QMT Features: April 2010
Breath of quality
When it comes to  production of precision plastic parts for inhalers and respirators, multisensor 3D technology helps Bespak breathe easy

King’s Lynn-based medical device manufacturer Bespak has installed a new SmartScope CNC 500 multi-probe compact CMM from OGP UK, the company’s fourth such machine on site. Used to measure a range of components for Bespak’s leading range of inhaler and respirator products, the SmartScope CNC 500 is already offering extensive programming, set-up and cycle time savings.

“We have many conventional tactile-based CMMs on site but for a new project we were looking for a system that would be both quicker and easier to use,” explains Bespak metrology engineer Peter Haken. “Vision seemed the way to go as it provides more control over the critical dimensions being measured. Once we had settled on vision, OGP were the only supplier worth considering as they offer a good production-based system that is both cost effective and easy to program. Many comparable systems seem only able to accommodate lab-based work.”

Production is certainly the core focus at King’s Lynn, where products include inhalers and medical check valves. As a division of Consort Medical, a leading group of healthcare companies focused on medical device technologies, the expansive Bespak site at King’s Lynn today employs around 500 people.

Most of the components for Bespak’s products are precision plastic parts (typically polypropylene) manufactured on injection presses in two, four or eight-cavity moulds. The OGP SmartScope CNC 500 performs production acceptance checks on a four-hourly basis; i.e. six times a day across a 24-hour operations.

“The operator will take a shot, allow it cool and mount it in a purpose-designed fixture on the table of the SmartScope CNC 500,” explains Mr Haken. “He then simply clicks an icon on the Measure X menu and the program runs automatically. Most programs take around 2 minutes to complete, although some are longer at around 5 minutes. In comparison with conventional CMM technology I would estimate the system is at least 25% quicker. However, in some instances, features that might take 3-4 minutes on a CMM only take around 1 minute using an OGP vision system.”

OGP’s Measure X metrology software provides the user with all the tools needed to make geometric measurements. The software quickly controls all probe changes, while inspection routines are recorded automatically and edited easily using icon driven commands. Data outputs can be customised with reports available in printed or digital formats.

Additional analysis of surface, profile, SPC and part-to-CAD comparisons can be collated by using seamlessly integrated companion application programmes. At Bespak, results from Measure X are output to an SPC package called QC-CALC.
Bespak parts measured on the SmartScope CNC500 are typically no more than 10mm long and no larger than 8mm in diameter, and despite the inclusions of several complex features, programs are  quick to create using Measure X, as Mr Haken explains.

“Programming is definitely one of the system’s core strengths,” he says. “They can be created easily and quickly despite the fact that we need to test against all features, as well as validate fixtures and complete R&R (repeatability and reproducibility) studies. We need to ensure that the system and the operator do not take up more than 20% of the tolerance.”

Considering the parts are plastic, there are some extremely challenging tolerances, such as ±0.05mm and ±0.025mm in some instances. However, SmartScope CNC has a high quality 12:1 zoom lens that provides excellent optical performance over its entire range. The  AccuCentric lens maintains accuracy by calibrating itself automatically with each magnification change. Furthermore, illumination is provided by SmartRing, OGP’s patented vector light that gives total control of lighting angles, making it easy to pick out important features for repeatable and accurate optical probing.

Bespak specified its SmartScope CNC 500 complete with Renishaw TP200, a compact, module-changing probe that uses strain-gauge mechanisms for higher accuracy and longer life than kinematic touch-trigger probes. According to Mr Haken, the touch probe comes in very useful for features such as bores, where vision technology can typically only measure at the top or bottom. The SmartScope CNC range has a measurement envelope of up to 1500mm x 2000mm x 400mm (X,Y,Z) making the machines suitable for large components or for multi-loading batches of smaller parts.

Bespak has three other OGP vision systems on site: two SmartScope ZIP 250 models that are both fitted with Renishaw tactile probes; and a SmartScope ZIP 400 with laser probe. With regard to the latter, the laser probe has yet to see much duty at Bespak, although this is set to change soon when a new device comes on stream featuring high quantities of depth measurement – the type of feature that can be measured rapidly using a laser probe. l
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