QMT Features: December 2014
Four step weight plan
Checking quality by weight is a quick way to ensure completeness


Customers demand flawless products, delivered in the right amount at the right time. It is a challenge for every manufacturing company to ensure that assembled products consist of an exact number of parts or items. In production areas, quickly checking quality by weight is a smart solution for accurate completeness control.

Quality control by weight is suitable for most production environments, but certain requirements have to be fulfilled to start quality control by weight. This article explains the four steps to accurately weighing for quality control.

Checking completeness of goods is essential to maintain brand integrity and avoid rework and costly returns. This applies for single products as well as for product packages or kits. However, checking processes have to keep up with production speed, even in manual assembly processes. Sometimes common optical and tactile quality checks are too slow, too costly or simply not suitable for a company’s desired application.

Weight-based quality control is an affordable, easy-to-implement and secure way to check completeness. Scales can detect non-visible defects, such as missing parts or left-over spare parts in assembled products. With weight-based quality control, you can check the completeness of assemblies or kits and the length of cables, ropes or wires. Weighing can indicate the intactness of casting or the application coating and lubricants quickly and securely.

With precision scales, it is also possible to check if kits comprising different items are complete. There are many ways to check product completeness, but none are as fast and simple as weighing.

Weighing in production
When there is a need to check samples from the production line or perform quality assurance by hand in manual production, compact scales are a viable alternative to inspection devices equipped with sensors or cameras. These accurate standalone instruments work well in a variety of applications and supply quality data to improve processes.

Checkweighing is most commonly used to control completeness of products, assemblies or kits. This process describes weighing a certain object against a preset target. Weighing installations can differ depending on how weighing or counting is performed in a factory. Checkweighing in production is done directly at or close to production machines or lines. In-process quality checks are often used in automated mass production of metal, plastic or electronic parts. Scales can be built into the conveyor belt to enable new possibilities for process and quality improvements.

Quality checks with high throughput

In manual quality-check applications, workers perform weighing applications by hand. They place a single work piece or batch on the scale, verify the result and remove the item in a repetitious process. This makes quality checks a quick and easy-to-learn process. Results appear quickly and easy-to-use weighing instruments facilitate fast operation and high throughput. In-line weight-based quality control scales can be connected via PLC to the respective assembly line. Even complex assemblies, such as motor blocks or solar panels, can be checked for various parameters, quickly and securely.

Start checking quality with weighing

The benefits of checking quality are clear, but how do you get started? Follow these four steps (see panel, top right) to quickly and effectively check quality in a production process.
Practical application examples

The following are examples of how two manufacturing companies implemented quality control with weighing in their processes.

Example 1: Quality control of assemblies by checkweighing
A global manufacturer of advanced pneumatic equipment checks products for intactness and completeness by weighing. In the manufacturing department, workers manually assemble air filters. With hundreds of filters processed a day, mistakes, such as missing parts or spare parts left inside filters, occur occasionally. However, the problem is not immediately visible to workers. To fulfill its high quality standards, weight-based quality control was introduced.

Results immediately changed for the better. Workers simply put a final product on the scale, and in a split second, they knew whether or not the product was complete based on predefined ideal piece weight and tolerances. The scale immediately indicates with a backlight display if products are out-of-specification and must go back to assembly. This speedy operation led to significant process improvements. Thanks to the speed and accuracy of the manual checkweigher, the company now only needs one operator for the job, which leaves the second operator free to do other productive work.

Example 2: Checking lubrication of motor blocks

Oil quantity is an important performance indicator for moving engine parts. Accuracy in the amount of oil applied can be critical. Oil shortage in a heavy-duty engine part, such as a piston, creates unnecessary wear, while too much oil impedes performance and is a waste of money. When trying to measure and apply lubricant on the assembly conveyor itself, speed also becomes an important factor. The lubricant has to be applied and checked within a short timeframe. Consistent reliable results that fulfill the automotive industry’s high standards are important. With scales, production engineers achieved a 30-second cycle time for transmission weighing/oil application. When a power train arrives at an engine block on lifting cylinders, weight measurement begins. As a result of this robust data gathering, oil application can be applied within tolerance relatively easily. This leads to an integrated weighing solution that is steady reliable and accurate.

Conclusion
Even when production processes become more accurate, random bad parts need to be detected. To ensure quality, defective pieces must be sorted out from the manufacturing process and incomplete shipments must not be sent. Weight-based quality control is a versatile, accurate alternative to costly sensor- and camera-based systems to check the quality of a wide range of products throughout the manufacturing process. It is suitable for metal, electronics, automotive or any other manufacturing industry segment. Either automated or manual settings give operators complete control of quality parameters in production.
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