Analysis of three different material for flywheel

Current selection of material and manufacturing process for the flywheel has been clearly described and critically evaluated in Project 2 - Analysis of current material and manufacturing process of flywheel but there are other materials and manufacturing process that can be used instead of current material and manufacturing process to increase the performance, reliability and cost effectiveness of flywheel. Three of these materials and their manufacturing process are discussed below.

Proposed Alternative Materials

Three materials for the flywheel other than aluminum alloys are high strength steel, titanium and titanium alloys and carbon fiber composite. These materials are selected after comparing them with aluminum alloys on the bases of mechanical properties and factors involves in material selection.

Mechanical Properties

According to Mouleeswaran Senthil Kumar and Yogesh Kumar (2012) following are the material mechanical properties which affects the flywheel factor of safety, maximum rpm, weight and kinetic energy.
·         Allowable stresses
·         Yield Strength
·         Density
·         Material Index

Allowable stress is point above which flywheel will burst like a pressurized cylinder and yield strength of a material allows him to go elastic deformation and to avoid sudden fracture. Allowable stress and yield strength of all the suggested materials is greater than the aluminum alloy which makes them better candidate for safer operation.

Low density of carbon fiber will result into a light weight flywheel and high density of titanium alloy and high strength steel will result into heavy weight flywheel than the aluminum alloy flywheel. Low density of carbon fiber composite leads to less mass which result into small amount of kinetic energy stored at fix rpm. Aluminum and titanium alloys have intermediate values and high strength steel have high density resulting into maximum amount of kinetic energy stored in a flywheel.

Material index is directly proportional to the angular velocity of flywheel, carbon fiber composite have highest value of material index means it can rotate at highest rpm than any other material. Aluminum alloys, high strength steel and titanium alloys have very small difference in material index value, so their rpm range is almost same. So at fix mass carbon fiber will have maximum kinetic energy followed by aluminum alloys, then titanium alloys and high strength steel will have least amount of kinetic energy stored.

Allowable stresses MPa
Density Kg/m^3
Material Index
M Pa (m^2)/Kg
Melting Temperature (oC)
Aluminum Alloys
463 - 671
High Strength Steel
1425 - 1540
Titanium Alloys grade 4
Carbon Fiber composite (epoxy resin)

Manufacturing Properties

According to Mikell P. Groover (2010) and Prof. Dr. Ahmet Aran (2007),  following are the manufacturing properties of a material that should be considered during material selection.

1.      Cast-ability
2.      Fluidity
3.      Pouring temperature
4.      Machinability
5.      Shrinkage

Cast-ability means how much easy it is to manufacture a quality finished product without the machine processes like surface finish and property enhancing process like heat treatment. Cast-ability of high strength steel, titanium alloy and aluminum alloy are almost the same but surface finish of the product made from carbon fiber is far better than other three materials.

Material fluidity means molten material ability to flow into the mold cavity. Due to the high density high strength steel have least fluidity value and aluminum alloy with less density have the highest value of fluidity.  More the fluidity less will be the damage done to cavity walls and better will be material distribution into the cavity. Carbon fiber composite have no concern with this property.

Pouring temperature is the temperature of the material at which it is poured into mold. Titanium alloy have the highest melting temperature among the other two metals and aluminum alloy have the least melting temperature. So more energy will be required for melting the titanium alloy than aluminum alloy, which increase the manufacturing cost of the product and also will take more time to solidify increasing the production time of product.

Every material has three phase liquid contraction, phase changing contraction and thermal contraction. Material having greater value of linear shrinkage need larger pattern than material having lower value of linear shrinkage. Shrinkage of material causes defects in material like void and shrinkage cavity formation. As the solidification start from outer walls toward the center and alloys solidify at a range of temperature rather than at fix temperature, this makes high concentration of one material at outer walls and concentration of other material at inner side of product. Usually material with low melting temperature solidifies at outer walls and material with high melting temperature usually solidifies at inner side.

Local Market Condition

Local market condition greatly affects the selection of material. Availability of high strength steel and aluminum alloy is good but availability of carbon fiber and titanium alloy is not as good because they are mostly use in aerospace industry.  Material you select should be easily available, cheap and should have continuous supply for nonstop manufacturing and reducing the throughput and inventory cost of material.

Environment affects

Material you select should not affect the environment that is melting of it should not emit harmful gases and waste material can be recycled. High strength steel, titanium alloy and aluminum alloys can be recycle easily but carbon fiber composite can be recycled directly.

Company ability to process material

Selection of material depends on the manufacturing facilities available and technical skills of labor working there. Manufacturing of parts using carbon fiber composite required highly skilled labor and special equipment’s where aluminum alloys, titanium alloys and high strength steel required intermediate skills and their equipment’s are also not much expansive.