Researchers at Ford Dearborn are keen to see additive manufacturing move on from its prototyping origins and into the mainstream volume production process
In itself, there is nothing new about the automotive industry’s use of the set of techniques generally known as additive manufacturing or 3D printing, in which objects are created by the successive application of thin layers of material one on top of another. Uptake began in the 1980s when, due to their initial use as a means of producing physical facsimiles of intended final products, they were known as ‘rapid prototyping’.
This has certainly been a hallmark of the way they have been employed by Ford, which has been using the approach as a “design verification tool” – a means of making physical facsimiles of intended final products to check on such factors as appearance – since 1988.
Confirmation is provided by Ellen Lee, Ford’s technical leader of additive manufacturing research, based at the company’s Research and Innovation Centre in Dearborn, Michigan. Nearly three decades later she says that the company is actively seeking ways to apply additive techniques “directly to our products”.
Nevertheless, the relatively slow speed at which additive processes actually make parts means that they are still not feasible as a manufacturing technique in a volume car environment. “It is not possible to use them today to make parts in volume applications,” Lee states flatly. In Ford’s case, therefore, she says their on-vehicle use is limited to “niche applications such as in our racing activities. There are 3D-printed parts that go onto the race track.”
Where the technique is beginning to make its presence felt in mainstream production processes is as a means of fabricating jigs and fixtures used in manufacturing operations. However, Lee says that its employment is still largely dependent on a recognition of its potential by particular individuals local to the plant concerned.
Quite simply, there needs to be “somebody who understands or has heard of the advantages you can gain from additive manufacturing.” As such, she says: “We have these local pockets but we are still working on how to align globally so that we can have best practices everywhere.”
Lee says that Ford also keeps an eye on how its use of additive techniques can be further developed. “We are continuing to try to push the envelope on what type of functional applications we can get,” she confirms, with “speed, size and materials” all being targeted as areas in which improvements can be made.
Partnering for progressWithin the last few months, details have been revealed of a major project in which Ford has taken part, aimed at radically reconfiguring the way that additive techniques can be implemented in a factory environment. The project has involved one of the major suppliers of additive manufacturing systems, US company Stratasys, and has developed prototype versions of two radically new techniques for implementing the additive process of fused deposition modelling (FDM), in which a heated liquid polymer material is extruded through a nozzle.
In essence, both have effectively abolished the need for the process to be confined within a conventional additive manufacturing machine, and have instead converted it into a procedure that takes place within a much wider manufacturing cell. In doing so the companies have sought to address limitations on the size and complexity of parts that can be made by additive techniques, and also, through the use of a new type of applicator, to greatly increase the rate at which material can be applied. Apart from Stratasys and Ford, other participants include aerospace giant Boeing and software and control system provider Siemens.
The two projects are called, respectively, the Infinite-Build and Robotic Composite 3D Demonstrators. The Infinite-Build approach involves two major reinventions of the way the workpiece and the applicator relate to each other. The first is the realignment of the direction in which material is applied through 90 degrees, so that instead of the workpiece being fabricated in successive horizontal layers, it is built up laterally by a nozzle that is oriented horizontally rather than vertically. The applicator itself moves vertically up and down and horizontally towards and away from the workpiece.
Ford’s project with Stratasys developed a new additive process techniques of fused deposition modelling, extruding a heated liquid polymer through a nozzleIn contrast with conventional additive procedures, the growing workpiece is not static but also moves horizontally at a right-angle to the applicator with the result that the installation effectively constitutes a large-scale continuous extrusion machine which, provided it is continually replenished with stocks of raw material, can produce fabrications of unlimited length.
By way of comparison, the largest workpiece that can be produced on one of the company’s conventional machines today is 3 x 2 x 3 feet (90cm x 60cm x 90cm) in the X, Y and Z-axes respectively.
The current demonstrator, by the way, allows for 30 inches of movement vertically and 40 inches horizontally, though there is no reason why those dimensions could not be increased. This is the initiative in which Ford has been particularly involved as a provider of analysis and advice derived from its own experience of real industrial requirements.
Meanwhile, the Robotic-Composite technique increases the number of axes of movement of the applicator relative to the workpiece; from the three that are possible within existing machines, to as many as eight. This is achieved by mounting the applicator on the arm of a five-axis robot – in this initial instance a Kuka machine – and the workpiece separately on a dynamic fixture which can both rotate through 360 degrees and move up and down because it is located at one end of an arm that is hinged at its base.
According to Stratasys, the technique allows complex fabrications to be produced with a much reduced need for an extraneous support structure that has to be removed subsequently, and also with a Z-axis as strong as its X and Y counterparts – something that can be difficult with conventional machines.
The company suggests that this may facilitate the additive production of parts with thin external elements such as fins or continuous undulating fabrications such as ducting. It also points out that if, for example, the robot was mounted on a rail to provide it with an ability to move laterally, then the size of the parts that could be produced would increased accordingly.
In both cases the new techniques make use of a ‘screw extruder’ that melts pellets of material by compression rather than by the direct use of thermal energy employed by the previous ‘heated tube’ approach. This helps produce a tenfold increase in the rate at which material can actually be applied to the growing fabrication compared with the previously attainable figure.
The actual extrusion rate in a specific instance depends on the particular material formulation involved, but according to the company the relevant figures for its widely used Ultem 9085 thermoplastic material would mean that today’s top build speed of 7.2 cubic inches/hour or 0.35 lb/hour would become 72 cubic inches/hour or 3.5 lb/hour.
Moreover, the company says it is already working on the development of a further extruder that would double even these figures so producing a twentyfold increase over current application rates and is hoping to be able to demonstrate it in 2017.
Third party developmentMuch of the development work on the Robotic-Composite approach was, in fact, carried by Siemens, and Andreas Saar, vice-president of manufacturing engineering solutions for Siemens PLM Software, says that the technique “marries and extends multi-axis hybrid additive deposition and robotic machining” and shows how robotics and 3D printing “can converge to unlock new opportunities for industry.”
In order to achieve this, Saar says a number of technical issues had to be confronted. “One of the main challenges we faced was in the area of precisely controlling the velocity and amount of material deposited along complex non-planar three-dimensional tool paths,” he explains. “This type of multi-axis control is necessary to produce final parts with complex shapes and repeatable mechanical properties.
With Robotic-Composite, an applicator is mounted on the arm of a five-axis robot with the workpiece on a dynamic fixture which can rotate and move verticallySaar indicates that this has been achieved for the most part through the application of existing solutions. “The demonstrator integrates advanced extrusion technology from Stratasys with an industrial motion platform powered by Siemens Motion Control and an integrated computer-aided design-to-product workflow enabled by Siemens’ PLM software business,” he states. He adds that a Siemens Sinumerik 840D sl CNC enhanced with the ability to work with an extrusion process controls and communicates motion performance.
Nevertheless, Saar confirms that the initiative still pushes the boundaries of what has previously been practicable. “The most innovative aspect of this project is the combination of additive manufacturing and advanced robotics to drive multi-axis material deposition of composites and other materials,” he states. “This approach allows structures to be completely reimagined and optimised, unconstrained by either the traditional limitations of composite lay-up or the layer-by-layer limitations and support material requirements of traditional 3D printing.”
Working within limitationsMeanwhile back at Ford, Ellen Lee says that in the immediate term the company still sees the role of additive technologies in its mainstream manufacturing operations as being limited to the production of jigs and fixtures. Even the projected ability of the Infinite-Build process to make fabrications much faster than previously will not make it feasible as a manufacturing technique for volume car production.
However, even at that level the potential for improvement is considerable. In particular, she identifies two likely benefits that should stem from the ability to make additive parts bigger and faster than previously. One is that the end-fabrication should have less parts than it would otherwise, meaning that it should be easier to assemble. It is quite possible for them to have “as many as twenty” component parts at the moment.
The other is that where the fixture is something that might be directly handled by a human operator – for instance as a means of picking up and carrying actual vehicle parts – then the possibility opens up of making fixtures customised to the physique and capabilities of particular individuals. “You could potentially personalise them to each operator you have,” she confirms, adding that this in turn could help “increase ergonomic efficiency and ultimately product quality.”
Lee also confirms that other possibilities open up further ahead. The ability of the Infinite-Build technique to make large curved parts means that it might have the potential to make mould tooling for compression moulding or composite lay-up procedures. She describes those applications as “very possible” with the additive materials that are available today.
At some future point she also says that additively manufactured injection moulding tooling may become a practicable option, though she indicates that may require some further development in formulations for appropriately robust additive composite materials.
As it is, Lee says there is already some use within Ford of additively manufactured mould tooling in its pilot and new product development operations. Moreover, she adds, gaining a fuller understanding of the “limitations of printed tooling” is a specific focus of current R&D activities.
As such, she also concedes that if printed tooling could be made both speedily and inexpensively it could still serve the needs of volume production simply by virtue of the fact that it could be used and replaced on a regular basis – perhaps every “few thousand” cycles. So, somewhere down the line is the possibility that mould tooling might cease to be regarded as high capital cost equipment with an outlay that might have to be amortised over several years of production, and come instead to be seen almost as a consumable.
That is obviously still a distant and theoretical prospect. Nevertheless, Lee indicates that Ford’s interest in the potential for large-scale additively manufactured fabrications is such that it intends to start operating an Infinite-Build installation as a development tool at a US location before too long – perhaps with the first half of next year.
More fundamentally the prospect is of additive techniques becoming a much more flexible and versatile set of tools right across the board. “We think this will enable us to get extra function from the technology that we cannot get today,” Lee states. “It will give us an enhanced ability to integrate and consolidate parts and means that we will be able to design for the function of the application rather than around the limitations of the manufacturing process.”
