Metal Casting Technologies : MCT JUN 2018 (2ND QRT)
20 www.metals.rala.com.au METAL Casting Technologies 2nd Quarter 2018 21 supported by the surrounding loose sand in the sand box. On completion of the build the loose, non-bonded sand is removed from the sand box and the printed parts removed for cleaning by air jet. Parts bonded with furan can then be assembled into the final mould since they do not normally require any subsequent curing. Due to environmental concerns furan may need to be replaced by other binders but at present parts bonded with phenolic or silicate binders need microwave curing before assembly. Silica sand is routinely used but it can be replaced by chromite, zircon or by synthetic ceramic beads depending requirements for temperature resistance and/or dimensional accuracy. Refractory ceramic coatings can be applied to the printed mould parts in the same manner as to moulds produced by conventional use of patterns or core-boxes. The 3DSP equipment used in the present work is shown in Figure 1. It was originally supplied by ProMetal RCT, Germany which is now part of the ExOne Group. Normally the sand layer thickness is 280 to 500μm and the build speed is 60-85 L/h. The build volume consists of an area of 1800mm x 1000mm with a depth of 700mm. Silica sand with average grain size of 260μm with a furan binder is used giving a typical strength of 180N/cm2 in printed sand test-pieces. Mould materials used in Thailand are currently imported from Germany. Some examples of finished 3DSP mould parts are shown in Figure 2. Trials using spherical feeders To date a number of trials have been carried out and castings with various designs successfully produced in Aluminium Bronze, Grey & Ductile Irons and Stainless Steel. Some examples of this work are outlined in this section. To prepare each mould by 3D printing at Speed 3D Mold a casting simulation program (SolidCast from Finite Solutions) was used to design the casting layout and the gating and feeding system. Figure 3 shows models of a five- blade propeller with a conventional cylindrical feeder and a spherical feeder. This casting design, with an overall diameter of 812mm and height 248mm, has been produced in C95800 Al Bronze (Cu-9%Al- 4.5%Ni-4%Fe-1%Mn) using both types of feeder. The casting weight is 71kg: the cylindrical feeding system required a poured weight of 141kg giving a yield of 50.3%, whereas the spherical feeding system used required a poured weight of 130kg, giving a yield of 54.6%. The castings produced using the spherical feeder were free from defects and are shown in Figure 4 together with the nature of the shrinkage typically observed in a spherical feeder. The feeder has retained its spherical shape with a central pipe region developed beneath the N. pole of the sphere. that, for current equipment and operational costs, 3DSP is economically suitable for short runs (<45) of castings with low complexity and for runs of up to 1000 for highly complex designs. The design freedom offered by 3DSP enables castings with geometric features such as vertical walls, overhangs, undercuts and honeycomb or mesh structures, etc. to be produced, and may enable optimized redesign of “solid” castings into skeleton or truss-type open structures to save weight and material [2,5]. Mould assemblies produced from 3DSP sections can be fitted with filters and insulation sleeves as for conventionally prepared moulds and may also allow the replacement of the normally- used cylindrical-shaped feeding heads by spherical-shaped feeders. Spherical feeders offer maximum volume to surface area ratio but are not easy to incorporate into conventional moulds. In seeking to improve casting yield and to reduce mould height to save time and mould material, this paper reports some initial progress in using spherical-shaped feeders in 3DSP moulds. Outline of 3DSP (binder-jetting) process Sand printers selectively apply resin-binder, at present furan is the most common, onto a layer of pre-mixed sand in a similar way to inkjet printing on paper: hence the process is often called binder-jetting. After the binder has been selectively dispersed onto each new layer of sand the build platform is incrementally lowered by a set amount and a new layer of sand is spread over the surface for bonding. Mould or core parts or array of parts are gradually built up as successive incremental horizontal layers, each part being FIGURE 2. Examples of printed mould parts ready to be assembled. TECHNICAL FEATURE Beckwith Macbro Resin Coated Sands Contact : Rob Dalla Via 30 Devon Road Devon Meadows, Melbourne Telephone: +61 3 5995 4244 Mobile: 0417 332 723 Fax: +61 3 5995 5030 E-mail: firstname.lastname@example.org Website: www.beckwithmacbro.com.au All grades of resin coated sand used for shell molding and shell cores for ferrous and non-ferrous applications PRODUCTS n Range of resin strengths from 1.0% to 5.0%. n Silica, Zircon, Chromite coated sands or blended mixes. n Coated Sands of different AFS typically from 50-90 AFS. n Thermal Reclaimed Coated Sands. n Frac Sand. SERVICES n Full technical and trouble shooting service. n On-site shell core and shell molding facility to evaluate the product applications. n Laboratory facility to ensure product quality. FORSALESHELLCOREMACHINESSHELLMOULDMACHINES FIGURE 3. Model of five-blade propeller showing (a) cylindrical and (b) spherical feeders. FIGURE 5. Model (a) and casting (b) of FCD 450 pump impeller. FIGURE 4. Propeller casting in C95800 (a & b) and the shrinkage pattern in the spherical feeder used in production. A A A B B B C THE DESIGN FREEDOM OFFERED BY 3DSP ENABLES CASTINGS WITH GEOMETRIC FEATURES SUCH AS VERTICAL WALLS, OVERHANGS, UNDERCUTS AND HONEYCOMB OR MESH STRUCTURES, ETC. TO BE PRODUCED, AND MAY ENABLE OPTIMIZED REDESIGN OF “SOLID” CASTINGS INTO SKELETON OR TRUSS-TYPE OPEN STRUCTURES TO SAVE WEIGHT AND MATERIAL.
MCT MAR 2018 (1ST QRT)
MCT SEP 2018 (3RD QRT) WHOS WHO OF METALS