Injection Molding of Fiber-Reinforced Plastic

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Injection Molding of Fiber-Reinforced Plastic
Refer to “Research on Strength Prediction Technology forFiber-Reinforced Plastic Injection-Molded Products” (page 20)

OGURA Shogo
R&D Sect. No.1, Production Technology R&D Center, Engineering Div.

1

What is Injection Molding?

ResinMold

Injection molding is a process for forming parts byheating resin and injecting the molten material into amold. This process enables the stable production of partsof complex geometry at a high-speed cycle. Plastic parts
manufactured by this process are used in a variety offields.

23Fig. 1 Schematic of injection molding

Features of Injection Molding ofFiber-Reinforced Plastic

FiberThe plastic used for structural members is reinforced
with glass or carbon fibers to be fiber-reinforced plastic(hereinafter “FRP”) with improved physical properties.
Injection-molded FRP is made from resin pellets mixed
with three-dimensionally distributed fibers of a length ofabout 100 µm. Like normal plastic, FRP can also beformed into complex geometries by injection molding(Fig. 1). However, FRP injection-molded parts have fiberorientations (fibers positioned in different orientations)that depend on how the molten resin flowed during themolding process (Fig. 2). FRP is more reinforced in thedirection of fiber orientation. This means that the physical properties in the direction parallel to the fiber orientation are different from those in the direction perpendicular to the fiber orientation. This is called “anisotropy ofphysical properties” and makes it difficult to predict thefinal quality of parts.
Prediction of Anisotropy of PhysicalProperties

To predict the physical properties of a composite ofresin and fibers, an approach called “homogenization”
may be used. Homogenization can be used to predict thephysical properties of a composite from the physicalproperties and geometry information of the individual

FibersHigh strength

Low strength

Resin injection port
Fig. 2 Overview of anisotropic physical properties

materials, i.e., fibers and resin in this case. Homogenization is thus a concept necessary for predicting the qualityof composites. Furthermore, for composites containing a
number of distributed short fibers, as seen in injectionmolded products, it is necessary to define how many fibers exist in which directions. To this end, a concept
called “fiber orientation tensor” is used. Fiber orientation
tensor is expressed in three major directions of fiber orientation and the ratio of fibers oriented in the respective
directions. For example, a fiber orientation tensor closer
to one (1) along an axis indicates that more fibers are oriented aligned along that axis. Thus, fiber orientation tensors can be used to quantitatively define the orientationof a number of fibers distributed in the plastic, thereby
enabling the prediction of anisotropy of physical properties of FRP injection-molded parts.

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KYB TECHNICAL REVIEW No. 67 OCT. 2023

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PMSM1)
Refer to “Characteristic Analysis of High-efficiency Hydraulic System” (page 10)

SHIBAHARA DaichiElectronic engineering Sect, Basic Technology R&D Center, Engineering Div.

12

What is PMSM?

1. 1 Acronym and Structure/Operation
PMSM is an acronym for Permanent Magnet Synchronous Motor. This is a motor that uses magnetic field flux
created by permanent magnets to run in synchronization
with an alternating-current (AC) power source. PMSMs
are classified as AC motors.
1. 2 Classification by Configuration
PMSMs can be divided by magnet arrangement into
Surface-mounted PMSM (hereinafter “SPM”) and Interior PMSM (hereinafter “IPM”). These types of PMSM
deliver different characteristics from each other depending on the combination with current control methods as
described below.
The SPM is suitable for low-speed, large-torque designand can smoothly run with low torque ripples Comparedto the IPM, the SPM can deliver liner torque responses
against a current and be more easily controlled.
With its higher degree of geometry design freedom,
the IPM can be designed to provide specific characteristics
tailored to the application. The range of speed at which
the IPM can be rotated is higher than that of the SPM.
1. 3 Characteristics
PMSMs can commonly deliver high power efficiency
over a wide operating range and output a high power
even with small-sized designs. On the other hand, theyrequires microcomputers and permanent magnets that use
rare earth elements, which make PMSMs more expensive
than the induction motors widely used in industrial applications. Therefore, PMSMs are suited to applications
where downsizing and efficiency enhancement are needed.

Varying Properties Depending onControl

2. 1 Control Methods
The PMSM control methods can generally be divided
into V/f control (open-loop control) and current vector(hereinafter just “vector”) control (closed-loop control).
The former is used in cost-oriented applications and thelatter used in performance-oriented ones. This section
describes the latter control method.
2. 2 Current Vector Control
On the plane of the d-axis corresponding to the direction of magnet flux (≈ physical angle of the magnets) andthe q-axis orthogonal to the d-axis, current components
of a three-phase motor are regarded as a vector. A methodof controlling the magnitude and angle (= current split
ratio between the d-axis and the q-axis) of these components is vector control. The vector can be determined byseveral approaches including MTPA control and weak
field control described in the following.
2. 3 Maximum Torque Per Ampere Control
MTPA control determines the current split ratio so as
to achieve the highest possible torque on the assumptionthat the vector is constant (= constant motor current).
This is a basic motor control strategy applied to caseswith no limited by voltage or current.
2. 4 Weak Field Control
In a high range of revolutions, the reverse induced voltage increases to reduce available current. Then, a negative
d-axis current can be used to cancel the magnet flux, lowering the reverse induced voltage. This expands the rangeof speeds to drive the motor. This weak field control strategy is applied to cases in the presence of voltage limit.
Reference1) MORIMOTO Shigeo, INOUE Yukinori: “Basics and Design
Method of Drive System for Energy Saving Electric Motors”
Kagakujyoho Shuppan Co., Ltd. (November 4, 2019)― 45 ―