Product category:
Vertical machining centres (VMC)
News Release from: Hurco Europe | Subject: Roeders RHP 800 machining centre
Edited by the Manufacturingtalk Editorial
Team on 14 July 2005
Machining centre mills, jig grinds and
measures
Precision machining centre - aimed at the mould and die industry - automatically performs high speed milling, jig grinding and coordinate measuring - in one clamping.
For producers of high-pressure die casting tools, speed and precision are a priority A new, high precision machining centre from the German manufacturer, Roeders, makes it possible to perform three different tasks automatically - high speed milling, jig grinding and coordinate measuring - in one clamping
This article was originally published on Manufacturingtalk on 5 Feb 2001 at 8.00am (UK)
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"Producers of die castings for the automotive sector face an extremely demanding market, and we are no exception", said Joerg Inselmann, managing director of AE Formen und Werkzeugbau in Schortens, Germany.
"The central sales division of our parent, the AE Group, does not automatically source its tools from us, but asks several different suppliers to quote." Inselmann continued: "Furthermore, we have to fill one fifth of our capacity by sourcing business from outside the group, in direct competition with German companies as well as tool producers in low-wage countries ranging from Poland through to China." The AE Group is a development partner for car manufacturers and their first tier suppliers as well as for the aerospace industry, and is a pioneer in ductile and weldable, high-pressure aluminium die castings.
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One of seven toolmaking centres, the Schortens facility produces 150 new production dies annually while refurbishing some 300 to 350 others.
A modern, high pressure die-casting tool is a complex assembly of up to several hundred different components made of high strength tool steel.
Due to its geometrical intricacy and the need for high precision, the toolmaker has to exploit a range of different machining processes, including high speed cutting, jig grinding and electric discharge machining (EDM), both wire-cut and sinking.
Copper and graphite EDM electrodes can take several hundred hours to machine.
In total, a complex die casting tool can take well over one thousand machining hours to produce.
Apart from the impact on costs, this leads to long delivery times.
All car manufacturers are in a continuous race to bring out new models, however, so suppliers need to be able to offer high quality tools in as short a lead-time as possible.
For this reason, toolmakers are very interested in solutions enabling them to automate critical process steps.
"Depending on its complexity, a typical high pressure die casting tool has between 10 and 90 bores that are precision ground," said Inselmann.
Until now, this process had to be performed manually by passing a small diameter grinding tool down the bore using a helical cutter path.
Grinding tool wear caused some uncertainty in the final diameter so the operator had to iterate slowly towards the desired result, entailing periodic stopping of the grinding process and hard gauging of the bore diameter.
This time-consuming process required up to 15 minutes per bore, even for an experienced operator, so for a fairly complex die, the total time required for bore grinding can easily total three full working shifts.
A further disadvantage of the process is that it does not harmonise with computer-based quality control.
The special feature of the RHP 800 machining centre is its versatility, making it possible to perform a maximum number of different tasks automatically, without having to unclamp and refixture the workpiece.
In addition to performing jig grinding, the new machine can produce savings in costs and machining time by maximising the high speed cutting element.
To help automate the jig grinding process, the machine installed at AE Formen Und Werkzeugbau in July 2004 has been equipped with an acoustic tool measuring system that determines the exact diameter of the grinding tool, which is used in conjunction with a dressing station to ensure that the tool profile is always within tolerance.
A further innovation is the integration of a touch probe and two different calibration gauges (ring and sphere) for measuring the component.
In cooperation with the customer, Roeders developed a function within its CNC system enabling it to control grinding operations automatically once the necessary parameters have been entered.
For this purpose, the control system mimics the strategy of a skilled operator by alternating grinding and measuring passes until the desired result is achieved.
The process is optimised by a sensor that is able to detect when the grinding tool contacts the workpiece, thus avoiding separate probing cycles and immediately generating data for quality control and documentation.
Another the machine's assets is measuring software enabling the control to assess by how much a die has distorted during hardening.
The control takes into account the geometrical changes and automatically redefines its zero point so as to minimise the error.
This makes it possible to reduce machining allowances for roughing, with subsequent minimisation of finishing and grinding operations.
"The prerequisite for taking full advantage of such features is, of course, that the machine exhibits the necessary static and dynamic precision," said Oliver Gossel, development manager at Roeders.
"An analysis of conventional machine layouts performed prior to starting the development project revealed that stick-slip on axis reversal was their main weak point".
" For our RHP series, we therefore opted for hydrostatic guideways, the thickness of the oil cushion being maintained within narrow limits to provide excellent stiffness".
"To this we added highly dynamic linear drives and a control system that has been optimised to minimise deviations during reversals of motion." Furthermore, care has been taken to minimise thermal movement.
The temperature of all key machine components - shafts, drives, oil and spindle - is kept constant by means of powerful heating/cooling systems.
A specific sensor enables the control system to detect and compensate for spindle growth.
The sum of all these features results in a system that is ideal for machining workpieces to very high precision, and having the ability to perform circular movements without deviations at quadrant intersections, a feature particularly important for precision grinding of bores.
The 17kW/36,000 rev/min HSK-50 spindle results in good metalcutting performance over the machine's 800 x 750 x 500mm working envelope, even when processing hardened material, regardless of whether roughing, finishing or jig grinding is being undertaken.
This makes it possible to perform between 70 and 80% of all jobs a tool on the machine.
Besides the related gains in accuracy, this saves having to refixture the workpiece repeatedly.
System accuracy has been verified by statistical analysis of workpiece dimensions that showed deviations of less than 2 micron in X and Z.
Work is on-going to adapt the jig grinding feature - a function not supported by the usual NC program code postprocessors - to accept parameters such as bore coordinates and diameters in the form of Excel tables, as output by many CAD systems.
These tables will then serve to generate the necessary NC codes automatically. Request a free brochure from Hurco Europe ...
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