JP2012000624A - Molding die - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a molding die having good coolability and free from a decline of strength in a small male molding die having a risk of lack of strength to a machining pressure caused by molding since the thickness of the die becomes thin because of a hollow structure such as a flow path for cooling or a heat pipe disposed inside.SOLUTION: An outer circumferential member 2 constituting the outer circumferential part of the molding die 1 and an inner member 3 constituting the inside of the molding die 1 are made to be separate members and are made to be a combination of members where the thermal conductivity and the linear expansion coefficient of the outer circumferential member 2 are smaller than those of the inner member 3. At a temperature during molding of a workpiece, the molding die is so configured that the inner diameter dimension of the outer circumferential member 2 is smaller than the outer diameter dimension of the inner member 3.

Description

  The present invention relates to a forming die, and more particularly, to cooling of a warm forging or hot forging die and improvement of life.

In warm forging and hot forging, the mold is cooled in order to prevent a decrease in life due to a rise in mold temperature and a decrease in accuracy due to thermal expansion. In the cooling method, a passage is formed inside a mold, a cooling fluid is circulated in the passage, and heat of the cooling fluid is removed by a cooling device provided outside.
In addition, there is a conventional technique (see Patent Document 1) in which a large number of heat transfer columns such as heat pipes are embedded in the mold to cool the mold.

JP 2005-138366 A

In the case of a small male mold, if a cooling channel or a hollow structure such as a heat pipe is provided inside, the thickness of the mold becomes thin, and the strength against the processing pressure associated with molding may be insufficient. Therefore, as shown in FIG. 5, the female mold 53 provided with the cooling flow path 54 is sufficiently cooled, but the cooling part 52 of the male mold 51 is arranged at a position away from the molding part of the workpiece W. Therefore, the cooling property of the mold 51 was low.
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a male forging die having good cooling performance and no strength reduction at low cost.

  In order to solve the above-mentioned problem, the invention according to claim 1 is characterized in that, in a male mold for molding a workpiece, an outer peripheral member constituting an outer peripheral portion of the mold and an inside of the mold are formed. The internal member is a separate member, the thermal conductivity of the internal member is made higher than the thermal conductivity of the outer peripheral member, and the surface roughness of the outer peripheral member and the surface roughness of the predetermined heat transfer portion at the contact portion between the outer peripheral member and the internal member The surface roughness of the internal member is set to a predetermined value or less, a contact ratio that is a ratio of the area of the real contact surface of the predetermined heat transfer unit to the apparent area of the predetermined heat transfer unit is set to a predetermined value or more, and the internal member The cooling part is provided at the end opposite to the predetermined heat transfer part.

The invention according to claim 2 is characterized in that, in the invention according to claim 1, the predetermined heat transfer portion is a closed curved surface surrounded by a group of intersections arranged at least continuously.
In the intersection group, a straight line connecting the outer edge portion of the surface portion of the mold, which is in contact with the workpiece when the workpiece is molded, and the contact surface of the outer peripheral member and the inner member intersects the contact surface. It is to make a point.

A feature of the invention according to claim 3 is that, in the invention according to claim 1 or 2, the distance between the cooling part and the predetermined heat transfer part is L (m), and the thermal conductivity of the outer peripheral member is λ1 ( W · m ⁻¹ · k ⁻¹ ), the thermal conductivity of the internal member is λ ₂ (W · m ⁻¹ · k ⁻¹ ), and the thermal conductivity of air is λ ₀ (W · m ⁻¹ · k ⁻¹ ), the surface roughness of the outer peripheral member of the predetermined heat transfer portion is δ ₁ (μmRz), the surface roughness of the inner member of the predetermined heat transfer portion is δ ₂ (μmRz), and the contact When the ratio is η,
170000 · η / ((δ ₁ +23) / λ ₁ + (δ ₂ +23) / λ ₂ ) + 1000000 · λ ₀ / (δ ₁ + δ ₂ )> λ ₁ · λ ₂ / (L · (λ ₂ −λ ₁ )).

A feature of the invention according to claim 4 is that, in the invention according to any one of claims 1 to 3, the linear expansion coefficient of the inner member is larger than the linear expansion coefficient of the outer peripheral member,
The outer peripheral member receives an expansion force due to thermal expansion of the inner member at a predetermined temperature.

  A feature of the invention according to claim 5 is that, in the invention according to claim 4, the predetermined temperature is a temperature of a male mold when the workpiece is molded.

  According to the inventions according to claims 1 to 3, since the heat conduction of the internal member is large, the cooling property is better than the mold manufactured by the external member alone and the temperature of the mold can be lowered. The moldability is improved and the life of the mold is increased.

  According to the inventions according to claims 4 and 5, the compressive force applied to the external member of the mold during molding cancels out the tensile force applied to the external member by the expansion force of the internal member, and therefore the maximum compressive force applied to the external member. Can be reduced. For this reason, the molding pressure can be increased and the productivity is improved.

It is the schematic which shows the cross section of the shaping | molding die of this embodiment. It is the schematic which shows the cross section of shaping | molding using the shaping | molding die of this embodiment. It is a schematic diagram explaining the difference in cooling property. It is the schematic which shows the cross section of shaping | molding using the shaping | molding die of the deformation | transformation aspect of this embodiment. It is the schematic which shows the cross section of shaping | molding using the conventional shaping | molding die.

Hereinafter, embodiments of the present invention will be described with reference to FIGS.
As shown in FIG. 1, the mold 1 has a two-layer structure in which an inner member 3 is disposed inside an outer peripheral member 2, and the inner member 3 is pressed against the outer peripheral member 2 by a push screw 4 and fixed in contact therewith. A liquid chamber 5 is provided at the end of the internal member 3 opposite to the A portion where the workpiece contacts during molding, a supply flow path 6 for supplying a cooling medium to the liquid chamber 5, and a discharge for discharging the cooling medium from the liquid chamber 5. A flow path 7 is provided.
The material of the outer peripheral member 2 is tool steel, and the material of the inner member 3 is a high thermal conductor (copper, aluminum, or an alloy thereof is preferable).

The molding operation of the workpiece W will be described with reference to FIG.
The mold 1 is fixed to the seat plate 9 by the fixture 8 so that the supply channel 6 and the discharge channel 7 are communicated with the channels 91 and 92 of the seat plate 9. The seat plate 9 is supported by the drive shaft 10 so as to reciprocate up and down. A female die 11 is fixed and arranged at the lower part facing the mold 1.
The workpiece W is molded by inserting the material of the workpiece W maintained at a predetermined temperature into the female mold 11 and lowering the molding die 1 to a predetermined position. The molded workpiece W is taken out from the female die 11 by a take-out device (not shown).

The principle of the heat transferability of the above two-layer structure will be described with reference to the schematic diagram of FIG.
The thermal conductivity of the outer peripheral member 21 and lambda _1, the thermal conductivity of the inner member 22 and lambda _2, the heat transfer rate from the outer member 21 to the inner member 22 and h. The workpiece contact portion side is the B end, the cooling side is the C end, and the distance between B and C is L. The heat transfer of the outer member 21 is the temperature of the B-end and T _1, it is assumed that there is no transfer of heat in addition to heat transfer to C from the temperature of the C-terminal and T ₃ B. The heat transfer inside the member 22 is the temperature of the outer member 21 of the B-end and T _1, the temperature of the inner member 22 of the B-end and T _2, the temperature of the C-terminal in addition to heat transfer from the T ₃ B to C Assume that there is no heat transfer.
The heat transfer amount Q ₁ per unit cross-sectional area of the external member 21 is Q ₁ = λ1 · (T ₁ −T ₃ ) / L, and the heat transfer amount Q ₂ per unit cross-sectional area of the internal member 22 is Q ₂ = λ ₂ · (T ₂ −T ₃ ) / L. Further, the heat transfer amount Q ₃ per unit cross-sectional area from the outer member 21 to the inner member 22 in B is Q ₃ = h · (T ₁ −T ₂ ), and in a steady state, Q ₂ = Q _3, so λ ₂ · (T ₂ −T ₃ ) / L = h · (T ₁ −T ₂ ).
The limit at which the heat transfer amount of the internal member 22 having the two-layer structure is larger than that of the integrated member of the external member 21 is Q ₂ ≧ Q ₁ , and λ ₂ · (T ₂ −T ₃ ) / L ≧ λ ₁ · (T ₁ -T ₃₎ / L from _{T 2 ≧ T 3 + (T} 1 -T 3) · λ 1 / λ 2 and may be accustomed. T ₂ is a modification of the formula λ ₂ · (T ₂ −T ₃ ) / L = h · (T ₁ −T ₂ ), and T ₂ = (h · T ₁ + λ ₂ · T ₃ / L) / (λ ₂ / L + h) (h · T ₁ + λ ₂ · T ₃ / L) / (λ ₂ / L + h) ≧ T ₃ + (T ₁ −T ₃ ) · λ ₁ / λ ₂ is the heat of the internal member 22 This is an expression indicating a condition that the transmission amount is larger than that of the integrated member of the external member 21. By arranging the formula for h, h ≧ λ ₁ · λ ₂ / (L · (λ ₂ −λ ₁ )). If the heat transfer coefficient from the external member 21 to the internal member 22 is h represented by this formula, 2 The heat transfer of the layer structure is larger than that of the unitary structure.

Here, it is known that the heat transfer coefficient h at the contact surfaces of the two solids is represented by the following equation.
The air thermal conductivity is λ ₀ , the surface roughness of the outer peripheral member 21 is δ ₁ , the surface roughness of the internal member 22 is δ _2, and the true contact of the predetermined heat transfer portion with respect to the apparent area of the predetermined heat transfer portion When the contact ratio, which is the ratio of the area of the surface, is η, the heat transfer coefficient h at the contact surface is
It is known that h = 170000 · η / ((δ ₁ +23) / λ ₁ + (δ ₂ +23) / λ ₂ ) + 1000000 · λ ₀ / (δ ₁ + δ ₂ ).
Here, when the two surfaces with fine irregularities are in contact, the convex portions are in contact with each other, and the concave portion is in a gap state and does not come into contact. The total sum of the areas of the actually contacting convex portions at this time is true Let the area of the contact surface be the apparent area of the sum of the areas of the recesses that are not in contact with the sum of the real contact areas.

From the above, the expression 170000 · η / ((δ ₁ +23) / λ ₁ + (δ ₂ +23) / λ ₂ ) + 1000000 · λ ₀ / (δ ₁ + δ ₂ ) ≧ λ ₁ · λ ₂ / (L · (λ ₂₋ λ ₁ )), the surface roughness δ ₁ and the thermal conductivity λ ₁ of the outer peripheral member 21, the surface roughness δ ₂ and the thermal conductivity λ _{2 of} the inner member 22, the workpiece molding part and the cooling If the distance L of the part and the contact ratio η of the true contact surface are selected, the cooling effect of the mold having the two-layer structure becomes higher than that of the one-piece.

Below, based on FIG. 1, the operation function of a present Example is demonstrated in detail about the example which used tool steel for the outer peripheral member 2 and used copper for the internal member 3. FIG.
First, the improvement in cooling performance will be described. Λ ₁ of the tool steel at a temperature of 800 k is 34 (W · m ⁻¹ · k ⁻¹ ), and the linear expansion coefficient is 14 × 10 ⁻⁶ (k ⁻¹ ). The λ ₁ of copper at a temperature of 800 k is 370 (W · m ⁻¹ · k ⁻¹ ), and the linear expansion coefficient is 20 × 10 ⁻⁶ (k ⁻¹ ). L is 0.03 (m), λ ₀ is 0.05 (W · m ⁻¹ · k ⁻¹ ), the outer member has a surface roughness δ ₁ of 30 (μmRz), and the inner member has a surface roughness δ ₂ . If 30 (μmRz), 170000 · η / 1.675 + 1000 ≧ 1248.016. If the equation is arranged, if η ≧ 0.0041, the cooling effect is higher than that of the single body. L is a distance from the upper end of the workpiece contact portion to the cooling portion as shown in FIG.
Here, it is known that η = 0.6 · P / H when the contact ratio η is the pressing pressure of the contact member is P (Mp) and the hardness of the soft material is H (Hv). 0.6 · P / H ≧ 0.0041. When H of copper is 50 (Hv), P ≧ 0.34 (Mp), and the required contact ratio η can be realized by pressing the copper inner member against the outer member with a pressure of 0.34 Mp or more.

Next, the effect | action which reduces the compressive force which acts on the outer peripheral member 2 by shaping | molding pressure is demonstrated.
In a state where the workpiece is not molded, the outer peripheral member 2 is given an expansion force by the inner member 3 and a tensile stress acts, and the inner member 3 determines the mutual dimension so that the reaction compressive stress acts. In FIG. 1, it demonstrates concretely by the dimension of D part.
_{Let TL be} the minimum temperature when molding a workpiece, and TH be the maximum temperature. If the inner diameter dimension of the outer peripheral member 2 is E and the outer dimension of the inner member 3 is F when the temperature is _TL in a state where they are not combined with each other, E ≦ F is set. When the temperature of the outer member 2 is the average linear expansion coefficient from T _L to T _H and alpha _1, the temperature of the inner member 3 is the mean linear expansion coefficient from T _L to T _H and alpha _2, the maximum temperature T _H when, the inner diameter of the outer member 2 dimensions of _{E · α 1 · (T H} -T L) , and the inner member 3 is the _{F · α 2 · (T H} -T L). Therefore, an increase in interference (diameter) due to the temperature rise becomes _{(F · α 2 -E · α} 1) · (T H -T L). The maximum temperature _TH is set so that the tensile stress acting on the outer peripheral member 2 due to the increase in the tightening margin does not exceed the allowable stress of the outer peripheral member 2.
By setting the inner diameter dimension of the outer peripheral member 2 and the outer dimension of the inner member 3 as described above, it is possible to reduce the compressive stress to the outer peripheral member 2 that acts during workpiece molding.

  In the above embodiment, an example in which tool steel is used for the external member has been described, but materials other than metals such as ceramics may be used.

<Deformation of this embodiment>
In the above embodiment, the structure in which the cooling medium is circulated in the liquid chamber 4 has been described, but the present invention is not limited to this.
As shown in FIG. 4, the cooling may be performed by bringing the cooling end of the internal member 33 into contact with the base 8 and releasing heat to the base 8 side. When the workpiece W is small and the amount of heat to be cooled is small, the effect can be obtained with this structure.

1: Mold 2: External member 3: Internal member 4: Push screw 5: Liquid chamber 6: Supply flow path 7: Discharge flow path 8: Fixing tool 9: Base 10: Drive shaft 11: Female mold

Claims (5)

  In the male mold for molding a workpiece, an outer peripheral member constituting the outer peripheral portion of the mold and an inner member constituting the inner part of the mold are separated from each other, and the inner member is formed by heat conduction of the outer peripheral member. The heat conductivity is increased, and the surface roughness of the outer peripheral member and the surface roughness of the inner member in the predetermined heat transfer portion of the contact portion between the outer peripheral member and the inner member are set to a predetermined value or less, and the predetermined heat transfer portion A molding die in which a contact ratio, which is a ratio of an area of a real contact surface of the predetermined heat transfer portion to an apparent area, is equal to or greater than a predetermined value, and a cooling portion is provided at an end opposite to the predetermined heat transfer portion of the internal member. The predetermined heat transfer portion is a closed curved surface surrounded by a group of intersections lined up at least continuously,
In the intersection group, a straight line connecting the outer edge portion of the surface portion of the mold, which is in contact with the workpiece when the workpiece is molded, and the contact surface of the outer peripheral member and the inner member intersects the contact surface. The mold according to claim 1, which is a point. The distance between the cooling unit and the predetermined heat transfer unit is L (m), the thermal conductivity of the outer peripheral member is λ1 (W · m ⁻¹ · k ⁻¹ ), and the thermal conductivity of the inner member is λ _2. (W · m ⁻¹ · k ⁻¹ ), the thermal conductivity of air is λ ₀ (W · m ⁻¹ · k ⁻¹ ), and the surface roughness of the outer peripheral member of the predetermined heat transfer portion is δ _1. (ΜmRz), when the surface roughness of the internal member of the predetermined heat transfer portion is δ ₂ (μmRz), and the contact ratio is η,
170000 · η / ((δ ₁ +23) / λ ₁ + (δ ₂ +23) / λ ₂ ) + 1000000 · λ ₀ / (δ ₁ + δ ₂ )> λ ₁ · λ ₂ / (L · (λ ₂ −λ ₁ The mold according to claim 1 or 2, wherein: The linear expansion coefficient of the inner member is larger than the linear expansion coefficient of the outer peripheral member,
The mold according to any one of claims 1 to 3, wherein the outer peripheral member receives an expansion force due to thermal expansion of the inner member at a predetermined temperature.   The mold according to claim 4, wherein the predetermined temperature is a temperature of a male mold when the workpiece is molded.

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