A second-tier supplier of light pressings and small assemblies to the automotive industry, Berck Ltd has installed a video measuring machine fitted with touch-probing capability at its West Bromwich facility.

This multi-sensor machine has greatly reduced the time taken by inspecting 2-D and 3-D sheet-metal components, improved measuring accuracy, and allowed the production of detailed quality reports for customers.

It also allows manufacturing processes to be optimised by providing detailed historical measurement data to be compared with current inspection results.

Two-thirds of Berck’s output goes to the vehicle-manufacturing industry in the UK and overseas; 40% of this is bracketry for engine compartments and wiring looms, while the remainder comprises precision electrical contacts associated with lights, windows and seats, for example. The other third goes to manufacturers of domestic electrical goods such as cookers, lighting equipment and plugs.

Components are stamped using progression tools (with up to 12 stages) on 23 presses — including 12 high-speed models — mainly from coil between 10 and 150mm wide and 0.1-3.5mm thick. The materials include brass (along with tin-plated varieties), mild steel, spring steel, copper, beryllium copper, phosphor bronze and aluminium.

For many years, Berck used an optical co-ordinate measuring machine (CMM) and a manual touch-probe CMM to inspect sheet metal parts and tools.

The former machine is nearing the end of its useful life, while the latter was recently dismantled because it was beyond economical repair.

Last year, realising that a new metrology solution would soon be required, quality manager Steve Bettridge visited the Advanced Manufacturing Show at the NEC, Birmingham, to see what alternatives were available.

He was keen to combine the functions of both CMMs in one machine, aware that 95% of the company’s throughput is based on the optical measurement of sheet metal components; only 5% is touch-probing components with steep sides, like fuse cups that have a dimensional tolerance of ±20µm and are difficult to inspect by optical auto focus.

Parts with complex external profiles such as radiator cap inserts are similarly difficult to measure optically. Touch probing is also used to assist the in-house toolroom by reverse-engineering inserted press tools — for which no drawings exist — to allow their re-manufacture.

Video-based measurement

After discarding the idea of combined touch probing and laser scanning on a CMM, because the level of accuracy this offered was not needed for pressed parts, and the cost was too high, Mr Bettridge looked at various video measuring machines and decided in favour of a Nikon Metrology iNexiv VMA-4540 CNC video measuring machine fitted with a touch-probing capability (www.nikonmetrology.com).

This machine had a larger ‘stage’ than other machines on offer, thereby offering greater versatility — and Nikon’s proprietary software was considered easy to use. Furthermore, although laser technology has not been adopted, there is the option to fit laser auto focus if the need arises.

The Nikon CNC video measuring machine has three light sources to ensure efficient inspection, whatever the type of product; episcopic (overhead), diascopic (transmitted light) and an eight-segment ring LED combine to provide comprehensive illumination and accurate edge detection. Since it was installed in April 2016, the iNexiv has been deemed “a resounding success”.

Berck’s optical-measuring routines are programmed conversationally in half the time required using G-code for the company’s previous machine.

Moreover, the stage on the Nikon instrument, with its 450 x 400mm working area, is four times the size, and the axis movements are considerably faster.

Comparing like with like, the high-speed iNexiv with its wide field of view and search capability offers automatic component recognition and alignment, allowing a given number of components to be measured 50% faster than on the previous machine.

Moreover, the parts do not have to be all the same; they can be families of different items arranged in a grid. Provided that the Nikon machine is programmed to inspect the series of components, it measures them all seamlessly and automatically, while the operator is working elsewhere.

Another advantage of the new inspection facility is its ability to measure folded 3-D sheet metal components optically, using its 200mm Z-axis stroke, 73.5mm vertical working distance and auto-focus capability.

The limitation of the previous instrument is that its Z axis was not sufficiently accurate to produce reliable results, necessitating the transfer of components to an optical projector to determine their depth.

Double handling in this way resulted in a measuring process that was more than twice as long.

Efficient touch-probing

For tactile inspection, the advantages of the CNC iNexiv over the previous manual touch-probe CMM are even more pronounced. For a start, the Nikon machine undergoes one 5min calibration cycle per week; this covers the use of all probes.

Idle time was considerably longer using the manual CMM, as it needed to be calibrated once per day for each probe used — and components had to be aligned by hand before each inspection routine could start.

On the Nikon machine, the position of the component is identified automatically, allowing the part to be measured with minimal delay; and if a change-over between the 2.5 mm ball probe and a star probe is required during the cycle, it is achieved automatically via a Renishaw rack.

Offering the example of inspecting 10 fuse cups, Mr Bettridge says it used to take 30min to complete the job manually, plus there was the risk of damaging the stylus due to human error. Now, the process takes 2min — a 15-fold time reduction (provided that the cycle is already programmed and stored).

“For such a simple component, it would only take 5min to program anyway. Furthermore, with Nikon Metrology’s AutoMeasure software, it is easy to create programs and automatically compare results against CAD models. Deviation of contours can be checked by overlaying digital charts from 2-D CAD data onto video images.”

The Nikon full-frame colour camera captures highly detailed pictures that are saved to Berck’s server to provide a reference for future process analysis and troubleshooting.

They may also be embedded in customer inspection reports produced by the software. Files of accompanying statistical data are downloaded automatically to an Excel spreadsheet, saving time compared with the previous manual procedure. Many other standardised reporting formats are also possible.

Programs from the previous optical machine are currently being edited to run on the Nikon video CMM; about 200 have been completed so far. In addition, 50 new programs have been created for the iNexiv, both for optical and touch-probe inspection.

Berck is also using a Nikon software package called iNexiv EDF (Extended Depth of Focus), which allows all-in-focus 3-D images of products to be created by stitching together multiple pictures taken at different Z-axis heights. Measurements can then be taken from the resulting composite facsimile for investigation, problem-solving and archiving.

In conclusion, Mr Bettridge said: “The software is surprisingly easy to pick up, provided that you have a basic knowledge of the principles of metrology. It is also reassuring that Nikon offers software updates for a minimum of 15 years, so our new inspection facility is future-proof.”