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DFM | Tracking data

Figure 2: Cycle time data captured from AST’s mould- mounted CVe monitoring device

Alternatively, it could be decided to run a tool on a shorter cycle time to free up production capacity. It is important to understand, however, that compo- nent quality can suffer if the cycle time is allowed to divert from the DFM predicted settings and fi nal moulding parameters. Consider the example of the POM medical component in Figure 1. This incorporates an undercut which has to be bumped off. During the DFM process, it was predicted it was necessary to eject the part at a defi ned cooling time when it was 85% frozen to ensure the dimension of the cylindrical sealing area remained within tolerance. The potential for cycle time changes to impact on product quality is clear in this example. If the cooling time is too long, the part will be too stiff at ejection and damage will occur during demoulding. If the tooling time is not suffi cient, the polymer will be too soft and will bow and not fl ip back into shape, putting the critical sealing dimension out of specifi cation. AST was involved in a recent tooling project for

Figure 1:

The bump off feature and sealing

diameter in this medical

component are very sensitive to mould

temperature and cycle time changes

production of an automotive connector component with a clip feature where a cycle time reduction was made by the moulder to free up additional production capacity. During the original DFM process it was determined to run the mould tool at the higher end of the allowed temperature range to achieve better weld line fusion (due to the higher temperature at the polymer fl ow-fronts). The connector ran in production for two years, during which no failures in the fi eld were experienced. During the third year of production,

however, the clip feature started to break. The cause of the problem was identifi ed as a small reduction in the mould temperature, which allowed the cycle time to be reduced by around fi ve seconds but reduced the polymer temperature at the fl ow- front and so resulted in a weld line weakness. Around two in every three connectors subsequently failed in the fi eld because of this weld line issue. A

62 INJECTION WORLD | January/February 2014

key factor in quickly identifying the cause of the problem was knowledge of the specifi ed cycle time and that being used in production. By making frequent checks on the cycle time, it is

possible for the project team to step in before produc- tion quality issues develop. A number of systems and devices are available today that trigger and record the activity of injection mould tools. These range from complete integrated systems such as those from BAKO and others, where every production moulding machine is providing data into a database for analysis, to solutions such as Männer’s moldMIND or AST Technol- ogy’s own CVe Monitor that stay with the mould tool. Integrated solutions can capture a great deal of data

but are, perhaps, more benefi cial for the plant operator than the mould owner. Mould-based systems are less powerful but offer the advantage of continuing to capture date wherever the tool is in the world. The CVe System, for example, can pull information on cycle time and mould activity. This data can be delivered from the production site to the mould owner using applications such as OnDemand or CVe Live. The data from the reports generated by these systems

can also be taken as a lessons learned for new projects, allowing future DFM work to be improved. Required cycle time changes in production will be highlighted and the component and mould tool could be revalidated in an additional DFM loop to check on root cause impacts and possible improve- ments.

About the author: André Eichhorn is general manager of Germany-based AST Technology. This is the latest instalment in a series of articles in which he discusses how product manufacturing problems can be

overcome by the application of Design for Manufacturing techniques. You can read the most recent articles in this series here, here and here.

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