We offer custom designed complete piston assemblies (with rings, pin and clips) from a variety of processes depending on the application and volume. An overview of the available technologies is listed below.
Permanent Mold Aluminum Pistons:
The most common process used to produce pistons is called the permanent mold process which makes use of a steel mold with single or multi-piece cores that create the inner features of the piston. This is the process used for most production OEM 4-stroke and 2-stroke engine pistons including ORV, motorcycle, automobile, marine and snowmobile pistons. The permanent mold process is a relatively low cost process for high volume applications that can justify the high up front tooling costs. It can produce pistons from a number of different alloys including alloys with improved strength at elevated temperatures so the technology can cover a wide range of applications. The advantages of the permanent mold process is relatively low part cost and the ability to create relatively complex geometry for strengthening ribs, weight reduction pockets etc. The disadvantage of the permanent mold process is that the tooling costs are quite high and when the material solidifies in the mold, there is potential for small defects like porosity that can limit the strength of the material. Permanent mold pistons can work well at very high specific output levels for small bore applications but are more limited in the specific horsepower levels they can support when the bore diameter gets over 75-80mm. We work with several casting suppliers to offer custom designed permanent mold pistons for applications that fall within the strength limitations of the available materials and have volumes high enough to justify the tooling costs.
Forged Aluminum Pistons:
High performance, large bore applications that require increased strength tend to use pistons created with a forging process. This is especially the case for 4-stroke pistons where it is the process of choice for high end applications like stock car and drag racing. Forged pistons start out as a solid cylindrical aluminum blank that is heated and impacted or pressed into a forging die to create the piston shape. The blanks are made from a wrought material that is initially extruded which creates a very dense part with minimal porosity. The low defect rate, increased ductility and fracture toughness are the primary drivers for the improved strength of a forged piston. The forging die used to create the inner features of the piston is typically a one piece feature that eliminates some of the options for strengthening ribs and weight savings pockets that can be created with the permanent mold process but some of those features can be machined in and the technology works very well for short aspect ratio pistons like those in 4-stroke racing pistons. The wrought materials generally tend to have less strength at elevated temperature than some of the high temperature casting alloys used for permanent mold pistons but the superior ductility and fracture toughness makes them a better choice for 4-stroke racing pistons which generally run at temperature levels where these alloys still have good strength. The operating temperature for high output 2-stroke pistons is generally out of range for most wrought alloys but we can produce forged pistons from an alloy with high Silicon content that has good strength at temperature for high output 2-stroke applications. We also offer pistons that we machine from forgings provided by a company called RSP that combines rapid solidification and forging to create pistons with exceptionally high strength at elevated temperatures. The performance advantages generally outweigh the disadvantages of the forging compared to a permanent mold piston for high performance 4-stroke pistons. The tooling costs are typically lower but the individual piece price tends to be higher. We tool and procure our forgings from a best in class manufacturer and can add machining operations to create many of the geometric features that can’t be created with the forging process alone.
Billet machined pistons:
Billet machined pistons are typically machined from the same wrought aluminum materials used to create forgings and can also be machined from, steel, cast iron or cast aluminum. Billet machined carbon fiber or carbon-carbon pistons can also offer advantages in some special applications. The fact that all surfaces are machined makes them relatively expensive but there are no tooling costs and part to part variations are minimal. We can produce billet pistons from all the above mentioned materials via a 5 axis CNC machining process.
