Industry Technical Publication · 2018

Use of Spherical Shaped Feeders in 3D Sand Printed Moulds

Nattinee Valun-araya, Ongkarn Chantarasukkasem and John Pearce

Metal Casting Technologies, Volume 64, 2nd Quarter, June 2018, pp. 19–23

CAD models of a five-blade propeller casting shown with a cylindrical feeder and with a spherical feeder — Comparison of cylindrical and spherical feeder designs. Figure from Metal Casting Technologies (2018).

Overview

The article reports initial progress in the use of spherical-shaped feeders in moulds produced by 3D sand printing (3DSP). Spherical feeders offer the maximum volume to surface area ratio, but they are not easy to incorporate into conventionally made moulds. The work examines whether replacing the normally used cylindrical feeding heads with spherical feeders can improve casting yield and reduce mould height, saving printing time and mould material.

Engineering Challenge

Conventional pattern-based mould making constrains feeder geometry. Spherical feeders are difficult to incorporate into conventional moulds, so cylindrical feeding heads are normally used instead, even though a sphere gives a more favourable volume to surface area ratio.

Conventional routes are also slow. As reported in the article, producing a conventional pattern alone could take up to three to four weeks, whereas an equivalent final 3DSP mould ready for casting required only days. Past experience in Thailand had shown that components such as propellers and impellers cast using traditional methods tended to show excessive dimensional variations and required significant balancing.

3D Sand Printing Approach

In binder jetting, resin binder is selectively applied onto successive layers of pre-mixed sand. Mould and core parts are built up layer by layer, supported by the surrounding loose sand, then cleaned by air jet and assembled into the final mould. Parts bonded with furan do not normally require subsequent curing.

Because the geometry comes directly from CAD data, the process allows vertical walls, overhangs, undercuts and honeycomb or mesh structures, and there is no dimensional play from pattern removal. That design freedom is what makes spherical feeders, and combinations of open and blind feeders, practical to produce.

The equipment used in the work was originally supplied by ProMetal RCT, Germany, now part of the ExOne Group. Casting layout, gating and feeding were designed with a casting simulation program (SolidCast from Finite Solutions).

Printed sand mould sections stacked on pallets, ready to be assembled into a complete mould — 3D printed sand mould parts prepared for assembly.

Two views of 3D sand printing equipment installed on the production floor at Speed 3D Mold — 3D sand printing equipment. Figure from Metal Casting Technologies (2018).

Technical Highlights

DesignSpherical feeder geometry in place of conventional cylindrical feeding heads
Process3D-printed (binder-jetted) sand mould parts assembled without patterns or core boxes
ConfigurationComplex feeder and mould configurations, including open and blind spherical feeders
ValidationPropeller and impeller casting trials in aluminium bronze, grey and ductile iron and stainless steel
SolidificationDirectional solidification and shrinkage behaviour observed within the spherical feeder
EfficiencyReduced mould height, with reported savings in binder and sand use of 15–20%

Industrial Examples

Five-blade propeller, C95800 aluminium bronze

Component: Five-blade marine propeller, 812 mm overall diameter, 248 mm high, casting weight 71 kg
Material: C95800 aluminium bronze
Engineering approach: Produced with both feeder types for comparison: a conventional cylindrical feeding system and a spherical feeding system.
Reported result: Cylindrical feeding required a poured weight of 141 kg (50.3% yield); spherical feeding required 130 kg (54.6% yield). Castings produced with the spherical feeder were free from defects.

FCD 450 double-suction pump impeller

Component: Double-suction pump impeller, 490 mm diameter, 303 mm high
Material: FCD 450 ductile iron
Engineering approach: Rigged in CAD with spherical feeders and cast from a 3D printed sand mould.
Reported result: Poured weight 252 kg for a final casting weight of 160 kg, giving 63.4% yield.

FC25 replacement impeller

Component: Pump impeller supplied as an urgent replacement part with no spares available
Material: FC25 flake graphite iron
Engineering approach: Replacement casting produced directly from a 3D printed sand mould using a spherical feeder.
Reported result: The replacement casting was supplied to the customer in five days.

FC25 replacement pump impeller casting with spherical feeder, shown from the side and from above — FC25 replacement impeller with spherical feeder.

The article also reports a stainless steel (304) propeller for a long-tailed racing boat — 170 mm in diameter, 250 mm long, weighing 7 kg and produced with a 70% yield — and the use of both open and blind spherical feeders for an FC25 casting used as a piston part for a marine diesel engine.

Publication Reference

Valun-araya, N., Chantarasukkasem, O. and Pearce, J. "Use of Spherical Shaped Feeders in 3D Sand Printed Moulds." Metal Casting Technologies, Volume 64, 2nd Quarter, June 2018, pp. 19–23.

Industry Technical Publication · 2018

This is an industry technical publication. Figures reproduced here are technical figures contributed by the Speed 3D Mold engineering team. Publication in Metal Casting Technologies does not constitute endorsement, certification or approval of Speed 3D Mold.

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