When completeness matters, weighing is a surprisingly simple solution for quality control. It is an effective and nearly fail-safe method for in-process or end-of-line quality tests. New weighing components allow for a broader application of weighing-based quality testing, including in-line testing with narrow tolerance windows and high throughput rates.
Nature of Serial Production
Take a moment to think about how high-tech devices, such as smartphones can be produced and sold at affordable prices. Low production cost has a lot to do with mass-production, miniaturization and production in low-cost countries. However, this all would not work if there was no dedicated focus on production yield and high-throughput rates.
Optimizing yield and throughput rates is a focus for most production managers. Those two criteria are important where products are manufactured with complex manufacturing processes, and when products include expensive materials. They also matter for products sold to competitive markets. Examples of these types of products include ball bearings for the automotive industry, high-precision parts for the medical industry or high-capacity batteries for miniaturized devices in the electronic industry.
Requirements for In-Process Control
For improving yield rates, typically a lot of In-Process Control steps are built into manufacturing processes. At each control point, defective parts are sorted out from the manufacturing process. This stops the addition of value to defective parts. However, End-Of-Line Control tests are even more important, as they prevent defective products being sold.
Requiring high throughput rates means that quality tests must be executed at typical intervals of the manufacturing process in order not to slow down the production output.
In case quality tests take longer than other intervals in the manufacturing process, the method of spot checking a certain sample is an option. This method works well with failure modes of systematical nature – e.g. a process drift. However, randomly appearing or behaving failure modes cannot be detected with enough security.
As a conclusion, if random impacts are expected, high-speed test steps are required to guarantee the checking of all manufactured parts. Even speed can be optimized if a test step can be performed in the processing line and the parts must not be extracted from the line and handed back to it. For In-Process Control sites like these, small sensors are required in order to fit into limited construction spaces on the line.
It is also important that the chosen method is able to properly resolve the respective criteria much better than the tolerance range at the respective control point.
Eventually, as human errors need to be avoided in serial production (individual bias in repetitive handling), in-line quality control methods will be automated.
Applying Gravimetrical Test Methods
Traditional methods for In-Process Control and End-Of-Line Control use electrical resistance, optical imaging, spectrometry, light beam and mechanical sizing. It wasn't until recently that weighing technology was used in spot-checking mode. This was mostly due to the design of traditional balances and scales, which did not fit seamlessly into machines and instruments. It also was not obvious that dimensions, coatings, shapes or completeness could be indirectly checked while looking at weight deviations or differences because traditional weigh modules didn't provide the required precision in a machine environment. Most importantly, the weighing process was simply too slow.
New Weigh Modules Do It
New technologies have been developed to provide a digital output signal that is easy to integrate into an automation concept. Furthermore, they provide the necessary accuracy with high resolution to reliably test according to the small tolerances of the aforementioned processes.
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Mettler-Toledo International Inc.
Im Langacher, Zip Code 8606
METTLER TOLEDO specializes in the area of precision instruments for professional use. METTLER TOLEDO laboratory instruments are used in research, scientific, drug discovery, and quality control labs, amongst many others in the pharmaceutical, chemical, food and cosmetics industries. METTLER TOLEDO comprehensive industrial solutions cover the various steps in a host of manufacturing processes at many of the same customers that laboratory serves. Solutions range from receiving raw materials through various manufacturing processes, in-line process control and end-of-line packaging control, to logistics and shipping. Increasingly, these solutions are fully integrated into the customer's IT environment, helping automate their workflows. In food retail, our offering for fresh food management ranges from receiving and pre-packaging, to in-store solutions for self-service departments, deli counters, and checkout terminals.