Method of making a molded fiber reinforced plastic leaf spring

A molded fiber reinforced plastic leaf spring. The spring has a curved central section composed of longitudinally extending fibrous strands impregnated with a cured thermosetting resin. The central section is generally rectangular in cross section having rounded upper and lower edges and a ground-off parting line disposed substantially at the neutral axis of the spring.

BACKGROUND OF THE INVENTION 
There has recently been considerable activity in the production of fiber 
reinforced plastic leaf springs for vehicles due to the substantial 
reduction in weight as compared to metal leaf springs. Fiber reinforced 
plastic leaf springs can be produced by winding fibrous strands 
impregnated with a thermosetting resin around a pair of spaced bushings. 
After the desired number of windings have been made to produce the 
required strength characteristics, the wound structure is placed in a mold 
and the thermosetting resin is cured. The resulting cured product consists 
of a generally curved central section and integrally connected end 
portions having openings or eyes adapted to receive connecting members. 
In other methods of manufacture, the curved central section of the leaf 
spring is molded separately from resin-impregnated fibrous material, and 
after molding, the ends of the central section are mechanically connected 
to metal end members having openings to receive connectors that connect 
the spring to a vehicle. 
It is desired that the curved central section of the spring have rounded, 
longitudinal edges because sharp edges tend to produce high stress areas. 
Rounded bottom edges can readily be produced in the molded structure by 
utilizing rounded corners for the female mold. However, in the past 
rounded upper edges have not been satisfactorily produced by molding. 
Grinding away the molded sharp upper edges acts to remove and sever the 
reinforcing fibers which reduces the strength characteristics of the 
spring. 
In any molding operation flash is produced at the parting line between the 
male and female molds. When molding a fiber reinforced plastic leaf 
spring, some fibers are carried into the flash and after molding, on 
removal of the flash, these fibers are ground away. If the flash is 
located at the upper portion of the spring, which is a high stress area, 
the removal of the flash and severing of the fibers at this location can 
adversely effect the physical properties of the spring. Furthermore the 
severed fibers tend to produce sharp needle-like projections which can be 
a hazard to handling of the spring. 
SUMMARY OF THE INVENTION 
The invention is directed to a molded fiber reinforced plastic leaf spring. 
The spring is composed of a curved central section, and end sections are 
integrally connected to the ends of the central section and have openings 
to receive connectors for attachment to the vehicle. 
The curved central section is generally rectangular in cross section having 
opposed upper and lower surfaces connected by side surfaces, and the 
longitudinal edges joining the side surfaces to the upper and lower 
surfaces are rounded or curved. 
The ground off flash at the parting line is located substantially at the 
neutral axis of the central action in a low stress area, so that any 
severing of fibrous material on removal of the flash will not adversely 
effect the physical characteristics of the spring. 
In accordance with the method of the invention, the curved central section 
of the spring is molded in a mold assembly consisting of a female mold and 
a cooperating male mold. The female mold includes a bottom wall and side 
walls which are connected to the bottom wall by rounded corners, while the 
male mold is composed of an upper wall and side walls which extend 
downwardly and are received within the side walls of the female mold. The 
side walls of the male mold are connected to the upper wall by rounded 
corners and the lower extremities of the side walls of the male mold 
terminate in generally flat surfaces. 
In the molding operation, the wound fibrous structure impregnated with the 
uncured thermosetting resin is placed in the female mold and the molds are 
then moved relative to each other to bring the male mold into registry 
with the female mold. Sufficient compressive force is applied to the male 
mold to bring the lower extremities of the side walls of the male mold to 
a point on the neutral axis of the spring. During the molding, the liquid 
resin and fibrous reinforcement may be squeezed out along the parting line 
between the side walls of the male mold and the adjacent side walls of the 
female mold to produce flash. As the flash is located on the neutral axis 
of the spring, the subsequent removal of the flash, after the molding 
operation, and severing of the fibrous material will not adversely effect 
the physical properties of the spring. 
The resulting molded leaf spring has rounded upper and lower longitudinal 
edges, obtained without machining or grinding, which reduces the stress 
concentrations at the edges. Because of this, the spring has better 
physicl properties per unit weight than prior art fiber reinforced plastic 
leaf springs. 
Other objects and advantages will appear in the course of the following 
description.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENT 
FIG. 1 illustrates a fiber reinforced plastic leaf spring 1 to be used for 
a vehicle and composed of a curved central leaf section 2 and end sections 
3. Each end section 3 is provided with a metal or plastic bushing 4 having 
an opening to receive a connecting member to attach the spring to a 
vehicle in the conventional manner. 
The central section 2 and end sections 3 are preferably composed of 
substantially continuous windings of fibrous material impregnated with a 
cured thermosetting resin. The fibrous reinforcement can take the form of 
mineral fibers, such as glass; vegetable fibers, such as cotton; animal 
fibers such as wool; synthetic fibers such as nylon, Dacron, or Orlon; or 
metal fibers, such as steel wire. 
The thermosetting resin can be any conventional thermosetting resin, such 
as an epoxy or polyester resin, used in forming fiber reinforced resin 
products. 
As shown in FIG. 3, the central section 2 is generally rectangular in cross 
section, having an upper surface 5 and a lower surface 6 connected by side 
surfaces 7. The longitudinal edges 8 connecting the upper surface 5 and 
side surfaces 7, as well as the longitudinal edges 9 connecting lower 
surface 6 and side surfaces 7, are generally curved or rounded which tends 
to reduce stress concentrations at these areas. 
In addition, longitudinal ribs 10 extend outwardly from each side surface 7 
and ribs 10 have flat upper surfaces 12 that lie generally along the 
neutral axis 13 of the spring. In the lower stress areas of central 
section 2, adjacent end sections 3, ribs 10 are less prominent and merge 
into the end sections. 
FIG. 2 illustrates schematically a manner of winding leaf spring 1 from 
continuous strands or rovings 14 of fibers impregnated with the uncured 
resin. In this method, the strands 14 are wound helically around the 
spaced bushings 4. When the desired number of layers are wound to obtain 
the required physical properties in the spring, the wound structure, with 
the tension relaxed, is placed in a mold assembly 15, with the two runs 16 
and 17 of the wound structure falling together in the bottom of the cavity 
18, in the female mold 19. 
The mold assembly 15 also includes a male mold 20 which is adapted to 
cooperate with the female mold 19 to mold the wound structure. As best 
illustrated in FIG. 4, cavity 18 of female mold 19 is defined by a bottom 
wall 21 and a pair of spaced side walls 22 which are joined to the bottom 
wall by rounded corners 23. Each side wall 22 is provided with a generally 
flat upwardly facing shoulder 24. 
Male mold 20 consists of an upper wall 25 and a pair of spaced downwardly 
extending side walls 26 which are received within the side walls 22 of the 
upper portion 30 of female mold 19. As illustrated in FIG. 4, the side 
walls 26 are connected to upper wall 25 by rounded corners 27. The lower 
extremities of side walls 26 terminate in flat surfaces 28 aligned with 
shoulders 24. 
After the wound structure of the central section 2 is placed in the cavity 
18 of the female mold 19 a predetermined force is applied to male mold 20 
to compress the wound material. The predetermined force applied to the 
male mold will bring the lower surfaces 28 of side walls 26 of male mold 
20 into general alignment with the neutral axis 13 of the spring section 
2. The neutral axis 13 lies midway of the height of central section 2, as 
illustrated in FIGS. 3 and 5. 
During the molding operation, a portion of the uncured resin, along with 
some fiber reinforcement may be squeezed or extruded outwardly along the 
parting line 29 between the male and female molds. The parting line is 
located at the junction between the outer surface of the side walls 26 of 
male mold 20 and the inner surface of upper portion 30 of female mold 19. 
Heat is normally applied to the fiber reinforced plastic structure during 
the molding operation to accelerate the cure of the thermosetting resin. 
Heat can be applied by placing the mold in an oven, or alternately 
employing a heating mechanism formed integrally with the male and female 
molds. 
After curing of the resin, male mold 20 is removed from the cavity 18 of 
the female mold and the molded structure is removed from the female mold. 
The material extruded along the parting line 29 during the molding 
operation will constitute flash which can be ground away to complete the 
operation. As the flash is located along the neutral axis 13, the grinding 
of the flash, and the severing of fiber reinforcement located in the 
flash, will not adversely effect the physical properties of the molded 
spring. 
As both the male and female molds have rounded corners as indicated by 23 
and 27, the molded central section 2 will have rounded upper and lower 
longitudinal edges 8 and 9 and this reduces high stress concentrations at 
these edges. 
Ribs 10 are formed by cooperation of shoulders 24 and surfaces 28 during 
the molding operation. In certain instances, the shoulders 24 can be 
eliminated, in which case the molded product, instead of having ribs along 
each side, will have upwardly facing edges or shoulders along each side. 
As the parting line between the male and female molds and the resulting 
flash is located substantially along the neutral axis, the removal of the 
flash and the severing of any fibrous reinforcement in the flash will not 
adversely effect the physical properties of the spring. Because of this, 
the spring has improved physical properties. 
Various modes of carrying out the invention are contemplated as being 
within the scope of the following claims particularly pointing out and 
distinctly claiming the subject matter which is regarded as the invention.