Feature Article

Setter-operator Melvyn Cornwall is pictured with the Haas VF8 that is used to machine the steel chambers at Paragon Engineering.

CNC machining firm Paragon Engineering was faced with the challenge of producing a mild steel chamber for the medical industry that weighs nearly one tonne and required 24 hours of almost continuous milling. At first, the company used costly solid carbide cutters in the production process. But the cutters did not have a particularly good service life and had to be scrapped if the cutting edges became chipped.

To optimise the production of the part, the company enlisted the help of tooling supplier Iscar, which largely replaced the use of carbide cutters with indexable-insert tools. That change, along with other refinements, have improved the consistency and speed of the production process and also lowered the costs associated with it, according to Paragon, which specialises in work for the medical and hi-fi sectors and also makes parts for astronomical telescopes, cameras and satellites.

“We have used Iscar cutting tools for more than a decade for prismatic machining and turning a wide variety of materials from aluminium and plastics through most types of steel to titanium, ceramics and composites,” comments joint owner and Managing Director, John Kent. They are one of several regular suppliers of tooling to our machine shop.

Iscar Multi Master mills using the company’s Chatter-Free, interchangeable solid carbide end mill heads remove the bulk of the material from the mild steel billet, leaving a smooth surface finish.

“Their local sales engineer, Phil Ginn, who keeps in regular contact, visited us at about the same time as we received a request from an existing medical customer to machine a series of large prototype chambers,” Kent adds. “Phil could see that the tooling we were using for the job was not optimal, so he set about analysing the best way to machine the part using Iscar cutters.”

The improvement has been dramatic, according to Paragon, as not only have tooling costs been reduced, but also surface finish is improved, saving the company a considerable amount of time when subsequently hand polishing the component. In addition, the noise generated during cutting is lower, improving the working environment for the firm’s machine operators.

Perhaps most significant, however, has been a reduction of 60% in the time needed to complete the part using the latest technology tools and carbide inserts from Iscar. “The job was previously taking far too long, making it difficult to make a profit on it,” adds Kent.

“Whereas we could charge £50 per hour for our capacity a few years ago, the recession and continuing loss of work to low-wage countries overseas means that the going rate now is nearer to £35 per hour.

A significant amount of undercutting is needed, for which an Iscar slitting cutter on a long extension arbour is used for both roughing and finishing.

“Being able to reduce machining times as dramatically as in this case by changing the tooling has made a big difference to the bottom line. “We moved to 24-hour running in February this year to extract maximum benefit from our capital investment in machines on the shop floor, which is also helping us to remain competitive.”

Around 75% of material volume is removed during machining of the steel chamber on the Haas 3-axis vertical machining centre, which has a 14.9-kW, 7500-rpm, 40-taper spindle and 1,626 × 1,016 × 762-mm axis travels. The component is machined dry, with air blast to remove chips from the cutting area instead of coolant. General tolerance is ±0.2 mm, although some features are tied down to 30 microns.

There are three main areas where significant improvements have been made following the use of tooling from Iscar. One is the use of high-feed, extra-long-reach Helido end mills for face milling, ramping and interpolation. The tools have double-sided, TiAlN PVD-coated SUMO TEC inserts with six cutting edges. They take successive, 1.0 mm cuts using 2300 rpm spindle speed and 4250 mm/min feed rate.

Close-up of the Iscar slitting cutter

After the component has been refixtured, Iscar’s Multi Master milling system is deployed, using the company’s new Chatter-Free, interchangeable solid carbide end mill heads. Using 2000 rpm spindle speed and 1000 mm/min feed, the 15.2-mm diameter, 120-mm long tools go down in 10-mm steps to rough out the bulk of the material efficiently. The same type of tool then finish-machines the chamber, leaving deep sidewalls with a good surface finish.

The third area where the tools have led to improvements in machining efficiency is during one of the last operations, where a significant amount of undercutting is needed. A 100-mm–diameter slitting cutter is mounted on a long extension arbour for both roughing and finishing.

The tool has six carbide inserts comprising a fine grain substrate coated using Iscar’s Sumo Tec TiAlN PVD process, which exhibits good resistance to chipping and wear. Paragon’s setter-operator, Melvyn Cornwall, confirmed that four hours of continuous machining are achieved before tip change is necessary.