Shaping Aerospace and Automotive Machining with Synthetic Diamond Solutions

In an increasingly competitive and fast-changing environment, Element Six, part of the De Beers group and a global leader in the development of synthetic diamond supermaterial solutions, is looking to the future and using its position of industrial leadership to develop materials that fully utilize synthetic diamond’s remarkable properties.

Customer demographics are changing, as are the societal influences that affect what we buy, the way we buy, and the factors we consider before we make a purchase. There is growing pressure on companies to not only understand what alterations are happening, but to also modify their business strategies in order to meet demand.

With the growing popularity of social media channels and wider accessibility to an internet connection, information is readily available, meaning ideas can spread around the world almost instantaneously. Staying ahead of the competition is harder than ever, and there has never been a bigger need for disruptive innovation in the automotive industry than now.

The Changing Dynamic of the Automotive Industry

MaaS (Mobility as a Service) is one primary concept that has the potential to disrupt the automotive sector. Permitted by advancements like artificial intelligence (AI), 5G networks and electric vehicles, new technologies bring the benefits of personal transportation whilst also being able to watch a film, play a game or even work.

Electrical energy will play a key role in driving those mobility platforms in the future, and it is thought around 10-20% of all cars sold will be propelled by a battery instead of a gasoline-based engine or a hybrid by 2030.

As a growing number of people relocate to larger cities, local governments are busy making sure residents are able to move around effortlessly and safely, while tightening the regulations around noise pollution and CO₂ emissions at the same time.

The move to car renting services, electric vehicles and shared transportation becomes ever-more appealing when taking this into consideration, heightening the pressure on the automotive industry to respond in order to meet changing consumer demands.

The internal combustion engine (ICE) and cars as we know them today are still very much in the picture, despite advancements leaning towards a more electrical-energy led industry.

When considering this, one of the key focal areas for Element Six is to continue developing materials that increase the fuel economy of the internal combustion engine and help to minimize the environmental impact.

In addition to an overall trend towards a reduction in the inefficient utilization of raw materials, efforts to decrease CO₂ will continue via the integration of improved combustion and more lightweight materials. The integration of more lightweight materials is actually just as relevant to electric and hybrid vehicles as it is to the ICE.

The changing nature of consumer preferences can be outlined in terms of customization, aesthetics, sustainability and intelligence. Put simply, customers are demanding more products that can be personalized, look and feel great, or are augmented with smart technology to provide additional services.

Further to this, consumers are far more conscious of purchasing products from companies whose vision and actions are aligned in some way to their own and that have been produced in a sustainable way.

Companies are grappling with how to satisfy these product demands in the world of manufacturing, and also how to incorporate similar technologies into their manufacturing processes whilst attracting the right talent to embrace the changing landscape.

Synthetic Diamond’s Role in Shaping the Future

Alchemists have sought to transform base metals into gold for thousands of years. It was the ultimate quest to transform a lowly element into one of the most highly prized and precious materials in the world.

Element Six does what the alchemists could not achieve, every day at facilities around the world; taking grey common graphite – one of the most common elements on the planet and one type of carbon – and changing its structure into diamond.

Diamond is one of the most useful and remarkable materials on the planet. Its wide scope of extreme properties make it the material of choice for applications as vast as the cooling of semiconductor devices, the purification of water and laser exit windows.

It is suitable for utilization in advanced computing and magnetometers due to its quantum properties. As an industrial material, it first came to prominence for its abrasive characteristics, and this article will outline its journey from boart – used in South Africa for drilling in the 1930s – to pioneering a cutting-edge cutting tool ready for the Industry 4.0 revolution.  

The Properties of Synthetic Diamond

Diamond has a diverse and unique range of properties. Not only is it the hardest known material, it also has high chemical inertness, the highest thermal conductivity, a low thermal expansion coefficient and thermal shock resistance. When doped with boron, it is also both a great electrical conductor and insulator.

The most widely employed diamond material in cutting tools is polycrystalline diamond (PCD), with a hardness of more than 50 GPa (compared to 20 GPa for cemented carbides, the next best class of cutting tool materials).  For decades, it has been employed to transform the productivity of aluminum alloy machining and wood machining for the automotive industry.

Diamond produced using chemical vapor deposition (CVD) as opposed to the high-pressure, high-temperature HPHT synthesis process, has a hardness of between 90-120 GPa.

This article will discuss how this increase in hardness directly leads to increases in tool life when machining one of the most abrasive materials in industrial use. In terms of cutting tool materials, diamond occupies the top left side of the hardness toughness properties map shown in Figure 1.

Figure 1. Cutting tool materials hardness and toughness properties map. Image Credit: Element Six

A Track Record of Productivity Improvement – Aluminum Machining in the Automotive Industry

A classic example of the productivity gains acquired using diamond is the machining of aluminum-silicon alloys widely employed for engine blocks and cylinder heads in the automotive industry. PCD diamond is utilized in this instance.

The examples illustrated here in the milling of locator faces in cylinder heads exhibit dramatic improvements in tool life machining, with 15 times more cylinder heads machined than cemented carbide, in a quarter of the time.

The advantages can be articulated in a number of ways, including increased asset utilization or reduced cost-per-part, but what is clear is that PCD is able to transform productivity. Aluminum will still be a key material for the future of the automotive market.

Figure 2. PCD ball milling of locator faces on an aluminum silicon alloy cylinder head. Cutting Speed (Vc) 600 m/min or transforms productivity in aluminum machining. Image Credit: Element Six

Fiber-reinforced polymers (FRP) could be used to complement aluminum. Carbon fiber reinforced polymers (CFRP) have been extensively used in high-end applications, such as motorsport and aerospace for many years now, in order to reduce weight.

This has led to heightened interest in the advantages of FRP in the automotive industry.  High specific strength and stiffness combined with relatively low weight makes CFRP materials perfect for a number of automotive applications.

In the adoption of CFRP in aerospace, one of the key challenges has been its poor machinability. Rapid tool wear often occurs because of its highly abrasive fibers and anisotropic nature. Diamond, in particular PCD, has been instrumental in the drilling, milling and trimming of CFRP and supporting its widespread adoption in aerospace.

The below chart illustrates an example of drilling a CFRP and aluminum stack. The number of holes drilled with Element Six AeroDianamics^TM PCD is over five times that of cemented carbide, and they were drilled twice as fast.

Figure 3. PCD support adoption of CFRP in the aerospace industry. Image Credit: Element Six

Metal Matrix Composites

Metal matrix composites (MMC) show a combination of excellent mechanical properties; these include high wear resistance, corrosion resistance and low weight. For the future of both the aerospace and automotive industries, MMC's are a key class of materials.

They will be employed within the aerospace industry for parts in the airframe, landing gear and fan exit guide vanes, and in the automotive industry for parts such as brake discs and calipers.

The poor machinability, for example the rapid development of severe wear of the cutting tool, is one of the key challenges in expanding the penetration of MMC’s in these industries.

The chart below shows the tool life improvements that can be acquired by utilizing different classes of diamond tools in the high speed turning of two very abrasive types of MMC (40% SiC-Al composite 3 micron particles – AMC640xa and a 25% SiC-Al composite 20 micron particles – AMC225xe).

By selecting the correct grade of PCD, tool life may be more than doubled and can be doubled again by moving to CVD diamond.

Figure 4. A comparison of the tool lives of different types of diamond tools in the turning of two types of MMC. Image Credit: Element Six

From Functional to Aesthetic

In industries other than automotive manufacturing, similar machining challenges are being faced, with the consumer electronics industry typically facing the same application demands as the automotive industry. In particular, the demand to machine a component to a specific geometrical tolerance as fast as possible, with maximum tool life.

However, in machining extreme aesthetics, there are some additional requirements, and the demand to meet nanometer surface roughness requirements on a modern day smartphone are more like a high-end watch than an automotive component.

Element Six has shown that in the high-speed milling of aluminum, a 40 nm surface finish can be attained by employing synthetic diamond tools. Be it aesthetic or functional, PCD’s exceptional properties allow extreme surface roughness requirements to be met.

Environmental Impact

In manufacturing, productivity gains are a crucial factor, but it is crucial to ensure gains are not achieved at the expense of environmental impact. Over 80% of the worldwide tooling market in metal cutting is built on scarce and critical raw materials, like cobalt and tungsten, according to the EU-funded project ‘Flintstone2020’.

The project aims to locate alternatives to these materials and diamond-based composites are a key pillar of the proposed alternatives. Along with the scarcity, growing attention is focusing on “life cycle analysis”, where again diamond materials like PCD and PCBN (polycrystalline cubic boron nitride) supply favorable alternative solutions to traditional cutting tool materials.

The Influence of the Digital Transformation

Industry 4.0 promises to optimize production efficiency and capacity and to create new business models via the collection and analysis of a large volume of data by networking devices and sensors.

In their UK-based Global Innovation Centre, Element Six is embracing the Industry 4.0 revolution where they have automated cutting tool testing, delivering productivity and resolution that seemed unimaginable only a decade ago. They are also working on adding intelligence to their materials.

In collaboration with a UK-based consortium, Element Six has developed a prototype sensor on a PCD tool (patent pending). This device permits a machine tool operator to establish the condition of a cutting tool without manual inspection.

The technological basis of the sensor is the graphitization phenomenon which happens within PCD. At elevated temperatures, diamond converts back to graphite and graphite is electrically conductive.

A laser can be employed to graphitize tracks selectively on a PCD tool surface and the resistance that is produced within the tool-embedded-sensor may be monitored, for example if resistance heightens this would show tool wear or breakage. Before trialing the prototype machining Titanium Ti-6AI-4V, the cutting operations were simulated.

Figure 5. An in-situ cutting tool senor on a PCD tool used in the machining of titanium. Image Credit: Element Six

Summary

For decades, diamond cutting tools have been employed to transform machining productivity for the automotive industry. These advanced cutting tool materials are now being focused on the challenges in the machining of lightweight materials such as MMC and CFRP.

This is in addition to supplying the data-sensing capability to allow Element Six to take advantage of the 4th industrial revolution, and decrease the impact of cutting tools on the environment and utilization of scarce raw materials.

This information has been sourced, reviewed and adapted from materials provided by Element Six.

For more information on this source, please visit Element Six.