Custom CNC manages aluminium profile machining

One CNC system controls dual 5-axis robot heads to machine aluminium window and door profiles of up to 9m long, on all six sides and in a single pass.

A customised standard CNC controller enabled special-purpose machinery builder, MKM International, to take a more radical, and production cost-saving approach in building an iegrated single-stage machining line for aluminium door and window profiles.

The automated end-to-end machining system replaced an old multi-stage, semi-manual production process.

In the MKM system, dual 5-axis robot heads machine aluminium profiles of up to 9m long, on all six sides and in a single pass.

Combined with bar code identification of materials, the new line dramatically increased production speed for a leading window and door manufacturer and eliminated sources of human error experienced with the older semi-automatic system.

A single NUM Axium CNC platform controls the entire machining system, including 10 motion axes on the robot heads as well as various sensors and actuators.

MKM chose the Axium platform for its processing power and because NUM was willing to work with MKM and customise the CNC controller to optimise performance.

One modification is the development of an interface to a harmonic drive motor, which combines a hollow shaft servomotor with backlash-free gearing.

The harmonic drive is used on MKM's 5-axis robot heads.

It provides the machining system with much higher than usual range of performance, fidelity of motion, and compactness ,when compared with alternative approaches such as using belts or planetary gearboxes.

The resulting compactness of the robot head allows it to make very tight movements, said MKM, while the stiffness of the system ensures that precision and accuracy is very high.

Compactness was also behind a second major modification: the integration of a specialised third-party spindle motor with NUM's digital drive and designed-for-purpose high-speed bus.

* Development - when MKM first started discussions with the customer to specify the new type of machine, the original concept was for a single robot machining head and a 'flip over' work holder, allowing the head to machine all the faces of the profiles in two steps.

However, as MKM gained knowledge of the process, it saw that productivity and precision could be increased by providing two robot heads, so that all six faces could be machined in one pass.

This would eliminate a complex materials handling element.

NUM is MKM's CNC technology partner and the two companies have cooperated together on numerous special-purpose machine projects.

After discussing the new aluminium processing concept, the parties worked out a way of controlling both heads using a single Axium CNC controller for cost effectiveness, as well as agreeing to modify the motor interfaces to optimise machining performance.

Manager of MKM International, Michael Koehler, said: "Support from NUM helps us compete with the largest machine tool builders, even though our products are often made in single or small volumes".

He added: "Many CNC makers charge large sums for engineering modifications, or can be unwilling to make them at all for low volume applications.

NUM's willingness to give us direct access to the CNC development team helps us to create special-purpose solutions more quickly and economically".

At NUM, Alexander Helmes said: "We focus on small to medium-sized OEMs, and a number of machine tool segments including special-purpose automation.

Our success is built on our products, but also on a partnership ethos.

We are happy to work alongside the machine tool company and take complete responsibility for the control system, as in this instance where we integrated third party products to create the best solution".

Various NUM products are used on the machine including an Axium CNC 'kernel', HP servo drives and motors, and I/O modules.

The spindle motors and harmonic drives are sourced from third parties.

NUM is also providing the user interface panel.

MKM programmed this to provide a simple application specific control and monitoring interface for users.

* Accuracy and fidelity of motion - NUM's servo drives and motors complement the CNC kernel with motion control capability that is highly optimised for machine tool applications.

Accuracy and fidelity of motion are central to the control loop, and are achieved by a number of novel measures including a high speed proprietary bus between the CNC kernel and drives, and fine interpolation of the movement profile by closing the positioning loop, at drive level, at 5kHz - an almost unprecedented speed in this application sector, said NUM.

This is combined with motors with optimised torque ripple and high inertia characteristics to suit the requirements of the mechanics in this segment.

NUM told manufacturingtalk that in general, automation is a question of how fast you can get from A to B.

But, for CNC operation, path accuracy is even more important.

NUM's control over the complete motion axis chain secures an unmatched performance with regards to speed and accuracy where it matters most: at the direct mechanical interface to the machine.

* About MKM - MKM specialises in turning a customer's manufacturing requirements into an efficient CNC processing centre.

The company has extensive experience in portal machines, processing machines, custom production lines, and in processing plastic and aluminium materials.

It has developed a number of tools that allow it to create application-specific solutions very rapidly, including robot machining heads and man machine interfaces.

MKM International is located at Koenigstrasse 128, D-32547 Bad Oeynhausen, Germany: http://www.mkm-international.de.

* About NUM - in the early 1960s, more than 10 years before the CNC control was starting to become widely accepted, NUM's first CNC controller was being developed.

NUM's strategy is to help current and future customers to construct better machines and thereby secure a competitive advantage.

The company focuses on a number of 'high end' CNC applications, where it undeniably has something extra to offer.

Headquartered in Switzerland, and with R and D facilities in Switzerland, France and Italy, NUM currently has more than 35 sales and service locations worldwide.

In addition to CNC hardware and software, NUM also develops and manufactures the core products having impact on the overall performance of the system including drives and motors.

NUM will also integrate and take responsibility for third party products in specific solutions in close cooperation with partners and customers, to provide a one stop shop for CNC solutions.

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