Improved Hardening Introduced

Automotive Manufacturing & Production, July, 2001

The problem. Say you're induction hardening crankshafts. In the conventional approach, U-shaped inductors are used. Each crankpin and main journal is heated by bringing the inductor close to the pin or main bearing surface; the crank is rotated at a speed in the range of 24 to 32 rpm. Given the configuration of the crankshaft, with the pin axis being offset radially from the main axis, there is an orbital motion involved. And the U-shaped inductors must go along for the orbit--and the relationship between the inductor and the workpiece must be precisely controlled. All things considered, this arrangement results in, according to Dr. Valery Rudnev and some of his colleagues at Inductoheat, Inc. (Madison Heights, MI), a piece of heat treating equipment that is "quite complex, sensitive, bulky, noisy, and costly." What's more, there are issues related to equipment maintainability, reliability, hardening pattern repeatability, and downtime. In addition to which, there is short inductor coil life: on the order of two weeks.

The solution. So, the people at Inductoheat have come up with an alternative, It is called "SHarP-C Technology." Which stands for "Stationary Hardening Process for Crankshafts." There is no need to rotate or move either the inductor or crankshaft during the heating and quenching cycles. And unlike setups using encircling clamp-type coils, there are not the high-current contacts that can occur with those coils; however, the heated features (main, pin, oil seal) "see" the inductor as an encircling cylindrical coil, which means that there is a consistent, symmetric heating pattern generated by the efficient, solid copper coil.

The benefits. The heating time is comparatively short: in the 1.5- 4-second range (vs. the conventional 7 to 12 seconds). The short heating time is not only beneficial from the standpoint of throughput, but it is actually said to improve the metallurgical properties of the hardened zone (e.g., grain growth is reduced), which tends to be clearly defined. Also short heating means there is minimal distortion of the part, generally limited to less than 0.025 mm.

Another advantage of the SHarP-C approach is that there is high controllability, such that it is possible to modify the hardness profile along the circumference of the pins and mains and across the width of the journal. Controllability is particularly useful in the oil hole area, given that there tends to be a difference of metal mass on either side of the hole, so the amount of heat needs to be adjusted, accordingly.

One thing that certainly is an increasing concern is the amount of energy required. SHarP-C equipment is designed so that there is efficient heat treating, which means that energy requirements are reduced compared with conventional machines. And there is also space-savings: the equipment can require just 20% of the floor space of a conventional rotational hardening machine.

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