QMT Features: November 2015
Lights out, but not in the dark
Integrated in-cycle measurement and post processing corrects for variation during lights out machining

Based in Veldhoven in the heart the Dutch technology belt, subcontractor Van Riet Metalworks specialises in the prototype and series production of steel and non-ferrous mechanical parts. In this market, accuracy is paramount and so the company invested in a Mazak Variaxis 5 axis machine tool with an automated pallet system which allows it to reduce the amount of human handling and so increase accuracy and reduce defects.  As well as streamlining its production processes, Van Riet is also able to cut labour costs and increase production by running the Variaxis unattended for 18 to 20 hours per day.

To drive this powerful machine tool, Van Riet invested in ESPRIT computer-aided-manufacturing (CAM) software by DP Technology supplied by local ESPRIT reseller Pimpel Benelux
Quality Control
Embarking upon its unattended milling mission, Van Riet Metalworks integrated an automatic measurement cycle within ESPRIT, mirrored in the machine tool’s post processor, so that deviations from the required part dimensions can be automatically corrected.

“When we arrive in the morning, we can be assured that the parts are correct,” says owner Ad van Riet.
“So, even when the tool wears down, we don’t worry because any deviation is automatically corrected. The moment the sizes fall outside the tolerances, the controller automatically goes back to the starting line of the operation and the operation is done again. “

If a measurement is out of tolerance to the extent that correction is impossible, the operation is aborted. For instance, if a measuring probe detects that a hole is too narrow, which indicates extensive tool wear, the tool is automatically replaced. In addition to Van Riet’s automatic quality-control processes, Foreman Bart van de Sande takes them a step further by measuring completed work pieces at random. “With intense usage, the tool becomes more inaccurate, but with the measurement probe on the machine you don´t see any deviation in the measurement results. Therefore, I check the machine at the same time,” he says.

Work offsets

Process security deals primarily with eliminating error and, when it comes to work offsets, embracing flexibility makes manufacturing more efficient, especially during the machining of multiple parts with varied offsets.
A work offset, or the orientation of the cutting tool – and therefore work piece – to the machine tool, is used to adjust the location of every tool loaded in the machine. On a mill, for instance, the work offset changes the position of the spindle in both the X and Y axes, and often the Z-axis, as well.

With local ESPRIT support, Van Riet Metalworks adjusted the Variaxis post processor to determine the work offset of the machine tool in three different ways. Using one method, the ‘zero point’ – or the intersection of the X, Y and Z axes – is set in the middle of the table and all faces are recalculated from that point. A second method entails operating with the zero point in space, which allows ESPRIT to calculate from that point.

A third method is to use one of the 300 zero points that Mazak has defined for the machine, combined with the zero points of ESPRIT. By default, the post processor for the Variaxis is written for 48 of these zero points, and Van Riet Metalworks has allowed Pimpel to customize up to 300. Even with multiple pieces on a pallet, this method ensures very precise milling operations.

“With this solution, we theoretically can create hundreds of extra zero points in the machine,” says van de Sande. “For Van Riet Metalworks, accuracy is the key to success.”

With a solid model, programming in ESPRIT is much easier than programming at the machine tool – and a reliable CAM simulation makes testing at the machine obsolete, van de Sande says. “You get a good product faster and eliminate error at the same time.”

Lead-Time Reduction
ESPRIT helps Van Riet Metalworks increase part quality and make production more predictable. Lead time is also shorter, and therefore the productivity of the machine higher, as complex parts can be programmed within one day. After a complex part is programmed, Van Riet needs just one product on the machine tool to fine-tune the program before milling defect-free parts unattended.

With ESPRIT, the company can maximize the capabilities of the 5-axis milling cell with a robot and pallets.
“The software is important to achieve continuous production,” van Riet says. “Thanks to our 5-axis machine and ESPRIT, milling these kinds of high-quality components is something we can do more efficiently.”
This streamlined efficiency translates into new opportunities to grow and creates greater flexibility. With the high degree of process security for its unattended milling activity, Van Riet Metalworks can even deliver repeat orders within a day. “If we have the material in-house, we can have complex repeat order pieces within a few hours if the customer is really in a hurry.”
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