Abstract
Aluminum metal matrix composite brake rotors with a lective ceramic function reinforcement gradient (FRG) have been developed for automotive applications. This paper will highlight the design, manufacturing, and testing of the rotors. Weight saving of an aluminum composite rotor in comparison to an industry standard cast iron rotor is 50-60%. With this material change comes design considerations to manage rotor temperature, rotor surface integrity, and friction. Manufacturing methods to meet the design constraints were needed to develop a viable high performance aluminum composite rotor. High pressure squeeze casting with soluble coring techniques were developed to incorporate the lective FRG MMC rotors. Dynamometer testing was performed, concentrating on brake friction and temperature to evaluate the macro and micro interfaces in the rotors. The rotors’ testing results indicate that a functional reinforced aluminum metal matrix composite rotor is viable option for front and rear brake applications in the automotive and commercial trucking market.
Introduction
The automotive industry has had an emphasis on light weighting, due to factors like NHTSA standards
[1] and consumer pressure. Brake rotors are a component that may not e the same emphasis as others, due to the pasnger safety requirement of a braking system or cost differential.
Metal matrix composites (MMC) are made of nonmetal materials disperd in a metal matrix. Aluminum MMC’s have and are being ud in components like pistons, cylinders, and brake disks. Aluminum MMC’s can be stir-cast to give incread strength, stiffness, thermal resistance and stability over aluminum.
REL Inc. and others [2] have directed efforts towards development of an aluminum MMC automotive rotor. A one piece internally vented rotor was the goal of REL’s efforts. This would allow for a lightweight rotor that would have the ability to reduce its temperature faster than a standard rotor. This is crucial for an aluminum MMC rotor to operate under heavy braking conditions. Standard iron rotors have the ability to operate at higher temperatures than an aluminum MMC rotor due to material differences. To compensate, a venting structure is needed to increa airflow and reduce running temperature.
Rotor Development
REL’s aluminum MMC material has a high ceramic content. A 50% ceramic volume fraction MMC is
achievable. This MMC material has a coefficient of thermal expansion of about half of aluminum. The MMC’s thermal diffusivity is also about half of aluminum’s.
In the path to developing an aluminum MMC one piece internally vented automotive rotor, there were three stages of development before the final prototype. This stages are as follows: Single blade
motorcycle rotor, solid one piece rotor, and three piece vented rotor. Figure 1. REL aluminum MMC motorcycle rotor and carrier
Development of Aluminum Composite Automotive Brake Rotors2016-01-1937
Published 09/18/2016 Taylor Erva, Adam Loukus, and Luke Luskin
REL, Inc.
CITATION: Erva, T., Loukus, A., and Luskin, L., "Development of Aluminum Composite Automotive Brake Rotors," SAE Technical Paper 2016-01-1937, 2016, doi:10.4271/2016-01-1937.
Copyright © 2016 SAE International
The single blade motorcycle rotors are for u by road motorcycles. They are generally thin (≈6mm) and have no center ction. The entire blade is compod of aluminum MMC with a function gradient. The rotors are being sold as OE replacements for lect street motorcycles.
The solid one piece automotive rotor is a single blade rotor with a center hub ction that has mounting for an automobile. The rotor is lectively reinforced, with the aluminum MMC ction being the friction ring of the rotor. The rotor has external vanes, to help regulate
temperature. The hub and venting ction are made of aluminum alloy.
Figure 2. REL solid one-piece aluminum MMC automotive rotor
Three piece vented automotive rotor is similar to the design of the one piece internally vented automotive rotor. It consists of a center hub ction and two rotor blade halves. Each rotor blade half holds half of the internal venting structure. The halves are bolted together and then to the hub. The rotor blade halves and venting ctions are
aluminum MMC. The hub is made of aluminum alloy.
Figure 3. REL vented three-piece aluminum MMC automotive rotor
One Piece Vented Automotive Rotor
springerThe automotive rotor has the features: Aluminum with lectively reinforced aluminum MMC ctions, one-piece construction, and
internal venting.
Figure 4. REL vented one-piece aluminum MMC automotive rotor
The rotor is made up of aluminum alloy and aluminum metal matrix composite material. The ceramic reinforced ctions of the rotor are the two braking surfaces. The rotor hub and venting ctions are made up of aluminum alloy. The MMC braking surfaces have a function reinforcement gradient (FRG). The ceramic density is
radially variable, with an increa in volume fraction from the interior to the perimeter of the preform. This radial change in ceramic volume fraction compensates for the increa in energy and stress on the outer ction of the rotor during braking.
A computational simulation was done to determine the thermal mechanical performance of a rotor during a stop. Results from the simulation show a difference in stress from the outer edge of the rotor to the inner edge. The pattern of higher stress on the outer edge of the rotor to lower stress on the inner edge of the rotor is followed in a simulation with 0% ceramic content and simulation with 100%
ceramic content.
Figure 5. Stress simulation with 0% ceramic content
Figure 6. Stress simulation with 100% ceramic content
Figure 7. Stress simulation: rotor edge comparison
Tensile testing of aluminum MMC samples was done. Samples of specific ceramic volume fractions were tensile tested and Poisson’s ratio was determined from the results. A trend of decreasing Poisson’s ratio as ceramic volume fraction increas can be obrved from the results. With this trend, a gradient of ceramic in the metal matrix composite ction of the rotor is ud to maintain a rotors integrity during a braking cycle. Higher stress regions have higher ceramic content than lower stress regions of the MMC braking surface.
Table 1. Poisson’s ratio of MMC
Aluminum alloy has a melting temperature of about 550°C lower than iron. However, aluminum MMC has a higher thermal披荆斩棘
conductivity than iron. The material constraints influenced the design of the rotor. The venting structure in the rotor provides a way for the rotor to regulate its temperature. The curved vanes produce a centrifugal air pump in the rotor when rotated. This airflow created by the pump transfers heat from the rotor to the air. The heated air is then pushed out of the vent. The thermal conductivity of aluminum MMC is higher than iron, so while heat from braking is absorbed faster by an aluminum MMC rotor, heat is dissipated at a faster rate.
Venting is crucial to the operation of this rotor.
Figure 8. Sectioned internally vented one-piece rotor
Manufacturing
To manufacture a brake rotor with a high ceramic content and a function reinforcement gradient, high pressure squeeze casting is necessary. The ceramic volume fraction in the in REL rotors cannot be easily achieved by stir cast MMC. To attain the content and
gradient of ceramic material, a preform of ceramic material is ud. This preform gets infiltrated by aluminum in a high pressure squeeze casting. The infiltration allows the aluminum to form the matrix around the ceramic material.
The method of infiltrating ceramic preforms with aluminum gives the ability to have a FRG. The infiltrated preforms are tailored to improve rotor performance. The move away from a stir-cast aluminum MMC method to a preform infiltration method, gives the ability to lectively reinforce the rotor.
The aluminum MMC ud in the automotive rotor is difficult to machine. Sections of the rotor, venting
structure and rotor hub, are not reinforced with ceramic. The ctions are not ud for braking and do not require improved properties. The majority of the machining required in the non-MMC areas of the rotor.
The internal venting in the one piece rotor is not machined and
requires a core. Using high pressure squeeze casting required a high strength core. A salt core had to be developed to withstand the
compressive force required, not be infiltrated, and not lo integrity with temperatures required for casting. The salt core is one piece and holds the negative pattern of the venting structure.
The asmbly ud for casting consists of two ceramic preforms, with a salt core in the middle. The casting asmbly is placed in the die and squeeze cast. The aluminum will infiltrate the preforms to create composite material, and be voided by the salt core, creating the初中英语语法总结
venting structure. All other aluminum in the casting will removed or
ud for rotor hub.
Figure 9. REL vented one-piece rotor manufacturing tup
ief
Testing
There were three types of testing done with the aluminum MMC rotors. Friction testing was done to determine the ability of a brake rotor to stop with a given t of brake pads. Integrity testing was done to obrve the ability of the rotors to withstand braking before failure. Temperature testing was ud to evaluate a rotors ability to manage heat added through braking. All tests were done on a brake
dynamometer. Thermocouples placed in rotors and pads are ud for temperature collection.
Friction Testing
Different brake pads were tested to determine the friction coefficient, brake pad wear and rotor wear when ud on aluminum MMC rotors. Non-asbestos organic (NAO) brake pads are preferred for aluminum MMC rotors. Metallic and mi-metallic brake pads are not ideal for the hardness of the composite rotors. All tests shown were completed using the same compound of braking material. It is a NAO brake pad lected for its compatibility with aluminum MMCs.
An aluminum MMC rotor was friction tested against a similar cast iron rotor. Both rotors were braked with the same composition of organic material and in the same caliper. The test followed the FMVSS 122 Standard, S7.1 to S7.5. After a brake warming and
burnish, the effectiveness tests consisted of six stops from 48.3 km/h (30 mph) and six stops from 96.6 km/h (60 mph) initiated at 65.5°C (150°F) brake temperature. The test concludes with four 128.7 km/h (80 mph) stops and four 160.9 km/h (100 mph) stops in succession. From the test, a brake coefficient of friction for each stop is
calculated. [3]
Figure 10. Cast Iron vs Aluminum MMC Friction Results
The cast iron and aluminum MMC rotors exhibited similar friction behavior in the test. Through the 30 mph and 60 mph stops, the coefficient of friction for both rotors varied between 0.40 and 0.44. On the 80 mph and 100 mph stops, the MMC rotor saw a steady decrea in its friction coefficient, while the cast iron rotor had a similar decrea but resisted fade better on the final stops.
Integrity Testing
With a lectively reinforced rotor, there are two or more different material expansion rates in the rotor as there are two different
materials. When subjected to braking, the heat added to the rotor is not constant, linear, or uniform throughout the rotor. Testing on the rotor was done to determine a brake rotors behavior during a heat cycle. Organic brake pads were ud. Results of the testing are determined visually. Cracking, paration, degrading, and gouging
sheets
are all evaluated and compared to other rotors.
北大青鸟培训机构Figure 11. Integrity testing paration results
Integrity testing done consisted of repeated braking without any external cooling. The rotor was stop
ped from 80 km/h (equivalent speed) at high braking pressure (4500 kPa target) until significant gouging occurred.puzzor
The results of the integrity testing indicate that the lectively
诚信做人reinforced rotor will not fail under temperature change. There was no visible layer paration or significant warping. Gouging occurred at high rotor temperature (≥540°C), exceeding the degradation temperature of the brake pads ud.
Temperature Testing
Evaluating the effectiveness of the venting structure in the rotors was done through temperature testing. The rate of cooling of a vented automotive aluminum MMC rotor was compared against a similar rotor with the venting blocked. Venting was blocked using an epoxy putty. Minimal amounts of epoxy was ud, to maintain the
similarities between the rotors. The test consisted of adding heat to a
rotor, through a braking cycle, then spinning the rotor at a constant speed (300 rpm). Temperatures are then monitored as the rotor cools down. No external air source was added.
Table 2. Vented vs Non-vented cooldown results
The comparative results of the cooling of the vented and non-vented rotors showed that the vented rotor will cool faster than a non-vented rotor. This verifies development from solid rotor, to internally vented rotor.
In the same manner as the previous test, a vented cast iron rotor was compared to the aluminum MMC vented automotive rotor. The
rotation speed was 330 rpm with a cooling wind with of 48.3 km/h.
Figure 12. Cast Iron vs Aluminum rotor cooldown results
The results of the cond temperature test shows the difference in the cooling rates between cast iron and aluminum MMC. The aluminum MMC cooled to 100°C in about half of the time that the cast iron rotor did. This difference in cooling rates allows an aluminum MMC
rotor to cool faster than a traditional brake rotor.
Figure 13. Aluminum MMC rotor dynamometer testing
A third temperature test was run on a dynamometer with two 280mm rotors. One rotor in the test was a prototype aluminum MMC rotor, while the cond rotor, like the previous test, was a vented cast iron rotor of similar geometry. The test consisted of ten stops from 80 km/hr equivalent speed and braking with a target maximum brake line pressure of 3500 kPa. There was approximately 20 conds between each stop. There was an external inline convective airflow produced by an industrial blower that matched the speed of the rotor,
simulating the operation of a vehicle. The dynamometer flywheel had
姜太公钓鱼愿者上钩的故事a moment of inertia of 78.25 kg*m^2.
Figure 14. Aluminum MMC vs cast iron operating temperature test
Results from the third temperature test show the operating
temperatures of a vented aluminum MMC rotor against a comparable cast iron rotor in an aggressive braking test. The MMC rotor
displayed a higher temperature gain per stop than the iron rotor, but also had a greater temperature loss between stops. The cast iron rotor had higher final temperature after the test, but displayed slightly
quicker braking, finishing the test in less time than the MMC rotor.
Figure 15. Iron rotor dynamometer testing
sonofthebitch
Production
REL mass produces aluminum MMC motorcycle rotors following the process of squeeze casting aluminum into a ceramic, post cast machining, and heat treatment. The production of a single piece
vented aluminum MMC rotor requires an extra component (salt core), two ceramic preforms, and an extra post process (salt removal). Although there are differences the production method of the single blade MMC motorcycle and the process needed for the vented MMC rotor, the method is adaptable to produce the vented MMC rotor.
