Since both flywheels and flexplates accomplish the same function and are somewhat similar in appearance, they are often referred to interchangeably, but are in fact two different parts.
A flywheel is used primarily in manual transmissions. It is attached to the engine crankshaft, and holds the ring gear that is used to crank the engine.
The flywheel connects directly to the clutch, stores energy to move the vehicle from inertia, and provides a friction surface for the clutch to attach to.
Because of this, flywheels are usually casted, and are thick and heavy, to allow for the surface for the clutch.
In addition, the heavy weight allows for more inertia once it is spinning.
A flexplate is used in automatic transmissions, and also carries the ring gear to the starter. However, in an automatic transmission, a torque converter replaces the clutch of a manual transmission, and the flexplate mounts the torque converter to the crankshaft. Since there is no clutch with its grinding motion to support, flexplates are much lighter and thinner. They are usually made by stamping, and the ring gear is welded on. Its thin and flexible (hence the name) frame can flex along its main axis, and take up the motion in the torque converter as the vehicle speed fluctuates.
Flywheel production: Flywheels are usually produced by the casting method, and for now, sand casting is the most common production process for flywheels. Depending on the application, the materials used are nodular iron, steel or aluminum. Once cast, the flywheel is finished by machining and boring.
Next, a square or rectangular steel bar of a preset length is bent into a circle configuration and the ends welded together, with the major diameter larger than the finished gear size.
The ring is then heated, and either stamped or bored to size on the minor diameter. Next, the gear teeth are hobbed onto the ring, and hardened to improve strength and resistance. Lastly, the ring is shrunk onto the flywheel.
Flexplate production: Flexplates are usually made in one of two ways – stamping or billeting. In the stamping process, sheet metal is stamped into the net shape of the flexplate and the ring gear is then welded on. Billeting is the process of machining a part from a solid piece of metal; in this process, either the flexplate is billeted and the ring gear welded on, or the entire flexplate, including the outer ring gear, is fashioned from a single piece of metal.
Stamped flexplates are the most common. Two-piece billeted plates are stronger due their thicker and more durable center plates, and are therefore used in applications requiring greater horsepower. One-piece flexplates are the strongest of the three, and usually integrate the ring gear onto the plate in one solid piece.
Flexplates and flywheel assemblies are used primarily to start the engine in a vehicle.
Flywheel: When the engine is started, the engine crankshaft turns, and its pinion gear engages with the ring gear of the flywheel to rotate it, in turn rotating the crankshaft on which it is mounted. The rotating crankshaft moves the engine parts through the combustion cycle to start the engine. Once the engine is running on its own, the weighted and balanced disc of the flywheel keeps the crankshaft running smoothly between combustion cycles, preventing the engine from slowing down between piston firings.
Lastly, the flywheel helps connect the engine to the transmission, enabling the torque power produced by the engine to flow through the transmission to the rest of the drive train to the wheels to mobilize the vehicle.
Flexplate: The flexplate replaces the flywheel in automatic transmission vehicles. The torque converter is bolted on to it, and it in turn is bolted onto the end of crankshaft, thereby delivering the rotation of the engine to the transmission.
AmTech manufactures ring gears for common automotive flexplate and flywheel applications, as well as for torque converter applications, in a variety of customer specified sizes and tolerances.