Rapid inspection of large parts

Founded in 1989, CMS Cepcor supplies aftermarket crusher spares, manganese-steel wear liners and other equipment to the mining and aggregate industries worldwide. In February, the company took delivery of its first CMM, an Altera M from LK Metrology to enhance the quality control of its products.
Previously, CMS Cepcor had been using a pair of manually-operated, portable, 6-axis arms with a 2.5-metre and a 3-metre reach to check components by touch-probing. This was a lengthy process, as well as being insufficiently precise to measure some parts. For example, it was challenging to inspect bearing seats with tolerances of 30 microns and shafts up to 500mm diameter that need to be accurate to within 20 microns. Additionally, some parts up to 400mm in diameter by 700mm long have eccentric tapers with drawing tolerances down to 15 arcseconds, which were problematic to check by hand.

A further difficulty was that sometimes an arm would be set up on a metrology fixture table and in the process of measuring multiple items, an urgent request would be made by shop floor staff for the arm to be transferred to a machine tool to evaluate the dimensions of a part in situ before it is removed from the machine. Les Hickens, Quality Manager at CMS Cepcor commented: “The LK CMM has a maximum permissible first term error of less than two microns, so is able to measure very large parts exactly and repeatably. It is at least an order of magnitude more precise than a portable arm, giving us confidence in the results. The high level of accuracy is particularly useful when we are discussing the dimensions of a lead-bronze bushing with a high coefficient of expansion. In such cases, both close-tolerance inspection and careful temperature management are important when reconciling our respective measurements. Our Altera M has thermal compensation, with a sensor built into each axis and a temperature probe supplied for attaching to the component under investigation. It would not be practical to wait 24 hours while a large, heavy casting normalises its temperature with that of the CMM.”

Many parts undergoing quality control are turned on a Doosan lathe and then milled and drilled in a second operation on an Honor Seiki vertical boring mill or a Norma machining centre. Consequently it was considered expedient for LK to supply the Altera M 30.15.10 with a Renishaw PH10MQ PLUS motorised indexing head and an SP25M probe for analogue contact scanning, capable of measuring up to 1,000 points per second. The system is able to verify any out-of-roundness much faster than if a touch probe is used to capture a succession of discrete points.

Innovmetric’s PolyWorks Inspector software was also supplied with the CMM. It is a facet of the installation that has delighted the CMS Cepcor metrology team, as it is simple to learn and use and makes training new operators easy. The same software is being retrofitted to the portable measuring arms, as well as a handheld optical scanner on site employed for checking very large castings, so only one seat of PolyWorks is needed, saving expense.

Mr Hickens concluded: “At CMS Cepcor, we are committed to excellence. Although we have been using the CMM for only a few months, it has resulted in a step-change in our metrology capability and the benefits are already tangible. The heightened precision ensures components are controlled carefully to the relevant specifications.”