Induction Shrink Fitting

Induction Shrink Fitting Systems - Overview

Induction shrink fitting refers to the use of induction heating to heat a component to a pre-set temperature to create thermal expansion to allow a second component to be inserted. Conversely the same technology can be used to expand components to allow them to be disassembled.

The controllability and precision of induction heating process make it an extremely effective solution to this type of application. As the heat is generated very quickly within the component itself very precise control is possible over the heated area thereby reducing distortion and allowing extremely quick efficient processing. Where components are to be disassembled it also allows rapid heat to be generated in the component to be removed before conduction can transfer heat to the main assembly thereby expanding this.

nduction Shrink Fitting Flywheels

The principle advantages of induction edge hardening over traditional methods such as flame hardening are as follows:

  • Precise control over the hearted zone leading to reduced distortion.
  • Accurate control of the temperature generated.
  • Significantly reduced energy costs due to the efficiency of the induction heating process.
  • Health and safety due to the removal of naked flames and pressurised gas storage systems from the process.
  • Easily repeated results and de-skilled setting and operating procedures.
  • Better quality product due to reduced scaling and better quality control due to the predictable nature of the process.
  • Reduced scrap due to reliability and repeatability of process.

All induction shrink fitting systems feature the same principle elements as follows:

  • An induction power unit
    The power and frequency of this unit is selected based on a variety of parameters including throughput, component thickness and the desired hardness pattern.
  • Cooling system for the power unit and coils
    Typically air blast coolers, refrigeration chillers and water to water cooler are utilised subject to climatic conditions and local requirements.

Optional elements for the system are sometimes required subject to the application as follows:

  • A Press Mechanism
    A press mechanism of some kind is sometimes required this will normally feature tooling to ensure accurate alignment of the parts to be assembled and either a pneumatic or hydraulic mechanism to press the parts together.
  • Temperature Control System
    Temperature control or monitoring by optical pyrometer or thermocouple to ensure correct temperature is achieved.

Induction Shrink Fitting - Case Study Automotive Starter Ring to a Flywheel

Application - Expand Starter Gear & Press onto Flywheel.
Component Details - 350mm diameter gear 12mm thick.
Process Requirement - Shrink Fit two components to form a single unit.
Induction Equipment - UT 111 200 5kW 100kHz Ultra-Tec power unit.
Feed System - IHP 35/22 10 Tonne hydraulic "C" press with specially designed alignment tooling.

The system features variable press pressure and sensors to detect overpressure and final position to ensure gear is fully home. Air blast is utilised to chill components to allow faster unload.

Power, time, pressure and temperature parameters are all set via a HMI panel in conjunction with a PLC based control system. Operator protection is via a light guard. Non contact optical pyrometer system to detect over temperature. Cooling system to cool power unit and coils.

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