Solving additive manufacturing’s problem of warpage and shrinkage
Calum Mills, Research and Development Design Engineer of Photocentric, explains how the inventor of LCD 3D printing was able to eliminate warping and shrinkage issues that are common within 3D printing.
This part was designed by Photocentric’s engineering team for an internal printer development project. From the start, the decision was taken to explore designing and optimising this part for Photocentric’s printing processes – to take advantage of the speed and cost benefits that bringing prototyping and production in-house would deliver.
Printing was also used extensively throughout the design and prototyping stages for other components that were later manufactured with conventional processes.
Development work was split between designing the part, its functionality, and optimising it for additive manufacture.
The design and development process
The iteration of initial designs and early prints through to the current design. A mixture of design changes were undertaken to optimise for printing and to add new features (including material selection, print settings and print optimisation).
The benefit of Photocentric’s process is the ease with which features and design changes can be implemented – these would be very expensive and time consuming with conventional methods such as moulding and sheet metal work.
V1 – DL110HB, back to front door that fused, thin wall cut-out fan hole, no webbing or liner, large blocky internal features, no internal supports, leather texture that wasn’t deep enough to form
V2 – DL110HB, added webbing to walls, thinner magnet holders, skeletonised internal features, web/strut support on back and inside, integrated lattice fan filter, no texture.
V3 – DL110HB, fully latticed liner (octet truss), leather texture, door rotated, and gap increased (with supports on print platform), thickened and optimised web supports inside.
V4 – Hard black vs DL110HB test, fully latticed liner, deep diamond texture on outside. One version with web supports and one with removed inner web supports. Greatly optimised and material reduced internal features. Logo added to front.
V5 – Hard black. Ferrofluid texture, fully latticed liner adjusted. Integrated fan mounts and plenum rather than extra part and a switch to Gyroid TPMS liner and filter.
V6 – Hard black. “Chocolate-blocked” floor to improve part cleaning and removal from platform, adjusted lattice line and filter to improve stiffness. Initial production of over a dozen produced.
The chassis was printed in Photocentric Daylight Magna Hard Black resin, as it was the most suitable for the project.
Printing at 250μm layer thickness saved time and with surface texturing on the visible panels, did not compromise the appearance of the unit. The print took 15 hours to complete, consuming 900ml of resin.
Due to the size of the part and the large number of small-celled lattice structures, care and attention was taken on the washing and drying of the part to ensure all residual resin was removed. The part was washed for around 15-20 minutes in Photocentric Resin Cleaner, rinsed thoroughly with warm water, and then air dried for 2 hours. The part was then post cured.
Once complete, the parts were removed hot from the cure unit and submerged in cold water to thermal shock – this allowed the part to be removed from the platform with little effort.
250μm layer thickness
Print time 15 hours
900ml of resin used
Parts washed and cured in 2 hrs 30 mins
Parts thermal shocked
Unique features enabled by additive manufacturing
Several features of the design were made possible by printing the chassis, as opposed to manufacturing with conventional methods:
Print-in-place magnetic door panel – this panel allows access to the internal components for assembly and maintenance and can be printed in-situ without needing a second print file. It also acts as support material for the aperture it covers, which has greatly reduced material wastage, and does not add any print time.
Fully integrated part fitting – using magnets and captive nuts to improve printability. In prototyping tapped holes and snap fits were also explored but are more difficult to optimise for mid-mass production.
Reduction of extra components required – many features can be directly integrated into the printed design for free. For example, cable ties can be replaced with printed retention clips, a fan filter and plenum were directly integrated into the side of the panel, and a diffuser panel for indicator LEDs. If manufactured conventionally, it is likely that the part would consist of multiple metal and plastic components with fasteners.
Customisation – different surface textures were explored and easily updated with each iteration, and a company logo also added to the front of the chassis. One-off alterations or future updates can be made with ease.
All of this is made possible by designing for the manufacturing process from the beginning. The addition of a latticed liner to the inside of the panels greatly improved stiffness, part strength and eliminated warpage without excessive material use.
Lattice liner applied to the side panel removing warpage
Panel without lattice layer warped
For this specific part, there are many benefits that our additive manufacturing process delivers when compared with conventional manufacturing processes. In terms of development, the rapid turnaround time in the prototyping stage has allowed design freedom and cut the development time drastically. The ability to have a fully customised part within 24 hours accelerated the process greatly.
Even after the design had matured to the point of being used in prototype units, the ability to adjust and change features without concern over tooling costs, manufacturing time or shipping time also had significant benefit. For example, being able to add mounting points for an extra component, or to trial a new feature became a far more straightforward proposition. As the prototyping stage uses the same process as the production stage planning ahead can be simplified too.
The all-in-one design of the printed part has innumerable benefits. Adding features like textures, lattices, or other complexities are almost free with printing, in sharp contrast to the cost of applying texture to an injection mould, for example. The real advantage comes when considering design for additive manufacture throughout the development process, rather than just as a prototyping method or a “what if” thought.