Lights out EDM machine

Citation

(2002), "Lights out EDM machine", Industrial Robot, Vol. 29 No. 6. https://doi.org/10.1108/ir.2002.04929faf.006

Lights out EDM machine

Lights out EDM machine

Keywords: Machining, EDM

The design, installation and commissioning of a robot-controlled EDM machining cell by UHK Rotaries has fulfilled a vision held by Mike Dunn, MD of Portway Tool and Gauge Limited for more than 20 years – by enabling “lights out” manufacture of complex tooling components for up to a fortnight at a time.

The new installation at Portway’s Stourbridge headquarters is thought to be the first in the world to provide such capabilities. It represents a £1/2 million investment for the company and incorporates two Charmilles 6030 automatic feed wire eroders, a co-ordinate measuring machine, an automated pallet system, a two tonne gantry crane and an industrial robot (see Plate 5).

“Automation is very much the route we have adopted to enable us to remain competitive in the face of strong overseas competition”, says Portway’s Mike Dunn. “A high proportion of our work is in the automotive sector, where OEMs purchase on a global basis. We find ourselves competing against suppliers not just throughout Europe, but from low labour rate Asian and Far Eastern countries as well. For us, minimising the amount of manual input is the only way forward.”

Plate 5 Workpieces mounted on custom designed pallets are automatically loaded and unloaded from the Charmilles wire EDM machines, then immersed in a rust inhabitor bath, before being transferred by the robot to the cell’s output conveyor.

Portway Tool and Gauge Limited is a £1.6 million turnover company with 26 employees. However, Mr. Dunn is quick to point out that the goal is not to reduce manpower: “It is simply to increase the productivity of the resources we have, in order to win more business.” “The use of wire EDM machines has already reduced our manual input significantly. But, the new robot-controlled cell takes this to another level.”

Using robots to load and unload machine tools is not new. It is only now that the technology has advanced to the point it can provide a practical solution to Portway’s specialist requirements.

In order to meet the extended unmanned running requirements, UHK devised a twin input conveyor arrangement to independently feed the Charmilles wire erosion machines. With freshly cut parts soaked in dielectric fluid left unattended for long periods, rusting of components was also identified as a potential problem – necessitating the use of an in-process inhibitor bath within the cell. Other key requirements included numerous guarding and safety interlocks to prevent operator injury, as well as the risk of damage to the process equipment.

In operation, workpieces measuring up to 700 m × 400 m are pre-loaded onto custom designed pallets. These are initially positioned at the CNIM station using the overhead crane. A set of datum measurements is automatically converted to machining offset information, which is downloaded – along with the appropriate CNC machining programme – to the selected EDM machine’s controller.

The pallet and workpiece are then transferred by crane to the cell, where they are loaded on to the input conveyor corresponding to that machine. A maximum of four pallets can be held at any time on each conveyor. The pallets subsequently move through the perimeter guarding to a stop, where they are picked by the Kuka KR250 robot and transferred to the appropriate wire eroder. An automatic location and clamping sequence locks the workpiece into position, before initiation of the EDM machine’s automatic cutting cycle.

The CNC machining programme may be as long as 30 hours, depending on component complexity, and provides parts accurate to better than ±1 micron. On completion, the EDM machine signals the robot to transfer the work pallet to the in-process wash / rust inhibitor station. After immersion and agitation by the robot, the components are withdrawn from the bath and tilted at an angle to assist draining. The process software is also designed to incorporate the introduction of an air blast to dry the components, if required. The pallets and workpieces are then transferred by the robot to the outflow conveyor.

“Adoption of a standard work pallet system provides a number of benefits”, comments Mr. Dunn. “Cycle down time on each EDM machine has been reduced to less than 5 min, compared to perhaps an hour using traditional methods. In addition, the system enables us to prioritise rush jobs if need, by moving them up the queue. In exceptional circumstances, we can even stop a machine mid-cycle and replace the work with a more urgent job. The system will remember the point it had reached in the cutting cycle, enabling the original machining sequence to be resumed automatically at the correct point in the CNC programme.”

Further refinements instigated at the customer’s request include a Web Cam to monitor the equipment’s operation. This approach was chosen in favour of a system that would trigger a telephone call to the operator in the event of a fault or breakdown.

“I believe that all our employees deserve their free time”, says Mr. Dunn. “Using the Web Cam, operators can check that the machines are running satisfactorily without leaving their own home. It is far less intrusive on their personal life and I believe encourages them to rectify any problems permanently, rather than to simply look for a quick fix.”

“A further benefit is that we can even allow customers access via our Web site, so they can monitor the progress of their own jobs if they wish.”

“Since going into production earlier this year, we have experienced very few teething problems”, reports Mr. Dunn. “To give an indication of its capabilities, the cell recorded over 200 h unmanned production during our Easter week shut-down. Performance like that speaks for itself. It not only enables us to achieve the highest standards of quality, but also helps us to bring delivery dates forward – by as much as 3 weeks on some jobs.”

With a typical Portway press tool valued at up to £30,000, such lead time reductions represent a significant cash flow benefit. In addition, the cost savings achieved through the equipment’s “lights out” capability enable Mr. Dunn to forecast a payback of less than 3 years on his company’s investment, making it an extremely cost-effective solution. Furthermore, with the cell already engineered to accommodate a third wire erosion machine, Portway has the potential to increase its output by a further 50 per cent without any increase in labour costs.

“When people consider automating their processes, they normally think in terms of mass producing identical products. That is the difference with our installation; every component is a one off”, adds Mr. Dunn.

For further information, please Contact: Uwe Klein at UHK Rotaries Ltd. Tel: 01564 795181; Web site: www.uhkrotaries.com