JP5502670B2 - Piston casting method - Google Patents

Description

  The present invention relates to a piston casting method in which a composite reinforcing material for strengthening a head portion is combined with the top portion of the head portion.

  As a method for casting such a piston, for example, as disclosed in Patent Document 1 below, a composite reinforcing material is placed on the bottom of a cavity of a mold, a molten metal is injected into the cavity, and the molten metal is added from above by a punch mold. A high-pressure casting method is known in which a piston is molded while pressing the molten metal into a composite reinforcing material.

Japanese Patent No. 2881152

  In the conventional casting method of such pistons, when the molten metal is pressed by the punch mold, the punch mold pressure acts directly on the composite reinforcement, causing damage to the composite reinforcement, or chilling the molten metal in the cavity. There is a risk of being contained in the molten metal.

  The present invention has been made in view of such circumstances, and it is possible to effectively infiltrate and compound the molten metal without damaging the composite reinforcing material installed on the bottom surface of the mold cavity. An object of the present invention is to provide a piston casting method capable of avoiding the containment of the chilled product in the molten metal of the cavity and obtaining the high-quality piston.

  In order to achieve the above-described object, the present invention provides a method for forming a composite piston on a bottom surface of a cavity formed in a mold when casting a piston formed by combining a composite reinforcing material for reinforcing a head portion at the top of the head portion. Reinforcing material is installed, and the mold includes a plurality of gates that open to the bottom surface of the cavity at the outer side in the radial direction of the composite reinforcing material and face the ceiling surface of the cavity, and the cavity at positions facing these gates. There are a plurality of overflow outlets opening in the ceiling surface of the main body, and an overflow pool connected to the overflow outlet. By injecting the molten metal from the gate toward the overflow outlet, the molten metal that has first passed through the cavity is removed. After discharging from the overflow outlet, the molten metal is infiltrated into the composite reinforcing material while being pressurized and filled into the cavity. It is a feature of the.

  According to the present invention, in addition to the first feature, a core pin that forms a hole in a pin boss portion of a piston is installed in the cavity, and the molten metal from the gate is avoided by avoiding the core pin. The second feature is that it is directed to the overflow outlet.

  In addition to the first feature of the present invention, an auxiliary cavity extending downward from the center of the bottom surface of the cavity is formed in the mold, and after the molten metal is pressurized and filled into the cavity and the auxiliary cavity, The third feature is that the molten metal in the auxiliary cavity is secondarily pressurized.

  Furthermore, in addition to the first feature, the present invention further includes a soluble core that forms a cooling oil passage in the head portion is placed on the upper portion of the composite reinforcing material installed on the bottom surface of the cavity, and the piston A fourth feature is that when the upper mold forming the hollow portion is closed, the soluble core is pressed together with the composite reinforcing material by a plurality of support pins that slidably pass through the upper mold.

  Furthermore, in addition to the first feature, the present invention has a fifth feature that the cavity is decompressed by supplying a vacuum pressure before the molten metal is injected from the gate into the cavity.

  According to the first aspect of the present invention, the first molten metal injected from the runner into the cavity is first passed through the cavity toward the overflow outlet and exits into the overflow pool. Therefore, even if a chilled product is generated in the first molten metal, the chilled product also passes through the cavity along with the flow of the molten metal, exits the overflow outlet, and is trapped in the overflow pool. Subsequently, the molten metal injected from the gate fills the cavity and covers the composite reinforcing material over the inner and outer peripheral surfaces, so that the molten metal penetrates well without damaging the composite reinforcing material as the molten metal pressure rises. In addition, it is possible to obtain a high-quality piston that is well compounded with the composite reinforcing material and the head portion is effectively reinforced with the composite reinforcing material.

  According to the 2nd characteristic of this invention, it can avoid that the flow of the molten metal which goes to an overflow exit from a gate contacts a core pin, and can contribute to ensuring of durability of a core pin.

  According to the third aspect of the present invention, after the molten metal is pressurized and filled into the cavity and the auxiliary cavity, the molten metal in the auxiliary cavity is secondarily pressurized, thereby increasing the density of the molten metal and the composite reinforcing material. It is possible to promote the penetration of the molten metal into the metal, and thus to obtain a highly durable piston having a high density and having the head portion effectively strengthened by the composite reinforcing material.

  According to the fourth feature of the present invention, when the upper die is closed, the soluble core is held together with the composite reinforcing material by a plurality of support pins that slidably pass up and down the upper die. During filling of the molten metal, the composite reinforcing material and the soluble core can be securely held at the fixed positions on the bottom surface of the cavity, and the displacement can be prevented. In addition, an annular cooling oil passage can be formed in the piston by melting and discharging the soluble core through the oil hole of the piston formed by the support pin after casting.

  According to the fifth aspect of the present invention, before the molten metal is injected from the gate into the cavity, the cavity is depressurized by supplying a vacuum pressure, whereby the chilled product generated in the molten metal at the initial injection is discharged to the overflow pool. At the same time, the quality of the casting piston can be further improved by preventing the molten metal filled in the cavity from being oxidized.

The side view of the piston for diesel engines which concerns on one Embodiment of this invention. FIG. 2 is a sectional view taken along line 2-2 in FIG. 1. FIG. 3 is a view taken in the direction of arrow 3 in FIG. The longitudinal cross-sectional view of the metal mold | die used for casting of the said piston. FIG. 5 is a sectional view taken along line 5-5 of FIG. FIG. 6 is a sectional view taken along line 6-6 in FIG. FIG. 7 is a cross-sectional view taken along line 7-7 in FIG. FIG. 8 is a cross-sectional view taken along line 8-8 in FIG. 4. FIG. 9 is a sectional view taken along line 9-9 in FIG. 4.

  First, a piston for a diesel engine cast according to the present invention will be described.

  As shown in FIGS. 1 to 3, a piston P for a diesel engine is made of an Al alloy and protrudes integrally with a head portion 1 having a plurality of ring grooves 1 a to 1 c on the outer periphery and a lower surface of the head portion 1. A pair of pin bosses 2, 2 that are provided and are arranged coaxially across the piston center axis, and a skirt 3 that extends from the peripheral edge of the lower end of the head portion 1 and connects both sides of the pair of pin bosses 2, 2 A chamber 4 into which fuel is injected during operation of the engine is formed at the center of the top surface of the head portion 1, and an annular, porous, for example, ceramic composite surrounding the chamber 4 The reinforcing material 5 is combined and bonded to the top of the head portion 1. The composite reinforcing material 5 reinforces the head portion 1 by combining with the base material of the piston P penetrating therethrough, that is, an Al alloy.

  The head portion 1 includes an annular cooling oil passage 7 adjacent to the lower end of the composite reinforcing material 5, and a pair of oil holes 8, 8 that open the cooling oil passage 7 to the lower surface of the head portion 1. Formed. The pair of oil holes 8, 8 are arranged apart from each other on one diameter line of the piston P. In the illustrated example, the uppermost ring groove 5 a is formed on the outer periphery of the composite reinforcing material 5. In the cooling oil passage 7, engine lubricating oil enters and exits through the oil holes 8, 8 during operation of the engine, whereby the piston 1, in particular, the head portion 1 is cooled.

  The shape of the piston P after casting is shown by a chain line in FIGS. As is clear from this, predetermined shaving allowances S1 and S2 are provided on the outer periphery of the piston P after casting, and the shaving allowance S1 on the outer periphery of the head portion 1 is the shaving allowance S2 on the outer periphery of the skirt portion 3. It is set larger. After casting, the piston P is formed by cutting the portions of the machining allowances S1 and S2. At that time, when the cutting allowance S1 is cut, the outer peripheral surface of the composite reinforcing material 5 is exposed.

  Next, a mold for casting the piston P will be described.

  In FIG. 4, the mold M advances and retreats from above the first side mold 11 and the second side mold 12 that open and close in the horizontal direction, and from above the first side mold 11 and the second side mold 12. The upper mold 13, the lower mold 14 that advances and retreats from below the first lateral mold 11 and the second lateral mold 12, and the first lateral mold 11 and the second lateral mold 12 are respectively horizontal. It comprises a first core pin 15 and a second core pin 16 (see FIG. 7) supported so as to be slidable in the direction, and one of the first side mold 11 and the second side mold 12 is Fixed type, the other is movable type. The mold M constituted by these is formed with a cavity 10 having a shape corresponding to an inverted state of the piston P with the head portion 1 facing downward when the mold M is closed. That is, the inner peripheral surface facing the cavity 10 of the first side mold 11 and the second side mold 12 corresponds to the outer peripheral surface of the piston P, and the lower end surface and the outer peripheral surface facing the cavity 10 of the upper mold 13 are the head portion 1. Corresponding to the inner peripheral surface of the skirt portion 3 and the outer peripheral surface of the first core pin 15 and the second core pin 16 facing the cavity 10 are the inner peripheral surfaces of the holes of the pair of pin boss portions 2 and 2. Correspond.

  The upper end surface of the lower mold 14 facing the cavity 10 corresponds to the top surface of the head portion 1. That is, the lower mold 14 is formed with a hollow cylindrical projection 14a corresponding to the chamber 4 of the head portion 1, and the hollow portion of the cylindrical projection 14a communicates with the cavity 10 and has a smaller volume than the cavity 10. Auxiliary cavity 10a. The lower mold 14 is provided with a cylinder hole 17 connected to the lower end of the auxiliary cavity 10a, and a secondary pressure piston 18 that can move forward and backward with respect to the auxiliary cavity 10a is slidably fitted into the cylinder hole 17. The

  As shown in FIGS. 4 and 5, the lower part between the mating surfaces of the first side mold 11 and the second side mold 12 is connected to a main runner 20 that communicates with a pouring port (not shown), and communicates with the main runner 20. An annular runner 21 surrounding the lower mold 14 and a plurality of gates 22, 22... Standing from the annular runner 21 along the lower mold 14 and opening on the bottom surface of the cavity 10 are provided. These gates 22, 22... Are arranged so as to open to the cavity 10 in the range of the shaving allowance S <b> 1 on the outer periphery of the head portion 1 in order to avoid the annular composite reinforcing material 5 installed at a predetermined position on the bottom surface of the cavity 10. The However, the first and second core pins 15 and 16 are disposed so as to avoid a position directly below (see FIG. 7).

  As shown in FIGS. 4, 8, and 9, the upper portion between the mating surfaces of the first side mold 11 and the second side mold 12 rises from the ceiling surface of the cavity 10 along the upper mold 13. A plurality of overflow outlets 23, 23..., An annular overflow passage 24 that surrounds the upper mold 13 while communicating with the upper ends of the overflow outlets 23, 23..., And an overflow that extends from the annular overflow passage 24 to one side. A reservoir 25 is provided.

  A gas venting device V is connected to the overflow reservoir 25. The degassing device V includes a vacuum passage 31 extending upward from the overflow reservoir 25, a vacuum tank 32 connected to the vacuum passage 31, a vacuum pump 33 for accumulating a vacuum pressure in the vacuum tank 32, a vacuum It comprises a control valve 34 that controls the opening and closing of the passage 31. The control valve 34 is a normally closed type and automatically operates in accordance with the position of a primary pressurizing piston (not shown) that pumps the molten metal 30 to the main runner 20. However, the valve is opened at a position where the molten metal 30 starts to be fed to the main runner 20, and is closed at a position where the molten metal 30 fills the overflow pool 25.

  Further, the upper die 13 is provided with a pair of support pins 27, 27 that pass through the upper die 13 slidably up and down, and these support pins 27, 27 correspond to the pair of oil holes 8, 8 of the piston P. Placed in position.

  Now, a method for casting the piston P using the mold M will be described.

  First, as shown in FIG. 4, the lower mold 14 is raised to a predetermined closed position, and the first side mold 11 and the second side mold 12 are closed so as to sandwich the lower mold 14. The upper mold 13 retreats the upper side of the first side mold 11 and the second side mold 12 to open the upper surface of the cavity 10.

  Next, the annular composite reinforcing material 5 is fitted on the outer peripheral surface of the cylindrical projection 14a of the lower mold 14 and installed on the bottom surface of the cavity 10, and the outer periphery of the small diameter portion 5c of the composite reinforcing material 5 is An annular soluble core 28 corresponding to the annular cooling oil passage 7 of the piston P, specifically, a salt core 28 is fitted and installed.

  In this state, after lowering the upper mold 13 to the closed position in the first side mold 11 and the second side mold 12, the pair of support pins 27, 27 are also lowered, and the lower ends thereof are salted. Press the core 28. Thus, the composite reinforcing material 5 is pressed against the bottom surface of the cavity 10 via the salt core 28 and held.

  Finally, the first core pin 15 and the second core pin 16 are advanced with respect to the upper mold 13, and the tips thereof are brought into close contact with the side surface of the upper mold 13.

  Next, the Al alloy melt 30 is pumped to the main runner 20 by the operation of a primary pressurizing piston (not shown). The position of the primary pressurizing piston immediately before the pumping is started is detected and the control valve 34 is detected. Is opened, the vacuum passage 31 is made conductive, and the vacuum pressure in the vacuum tank 32 is transmitted to the overflow reservoir 25 and the cavity 10 to depressurize the interior. As a result, the gas remaining in the cavity 10 is sucked into the vacuum tank 32 and discharged from the vacuum pump 33 to the outside. Therefore, the pressure reduction of the cavity 10 needs to be performed at least before the molten metal 30 reaches the cavity 10.

  Thereafter, the molten metal 30 is injected into the annular runner 21 through the main runner 20 and further into the cavity 10 from the plurality of gates 22, 22. At this time, the reduced pressure of the cavity 10 facilitates the inflow of the molten metal 30 into the cavity 10.

  Incidentally, as described above, the plurality of gates 22, 22... Are arranged so as to open to the cavity 10 in the range of the cutting allowance S1 on the outer periphery of the head portion 1 in order to avoid the annular composite reinforcing material 5. Are opened at positions corresponding to the plurality of gates 22, 22... So that the first molten metal 30 injected from the gates 22, 22. Upon receiving the pressure, the cavity 10 is smoothly passed through to the overflow outlets 23, 23..., Exits and stored in the overflow reservoir 25. The position of the primary piston at this time is sensed, the control valve 34 is closed, the vacuum passage 31 is shut off, and the molten metal 30 is prevented from entering the vacuum passage 31.

  Thus, even if a chilled product is generated in the molten metal while the first molten metal passes through the relatively cool main runner 20 and annular runner 21, the chilled product passes through the cavity 10 together with the flow of the molten metal. , Overflow outlets 23, 23... In particular, the pressure reduction of the cavity 10 promotes the discharge of the chilled product into the overflow pool 25 and suppresses the oxidation of the molten metal filled in the cavity as much as possible, thereby further improving the quality of the casting piston P. Can contribute.

  Also, the gates 22, 22 ... and the overflow outlets 23, 23 ... are arranged so as to avoid the first and second core pins 15, 16, so the molten metal 30 from the gates 22, 22 ... to the overflow outlets 23, 23 ... Can be prevented from coming into contact with the first and second core pins 15, 16, which can contribute to ensuring the durability of the core pins 15, 16.

  Subsequently, the molten metal injected from the gates 22, 22... Fills the cavity 10 and the auxiliary cavity 10a and covers the composite reinforcing material 5 over the entire inner and outer peripheral surfaces thereof. As the pressure rises, the molten metal 30 penetrates well into the porous composite reinforcing material 5 without damaging it, and can be combined well with the composite reinforcing material 5. Meanwhile, the composite reinforcing material 5 and the salt core 28 are pressed against a fixed position on the bottom surface of the cavity 10 by the pair of support pins 27, 27, and are reliably prevented from moving from that position.

  Next, while the primary piston is in an activated state, the molten metal 30 in the auxiliary cavity 10a is pressurized again by the operation (raising) of the secondary pressure piston 18. Thereby, while increasing the density of the molten metal 30, the penetration of the molten metal 30 into the composite reinforcing material 5 can be promoted.

  After the melt 30 in the cavity 10 and the auxiliary cavity 10a is solidified, the support pins 27 and 27, the first and second core pins 15 and 16, the upper mold 13, the lower mold 14, the first side mold 11 and the first The two side molds 12 are sequentially retreated, the cavity 10 is opened, the casting piston P is taken out, unnecessary runner moldings and burrs at each part are removed, and then one oil molded by the support pins 27 and 27 A dissolved cleaning liquid (for example, water) is injected into the hole 8 to dissolve the annular salt core 28, and the other salt 8 is discharged. Thus, an annular cooling oil passage 7 is formed in the head portion 1.

  Finally, the casting piston P is cut as described above to obtain the piston P shown in FIGS. Thus, it is possible to efficiently cast a piston P that does not contain a chilled product, has the composite reinforcing material 5 firmly bonded to the head portion 1, and has a high density and high durability.

  The present invention is not limited to the above embodiment, and various design changes can be made without departing from the scope of the invention. For example, a plurality of main runners 20 communicating with a common pouring port can be formed radially, and a plurality of cavities 10 communicating therewith can be arranged to obtain a plurality of casting pistons P.

P ··· Piston M ··· Die 1 ··· Head portion 2 ··· Pin boss portion 3 ··· Skirt portion 5 ··· Composite reinforcement 10 · ... Cavity 10a ... Auxiliary cavity 13 ... Upper molds 15, 16 ... Core pins (first and second core pins)
22 ... Gate 23 ... Overflow outlet 25 ... Overflow reservoir 27 ... Support pin 28 ... Soluble core 30 ... Molten metal

Claims (5)

In casting a piston formed by combining a composite reinforcing material (5) for reinforcing the head portion (1) at the top of the head portion (1),
The composite reinforcing material (5) is installed on the bottom surface of the cavity (10) formed in the mold (M), and the mold (M) has the composite reinforcing material (5) in the radial direction outside the composite reinforcing material (5). A plurality of gates (22) that open to the bottom surface of the cavity (10) and face the ceiling surface of the cavity (10), and a plurality of gates that open to the ceiling surface of the cavity (10) at positions facing these gates (22). An overflow outlet (23) and an overflow pool (25) connected to the overflow outlet (23) are provided, and the molten metal (30) is injected from the gate (22) toward the overflow outlet (23). The molten metal (30) that first passed through the cavity (10) is discharged from the overflow outlet (23), and then the molten metal (30) is pressurized and filled in the cavity (10). And wherein the infiltrating composite reinforcement (5), a piston casting methods. The method for casting a piston according to claim 1,
In the cavity (10), a core pin (15, 16) that forms a hole in the pin boss portion (2) of the piston (P) is installed, and an injection molten metal from the gate (22) is supplied to the core pin. (15, 16) The piston casting method is characterized in that the piston is directed toward the overflow outlet (23). The method for casting a piston according to claim 1,
An auxiliary cavity (10) extending downward from the center of the bottom surface of the cavity (10) is formed in the mold (M), and the molten metal (30) is formed into the cavity (10) and the auxiliary cavity (10). A method for casting a piston, characterized by subjecting the molten metal (30) in the auxiliary cavity (10) to secondary pressure after being pressurized and filled. The method for casting a piston according to claim 1,
A soluble core (28) forming a cooling oil passage (7) in the head portion (1) is placed on the upper part of the composite reinforcing material (5) installed on the bottom surface of the cavity (10), When the upper mold (13) that forms the hollow portion of the piston (P) is closed, the soluble core (28) is provided by a plurality of support pins (27) that slidably pass through the upper mold (13). ) Together with the composite reinforcing material (5). The method for casting a piston according to claim 1,
A method for casting a piston, wherein the cavity (10) is depressurized by supplying a vacuum pressure before the molten metal (30) is injected from the gate (22) into the cavity (10).

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