Hoosier Pattern Inc
Hoosier sand mould
3D printed sand casting produced by Hoosier Pattern with ExOne's S Max platform.
Hoosier Pattern Inc. was founded in 1997, has grown to house a workforce of around 50 people and nearly 30 production machines, and prides itself on delivering cores and moulds on time and at the desired quality of its customers.
In 2013, the company became the first pattern making shop in the Americas to own and operate a 3D sand printer in-house. A year later, one of its customers purchased its own printing platform and leant on Hoosier to operate it out of its Decatur, IN facility. And since July 2018, Hoosier has been running a third sand printer – all ExOne S Max machines – and an FDM system for prototyping and low volume run patterns.
The company is a champion of additive manufacturing (AM) technology, putting its fleet of machines into action day in day out, week in week out, successfully shipping sand printed cores and moulds from Indiana, throughout the state, country and continent, and as far as Brazil, the UK, India and China.
Having sampled an AMUG Conference presentation delivered by Dave Rittmeyer, a self-confessed journeyman pattern maker who currently occupies the role of Customer Care and Additive Manufacturing Manager at Hoosier Pattern, TCT sought to glean insights from a company with more than half a decade’s experience of running a 3D sand printer.
Through both discussions, Rittmeyer put the emphasis on regular maintenance of machinery, gave pointers on how to approach design, and bemoaned the all too frequent carelessness of freight companies. Amidst it all, he advises what to do and what not to do should you operating a 3D sand printer.
DO: 'A CLEAN MACHINE IS A HAPPY MACHINE'
Hoosier has created a cleaning schedule to make sure the insides of the mixing chambers, the bottom and inside of the recoater and the outside of the printhead are all scrubbed on a daily basis. A full wash out is a weekly occurrence, where pieces of the recoater are pulled out and soaked in a chemical solution. The windows and exterior of the machine are also wiped down regularly. “Keep everything clean. That way no sand or binder gets built up anywhere where it shouldn’t. If it does, it could potentially cause a failure on a job box we’re running.”
DON'T: DESIGN TOO MANY BLIND AREAS
When designing cores and moulds, Rittmeyer recommends not implementing too many areas that you will struggle to see when the print is finished. “Too many of those increase your risk of a bad casting, so design it so it can be seen and cleaned. Try to avoid very thin sharp edges. You’re better off with obtuse angles if possible, rather than an acute angle.”
DO: DESIGN SO YOU CAN HANDLE
With the ability to print the size of the build volume – in the case of an ExOne S Max, that’s 1800 x 1000 x 700 mm – there’s potential for the printing of large cores and moulds. But they’re typically not the easiest, or safest, things to handle. Rittmeyer suggests incorporating rods into the design – all the way through the print if possible – and perhaps even inserting steel plates to evenly disperse the weight.
DO: CONTROL THE ENVIRONMENT
Hoosier has installed technology to enable the air conditioning and furnaces to work together with a mister system to ensure the room in which the printers are kept is neither too dry nor too humid. “If it becomes too humid in the room, the sand may not flow out of the recoater properly, which means it won’t have anywhere for the binder to spray onto and bond together, so it’ll have trenching or just stop laying sand altogether. And vice versa, if it becomes too dry, the sand may start to free flow out of the recoater.”
DON'T: BE IN A HUGE RUSH WHEN YOU'RE EXTRACTING YOUR MOULD
Take your time and be careful. Remove as much unbonded sand as you can to make it lighter and easier to handle. And if you’re vacuuming holes out it can create a vortex in a wind tunnel and could erode itself very quickly.
DO: TEST EVERYTHING
Hoosier tests every print in every job box. Each print is weighed. Each is measured to get the length, width and height. A scratch test is carried out. A permeability puck will be produced to gauge printability in the first instance. Loss on ignition tests will be run.
DO: GIVE EVERY JOB BOX A SERIAL NUMBER
Applying serial numbers to each print run will help you keep order of them for quality control. “Every item in that box will have that number on it so if there is a quality issue, I can locate and isolate them for quality control. If somebody ordered 500 cores over multiple printers, this way I know which cores were printed when. That’s something that absolutely needs to be done.”
DON'T: EXPECT YOUR COURIER TO GIVE DUE CARE TO YOUR SHIPMENT
Packaging properly is paramount in order to not undo all the work it has taken to design, print, and extract your moulds or cores. Rittmeyer and his team have learnt the hard way that freight companies are not always too gentle when handling the wooden crates that Hoosier Pattern’s sand prints are shipped in. Deliveries have all too often turned up on doorsteps as nothing more than mounds of sand because of insufficient packaging, poor handling, bumpy roads or combinations of the three.
“Everything is packed with foam around it. Foam is pretty much the only thing that will touch, whether it’s a sand core or a mould. If it’s a very fragile core, or if we’re worried about shipment, what we’ll do is we’ll actually print a box as we’re printing the core around the outside of it and we’ll ship it right inside that box, and again it’s packaged with foam. We’ll do that for very fragile impeller cores that have a very thin discharge or for water jacket cores for car motors, for example.”
