RU203832U1 - DEVICE FOR PRESSING CERAMIC POWDER MIXTURE - Google Patents

Abstract

The utility model relates to the field of powder metallurgy, namely to equipment for compacting powdered materials from fine powders into briquettes. The device for pressing a cermet powder mixture contains an upper base with an upper punch placed in it and a lower base with a lower punch located in it. In the lower base, side punches are placed, made with the possibility of moving towards each other, forming a closed cavity for placing a cermet powder mixture intended for pressing a briquette. Each side punch is made composite, consisting of several separate parts in contact with each other, with the possibility of relative movement towards each other. Each part of the integral side punch is equipped with a reciprocating drive. As a result, the quality of pressing is improved due to layer-by-layer compaction of the powder mixture by radial compression with axial force support and release of pressing out of one pair of sides of a rectangular briquette from compressive stresses. 9 ill.

Description

The utility model relates to the field of powder metallurgy, namely, equipment for compacting powdered materials from fine powders into briquettes introduced into metal melts as alloying or modifying additives or intended for subsequent sintering.

Known mold for pressing briquettes from a powdery material, containing a lower base, with a matrix placed in it, a lower punch, an upper matrix, an upper plate, with an upper punch placed on it, on the lower base there is a lateral punch in contact with both the upper and lower matrices and forming three walls of a closed matrix cavity, while the upper matrix and the lateral punch are equipped with independent drives, and the upper matrix and the punch are made with the possibility of reciprocating movement of the forming compacted workpiece.

(see Patent for utility model No. 160347, IPC B21J 5/00, B23D 15/40, B26F 1/00, 2016).

The disadvantage can be attributed to contact friction on the walls of the matrix, which, in some cases, leads to the destruction of the briquette during its extrusion.

Known is a mold for pressing briquettes from a powdery material, comprising an upper base with an upper punch placed therein and a lower base with a lower punch located therein. In the lower base, side punches are arranged in pairs opposite to each other, made with the possibility of moving towards each other, while each pair of them moves in its own plane. The working cavity of the mold is formed by the upper, lower and four side plates, each of which contacts the working surface of one of the punches. The pressing of the briquette, depending on the technology being implemented, is carried out either by the simultaneous movement of all the plates towards the common geometric center of the working cavity, with the subsequent reversal of their movement, or by moving the side plates located opposite each other, or by moving the upper and lower plates, or by moving a pair of side plates ...

(see RF Patent No. 2510308 class B22F 3/02, B22F 3/03, B30B 15/02, 2014) - the closest analogue.

As a result of the analysis of the execution of this mold, it should be noted that its design does not provide for the possibility of multi-stage deformation by upsetting-expansion methods with a change in the deformation pattern, for example, tensile compression in the forming cycle, in which the direction of movement of the working bodies (plates) does not have the ability change the direction of movement along three coordinates, both in one and in opposite directions.

The above disadvantages do not allow the use of non-monotonic deformation technologies during the operation of the mold, a feature of which is the alternation of compression, stretching and twisting operations during pressing, the use of which increases the density, reduces the anisotropy of the pressed briquettes and ensures the production of high quality products.

The technical result of the claimed utility model is to improve the quality of pressing due to layer-by-layer compaction of the powder mixture by radial compression with axial power support and by releasing one pair of sides of a rectangular briquette from compressive stresses in the process of pressing out. Shear stresses arising in the peripheral layers of the workpiece, from the action of friction forces, provide additional compaction of the powder mixture and, ultimately, a uniform distribution of density over the briquette volume.

The specified technical result is achieved in that a device for pressing a cermet powder mixture containing an upper base with an upper punch placed in it and a lower base with a lower punch located in it, in the lower base there are side punches made to move towards each other, form a closed a cavity for placing a cermet powder mixture intended for pressing a briquette, each side punch is made of a composite, consisting of several separate parts in contact with each other, having the possibility of relative movement towards each other, while each part of the composite side punch is equipped with a reciprocating drive ...

Improving the quality of the briquette and improving its structure is ensured by eliminating material discontinuities in the volume of the pressed briquette.

The design of the device provides the possibility of layer-by-layer mixing of the inner and outer layers of the powder mixture, while increasing the density at a lower external pressure due to layer-by-layer compression of the briquette being pressed.

The component parts of the side punches, acting according to a certain program with a given cyclicity, change the volume of the matrix cavity in the direction perpendicular to the movement of the upper and lower punches, have a significant effect on changing the direction of flow of the material of the powder mixture.

Compression of the powder mixture can be carried out cyclically, simultaneously or sequentially along two mutually perpendicular axes of the Cartesian coordinate system, due to the independent, independently of each other, movement of the component parts of the side punches, simultaneously, in pairs or sequentially in the direction of the vertical coordinate axis, with alternating direction of action of forces axial compression.

Moving the punches, then towards the approach to the general geometric center, then moving away from it, with an increase in the values of the specific forces attributable to each, separately taken pair of parts of the side punch, with each change of the cycle leads to a decrease in the absolute values of the compressions, while realizing the pressing conditions according to the "compression-extension" scheme.

The essence of the declared utility model is illustrated by graphic materials, where:

in fig. 1 - Diagram of the device, front view, initial position, the moment of filling the powder blank into the matrix cavity;

in fig. 2 - Diagram of the device, top view, section A-A in Fig. one;

in fig. 3 - Diagram of the device, left side view, longitudinal section B-B according to Fig. one;

in fig. 4 - Diagram of the device, front view, cross-section BB according to FIG. 2, the moment of double-sided axial compression of the cermet powder mixture 27 by punches 10, 11 and radial shift, on the left side by moving the central lateral punch 13 towards the central axis, on the right - by moving the extreme lateral punches 15, 17 towards the central axis;

in fig. 5 - Diagram of the device, front view, cross-section BB according to FIG. 2, the moment of movement of the left extreme lateral punches 12, 14 towards the central axis, the central 13 movement to the sides from the central axis until the alignment of their end planes, at the same time, at the same time, on the right side, the movement of the central punch 16 away from the central axis of the device, while the extreme punches 15, 17 move towards the central axis until they intersect with the central channel 7;

in fig. 6 - Diagram of the device, front view, cross-section BB according to FIG. 2, the moment of layer-by-layer compression with a shift of the side surface of the workpiece; the right central punch 16 to align its end surface with the end surfaces of the extreme punches 15, 17 and the wall of the central channel 7;

in fig. 7 - Diagram of the device, front view, cross-section BB according to FIG. 2, the moment of compression of the lateral surface of the powder briquette 29 by an amount exceeding the value of the elastic aftereffect in this direction of compression, preparation of the molded part for removal from the matrix cavity;

in fig. 8 - Cutout I according to FIG. 7, the moment of compression of the side surface of the briquette 29 by an amount exceeding the value of the elastic aftereffect in this direction of compression, preparation of the molded briquette 29 for removal from the matrix cavity of the channel 7;

in fig. 9 - Diagram of the device, front view, cross-section BB according to FIG. 2, the moment of removal of the molded briquette 29 from the matrix cavity of the channel 7.

The device for pressing the cermet powder mixture consists of lower 1 and upper 2 plates, connected by guide columns 3. The guide columns 3 are pressed into the lower plate 1 and are in contact with the guide bushings 4 of the upper plate 2, which has the possibility of reciprocating movement along the guide columns 3 relative to the lower slabs 1.

On the bottom plate 1, a base 5 is fixed, in which a matrix 6 is located, in which vertical through 7, side 8, 9 channels are made, in which the upper 10, lower 11 punches and side punches, respectively, have the ability to move.

Side punches are made of parts 12, 13, 14 (left in the plane of the drawing) and parts 15, 16, 17 (right in the plane of the drawing). The operation of the punches is controlled from the control unit through the corresponding rods of the hydraulic cylinders 18, 19, 20, 21, 22, 23, 24, 25.

Thus, the upper punch 10 is connected to the rod of the hydraulic cylinder 18, the lower punch 11 - to the rod of the hydraulic cylinder 19, the composite side punches of the left side 12-13-14 (reference point in Fig. 1) are connected to the rods of the hydraulic cylinders 20, 21, 22, and the side punches of the right side, respectively, with the rods of the hydraulic cylinders 23, 24, 25.

An insert 26 is installed on the upper plate 2, centering the upper punch 10 in the XOY plane.

The device works as follows.

Powder mixture 27 (Fig. 4) is poured into the matrix cavity of the device through a funnel 28. After pressing, the powder mixture 27 takes the form of a briquette 29 (Fig. 9) with a cross-section of a vertical channel 7 (Fig. 9), despite the fact that the transverse the section of the briquette in the process of pressing changes depending on the location of the side 12-13-14; 15-16-17 and central punches 10-11 (Fig. 1).

To reduce the amount of movement of the punches and, accordingly, the overall dimensions of the device, the powder mixture 27 can be pre-compressed with a density of up to 0.36 theoretical density, a cross-sectional size 10-15% smaller, the cross-section of the window of the vertical channel 7 of the matrix cavity.

The lower plate 1 of the device is fixed with the installation bolts on the table of the hydraulic press with a force of 63 to 100 tf, the upper plate 2 is attached to the press slider.

An example of pressing a briquette

Stage 1.

The press slider is lifted up, to the extreme upper position.

The vertical lower punch 11 is retracted to the extreme lower position, the component parts of the lateral punches of the left side 12-13-14 and the right side 15-16-17 are also retracted to the extreme lateral positions (Fig. 1). A powder mixture 27 is poured into the matrix 6 through a funnel 28, which spills out through the central channel 7 of the matrix 6 and fills the gap formed by the inner side channels 8 and 9 of the matrix 5 (Fig. 1).

Stage 2.

The press is switched on and the press slider begins to move until the ends of the guide bushings 4 come into contact with the upper surface of the base 5 and pressure is exerted by pressure, which makes it possible to keep the mold from spontaneous opening.

The upper plate 2 is lowered by the press slide until the lower end of the guide bushings 4 closes with the upper end of the base of the matrix 6, the lower plate 1, while the internal cavity formed by the central channel 7 and the side channels 8, 9 is closed in the matrix 6. 18-19 (upper), 20-21-22 and 23-24-25 (lateral), responsible for the movement of the upper 10, lower 11 punches and composite left 12-13-14 and right 15-16-17 side punches, respectively, and produce sequentially alternating, simultaneous and other movement (Fig. 4).

Upon reaching the powder workpiece relative density of the order of (0.36-0.42)% theoretical, change the speed of movement of all punches relative to the speeds of movement of each other. For example, the speed of the central side punches 13, 16 is slowed down in relation to the upper 12, 15 and lower 14, 17 punches in contact with them in the horizontal plane, respectively, and the movement speeds of the vertical upper punch 10 and the vertical lower punch 11 are consistent with each other and are maintained at the level corresponding to a given back pressure, providing a calculated elastically deformed state of the material of the powder mixture 27, forming a briquette 29 (Fig. 5, 6).

- stage number 3

The horizontal planes of the working ends of the vertical lower 11 and vertical upper 10 punches are set at the cut level of the lateral channels 8-9 of the matrix 6 (Fig. 7).

The drives of the rods 20-21-22 of the precast left punch 12-13-14 and drives of the rods 23-24-25, of the prefabricated right punch 15-16-17 move the prefabricated lateral punches towards the common geometric center by a value of Δ equal to the value of the elastic aftereffect material of the workpiece in cross section (Fig. 8).

When the powder billet reaches the specified density, the side punches 12-13-14 and 15-16-17 are simultaneously retracted to the level of the vertical cut of the side channels 8, 9 of the matrix 6.

- stage number 4.

The finished briquette 29 is removed by moving the vertical lower punch 11 upward until the extruded briquette 29 is removed from the matrix channel 7 (Fig. 9), simultaneously with the rise of the press slider, and with it the upper plate 2 and the vertical upper punch 10 to the extreme upper position.

Justification

The operation of the device is presented by an example of multistage pressing of aluminum granules, including deformation operations: compression - tension - shear - compression, spaced in time.

The term "compression" means the movement of opposing punches towards each other, while the distance between them decreases.

The term "stretching" refers to the movement of opposing punches to the sides, which increases the distance between them.

There is a layer-by-layer "stretching" and / or "compression". In this case, one side punches opposite to each other increase the distance between themselves, while adjacent pairs of punches in contact with them along the horizontal plane move towards each other.

There is the term "compression-shear", in this case, some side punches of different layers move towards each other (for example, 12-16) towards the geometric center, while the others in contact with them in the horizontal plane either stand still , when moving vertical punches towards each other, or move in opposite directions (for example, 13-15).

There is the term "tension-shear", in this case, the side punches of one layer move from the center (for example, 12-15), while the others in contact with them in the horizontal plane or stand still when the vertical punches move towards each other. to a friend, or move to a geometric center (for example, 13-16).

Stage 1 (fig. 1, 4, 5)

In a matrix cavity with a volume of 136 cm ³ (2 × 2 × 34 cm) were poured 100 g of spherical APV aluminum granules with a diameter of 0.2 ÷ 5 mm, used for the production of aluminum flux-cored wire for steel deoxidation (Fig. 1).

The bulk density of the aluminum granules was 0.75 g / cm ³ .

Technological modes were determined by modeling using a tensor-nonlinear model of damage accumulation described by the equation:

- поверхность предельных деформаций при стационарном деформировании;

- показатель напряженого состояния; σ - среднее напряжение; σ_u - интенсивность напряжений;

- параметр чувствительности пластичности к напряженному состоянию; μ_σ - параметр Лоде; β_ij - направляющий тензор приращений деформаций; δ_ij - дельта-символ Кронекера.where ψ _ij - damage deviator tensor; n, a , b - model parameters; E _u - accumulated deformation; E _* - accumulated deformation before destruction;

- surface of ultimate deformations during stationary deformation;

- an indicator of a stressed state; σ is the average stress; σ _u - stress intensity;

- parameter of sensitivity of plasticity to stress state; μ _σ is the Lode parameter; β _ij - directing tensor of strain increments; δ _ij is the Kronecker delta symbol.

At the first stage, deformation was carried out according to the scheme of axial compression - radial stretching of the powder mixture:

it follows from the tensor model that β _ij = const (Figs. 4, 5 and 6)

Where

удовлетворяет условиям:Damage function

satisfies the conditions:

ϕ (0) = 0, ϕ (1) = 1,

can be represented by a quadratic expression:

The accumulated strain ε _u has the form

- интенсивность скоростей деформации; t, τ - время; ε_*=ε_*(η) - кривая предельных деформаций при стационарном деформировании (η=1) для начального состояния материала, С - материальная константа (0≤С≤1);

- показатель напряженного состояния; σ, σ_u - среднее напряжение и интенсивность напряжений соответственно.Where

- intensity of strain rates; t, τ - time; ε _* = ε _* (η) is the curve of ultimate deformations during stationary deformation (η = 1) for the initial state of the material, C is a material constant (0≤C≤1);

- indicator of stress state; σ, σ _u - average stress and stress intensity, respectively.

The second invariant of the damage tensor is taken as a measure of damage:

From relations (2), (4), (6) it follows that of the two quantities a and b, independent is

while

where D = | β _ij | is the third invariant of the tensor.

Vertical upper 10 and lower 11 punches produced double-sided compression of granules at a speed of ₂₁ + ϑ ₆ = ϑ _{6 + 21} = 12 mm / s, with simultaneous movement of the central left side punch 13 and extreme lateral punches 15, 17 of the right side at a speed equal to ϑ _{(13), (15-17)} = 3 mm / s, towards the common geometric center, thus, the total speed of movement of the prefabricated side punches was (Fig. 5):

ϑ _{(7-8-9) + (10-11-12)} = 6 mm / s.

Briquette 29 acquired a density of ρ ₁ = 2.24 g / cm ³ , which was 80% of the theoretical density, the height of the briquette was 112 mm. Axial (P _p ) pressing pressure was 400 MPa, lateral pressure (P _side ) on composite punches (12-13-14) - (15-16-17) was determined from the ratio:

0.2⋅P _ρ ⋅ξ≤P _side ≤0.5⋅P _ρ ⋅ξ

where ξ is the lateral pressure coefficient,

In turn, the lateral pressure coefficient is determined by the formula:

where μ is Poisson's ratio.

For aluminum, the lateral pressure coefficient is taken to be

ξ = 0.51,

whence the lateral pressure range (max, min):

Upon reaching the relative density of 0.8 of the theoretical, the speed of movement of the prefabricated side punches was divided:

- the speed of the lateral central punches 13 and 16 left

ϑ _{(13) + (16)} = 6⋅mm / s;

- the speed of vertical punches ϑ _(10-11) was halved, and amounted to

ϑ _{(10) + (11)} = 3⋅mm / s,

at the same time, uniform braking of the speed of movement of the side punches was carried out in such a way that at the end of the lateral compression of the surfaces of the ends of the side punches (12-13-14) and (15-16-17) they would be aligned with the vertical shear plane of the side channels 8, 9 of the matrix 6 ...

The total speed of movement of axial punches (10-11) in the vertical direction towards each other was determined from the condition of complete filling of the generating channel 7 by the workpiece. This condition is expressed by the law of conservation of masses for an equal time interval Δτ and is written by the equation:

ρ ₁ ⋅ΔS ₀ ⋅ϑ _{(10 + 11)} ⋅Δτ = ρ ₂ ⋅ΔS ₁ ⋅ϑ _{(12-13-14) + (15-16-17) Δτ} ,

where ΔS ₀ is the cross-sectional area of the workpiece in the vertical channel, ΔS ₁ is the cross-sectional area of the workpiece in the horizontal channel, ρ ₁ is the relative density at the beginning of compaction, ρ ₂ is the relative density of the briquette at the end of the compaction, ϑ _{(10 + 11)} is the total speed of movement of axial vertical punches 10 and 11.

Thus, the total speed of movement of axial vertical punches ϑ _{10 + 11} away from the geometric center was determined from the condition:

If the speed of movement of axial vertical punches (ϑ _{10 + 11} ) will exceed

then there will be incomplete filling of channel 7, and the geometry of the product will not correspond to the given shape.

On the other hand, if the speed of the axial punches is less than the obtained expression

then the side channel 8-9 will be completely filled, but the pressing process will not stop, since the speed of movement of the side punches 12-13-14, 15-16-17 decreases.

In this case, the axial punches switch to work according to the "power support" mode, establishing a power balance over the volume of the workpiece. When aligning the working ends of the side punches (12-13-14) and (15-16-17) according to the level of the vertical cut of the side channels 8-9 of the matrix 6, stage No. 2 goes to stage No. 3.

и

The relative density of the briquette at the exit from stage No. 2 was 0.96 of the theoretical, while the height of the briquette H corresponded to the height of the assembled side punch

and

Stage 2 (fig. 6, 7, 8)

The patterns of damage accumulation at the second stage of non-monotonic pressing (compression - tension - shear) are as follows:

- ресурс пластичности, Δε_i - накопленная деформация на i-ом переходе (этапе),

- параметр чувствительности пластичности к напряженному состоянию, J - инвариантный параметр, определяемый выражением:Here

- plasticity resource, Δε _i - accumulated deformation at the i-th transition (stage),

- parameter of sensitivity of plasticity to stress state, J - invariant parameter, determined by the expression:

- косинус угла излома траектории деформации,Where

- cosine of the bend angle of the deformation trajectory,

where the superscript (1, 2) indicates the number of the deformation step.

For the value of the parameter С = 0, expression (9) takes the form

When deforming a porous material under conditions of simple deformation (compression, tension, shear), the following conditions are met:

β _ij = const, D = const, η = const,

The quantity D, like the Lode exponent

(dε ₁ ≥dε ₂ ≥dε ₃ ) characterizes the type of deformations (all-round compression, axial loading or compression-shear), there is an unambiguous relationship:

When determining the ultimate deformations ε _* = ε _* (η), which characterize the critical state of the workpiece material, the test conditions are selected under which the Lode exponent is constant during deformation, μ _ε = const.

The tensor fracture model makes it possible to establish that when the workpiece is deformed by alternating shear carried out sequentially in different planes, the following conditions must be met:

n - количество этапов деформирования;

- направляющий тензор деформации на m-ом этапе деформирования;

- интенсивность деформации на m-ом этапе деформирования; ε_*с - предельная деформация материала заготовки на сдвиг. С учетом выше сказанного закономерности накопления повреждений при немонотонном двухэтапном деформировании (9) можно представить в видеWhere

n is the number of stages of deformation;

- the guiding strain tensor at the m-th stage of deformation;

- the intensity of deformation at the m-th stage of deformation; ε _{* с} - ultimate shear deformation of the workpiece material. Taking into account the above, the regularities of damage accumulation during nonmonotonic two-stage deformation (9) can be represented as

Modeling the process of compaction of the powder mixture made it possible to select the specified ratio of volume-mass-density.

The horizontal planes of the working ends of the vertical lower 11 and upper 10 punches are set according to the level of the corresponding upper and lower planes of the through lateral channel 8-9 of the die 6. Rod drives (20-21-22) of the precast left punch (12-13-14) and rod drives (23-24-25) of the prefabricated right punch (15-16-17) carry out the movement of the precast side punches to the side of the common geometric center by the value Δ equal to the value of the elastic aftereffect of the workpiece material in the cross section.

When the powder briquette 29 reaches a predetermined density, the side punches (12-13-14) and (15-16-17) are simultaneously retracted to the level of the vertical cut of the side channels 8-9 of the matrix 6 (Fig. 7).

Stage 3 (fig. 9)

The calculation of the third stage of non-monotonic deformation (compression-tension-shear) is presented in the form of the equation:

функцию повреждений ϕ можно представить в виде двух разных выражениях:where ψ _u is the intensity of damage;

the damage function ϕ can be represented in the form of two different expressions:

where c, n - experimentally determined parameters of the model; (ε _u ) _m - accumulated deformation by the end of the 2nd stage ((ε _u ) ₀ = 0); (ε _{* с} ) _m is the limiting deformation corresponding to the stress state diagram at the m-th stage; J ₁₂ , J ₁₃ , J ₂₃ are invariant parameters determined by the guiding strain tensors (J _ij is determined by the guiding strain tensors at the i-th and j-th stages) and varying from (-1) to (+1).

Residual resource of plasticity at the second (ψ _{* 2} ) and third (ψ _{* 3} ) stages have the form, respectively:

(ε_*c)_i - предельная деформация материала при стационарном деформировании в условиях, реализованных на i-ом этапе;

- использованный ресурс пластичности на первом этапе (сжатие); ψ₂ - использованный ресурс пластичности на втором этапе; ψ₃ - остаточный ресурс пластичности на третьем этапе.Where

(ε _{* c} ) _i is the ultimate deformation of the material during stationary deformation under the conditions realized at the i-th stage;

- used plastic resource at the first stage (compression); ψ ₂ - used plastic resource at the second stage; ψ ₃ - residual plastic resource at the third stage.

Damage functions (18), (19) can be reduced to the linear principle of damage accumulation at с = 0 and n = 1, and are also identical at

c = 1 and n = 2.

In accordance with the above notation and the use of a quadratic approximation for the damage function (18), the expression for the function F _m takes the following form:

The molded briquette 29 was pushed out of the die 6 by the lower punch 11, while the speed of movement of the lower punch 11 was less than the speed of movement of the upper punch 10 by 5-10%,

ϑ ₁₀ = (0.05-0.1) ⋅ϑ ₁₁

A briquette was obtained with external dimensions of 20.1 × 20.1 × 92.5 mm, with a density of 2.695, which was 99.8% relative to the theoretical density of cast aluminum - ρ _t = 2.7 g / cm ³ .

Metallographic and electron microscopic analysis of the structure of a pilot batch of briquettes showed a high quality of briquettes.

Claims (1)

A device for pressing a cermet powder mixture, containing an upper base with an upper punch placed in it and a lower base with a lower punch placed in it, in the lower base there are side punches made to move towards each other, forming a closed cavity for placing a cermet powder mixture, intended for pressing a briquette, characterized in that each side punch is made composite, consisting of several separate parts in contact with each other, having the possibility of relative movement towards each other, while each part of the composite side punch is equipped with a reciprocating drive.

Images