ENT 244 Manufacturing Engineering Processes Rapid Prototyping Processes

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ENT 244 Manufacturing Engineering Processes Rapid Prototyping Processes and Operations by IMADUDDIN HELMI WAN

ENT 244 Manufacturing Engineering Processes Rapid Prototyping Processes and Operations by IMADUDDIN HELMI WAN NORDIN Copyright © 2010 Pearson Education South Asia Pte Ltd

Introduction q q q There is need to produce a single prototype of a

Introduction q q q There is need to produce a single prototype of a designed part or system before investing into assembly lines Main reasons are high capital cost and long preparation time for tooling and production setup A technology that speeds up the iterative productdevelopment process is rapid prototyping (RP)

Introduction q Development of a new product, a need to produce a single example,

Introduction q Development of a new product, a need to produce a single example, or prototype, of a designed part, before allocation of large amount of product. A new technology which considerably speeds the iterative product development process is the concept and practice of rapid prototyping. To make prototype in minimum possible lead times based on a CAD model of the item. The traditional method (machining) require several weeks, sometimes longer, depending on part complexity and difficulty in ordering materials. The designer can therefore visually examine and physically feel the part and begin to perform tests and experiments to assess its merits and shortcomings.

Introduction q 1. 2. 3. 4. q The advantages rapid prototyping (RP) are: Physical

Introduction q 1. 2. 3. 4. q The advantages rapid prototyping (RP) are: Physical models of parts can be produced from CAD data files Prototype can be used to produce the final parts Prototype can be used in subsequent manufacturing RP can produce actual tooling for manufacturing operations Rapid-prototyping processes can be classified into subtractive, additive, and virtual group

Introduction q Subtractive Process - material removal from a workpiece that is larger than

Introduction q Subtractive Process - material removal from a workpiece that is larger than the final part - involves machining, primarily milling and turning, using dedicated Computer Numerical Control (CNC) machine. The CNC milling machine then contours the part layer by layer from a solid block of starting material q Additive Process - all of which work by adding layers of material one at a time to build the solid part from bottom to top. - starting materials include (1) liquid monomers that are cured layer by layer into solid polymers, (2) powders that are aggregated and bonded layer by layer, and (3) solid sheets that are laminated to create the solid part.

Introduction Virtual prototyping q a software form of prototyping that uses advanced graphics and

Introduction Virtual prototyping q a software form of prototyping that uses advanced graphics and virtual-reality environments to allow designers to examine a part q Uses complex software and three-dimensional graphics routines q It has the advantage of affording an instantaneous rendering of parts for evaluation q More advanced systems are costly and have very steep learning curves

Introduction

Introduction

Introduction

Introduction

Subtractive Processes q q q Making a prototype can take from weeks to months

Subtractive Processes q q q Making a prototype can take from weeks to months depending on part complexity and size Requires skilled operators using material removal by machining and finishing operations To speed up the process, subtractive processes are used: 1. Computer-based drafting packages 2. Interpretation software 3. Manufacturing software 4. Computer-numerical-control (CNC) machinery

Additive Processes q Additive rapid-prototyping operations consist of 1. Stereolithography 2. Multijet/polyjet modeling 3.

Additive Processes q Additive rapid-prototyping operations consist of 1. Stereolithography 2. Multijet/polyjet modeling 3. Fused-deposition modeling 4. Ballistic-particle manufacturing 5. Three-dimensional printing 6. Selective laser sintering 7. Electron-beam 8. Laminated-object manufacturing

Rapid Prototyping Technologies • The classification method is based on the form of the

Rapid Prototyping Technologies • The classification method is based on the form of the starting material in the RP process: (1) liquid-based, (2) solid-based, and (3) powder-based. Liquid-Based Rapid Prototyping Systems • Stereolithography (SLA). SLA is a process based on the principal of hardening (curing) a liquid photopolymer, using a directed laser beam to solidify polymer into a specific shape. • Containing a mechanism whereby a platform can be lowered and raised, is filled with a photocurable liquid acrylate polymer. • The liquid is a mixture of acrylic monomers, oligomers (polymer intermediates) and a photoinitiator. • When the platform is at its highest position, depth-a, the layer of liquid above it is shallow. • A laser generating an ultraviolet beam, is now focused upon a selected surface area of the photopolymer and then moved in the x-y direction.

Figure 6. 1: Schematic illustration of the stereolithography process and part of SLA

Figure 6. 1: Schematic illustration of the stereolithography process and part of SLA

 • The beam cures that portion of the photopolymer and thereby produces a

• The beam cures that portion of the photopolymer and thereby produces a solid body. • The platform is then lowered sufficiently to cover the cured polymer, and the sequence is repeated. The process is repeated until level-b is reached. • Generate a cylindrical part with a constant wall thickness, the platform is now lowered by a vertical distance-ab. • At level-b, the x-y movements of the beam are wider, a flange-shaped portion that is being produced. • Process is repeated, producing another cylindrical section between levels-b and c. • Tolerance depends on sharpness of the laser, typically 0. 0125 mm. • Cycle times range from a few hours to a day. • Maximum part size is 0. 5 m x 0. 6 m.

Additive Processes: Stereolithography q q This process is based on the principle of curing

Additive Processes: Stereolithography q q This process is based on the principle of curing (hardening) a liquid photopolymer into a specific shape A laser generating an ultraviolet (UV) beam is focused upon a selected surface area of the photopolymer and then moved around in the x–y plane

Additive Processes: Stereolithography q q Solid parts can be produced by applying special laserscanning

Additive Processes: Stereolithography q q Solid parts can be produced by applying special laserscanning patterns to speed up production Total cycle times range from a few hours to a day Used with highly focused lasers to produce parts with micrometer-sized features When used to fabricate micromechanical systems, it is called microstereolithography

Solid-Based Rapid Prototyping Systems • Fused-Deposition Modeling (FDM). FDM is an RP process in

Solid-Based Rapid Prototyping Systems • Fused-Deposition Modeling (FDM). FDM is an RP process in which a filament of wax or polymer is extruded onto the existing part surface from a workhead to complete each new layer. • The workhead is controlled in the x-y plane during each layer and then moves up by a distance equal to one layer in the z-direction. • The starting material is a solid filament with typical diameter = 1. 25 mm fed from a spool into the workhead that heats the material to about 0. 5ºC above its melting point before extruding in onto the part surface. • The extrudate is solidified and cold welded to the cooler part surface in about 0. 1 second. • If support are needed, a dual extrusion head and a different material is used to create the supports. The second material is designed to readily be separated from the primary modeling material. • The layer thickness can be set anywhere from 0. 05 to 0. 75 mm. • About 400 mm of filament material can be deposited per second by the extrusion workhead in widths (road with) that can be set between 0. 25 and 2. 5 mm.

Figure 6. 3: Schematic illustration of the fused deposition modeling process

Figure 6. 3: Schematic illustration of the fused deposition modeling process

Additive Processes: Fused-deposition Modeling q In the fused-deposition-modeling (FDM) process, a gantry robot–controlled extruder

Additive Processes: Fused-deposition Modeling q In the fused-deposition-modeling (FDM) process, a gantry robot–controlled extruder head moves in two principal directions

Additive Processes: Fused-deposition Modeling q q Some of the common support structures used in

Additive Processes: Fused-deposition Modeling q q Some of the common support structures used in rapidprototyping machines The layers in an FDM model are determined by the extrusion-die diameter This thickness represents the best achievable tolerance in the vertical direction Flat wire metal deposition uses a metal wire instead of a polymer filament

 • Three-Dimensional Printing (3 DP). 3 DP builds the parts in the usual

• Three-Dimensional Printing (3 DP). 3 DP builds the parts in the usual layer-bylayer fashion using an ink-jet printer to eject an adhesive bonding material onto successive layers of powders. • The binder is deposited in areas corresponding to the cross sections of the solid part, as determined by slicing the CAD geometric model into layers. • The binder holds powders together to form the solid part, while the unbonded powders remain loose to be removed later. • While the loose powders are in place during the build process, they provide support for overhanging and fragile features of the part. • When the build process is completed, the part is heat treated to strengthen the bonding, followed by removal of the loose powders. • To further strengthen the part, a sintering step can be applied to bond the individual powers. • 3 DP process can be described: ~ a layer of powder is spread on the existing part-in-process. ~ an ink-jet printing head moves across the surface, ejecting droplets of binder on those regions that are to become the solid part. ~ when the printing of the current layer is completed, the piston lowers that platform for the next layer.

 • The starting material in 3 DP are powders of ceramic, metal, or

• The starting material in 3 DP are powders of ceramic, metal, or cermet, and binders that are polymeric silica or silicon carbide. • Typical layer thickness ranges from 0. 10 to 0. 18 mm. Figure 6. 6: Schematic illustration of the three-dimensional printing process

6. 4 Application Issues in Rapid Prototyping • Design. This was the initial application

6. 4 Application Issues in Rapid Prototyping • Design. This was the initial application area for RP systems. Designers are able to confirm their design by building a real physical model in minimum time using rapid prototyping. • Benefits it’s (1) reduced lead times to produce prototype components, (2) improved ability to visualize the part geometry due its physical existence, (3) earlier detection and reduction of design errors, and (4) increased capability to compute mass properties of components and assemblies. • Engineering Analysis and Planning. Existence of part allows certain engineering analysis and planning activities to be accomplished that would be more difficult without the physical entity. • Some of the possibilities are: (1)Comparison of different shapes and styles to determine aesthetic appeal of the part, (2) analysis of fluid flow through different orifice shapes using physical in valves fabricated by RP, (3)stress analysis of a physical model, and (4) fabrication of preproduction parts by RP as an aid in process planning and tool design.

 • Tooling and Manufacturing. The trend in RP applications is toward its greater

• Tooling and Manufacturing. The trend in RP applications is toward its greater use in the fabrication of production tooling and in the actual manufacture of parts. • Called rapid tool making (RTM) when RP is used to fabricate production tooling. Two approach for RTM: (1) indirect RTM, in which a pattern is created by RP and the pattern is used to fabricate the tool, and (2) direct RTM, in which RP is used to make the tool itself. • Examples of indirect RTM include RP patterns for sand molds in sand casting and making electrodes for EDM. • Examples of direct RTM include 3 DP to create a die of metal powders followed by sintering and infiltration to complete the die. • The problems with rapid prototyping include part accuracy, limited variety of material, and mechanical performance.

Table 6. 1: characteristics of Rapid Prototyping Technologies

Table 6. 1: characteristics of Rapid Prototyping Technologies