RAYS Engineering Japan is used as the primary example of how a forged wheel is made.

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Forged Aluminum Alloy Analysis
Application: Automotive Wheel
Lucas T. P. Silva., ASCE
Undergraduate Civil Engineering Student, University of Massachusetts Lowell, 1 University
Ave, Lowell, MA 01852; e-mail: lucas_silva@student.uml.edu.
ABSTRACT
The process of forging a metal such as aluminum alloy is very beneficial in Motorsport
applications where strength and reduction of weight is of high priority. Forging creates a denser
grain in the metal, increasing strength and requiring less material to be used therefore allowing
for lighter wheels. Aluminum alloy is introduced. Gravity cast and flow formed aluminum
wheels are introduced for comparison reasons. Forged aluminum wheels are introduced. Cast
wheel manufacturing process is explained. Flow form wheel manufacturing process is explained.
Forged aluminum manufacturing process is explained with RAYS engineering as a primary
example. Benefits of a forged aluminum wheel vs other aluminum wheels made using other
manufacturing processes is explained. Forged aluminum wheel testing explained and compared
to cast and flow formed aluminum wheels. The Japanese wheel industry JWL and VIA standards
and certification is explained.
INTRODUCTION
In automotive vehicles wheels are what keeps the car up and moving in conjunction with
the suspension and other components. In automotive motorsports like racing and drifting, not
only do wheels need to be strong to cope with high G forces acting on the structure of the wheel
but they also need to be lightweight to reduce rotational mass. The lighter the vehicle is the
quicker and more efficient it can move.
There are three main types of aluminum wheels and production processes. Cast or gravity
cast, flow formed, and forged. Cast being the least expensive and and forged being the most
expensive. Normal mass production cars usually come equipped with cast aluminum wheels,
which are durable for the most part, inexpensive to produce but not very lightweight. Sometimes
they are an add-on option for base model cars that come equipped with heavy non expensive
steel wheels. Race cars or high performance production cars utilize forged aluminum wheels that
are extremely durable and weigh less than a cast aluminum wheel. This is due to the benefit of
the forging process of the alloy that compresses the molecules of the alloy closer together,
making it stronger, and because it is stronger, less material is required to achieve higher strength.
Because the forging process is so complex the price difference between a forged wheel and a

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normal cast wheel is usually very large but always worth the benefits.
ALUMINUM ALLOY
Aluminum is a chemical element in the boron group. It is a silvery-white, soft,
nonmagnetic, ductile metal. Aluminum metal is so chemically reactive that native specimens are
rare and limited to extreme reducing environments. Instead, it is found combined in over 270
different minerals (Shakhashiri, B. Z., 2008).
Aluminum is remarkable for the metal's low density and its ability to resist corrosion
through the phenomenon of passivation. Aluminum and its alloys are vital to the aerospace
industry and important in transportation and structures.
Figure 1. Aluminum (pure) (Wikipedia.com)
CAST & FLOW FORMED ALUMINUM WHEEL MANUFACTURING
Cast and flow forming manufacturing methods are more affordable to manufacture than a
forged wheel and as stated before are commonly used in normal passenger cars where weight
savings and extreme strength are not a priority. There are various types of cast wheel
manufacturing processes and tirerack.com does a nice job of explaining them, shown below
along with the explanation of the flow forming process.
One-Piece Cast Wheels
This is the most common type of aluminum wheel. The casting of wheels is the process
of getting molten aluminum inside a mold to form a wheel. There are different ways this can be
accomplished and although it sounds simple, this is truly an art when done properly.

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Gravity Casting
Gravity casting is the most basic process of pouring molten aluminum into a mold
utilizing the earth's gravity to fill the mold. Gravity casting offers a very reasonable production
cost and is a good method for casting designs that are more visually oriented or when reducing
weight is not a primary concern. Since the process relies on gravity to fill the mold, the
aluminum is not as densely packed in the mold as some other casting processes. Often gravity
cast wheels will have a higher weight to achieve the required strength.
Low Pressure Casting
Low pressure casting uses positive pressure to move the molten aluminum into the mold
quicker and achieve a finished product that has improved mechanical properties (more density)
over a gravity cast wheel. There is a slightly higher production cost over gravity casting, but low
pressure casting is the most common process approved for aluminum wheels sold to the O.E.M.
market. Some companies offer wheels that are produced under a higher pressure in special
casting equipment to create a wheel that is lighter and stronger than a wheel produced in low
pressure, but there's a higher cost associated with the process. Low pressure cast wheels offer a
good value for the aftermarket while still maintaining strength and a lighter weight.
Spun-Rim, Flow-Forming or Rim-Rolling Technology
This specialized process begins with a low pressure type of casting and uses a special
machine that spins the initial casting, heats the outer portion of the casting and then uses steel
rollers pressed against the rim area to pull the rim to its final width and shape. The combination
of the heat, pressure and spinning create a rim area with the strength similar to a forged wheel
without the high cost of the forging. Some of the special wheels produced for the O.E.M. high
performance or limited production vehicles utilize this type of technology resulting in a light and
strong wheel at a reasonable cost. O.Z. has used this technology for several years in their
production of racing wheels for Formula One and Indy cars.
Grain Structure of Cast and Flow Formed Aluminum
Although flow forming a cast wheel doesn’t net the strongest possible aluminum alloy, it
is a large improvement over normal cast manufacturing. A gravity cast aluminum wheel relies on
gravity to fill in all the areas of the mold with the molten aluminum alloy. This means there isn’t
much pressure being applied to the molecules of metal, therefore the metal isn’t very dense or
compact and there is almost always room for air.
A flow formed wheel is actually created from a cast template. As explained on BBS.com
"Flow Forming" is a procedure that uses 3 hydraulic rollers and tremendous pressure to “Form”

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the inner rim area. Through this process, the hydraulic rollers force the cast material to conform
to the profile of the massive steel tooling. During the process, the full width of the rim is
created. The pressure used in this process actually changes the mechanical properties and the
grain structure of the cast rim area to have strength, stiffness and impact values closer to that of a
forged rim. "Flow Forming" also helps reduce the weight up to 15% when compared to a
standard cast wheel. The overall “Stiffness to Weight Ratio” is very good and can deliver a high
level of performance at a cost that is much lower than a forged wheel.
Figure 2. Stages of cast aluminum wheel being “Flow Formed”. (BBS.com)
The pressure used in this process actually changes the mechanical properties and the
grain structure of the cast rim area to have strength, stiffness and impact values closer to that of a
forged rim. "Flow Forming" also helps reduce the weight up to 15% when compared to a
standard cast wheel. The overall “Stiffness to Weight Ratio” is very good and can deliver a high
level of performance at a cost that is much lower than a forged wheel. (BBS.com)

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Figure 3 & 4. Material x-section (grain structure) comparison of “Standard” to “Flow-Formed” areas. (BBS.com)
FORGED ALUMINUM WHEEL MANUFACTURING
Forging is a manufacturing process where metal is pressed, pounded or squeezed under
great pressure to produce high-strength parts. Forged aluminum is ideal for applications where
performance and safety are critical but a lighter-weight metal is needed for speed or energy
efficiency. There are primarily three types of forging processes: open-die forging, ideal for larger
aluminum components; closed-die forging, well-suited for more intricate designs and tighter
tolerances; and ring-rolled forging used to create high-strength ring-shaped applications
(Aluminum.org).
This manufacturing method is the ultimate in one-piece wheels. When manufacturing a
forged wheel, a solid billet is usually forced between forging dies under an extreme amount of
pressure. This creates an aluminum wheel that is very dense, very strong and therefore can be
very light. The costs of tooling, development, equipment, etc., make this type of wheel very
exclusive and usually demand a high price in the aftermarket. (Tirerack.com)
RAYS Engineering Forged Wheels – The Pursuit of the Perfect Wheel
RAYS engineering is the golden standard when it comes to forged aluminum wheel
engineering and manufacturing and will be used in this research paper as a primary in depth
example of how a forged wheel is created. RAYS Co. Ltd., established in 1973, is the premier
Japanese manufacturer of high end wheels for both Motorsports and street use. By following
their virtual goal of "contributing to the promotion of motor sports culture," RAYS continues to
manufacture wheels with innovative design and the highest technology. The unique forging
process used by RAYS is believed to be the best possible way to create a light weight and and
very durable wheel. (Karol Czerwiński)
From the conceptual stage, the engineers at RAYS utilized all the data supplied to

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them through exhaustive data collected from real world situations and especially
from racing to plan the proper high performance wheel for the correct application.
Through this research and development, RAYS has established the following main
fundamental concepts when developing a wheel:
1. Strength
2. Lightness
3. Exterior Design
4. Balance
The Real Forged Wheel Technology Produced by RAYS
In the pursuit of the perfect wheel, RAYS has established that a high performance wheel
must exhibit the following attributes: Superior Strength, Exceptional Lightness, Leading Edge
Design, and Complete Balance. RAYS has chosen that their best wheels must be manufactured
by forging. RAYS has developed their own proprietary forging techniques in 1998 that allow
them to progressively grow closer to their goal of making the “perfect wheel”. (Karol
Czerwiński)
A RAYS Mono-block Forged Wheel begins its life as a piece of solid aluminum billet.
The aluminum used is aircraft grade aluminum (6061) which is important for forging due to its
high tensile strength, hardness, and light weight. Each aluminum billet is then super heated in a
specialized furnace that can precisely control the time to heat and the proper temperature for
correct forging. The billet is then subjected to over 8,000 TONS of pressure to achieve its initial
shape. This process will start the organization of the microstructure of the aluminum which is
called the “Metal Flow Line” or “Fiber Flow”. The forging pressurizes the aluminum which
increases the density of the metal. This allows the metal to become durable. A “Normal” forged
wheel manufacturer will utilize a forging press which will forge a “pancake” or a flat surface,
which will be machined to achieve its desired shape. A RAYS forged wheel is “mold forged”
where the center disk’s shape is actually forged into the design. This allows for the continuity of
the “Metal Flow Line” which allows for an even stronger type of forged wheel with no
disruption in the flow of the metal. The Metal Flow Line equals minimum machining which
simplifies the product and is also proof of its inherent strength. The Forged disk will be subjected
to additional forging to finalize the shape of the spoke in preparation for the elongation of the
rim. This maximizes the metal flow line within the center disk. (Karol Czerwiński)

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Figure 5. Mold forging (Rayswheels.co.jp)
Like the fibers of a human muscle, the “Metal Flow Line” or “Fiber Flow” in addition to
being strong, also exhibits flexibility. A cast wheel is prone to cracking due to the porosity or air
pockets that reside in the metal alloy due to the casting process. The “Metal Flow Line” is not
only more resistant to impacts, but in the case of a severe impact, will tend to bend rather than
crack. This is an important safety feature of a RAYS forged wheel. (Rayswheels.com.jp)
Fiber flow lines form the muscular system for metal. Forging is a method of molding
metal that involves applying pressure to the metal. In this process, while the metal's fibers are
miniaturized, the density of its inner tissue increases as the fibers align in a clear direction.
Consequently, like a bundle of fibers, a tissue of metal is created that can withstand external
force effectively. The metal tissue created in this way is the fiber flow lines. These give the
wheel its strength in a similar way to how a muscular system gives strength to a living organism.
Unless they are properly controlled, however, the fiber flow lines may not demonstrate their
outstanding characteristics to the full. (Rayswheels.com.jp)

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Figure 6. Metal grain being compressed to form “Fiber Flow Lines”. (Rayswheels.com.jp)
Fiber flow lines vary according to the method used. With the design mold-form forging
method used by Rays, molds are used in all of the processes involved in the forming of fiber
flow lines. This makes it possible to align the fiber flow lines precisely to create the ideal form
(mold shape). Uninterrupted fiber flow lines produce greater strength, allowing the material to be
more thinly shaped. This makes it possible to push wheel weight reductions to the limit.
This figure provides a clear illustration of the difference in fiber flow lines obtained with Rays'
forging method (left) and those obtained from machine forging (right), which involves the
product being designed as it is cut. While Rays' fiber flow lines are uninterrupted, those created
using machine forging tend to be interrupted, which leaves machine forged wheels at a
disadvantage in terms of strength. This difference is evident in the strength of the wheels, but
uninterrupted fiber flow lines are also more advantageous when it comes to weight reduction.
(Rayswheels.com.jp)
Figure 7. Rays undisturbed “Flow Lines”. (Rayswheels.com.jp)
The next step of the RAYS forging process involves the RAYS world class RM-8000
Machine. This machine has been developed exclusively by RAYS Engineering and this process
is patented for use only by RAYS. This special forging process integrates the final forming of the
center and the spinning elongation of the rim into one process. This not only simplifies the
forging process, it helps to create the perfect continuity of the “Metal Flow Line” from the center
disk all the way to the rim edge. RAYS RM Forging process allows for a completely forged
wheel. If calculated there is approximately 12 Tons of pressure applied to each square millimeter
of the aluminum. This allows for superior wheel durability and with this durability, the wheel
can be manufactured with ultra thin cross-sections for maximum lightness. Strength and
Lightness – This is the key to RAYS Wheel superiority. (Karol Czerwiński)
Once the center portion and the initial rim has been formed. The rim is then cold forged to

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extend the rim to its desired width. This is where the true durability of the metal flow shines
where a RAYS Forged wheel will exhibit rim cross sections as thin as 2.5 millimeters. The
formed wheel is then heat-treated to further refine the material and increase the hardness of the
aluminum. Once the aged wheel is heat treated, the wheel is then submerged in a cooling tank to
lock the hardness into the material. This process is an important part of the overall manufacturing
of the wheel. Through RAYS vast knowledge of wheel manufacturing techniques and heavy
investment in the proper tools, a wheel can be exposed to precisely controlled heating and
cooling temperatures to ensure the proper refinement of the aluminum alloy. (Karol Czerwiński)
RAYS utilizes the latest in CNC Robotic cutting technology to machine all necessary
sections such as center bore, lug hole, and wash areas to a tolerance of a hundredth of a
millimeter. Manufacturing wheels at such slight tolerances ensures consistency throughout each
product manufactured by RAYS. After each process, every wheel is subject to inspection
utilizing advanced quality sample testers including X-Ray inspection machine, Amsler multi-
purpose tensile tester, electron scanning microscope, and eddy current flaw testing machine.
Each wheel is Shot-blasted in preparation for the finishing treatment. The Shot-blasting process
involves thousands of tiny industrial grade ball bearings pounding the wheel in a controlled
environment to further harden the surface of the aluminum. Each wheel is coated with high-
grade surface treatments that are able to cope with severe conditions. Resistance to heat, sun, and
corrosion are considered when choosing strong, yet visually appealing finishes. (Karol
Czerwiński)
Rigidity Analysis
Rays has involved excellence in engineering as well. Most of Rays engineers are also
engaged enthusiasts who have a clue, not your typical corporate drones. State of the art modeling
techniques such as Finite Element stress Analysis commonly known as FEA are used to optimize
design, giving the best strength and stiffness for the lowest weight. FEA allows the engineers to
pair weight to a minimum and make stronger more durable wheels by being able to predict stress
concentrations within the structure of the wheel when load is applied. FEA is integrated into the
CAD (Computer Aided Design) drafting system and the engineers can use this data to quickly
change the design and verify what each change can do to the strength, weight and durability of a
wheel before the first prototype part is made. (MotoIQ.com)
Rays boasts the most advanced rigidity analysis technology available. But it's not the
analytical technology itself that is important. In terms of wheel strength, trade-offs need to be
made between the wheel's weight and its design. The lighter a wheel is, the weaker it tends to be.
Rigidity analysis helps developers find a good balance between the two, but it doesn't reveal
which is the best option. How can developers maintain wheel strength for a particular design?

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What shape is the more sensible option? To find the optimal balance, know-how and experience
count. It's because the company's rigidity analysis technology is capable of identifying the best
option that Rays can claim to be the leading developer of wheels. (Rayswheels.com.jp)
JWL, RAYS JWL+R Spec Standards, and Testing
Rays wheels for both OEM and aftermarket applications are built to exacting JWL standards.
JWL is a standard of the Japanese government where a wheel must pass a brace of grueling
durability tests to be legal for street use. The wheels must pass tests for rotary and radial fatigue,
a strenuous test where a wheel with a tire is loaded with a heavy weight to simulate a car's weight
then run at a heavy side and up and down cyclical load for a required number of cycles. Then the
same wheel if it passes is subjected to a 13 and 90-degree impact test where it is hit with a
calibrated hydraulically driven pendulum. The wheels must not deform excessively, crack, debead
the tire or lose air pressure. As further proof, Rays has their own internal standard JWL+R where
their wheels must exceed the JWL tests by 100% even for their lightest wheels. Ever wonder what
sort of testing is done on Volk knockoffs? Probably none with a fake JWL stamp. (MotoIQ.com)
Figure 8. Fatigue testing machine. (MotoIQ.com)
JWL (Japan Light Alloy Wheel) is a compilation of Safety Standards for Passenger Car
Wheels approved by the Japanese Ministry of Transport. All wheel products are registered under
VIA (Vehicle Inspection Association) regulations after strict quality testing by three types of
testing methods approved by JWL (Japan Light Alloy Wheel) Testing Council.
JWL is essentially the minimum safety requirement in Japan for wheel production. It is in
place to prevent knock off companies from manufacturing cheap unsafe cast aluminum wheels,
which is the cheapest and easiest to make. But it is also the weakest. Rays not only makes
fantastic cast wheels, but they obviously make some of the best forged wheels on the market.
Their wheels are so superior in quality that they invented their own, stricter, safety standards on

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top of the already mandatory JWL standards. This new standard is called RAYS JWL+R Spec.
This goes to show the level of engineering that goes into their wheels. The test results below
show how much stronger a forged wheel is compared to a cast wheel.
RAYS JWL+R Spec 1 standards refer to RAYS cast wheels which are designed and
manufactured utilizing RAYS vast wheel experience to ensure lightness and durability. RAYS
designs their cast wheels to have the proper reinforcement in the appropriate areas to avoid
unnecessary weight, and retain the proper structural integrity.
RAYS JWL+R Spec 2 standards apply to RAYS Forged wheels, our main focus, which are
designed and manufactured to exhibit the ultimate in durability, strength, and lightness. The
“Metal Flow” within a RAYS Forged wheel ensures the ultimate in strength which allows RAYS
to design wheel cross-sections as thin as 2.5 millimeters, which results in unmatched lightness
paired with ultimate strength.
Cornering Fatigue Test (Drum Endurance Test):
JWL pass criteria: 500,000 cycles.
JWL+R Spec 1 pass criteria: 800,000 cycles.
JWL+R Spec 2 pass criteria: 1,000,000 cycles
The purpose of this test is for checking wheel rim strength and durability.
Radial Load Fatigue Test (Rotary Bending Test):
JWL pass criteria: 100,000 cycles.
JWL+R Spec 1 pass criteria: 150,000 cycles.
JWL+R Spec 2 pass criteria: 200,000 cycles.
The purpose of this test is for checking durability of the wheel disc. The spokes strength is
gauged by this test.
13 Degree Impact Test:
JWL pass criteria: 594 kg.
JWL+R Spec 1 and Spec 2 pass criteria: 610 kg.
The main purpose of test is for checking strength between rim and disc cross section.
CONCLUSION
Forging: a great combination of strength, lightness and ductility. The mechanical and
physical strength characteristics of a forged wheel are equally distributed throughout the wheel

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on a molecular level. The result is far greater strength and resistance than an equivalent cast
wheel, vastly improving the performance of the wheel when faced with impacts and high levels
of load stress. A forged wheel is far lighter than an equivalent cast wheel. The weight reduction
benefit of forged wheels serves to improve the overall performance of a vehicle by reducing the
vehicle unstrung mass and improving the performance characteristics of the suspension,
improving both road holding ability and dynamic cornering. The lightweight characteristics of
the forged wheel mean that it will demonstrate a lower angular momentum. In practical terms
this lends an improved driving dynamic through lower power consumption during acceleration
and better braking power. (OZracing.com)
REFERENCES
Shakhashiri, (2008). “Chemical of the Week: Aluminum” <SciFun.org> (Nov. 30, 2016)
Kojima, 2010. “A Look at the Technology Behind RAYS Wheels” <http://www.motoiq.com> (Nov.
30, 2016)
“Forged Technology” <https://www.rayswheels.co.jp> (Nov. 30, 2016)
“Wheel Tech” <http://www.tirerack.com> (Nov. 30, 2016)
“BBS Flow Forming Process” <http://www.bbs-usa.com> (Nov. 30, 2016)
“Forging” <http://www.ozracing.com> (Nov. 30, 2016)
Czerwiński, (2012) “RAYS” <https://www.scribd.com> (Nov. 30, 2016)
“Forging” <http://www.aluminum.org> (Nov. 30, 2016)