Additive layer manufacturing

Creating public and commercial enthusiasm for engineering research projects is often an uphill struggle but students from Exeter University have achieved it with ease. The interest surrounds a masters project, set by Dr. Liang Hao to encourage engineering students to push the boundaries of additive layer manufacturing (ALM) technologies and work with an appealing and highly commercial material, chocolate. It will also widen the existing applications of this technology from its current applications in aerospace, Formula 1 racing cars and the medical field.

The challenging venture has certainly attracted some leading industry support, obtaining assistance from electronic component supplier Farnell, linear motion specialist HepcoMotion and perhaps unsurprisingly chocolate giant, Cadbury. The engineering team's work has led to the development of ChocALM, a process that can produce a 3D object of any shape in chocolate from a computer design.

ChocALM can be likened to 3D printing or deposition except that the confectionary structure is created by the application of layers of chocolate. A 3D computer image, usually in the form of an STL file, is the starting point. The software then breaks down this image into layers, applies co-ordinates for deposition and maps the necessary path. The build process works by squirting chocolate over the path of a layer and then lowering the surface where the chocolate is deposited to make space for the next layer.

The innovative machine comprises a three-axis Cartesian co-ordinate system connected to a temperature controlled chamber. Tempered chocolate is pumped to an extrusion unit and forced out through the nozzle. The exiting chocolate is the filament that is deposited on a build plate contained in the z-axis table in a layer-by-layer fashion to form a 3D shape with a unique design which could be as complex as someone's face.

Linear movement is provided by five HepcoMotion® PDU2 belt driven units. "This product is ideal for our machine as its zero backlash has allowed us to guarantee a tolerance in the deposition system of 0.6mm," explained team leader, James Bulleid "Also the motor mounting and keyed shaft have made it possible for us to attach suitably sized stepper motors using motor mounts made by the project team."

The behavioural characteristics of chocolate are unique. It is a complex substance that exists in six different crystalline forms only two of which are palatable. To reach those tasty forms the chocolate must be tempered to melt out the other four. The tempering process is via heated reservoirs of water and requires the chocolate to be heated to roughly 45°C then cooled to 23°C. It is then stirred and re-heated to 27°C and maintained at that temperature for extrusion.

As ChocALM is still very much in the development phase, food grade components have not yet been specified. The machine has been designed however so that food grade materials and components, such as the HepcoMotion® PDU2 units, can easily be incorporated for commercial use.

ChocALM is a project that is set to inspire masters' students for a few years to come. Dr. Liang Hao, together with Exeter Advanced Technologies (X-AT), will continue to run this project with the aim of achieving commercial production of personalised chocolates and develop more advanced capabilities. These will include the development of the current design to incorporate two nozzles for the concurrent deposition of two different types of chocolate. Additionally, active cooling of the deposited chocolate will be investigated to speed the build process.

As James Bulleid emphasises: "There is still a lot to learn regarding the extrusion process. We need to understand more about exact flow characteristics of the chocolate in the barrel so that the nozzle design can be perfected." He continues, "The market opportunity for personalised chocolates is huge. The current methods of manufacturing custom designed chocolates use a mould which is expensive and inflexible. Ultimately ChocALM offers incredible potential."

In the meantime the project team plans to show the ChocALM machine in a Public Communication Partnership Project as an example of advancing technology. Its aim will be to attract further co-operation with specialist engineering companies similar to HepcoMotion® and to raise the profile of engineering amongst the public at large. "It's a great example of how engineering skills can be applied to create an exciting and commercially attractive product," Dr. Liang Hao concludes.

The project has attracted international interest too. The young engineers' innovative use of ALM technology will be presented in Florida later this month, as they have been invited to attend one of the largest international conferences and expositions on rapid prototyping and manufacturing.