Introduction

Founded 20 years ago, Dr.-Ing. Klaus Brankamp System GmbH, Germany, is a manufacturer of process monitoring systems that find particular use as measuring instruments in industrial manufacturing. Brankamp offers a wide range of hardware for product quality, as well as such computer-aided quality control software as SPC and PMV (all CAQ modules). For guaranteed quality, most of the company’s monitoring units feature large LCDs to allow process observation, especially important in the metal working industry. Those units are designed for all cutting, pressing, cold forming, and assembly processes.

Brankamp, which recently began the exclusive marketing world-wide of the new ProcessMonitoring® systems of the US company Textron, is recognised as the pioneer of process monitoring technology and is the only company to develop and produce systems for all branches of the metal processing industry. Brankamp systems are intended to prevent process errors; or, if malfunctions occur, to immediately switch off the machinery, thereby averting or limiting any damage. “This new piece of equipment will enable us to offer our customers an even larger product range in future”, Brankamp's authorised signatory Hans-Peter Schneider told EuroWire. This article reviews the advantages of Brankamp process monitoring with flaw detection by the eddy current technique.

Measurably fewer downstream flaws

The combination of process monitoring and flaw detection by the eddy current technique constitutes an efficient and economical method for detecting material flaws in safety-relevant component parts, without any reduction of production speed. Downstream flaws - which are especially time-consuming, labour-intensive, and expensive - may thereby be considerably reduced.

Eddy current sensor and magnetization coils in the wire feeder section.
Flaws in wire material may cause cracking during forming

More stringent quality requirements for cold forming have resulted in specifications, which often stipulate safety-component parts completely free from cracks or flaws. Since minor material deficiencies (such as longitudinal, transverse, or surface cracks) have little influence in forming and its associated pressing forces, additional flaw detection is becoming necessary for such components.

Advantages of flaw detection upstream of the press

Flaw detection may be accomplished by a number of different methods, either on the input material (such as the wire before pressing) or on the eventual formed part. Eddy current testing of the wire material - prior to shearing and forming - of the incoming material directly on the machine is an automated, economical process. Its great advantage is the testing along the full length of the component part. By contrast, single-part inspection in the formed condition provides only partial testing for flaws or cracks because of the complex geometry of the individual parts.

Brankamp PK 550 Process monitoring system with wire flaw detector

For flaw detection, the wire is uncoiled from the reel and passed through the straightener, the magnetisation unit, and the circular coils. The material is examined by non-contact eddy current testing for a variety of material defects (cracks, pores, fins, seams, etc.). When a defect is found on the wire material, a fault output signal is generated for evaluation by the Brankamp PK 550 process monitoring system.

Adjustable sorting tolerances

The machine operator need only enter the appropriate spacing of the eddy current sensor as determined by, for example, shearing stage or desired cutting length. These values define how many strokes a defective wire section will require until shearing and subsequent forming. A sorting tolerance may be adjusted to control the time of opening of the sorting gate. In a sample case, the sorting gate will open four sections before the defective section, and will not re-close until four strokes after the non-conforming part. Inaccuracies in wire feeding and ejection of the parts up to the sorting gate are thereby compensated. Higher sorting tolerances will ensure that all non-conforming parts are reliably sorted out, even in instances of large spacings between eddy current sensor and sorting gate.

Sorting queue with flaw detector (1) and sorting gate (2)

The basic record for process monitoring contains data on the number of forming stages and the spacing between sorting switch and the last pressing stage. Brankamp’s PK unit will monitor all machine stages and detect typical process malfunctions during forming. Additionally, the company’s Quattromatic envelope-curve method permits head cracks to be detected. These are caused during heading by the cracking of wire sections not damaged earlier. The inner envelope curve ensures that minor changes of force will be detected and utilised for actuation of the sorting gate following the forming operation. Simultaneous sorting is useful here, since a nonconforming part may be detected either by flaw detection or by the process monitoring associated with the various forming stages.

Clear display aids interpretation of results

The Brankamp PK 550 system also enables the operator to check the results of flaw detection and hence to perform sorting right on the display. The sorting “queue” will indicate the cracked wire areas, so that the defective parts may be removed systematically at the sorting gate and the monitoring results on the component parts checked directly. Flaws or cracks in the wire will be more readily visible on the formed part. This permits more accurate interpretation of faults than is possible, for instance, with wire sections sorted out before forming. Also, the load distribution inside the press will be influenced by rejected sections. This results in more consistent product quality.

Conclusion

Because the quality of wire materials can fluctuate widely, a combination of Brankamp process monitoring and materials flaw detection can provide the wire-making plant with a significant protective mechanism. With this technology installed, defects in the range of 2% to 13% of the wire material have been detected by eddy current testing and sorted out via the sorting gate.