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Shrink Fitting an Assembled Wrist Pin into a Connecting Rod

Objective: To assemble connecting rods; the client was looking for better control of the heat delivered to the assembly.

Equipment: Ambrell EASYHEAT 3.5 kW, 150-400 kHz solid state induction power supply with a workhead and coil specifically designed for this application.

Frequency: 210 kHz

Material: Rod has an OD of 0.9125” (23.18 mm), knuckle has an ID of 0.9125” (23.18 mm) with an interference of 0.0001” (0.0025 mm). Knuckle assembly is forged steel.

Temperature: 400 °F (204 °C)

Testing: A six-turn helical coil was used to heat the connecting rod for 13 seconds. The coil was perpendicular to the axis of the bore to promote even heating around the circumference. The connecting rod was then assembled with the piston for shrink fitting.

Benefits:

• More accurate control of heat vs a flame burner. Induction only heats the knuckle, not the whole part.
• A lower temperature was used to prevent discoloring.
• Increased productivity due to repeatability and ease of operation. A foot pedal and timer was used.
• No product contamination.