Dust free trimming, finishing and repairs made simple?

Dust free trimming, finishing and repairs made simple?

Reinforced Plastics  Volume 00, Number 00  April 2016 www.reinforcedplastics.com FEATURE Dust free trimming, finishing and repairs made simple? R...

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Reinforced Plastics  Volume 00, Number 00  April 2016

www.reinforcedplastics.com

FEATURE

Dust free trimming, finishing and repairs made simple? Rodney Hansen Dark Matter Composites Ltd.

A few years ago if someone offered me extracted tools, saying that they could provide dust free trimming and finishing operations, I would have looked at them skeptically and thought to myself ‘really? I don’t think so’. A few years on and now I am the one on the receiving end of the incredulous looks and skeptical responses. That is until a short demonstration shows dust free operations are possible. Trying to convey in text what can be easily demonstrated in practice isn’t so easy, but it helps if we tackle the issues head on. The majority of composites that are processed are either carbon or glass thermosets, so let’s focus on these. Irrespective of the type of trimming and finishing operations and extraction used, the dust produced is highly abrasive. Contamination of any running equipment will just lead to high wear rates, be it bearings, gears or drive chains. When it comes to electrical equipment, carbon fiber dust is

Extracted 3 inch diamond disk cutter. E-mail address: [email protected]

conductive and can lead to shorting. Some believe that these issues are usual when dealing with composites, whereas others are unaware that equipment failures and increased maintenance are related to the process. When it comes down to the protection of personnel, inhaled dust is the key concern. This is where our story started a few years ago. As a training and consultancy provider to the composites industry, we needed to better address the dust generated during our trimming and repair courses. We thought ‘if we look hard enough, there will be an off the shelf solution that will make our life easier’. Many of our customers at the time were using air fed face masks and full coveralls to protect personnel performing the operations. However, breathable air can be problematic if not maintained properly and if the operator is protected, what about the work area and others within it? Like most composite companies, we often end up modifying tools to suit our needs. As this was such a long term issue we assumed someone would have the solution readily available. No chance! What we found were tool, extractor, abrasives and cutter manufacturers all provided solutions to parts of the problem, but they didn’t interact with each other and complete solutions were not readily available. However, a number of manufacturers wished to work with us to address the problem, as it turned out that no company supplied extracted equipment specifically aimed at the composites industry. Before we knew it, we were conducting extensive equipment trials, having tools modified to meet our needs and using them inhouse and on our courses. Customers then started to ask ‘Where

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1 Please cite this article in press as: R. Hansen, Reinf. Plast. (2016), http://dx.doi.org/10.1016/j.repl.2016.03.001

REPL-668; No of Pages 5 FEATURE

Reinforced Plastics  Volume 00, Number 00  April 2016

FEATURE Extracted air router with special fluted diamond cutter – The flutes pick up dust from the opposite side of sandwich panels.

Free hand trimming with extracted air router.

can we buy these?’ and we now find ourselves selling equipment for trimming, finishing and repair of composites ‘dust free’. Starting from first principles, ceramic materials (carbon and glass) and hard/brittle thermoset resins are best cut and trimmed by grinding the material away, as toothed/sharp edges tear the material and blunt quickly. Grinding of these materials results in dust projected from the grinding head which can become either a projectile or airborne. Projected material is easy to deal with, it’s heavy and based on trajectory, size and weight, will only travel a set distance before hitting the ground. There is very little risk of breathing in this material if it is aimed away from the operator. However, very small particulates, once thrown up into the air, can easily become suspended and are then airborne. Airborne dust is the main concern as it can be considered as possibly contaminated air. Although we worry about what we see as being the problem, it’s what is there that we cannot see that we really must address. Synthetic dust is not good for us, for example glass dust is an

irritant and some resins are hygroscopic, so we need to do something about it. To overcome the issue, many companies resort to large extraction units connected to CNC machines, or booths/downdraft tables for manual trimming. The reality is that 80–90% of local exhaust ventilation (LEV or in simpler terms, extraction) doesn’t work because it is not used correctly. If you have this type of extraction in operation and the enclosure has a cloud of dust ever present, there is insufficient air movement to remove the dust from the air. Regardless of enclosure size, there must be sufficient clean air entering the enclosure at the rate it is being extracted, to ensure adequate airflow. To clean air via filters, the air must flow over the filter fast enough to carry the contamination, but slowly enough to capture it. If there is insufficient airflow across the cutting/grinding operation, stagnation occurs resulting in loss of extraction performance. When it comes to on-tool extraction, the same is true; there must be sufficient airflow across the cutting/grinding head and through the shroud and extractor unit to capture the airborne dust generated. The problem here is that different tools and extraction shrouds require different levels of vacuum volume and pressure, but most extraction is fixed and not variable. For installed high vacuum systems this results in some tools performing well while others generate high levels of noise, sometimes even whistling at high pitch, making for a noisy, unpleasant work environment. Fixed speed extraction units may suit one tool, but then become very limited in further applications. The solution is to have an

2 Please cite this article in press as: R. Hansen, Reinf. Plast. (2016), http://dx.doi.org/10.1016/j.repl.2016.03.001

REPL-668; No of Pages 5 FEATURE

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Reinforced Plastics  Volume 00, Number 00  April 2016

Extracted air router cutting through a glass and nomex honeycomb panel using a jig.

extraction unit that can be tuned to each tool in terms of vacuum volume and pressure giving the most effective dust capture at source. For example, at one extreme a 125 mm disk cutter has a large shroud where a high vacuum volume is required at low pressure (our DMP0146 kit requires approx. 140 m3/h at 9000 Pa), whereas a small air router with complex shroud geometry requires low vacuum volume at high pressure (our DMP0145 kit requires 5 m3/h at 20,000 Pa). The majority of extraction units cannot provide this range of vacuum control, making them ineffective in dust capture over a wide range of tools. We only supply two portable extraction units which can be tuned to a full range of extracted air tools. When we demonstrate our tools we know the settings to use right at the offset, which we also provide in full with the equipment manuals. The next issue to address is the tool itself. Many are designed for general use and a wide range of applications; however, what works in one instance does not necessarily work in another. Some shrouded tools become heavy and cumbersome making them difficult to use and control. Retro fit shrouds are a cheap solution but are only effective if designed with a particular tool in mind. Simple things such as the shroud position and adjustment, inter-connections, exhausts, airline and vacuum connections all need to be designed to ensure the tool remains effective and there is sufficient air movement over the cutting/grinding head. There are often two

Box 1 Drilling without de-lamination There are always issues with post-processing composite parts. The time and money invested to get to the final stage is often high. When we drill composites materials the aim is to drill quickly and cleanly without causing delamination of the part. The right combination of speed and drill bit make this achievable. Diamond coated drill bits work best at high speed, and drilling at 20,000 rpm suits these drill bits. Yes, that’s correct, a 20,000 rpm drill but it does need to be limited to 6.35 mm/¼00 drill bits. The speed of drill allows the diamond grit to grind away the material with no de-lamination on breakthrough. When combined with a collapsible extraction shroud, the dust is captured from both sides of the part via the drill flutes. The collapsible shroud also exerts back pressure, reducing the risk of poor break-through caused by the user exerting too much force on the drill. The result is that the quality of drilling operations improves and the operation only requires single sided access and no backing support.

Extracted air router cutting through an aluminum sandwich panel.

key issues to consider when using extracted tools, the weight of the vacuum hose and the restricted view of some cutting/grinding heads. First instinct is for the operator to throw the hoses over a shoulder, but the use of swivel joints, coaxial air/vacuum hoses and overhead hose supports frees up the operator and reduces the weight at the tool. Flexible transparent shrouds are provided on many tools making them easy to use. Some tools need metal shrouds which ideally need guide bases fitted. This allows the user to follow simple jigs making the operation even easier. Even mold and part design can provide part surfaces which can be used to rest a guide base against, allowing for accurate operations. Next comes the cutting/grinding head materials and geometry. To be effective, these need to be harder than the part’s materials. Typically carbide and diamond coated cutting/drilling heads are used as well as silicone-carbide abrasives. Yes, these may be more expensive than standard materials, but they last longer and are best suited to carbon/glass composites. Their use can reduce the trimming and finishing operations required, giving better results, as well as reduce the time taken to perform an operation. Some are readily available ‘off the shelf’ from numerous suppliers, such as diamond coated cutting wheels, where others are designed for specific operations, such as the surface planers used in our repair kits and the fluted diamond cutters used with our routers. Where we supply special cutters, they have been specifically designed to get the best combination of performance in terms of material removal, dust extraction at source and quality of finish for a specific task. The key issue is that extracted tools and portable extraction is only a part of the solution. It is not for everyone, it often depends 3

Please cite this article in press as: R. Hansen, Reinf. Plast. (2016), http://dx.doi.org/10.1016/j.repl.2016.03.001

REPL-668; No of Pages 5 FEATURE

Box 2 Routing of laminates and sandwich panels

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Due to customer demand, we have also developed a lightweight air router consisting of a Dynabrade air motor fitted with a bespoke extraction shroud that is small enough to hold in one hand and only weighs 830 g. The shroud has been designed to get the best dust capture around the full tool head, allowing it to be used in any direction. During extensive customer trials, the router has proven to be effective at trimming solid glass and carbon laminates as well as sandwich panels with foam and honeycomb cores. Router cutting along composite laminates leaves a good, clean edge. The bespoke fluted diamond cutters also capture dust from the underside of the material making the router highly effective when trimming both intricate and large parts in open shop floor areas and on-site. It is particularly suited to marine production, sandwich panel fabrications, construction sites and aerospace parts that do not fit into a trim room. During trials, the tool was also used with a standard carbide cutter, to mill aerospace grade aluminum blocks embedded within sandwich panels. The material was removed dry, without the use of cooling fluid and with all the aluminum shavings captured at the cutting head. This makes the router an ideal tool for production and rectification work. on the shape, size and production rate of the parts, sometimes extracted CNC equipment and trim booths are best. When it comes to large open work areas with a wide range of operations scattered around, extracted tools and portable extraction units can be very effective.

Reinforced Plastics  Volume 00, Number 00  April 2016

To get the best from extracted tools and dust extraction units requires quite a bit of work and if you don’t get it right, it becomes ineffective very quickly, leading to a lack of use and a return to old practices. So why bother? Take a look around your shop floor to establish if your trimming and finishing operations result in a level of dust contamination, be it localized or widespread. Where is it coming from? Do you see it arrive at a particular instance or does it appear overnight when it has had time to settle? Once it is loose, cleaning and control is difficult. If it is dealt with properly at source, even cleaning activities become reduced. Using simple methods of dust control, such as wiping surfaces with a damp micro-fiber cloth prevents dust spreading. Using an airline to blow dust off a part and into the air (making the dust airborne) spreads it everywhere, increasing the problem. The development of extracted tools and extraction specifically for composite processing wasn’t something we ever intended to do, it happened because we needed a solution and we took the decision to use best practice and invest in the best equipment available for our own use and for use on our courses. We have learned a great deal about dust capture and extraction for composite processing, which has taken us a few years of experimenting, with a lot of support from both Dynabrade and Festool throughout. We have become their composite specific technical partners and they continually assist us in developing composite specific solutions. The off-shoot of all this effort is that our trimming and repair activities and courses are clean, regular maintenance and cleaning activities are reduced and valuable file servers, computers and electrical equipment is protected.

Box 3 Consistent step sanded repair surfaces

Step sander with small circle jig fitted.

The increased use of carbon fiber composites in highly loaded structural parts means that repair of these parts will become more frequent in future. One key concern is the risk of carbon fiber dust (generated from grinding carbon composite repair surfaces) shorting expensive, and often critical, electrical circuitry, be it an aircraft, lifeboat, luxury sports car, etc. This lead to the development of the Dark Matter Composites Step Sanding Tool Kits. Our prime focus during the development of these repair kits was for effective material and dust removal at source, followed by how to effectively apply the tools to the composite repair process. The kits combine modified Dynabrade air motors/routers, bespoke diamond surface planers and flexible jigs (that address parts with internal or external double curvature), all of which have been designed to work together to give optimal results. A range of diamond planning heads allow removal of a range of composite materials from coarse to fine, including gel coats, hand laid chopped strand mats, woven prepreg fabrics, uni-directional, stitched and veil fabrics. The kit has been designed to be used cross sector, including civil, marine and automotive, through to aerospace repairs. The tools allow consistent step sanded surfaces to be prepared in less time than scarf surfaces, typically 50–75% faster. When the equipment is paired with a suitable dust extraction unit (also available from Dark Matter Composites), the on-tool extraction is so effective at removing the dust generated at point of source that it eliminates the need for containment curtains and dust masks during the surface preparation activity.

4 Please cite this article in press as: R. Hansen, Reinf. Plast. (2016), http://dx.doi.org/10.1016/j.repl.2016.03.001

REPL-668; No of Pages 5 Reinforced Plastics  Volume 00, Number 00  April 2016

testament to the industry that companies want to implement change to improve the working conditions and environment for their staff. Really good tools last longer, but so do a happy, healthier workforce!

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It is good to see more composites companies are realizing that investing in extracted air tools and portable extraction can save time and money during trimming and repair operations and it can be cheaper than poorly specified and installed plant. It is also a

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5 Please cite this article in press as: R. Hansen, Reinf. Plast. (2016), http://dx.doi.org/10.1016/j.repl.2016.03.001