MAG
Magnesium
Injection
Molding
DESIGN GUIDE
PHILLIPS PLASTICS CORPORATION
®
Phillips Plastics Corporation
®
Serving original equipment manufacturers in virtually every market since 1964,
Phillips Plastics Corporation® has established itself as one of the premiere sources
for the design and manufacture of custom plastic and metal injection molded
components. Today, Phillips Plastics employs over 1,600 people in 15 locations
throughout the United States.
phillipsmetals.com
What is Magnesium
Injection Molding?
Magnesium injection molding (MAG) produces
components with attributes that include superb
quality, high repeatability, dimensional precision,
and design flexibility. The magnesium injection
molding process is similar to plastic injection
molding, with mechanical properties equivalent
to or better than die-cast components. Phillips
Plastics’ acquisition of the oldest magnesium
injection molding operation in North America,
combined with its extensive knowledge of the
injection molding process, ensures customers
receive the expertise necessary for the design
and development of the most complex magnesium injection molding programs.
Magnesium Market Trends
The use of magnesium is beginning to expand rapidly in an array
of markets, including the medical, automotive, and recreational
fields. Products made with this metal are light-weight, strong,
environmentally friendly, recyclable, and beneficial in conserving
energy and helping meet CAFÉ requirements.
The Magnesium
Molding Process
Magnesium injection molding is a single step,
semi-solid molding process that combines the
best of plastic injection molding and die-casting.
Chips of magnesium alloy are fed into a heated screw and barrel where the alloy is thermally and
mechanically processed into a semi-fluid state and is injected directly into the tool cavity. In contrast
to the higher temperatures necessary for die-casting, magnesium injection molded components are
processed at temperatures more than 100 degrees Fahrenheit cooler. The resulting semi-solid properties
allow the metal alloys to flow like a thermoplastic with a more controlled, laminar flow. The magnesium injection molding process delivers net shaped components with many inherent benefits which
include: superior strength to weight ratios, EMI/RFI shielding, better straightness and flatness, heat
dissipation, low porosity, and tighter tolerances, which may reduce or eliminate some secondary
machining operations.
Thixotropic Structure
Conventional dendrite
formation in semi-solid alloy
Thixotropic structure
of semi-solid alloy
resulting from stirring
Conventional Die-Casting
Cold Chamber
Magnesium Injection Molding
Hot Chamber
Prototype Capabilities
Phillips offers several prototyping capabilities,
which provide solutions to questions and concerns
regarding product design and performance. For
customers that want to test prototype parts, Phillips
offers in-house stereolithography (SLA), and can
supply many other rapid prototyping technologies,
including machining. Should actual injection molded
prototypes be required, P20 prototype tools or a
pull-ahead cavity production tool option is available.
EMI/RFI
Phillips offers six shielding methods for products
requiring immunity from EMI/RFI generators – electroless plating, conductive paint, vacuum metalizing,
imbedded mesh, conductive foil, and magnesium.
Magnesium injection molding is a single step, semi-solid
molding process in which chips of magnesium alloy are fed
into a heated screw and barrel where the alloy is thermally
and mechanically processed into a semi-solid state and
injected directly into a tool cavity.
Secondary Operations
Phillips Plastics can provide secondary operations,
many in-house, to meet a wide range of specified
requirements. Some of the most common secondary
operations include: trimming, vibratory or tumble
deburring, drilling/tapping, CNC machining, electroplating, assembly, and painting/decorating.
Machining
Magnesium is the easiest metal to machine and is
used as a benchmark for all other metals. However,
there are still machining guidelines that must be
adhered to. Magnesium can be machined at high
speeds and feeds and tooling should be sharpened
or ground to specific criteria. Magnesium can be
machined in a dry or wet system. Generally, a wet
machining process is used for higher volumes and
a dry machining process is used for lower volumes.
Various surface finishes can also be achieved while
machining magnesium, which includes profiling
parting lines that result in an improved aesthetic appearance. Punching or piercing holes with the trim
die can eliminate some machining operations. Also,
thread-forming screws, specifically designed for use
with magnesium, can eliminate tapping operations.
Capability Options
Phillips’ magnesium injection molding capabilities
include: conventional single shot, overmolding with
plastic, and insert molding. Insert molding metals into
magnesium alloys can be accomplished with almost
any type of insert, including dissimilar metals, as
long as the insert does not have a lesser melting
point than the alloy. Complexity and part design are
considerations with regards to part cost. Hinges and
tongue and groove features (popular when considering a plastic part with a magnesium part for rigidity
characteristics) are all items that can be incorporated
into the product design and easily molded into the
parts. Additionally, these designs can help eliminate
visible parting lines on critical surfaces.
Environmental Considerations
Magnesium injection molding is an environmentally friendly, 100% recyclable process
that uses no ozone layer depleting gases.
A closed operating system, running at lower
than melting temperatures, eliminates molten
metal hazards and prevents the generation
of oxides. Magnesium, weighing 1/4 the
weight of steel and 1/3 lighter than aluminum,
is the eighth most abundant element in the
earth’s surface and can be safely manufactured in a low hazard environment.
Assembly Considerations
Phillips’ in-depth knowledge of the entire manufacturing
process, combined with its assembly services, provides
customers with true turnkey capabilities. Phillips
provides customers an unparalleled range of assembly
services, which includes: component design, design
for manufacture, and quotes for assembly and finishing operations.
Metallurgical Lab
Phillips’ in-house metallurgical lab is an integral part
of the Thixomolding® process with people exclusively trained to perform microstructure studies on
materials. This lab gives Phillips the capability to
fully monitor and analyze materials, and aids in the
development of the magnesium injection process.
Design Considerations
Walls and Wall Thickness
The walls should be kept as uniform in thickness as possible. Thick sections will be more likely to have
porous centers than thin ones. The magnesium injection molding process has the ability to produce
a higher percent of solids than conventional die-casting thus reducing porosity issues. Magnesium
injection molding can produce walls as thin as 0.015 inch. A general rule is that the flow distance of
the metal will be 100 times the thickness of the wall. However, Phillips has experience with walls as
thin as 0.050 inches with flow distances as much as 6 inches (120 times the thickness). The ability to
place a gate close to the thin sections to be filled, greatly enhances successful filling of thin walls.
Wall thickness should be as uniform as possible to avoid local hot spots during solidification.
Design Considerations (continued…)
Ribs
Ribs should be used to obtain maximum strength
of a wall as well as brace or strengthen a sidewall or
surface. The thickening of walls does not add strength
as well as a properly designed part incorporating ribs.
Deep, thin ribs, or ribs that are spaced close together,
should be avoided unless sufficient ejection can be
designed into the tool.
Thicker sections such as bosses and ribs generally
will not cause sinks on walls as in the plastic injection
molding process. The ability to now place a screw boss
tangent to an outside wall of an assembly without
concern of sink, allows the designer more freedom
for other components.
Avoid Sharp Corners
Sharp corners should be avoided and a progressive
change in shape is recommended to help the metal
flow during die filling to avoid turbulence. Fillets
and blend radii should be used to strengthen
the components and enhance die life.
Draft
All molded surfaces, normally perpendicular to
the parting line of the injection molding die, require
draft (taper) for proper ejection of the mold from the
die. A draft of 1 degree is recommended. Less draft
can be used on longer draws while short draws
require more draft. Zero draft is possible but the
design must allow for sufficient ejection to keep the
part from distorting. Precision tolerances for draft call
for a draft on inside walls at 1 degree per side, with
outside walls requiring half this amount of draft.
Inserts
Inserts are pieces of material, usually metal, that
become an integral part of the component. Inserts
are usually set in the die and magnesium is molded
around that portion of the insert that is left exposed
in the die cavity. However, before designing an insert
as part of a component, consider that inserts slow
machine cycles and increase the cost of recycling
scrap. Often times, inserts can be installed by a secondary operation, such as pressing or screwing, as
economically as molding them into the component.
Undercuts
An undercut is a recess in the sidewall or core hole
of a mold. Undercuts can be formed using slides and
lifters. Slides are used to form undercuts on the outside
of the component and can be either mechanically or
hydraulically actuated. Lifters are used to form undercuts on interior wall surfaces and are designed
similar to lifters in a plastic injection mold.
Hinges
Hinges can be incorporated into the design and
are easily molded. With plastics, the flexural/fatigue
characteristics permit an integral molded-in hinge
that connects the container and the lid, commonly
referred to as a living hinge. However, even though
the properties of magnesium do not permit a living
hinge, the flow characteristics of magnesium will allow for a wide variety of hinges and hinge designs.
Tongue and Groove
Tongue and groove can be incorporated into the
product design and easily molded into the parts. This
type of joint is highly recommended when joining
a plastic part to a magnesium part.
Creep
Creep is plastic deformation of metals that are held
for long periods under stresses less than the normal
yield strength. Creep is a design consideration only
when components are operated at temperatures above
250 degrees Fahrenheit for extended periods.
Magnesium alloys are known for poor creep behavior
at elevated temperatures when compared to aluminum
or ferrous alloys, although they do perform better than
most plastics. However, creep is generally a design
concern only if the magnesium component will operate at elevated temperatures on a sustained basis.
If the component is designed for tensile or compressed
loads at elevated temperatures, creep needs to be
addressed early in the design phase.
Snap Fits
Because magnesium’s mechanical properties
include excellent stiffness and poor elasticity, snap
fit designs between two magnesium parts are not
encouraged. Snap members would need to be long
enough to allow proper deflection without stressing
or fracturing the magnesium. Many designs may not
allow for this amount of length.
Successful snap fit designs between magnesium
and plastic can be achieved as long as the plastic
becomes the flexible member and you use good
plastic design principles.
Flammability
The issue that magnesium burns when subjected to
high temperature is a design consideration that is
not generally a great concern. For more information
and to see a video on how magnesium really burns,
visit the magnesium molding capabilities on Phillips’
Web site at www.phillipsplastics.com.
Phillips Plastics can provide secondary operations,
many in-house, to meet a wide range of specified
requirements.
Dimensional
Considerations
Dimensional Considerations
Magnesium injection molded components may be designed to a tighter tolerance than conventional
die-castings. Phillips has found that magnesium injection molded components can be designed using
North American Die Cast Association (NADCA) – Precision Standards. The superior dimensional
stability of the magnesium injection molding process allows the designer greater flexibility in
design, while holding tighter tolerances.
Moving Die
Moving die components (also called moving die
parts) are most commonly core slides (or pulls)
used to form inset holes or features in die-casting.
Precision Tolerance
Added to Linear Dimension (Projected Area)
Up to 21 to 50 inches2
+ 0.004
51 to 100 inches2
+ 0.006
101 to 200 inches2
+ 0.008
201 to 300 inches
+ 0.011
2
Tolerances shown are plus (+) values only
Source: NADCA Product Specification
Standards for Die Casting/Sec. 4A/9-2006
Linear Dimension
Any dimension to features of the die molding that
is formed in the same die component (half). Any
straight-line dimension on a part of die print.
Precision Tolerance
Basic Tolerance
Up to 1 inch (25.4 mm)
± 0.002
(± 0.05 mm)
Additional Tolerance
For each additional inch
± 0.001
Over 1 inch (25.4 mm)
(± 0.025 mm)
Source: NADCA Product Specification
Standards for Die Casting/Sec. 4A/9-2006
Machining Stock Allowance
Precision Tolerance
The best mechanical properties are achieved
on the skin of the component. Removing the
skin completely will adversely affect the
strength of the design.
Generally, the minimum machining stock
allowance is 0.010 inch. The maximum
amount is a combination of the minimum
stock allowance and the machining and
casting tolerances.
Source: NADCA Product Specification
Standards for Die Casting/Sec. 4A/2000
Linear Tolerances
0.05
0.045
Tolerance in ± Inches
0.04
0.035
0.03
0.025
0.02
0.015
0.01
0.005
0
1
2
3
4
5
6
7
8
9
10
11
12
(25.4)
(50.8)
(76.2)
(101.6)
(127.0)
(152.4)
(177.8)
(203.2)
(228.6)
(254.0)
(279.4)
(304.8)
Tolerance Zone in Inches (mm)
Al, Mg, Zn Standard Tolerance
Cu Standard Tolerance
Al, Mg, Zn Precision Tolerance
Cu Precision Tolerance
Flatness
Precision Tolerance
Maximum Dimension of Die-Cast Surface
Up to 3.00 inches
0.005
(76.20 mm)
(0.13 mm)
Additional Tolerance
For each additional inch
0.002
(25.4 mm)
(0.05 mm)
The maximum dimension is the diameter
of a circular surface or the diagonal of a
rectangular surface
Source: NADCA Product Specification
Standards for Die Casting/Sec. 4A/9-2006
Flatness Tolerance
0.05
0.045
Tolerance in ± Inches
0.04
0.035
0.03
0.025
0.02
0.015
0.01
0.005
0
1
2
3
4
5
6
7
8
9
10
11
12
(25.4)
(50.8)
(76.2)
(101.6)
(127.0)
(152.4)
(177.8)
(203.2)
(228.6)
(254.0)
(279.4)
(304.8)
Tolerance Zone in Inches (mm)
Standard Tolerance Zone
Precision Tolerance Zone
Parting Line
A witness line that is cast on the part formed where
the two halves of the die or mold meet in closing.
Precision Tolerance
Added Linear Tolerance (Projected Area)
Up to 10 inches2
+ 0.0035
11 to 20 inches2
+ 0.004
+ 0.005
21 to 50 inches2
51 to 100 inches
+ 0.008
2
2
+ 0.012
201 to 300 inches2
+ 0.016
101 to 200 inches
Tolerances shown are plus (+) values only
Source: NADCA Product Specification
Standards for Die Casting/Sec. 4A/-2006
Parting Line Tolerances
0.03
Tolerance in ± Inches
0.025
0.02
0.015
0.01
0.005
0
10
20
50
100
200
300
(64.50)
(129.0)
(322.6)
(645.2)
(1290)
(1935)
Projected Area in Inches Square (cm sq)
Al, Mg Standard Tolerance
Cu Standard Tolerance
Zn Standard Tolerance
Al, Mg Precision Tolerance
Cu Precision Tolerance
Zn Precision Tolerance
Draft
The taper given to cores and other parts of the die
cavity to permit easy ejection of the casting.
Precision Tolerance
Minimum precision draft for inside walls is
generally recommended at 0.75 degrees
per side, with outside walls requiring half
as much draft.
Draft should be calculated based on the
formula shown in the Draft Requirements
Section of the NADCA standard.
Source: NADCA Product Specification
Standards for Die Casting/Sec. 4A/2000
Cored Holes or Cut,
Formed and Pipe Treads
Dimensions for depth, diameter, and draft
are provided in the NADCA standard.
Source: NADCA Product Specification
Standards for Die Casting/Sec. 4A/2000
Equipment List
Molding Equipment
· 2 – 220 metric ton or 245 U.S. ton Thixomolder®
· 2 – 500 metric ton or 550 U.S. ton Thixomolder®
· 2 – 650 metric ton or 715 U.S. ton Thixomolder®
· 1 – 850 metric ton or 935 U.S. ton Thixomolder®
Deburring Equipment
· 4 cu. ft. to 18 cu. ft. vibratory deburring machines
· 1 tumble/blast deburring machine
Tooling
Machining Equipment
· Assortment of CNC and special purpose
machining equipment
Tool Construction
Tooling for the magnesium injection molding process
is designed like a die-casting tool. However, some of
the more intricate plastic tooling components can be
incorporated such as small lifters and cams. Slides,
both mechanical and hydraulic, are easily incorporated into tool designs. Zero draft conditions can be
designed into the tool as long as adequate ejection
can be provided.
Traditional tool steels are recommended. Cavity
inserts for production tooling can be made from
H-13 and holder blocks made from 4140. Low volume
market-entry and prototype tools can be made using
P-20 tool steel.
Lab
· Metallographical sample preparation equipment
· Olympus 1x70 metallurgical microscope
· Archimedes density measurement device
Machine Specifications
Locking Tonnage
245 to 935 U.S. Ton
(220 to 850 Metric Ton)
Mold Size Range
Tool Life
12"x 12" x 9.5" to
61" x 61" x 41.5"
Probable tool life for Magnesium Injection Molding
Functional parts
Aesthetic parts
500,000 shots
150,000 shots
Tools used to make magnesium components will last
3-5 times longer than those used to produce aluminum
parts. Aluminum has a high affinity for iron and will
actually dissolve mold components with each shot.
Magnesium, on the other hand, cannot dissolve
iron components, thus a longer tool life.
LxWxT
(305 mm x 305 mm x 240
mm to 1550 mm x 1550
mm x 1050 mm)
Injection Volumes
0.1 lb to 12 lb
(45 grams to 5445 grams)
Projected Area
3.5 to 200 inches2
(22.5 cm2 to 1290 cm2)
Coatings
Electrodeposition (e-coat) Process
The e-coat process applies paint to the part in a tank of water-based solution.
The paint is “grown” on the surface using electricity and covers the entire part
with a uniform coating. These paint tanks are dedicated to one paint only and are
not changed. Various colors or gloss levels of paint are available, but only one is
dedicated to the tank due to the high cost of change-over. For full coverage of
paint on the part, this efficient system could be the least expensive coating process.
Standard Coatings for Magnesium
Conversion Coatings
Chromate
Non-Chromate
Iron Phosphates
Alodine
Anodizing
Tagnite
Keronite
Anomag
Powder Coating
Phillips Plastics’ magnesium injection molding
produces components with attributes that include
repeatability, dimensional precision, superb quality,
and design flexibility.
Types of Plating
Electroless plating – a chemical process
used to deposit layers of copper and nickel
Powder coating is a method of applying a coating
to the part in the form of powder (ground resin)
using special paint guns. The powder and part are
charged to attract each other and provide a method
of adhesion in the dry state until the resin is melted
and bonded to the substrate. Because no solvents
are used, there is no discharge into the atmosphere.
Disadvantages of this process are that masking the
part for selective painting can be more difficult and
expensive than liquid. Powder coating also needs
to be cured at higher temperatures than liquid (350
- 400°F), which can lead to outgassing of the magnesium. Many types of resins can be applied (like
liquid) such as polyurethane and epoxy, and in the
right application, can be less expensive than liquid
paints. Leveling or flow of the paint can also be a
problem (polyester polyurethane is the best). Single
coat multi-colors like hammertones can be applied,
and powder coating can achieve very attractive textures.
Liquid Paints
Liquid paints require low temperature curing, good
leveling, and detailed masking. Liquids are easier to
shade or color match in-house. The types of paint,
Phillips recommends, are epoxy or polyurethane.
onto molded parts. This can be done on one
or two sides of a part, with two sides being
the lowest cost because there are no masking
or selective plating requirements. Electroless
plating provides excellent surface conductivity
for in-process testing and interconnection to
other parts. At this time, Phillips Plastics offers
electroless nickel as a functional coating.
Metal plating – most metals can be plated
onto magnesium including chrome. Bright
nickel is used to plate magnesium in the place
of chromium. Precious metals can also be
used to plate magnesium. The precious metals
are: pure (99.9%) or bright (99.7%) gold,
silver, or platinum.
Hydrographics
A process used to apply a pattern finish to threedimensional parts, adding cosmetic appeal and
surface protection to the product.
Corrosion
As with many active metals, corrosion is an issue
that should be addressed early in the design of the
component. Today’s high purity magnesium alloys
exhibit excellent corrosion resistance and can be used
with confidence in many applications. The two types
of corrosions that are addressed are atmospheric
and galvanic.
Atmospheric Corrosion
Unprotected magnesium alloys exposed to atmospheres that do not contain salt spray will develop
a gray film. This film will provide some corrosion
protection; however, if the surface comes in contact
with materials that hold moisture or chlorides and
sulfates, the unprotected surface will corrode. This
type of corrosion is easily overcome by the proper
application of a suitable surface coating.
The following table depicts magnesium alloy corrosion rates (using a standard ASTM test) compared to
aluminum and steel. The most popular magnesium
alloy, AZ-91-D, corrodes significantly less than either
carbon steel or 380 aluminum.
Salt Spray Corrosion Performance*
Magnesium vs. Iron and Aluminum
Material
Corrosion Rate (mils/yr)
Carbon Steel
30
Aluminum 380 (die-cast alloy)
13
AZ-91-D Magnesium Alloy
4
AM-50-B Magnesium Alloy
13
AM-60-B Magnesium Alloy
13
AS-41-B Magnesium Alloy
4
AE-42-A Magnesium Alloy
6
*10-day ASTM B-117 Salt Fog
Source: ASTM
Standard for Galvanic Corrosion
Galvanic Corrosion
When designing a magnesium component, galvanic
corrosion must be addressed. Galvanic corrosion
occurs when the magnesium component is brought
into intimate contact with a dissimilar metal in the
presence of an electrolyte. An electric current can
be generated when such conditions exist, with
magnesium being the sacrificial component.
Designing contact points to incorporate insulating
components can easily prevent galvanic corrosion.
If the electric circuit is broken, galvanic corrosion is
stopped. Also, design connection points in such a
manner that water is not likely to collect near the joint.
Remember to choose metals more compatible with
magnesium, and insulate against electrical contact.
Magnesium provides many inherent benefits for
programs in all markets including, medical, lawn and
garden, appliance, consumer, telecommunications,
defense, recreational, and automotive.
Relative Effects of Various Metals on Galvanic Corrosion of Magnesium Alloys
Group #1
Group #2
Group #3
Group #4
(Least effect)
Group #5
(Greatest effect)
Aluminum Alloys
Aluminum Alloys
Alclad 2024
Zinc-plated Steel
Low-carbon Steel
5052
6063
Aluminum Alloys
Cadmium-plated Steel
Stainless Steel
5056
7075
2017
Monel
6061
3003
2024
Titanium
Alclad 7075
Zinc
Lead
Copper
Brass
Phillips Plastics Corporation At A Glance
· Established in 1964, Phillips Plastics is a privately held
custom injection molder of plastic and metal
· Phillips Plastics is a technology driven Company, providing
contract manufacturing services to original equipment
manufacturers in the automotive, appliance, telecommunications, consumer electronics, industrial, medical,
defense, and recreational markets
· Fiscal year 2006 sales were approximately $260 million
· Phillips Plastics employs more than 1,600 people; supported by a network of 814 production people, 31 quality
assurance people, 20 designers, 166 engineers (includes
design, process, and manufacturing), and 115 toolmakers (includes tool managers, coordinators, team leaders,
mold makers, mold polishers, machinists, jig and fixture,
EDM specialists, and apprentices)
· Total number of presses is 254, ranging in tonnage from
0.44 to 935
· Phillips Plastics consists of 15 locations throughout the
United States, occupying over 718,737 square feet, with
total manufacturing square footage equaling 333,658
square feet
· Facilities are certified to TS16949:2002, ISO 14001, and
ISO 9001:2000. Our medical facilities are registered with
the FDA for medical device manufacturing. Facility certificates will be supplied upon request
PHILLIPS PLASTICS CORPORATION®
Opportunity Development
877.508.0260
info@phillipsplastics.com
phillipsmetals.com
© 2007 Phillips Plastics Corporation®