Application Note: Heat Treatment Defects on Camshaft Lobes

The problem: Soft spots on cam lobes

The production of defect-free engine components is critical to any vehicle manufacturer and supplier. Even in the most highly controlled production processes, things happen: tools break, motors stop, and heat treat processes fail. It is obvious when tools and motors are damaged, but it is not so obvious when the heat-treating process is malfunctioning. This typically requires specialized inspection.

In this case, the customer discovered soft spots on cam lobes due to a break down in the cleaning system and parts were being heat treated with debris on the surface. The manufacturer was initially only able to detect these defects using nital etch and were in search of a non-destructive method in order to reduce scrap costs.

The testing method: Non-destructive Barkhausen noise analysis

Barkhausen noise (BN) is non-destructive and sensitive to material stress and hardness which made it a suitable replacement for nital etching. The camshafts were placed in a test stand and a sensor was lowered on to each lobe and the cam was then rotated. The response was detected on a BN analyzer and data acquisition software automatically made the pass/fail determination.

Barkhausen noise measurement on camshaft lobe with CamScan 100 — Figure 1: Camshaft sensor on camshaft.

The results

Graphical Barkhausen response showing heat treatment defect (soft spot) on cam lobe (etched lobe shown)

Instruments used for this application:

CamScan 100

CamScan100 is a semi-automated grinding burn and heat treatment defect detection system for low-volume applications. CamScan100 is designed for quality control needs of small to medium sized circular symmetrical parts like passenger car shafts.

Rollscan 350

Barkhausen noise signal analyzer Rollscan 350 is designed for surface quality control and testing of near-surface defects such as grinding burns, heat treatment defects, as well as changes in stress and microstructure in a wide variety of ferritic steel and other ferromagnetic materials.