JP2010188369A - Method of manufacturing machine part using cold forging and method of cold forging the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To manufacture a product capable of fully securing strength of the product, by manufacturing a machine part conventionally manufactured by using hot forging, by using cold forging. <P>SOLUTION: A plastic strain is applied to a portion requiring strength in the machine part, when manufacturing the machine part by using the cold forging. A shape before machining is determined by providing a machining margin to a shape of the machine part. A shape before increasing strength is determined based on an amount of plastic strain applying for increasing strength of the portion requiring strength in the shape before machining. The cool forging is performed while applying strain in a strength increasing step so that the shape before increasing strength may become the shape before machining. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a method of manufacturing a machine part using cold forging.

Conventionally, mechanical parts such as crankshafts, connecting rods, and transmission gears used in vehicles such as large screws and automobiles are manufactured by hot forging (for example, Patent Document 1 and Patent Document 2).
In the manufacturing method of the connecting rod of Patent Document 1, first, hot forging is performed on the material that is the source of the connecting rod, and a large end portion, a small end portion, and a column portion having a substantially H-shaped cross section that connects these are provided on the outer peripheral portion. The connecting rod with burrs is formed by the hot forging process, and then the burrs generated on the outer periphery of the hot forged connecting rod are removed by the burring process, and the connecting rod is applied to the large end, small end and column section. Cold coining was performed by the cold coining process.

  Moreover, in the manufacturing method of patent document 2, after making the steel material used as the connecting rod into the higher one of lower limit temperature of solidus temperature x0.94 or 1250 degreeC, upper limit temperature is liquidus line x0. The connecting rod was manufactured by performing ultra-high temperature forging so that 85% or more of the material surface was in contact with the mold in the above temperature range.

JP 2006-31978 A JP 2005-54228 A

Thus, machine parts such as large screws were manufactured using hot forging, but in recent years, hot forging such as large screws has been used in order to reduce CO ₂ emissions in the component manufacturing process. Even in the case of machine parts that have been manufactured in the past, there is a growing demand for manufacturing using cold forging.
However, when a machine part such as a large screw manufactured by hot forging is manufactured by switching to cold forging, the following problem occurs only by switching the forging method. When a product is manufactured by hot casting, heat treatment such as quenching and tempering is performed after hot forging to obtain a required component strength. In order to obtain a component strength equivalent to that of hot forging while still in cold forging, it is necessary to use a steel material having high strength. However, such a steel material has a high deformation resistance during cold forging and tends to deteriorate the life of the mold. Moreover, since workability is also inferior, the parts are likely to crack. On the other hand, in order to obtain low deformation resistance and high workability as in hot forging, it is necessary to use a soft steel material, and the actual situation is that sufficient strength required for products cannot be ensured.

  The present invention provides a method for manufacturing a machine part and a method for cold forging using cold forging that can sufficiently ensure the strength of the product when manufacturing the machine part using cold forging.

In order to achieve the above object, the present invention takes the following measures.
That is, the means of the present invention is that when a machine part is manufactured using cold forging, it has a strength increasing step by applying plastic strain to a portion of the machine part that requires strength. A shape before machining is determined by giving machining allowance to the shape of the machine part, and the amount of plastic strain to be given to the shape before machining to increase the strength to the portion requiring the strength is determined. It is preferable to perform cold forging while adding strain in the strength increasing step so that the shape before increasing strength is determined based on the shape before increasing strength so that the shape before increasing strength becomes the shape before machining.

The mechanical parts are: C: 0.005 to 0.045 mass%, Si: 0.005 to 0.4 mass%, Mn: 0.3 to 1 mass%, P: 0.05 mass% or less (0% S: 0.005 to 0.05 mass%, Al: 0.005 to 0.06 mass%, N: 0.008 to 0.025 mass%, and the formula (1) is satisfied, and the balance Is preferably made of a material consisting of iron and inevitable impurities and satisfying N: 0.007% by mass or more as a solid solution state.
The plastic strain amount is preferably 8 or less (excluding 0). Furthermore, the amount of plastic strain is preferably 1 or more and 5 or less.

The amount of plastic strain is preferably obtained from a model formula based on any one of yield stress (YP), maximum stress (TS), strength (h), and fatigue strength (i) or from a previously acquired database.
In the cold forging in the method of manufacturing a machine part using the cold forging described above, it is preferable to perform extrusion die forging or compression partial reduction.

  ADVANTAGE OF THE INVENTION According to this invention, when manufacturing a machine part using cold forging, the product which can fully ensure the intensity | strength of a product can be manufactured.

It is the flowchart which showed the manufacturing method of the machine components using cold forging. The manufacturing method of a large sized screw (mechanical part) is illustrated.

The manufacturing method of the machine parts using the cold forging of this invention is demonstrated.
In the method of manufacturing a machine part according to the present invention, machine parts such as large screws, crankshafts, connecting rods, transmission gears and the like that have been conventionally manufactured by hot forging are manufactured by using cold forging. Hereinafter, the manufacturing method will be described using a large screw as a representative example.
FIG. 1 shows a procedure of a method for manufacturing a machine part, and FIG. 2 shows a procedure of a method for manufacturing a machine part. In this manufacturing method, the contents of the design stage are also included, and the product shape determination process to the material shape determination process, which will be described later, are the design stage (pre-processing stage), and the subsequent processing is concrete. It becomes a stage.

As shown in FIGS. 1 and 2, first, when manufacturing the large screw 1, the product shape A of the large screw 1 is determined (S1: product shape determining step). That is, machining is performed after cold forging (after strength increase), but the shape of the large screw 1 after the completion of the machining, that is, the product shape A of the large screw 1 when made into a product is shown in the production drawing. Determine from. This shape is often determined by user demand.
Next, a shape B before machining is determined by adding (adding) a machining allowance to the product shape A determined in the product shape step S1 (S2: shape process before machining).

For example, in the pre-machining shape step S2, the dimension of machining allowance (for example, several mm) at each location is added to the product contour line (manufactured contour line) L1 of the large screw 1 and after cold forging. A shape B before machining that can be formed by cold forging is determined by obtaining a contour line (contour line after increasing strength) L2.
Then, based on the amount of plastic strain ε to be imparted to the pre-machining shape B determined in the pre-machining shape step S2 to increase the strength for the portion requiring strength, the shape before the strength increase (pre-strain shape) C is determined (S3: shape determination step before increasing strength).

For example, when the shaft portion 2 of the large screw 1 requires strength, a plastic strain is applied to the post-forging contour L3 after cold forging (after strength increase) of the shaft portion 2 separately from the machining allowance. The shape before strength increase (shape before distortion) C is determined by adding as much as possible dimension ε (amount of distortion) to obtain the contour line L4 before distortion.
In this pre-strength shape determination step S3, during cold forging described later (strength increasing step), plastic strain is intentionally applied to a portion requiring strength, and that portion (portion requiring strength) The amount of plastic strain is calculated in order to increase TS (tensile strength) and YS, that is, to increase the strength at a necessary portion.

In the conventional technique, the large screw 1 is manufactured by hot forging and subsequent heat treatment to ensure the strength. However, the large screw 1 that has been hot forged is simply changed to cold forging. As described above, there are places where the required strength cannot be obtained in advance.
Therefore, in the present invention, the strength of the parts is increased by intentionally applying plastic strain to the portion where the strength cannot be obtained only by cold forging by the conventional method. In other words, the conventional large-sized screw 1 that has been hot forged does not have residual strain. However, in the present invention, cold forging is intentionally applied by applying residual strain to a portion that improves strength. The strength can be secured even if it goes. Here, the amount of plastic strain to be applied is set to 8 or less (excluding 0). If the amount of plastic strain is greater than 8, the strength is so high that parts cannot be processed by cold forging, so the amount of plastic strain must be 8 or less. The amount of plastic strain to be applied is preferably 1 or more and 5 or less. If the amount of plastic strain to be applied is less than 1, sufficient component strength cannot be obtained, and if it is greater than 5, the workability of the steel material starts to deteriorate, so that the component is likely to crack.

In the shape determination step S3 before increasing strength, the amount of plastic strain may be set according to the degree (amount) of applying TS (tensile strength). For example, the plastic strain amount ε may be determined using the model expressions shown in Expressions (2) to (5) or a database acquired in advance. That is, the plastic strain amount may be obtained from a model formula based on any one of yield stress (YP), maximum stress (TS), strength (h), and fatigue strength (i), or from a database acquired in advance.
ε = f ⁻¹ (YP) (2)
ε = g ⁻¹ (TS) (3)
ε = h ⁻¹ (strength) (4)
ε = i ⁻¹ (fatigue strength) (5)
Where f: function of stress-strain curve (plastic strain curve), g: function of maximum stress-strain curve (plastic strain curve), h: function of strength-strain curve (plastic strain curve), i: fatigue strength- It is a function of a strain curve (plastic strain curve).

Further, the plastic strain may be applied to a portion requiring strength, and as described above, the plastic strain is not limited to the shaft portion as described in the large screw 1 and may be appropriately selected.
After determining the pre-intensity shape (pre-strain shape) C, the material size of the large screw 1 is determined from the pre-intensity shape C (width, height, volume, etc.) (S4: Material shape determination step). For example, when the large screw 1 is manufactured, since the round bar 3 is used, the diameter, length, and the like of the round bar 3 are determined from the shape C (width, height, volume, etc.) before increasing the strength.
Next, when the initial shape of the material is determined, preliminary processing is performed so that the material has a shape before increasing strength (shape before strain) C by hot forging or machining (S5: preliminary processing). Process).

And after making the material into the shape of the pre-intensity shape (pre-strain shape) C in the pre-processing step S5, the material is cold while giving plastic strain to the portion requiring strength so as to become the pre-machining shape B. Forging is performed (S6: strength increasing step).
For example, as described in the design stage, since the strength of the shaft portion 2 is increased in the large screw 1, cold forging is performed while straining the shaft portion 2 in the strength increasing step S6. Specifically, in this strength increasing step S6, compression or the like (partial reduction) is performed so that the pre-strained contour line L4 corresponding to the shaft portion 2 matches the post-forging contour line (contour line after increasing strength) L2. Strain is added, thereby increasing the TS (tensile strength) of the shaft 2.

And after cold forging (after strength increase), it is set as product shape A by machining with respect to the material of the shape B before machining (S7: machining process).
The method for performing cold forging is not limited, and axial compression (compressed partial compression) may be performed, extrusion molding (extrusion die forging) may be performed, or die forging may be performed. Also good. Moreover, it is preferable that the temperature of the atmosphere at the time of cold forging (cold processing) is less than 200 ° C., and the pre-processing temperature of the material is less than 100 ° C.
In the above description, the strength increasing step (cold forging step) S6 is performed after the preliminary processing step S5. However, as shown by the arrow S in FIG. The strength increasing step (cold forging step) S6 may be directly performed on the round bar 2 determined in the material shape determining step S4. In other words, in this case, while performing cold forging so as to obtain a shape with machining allowance, straining according to the amount of plastic strain ε is performed on a portion requiring strength (for example, a shaft portion). Become.

Next, materials for machine parts will be described.
The material of the mechanical part mentioned above is C: 0.005-0.045 mass%, Si: 0.005-0.4 mass%, Mn: 0.3-1 mass%, P: 0.05 mass% or less (Excluding 0%), S: 0.005 to 0.05 mass%, Al: 0.005 to 0.06 mass%, N: 0.008 to 0.025 mass%, and the formula (1) The balance is made of iron and inevitable impurities, and satisfies N: 0.007% by mass or more as a solid solution state.
This material has a characteristic that TS and YS are improved when plastic strain is applied, and TS is improved in proportion to the plastic strain applied. The material will be described, but any material can be used as long as TS and YS are improved when plastic strain is applied, and the material is not limited to the material described in this embodiment.

[C: 0.005 to 0.045% by mass]
C is an element that greatly affects the formation of the structure of the steel material, and in order to make the structure a ferrite single-phase structure, it is necessary to reduce as much as possible, and if excessively contained, pearlite is generated in the structure of the steel material, Deformation resistance may be excessive due to work hardening of pearlite. For these reasons, the C content needs to be 0.045% by mass, preferably 0.043% by mass or less, and more preferably 0.040% by mass or less. However, if the C content is extremely low, deoxidation during melting of the steel material becomes difficult, so the lower limit is preferably 0.005% by mass, more preferably 0.01% by mass or more, and still more preferably Is 0.015 mass% or more.

[Si: 0.005 to 0.4 mass%]
Si is effective as a deoxidizing element during melting. When the Si content is less than 0.005% by mass, deoxidation becomes insufficient and blow holes are generated during melting. However, if the Si content becomes excessive and exceeds 0.4 mass%, the deformation resistance is increased due to the solid solution strengthening of Si, and cracks may become remarkable. The Si content is preferably 0.006% by mass or more (more preferably 0.007% by mass or more), preferably 0.35% by mass or less (more preferably 0.32% by mass or less).

[Mn: 0.3 to 1% by mass]
When the N content in the steel material is increased, cracks are likely to occur due to dynamic strain aging due to heat generation during processing, but Mn has the effect of improving the workability at that time and suppressing cracks. In order to exhibit such an effect effectively, it is necessary to contain 0.3 mass% or more, preferably 0.35 mass% or more, more preferably 0.40 mass% or more. On the other hand, if Mn is contained excessively, not only the deformation resistance becomes excessive, but also the structure non-uniformity due to segregation occurs, so it is necessary to make it 1% by mass or less, preferably 0.95% by mass or less, more Preferably it is 0.90 mass% or less.

[P: 0.05% by mass or less (excluding 0%)]
Phosphorus (P) is an unavoidable impurity, but when it is contained in ferrite, it is an element that segregates at the ferrite grain boundaries and degrades cold workability. It is also an element that causes solid solution strengthening of ferrite to increase deformation resistance. Therefore, from the viewpoint of improving cold workability, the P content is 0.05% by mass or less. Although it is preferably 0.03% by mass or less, it is industrially difficult to make the P content 0%.
[S: 0.005 to 0.05 mass%]
Sulfur (S) is an unavoidable impurity like P, and is an element that precipitates in the form of a film at the grain boundary as FeS and degrades workability. It also has the effect of causing hot brittleness. Therefore, from the viewpoint of improving the deformability, the S content is set to 0.05% by mass or less (preferably 0.03% by mass or less). However, it is industrially difficult to reduce the S content to 0%. In addition, since S has an effect of improving machinability, it is preferable to contain 0.005% by mass or more, more preferably 0.008% by mass or more from the viewpoint of improving machinability. Is done.
[Al: 0.005 to 0.06% by mass]
Al has a strong deoxidation effect and can improve the internal quality of the steel material. Moreover, it combines with N in steel to form AlN, and has the effect of regulating the ferrite crystal grains. In order to exhibit these effects effectively, 0.005 mass% or more of Al is required. Moreover, 0.01 mass% or more is preferable and 0.015 mass% or more is still more preferable. If the Al content is less than 0.005% by mass, gas defects are likely to occur during melting, and cracks are likely to occur during cold forging. On the other hand, if it exceeds 0.06% by mass, the amount of solute N is reduced, and a predetermined component strength cannot be obtained. Al is preferably 0.05% by mass or less, more preferably 0.04% by mass or less.

[N: 0.008 to 0.025 mass%]
Nitrogen (N) is an important element for obtaining a predetermined strength by static strain aging after processing. In order to exert such effects, the N content needs to be 0.008% by mass or more. However, if the N content becomes excessive and exceeds 0.025 mass%, the influence of dynamic strain aging during processing becomes more significant than static strain aging, and the deformation resistance increases. In addition, the minimum with preferable N content is 0.0085 mass% (more preferably 0.009 mass% or more), and a preferable upper limit is 0.023 mass% (more preferably 0.02 mass% or less).

The material used for the machine part is characterized by promoting static strain aging without increasing the deformation resistance by setting a predetermined amount of solid solution N (solid solution N). In order to ensure a predetermined strength after cold working, the amount of solute N needs to be 0.007% by mass or more. However, if the amount of solute N becomes excessive, the cold workability deteriorates, so that the amount is preferably 0.025% by mass or less.
In addition, content of the solid solution N in this invention is a value calculated | required by subtracting N amount in all N compounds from total N amount in steel materials based on JISG1228. A practical method for measuring the content of this solid solution N is exemplified below.
(A) Inert gas melting method, thermal conductivity method (total N content measurement)
The sample cut out from the test material is put in a crucible, melted in an inert gas stream to extract N, the extract is transferred to a thermal conductivity cell, and the change in thermal conductivity is measured to determine the total N amount. Ask.
(B) Ammonia distillation separation indophenol blue spectrophotometry (measurement of total N compound amount)
A sample cut out from the test material is dissolved in a 10% AA-based electrolytic solution, subjected to constant current electrolysis, and the total amount of N compounds in the steel is measured. The 10% AA electrolyte used is a non-aqueous solvent electrolyte consisting of 10% acetone, 10% tetramethylammonium chloride, and the remainder methanol, and does not generate a passive film on the steel surface.

  About 0.5 g of the sample material is dissolved in the 10% AA electrolyte solution, and the resulting insoluble residue (N compound) is filtered through a polycarbonate filter having a hole size of 0.1 μm. The obtained insoluble residue is decomposed by heating in a chip made of sulfuric acid, potassium sulfate and pure copper, and the decomposition product is combined with the filtrate. After making this solution alkaline with sodium hydroxide, steam distillation is performed, and the distilled ammonia is absorbed in dilute sulfuric acid. Further, phenol, sodium hypochlorite and sodium pentacyanonitrosyl iron (III) are added to form a blue complex, and the absorbance is measured using an absorptiometer to determine the total N compound amount.

The total amount of N compounds determined by the method (b) can be subtracted from the total N amount determined by the method (a) to determine the solid solution N amount.
In materials used for machine parts, solute C greatly increases deformation resistance and does not contribute much to static strain aging, while solute N does not increase deformation resistance and promotes static strain aging. Therefore, it has the effect of increasing the strength after processing (after applying strain).
Therefore, in this material, in order to increase the hardness after processing without increasing the deformation resistance during processing, the C content [C] and the N content [N] It is necessary to satisfy the relationship. When the value on the right side of Equation (1) (= 10 [C] + [N]) exceeds 0.3 (mass%), the C and N contents become excessive and the deformation resistance becomes excessive. .

Note that the value of (10 [C] + [N]) is preferably 0.29 or less, and more preferably 0.28 or less.
0.3 ≧ (10 [C] + [N]) (1)
However, [C] and [N] indicate the contents (% by mass) of C and N, respectively.
The components of the material are as described above, with the balance being iron and inevitable impurities.
By manufacturing the large screw 1 by the forging method shown in the present invention using the above-mentioned materials, conventionally, the large screw 1 can be manufactured only by using hot forging. It can be manufactured. Note that the manufacturing method of the present invention can be applied not only to the large screw 1 but also to automotive parts such as crankshafts, connecting rods, transmission gears, and other machine parts that have been processed by hot forging so far. it can.

1 Large screw 2 Shaft 3 Round bar

Claims (7)

  When manufacturing machine parts using cold forging, the machine parts using cold forging characterized by having a strength increasing step by applying plastic strain to the parts requiring strength in the machine parts Manufacturing method. A shape before machining is determined by giving machining allowance to the shape of the machine part, and the amount of plastic strain to be given to the shape before machining to increase the strength to the portion requiring the strength is determined. After determining the shape before strength increase based on
The machine part using cold forging according to claim 1, wherein cold forging is performed while straining in the strength increasing step so that the shape before increasing the strength becomes the shape before machining. Manufacturing method.   The mechanical parts are: C: 0.005 to 0.045% by mass, Si: 0.005 to 0.4% by mass, Mn: 0.3 to 1% by mass, P: 0.05% by mass or less (0% S: 0.005 to 0.05 mass%, Al: 0.005 to 0.06 mass%, N: 0.008 to 0.025 mass%, and the formula (1) is satisfied, and the balance The machine using cold forging according to claim 1 or 2, wherein the machine is made of a material made of iron and inevitable impurities and satisfying N: 0.007% by mass or more as a solid solution state. Manufacturing method of parts.   The said plastic strain amount is 8 or less (except 0), The manufacturing method of the machine parts using the cold forging in any one of Claims 1-3 characterized by the above-mentioned.   The said plastic strain amount is 1 or more and 5 or less, The manufacturing method of the machine components using the cold forging in any one of Claims 1-3 characterized by the above-mentioned.   The amount of plastic strain is obtained from a model formula based on any one of yield stress (YP), maximum stress (TS), strength (h), and fatigue strength (i), or from a previously acquired database. The manufacturing method of the machine component using the cold forging in any one of Claims 1-5.   A cold forging method in which extrusion die forging or compression partial reduction is performed in the cold forging in the method of manufacturing a machine part using cold forging according to claim 1.

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