JPS5814935B2 - Leaf spring manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a leaf spring made of a fiber-reinforced composite material that has mechanical properties comparable to those of steel, has excellent impact resistance, fatigue resistance, and safety, and is effective in reducing weight. It is.

More specifically, a thread or strip of glass fiber or carbon fiber is impregnated with a thermosetting resin on a mandrel having at least one arc corresponding to the shape of the leaf spring.
Symmetrically in the thickness direction with the neutral axis as the axis of symmetry, the outermost layer is glass fiber reinforced resin (hereinafter referred to as GFRP), the inner layer is carbon fiber reinforced resin (hereinafter referred to as CFRP), and the center layer including the neutral axis is glass fiber reinforced resin. A method for manufacturing a leaf spring, which comprises the steps of: filament winding or winding and lamination, and then cutting the cured molded product into individual leaf spring units to obtain a large number of leaf springs. It is related to.

The structure of the leaf spring obtained according to the present invention is expressed by the following formula (E1, E2, E3 are the elastic moduli of GFRP and CFRP forming the first, second and third layers shown in FIG. 2, t1
, t2, t3 are thicknesses from 0-σ (neutral axis) shown in FIG. 2).

Resource and energy conservation have become global issues.

Improving the fuel consumption efficiency of automobiles has become a current issue, and two measures to achieve this goal include reducing the weight of automobiles.

In order to reduce the weight, lighter materials such as light alloys, plastics, and fiber-reinforced composite materials are being considered for various parts, and these are being used instead for structural parts that do not require mechanical strength.

However, as there are no materials that are sufficiently reliable in terms of strength, modulus of elasticity, fatigue resistance, impact resistance, etc. for the main structural materials of automobiles, such as the important bodies, drive shafts, and leaf springs, metals are still used. It is mainly used for
Therefore, many problems remain in effectively reducing the weight of automobiles.

The purpose of the present invention is to produce a leaf spring made of fiber-reinforced composite material that is lighter and has superior mechanical properties such as fatigue resistance, impact resistance, and friction resistance compared to steel leaf springs, and is highly safe. It provides:

By using the leaf spring obtained according to the present invention, weight reduction can be achieved and it can greatly contribute to fuel savings.

One of the characteristics of leaf springs made of fiber-reinforced composite materials is that, unlike steel, there is no reduction in material life due to rust or corrosion, metal fatigue, or the occurrence of accidents associated with this.

It has been reported that carbon fiber reinforced resin and glass fiber reinforced resin composite materials are used to reduce the weight and improve mechanical properties of leaf springs.

However, there is a fundamental problem in using these CFRP and GFRP alone.

That is, CFRP has poor impact resistance, and GFRP has poor fatigue resistance, so that they alone lack the various performances and suitability required for leaf spring structural materials.

A leaf spring having a hybrid structure in which a layer made of CFRP and a layer made of GFRP are integrally molded is known, particularly a leaf spring having a GFRP layer in the center and a CFRP layer in the outer layer.

This is because the bending rigidity is high and the elongation of CFRP is low, so the absorbed energy is small, and the impact strength of CFRP is low, so if it is hit by foreign objects such as pebbles or metal pieces while driving, it may cause damage and lead to an accident. There is.

Furthermore, leaf springs having a GFRP layer as an outer layer and a CFRP layer as an inner layer are also known.

However, it is meaningless to use expensive CFRP for the center layer, which is hardly subjected to stress, and since the fatigue strength of 10,000 GFRP is high, there are problems such as poor durability depending on the ratio of the thickness of the GFRP layer and the CFRP layer. there were.

Most of the conventional manufacturing of leaf springs using fiber-reinforced composite materials is by the so-called lamination method such as the hand lay-up method, and this method not only limits the quantity but also increases the cost due to the long molding time.

Furthermore, there were problems such as inconsistent quality, which could lead to accidents.

The inventor has found that the mechanical properties of these conventional steels are as good as
Moreover, the present invention was achieved as a result of repeated fatigue research into manufacturing leaf springs made of fiber-reinforced resin composite materials that are effective in reducing weight and have excellent impact resistance, fatigue resistance, and safety.

That is, the present invention uses glass fiber impregnated with a thermosetting resin,
Carbon fiber is a yarn or a strip-shaped material that is placed on a mandrel consisting of multiple arcs corresponding to the shape of a leaf spring, and symmetrically in the thickness direction with the neutral axis as the axis of symmetry, with the outermost layer being a GFRP layer and the inner layer being a CFRP layer. After filament winding or winding lamination is performed so that the center layer contains a laminated structure of GFRP layers, it is cured, and then the molded product is extracted from a mandrel and cut into predetermined dimensions to simultaneously manufacture a large number of leaf springs. It is something.

FIG. 2 is a conceptual diagram showing the cross-sectional structure of a leaf spring obtained according to the present invention.

4 and 6 are GFRP layers, and 5 is a CFRP layer.

In the present invention, impact resistance is improved by using GFRP, which has better impact resistance than CFRP, for the outermost layer of No. 6.

The inner layer (intermediate layer) of No. 5 covers the strength characteristics required for leaf springs by using CFRP, which has high elastic modulus, fatigue resistance, and excellent vibration damping properties.

The center layer of No. 4 does not need to be very strong due to the stress distribution, so by laminating GFRP made of inexpensive glass fiber, a lightweight leaf spring with excellent mechanical properties and high safety can be manufactured. Ru.

Regarding the ratio of the thickness of each layer of the leaf spring obtained by the present invention, the thickness of the first layer, second layer, and third layer in FIG.
The bending elastic modulus (JISK-6911) of the material of each layer is E1, E2, E3, and the thickness is tl.
, t2, t3, and t3-t2Th0.
It has been found that one that satisfies the 5th tone is preferable.

For example, the service life will not be sufficient.

In order to protect the CFRP layer from collisions with foreign objects such as pebbles and metal pieces, the thickness t3-t2 of the outermost GFRP layer is preferably 0.5 mm or more.

It is preferable that t1 is 0.5t2 or less.

If t1≦0.5t2, the number of expensive CFRP layers can be reduced with almost no effect on bending rigidity or maximum load.

In the case of t1)0.5 t2, the decrease in the maximum load cannot be ignored.

By selecting <tl z t2 s t3 as described above, it is possible to obtain an economical leaf spring that is lightweight, has excellent impact resistance and fatigue resistance, and is highly safe.

Furthermore, in the leaf spring according to the present invention, the interlaminar shear strength S1, especially the fatigue interlaminar shear stress SF after repeated loading
Since a GFRP layer with a small amount is used for the center layer, even if fatigue or an unexpected large load is applied, delamination will occur between the center GFRP and CFRP before the entire leaf spring ruptures. is possible, which provides security.

A thermosetting resin can be used as the resin constituting the GFRP and CFRP of the present invention.

Examples of thermosetting resins include epoxy resins, unsaturated polyester resins, phenol resins, alkyd resins, furan resins, and melamine resins.

The reinforcing fibers are used in the form of filament yarns, spun yarns, strands, etc., which are impregnated with a thermosetting resin and then filament wound by changing the winding angle.

In this case, yarn prepreg may be used.

Alternatively, a tape or sheet in which fibers are uniformly arranged in one direction, or a belt-like material such as felt, nonwoven fabric, knitted fabric, or woven fabric is impregnated with a resin and then rolled and laminated.

In this case, prepregs of these strips may be used.

After filament winding or winding and lamination, the cured molding can be cut into leaf springs.

In the present invention, the arc corresponding to the shape of the leaf spring means a part of a circle, an ellipse, a hyperbola, a parabola, etc., or a part of a curve formed by a multidimensional function.

The present invention will be explained below with reference to Examples, but the present invention is not limited to these Examples.

Implementation row 1 Length 1400 with three identical circular arcs as shown in Figure 1
In order to make glass fibers impregnated with bisphenol type, epoxy resin, and carbon fibers on a mm mandrel so that they are symmetrical in the thickness direction with the neutral axis as the axis of symmetry, we first set the glass fibers so that θ in Figure 1 is ± ± with respect to the mandrel axis. Filament winding at 45° with 3 thicknesses, then 2 carbon fibers
The filament was wound so that θ in FIG. 1 was 0° so that the thickness of the glass fiber was 3 mm.

So that the center layer including this neutral axis becomes symmetrical,
Filament winding to a thickness of mm, and finally filament winding to a thickness of 3 mm with glass fiber as the outermost layer at ±45 degrees at 150℃ for 30 minutes at 7 kg/cm
It was cured at a pressure of 2.

Next, this molded product was pulled out from the mandrel, and the molded product was cut into rounds with a width of 70 mm, and the arc end portion was cut into 3 pieces.
Sixty Lee 7 springs were manufactured from four mandrels.

Three leaf springs were randomly selected from among these leaf springs and various performances were measured, and the results are shown in Table 1.

As is clear from the table, the rigidity ratio is almost the same as that of the steel leaf spring.

The leaf spring made of the fiber-reinforced composite material according to the present invention weighs about 173 times less than the leaf spring made of steel, which is a significant reduction in weight.

Example 2 Using the same mandrel as in Example 1, glass cloth prepreg and unidirectional carbon fiber prepreg impregnated with Q-1112 type epoxy resin (manufactured by Toho Bethlon Co., Ltd.) were applied to the first and third layers in Fig. 2. is glass cloth prepreg, the second layer is 10,000 sided carbon fiber prepreg, and the thickness of each layer is t.
1, t2, and t3 as shown in Table 2, and compression molded by pressing at 150°C and 7 kg/cm2 for 1 hour to obtain a width of 50 mm and a length of 1200 WIn.
, 2 with a radius of curvature of 1100 m and a thickness shown in A1,2
Seed leaf spring was obtained.

As shown in Table 2, the breaking load Wk when both ends of these leaf springs were supported and a load was applied to the center was better, but the fatigue breaking load after 106 repeated loads was 1.
was better.

When the same glass cloth prepreg and unidirectional carbon fiber prepreg were molded separately under the above conditions, the bending elastic modulus was 2.3 ton/mj (: Et = Es) and 1, respectively.
4 ton/ya (: E2).

[Brief explanation of the drawing]

FIG. 1 shows an example of a mandrel used in the present invention. FIG. 2 is a conceptual diagram showing the cross-sectional structure of the leaf spring according to the present invention. 1: mandrel, 2 arcs, 3: filament, 4: first layer (center layer), 5: second layer (inner layer), 6: third layer (outermost layer).

Claims (1)

[Claims] 1 A mandrel having multiple arcs corresponding to the shape of the leaf spring is made of glass fiber, carbon fiber yarn or band-like material impregnated with thermosetting resin as the outermost layer symmetrically in the thickness direction with the neutral axis as the axis of symmetry. is glass fiber, inner layer is carbon fiber,
As the central layer containing the neutral axis consists of a glass fiber structure,
A method for manufacturing leaf springs, which comprises cutting the cured molded product into individual leaf spring units after filament winding or winding and lamination.