• RAPID PROTOTYPING PROCESSES

rapid protyping is fast becoming one of the essential technologies that allows manufacturers to improve product quality and reduce both time to market and the cost of new lines,as part of a concurrent engineering stategy s

KRUFTH CLASSIFICATION:

Basically Rapid Prototyping processes are classified into two main groups .

Here we are including the classifications in a tabular form .

TABLE.

MATERIAL ACCRETION

MATERIAL REMOVAL

Further Material Accretion processes are classified as follows

LIQUID-BASED

liquid based technologies may involve the solidification of a resin on contact with a laser,solidifying an electrosetting fluid, or melting and setting the prototype material.

DISCRETE PARTICLES

Processes using powders compound them either with a laser or by the selective application of binding agents.

SOLID SHEETS

Those processes that use solid sheets may be classified according to whether the sheets are bonded with a laser or with an adhesive.

INPUT: all the processes have input from a 3D solid CAD model,usually as slices.The designer therfore first uses a CAD package to design the product.This model is tessellated and exported as an STL file(the current industry standard for faceted models- although itmay be possible to slice models directly from the CAD file without first faceting them) some software may add supports,if necessary,to brace any over hangs .The model is then sliced and the slices sent to the RP machine for the production of the final part.

STEREOLITHOGRAPHY: This uses a photosensitive monomer resin that forms a polymer and this uses photo polymerising resins.Data from the CAD model are used to produce a mask,through which the entire layer can be illuminated with a UV lamp.This means that the resin is fully cured and no post curing is necessary.The excess resin is wiped away and any spaces are filled with wax.

LIQUID THERMAL POLYMERISATION: This is similar to SL except the resin is thermosetting and an infrared laser is used to create the voxels.

BEAM INTERFERENCE SOLIDIFICATION: This uses two laser beams mounted at right angles,emitting light at different frequencies to polymerise resin in a transparent vat.The first laser excites the liquid to a reversible metastable state,the second polymerises the excited resin

HOLOGRAPHIC INTERFERENCE SOLIDIFICATION: This promises to abandon the practice of building upthe model in slices,using a holographic image to solidify an entire surface.

ELECTROSETTING: This is a completely different,in which electrodes are printed onto a conductivematerial such as aluminium.Once all the layers have been printed,they are stacked,immersed in a bath of electrosetting fluid and energised.The fluid between the electrodes then solidifies to form the part;the unwanted aluminium may be trimmed from the part.

MOLTENMATERIAL: There arefour technologies that involve melting and solidification of the part material.

BALLISTIC PARTICLE MANUFACTURE: a stream of molten material is ejected from a nozzle;the material separates into droplets,which hit the substrate and immediately cold weld to form the part .A rough substrate ngives better thermal contact,which reduces stresses within the part.

FUSED DEPOSITION MODELLING: Machine consists of movable head to deposit a thread of molten material onto a substrate.The build material is heated to just above its melting point so that it solidifies immediately after extrusion and cold welds to the previous layers.The process requires a steady nozzles speed and material extrusion rate,and support for overhanging parts;the speed of the head affects the overall layer thickness.

THREE_DIMENSIONAL WELDING: this uses an arc-welding robot to deposit weld material on a platform as simple shapes,which may then be built into more complex structures.

MASKING AND DEPOSITING: This is an experminental layer-by-layer process involving spraying molten matal through a disposable mask cut from pressure-sensitive labelling paper.A negative mask is then placed over the part and a layer of support material with a low melting point is sprayed.Once the part is completed,the support material may be melted to leave the final prototype.