A Seminar report OnSolid Ground Curing Introduction Solid Ground Curing is a liquid based Rapid Prototyping technique developed in 1991 by Cubital Ltd. Cubital was found in 1987 as an internal R&D unit at Seitex Corporation Ltd. SGC is based on the principle of the photo polymerisation. Whole layer is polymerized at a time unlike “point by point” in Stereolithography. Solid Ground Curing, also known as the Solider Process, is a process that was invented and developed by Cubital Inc. of Israel. The SGC process uses photosensitive resin hardened in process uses photosensitive resin hardened in layers as with the Stereolithography (SLA) process. However, in contrast to SLA, the SGC process is considered a high-throughput production process. This is used to mask the uniform illumination of the UV lamp. from a liquid photopolymer resin that solidifies when exposed to UV light. a toner which adheres to the substrate electrostatically. only change being the whole layer is cured at a time. (8 times faster than other existing RP Processes) Principle The principle behind SCG process is Photo Polymerization and Mask Generation. Process is same as Stereolithography. layer by layer. Photo Polymerization: Parts are built. The image is formed by depositing black powder. offered good accuracy and a very high fabrication rate. Many parts can be created at once because of the large work space and the fact that a milling step maintains vertical accuracy. When . making the process faster. the electrostatic toner is removed from the substrate for reuse and the pattern for the next layer is similarly “printed” on the substrate. While the major advantage of the method is it. a process similar to the Xerography process used in photocopiers and laser printers. After exposure. The high throughput is achieved by hardening each layer of photosensitive resin at once. Mask Generation: The mask is created from the CAD data input and “printed” on a transparent substrate (the mask plate) by an nonimpact ionographic printing process. Polymerization is the process of linking small molecules (known as monomers) into chain-like larger molecules (known as polymers). after undergoing several complex chemical energy transformation steps. P•. . which are mixed with the monomers. Photoinitiator molecules. M. These molecules then react with a monomer molecule to form a polymerization initiating molecule. The source of a photochemically generated radical is a photoinitiator. with energy of hν . Once activated. a cross-linked polymer is said to be formed. are exposed to a UV source of actinic photons. forming longer molecules. PM•. which reacts with an actinic photon to produce the radicals that catalyze the polymerization process. The free-radical photopolymerization process is schematically presented in Figure below.the chain-like polymers are linked further to one another. additional monomer molecules go on to react in the chain propagation step. This is the chain initiation step. The photoinitiators absorb some of the photons and are in an excited state. Photo polymerization is polymerization initiated by a photochemical process whereby the starting point is usually the induction of energy from the radiation source. PMMM• until a chain inhibition process terminates the polymerization reaction. This catalyst is usually a free radical which may be generated either thermally or photochemically. Pi. Some of these are converted into reactive initiator molecules. A catalyst is required for polymerization to take place at a reasonable rate. Also. The photo polymerized molecules must also possess sufficient strength to remain structurally sound while the cured resin is subjected to various forces during recoating. the resulting polymer will be crosslinked.Fig. During polymerization. if the monomer molecules have three or more reactive chemical groups. Schematic for a simplified free-radical photo polymerization The longer the reaction is sustained. and this will generate an insoluble continuous network of molecules. it is important that the polymers are sufficiently cross-linked so that the polymerized molecules do not redissolve back into the liquid monomers. the higher will be the molecular weight of the resulting polymer. . The optical mask is then positioned precisely above the workpiece which already been spread with a thin layer of Liquid photopolymer and under a high power UV lamp (2000W) ready to be exposed.Process Fig. The Solider computer then slices the whole composition together into layers and generates a precise raster image of each layer. This image is sent to the mask plotting unit in the machine and a high resolution.) The process starts with the creation of three dimensional composition of the parts to be made in the next run and the definition of layer thickness. precise optical mask is generated by means of electrostatic charges and black toner powder. Solid Ground Curing process (Courtesy Cubital Ltd. . ready for the next cross section to be drawn. The pattern of the cross section of the model at this layer is fully cured due to the high power lamp and the length of exposure time. Now we have fully solid layer that is made partly from plastic and partly from wax. The workpiece now passes under a milling disk that trims off the layer's surface down to the desired thickness. A cold plate is lowered on to the surface of the layer. A thin layer of melted wax is then spread over the surface. . A new layer of liquid photopolymer is then spread and the whole process starts once again.A shutter is opened for about 3 seconds and the resin is exposed and cured by the light passing through the mask. Equipment The work station or the equipment manufactured by the cubital Ltd. cooling down the wax and solidifying it. creating a flat. The work piece now passes under an aerodynamic sucker that pumps away all the residual liquid from the surface. The wax is melted away in a microwave oven. Unexposed areas on the layer surface remain in liquid state. smooth surface ready for the next layer. filling all the voids and cavities left after the removal of the residual liquid. After the last layer is done. Is as shown in the figure below. which is actually a plate of glass. moves back to the mask plotting unit and is being discharged and erased. The mask. we have a block of wax. or by using a hot air gun or even using plain warm water and the finished model is ready for use. leaving behind only the cured pattern. within which the model or models are embedded. . The Solider 5600. General layout of a SCG Machine Models and Specifications Cubital’s products include the Solider 4600 and Solider 5600. Cubital’s sophisticated high-end system. provides a wider range and options for the varied modeling demands of Solid Ground Curing. The Solider 4600 is Cubital’s entry level three-dimensional model making system based on Solid Ground Curing. Table below summarizes the specifications of the two machines.Fig. accurate. and can be mechanically finished. This is due to the full curing of every layer. sturdy. they are much less brittle. Parallel Processing of several parts at a time. Minimum shrinkage effect. It has good fault tolerances. Unique part properties. It has a high speed throughput that is about eight times faster than its competitors. This is due to the curing process that minimizes the development of internal stresses in the structure. As a result.Advantages Parallel processing. Fig. High structural strength and stability. The solid wax supports the part in all dimensions and therefore a support structure is not required. Its production costs can be 25% to 50% lower. . Self-supporting. Removable trays allow job changing during a run and layers are erasable. Fault tolerance. machinable. The part that the Solider system produces is reliable. which have to be cleaned from the machine. Comparison with other RP Techniques The table below shows comparison of SCG with other RP Techniques with respect to different parameters.Disadvantages Requires large physical space. Thus. some wax may be left behind. It is difficult to remove wax from parts with intricate geometry. The size of the system is much larger than other systems with a similar build volume size. Waste material produced. Wax gets stuck in corners and crevices. Noisy. The milling process creates shavings. The Solider system generates a high level of noise as compared to other systems. . acrylic tooling. spray metal tooling. exhibitions and pre-production sales. Investment casting. functional analysis. operation and reconstruction planning and custom prosthesis design. design proofing. and inter-professional communication. integration and fitting. engineering testing. tool-free manufacturing of plastic parts. Diagnostic. sand casting. Tooling and casting applications. Silicon rubber tooling. Mold and tooling. and plaster mold casting. market research.Selection of the SCG Process The flow chart below shows when to select SCG process for rapid prototyping and when not to. and rapid. Applications General applications. Medical imaging. . epoxy tooling. surgical. Conceptual design presentation.