pre-compaction press speed
and acceleration of the upper punches and the lower punches.
Description
TECHNICAL FIELD
[0001] The invention concerns a method and an apparatus for
producing multi-level or stepped components compressed to higher
densities through a shock (impact) compression, or a combination of
a static compaction and shock compression.
[0002] At compaction of powdered material to higher densities of
final component shapes, including steps or multi-levels with axial
pressing techniques, consideration must be taken into account that
the fill volume for each level or step is relatively different.
Because of powder material's tendency to compact in vertical
columns and generate little hydrodynamic flow, the column for each
of the component levels must be compensated for a filling volume
corresponding to the final level height and the target density of
the component. Excessive density variations may result in crack
initiation of the final component and distortion of the component
during sintering.
[0003] Patent SE-0200230-1 discloses an invention for producing a
material body from powdered material. The material is for example
in the form of powder, pellets, grains and the like and is filled
in a mould, pre-compacted and compressed by at least one stroke,
from one, two or more sides simultaneously, using one, two or more
striking units emitting enough kinetic energy to form the body when
striking the material, causing coalescence of the material.
[0004] Patents PCT/SE01/01670, PCT/SE01/01671, PCT/SE01/01672,
PCT/SE01/01673 and PCT/SE01/01674 disclose a method of producing
metal, polymer, multi-layer, ceramic and composite bodies by
coalescence, wherein the method comprises the steps according to
the invention described in patent SE-0200230-1 above.
[0005] Techniques compensating for the relative difference in
compaction volume for each level of the component are well known
and used in the art of compacting multi-level (stepped) components
of conform density using conventional axial PM presses. To produce
components with as close to homogeneous density as possible and
step height as large as possible, the filling height of the powder
is individually adjusted by using a multiple of punches, preferably
one punch for each step. Each of the punches are displaced
relatively to each other using individually controlled press rams.
These methods for compaction of powder to higher densities of
multi-level components, concern axial pressing techniques
compacting the powder in a slow motion sequence. These methods of
correction of the filling height for each step in combination with
a shock (impact) compression process will not be applicable for
compensation of the density of each step, due to that the punches
during the shock compression operation, with respect to
fundamentals of impact mechanics, preferably can be managed with a
relatively equidistant displacement of each of the lower punches,
and/or a relative equidistant displacement of each of the upper
punches. Using the known technologies would render a varying target
density of the material above each of the lower punch surfaces and
initiated cracking.
[0006] Patent SE-0202324-0 discloses a DFIER-machine for
compression and compaction of a working material into a desired
shape using a combination of shock compression and static
compaction of material. The working material is for example in the
form of powder, pellets, grains and the like and is filled in a
moulding die cavity, compacted to a body of higher density. The
machine comprises an outer system and an inner system. The outer
system comprises at least one or more impact units, an upper and/or
lower, each comprising an impact ram. The inner system comprises at
least one or more static press units, each comprising a static
press ram, and a tool unit. The lower units of the inner and outer
systems, can be exchanged for a common stationary anvil and a lower
punch. The tool unit comprises a moulding die mounted in a moulding
die table or carrier, one, two or more upper punches individually
controlled in position and load, and one, two or more lower punches
individually controlled in position and load. The central system
comprises a movable moulding die carrier, which holds a moulding
die. The upper punch of the tool unit is removably connected to the
inner system's upper static ram and the lower punch of the tool
unit is removably connected to the inner system's lower static
ram.
[0007] The process cycle of the DFIER-machine involves two main
operations in processing the material to higher densities. The
first operation is a pre-compaction operation where the material is
densified to a pre-compressing gross shape. The second operation is
the shock compressing operation. The said compressing operation is
performed by retaining the static pressure on the inner system and
hence the working material simultaneously with a generation of an
impact by accelerating the impact ram(s) at least one or more
times. The shock wave is created and transferred to the working
material through the press ram(s) and the punches while the
pressure from the press ram(s) is retained. The impact unit(s)
delivers enough kinetic energy to form the material into a body
when striking the material, causing coalescence or higher density
of the material to the predetermined final body of higher density
according to a method described in patent SE-0200230-1.
STATE OF THE ART
[0008] Patent GB 2265567A discloses a process for producing stepped
pressed components from powder based material where powder material
is filled in a cavity of a moulding die, compressing the material
between relatively movable lower punches and at least one movable
upper punch relative the lower punches, where each punch surface
corresponds to each level of the stepped component, monitoring
deviations of the filled amount of the material, from a desired
value such that the steps have approximately the same density, by
altering the filling volume of the moulding die cavity, by
individually adjusting the filling levels of the bottom rams, being
the distance of punch surfaces of the bottom rams from the moulding
die top edge, such that the ratios of the adjusted filling levels
correspond, in a first approximation, to the ratios of desired
heights of the respective associated steps of the pressed article.
The method to adjust the filling level of each step is performed by
correcting each of the bottom punches individually. The individual
filling levels in at least a first approximation being in a
relationship to each other, which corresponds to the relationship
of the desired heights of the levels of the pressed component,
implying that the greater the desired height of the desired
associated step, the greater the individual amount of
correction.
[0009] The described patent discloses a method for producing
stepped components, where after pressing the material performed
according to the invention has reached its final state of
processing an approximate homogeneous density is obtained in the
component. However, this method refers to conventional powder press
machines with a low press displacement velocity (static
pressing).
[0010] Powder densification with methods and machines disclosed in
the patents WO 9700751 and WO 0222289, machine solutions without
apparatus and methods for individual punch control in press force
and position for tool systems including two or more punches on
either upper or lower side of the moulding die, where each punch
corresponds to respective associated steps of the final material
body produced, may therefore not be possible.
[0011] In the two patents, WO 9700751 and WO 0222289, no
descriptions or claims are mentioned or examples given on how to
pre-compact the material in the moulding die cavity for producing
multi-level components. Neither are there a solution or claims
mentioned or examples given on how to compensate the filling volume
in the moulding die cavity, to produce a stepped component by means
of shock (impact) compressing the powder. The patents do not
include methods and apparatus to compensate the powder densities of
the powder columns for each corresponding and associated steps of
the shock compressed material body, which is necessary in order to
achieve a homogeneous density in all the stepped sections of the
final body produced.
[0012] The said machines can therefore not produce multi-level
components of a homogeneous target density throughout the stepped
sections of the component, due to the lack of individual punch
control and therefore compensation.
Multi-Level Component Approaches
[0013] There are three different approaches for manufacturing of
multi-level components. They have different degree of success
because of technical limitations due to difficulty in compensation
for density gradients.
[0014] One approach of producing multi-level components may be
performed by stepped dies, slotted punches or fixed stepped
punches, but they all result in heterogeneous densities and
cracking. These ways will limit the step height between each level
or result in a heterogeneous density distribution in the final body
produced, due to the equidistant absolute compression displacement
for each of the component steps, resulting in a higher density in a
shorter powder column above the stepped or slotted lower punch
relative to a higher powder column above the same lower punch.
[0015] A second approach is to perform shock compressing directly
by shock compression without a pre-compaction operation. This may
be performed by shock compressing each individual punch one by one.
A lower step of the final component requires a higher compression
ratio and a correspondingly higher punch. The impact ram may
compact one punch at a time beginning with the highest, i.e. with
the punch base closest to the impact device. The compression at the
impact may result in a displacement such that the highest ram base
will end flush the second highest punch base. A second or the same
shock stroke on both the highest and second highest punches will
displace these two punches so that their punch bases will end flush
the third highest punch, and the shock sequence is repeated until
all powder columns between the associated punches have been
compressed to a higher density.
[0016] A third approach to produce stepped components may be
performed according to the following:
[0017] Powder is filled in a moulding die cavity. The moulding die
cavity comprises a moulding die and one, two or more lower punches
inserted into it from the lower side. The lower punches may be
stepped or positioned so that the press surfaces have a relative
offset to each other. The moulding die is closed by inserting one,
two or more top dies. The top punches may be of different length so
that when pressed into the powder, different ratios of compaction
is obtained under the individual punches. The heights of the
punches are such that the relative offset distance between the
punch press surfaces corresponds to the step heights of the
associated steps of the final component, and with all the punch
bases in flush.
[0018] The procedure of shock compressing the powder material to a
final material body, including for stepped surfaces, is performed
by an alternative pre-compaction wherein the punches are pressed
from at least one side. The upper punches, of different lengths,
are positioned on the powder surface. The press ram will first meet
contact with the highest punch, press it into the powder until the
said punch base is in flush with the base of the second highest
punch. The press device will then continue pressing the two punches
into the powder in a parallel motion. The pre-compaction will end
with all punch bases ending flush with each other.
[0019] The shock compression is performed with the shock (impact
ram) device impacting on the punches. The punches will be displaced
in a parallel and equidistant motion until the geometry of the
final body is met. The shock compression may also be performed
according to the setup described without the pre-compaction
operation, for machines without means or devices to perform a
static pre-compaction operation. The initial positions of the
punches are in this case retracted from the powder surface so that
all the punch bases end flush. The shock compression is performed
with the shock compression device impacting on the punch bases. The
punches will be displaced into the powder, with an impact energy of
a magnitude such as the final shape of the component is met.
[0020] However, the described approaches will give a heterogeneous
density distribution in the different stepped sections of the final
component and also render undesired powder flow between the powder
columns above each of the lower punches. Furthermore, it will be
suffering from technical difficulties such as positioning the
punches during filling, fixation of the punches before the shock
compression stroke and retracting the punches after ejection.
Furthermore, these methods may also suffer from uncontrolled
effects as a result from internal shock wave such as crack
initiation.
DISCLOSURE OF THE INVENTION
[0021] The disclosure of the present invention includes a method
and an apparatus to produce multi-level or stepped components with
conform or predetermined target density from powdered material,
produced with means of shock (impact) compression or static
compaction in combination with shock compression.
[0022] The method compiles the main steps of: [0023] a) filling a
moulding die cavity, comprising a moulding die and at least two
relatively movable lower punches closing the lower section of the
moulding die, with powdered material. The filling volume
constitutes of the volumes above each of the lower punches pressing
surfaces and of the top surface of the moulding die. [0024] b)
compensation of the fill volume of each powder column above each of
the lower punch press surfaces by adjusting the column height, by
individual relative displacement of the lower punches such that the
filling volume of each powder column corresponds to respective
associated steps and target density of the final pressed component
as well as for possible powder gradient in each powder column, any
powder gradients, and any possible powder flow that may occur
between the the powder columns. [0025] c) pre-compaction (static
compaction) of the powder columns between each of the lower punch
press surfaces by individual and relative displacement of the lower
punches, and at least one relatively movable upper punch to a
predetermined and individual pre-compacted density of each of the
powder columns, where the pre-compacted density is compensated for,
such that each powder column are related to each other with respect
to the target density of the final body produced (the component),
possible powder flow and density gradients between each of the
powder columns that may occur during the pre-compaction and the
shock compression operations and the equidistant displacement of
all lower punches and equidistant displacement of all upper punches
during the shock compression. [0026] d) shock compressing the
pre-compacted body by an equidistant displacement of all the lower
punches relative to an equidistant displacement, not necessarily
the same as for the lower punch displacement, of one, two or more
upper punches, for which the predetermined target density is
obtained for all the powder columns above each of the lower punches
press surfaces rendering in a conform and predetermined target
density throughout the material body produced. The shock
compression may be performed on a single side or a multiple of
sides. [0027] e) Compensation of the powder density, necessary to
obtain homogeneous density in the stepped sections of the final
component, may also be performed during shock compression. This is
performed by controlling the punch motion individually so that the
energy transmitted to the powder is controlled. This could be
performed by three different approaches: [0028] i) Each punch may
be subjected to an additional static pressure applied during the
shock compression. This will enhance the acceleration displacement
of the punch into the powder column below or above the punch press
surface. Each punch may be individually controlled such that each
punch is subjected to an individual pressure, i.e. a higher static
pressure will enhance the ratio of densification of the powder
column below or above the punch press surface. The static pressure
may also be applied prior to and/or retained after the shock
compression. [0029] ii)The static pressure on any of the punches
may act in a counter-acting direction to the direction of shock
compressing, meaning braking the punch motion relative any other
punch so that the braked punch transfers less compression energy to
the powder column below or above the punch press surface. The means
of braking any of the punches included in the tool may not
necessarily be performed by a counter-acting static pressure.
[0030] iii)The mass of the punches may be adjusted relatively to
each other. A punch with a relatively higher mass will have a lower
velocity and hence reduced energy compressing the powder column
facing the punch press surface, resulting in a decreased density of
the same powder column relative the powder column compressed with a
punch of lower mass.
[0031] The invention also includes an additional static press
operation including an equidistant displacement of all the lower
rams controlling the lower punches, and a counter-acting
equidistant displacement, not necessary the same as for the lower
ram displacement, of all the upper rams controlling the upper
punches, during the final stage of the pre-compaction operation.
The relative displacement of the punches during pre-compaction
will, in the case of including the additional static press
operation, compensate for the possible density changes the said
operation will inflict on each powder column between each of the
corresponding upper and lower punches. The said additional static
press operation will ensure that each punch has solid mechanical
contact with the shock compressing device during the shock
compressing operation, transmitting the shock impact energy to all
of the punches.
[0032] The lower punches will have specific lengths in relation to
each other, with respect to the step heights that corresponds to
respective associated steps of the lower side of the final body
produced, so that the bases of each of the punches end exactly at
the same plane, or are stacked onto each other in a manner that
allows for solid mechanical contact between the punch bases. The
upper punches will have specific lengths in relation to each other,
with respect to the step heights that corresponds to respective
associated steps of the upper side of the final body produced, so
that the bases of each of the punches ends exactly at the same
plane, and are stacked onto each other in a manner that allows for
solid mechanical contact between the punch bases. This arrangement
will allow for the exact equidistant displacement of the punches
during the shock compression operation and the possible additional
static press operation.
[0033] Correction of the individual powder columns' density may be
performed in a feedback operation based on position and press force
measurements on the corresponding powder columns' lower and upper
punch of the previous process cycle. The reference press force and
position measurement may preferably be performed at the end of the
pre-compaction operation.
[0034] The disclosure of the apparatus includes a press machine for
producing stepped components from powdered material, including a
press device for individual punch position during the
pre-compaction operation and device for shock compression of the
pre-compacted material. The pre-compaction may be omitted so that
only the shock compression is performed.
[0035] The press device comprises one or a multiple of static press
rams connected to one, two or more punches. The press ram controls
the position of the punch(es) connected to it, and also applies the
press force on the punch in order to compact the powder. The press
device may be single sided or multiple sided. The press device
allows for individual position, velocity, acceleration, and force
drive adjustments of any or all the lower and upper punches. The
press device may position the punches so that all punches on one
side of the powder, will have solid mechanical contact with the
shock compression device during the compression operation.
[0036] The shock or impact compressing device creates kinetic
energy through an impact stroke onto the press device, such that
the shock pulse is transferred through the press device and punches
to the material in the moulding die. The impact stroke may also be
performed directly to the punches without the involvement of the
press device. The shock compression device includes an upper and a
lower shock ram, positioned axially with the punches on either side
of the same. The lower side of the shock compressing device may be
replaced with a static anvil, and consequently the shock
compression is performed from a single side. When shock compression
is performed from a single side, pre-compaction, including filling
and pre-compaction corrections, are performed in the same manner as
previously described, with the exception that the whole package of
the inner system in a last operation is positioned with the lower
press device resting on the anvil or in the case of omitted press
device with the punches resting on the anvil. This means that the
press device including all upper and lower punches and the moulding
die performs a downward axial motion, without any relative
alteration in punch or moulding die motions nor in press force
between the upper and lower punches.
[0037] The apparatus' system that monitors the press force and the
positions of each punch separately and passing the monitored force
and position data to the control system, which compares the data
with correspondingly allocated desired values, and wherein the
control system is arranged such that, when the monitoring data
deviates with the allocated desired values, the filling volume of
the individual powder column above corresponding lower punch is
corrected appropriately.
BRIEF DESCRIPTION OF THE DRAWINGS
[0038] In the following detailed description of the invention, two
preferred embodiments will be described with reference to the
accompanying drawings:
[0039] FIG. 1A shows a cross-section view of a tool system,
including a moulding die (1), three lower punches (2,3,4), a core
rod (5), an upper punch (6), and an uncompacted powder (7), when in
filling position
[0040] FIG. 1B shows the same tool system (1,2,3,4,5,6) in position
after pre-compaction FIG. 1C shows the same tool system
(1,2,3,4,5,6) in position after final pre-compaction adjustment
[0041] FIG. 1D shows the same tool system (1,2,3,4,5,6) after the
shock compression operation FIG. 2A shows a cross-section view of
an tool system including a moulding die (1), and three lower
punches (2,3,4), core rod (5), upper punch (6), and un-compacted
powder (7) when in filling position
[0042] FIG. 2B shows the same tool system (1,2,3,4,5,6) in position
after pre-compaction
[0043] FIG. 2C shows the same tool system (1,2,3,4,5,6) including
an intermediate punch adjustment device (10), in position after
final pre-compaction adjustment
[0044] FIG. 2D shows the same tool system (1,2,3,4,5,6), including
an intermediate punch adjustment device (10), after the shock
compression operation
[0045] FIG. 3 shows the first examples embodiments tool member
motion versus time and an illustration of the corresponding density
for each of the powder columns above each of the lower punch press
surfaces
DETAILED DESCRIPTION OF THE INVENTION
Embodiment According to FIG. 1
[0046] The first embodiment of the invention will be described as
an example with the reference to FIG. 1 and FIG. 3. The figure
shows a tool for powder compression, which includes a moulding die
(1), three lower punches (2,3,4), a core rod (5), and an upper
punch (6), in four different process stations A, B, C and D, in the
process of producing a multi level component with a combination of
a static compacting and a shock compressing according to the
invention.
[0047] The moulding die (1), the core rod (5) and the said lower
three punches together constitute a moulding die cavity. The inner
lower punch (4) has a bore through which the said core rod is
guided coaxial with the said inner lower punch ending flush with
the upper surface of the moulding die (1) and creates a through
hole in the final body produced (9).
[0048] The three lower punches are arranged coaxially in one
another relatively divided in the axial direction. FIG. 1A shows
the tool in its filling position. The lower punches (2,3,4) are
positioned in predetermined positions, such that the filling volume
of uncompressed powder (7) above each of the punch press surfaces
and the top moulding die surface correspond to the associated final
body step height and the target density of the final body produced.
The filling height of the powder column above each of the lower
punch press surfaces in relation to the respective associated steps
of the final body produced can be described as: h filling .times.
.times. height = .rho. target .times. h target .rho. apparent
##EQU1## where index target refers to final body produced and index
apparent refers to the filling powder density. The filling height
may also be corrected for density gradients occurring in the powder
column or powder flow that may occur between the powder columns
during any of the proceedings involved in forming the final body
(1). The moulding die (1) is closed by inserting the upper punch
(6) into it.
[0049] The pressing process begins with a pre-compacting operation
moving all the lower punches in an upward relative motion towards
the said moulding die upper surface and at the same time moving the
upper punch (6) in a counter-acting motion (d). The relative
motions of the lower punches (a), (b) and (c) during pre-compaction
are performed so that the punch bases at the end of the
pre-compaction are in parallel and will have a solid mechanical
contact with the shock compressing device during compressing.
[0050] The relative motions of each of the lower punches relative
to the upper punch and the punch heights of each lower punches are
such that a pre-determined density is obtained in one of the powder
columns. The two other powder columns' heights are functions of the
first powder column density, the final component associated step
height, target density of the final body produced (9), and the
equidistant punch motion (e). The punch displacements during the
pre-compaction operation for each of the said lower punch surfaces
are illustrated as the displacement steps (a to c) in FIG. 1
correspondingly. FIG. 1B shows the positions of the lower and upper
punches after the pre-compaction operation is completed. The
pre-compacted powder columns are shown as indexed 8-2, 8-3 and 8-4.
Since the shortest powder column (8-3) will encounter the largest
compression ratio during the shock compression, the pre-compacted
column (8-3) must therefore be compensated with a lower density
than for a higher powder column (8-4) and (8-2). The relative
movement of the lower punch (4) below the highest powder column
(8-4) must therefore perform the longest pre-compaction
displacement.
[0051] The height of any of the powder columns for a predetermined
pre-compacted density, e.g. (8-4), is a function of the target
density of the final body produced and the height of the component
level to the corresponding associated step of the final body (9)
according to: h 8 - 4 = .rho. target .times. h target .function. (
8 - 4 ) .rho. 8 - 4 ##EQU2## where h.sub.8-4 and .rho..sub.8-4
refers to the pre-compacted height and density of the powder column
above the lower punch (4) and h.sub.target(8-4) is the final
component height above the punch (4) press surface in the final
body produced. The equidistant punch motion (e) of the punches is
given by the relation: e=h.sub.8-4-h.sub.target(8-4)
[0052] The height of the two other powder columns are given by
adding the equidistant displacement (e) to the corresponding
associated step of the final body (9).
[0053] The pre-compacting operation is performed in a slow static
press motion, what could be described corresponding to conventional
PM press techniques such as disclosed in patent GB 2265567A.
Throughout the described embodiment the moulding die (1) is fixed
and all punch movements are performed relative to the moulding die
in controlled motions. The movements of the punches are performed
with different accelerations and velocities relative to each other
such that the compressed powder, with respect to the fill volume
and pre-compacted volume, is compacted as uniformly as
possible.
[0054] During the shock compression operation the punch side facing
the impact and static press rams must be arranged so that they all
will be exposed to the same impact energy density by surface,
transferring the energy to the powder column in the form of an
equidistant displacement and consequently resulting in a
densification of the individual powder pillars to the same target
density throughout the component. The shock compression energy is
such that the lower punches are displaced equally the distance (e)
and such that the upper punch is displaced the distance (f). The
distances e and f may be equal.
[0055] FIG. 1C shows the tool and pre-compacted powder in the
pre-compaction adjustment operation. The upper punch (6) is
displaced a distance f' downwards and the lower punches (2,3,4) are
displaced equidistantly e'. This operation will ensure that all
punch bases' surfaces are positioned flush prior to perform the
shock compression. If the pre-compaction adjustment operation is
performed, the compressing distances e and f are reduced with the
distances e' and f' correspondingly. The density corrections are
illustrated in FIG. 3 through the process operation of filling,
pre-compacting and shock compressing.
Embodiment According to FIG. 2
[0056] The second embodiment of the invention is a variant of the
first embodiment by means of arranging the base sides of the
punches so that a parallel motion of all punches could be achieved.
In order to transfer the kinetic impact energy to the powder,
generated by the shock compressing device, a solid mechanical
connection must be present between the shock compressing device and
all of punches associated to respectively upper or lower sides of
the moulding die. In the first embodiment this is performed by
adapting the punch lengths to the step height of the final body
produced, such that when the punches are in their final positions
of the process cycle, the bases of the punches end flush. A static
compacting ram or a shock compression ram can in this position of
the punches (2,3,4), generate a parallel and equidistant movement
of all the said punches.
[0057] The arrangement according to the second embodiment for
arranging a solid connection between the punches and the shock
compressing is achieved by inserting an intermediate punch
adjustment device (10) at the base of the punches. The intermediate
punch adjustment device (10) has an interface surface facing the
punches including steps on which each of the punches (2,3,4) are
positioned. The opposite side of the said intermediate punch
adjustment device surface is planar and parallel to the shock
compression ram. The relative height between each step of the
intermediate punch adjustment device (10) corresponds to the
relative step height of the final body produced. This means that
when all punches (2 to 4) are of equal length and positioned on the
steps in the intermediate punch device (10), the relative position
of the press surfaces of the said punches coincide with the steps
of the final body produced. All process operations and apparatus
means are the same as for the first embodiment.
* * * * *