NIC-MfrsGuide-Ebook2

A Manufacturer’s Guide To Plastic Injection Molding NicoletPlastics.com | 1
A Manufacturer’s Guide To
Plastic Injection Molding

T A B L E O F C O N T E N T S
5 Tips For Issue-Free
Injection Molding. . . . . . . . . . . . . . . . . . . . . . . 3-4
Material Matters. . . . . . . . . . . . . . . . . . . . . . . . 5-9
Metal vs. Plastic. . . . . . . . . . . . . . . . . . . . . . . 10
Success Stories. . . . . . . . . . . . . . . . . . . . . . . . 11-12

5 Tips For Issue-Free Injection Molding
Tip 1: Consistent Wall Thickness
Material thickness is one of the most critical factors in part design. Adhering to uniform
thickness in the part design process will help you to avoid manufacturing issues later on.
Minimalizing material use should be on the mind of a designer in regard to cost, however;
achieving an ideal wall thickness can be a balance between the strength of the material
and weight which are important factors to the part’s overall durability and cost.
Parts that are designed with uniform walls will not warp, will fill properly and fit together
because variable shrinkage is minimized. Wall thickness variations should not exceed 10%
in high mold shrinkage plastics. Even just a slight discrepancy can present processing and
quality problems.
Tip 2: Proper Gate Location
If varying wall thickness cannot be avoided, then designers should provide for proper gate
location. If this is not supplied, then attaining uniform pack of the molded part will be nearly
impossible. The most effective gate location is when the melt enters at the thickest part of
the cavity and then flows to the narrower areas.
Tip 3: Optimal Wall Thickness
There is no maximum wall thickness for injection-molded parts and in most circumstances;
strength and product requirements will determine the optimal thickness for a part.
Designers are focused on determining a part’s minimum wall thickness required because
thinner is almost always less expensive because they require less material and cool faster.
Tip 4: Avoid Sharp Corners
Sharp corners are an important feature to avoid because they can greatly increase the
stress concentration and lead to part failure. It is imperative to avoid part stress because
it can cause warpage, sink marks, cracking, premature failure and more. While some
stress in a part is expected, the stress factor should always be kept in mind to ensure the
integrity of the part.
Rounded corners ease plastic flow, so it is recommended that engineers generously radius
the corners of all parts. As the plastic goes around a well-proportioned corner, it will not
be subjected to area increases and abrupt changes in direction. Cavity packing pressure
stays consistent. This leads to a strong, dimensionally stable corner that will resist post-
mold warpage.

5 Tips For Issue-Free Injection Molding (cont.)
Tip 5: Add Sufficient Draft
Draft refers to the angles incorporated into your part design that aid in the ejection process
from the mold. The amount of draft required for your part will vary depending on material
thickness and texture. Consider the shrink properties of the material as it hardens. By
tapering the sides of a mold to a recommended draft angle, the part will be easier to remove.
When considering cost and manufacturability, the ideal draft angle is the largest angle that
will not lessen the customer’s satisfaction with the product.


ACETAL (generic name)
Brand Names:
Relative Cost: Medium
Mechanical Properties:
• Strength: Medium
• Impact Resistance: Medium
• High Temp Strength: Medium-Low
Moldability Charactersitics:
• Warp and Dimensional Accuracy,
Molded: Fair
• Fills Small Features: Fair
• Voids in Thick Sections: Poor
• Sink in Thick Sections: Good
• Flash: Good
• High Temperature Hard on Mold
Ejectors: Fair

NYLON 6/6 (generic name)
Brand Names:
• Impact Resistance: High
Molded: Fair
• Fills Small Features: Excellent
• Voids in Thick Sections: Good
• Sink in Thick Sections: Fair
• Flash: Poor
Ejectors: Fair

NYLON 6/6, GLASS FILLED (generic name)
Brand Names:
• Strength: High
• High Temp Strength: High
Molded: Fair
• Fills Small Features: Good
• Voids in Thick Sections: Excellent
• Flash: Fair
Ejectors: Fair
MATERIAL MATTERS


POLYPROPYLENE (generic name)
Brand Names:
Relative Cost: Low
• Strength: Low
Molded: Fair
• Voids in Thick Sections: Poor
• Sink in Thick Sections: Poor
• Flash: Poor
Ejectors: Good

HIGH DENSITY POLYETHYLENE (HDPE) (generic name)
Brand Names:
Relative Cost: Low
• Strength: Low
• High Temp Strength: Low
Molded: Fair
• Voids in Thick Sections: Unknown
• Sink in Thick Sections: Poor
• Flash: Poor
Ejectors: Good

POLYCARBONATE (generic name)
Brand Names:
Relative Cost: Medium-High
• High Temp Strength: Medium-High
Molded: Good
• Voids in Thick Sections:
Fair to Good
• Flash: Good
Ejectors: Good


ACRYLONITRILE BUTADIENE STYRENE (ABS) (generic
name)
Brand Names:
Relative Cost: Low
• Strength: Medium-Low
Molded: Good
• Flash: Good
Ejectors: Good

POLYCARBONATE/ABS ALLOY (generic name)
Brand Names:
• High Temp Strength: Medium
Molded: Good-Excellent
• Flash: Good
Ejectors: Good

POLYETHERIMIDE (generic name)
Brand Names:
Relative Cost: High
• Strength: Very High
• High Temp Strength: High
Molded: Good-Excellent
• Voids in Thick Sections: Fair
• Flash: Good
Ejectors: Poor


POLYETHERMIDE, FIBER REINFORCED (generic name)
Brand Names:
Relative Cost: High
• Strength: Very High
• High Temp Strength: Very High
Molded: Good
• Voids in Thick Sections: Fair
• Flash: Excellent
Ejectors: Poor

POLYBUTYLENE TEREPHTHALATE (generic name)
Brand Names:
Relative Cost: Medium-High
Molded: Fair
• Flash: Fair
Ejectors: Good

POLYSTYRENE (generic name)
Brand Names:
Relative Cost: Low
• Strength: Medium-Low
• Impact Resistance: Low
Molded: Good
• Fills Small Features: Good
• Flash: Fair
Ejectors: Good


THERMOPLASTIC ELASTOMER (generic name)
Brand Names:
Relative Cost: Low-Medium
• Strength: Low
Molded: Poor
• Flash: Poor
Ejectors: Excellent

ACRYLIC (generic name)
Brand Names:
• Impact Resistance: Low
Molded: Good
• Flash: Good
Ejectors: Good

Metal vs. Plastic
Are there benefits of using plastic over metal? Absolutely.
The benefits of plastic have everything to do with chemistry, and the most basic
building blocks of plastics – monomers (groups of atoms that make a unit cell.)
These monomers are combined in limitless ways to form polymers, or plastics, that
are unique to specific design and product performance requirements.
The resulting plastics that we utilize have:
ÆÆ Unlimited characteristics that are tailored to meet your needs
ÆÆ The flexibility to be made into any desired shape
ÆÆ The benefits of a safe, durable and high-performing product
ÆÆ The advantages of a lightweight product, thus saving energy in the production
process and reducing the costs of shipping
ÆÆ A lower production cost
ÆÆ A faster manufacturing time

CASE
STUDY
INVIVO CORPORATION
49 Parts. 1 Solution.
As Invivo Corporation began to finalize the design of its
innovative Luminescence Breast Coil System and Biopsy
Device (LBS), Dean Walters, Invivo’s Lead Engineer for
the project, began consulting with the engineers of Nicolet
Plastics Inc. (NPI)
“We’ve worked with NPI for 25 years,” notes Walters.
“And experience has shown that it’s best to involve the
NPI engineers early in the process because they use their
expertise with plastics to optimize product designs, the
mold and tooling processes and even materials selection
to give us more cost-effective, high-quality options.”
The design of Invivo’s LBS – a device that provides
illumination, superior imaging, immobilization and needle
guidance for interventional biopsies – was particularly
challenging. Not only would the disposable device need
to meet the highest sterility standards, it had to have
exceptional mechanical strength in order to provide
stability, and had to be composed of both biocompatible
and flame retardant materials that wouldn’t image during
an MRI scan. This meant improving designs with product
development engineering.
“Some components were designed ahead of time, but NPI
reviewed all our specs,” explained Walters.

CASE
STUDY
INVIVO CORPORATION
49 Parts. 1 Solution.
At the start of each part development, NPI asks customers’ engineers a series of questions
about their product requirements to see what alternative materials and production avenues
are open for consideration. NPI’s philosophy is to make the process as cost effective
as possible, without minimizing the quality of the product. The process incorporates a
powerful combination of engineering and product development. The engineers of NPI
customers are not always well-versed in plastics, so the team’s expertise helps customers
discover alternative designs, materials and production methods they may not be aware of
to ultimately get their product to market on time and under budget.
At project completion, Walters stated, “Some of the LBS’s more complex tools had side
actions, and we had to work with NPI to determine directions of pull. We couldn’t have
finished the design without their input.”
Resources: http://injectionmolding.blog.quickparts.com/about/
EQUALS
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