WO2013128500A1 - ダイカスト製品の強度評価方法及びダイカスト製品 - Google Patents
ダイカスト製品の強度評価方法及びダイカスト製品 Download PDFInfo
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- WO2013128500A1 WO2013128500A1 PCT/JP2012/004686 JP2012004686W WO2013128500A1 WO 2013128500 A1 WO2013128500 A1 WO 2013128500A1 JP 2012004686 W JP2012004686 W JP 2012004686W WO 2013128500 A1 WO2013128500 A1 WO 2013128500A1
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- die
- cast product
- strength
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- fracture
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- XDTMQSROBMDMFD-UHFFFAOYSA-N C1CCCCC1 Chemical compound C1CCCCC1 XDTMQSROBMDMFD-UHFFFAOYSA-N 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/22—Investigating strength properties of solid materials by application of mechanical stress by applying steady torsional forces
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22C—FOUNDRY MOULDING
- B22C19/00—Components or accessories for moulding machines
- B22C19/04—Controlling devices specially designed for moulding machines
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22C—FOUNDRY MOULDING
- B22C9/00—Moulds or cores; Moulding processes
- B22C9/22—Moulds for peculiarly-shaped castings
- B22C9/24—Moulds for peculiarly-shaped castings for hollow articles
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D17/00—Pressure die casting or injection die casting, i.e. casting in which the metal is forced into a mould under high pressure
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60R—VEHICLES, VEHICLE FITTINGS, OR VEHICLE PARTS, NOT OTHERWISE PROVIDED FOR
- B60R25/00—Fittings or systems for preventing or indicating unauthorised use or theft of vehicles
- B60R25/01—Fittings or systems for preventing or indicating unauthorised use or theft of vehicles operating on vehicle systems or fittings, e.g. on doors, seats or windscreens
- B60R25/02—Fittings or systems for preventing or indicating unauthorised use or theft of vehicles operating on vehicle systems or fittings, e.g. on doors, seats or windscreens operating on the steering mechanism
- B60R25/021—Fittings or systems for preventing or indicating unauthorised use or theft of vehicles operating on vehicle systems or fittings, e.g. on doors, seats or windscreens operating on the steering mechanism restraining movement of the steering column or steering wheel hub, e.g. restraining means controlled by ignition switch
- B60R25/0211—Fittings or systems for preventing or indicating unauthorised use or theft of vehicles operating on vehicle systems or fittings, e.g. on doors, seats or windscreens operating on the steering mechanism restraining movement of the steering column or steering wheel hub, e.g. restraining means controlled by ignition switch comprising a locking member radially and linearly moved towards the steering column
- B60R25/02115—Fittings or systems for preventing or indicating unauthorised use or theft of vehicles operating on vehicle systems or fittings, e.g. on doors, seats or windscreens operating on the steering mechanism restraining movement of the steering column or steering wheel hub, e.g. restraining means controlled by ignition switch comprising a locking member radially and linearly moved towards the steering column key actuated
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- E—FIXED CONSTRUCTIONS
- E05—LOCKS; KEYS; WINDOW OR DOOR FITTINGS; SAFES
- E05B—LOCKS; ACCESSORIES THEREFOR; HANDCUFFS
- E05B15/00—Other details of locks; Parts for engagement by bolts of fastening devices
- E05B15/16—Use of special materials for parts of locks
- E05B15/1614—Use of special materials for parts of locks of hard materials, to prevent drilling
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
- G01N29/04—Analysing solids
- G01N29/11—Analysing solids by measuring attenuation of acoustic waves
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/0058—Kind of property studied
- G01N2203/006—Crack, flaws, fracture or rupture
- G01N2203/0067—Fracture or rupture
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2291/00—Indexing codes associated with group G01N29/00
- G01N2291/02—Indexing codes associated with the analysed material
- G01N2291/023—Solids
- G01N2291/0234—Metals, e.g. steel
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2291/00—Indexing codes associated with group G01N29/00
- G01N2291/02—Indexing codes associated with the analysed material
- G01N2291/028—Material parameters
- G01N2291/02827—Elastic parameters, strength or force
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2291/00—Indexing codes associated with group G01N29/00
- G01N2291/04—Wave modes and trajectories
- G01N2291/044—Internal reflections (echoes), e.g. on walls or defects
Definitions
- the present invention relates to a die-cast product strength evaluation method and a die-cast product (for example, an aluminum die-cast column housing) used in an electric power steering device for a vehicle.
- a die-cast product for example, an aluminum die-cast column housing
- a steering lock device that not only stops the engine when the key of the ignition switch is pulled out but also disables the steering wheel to be rotated is generally used.
- the steering column which is the main body and the mounting portion of the steering lock device used in this way needs to be stiff and cannot be easily broken.
- JIS D5812 and the like stipulate that there is no abnormality in function even when the steering shaft is locked and a torque of 200 Nm is applied to the steering shaft.
- the steering column is often made of a light metal die cast such as aluminum or magnesium for weight reduction, and has an internal defect, so it breaks when excessive torque is applied. How to evaluate the strength is important. In particular, a decrease in strength due to a fractured chill layer is known as an internal defect of die casting, and an inspection of the fractured chill layer is required for strength evaluation.
- Patent Documents 1 to 3 disclose the following methods for inspecting such a broken chill layer.
- a component (Pb) that is easily detected by a broken chill layer detecting device such as radiation, magnetism, and ultrasonic waves is mixed with a sleeve lubricant and applied to the inner surface of the sleeve.
- a technique for increasing the detection sensitivity of the broken chill layer by entering the tee is disclosed.
- Patent Document 2 discloses a technique for obtaining disperse information of a fractured chill layer in a non-destructive state by measurement combining an ultrasonic flaw detection method and an X-ray CT scan.
- the first internal defect three-dimensional distribution data is acquired by irradiating an aluminum die-cast product with ultrasonic waves and detecting a cast hole and a broken chill layer of the aluminum die-cast product based on sound wave information from the aluminum die-cast product.
- X-ray CT measurement of the same aluminum die-cast product is performed to detect the casting cavity of the aluminum die-cast product from a plurality of cross-sectional images of the aluminum die-cast product, and the second internal defect three-dimensional distribution data is obtained, and the first internal defect is obtained.
- the three-dimensional distribution data and the second internal defect three-dimensional distribution data are compared to obtain the three-dimensional distribution data of the fractured chill layer of the aluminum die cast product.
- Patent Document 3 discloses a simple fracture chill layer inspection method in which a test piece is cut out from a runner portion, the cut surface is polished and corroded, the fracture chill layer is observed and the fracture chill layer area ratio is calculated. ing.
- Patent Document 4 As another strength evaluation method for aluminum die-cast products, in Patent Document 4, ultrasonic flaw detection is performed on an aluminum die-cast product having a composite member therein, the distance from the surface to the composite member, and the molten aluminum for the composite member.
- a technique is disclosed that determines the quality by measuring the impregnation state, the state of cracking, and the like.
- Patent Document 1 since a special inspection device is required, it takes a lot of work time, and the strength cannot be evaluated at the casting site, and the measurement detection accuracy is not sufficient. could not.
- Patent Document 1 has a merit that nondestructive inspection can be performed, but it is necessary to conduct a survey using special equipment such as radiation, magnetism, and ultrasonic waves after casting, which requires a lot of work time, and at the casting site.
- the strength could not be evaluated with high accuracy because the measurement detection accuracy was not sufficient.
- Patent Document 2 has the merit that non-destructive inspection can be performed in the same manner as Patent Document 1, but it is necessary to conduct a survey using a special instrument such as ultrasonic flaw detection and CT scan after casting, which requires a lot of work time, and casting.
- a special instrument such as ultrasonic flaw detection and CT scan after casting
- the strength cannot be evaluated on site, and since the measurement detection accuracy is not sufficient, the strength cannot be evaluated accurately.
- Patent Document 3 has the advantage of not requiring special inspection equipment, but it requires polishing and corrosion and requires a lot of work. Furthermore, since the inspection piece is cut out from the runner instead of the product, it is accurate. The strength cannot be evaluated.
- the strength evaluation method of the aluminum die-cast product described in Patent Document 4 only measures the degree of impregnation and cracking of an aluminum die-cast product having a composite member therein, and does not have a composite member. It does not evaluate the strength of the product.
- the strength evaluation method for aluminum die-cast products described in Patent Document 2 enables evaluation of aluminum die-cast products without composite members. For example, all parts of large aluminum die-cast products or complex aluminum die-cast products can be evaluated. It is practically difficult to test for. An actual aluminum die-cast product cannot avoid internal defects such as a cast hole, and sometimes breaks starting from the internal defects. Also, aluminum die-cast products often have complicated shapes, and it is difficult to detect internal defects by, for example, ultrasonic flaw detection, and it is not clear which part should be evaluated for strength. Absent.
- the present invention has been made in order to solve such problems.
- the purpose of the present invention is to reduce the working time, perform strength evaluation (strength guarantee) each time at the casting site, and provide a die cast product that can obtain strength evaluation with high accuracy. It is to provide a strength evaluation method and a die-cast product.
- Another object of the present invention is to provide a die-cast product strength evaluation method and die-cast product capable of appropriately evaluating the strength of an actual die-cast product and capable of obtaining a die-cast product having a predetermined strength. It is.
- a method for evaluating the strength of a die-cast product includes a casting step of casting a die-cast product, A destructive process for performing a fracture test of the die-cast product after casting; Strength reduction rate calculation step of measuring the area ratio of the fractured chill layer existing on the fracture surface of the die-cast product in the fracture process and calculating the strength reduction ratio from the relationship between the twist fracture torque value and the area ratio in the fracture process
- the casting process is a casting process based on JIS D5812
- the die cast product is an aluminum column housing
- the break test is a twist test of the die cast product.
- the die-cast product is preferably used for a steering lock with an ignition switch for an automobile steering.
- an aluminum die-cast column housing is an aluminum die-cast column housing whose strength is evaluated by the strength evaluation method of the die-cast product, A hole for steering lock is formed, Fracture chill that occupies the area of the fracture surface from the fracture starting point when the steering lock hole is broken by the torsion test to a stress range that is 1/2 or more of the maximum stress acting on the fracture starting point determined by stress analysis
- the layer area ratio is less than 10%.
- the die cast product strength evaluation method is a method for evaluating the strength of a die cast product, wherein the high stress portion is obtained by performing stress analysis on the die cast product in advance. Ultrasonic inspection of internal defects in a predetermined range of the part, and when the defect rate obtained by dividing the total area of the internal defects in the predetermined range by the total inspection area is equal to or less than a predetermined value set in advance, the die cast product has a predetermined strength. Evaluate to have.
- the predetermined range of the high stress portion is preferably a stress range of 50% or more of the maximum stress of the high stress portion.
- the die-cast product is a die-cast product whose strength is evaluated by the strength evaluation method of the die-cast product, and the defect rate is 0.5% or less.
- the die-cast product is a column housing used in an electric power steering device for a vehicle, and the high stress portion is a key lock portion of the column housing.
- a die cast product strength evaluation method and a die cast product that can shorten the working time, can evaluate the strength each time at the casting site, and can obtain the strength evaluation with high accuracy.
- the strength evaluation method for a die-cast product of another embodiment of the present invention for a high-stress part of a die-cast product obtained in advance by stress analysis, an internal defect in a predetermined range of the high-stress part is ultrasonically detected. Since the die cast product is evaluated to have a predetermined strength when the defect rate obtained by dividing the total area of the internal defects in the predetermined range by the total flaw detection area is equal to or less than a predetermined value set in advance, the actual die cast product Can be properly evaluated.
- the strength of the die-cast product can be more appropriately evaluated by setting the predetermined range of the high stress portion to be a stress range of 50% or more of the maximum stress of the high stress portion. Further, according to the die cast product of another embodiment of the present invention, the strength evaluation is performed by the die cast product strength evaluation method of an embodiment of the present invention, and the total area of internal defects in a predetermined range of the high stress portion is determined as the total flaw detection area. By setting the defect rate divided by 0.5% or less, a die-cast product having a predetermined strength can be obtained.
- the present embodiment includes a casting step (S1), a fracture step (S2), a strength reduction rate calculation step (S3), and a strength evaluation area rate calculation step (S4). .
- the casting process in the present embodiment is a process of die casting using, for example, JIS H5302 Al—Si—Cu-based aluminum alloy ADC12.
- the die cast product obtained in this step is preferably the steering column housing 3 of the automobile steering apparatus shown in FIG.
- the fracture process in the present embodiment is a process of performing a fracture test at the casting site for the die cast product obtained in the casting process.
- This break test is preferably a torsion test. Specifically, as shown in FIG. 3, the torsion test is performed by the key lock jig 1 bolted to the steering column housing (die-cast product) 3 from the key hole of the steering column housing 3 to the steering column housing 3. A convex key portion that protrudes toward the inner diameter side is provided, and the torque transmitting shaft 2 is formed with a concave portion that fits into the key portion.
- Torque input from the torque transmission shaft 2 is transmitted to the key hole portion 4 of the steering column housing 3 via the convex key portion of the key lock jig 1, and the steering column housing is moved from the corner portion of the key hole portion 4 as a starting point. Break.
- ⁇ Strength reduction rate calculation step> the area ratio of the fractured chill layer existing on the fracture surface of the die cast product in the fracture process is measured, and the strength reduction rate is calculated from the relationship between the twist fracture torque value in the fracture process and the area ratio. It is a process of calculating.
- the strength evaluation area rate calculation step is a step of calculating the strength evaluation area rate of the die-cast product based on the strength reduction rate calculated in the strength reduction rate calculation step. Specifically, first, a threshold value of ⁇ 3 ⁇ ( ⁇ : standard deviation) is obtained by using the intensity decrease rate calculated in the intensity decrease rate calculating step as an average value. And it is the process of calculating the strength evaluation area ratio of the die-cast product from this threshold value and a preset strength range.
- Table 1 is a table
- ⁇ Strength reduction rate calculation step> Next, the vicinity of the origin of the fracture surface was observed with a stereomicroscope, the fractured chill layer was identified, and the fractured chill layer area ratio was calculated. The calculation results are shown in Table 1. At this time, for the fracture surface, a stress value acting as a starting point is calculated in advance by stress analysis, and a stress range until the stress value becomes 1 ⁇ 2 is set as a fracture surface observation range. In this example, the observation range of the area ratio of the fractured chill layer was from the starting point to the 15 mm position.
- FIG. 4A is a fracture surface of “Example 1” in Table 1
- FIG. 4B is a fracture surface of “Comparative Example 1” in Table 1.
- FIG. A portion surrounded by a broken line in FIG. 4B is a portion where the area (rate) of the fractured chill layer is observed (calculated).
- the area ratio of the broken chill layer is actually estimated at the casting site, it can be simplified if a limit sample is prepared in advance.
- the relationship between the torsional fracture torque value obtained in the strength reduction rate calculation step and the area ratio of the fractured chill layer can be plotted as in the graph shown in FIG. In FIG. 5, Examples 1 to 16 are indicated by “ ⁇ ”, and Comparative Examples 1 to 6 are indicated by “ ⁇ ”.
- a straight line L1 indicating the “strength reduction rate” is defined from the plotted examples and comparative examples.
- This straight line L1 is calculated
- each point on the straight line L1 indicating the “strength reduction rate” is defined as an average value
- the lower control limit line L2 defined by ⁇ 3 ⁇ ( ⁇ : standard deviation) is defined as a “threshold value”.
- the strength evaluation area ratio (the area ratio range of the fractured chill layer suitable as an example (in FIG. 5, R1))) is calculated.
- the torsion breaking torque value is set to “260 Nm or more” as the “required strength range” of the target die casting product
- a die casting product suitable as an example is broken based on the lower control limit line L2.
- a die-cast product having a chill layer area ratio of 10% or less (strength evaluation area ratio) is evaluated for strength.
- the fracture surface of the die-cast product subjected to the fracture test is observed, and the strength reduction rate is estimated on the basis of the fracture chill layer area ratio in the obtained fracture surface.
- a simple and reliable strength evaluation method can be provided. This means that the equipment required for inspection is special and takes a lot of work time, as in the conventional strength evaluation method by fracture chill layer inspection, such as polishing the cut surface and observing with an optical microscope, or using ultrasonic flaw detection. Can be resolved. Conventionally, the strength was evaluated only with the torsional breaking torque value, so the reliability was not sufficient due to the deformation of the jig, the product setting error, and the fluctuation of the manual torque addition speed. The strength can be evaluated well.
- the present invention can be applied not only to simple strength evaluation but also to setting of proper die casting conditions. Specifically, as shown in this example, by setting the molten metal temperature to 670 ° C. or higher, preferably 680 ° C. or higher, the fracture chill layer area ratio can be set to 10% or lower, and sufficient strength can be secured.
- FIG. 6 is an explanatory diagram of a 6-axis movable ultrasonic flaw detector used in the strength evaluation method for a die-cast product according to the present embodiment
- FIG. 6a is an overall view of the device
- FIG. 6b is a detailed view of an inspection object and a turntable.
- FIG. 6 c is an explanatory diagram of internal defect flaw detection.
- Reference numeral 11 in the drawing is an aluminum die-cast product whose strength is evaluated in the present embodiment, for example, a column housing of an electric power steering apparatus.
- an aluminum die-cast product (column housing) 11 is mounted on the turntable 12, and the probe (probe) 13 is moved downward from above while rotating the turntable 12, so that the aluminum die-cast product (column The inside of the housing 11 is flaw-detected. Since the die-cast product (column housing) 11 of this embodiment has a cylindrical portion, a high-stress portion (described later) of the cylindrical portion is flaw-detected by an ultrasonic flaw detector to detect internal defects.
- an evaluation gate was set between the surface echo and the bottom echo of the aluminum die cast product (column housing) 11.
- the evaluation gate means a flaw detection range in the ultrasonic irradiation direction or the reflection direction.
- ultrasonic flaw detection ultrasonic waves oscillated from the probe 13 are reflected by the surface and bottom surface of the aluminum die cast product (column housing) 11 and returned. The reflected waves become the surface echo and the bottom echo, respectively.
- FIG. 7b when the internal defect 14 exists in the flaw detection range of the aluminum die cast product (column housing) 11, a defect echo appears between the surface echo and the bottom echo, that is, in the evaluation gate range.
- the inner diameter of the cylindrical portion of the column housing which is the die-cast product 11 of this embodiment, is ⁇ 38 mm, and the flaw detection range was set to a range of 12 mm in the axial direction of the cylindrical portion as will be described later. Further, when the inner peripheral surface of the cylindrical portion of the aluminum die-cast product (column housing) 11 is turned, it becomes easier to detect a defect echo because ultrasonic waves are less likely to be irregularly reflected on the inner peripheral surface.
- FIG. 9 shows the flaw detection range of the high stress portion (key lock portion) 15 of the die cast product (column housing) 11 of this embodiment.
- internal flaw detection is performed in a range of 12 mm in the axial direction of the cylindrical portion of the column housing, including the portion with the highest stress described above.
- This internal flaw detection range is a stress range of 50% or more of the maximum stress.
- Ultrasonic flaw detection is performed inside the aluminum die cast product (column housing) 11 within the internal flaw detection range including the high stress portion (key lock portion) 15, and the aluminum die cast product (column housing) 11 is slit as shown in FIG.
- An internal defect is illustrated on a diagram in which the inside is developed by cutting from the portion.
- FIG. 11 is a flaw detection image by ultrasonic flaw detection in the flaw detection range of the aluminum die-cast product (column housing) 11 described above.
- the flaw detection range is 12 mm in the height direction and the entire inner circumference of the cylindrical portion
- the horizontal axis of the image is 119 mm (inner circumference of inner diameter ⁇ 38 mm)
- the vertical axis is 12 mm.
- FIG. 12 shows the flaw detection image with 50% echo intensity as a threshold value and binarized above and below and color-coded.
- the light gray portion in the figure is an internal defect having an echo intensity of 50% or more.
- the 50% echo intensity is an echo intensity when a master test piece having a defect area of 0.2 mm 2 is adjusted to have the same area even in image analysis described later.
- FIG. 13 shows an image analysis of the area of each internal defect having an echo intensity of 50% or more shown in FIG. A pixel number of 20 pixels or less (area 0.2 mm 2 or less) was determined as having no problem in strength, and was excluded from the evaluation target of internal defects.
- Table 2 below shows the area of all internal defects analyzed in this way.
- the total area of these internal defects 4.99mm 2, the total flaw area is 1400 mm 2.
- the total area of internal defects is divided by the total flaw detection area, the value is defined as the defect rate, and the internal defect state and the strength of the aluminum die cast product are evaluated based on the size of the defect rate.
- the number of twists until the destruction was repeated by repeating the cycle was determined by looking at the safety factor and setting the torque value to 200 Nm, which is twice the prescribed 100 Nm.
- Table 3 below shows the relationship between the defect rate of internal defects in the high stress portion (key lock portion) 15 and the number of twists at the time of destruction in the twist test.
- FIG. 14 is a graph showing the results of Table 3.
- the ultrasonic flaw detection range in particular, the range in the axial direction of the cylindrical portion of the column housing was changed for verification.
- internal flaws were subjected to ultrasonic flaw detection in a stress range of 80% or more of the maximum stress obtained by the stress analysis described above.
- the internal defect flaw detection range in the axial direction of the cylindrical portion of the column housing was 4 mm as shown in FIG.
- the column housing in which the internal defects were detected was subjected to the same torsion test as described above, and the number of twists until it was broken was obtained.
- Table 4 below shows the relationship between the defect rate of internal defects in the high stress portion (key lock portion) 15 and the number of twists at the time of the torsion test destruction.
- FIG. 16 is a graph showing the results of Table 4.
- ultrasonic flaw detection is performed on a high stress portion of the column housing (die cast product) 11 obtained in advance by stress analysis.
- the defect rate obtained by dividing the total area of the internal defects in the predetermined range by the total flaw detection area is equal to or less than a predetermined value set in advance, the column housing (die-cast product) 11 is evaluated as having a predetermined strength. Therefore, the strength of the actual column housing (die-cast product) 11 can be properly evaluated.
- the strength of the column housing (die-cast product) 11 can be more appropriately evaluated by setting the predetermined range of the high stress portion to be a stress range of 50% or more of the maximum stress of the high stress portion.
- the defect rate is 0.5% or less by performing the strength evaluation by the above-described strength evaluation method and dividing the total area of internal defects in a predetermined range of the high stress portion by the total flaw detection area. As a result, a column housing (die-cast product) 11 having a predetermined strength can be obtained.
- this invention is not limited to this, A various change and improvement can be performed.
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Abstract
Description
このように使用されるステアリングロック装置の本体及び取付部であるステアリングコラムは、堅ろうで容易に破壊できないものである必要がある。例えば、JIS D5812等には、ステアリングシャフトをロック状態にして、200Nmのトルクを当該ステアリングシャフトに加えても機能に異常なきことと規定されている。
特に、ダイカストの内部欠陥として破断チル層による強度低下が知られており、強度評価のためには破断チル層の検査が必要となる。
まず、特許文献1には、放射線、磁気、超音波等の破断チル層検出装置で検出し易い成分(Pb)をスリーブ潤滑剤に混ぜスリーブ内面に塗布し、Pbが破断チル層と伴にキャビティー内に入ることで破断チル層の検出感度を上げる技術が開示されている。
具体的には、アルミダイカスト製品に超音波を照射してアルミダイカスト製品からの音波情報に基づいてアルミダイカスト製品の鋳巣と破断チル層を検出して第1の内部欠陥3次元分布データを取得し、同じアルミダイカスト製品をX線CT測定してアルミダイカスト製品の複数の断面画像からアルミダイカスト製品の鋳巣を検出して第2の内部欠陥3次元分布データを取得し、第1の内部欠陥3次元分布データと第2の内部欠陥3次元分布データを比較してアルミダイカスト製品の破断チル層の3次元分布データを取得する。
また、アルミダイカスト製品の他の強度評価方法として、特許文献4では、内部に複合部材を有するアルミダイカスト製品に対して超音波探傷を行い、表面から複合部材までの距離、複合部材に対するアルミニウム溶湯の含浸状態、割れの状態などを測定し、良否の判別を行う技術が開示されている。
具体的には、特許文献1は、非破壊検査できるメリットがあるが、鋳造後に放射線、磁気、超音波等の特殊機器を用いた調査を行う必要があり、作業時間も多くかかり、鋳造現場で強度評価できない上、測定検出精度が十分でないため、精度良く強度評価することができなかった。
さらに、特許文献3は、特殊な検査設備を必要としないメリットがあるが、研磨、腐食が必要で作業時間が多くかかり、さらには、製品ではなくランナー部から検査片を切出すため、精度良く強度評価することができない。
また、本発明の他の目的は、実際のダイカスト製品の強度を適正に評価することができ、所定の強度のダイカスト製品を得ることが可能なダイカスト製品の強度評価方法及びダイカスト製品を提供することである。
鋳造後のダイカスト製品の破断試験を行う破壊工程と、
該破壊工程における上記ダイカスト製品の破断面に存在する破断チル層の面積率を測定し、上記破壊工程における捻り破断トルク値と上記面積率との関係から強度低下率を算出する強度低下率算出工程と、
上記強度低下率を平均値として、-3σ(σ:標準偏差)の閾値を求め、この閾値と、予め設定された強度の範囲とから上記ダイカスト製品の強度評価面積率を算出する強度評価面積率算出工程とを含む。
また、上記ダイカスト製品の強度評価方法は、上記ダイカスト製品が自動車用ステアリングのイグニッションスイッチ付きステアリングロックに使用されることが好ましい。
ステアリングロック用穴が形成され、
上記捻り試験によって上記ステアリングロック用穴を破断させたときの破断起点から応力解析により求めた上記破断起点に働く応力最大値の1/2以上となる応力範囲までの破断面の面積に占める破断チル層の面積率が10%未満である。
また、上記ダイカスト製品は、上記ダイカスト製品の強度評価方法で強度が評価されたダイカスト製品であって、上記欠陥率が0.5%以下である。
また、上記ダイカスト製品が、車両の電動パワーステアリング装置に用いられるコラムハウジングであり、上記高応力部が上記コラムハウジングのキーロック部であることが好ましい。
また、本発明の他の実施形態のダイカスト製品によれば、本発明のある実施形態のダイカスト製品の強度評価方法で強度評価し、高応力部の所定範囲の内部欠陥の合計面積を全探傷面積で除した欠陥率を0.5%以下としたことにより、所定の強度のダイカスト製品を得ることができる。
以下、ダイカスト製品の強度評価方法の第1実施形態について、図面を参照して説明する。
本実施形態は、図1に示すように、鋳造工程(S1)と、破壊工程(S2)と、強度低下率算出工程(S3)と、強度評価面積率算出工程(S4)とから構成される。
本実施形態における鋳造工程は、例えば、JIS H5302のAl-Si-Cu系アルミニウム合金ADC12を用いて、ダイカスト鋳造する工程である。この工程で得られるダイカスト製品は、図2に示す自動車操舵装置のステアリングコラムハウジング3であることが好ましい。
本実施形態における破壊工程は、上記鋳造工程で得られたダイカスト製品に対して、その鋳造現場において破断試験を行う工程である。この破断試験は、捻り試験であることが好ましい。
この捻り試験は、具体的には、図3に示すように、ステアリングコラムハウジング(ダイカスト製品)3にボルト締結されたキーロック冶具1は、ステアリングコラムハウジング3のキー穴から、ステアリングコラムハウジング3の内径側に突出する凸形状のキー部を有しており、トルク伝達用シャフト2にはキー部と嵌め合う凹部が形成されている。トルク伝達用シャフト2から入力されたトルクはキーロック冶具1の凸形状キー部を介してステアリングコラムハウジング3のキー穴部4に伝達され、キー穴部4の角部を起点としてステアリングコラムハウジングを破断する。
強度低下率算出工程は、上記破壊工程における上記ダイカスト製品の破断面に存在する破断チル層の面積率を測定し、上記破壊工程における捻り破断トルク値と上記面積率との関係から強度低下率を算出する工程である。
強度評価面積率算出工程は、上記強度低下率算出工程において算出された強度低下率に基づいて上記ダイカスト製品の強度評価面積率を算出する工程である。具体的には、まず、上記強度低下率算出工程において算出された上記強度低下率を平均値として、-3σ(σ:標準偏差)の閾値を求める。そして、この閾値と、予め設定された強度の範囲とから上記ダイカスト製品の強度評価面積率を算出する工程である。
まず、JIS H5302のAl-Si-Cu系アルミニウム合金ADC12を用いて、表1に示す条件にてダイカスト鋳造して、実施例1~16及び比較例1~6のステアリングコラムハウジングを得た。
<破壊工程>
次に、実施例1~16及び比較例1~6の各ステアリングコラムハウジング1を、図3に示す捻り試験機を用いて捻って破断させ、破断時の捻りトルク値を測定した。測定結果を表1に示す。
次に、破断面の起点部近傍を実体顕微鏡で観察し、破断チル層を識別し、破断チル層面積率を算出した。算出結果を表1に示す。このとき、破断面は予め応力解析により起点に働く応力値を算出し、その応力値の1/2となるまでの応力範囲を破断面観察範囲とする。本実施例では、破断チル層の面積率の観察範囲は、起点部から15mm位置までとした。
ここで、強度低下率算出工程で得られた捻り破壊トルク値と破断チル層の面積率との関係が図5に示すグラフのようにプロットできる。なお、図5中、実施例1~16は「○」で示し、比較例1~6は「◆」で示した。
その後、図5に示すように、「強度低下率」を示す直線L1上の各点を平均値として、-3σ(σ:標準偏差)で規定される下部管理限界線L2を「閾値」として規定する。そして、この下部管理限界線L2と「要求強度の範囲(図5中、R2で表示)」とから、強度評価面積率(実施例として好適な破断チル層の面積率の範囲(図5中、R1で表示))を算出する。例えば、対象となるダイカスト製品の「要求強度の範囲」として、捻り破壊トルク値が「260Nm以上」と設定された場合、実施例として好適なダイカスト製品は、下部管理限界線L2に基づいて、破断チル層の面積率が10%以下(強度評価面積率)のダイカスト製品が強度評価される。
次に、ダイカスト製品の強度評価方法の第2実施形態について図面を参照しながら説明する。
図6は、本実施形態のダイカスト製品の強度評価方法で用いられる6軸可動超音波探傷装置の説明図であり、図6aは装置の全体図、図6bは被探傷物とターンテーブルの詳細図、図6cは内部欠陥探傷の説明図である。図中の符号11は、本実施形態で強度を評価する対象となるアルミダイカスト製品であり、例えば電動パワーステアリング装置のコラムハウジングである。
また、本実施形態のダイカスト製品によれば、上記の強度評価方法で強度評価し、高応力部の所定範囲の内部欠陥の合計面積を全探傷面積で除した欠陥率を0.5%以下としたことにより、所定の強度のコラムハウジング(ダイカスト製品)11を得ることができる。
以上、ダイカスト製品の強度評価方法の第2実施形態について説明してきたが、本発明はこれに限定されずに、種々の変更、改良を行うことができる。
2 トルク伝達用シャフト
3 ステアリングコラムハウジング
4 キー穴部
11 ダイカスト製品(コラムハウジング)
12 ターンテーブル
13 探触子
14 内部欠陥
15 高応力部(キーロック部)
Claims (8)
- ダイカスト製品を鋳造する鋳造工程と、
鋳造後のダイカスト製品の破断試験を行う破壊工程と、
該破壊工程における前記ダイカスト製品の破断面に存在する破断チル層の面積率を測定し、前記破壊工程における捻り破断トルク値と前記面積率との関係から強度低下率を算出する強度低下率算出工程と、
前記強度低下率を平均値として、-3σ(σ:標準偏差)の閾値を求め、この閾値と、予め設定された強度の範囲とから前記ダイカスト製品の強度評価面積率を算出する強度評価面積率算出工程とを含むことを特徴とするダイカスト製品の強度評価方法。 - 前記鋳造工程がJIS D5812に基づく鋳造工程であり、前記ダイカスト製品がアルミ製コラムハウジングであり、前記破断試験が前記ダイカスト製品の捻り試験であることを特徴とする請求項1に記載のダイカスト製品の強度評価方法。
- 前記ダイカスト製品が自動車用ステアリングのイグニッションスイッチ付きステアリングロックに使用されることを特徴とする請求項1又は2に記載のダイカスト製品の強度評価方法。
- 請求項3に記載のダイカスト製品の強度評価方法によって、強度が評価されたダイカスト製品であって、
ステアリングロック用穴が形成され、
前記捻り試験によって前記ステアリングロック用穴を破断させたときの破断起点から応力解析により求めた前記破断起点に働く応力最大値の1/2以上となる応力範囲までの破断面の面積に占める破断チル層の面積率が10%未満であることを特徴とするダイカスト製品。 - ダイカスト製品の強度を評価する方法であって、前記ダイカスト製品を予め応力解析して求めた高応力部に対し、当該高応力部の所定範囲の内部欠陥を超音波探傷し、当該所定範囲の内部欠陥の合計面積を全探傷面積で除した欠陥率が予め設定した所定値以下であるときに当該ダイカスト製品が所定の強度を有すると評価することを特徴とするダイカスト製品の強度評価方法。
- 前記高応力部の所定範囲は、当該高応力部の最大応力の50%以上の応力の範囲であることを特徴とする請求項5に記載のダイカスト製品の強度評価方法。
- 請求項5又は6のダイカスト製品の強度評価方法で強度が評価されたダイカスト製品であって、前記欠陥率が0.5%以下であることを特徴とするダイカスト製品。
- 前記ダイカスト製品が、車両の電動パワーステアリング装置に用いられるコラムハウジングであり、前記高応力部が前記コラムハウジングのキーロック部であることを特徴とする請求項7に記載のダイカスト製品。
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EP2821772A1 (en) | 2015-01-07 |
EP2821772A4 (en) | 2015-10-21 |
CN103635787A (zh) | 2014-03-12 |
CN103635787B (zh) | 2015-07-15 |
JPWO2013128500A1 (ja) | 2015-07-30 |
WO2013128500A9 (ja) | 2014-10-16 |
US20150044090A1 (en) | 2015-02-12 |
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