Time is money: Materia trims times at Plastic Mouldings Northern

“Low volume, high tolerance work is the bedrock of our business”, says Mark Rigg, Managing Director of Plastic Mouldings Northern (PMN), a specialist manufacturer of plastic vacuum formed products since 2002. “While many vacuum formers specialise in high-volume projects, we pride ourselves on our versatility, excelling at both high and low-volume production. Some clients trust us with orders as small as five units of a specific part, and on various projects, we meticulously trim parts to achieve tolerance accuracy within +/-0.2mm.”

Excelling in this niche has enabled the Co. Durham based vacuum former to establish an enviable customer base that spans the automotive, aerospace, agricultural and scientific sectors, and includes high profile names such as The London Underground, McLaren, Bentley, Rolls Royce, Jaguar, JCB, Hitachi, Bosch and BA Systems. PMN’s investment in two Materia CL CNC machining centres has been vital in attracting these prestigious customers and delivering on their quality and tolerance demands.

“This was the reason for purchasing our first Materia CL in 2021,” recalls Mark. “One of our automotive customers asked us to produce some parts for them and we were struggling to hit the tolerances - we could only reach +/-0.7-0.8mm. As soon as we moved production onto the Materia, we were able to reduce that by more than half.”

One such part that requires very high tolerance accuracy is a car battery pack cover.

“Covers have to be trimmed to the correct height for good reason; if they are left with an overhang, the plastic may touch the part and cause interference, and if they are trimmed too short, this will create a gap which means the battery is unprotected and could spark and catch fire,” explains Mark.

Continuous rotation: a unique spin on machining
Two design features on the Materia CL have enabled PMN to master these tricky jobs. The first of these is continuous c-axis rotation on the electrospindle.

Conventional belt-driven spindles can only rotate within 720 degrees (just under two full revolutions) before their movement is hindered and the spindle has to retract, rewind and restart. This impacts efficiency and, as the belt wears, finishing quality diminishes.

By contrast, Biesse utilises a five-axis electrospindle that can rotate freely without having to stop and reset itself thanks to the innovative design of the patented infinite c-axis. This clever electrospindle will work all around the workpiece without having to rewind itself. The use of a direct-drive motor rather than a belt also means there is no decline in performance over time from wear and tear.

There are two main benefits to utilising a spindle with endless rotation: cycle time is reduced considerably because there is no ‘dead’ time while the spindle is stopping, unwinding and resetting, and, most importantly to PMN, this continuous rotation eliminates mismatch lines on the trimmed part.

“We are definitely seeing the benefits of continuous rotation. Not only does it save time, it also gives us a better finish,” says Mark.

An example of where continuous rotation comes into its own at PMN is when trimming ABS seat backs.

“With our old machine we would get halfway around the part and then have to lift out the head and respin it, which sometimes resulted in nicks and steps or mismatched trim lines. With infinite c-axis rotation, we can go all the way round the part in one continuous action, producing a smooth, even trim line,” says Mark.

Automatic tool measurement maintains accuracy
The other feature that comes into play on these jobs is automatic tool measurement. Over time, the tool wears, and if left unchecked, this will affect accuracy. The Materia will regularly measure tool length to test how much it has worn and will recalibrate the programme to take this into account, ensuring accuracy does not slip over time.

In upgrading its CNC operation, another of PMN’s objectives was to increase productivity.

“We make sure that every job we do is profitable whilst maintaining fair and competitive pricing - this was one of the reasons for upgrading our CNC machines. We haven’t increased our prices on some parts for up to five years because we don’t want to shift the burden of higher costs onto our customers. We prefer to take a different approach: improving efficiency to protect our margins. If we can produce more quickly, we don’t have to increase the price of the part,” explains Mark.

Materia increase in productivity
PMN says the Materia CNCs process most parts 20% faster than its previous machines. This is down to a combination of factors: the rigid electro-welded structures that eliminate vibration and support faster cycle times, the upgraded Siemens controls that drive greater accuracy, and the powerful 11kW head with an eight-position automated tool changer.

“This is a great time saver; it allows our operators to change between different processes and profiles quickly and without any manual intervention,” says Mark, of the automatic tool change facility.

As well as powering through jobs more quickly, the high-performance head can cope with a broader range of composite materials, nylons and acrylics.

“Because nylon and acrylic are denser, harder materials, they are more difficult to machine than some of the other materials we work with, such as ABS, HIPS, HPDE and polycarbonates. Thanks to the powerful head on the Materia we can process them with ease; we are currently forming and trimming a part from 10mm thick acrylic, which we wouldn’t have been able to touch previously, and are taking lots of orders from automotive and aerospace customers for nylon jig fixtures,” says Mark.

Strong suction supports fast processing
The machines are also equipped with 2 x 140m3 vacuum pumps, which ensure that parts are held firmly in place on the table whilst they are being worked on. By eliminating vibration and movement, the high-pressure vacuum system allows faster cycle times and more accurate machining.

Purchasing two new CNC machines in three years is a sizeable investment for an independently owned family business, but the rationale is that it will prepare PMN for the next chapter.

“Our manufacturing capacity has grown significantly year on year and it is now time to focus on upgrading our machinery so that we can improve efficiency and further increase this capacity. What we want to do for the future of PMN is to complete the upgrading programme that we have started with the investment in the Biesse machines. This will ensure the next generation is in the best possible position to take the business forward, whilst maintaining PMN’s reputation for high quality vacuum forming of challenging parts,” says Mark.

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