Tech/ME 140 Lecture 3. Design Process, DFM/DFA, and Rapid Prototyping Techniques. Product Development Process. The Design Process. Has 5 Steps: Step 1: Conceptualization Step 2: Synthesis Step 3: Analysis Step 4: Evaluation Step 5: Documentation. Divided into two: Typical design and
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Design Process, DFM/DFA, and Rapid Prototyping Techniques
Typical design and
Typical design relates to repetitive design
Atypical design is for new product:
May involve market study or research to determine customers’ need or other need
May also emerge from request from customers
Can be other unexpected opportunitiesStep 1: Conceptualization Or Recognition of Need & Definition of the Problem
Definition: DFM is the method of design for ease of manufacturing of the collection of parts that will form the product after assembly.
Easy and cost efficient to manufacture
Applies to all manufacturing processes
It is relative to:
Material Form and Shape
Design and Shape
Symmetry eliminates reorientation
Symmetry of a part
makes assembly easier
Definition: DFA is the method of design of the product for ease of assembly.
A process by which products are designed with the following in mind:
Ease of assembly
Contains fewer parts
Takes less time to assemble
Reduces assembly costs
Easy orientation and insertion of parts
‘..If more than 1/3 of the components in a product are fasteners, the assembly logic should be questioned.’
Not all designs can be machined by all machines
Design must align with machining process
Machining process must align with part form
Material must match machine selected
Material size must fit machine selected
Solid cylindrical parts with multiple shapes
Solid tapered parts with multiple shapes
Prototypes of few orders
Automated process for small hardware items like screws, nuts, bolts etc.
Milling is for solid prismatic parts
Ideal for multi-axis machines
Ideal for multi-sided parts
Ideal for complex prototypes
Best/simplest available process
Avoid too complex designs when possible
The need for rounds and fillets
The fact that plastic materials are in various forms and shapes
Using biodegradable plastics when possible
The difference in thermoplastics and thermosets
Using only recyclable plastics when possible
Stereolithography (SLA) is the most widely used type of rapid prototyping. Stereolithography produces 3D parts by curing successive layers of UV-curable resin. The parts of the resin that the laser cures in each layer are defined by a CAD model of the part. Because of the accuracy and ability to produce highly detailed parts, Stereolithography is excellent for concept models, masters, assemblies, and patterns for investment casting.
Solid Ground Curing (SGC), is somewhat similar to stereolithography (SLA) in that both use ultraviolet light to selectively harden photosensitive polymers. Unlike SLA, SGC cures an entire layer at a time. First, photosensitive resin is sprayed on the build platform. Next, the machine develops a photomask (like a stencil) of the layer to be built. This photomask is printed on a glass plate above the build platform using an electrostatic process similar to that found in photocopiers. The mask is then exposed to UV light, which only passes through the transparent portions of the mask to selectively harden the shape of the current layer.
FDM is one method to develop rapid prototypes or models. The FDM machine builds the part by extruding a semi-molten filament through a heated nozzle in a prescribed pattern onto a platform. ... available from Stratasys, the inventor of Fused Deposition Modeling technology
In Selective Laser Sintering (SLS), thermoplastic powder is spread by a roller over the surface of a build cylinder. The piston in the cylinder moves down one object layer thickness to accommodate the new layer of powder. The powder delivery system is similar in function to the build cylinder. Here, a piston moves upward incrementally to supply a measured quantity of powder for each layer.
A laser beam is then traced over the surface of this tightly compacted powder to selectively melt and bond it to form a layer of the object. The fabrication chamber is maintained at a temperature just below the melting point of the powder so that heat from the laser need only elevate the temperature slightly to cause sintering. This greatly speeds up the process. The process is repeated until the entire object is fabricated.
Developed by BPM technology, it sprays
material (wax) in 0.002" drops at rates of 12,500 drops per sec to build up slices. The elevator drops as slices are formed. Variable slice thickness is set by changing the flow rate. Part material supports are made from water soluble wax (polyethelene glycol) and are removed after completion by placing the model in water.
3D Printing and Deposition Milling (3DP) is a low-end version of additive fabrication technology. One variation consists of an inkjet printing system. Layers of a fine powder (either cornstarch or plaster) are selectively bonded by "printing" a water-based adhesive from the inkjet printhead in the shape of each cross-section as determined by a CAD (computer aided design) file. Alternately, these machines feed liquids, such as photopolymer, into individual jets that deposit tiny droplets as they are scanned to form a layer of the model. The liquid hardens after being deposited. Materials available for spraying include glue, wax, and photopolymer. Photopolymer Phase machines employ an ultraviolet (UV) flood lamp mounted in the print head to cure each layer as it is deposited.
Direct Shell Production Casting (DSPC) is a revolutionary patternless casting process for metal parts in which the casting molds are generated automatically, directly from 3-D CAD data. With DSPC there is no need for physical patterns, core boxes or any other tooling, and no part-specific setup. The only "pattern" is the CAD design itself. DSPC enables production of a functional metal prototype or parts without a production tool. DSPC works by producing ceramic molds directly from a CAD file, which are then poured with any metal alloy, obtaining a fully functional part in a matter of days. A ceramic mold can be made with an integral core, which separates it from other rapid prototyping methods that have no way of incorporating complex cores in their plastic, wax, or paper patterns. DSPC is a proprietary technology developed at Soligen. Its core technology is based on Three Dimensional Printing (3DP) a patented technology invented at the Massachusetts Institute of Technology (MIT), and licensed exclusively, on a worldwide basis, to Soligen for the metal casting field of use.