JPH07268406A - Piston manufacturing method and apparatus - Google Patents

Abstract

(57) [Summary] [Purpose] In order to manufacture a highly reliable piston with little variation in strength as a whole and no defects in strength, in consideration of the shape of the piston, plasticity is applied at each part in the green compact. Be able to force flow. [Structure] A recess 8 is provided at the center of the upper surface, an annular projection 9 is provided at the outer peripheral edge of the recess 8, and the height is lower than the step surface 10 and the projection 9 formed of the outer peripheral surface of the projection 9. Using a lower mold 4 having a molded outer peripheral surface 11 and an upper mold 5 having a convex portion 12 on the lower surface and a projecting portion 13 at the center of the lower surface of the convex portion 12 to be processed The flat lower surface 1b of the green compact 1 is placed on the projecting portion 9 of the lower mold 4, and the concave portion 2 formed at the central portion of the upper surface 1a of the green compact 1 is projected on the upper mold 5. By placing the green compact 1 corresponding to the portion 12 and pressing the green compact 1 between the lower mold 4 and the upper mold 5 in a high temperature state, a plastic flow in the green compact 1 is forcibly generated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for manufacturing a piston for an internal combustion engine from a powder compact (preform), and more specifically, a powder using an upper mold and a lower mold. The present invention relates to a manufacturing method and a manufacturing apparatus for molding a piston from a green compact by a forging method.

In the present specification, "powder" means
Al-based composite material powders (including mixed powders of aluminum and ceramics) obtained by adding ceramics as reinforcing particles to conventional aluminum alloy powders, rapidly solidified powders, and powders for various intermetallic compound dispersion strengthened aluminum alloys. To do.

[0003]

2. Description of the Related Art It has been reported that a piston shape is directly obtained by conventionally known powder forging without going through a material manufacturing process by hot extrusion from aluminum alloy powder or the like. Thus, if the piston shape is directly obtained by the conventionally known powder forging, the hot extrusion step can be omitted, and the advantage that the piston manufacturing step can be simplified and the manufacturing cost can be reduced can be achieved. is there.

[0004]

However, in the past, no proposals have been made regarding the shape of powder compacts (preforms) used as raw materials and the features of the structure of molds used for molding pistons. The reality is that they do not.

Under these circumstances, a general cylindrical green compact is used as a raw material and has a pressing surface having a shape suitable for casting (a shape corresponding to the shape of the piston to be manufactured). I have no choice but to use molds and lower molds,
In this case, the following problems have been confirmed by trial manufacture experiments.

That is, a cylindrical green compact 50 as shown in FIGS. 11A and 11B is placed on the flat upper surface 51a of the lower mold 51 as shown in FIG. Lower surface (pressing surface) with a simple step shape that matches the shape of the piston that should be
By operating the upper die 52 having 52a and press-molding under high temperature, the piston 53 having a predetermined shape (see FIG.
3) is produced, there will be a region where plastic flow does not occur at all during pressing and a region where plastic flow occurs remarkably.

Specifically, while plastic flow occurs in the direction indicated by the arrow in FIG. 13 and plastic flow occurs in an amount proportional to the length of the arrow, it substantially occurs in the area indicated by cross hatching α in FIG. Since no plastic flow occurs at all, a plurality of regions indicated by cross hatching α are present as defective portions. That is, when a material is obtained from a powder based on aluminum, it is necessary to give a plastic flow that crushes a strong oxide film covering the surface of the powder. If it does not flow, the strength is significantly reduced and it becomes a defective portion.

For this reason, the strength of the piston 53 obtained by the above-described method and apparatus greatly differs depending on each part and cannot be put to practical use.

The present invention has been made in view of the above circumstances, and an object thereof is to manufacture a highly reliable piston having little variation in strength and no defect in strength. SUMMARY OF THE INVENTION It is an object of the present invention to provide a method and an apparatus for manufacturing a piston in which plastic flow can be forcibly generated at each site in the green compact in consideration of the shape of the piston.

[0010]

In order to achieve the above-mentioned object, in the method of manufacturing a piston according to the present invention, a recess is provided at the center of the upper surface, and an annular protrusion is provided at the outer peripheral edge of the recess. A lower mold having a stepped surface formed of the outer peripheral surface of the protrusion and an outer peripheral surface formed to be lower than the protrusion, and a protrusion on the lower surface and protruding at the center of the lower surface of the protrusion. And a flat lower surface of the green compact, which is an object to be processed, is placed on the protrusion of the lower metal mold, and is formed at the center of the upper surface of the green compact. By arranging a concave portion corresponding to the convex portion of the upper mold, and pressing the green compact between the lower mold and the upper mold at a high temperature,
A plastic flow in the green compact is forcibly generated.

Further, in the method of manufacturing a piston according to the present invention, a step portion is formed which has a recessed portion at the center of the upper surface, an annular protrusion at the outer peripheral edge of the recessed portion, and an outer peripheral surface of the protrusion. A lower die having a surface and an outer peripheral surface formed lower than the protrusion, and an upper die having a protrusion on the lower surface and having a protrusion at the center of the lower surface of the protrusion,
The flat lower surface of the green compact which is the object to be processed is placed on the protrusion of the lower mold, and the concave portion formed at the center of the upper surface of the green compact is used as the convex portion of the upper mold. Correspondingly arranged, the green compact is pressed at a high temperature between the lower mold and the upper mold,
At this time or immediately thereafter, a pair of push pins are pressed and inserted into a side portion of the side surface of the green compact corresponding to the piston pin insertion hole in a part of the thickness of the side portion, so that To form the recess and mold the piston material,
After that, the piston pin insertion hole connected to the recess formed on the side surface of the piston molding material is cut.

Further, the piston manufacturing apparatus according to the present invention comprises: (A) a hollow portion provided at a central portion of the upper surface, and a flat shape of a green compact which is provided at an outer peripheral edge portion of the hollow portion and is an object to be processed. A lower die having an annular protrusion on which the lower surface is placed, a step surface formed by the outer peripheral surface of the protrusion, and an outer peripheral surface that is continuous with the step surface at a position lower than the protrusion, B) An upper mold having a convex portion provided at the center of the lower surface and press-fitted into a concave portion formed at the central portion of the upper surface of the green compact, and a protruding portion provided at the central portion of the lower surface of the convex portion, C) An outer peripheral die disposed opposite to the outer peripheral surface of the green compact placed on the protrusion of the lower die, respectively.

Further, in the piston manufacturing apparatus according to the present invention, insertion holes are provided in the outer peripheral mold at positions facing each other, and a pair of push pins are slidably arranged in these insertion holes. There is.

[0014]

By the use of the specially shaped powder compact, the upper mold and the lower mold as described above, the powder compact can be directly obtained when the piston shape is directly obtained without the raw material manufacturing process by hot extrusion. When the body is molded (when pressed under a high temperature condition), plastic flow in the green compact is fully generated throughout the entire body, and there are few partial defects and the strength of each part is almost uniform. The piston is obtained.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described below with reference to FIGS.
Will be described in detail with reference to.

FIG. 1 shows a green compact (preform) 1 as a piston material used in this example. The green compact 1 is a lightweight and high strength intermetallic compound dispersion strengthened aluminum. It is composed of alloy powder, aluminum alloy powder in which a precursor composite of an intermetallic compound is compounded, and the like.

Specific examples of the material of the green compact 1 include the materials 1 to 5 shown in Table 1 below.

[0018]

[Table 1]

As shown in Table 1 above, in this example,
Compared with alloys (AC9A, A2218-T6, etc.) that have been generally used as piston materials, materials having excellent physical properties such as strength, Young's modulus, and coefficient of linear expansion are used. . In particular, the material using Al ₃ Ti as the dispersion strengthening particles has a low room temperature strength, but it is recognized that the strength is remarkably improved and maintained from 300 ° C. or higher. Also, Mg
The material to which Si is applied is characterized by remarkable high strength and low specific gravity in the temperature range from room temperature to 400 ° C. Furthermore, the one containing 30 wt% of MgSi is
It is known that the linear expansion coefficient is as low as 16.7 × 10 ⁻⁶ / ° C.

In molding the green compact 1 with such a material, a special shape is used instead of the conventional cylindrical shape. In this example, when the piston head part is on the lower side and the skirt part is on the upper side, press molding is performed.
As shown in FIGS. 1A and 1B, a concave portion 2 is formed at the center of one end surface (upper surface) 1a of a cylindrical shape, and the other end surface (lower surface) 1b is formed flat. The specific shape of the recess 2 is a bottomed cylindrical shape having a cylindrical surface 2a and a circular bottom surface 2b.

On the other hand, as shown in FIG. 2, a piston manufacturing apparatus 3 for manufacturing a piston by press-molding the green compact 1 under a high temperature condition, as shown in FIG. An upper die 5 and an outer die 6 arranged to face the outer circumferential surface 1c of the green compact 1 are provided.

The pressing surfaces of the lower mold 4 and the upper mold 5, that is, the upper surface 4a of the lower mold 4 and the lower surface 5a of the upper mold 5 have a special shape.

First, as shown in FIGS. 2 and 3, on the upper surface 4a of the lower mold 4, a circular recess 8 is provided at the center thereof, and at the outer peripheral edge of the recess 8. The annular projection 9 on which the flat lower surface 1b of the green compact 1 that is the object to be processed is placed, the step surface 10 formed by the outer peripheral surface of the projection 9, and the step surface 10 lower than the projection 9 The outer peripheral edge surface 11 is continuous with the stepped surface 10 at the position. The outer peripheral diameter dimension L ₁ of the annular projection 9 is set to be slightly smaller than the outer peripheral diameter dimension L ₂ of the lower surface 1b of the green compact 1 (see FIG. 2), and the outer peripheral surface 11 is compressed. It corresponds to the outer peripheral edge of the lower surface 1b of the powder 1.

On the other hand, as shown in FIGS. 2 and 4, on the lower surface 5a of the upper die 5, there is provided a cylindrical convex portion 12 which is provided in the center and is press-fitted into the concave portion 2 of the green compact 1. Each of the protrusions 12 has a protrusion 13 provided at the center of the lower surface of the protrusion 12. The diameter of the convex portion 12 is equal to that of the concave portion 2 of the green compact 1.
It is set slightly larger than the diameter of.

Further, in the upper mold 5 of this example, the convex portion 1
Two annular step portions 14 and 15 are provided on the outer peripheral portion of 2. Then, these annular step portions 14 and 15
Are arranged so as to substantially correspond to the annular protrusion 9 of the lower mold 4.

As shown in FIG. 2, the outer peripheral die 6 has a cylindrical surface 17 with which the outer peripheral surface 1c of the green compact 1 is slidably contacted. The upper mold 5 is slidably accommodated. Further, the outer peripheral die 6 has a pair of insertion holes 19,
20 are formed, and cylindrical push pins 21 and 22 are slidably inserted and arranged in these insertion holes 19 and 20, respectively. The diameters of the push pins 21 and 22 are set to be slightly smaller than the diameter of the piston pin.

Next, the operating procedure and its operation when manufacturing a piston using the manufacturing apparatus 3 having the above-described structure will be described below.

First, as shown in FIG. 2, the lower surface 1b of the green compact 1 heated to a high temperature (400 to 550 ° C.) is placed on the annular projection 9 of the preheated lower die 4, By driving the preheated upper mold 5 downward toward the green compact 1, the green compact 1 is sandwiched between the lower mold 4 and the upper mold 5, and a predetermined temperature is maintained. Press molding into a piston shape.

At the time of press molding, as shown in FIG. 5, as the convex portion 12 of the upper die 5 is pressed into the concave portion 2 of the green compact 1, the upper surface 1a of the green compact 1 is pressed into the upper die 5. And the lower surface 1b of the green compact 1 is molded along the shape of the upper surface 4a of the lower mold 4.

At this time, plastic flow occurs in the green compact 1 as shown by the arrow in FIG. The arrow in FIG. 5 indicates the direction of plastic flow in each part, and the length of the arrow corresponds to the degree of plastic flow in each part. The longer the arrow, the more plastic flow. It means that it has occurred remarkably.

Since the depression 8 and the protrusion 9 are provided on the lower die 4, the protrusion 9 of the lower die 4 among the respective parts of the green compact 1 is shown in FIG. Plastic flow is remarkably generated in a portion between the convex portion 12 and the step portion 14 of the upper die 5 and the concave portion 8 of the lower die 4 and the convex portion 1 of the upper die 5.
The powder wraps around between the two. Further, sufficient plastic flow is generated toward the outer peripheral edge surface 11 of the lower mold 4, and sufficient plastic flow is generated toward the step portion 15 of the upper mold 5.

Since the protrusion 13 is provided at the center of the lower surface 5a of the upper mold 5, the central portion of the green compact 1, that is, the recess 8 of the lower mold 4 and the protrusion 13 of the upper mold 5 are formed. Sufficient plastic flow also occurs in the portion between and.

However, in the press molding of only the lower mold 4, the upper mold 5, and the outer peripheral mold 6, a portion indicated by cross hatching β in FIG. 5, that is, a vertical intermediate portion on the outer peripheral surface 1c side of the green compact 1 is formed. A and a portion B corresponding to the corner between the convex portion 12 and the step portion 14 of the upper die 5 have some plastic flow, but the plastic flow is dull, and these portions A and B are likely to be defective portions. .

In particular, since the intermediate portion A is a portion corresponding to the pin boss portion of the piston, if that portion becomes a defective portion having low strength, it will seriously impair the function of the piston.

Therefore, in this example, the outer peripheral mold 6 is pressed during or immediately after the pressing by the lower mold 4 and the upper mold 5.
6, the push pins 21, 22 are pushed out toward the side surface 1c of the green compact 1 at a high pressure, whereby the piston pin insertion hole of the side surface 1c of the green compact 1 is pushed. The plastic flow of the powder is to be forced to occur at the location where the pit is to be formed, as indicated by the arrow in FIG.

By the above operation, as shown in FIG. 7, the head portion 25a, the pin boss portion 25b, and the skirt portion 25c are provided, and a pair of bottomed cylindrical recesses 23, 24 are provided at predetermined positions on the side surfaces. The piston material 25 is obtained. Then, the recesses 23, 24 of the piston material 25 are subjected to cutting (pin hole processing), so that the pair of piston pin insertion holes 26, 2 facing each other as shown in FIG.
A product piston 28 having 7 is obtained. In the pin hole processing, since the defect is eliminated by pressing the pin boss portion 25b with the pressing pins 21 and 22, the processing operation can be performed more easily.

When the piston 28 is obtained from powder using the piston manufacturing apparatus 3 as described above, it is judged that the piston 28 is manufactured by the manufacturing method of this embodiment.
This can be easily done by examining the flow line flow due to strong corrosion of the cross section. It can be considered that this is typically found in, for example, a steel crankshaft forging, and the shape of the mold surface, the way of dividing the mold, etc. can be understood by observing the flow direction of this flow line. Similarly, by examining the flow line of the powder forged aluminum piston, especially the cross section of the pin boss portion 25b, the manner of plastic flow of the powder can be known, and by this, it can be confirmed whether or not the method of this example has been carried out.

According to this example, since the powder as described above is used as the material for the piston, the piston 2
8 can be made extremely lightweight, and vibration can be reduced and responsiveness can be improved.

Further, since it is possible to sufficiently withstand an excessive heat load, it becomes possible to raise the combustion temperature of the internal combustion engine. That is, the thermal efficiency can be improved and a high output can be obtained.

Further, the piston material is particularly useful for an engine that has been in a severely lubricated state, for example, a piston of a large displacement two-cycle engine, and a complicated lubrication mechanism can be simplified.

Moreover, the piston obtained in this example is
As described above, since it is possible to generate sufficient plastic flow in each part of the green compact 1, there is less variation in strength as a whole compared to the piston obtained by the conventional powder forging method, and high reliability is achieved. Will be things.

Further, in this embodiment, since the piston is braked directly from the powder without performing the hot extrusion of the piston material, the hot extrusion step can be omitted and the manufacturing cost can be reduced. be able to.

The embodiment of the present invention has been described above.
The present invention is not limited to this embodiment, and various modifications and changes can be made based on the technical idea of the present invention. For example, the shape of the recess 2 formed in the green compact 1 is as shown in FIG.
The shape is not limited to the shape as shown in FIG. 9, but may be a conical shape or a truncated conical shape as shown in FIG. 9A or 9B, if necessary. Furthermore, the upper die 5
The shape of the protruding portion 13 provided on the base may be a conical shape or a truncated cone shape as shown in FIG.

[0044]

As described above, the piston manufacturing method and apparatus according to the present invention have the recessed portion at the center of the upper surface and the annular protrusion at the outer peripheral edge of the recessed portion.
And a lower mold having a step surface formed of the outer peripheral surface of the protrusion and an outer peripheral edge surface formed to be lower than the protrusion, a protrusion on the lower surface, and a protrusion at the center of the lower surface of the protrusion. By using the upper mold and forcing the plastic flow in the green compact, it is possible to prevent a defective portion from being significantly generated.
As a result, it is possible to manufacture a highly reliable piston with little strength variation and no strength defect.

Therefore, according to the present invention, there is an advantage that a high quality piston can be obtained although the hot extrusion step can be omitted and the manufacturing cost can be reduced.

Further, according to the present invention, a pair of push pins are pressed against a part of the side wall of the powder compact corresponding to the piston pin insertion hole formed in the pin boss portion of the piston against a part of the thickness of the side part. By inserting it, the plastic flow in this part is forcibly and remarkably generated, so that it is possible to prevent the defect of the part of the piston pin insertion hole formed in the pin boss portion, and consequently the piston pin insertion hole. It becomes possible to perform the cutting process (pin hole process) more easily.

[Brief description of drawings]

1A and 1B show a green compact (preform) used in a piston manufacturing method according to the present invention, in which (a) is a plan view of the green compact and (b) is a sectional view of the green compact. is there.

FIG. 2 is a sectional view showing a piston manufacturing apparatus for carrying out the piston manufacturing method according to the present invention.

FIG. 3 is a bottom view of the lower mold of the piston manufacturing apparatus according to the present invention.

FIG. 4 is a plan view of an upper die of the piston manufacturing apparatus according to the present invention.

FIG. 5 is a cross-sectional view for schematically explaining a state of plastic flow of powder when a green compact is pressed between a lower mold and an upper mold.

FIG. 6 is a cross-sectional view for schematically explaining a state of plastic flow of powder when a push pin is pushed into a side portion of the green compact.

FIG. 7 is a sectional view of a piston material obtained by the piston manufacturing apparatus according to the present invention.

FIG. 8 is a cross-sectional view of a piston as a product obtained by subjecting a piston material to pin hole processing.

9 (a) and 9 (b) are cross-sectional views each showing a modified example of the green compact used in the piston manufacturing method according to the present invention.

FIG. 10 is a cross-sectional view showing a modified example of the upper mold.

11A and 11B are views showing a green compact generally used in a conventional piston manufacturing method, wherein FIG. 11A is a plan view of the green compact, and FIG. 11B is a sectional view of the green compact. .

FIG. 12 is a sectional view of a conventional piston manufacturing apparatus.

FIG. 13 is a cross-sectional view for schematically explaining a state of plastic flow of powder when a conventional piston manufacturing apparatus is used.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Green compact 1a One end surface (upper surface) 1b The other end surface (lower surface) 2 Recessed portion 3 Piston manufacturing device 4 Lower die 4a Lower surface 5 Upper die 5a Upper surface 6 Outer peripheral die 8 Recessed portion 9 Projection portion 10 Stepped surface 11 Outer peripheral edge Surface 12 Convex part 13 Projection part 21,22 Push pin 23,24 Recess 25 Piston material 26,27 Piston pin insertion hole 28 Piston

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location B22F 3/02 101 C

Claims (4)

[Claims] 1. A recessed portion is formed at a central portion of an upper surface, an annular protruding portion is provided at an outer peripheral edge portion of the recessed portion, and the stepped surface formed by the outer peripheral surface of the protruding portion and the protruding portion are formed lower than the stepped surface. Using a lower mold having an outer peripheral surface and an upper mold having a convex portion on the lower surface and having a protrusion at the center of the lower surface of the convex portion, a flat lower surface of the green compact to be processed is used. Is placed on the protrusion of the lower mold, and the concave portion formed in the central portion of the upper surface of the green compact is arranged corresponding to the convex portion of the upper mold,
Manufacture of a piston, characterized in that the green compact is forcedly formed between the lower mold and the upper mold in a high temperature state so as to force a plastic flow in the green compact. Method. 2. A recessed portion is formed at a central portion of the upper surface, an annular protrusion is formed at an outer peripheral edge portion of the recessed portion, and the stepped surface formed by the outer peripheral surface of the protrusion is formed to be lower than the protrusion. Using a lower mold having an outer peripheral surface and an upper mold having a convex portion on the lower surface and having a protrusion at the center of the lower surface of the convex portion, a flat lower surface of the green compact to be processed is used. Is placed on the protrusion of the lower mold, and the concave portion formed in the central portion of the upper surface of the green compact is arranged corresponding to the convex portion of the upper mold,
The green compact is pressure-molded between the lower mold and the upper mold in a high temperature state, and at this time or immediately thereafter, a side portion of the side face of the green compact and corresponding to the piston pin insertion hole. By pressing a pair of push pins into a part of the wall thickness of the side part to form a pair of recesses to form a piston material, and then forming a piston material on the side surface of the piston molding material. A method of manufacturing a piston, characterized in that a piston pin insertion hole connected to the recess is machined. (A) An annular protrusion provided at a central portion of an upper surface and an outer peripheral edge portion of the concave portion, on which a flat lower surface of a green compact to be processed is placed. A lower mold having a stepped surface formed by the outer peripheral surface of the protruding portion and an outer peripheral surface continuing to the stepped surface at a position lower than the protruding portion; An upper die having a convex portion press-fitted into a concave portion formed at the center of the upper surface of the powder, and a protruding portion provided at the central portion of the lower surface of the convex portion; and (C) on the protruding portion of the lower die. And a peripheral die placed opposite to the outer peripheral surface of the green compact placed on the piston. 4. The piston according to claim 3, wherein insertion holes are provided in the outer peripheral mold at positions facing each other, and a pair of push pins are slidably disposed in these insertion holes. Manufacturing equipment.