INSPECTION FOR THE SMART FACTORY PART I: ADDITIVE MANUFACTURING

Transcription

1 INSPECTION FOR THE SMART FACTORY PART I: ADDITIVE MANUFACTURING

2 OVERVIEW The importance of metrology the science of measurement to manufacturing industry is largely underestimated, except by engineers. Sir Joseph Whitworth, the 19th Century inventor of early measurement standards, said You can only make something well if you can measure it. To offer a small qualification, perhaps, you can only make something well repeatedly, if you can measure it. Measurement can be taken for granted but it is of absolutely critical importance to manufacturing, in all sectors. In automotive, inspection of parts is normally in a batch test cycle, of varying number, to ensure there is uniformity. Aerospace, however, has to work on 100% inspection; every part after the first part you measure has to be identical. Official estimates from the National Physical Laboratory in the UK say that up to one fifth of the total value of UK manufacturing activity is in product verification. Measurement ensures products work and operate safely. Product inspection, one of the main applications of measurement in manufacturing, benefits manufacturers in several ways. If there are problems in a part you find them before the end-user, and if you measure and understand your processes you can make them more efficient, says Philip Hewitt, Manufacturing Product Manager at Autodesk. The challenge is global and institutions such as The Physikalisch-Technische Bundesanstalt, the National Metrology Institute of Germany, are also working on better, real-time metrology methods for manufacturing to raise productivity. This investigative and validation role of measurement applies doubly to additive manufacturing because these processes are not fully understood yet. As manufacturing becomes more responsive, connected, quick and customizable, new and more flexible metrology techniques for machined, moulded, cast and additively manufactured (AM) parts will become more important. THE TECHNICAL CHALLENGE The inspection of products for verification presents challenges for any conventionally manufactured part. Accuracy, reliability and cost of measurement, speed and where in the process of manufacture the measurement should reside, are the main challenges. Machine tool probes and coordinate measurement machines, or CMMs, are still the cornerstone equipment for industrial measurement. CMMs are commonplace in industry for taking 3D measurements of parts and in recent years the lab-based CMM has been joined by mobile and robot-mounted CMMs and non-contact scanners for fast, post process monitoring and measurement. For an additively manufactured component, there are more variables than for a machined part. Here metrology needs to measure dimension and material quality because these are unknown. Additionally, additive manufacturing (AM) can make intricate geometries and internal structures which you may not be able to inspect with a traditional CMM. Therefore you have to think of new, clever techniques to inspect these parts, if you can t see them from outside the component, says Robert Bowerman, Consultant Engineer at Autodesk. However, this is merely to assess the geometrical properties in the component, its shape and tolerances. An AM process simultaneously creates the geometry and the material; you are creating it from nothing and no data exists on the quality of the material before it is manufactured. Because of this, additional inspection is required in order to identify whether there is residual stress, fatigue or any other physical defect in the properties of the AM component. This differs from subtractive manufacturing, in which much is already known about the properties of the e.g. steel or titanium billet, or composite lay-up, before it is machined. Hybrid manufacturing An increasingly common technique is using a combination of additive and subtractive manufacturing processes to produce a near net shape of a part then machine it back, sometimes marginally, to the intended shape. Using an AM machine, then a machine tool, or one of a new generation of hybrid manufacturing machines combining both technologies, can effect this. An example is the manufacture of cylinder heads and all their accurate sub-components. Autodesk and other companies are now making these, currently for test applications, using AM processes and then shaving off a small layer to reach the desired tolerances. This is only possible with some kind of inprocess inspection, says Autodesk s Phil Hewitt. The process may be interrupted but, if you are changing from additive to subtractive, then you have to do some level of inspection in-process, or between processes. So a suitable metrology solution is needed here as this method grows.

3 ADDITIVE MANUFACTURING AND INSPECTION CRITICALITY There are seven types of additive manufacturing as defined by the ISO*. The two most commonly used for producing metal components in industry are Power Bed Fusion (PBF) and Directed Energy Deposition (DED). DED combines a material and energy source to deposit a material onto either a starting point or a previously made component. One common method of DED feeds metal wire into an arc, identical to a normal welding process. The manipulation of the wire and arc can be driven to deposit layers of metal, at high rates, to produce an additively manufactured part. INSPECTION FOR INDUSTRY 4.0 As smart, flexible factory technologies develop, metrology equipment providers like FARO have produced tools that take inspection all the way from tooling and mould and die design to the final verified part. Industry 4.0 or 4IR are the now familiar terms used to describe connected, flexible and data sharing factories. New metrology methods, involving more non-contact and in-process techniques, remove human intervention and that, connected to a Manufacturing Execution System, for example, can receive, validate and pass the measurements automatically, will be essential to the advancement of the smart factory. The smart factory approach is to do the metrology in process, to remove the separate and isolated CMM stage. FARO has always been driving the movement to get CMM equipment out of the inspection lab and upstream into the shop floor, so you can save time, reduce scrap, and rework upstream, says Chuck Pfeffer, Director, Product Management Factory Metrology at FARO Technologies. You should not invest time and money into working parts that are already bad, when you can identify and rework them early or eliminate rework altogether. Several FARO products have been specifically designed to work in the smart factory where speed, accuracy and portability are key. Measurement technology and methods are advancing as part of the wider smart factory drive. The Future Metrology Hub, a 25m centre of excellence in metrology research, was launched in the UK in September this year (2017). Funded partly by the Engineering & Physical Sciences Research Council, its job is to accelerate these new metrology techniques to assist with the adoption of Industry 4.0. Hub director Professor Jane Jiang said By embedding metrology inside the process, using universal metrology informatics and running this through the whole value chain, we can achieve a step change in manufacturing productivity. Smart metrology analytics (for assessing which data to use), design for verification platforms and process control systems are some of the other research areas. Faster reliable inspection for additive manufacturing is more challenging because the additive processes are not as accurate as cutting metal. But metrology is essential to make AM a true smart factory process. You need to check that you have added material where you think you have, says Autodesk s Phil Hewitt. With near net shape manufacture, you can add more metal than is necessary but if the measurement is very effective, the process can be made more efficient by simply adding the minimum amount of material and removing the smallest amount to achieve the desired shape. Good metrology will also reduce AM feedstock and cost. The more effective your measurement, the less excess stock you need; the closer to near net shape, the less rework it needs, says Hewitt. While you are manufacturing the component you are simultaneously manufacturing the material as well. In subtractive manufacturing, the work piece is a block of material and typically the engineer would expect to know any defects in that block. Due to the technology s higher rate, DED methods are typically used for manufacturing larger components that will subsequently be machined to achieve the net shape component. Autodesk is undertaking research to better understand the DED process and is developing software to drive DED platforms. A critical aspect of additive manufacturing is that very little in the way of in-process inspection is currently being carried out. This fact needs to be addressed and systems developed in order to overcome AM inspection issues. While you are manufacturing the component you are simultaneously manufacturing the material as well. In subtractive manufacturing, the work piece is a block of material and typically the engineer would expect to know any defects in that block, says Rob Bowerman, at Autodesk. Manufacturing a product additively incurs a complex and dynamic thermal environment, where the operator wont know if there are defects in the component when its finished. This is why you need rigorous inspection procedures for AM parts, potentially more so than for subtractively manufactured parts. AM is also unique in that, because there is often no fixed tooling, you can make modifications mid-run. You can have 10 different models of one part, or even have a custom version of a part that comes off nearly every time, says FARO s Chuck Pfeffer. Those types of parts would have special inspection criteria because each would be different, non-standard. STANDARDS Standards drive precision engineering but there are currently no universal standards for how additive part must be inspected. Instead, there are multiple inspection processes to ensure AM parts are sufficient for the safety requirements of their end-use; these are very application dependent aerospace has higher levels of criticality than oil and gas, for example. So the industrialization of AM will have a big knockon effect on the standards industry, challenging organizations such as ISO, British Standards Group and the NPL to set suitable standards for AM metrology in fast-paced, flexible factories. *ISO additive manufacturing standards

4 HARDWARE I SMART ADDITIVE MANUFACTURING METROLOGY Two main developments in metrology hardware to service the smart factory are non-contact measurement and portability. Metrology technology providers such as FARO have developed equipment to measure parts flexibly, quickly and accurately in the future factories that need to be agile to cope with small batches and volume customization. Portable CMMs (coordinate measurement machines) can move anywhere on the factory floor. A solution from FARO couples a contactless scanner with an arm probe capability, where the hard probe and the Laser Line Probe communicate interchangeably without having to remove either component. Users can digitize simple features with the hard probe and quickly scan across diverse surface materials regardless of contrast, reflectivity or part complexity without any special coatings or target placement. A key feature of the new hardware is flexibility. Scanning arms can inspect features that are needed based on the specific part it is measuring. Our product ScanArm could easily scan 10 different parts in 10 different ways, whereas a standard CMM would take more effort to programme it for 10 different variations of the part, says Chuck Pfeffer. The flexibility of such scanning arms makes them perfectly suited to the measurement of additively manufactured parts. Non-contact portable scanners provide high resolution, non-contact measurement for high quality inspection and factory automation applications. HARDWARE II SPEED AND SAFETY Imager Arrays Scanning imager arrays places a group of metrology-grade non-contact scanners together that capture millions of high resolution 3D coordinate measurements in seconds. Smart sensors allow multi-imager array configurations that expand the scan area to deliver fast, automated and comprehensive inspections, which increases cycle times. The array can be configured to measure parts that are on a production line, that is in process inspection for mass production. It also applies well to multiple AM parts, which can be measured by the array in different orientations as they exit the printer or AM machine. Pfeffer says: These array units can be connected to an Industry 4.0 networked database where you can keep track of your inspection statistics and feed them back into the production system. Again the theme is flexibility and speed, especially for products that all have different dimesions. These array units can be connected to an Industry 4.0 networked database where you can keep track of your inspection statistics and feed them back into the production system. Cobots, safety and smart metrology As factories get smarter, more are using portable and cobot-mounted measurement tools. One driver of this is safety. Cobots have in-built sensitivity to humans which comply with TS/ISO15066, the technical specification that defines how hard a body can be hit. Some measurement systems are located inside a highly secure, gated robot cell, which slows down throughput and makes it difficult to interact with the product. This is where industry needs to go to achieve the throughput it needs and limit cost relating to automation safety measures while increasing flexibility, says FARO s Pfeffer. Some are provided as single devices, but they can be mounted on a robotic device to position the scanner correctly for the user. FARO s solution, for example, uses a cobot integrated on a mobile cart that can be quickly moved to where measurement tasks are required. An extremely flexible solution, depending on how many and how different the parts are, portable scanners can collect all the data with a pre-programmed set of scans and apply different analysis via software. Or they could be programmed to collect data with part-specific scanning programs for different variations of a single part as well. The aim is to reduce cycle times for inspection and eliminate scrap and costly rework. It is well suited to AM parts, which have innate product variability, due to its ability to quickly programme for different parts with variations and do automated inspections. Our FARO Factory Robo-Imager Mobile can be easily and quickly programmed for a new part, which suits additive manufacture because you may have a new part every time, says Pfeffer. For the end user, the latest generation of metrology equipment also require less understanding of the way a part is measured so they yield a highly efficient, repeatable and reliable process.

5 CASE STUDIES 1. Cylinder head case study Autodesk has additively manufactured very lightweight cylinder heads for a motorsport application. Made with internal latticing, the parts weigh much less than would have been possible with conventional casting and machining. In changing to a new [AM product] market, we have to change our workflows, because delivering the prototype is all about speed. In manufacturing, it s different; it s about quality at the lowest possible cost, says Carl Fruth, CEO of partner FIT Technology Group in Germany. This is a challenge with AM. Autodesk Netfabb software helps standardize the CAD data from various customer sources and optimize it for their additive manufacturing process. It takes a conventional CAD design of a cylinder head through to AM production, using new design techniques for additive manufacture, build preparation, process simulation, inspection and machining. Although this is an expensive process it derives much better physical properties and is much lighter. AM has allowed FIT to produce a very high performing part that is very close to the end product, then they just machine the finished surface. The amount of material that is removed is tiny, it s almost like a skim, says Autodesk s Phil Hewitt. 2. Airbus - Internal partition wall Aircraft major Airbus has used autogenerative design software to create what has been called the world s largest 3D printed airplane cabin structural component. And it has taken inspiration from nature in doing so. Using Autodesk generative design algorithms, Airbus created a new dividing wall that separates the main passenger seating area from the plane s galley and flight attendant jumpseats. Airbus called the new dividing wall a bionic partition because its internal structure mimics biological structures created in nature. SOFTWARE What is the software solution for additive manufactured parts? Autodesk s main platform for designing and optimizing for additive manufacture is Netfabb. It is designed to improve workflows so designers changing a normal CAD drawing for AM can accelerate the process. Autodesk has software components in all the areas where AM interfaces with metrology, positioning and fixturing (robots and cobots), and simulation. Simulation, the creation of a digital twin to interrogate a part s properties when it will be fabricated, is an important part of the smart factory. We have a simulation tool that, at the physics level, gives a better understanding of what you think you will create in AM, says Autodesk s Hewitt. Metrology: As well as software used in the design of AM parts, it is used to programme different types of machines for additive processes, for taking measurements of parts and assessing their suitability for AM or conventional machining, as appropriate. We have all of those components in Autodesk, says Hewitt. Autodesk Netfabb is connected software specifically designed for additive manufacturing and design. It helps streamline workflows, reduce build errors and accelaerate product development. Generative design, additive manufacturing and the development of new materials are already transforming the shape of manufacturing and companies like Airbus are showing what is possible, said Autodesk chief technology officer Jeff Kowalski. This is not just an interesting hypothetical experiment this is a fully functioning component we can expect to see being deployed in aircraft in the near future. We re looking forward to further collaboration with Airbus on new components and designs for current and future aircraft. We have a simulation tool that, at the physics level, gives a better understanding of what you think you will create in AM.

6 CHALLENGES FOR AM INSPECTION The main challenges for AM are the same as for the age-old casting or forging processes: repeatability. Synthesizing a three-dimensional object is not as repeatable as cutting material from billets of metal with known properties. Much of the current interest is in making this field more straightforward, more standardized, says Hewitt. At the most fundamental level the repeatability of the machines and processes is problematic today, so improving this is one of the keys to making AM more reliable at lower cost. In measurement of AM, the challenge is to make critical components that require internal inspection. This challenge exists for any type of manufacturing. Where AM has the advantage is that some part designs could not be made with another process. For example some of the injection modules for jet engines can only be made with an AM process because the internal components cannot be cast or machined. You can only inspect these optically or by cutting them open and probing them. CT (computer tomography) solutions tend to be very expensive, says FARO s Pfeffer. Part of the value of AM is it can make parts that couldn t be made before but now we need a method of inspection that is as flexible as the manufacturing. The next step in the evolution of inspection for additive manufacture is to perfect a flexible inspection process that can deal accurately with a part that can be different every single time, in higher volume production. This could be contact or non-contact, and probably mobile. Imagine applying the GPS principle to everything inside a factory with satellites that are fixed around the building, with seeing and recognition capability. Then the metrology capability is embedded within the building. The Future A further step into true Industry 4.0 territory is factory metrology based on GPS technology, in a truly contactless system. Professor Paul Shore is head of engineering at the NPL and an experienced precision engineer. The NPL is working with industry partners on a GPS navigation system that could be applied to a factory. Imagine applying the GPS principle to everything inside a factory with satellites that are fixed around the building, with seeing and recognition capability. Then the metrology capability is embedded within the building, he says. The challenge is to link this to all the machines and measurement systems in there to improve the whole effectiveness of the factory. Useful Iinks Additive manufacture of a cylinder head FARO Factory Robo-Imager Mobile Software for additive manufacture design Airbus bulkhed case study 3D printing married to casting Generatively designed Airbus partition EPSRC Future Metrology Hub

7 INSPECTION FOR THE SMART FACTORY PART I: ADDITIVE MANUFACTURING