QMT Features: March 2007
If the cap fits...
A shopfloor SPC system dramatically reduces data logging errors and improves production processes at bottle manufacturer, Constar.


There is a lot more to plastic bottle production than you might expect and the closures (or caps to most of us) present a number of challenges to those creating them in large quantities.  Constar is one such company and it has been working closely with MES software provider, Lighthouse Systems, for several years to implement quality processes to improve the company’s performance and reduce customer complaints. 

 The relationship between the two companies dates back four years or so when Constar was looking for an alternative to its rather cumbersome, paper-based processes for quality control in its UK, European and US facilities.  The company looked at a number of options before choosing to work with Lighthouse and implement its Shopfloor Online software in its European HQ in Sherburn-in-Elmet, North Yorkshire. 

Lee Thomas, Quality Manager, Lab and Customer Services, comments, “The old, manual system was full of errors and we needed to put a stop to data falsification as a means of operators saving time by recording data ahead of schedule, or through the manipulation of recorded data.  We were also looking for a system that would limit the number of ‘forgotten’ checks by providing visual reminders that checks are necessary at predetermined times.” 

 The new, automated approach was implemented to provide more accurate views of Constar’s processes by delivering SPC data on which managers could base assertions and improve plant performance.  The software was implemented within the closures department and then spread across the company to provide quality data regarding bottles and pre-forms.  It was expected that Shopfloor Online would dramatically reduce errors in the logging of data and therefore provide more accurate information on the quality of production runs.   Thomas adds, “Improved availability and accuracy of quality data improves the level of service we are able to offer customers and therefore reduces the number and gravity of customer complaints we receive.  The net of this is significant efficiencies across the board.” 

Production process improvements

There are many similarities in the various production processes and as many differences.  A first lift is performed in each area of the Constar business to provide quality data that will determine whether the machines are fit for production.  For this process, manual gauges are used to measure the products and the data collected is then passed electronically to the Lighthouse system where it can be analysed and managers can determine whether the production run is within certain, pre-specified quality parameters. Any out of spec measurements at this stage result in changes to the production machines and a repeat of the first lift process. Production only begins when all measurements are within the specification limits set by the customer. 

 The first lift for pre-forms is similar to the process for bottles but tends to check more parameters.  The measurements here are carried out on a co-ordinate measurement machine (CMM) from Mitutoyo.  The CMM outputs a text file which is picked up by Lighthouse’s Shopfloor Online and cleared for production if the data meets the agreed criteria. This department also carries out running checks throughout the production process and at pre-determined intervals (21 day cycle). 

 Thomas comments, “Cavities deteriorate over time and we need to be sure that we spot the signs at the earliest possible stage, otherwise the waste is significant.  The ability to check performance of the cavities at regular points means that we can blank those that are under-performing without shutting down the machines and therefore keep production running.  Only when a certain number of cavities are out of spec do we cease production on a machine and replace the equipment.  Knowing the optimum time to do this is an essential part of our business.”

 The closures department is the most intense user of the Lighthouse quality systems.  Here, they are used constantly, recording measurements and carrying out running checks via the CMM. It is also here that the greatest benefit has been felt. 

 Thomas explains, “Having SPC data readily available makes such a difference to us.  The manual process would show a huge spread of results and that was resulting in a higher level of customer complaints, especially where tamper band quality was concerned.  The tamper band cutting process is incredibly precise so that they release under a certain amount of pressure only.  Because we can now monitor the SPC information we know when the tamper cutting blade needs to be replaced and can therefore prevent issues of bands not functioning correctly.  The spread of results is now very fine and quality is markedly improved.”  l

email: info@lighthousesystems.com
www.lighthousesystems.com

  
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