Components made by additive manufacturing technologies (AM) have more variables than machined parts. Faster inspection for additive manufacturing is more challenging because AM processes are not as accurate as metal cutting. Better metrology for AM will help reduce AM feedstock and costs.
As manufacturing becomes more responsive, connected, quick and customizable, new and more flexible metrology techniques for machined, molded, cast and AM parts will become more important.
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 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.
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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.
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, and 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.
The UK’s Future Metrology Hub, a centre of excellence in metrology research, has the job to accelerate 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.