Models are mostly milled from a special plastic known in the industry as Ureol . It is a PU resin soaked with filler and is used primarily in model and mould making. The milled moulds are then encased in a moulding box f illed with moulding sand and compressed by stamping, pressing or machine vibration. When the model is removed, a negative mould is left in the sand into which the molten metal is then poured to make the prototype.
Sammer, whose customer base includes leading corporate names such as BMW, AVL and Nemak uses Blum-Novotest’s FormControl measuring software that was installed in its seven 3- and 5-axis machining centres in Eugendorf.
Measuring Software
The software is used to measure every milled item in the machining centre. It measures contours, bores, angles or distances. “A big benefit of the software is that we are able to measure our workpieces in their original clamp fixtures in the machining centre,” says production manager Johann Pucher, who has been working for Sammer for 40 years. “So the time-consuming process of unclamping, transporting to the measuring machine, measuring, re-clamping, aligning and reworking is now a thing of the past.”
The range of highly complex moulds which Sammer makes for its customers is widespread and tight tolerances of five hundredths are the norm. The measuring software, a complete package, enabled each production operative to design, machine and measure each component himself.
First the CAD data is imported into the programme. In the programme, the measuring points can be optimised and new ones added or existing ones moved by a mouse-click on the PC.
Ready For Export
Automatic PC-based collision control prevents unintentional collisions between the workpiece and probe. The NC programme is transferred to the controller and the measuring sequence can be started. After the measurement, the results are sent back to the PC, then the individual measuring points can be colour coded, enabling tolerance evaluations to be made easily. At the end, a measuring report presenting the individual measuring points in tabular form can be exported.
Before the software was installed, Sammer relied on the quality of the milled moulds. This was sometimes problematic, because setting errors, tool wear or machine temperature drift could quickly cause the tight tolerances to be exceeded. Today, by contrast, the Austrian company is able to verify the quality of the work pieces it mills. Previously, if an error occurred in the customer’s casting process, the mould was sent back to Sammer for reworking. Now the model and mould maker has the measuring report documenting the quality of the milled moulds.
Managing director Günter Sammer adds: “The reports are now an essential tool for us, not least because some customers actually stipulate them. And a report is produced and saved for each workpiece we mill, enabling us to react to any refer-backs. It is especially beneficial as it entails no additional work for the production staff. Quite the opposite: the reports are generated almost entirely autonomously, and can be immediately edited as necessary.”
Tight Tolerances
The material properties of the plastics for the milling process enable ultra-fast cutting speeds. Nevertheless, some moulds spend as much as 50 hours in the machining centre being milled. Such components are of course very expensive – due to the long machine running times alone – so it is essential to avoid any machining errors.
Large components can easily have more than 100 measuring points on them. When working to ver y tight tolerances, Sammer sets several points manually, as a precaution. Other moulds are made of steel. Tool wear is a bigger concern in those cases than when machining plastics. For steel components, the workpiece is measured during machining, so as to guarantee perfect quality. Lots of different plastic moulds are made, however – sometimes five to eight per day.
The costs vary widely, because the specialists at Sammer not only collate milling data and mill the components, but often also prepare the CAD data and design components prior to milling, and sometimes also fabricate and assemble slit dies and ejector or closure systems. In view of such complex processing and the associated high cost, it is essential to install safeguards and monitor quality. Sammer has been using the software since 2010 and appreciates its user-friendliness.
APMEN Sept 2016, Metrology & Design
