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ME170 CAD. Design for Manufacture Instructor: Mike L. Philpott [email protected] Including an introduction to Sheet Metal, Injection Molding of Plastics, and Rapid Prototyping.

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Design for manufacture instructor mike l philpott mphilpot@illinois edu

ME170

CAD

Design for ManufactureInstructor: Mike L. [email protected]

Including an introduction to Sheet Metal, Injection Molding of Plastics, and Rapid Prototyping


1990s DFMA software – stand alone software based on MTM standard times and empirical models (e.g. Boothroyd and Dewhurst)

Designers needed to know cost early in design to do what-if analysis and explore alternative designs before expensive hard tooling decisions finalized

Advent of solid modeling with access to full solid definition of the part and assembly

Design to Cost (DTC) strategies in place, due to high overseas competition, but no practical tools

Need to know early if cost targets are being met - redesign if necessary before its too late.

Design for Manufacture (DFM) Overview


Understanding Manufacturing Cost of Consumer Products standard times and empirical models (e.g. Boothroyd and Dewhurst)

– predominantly Sheet metal and Injection Molded Plastic

Look at retail prices…divide by 3!


Design for Manufacture (DFM) Example standard times and empirical models (e.g. Boothroyd and Dewhurst)

A simple fork end for Pneumatic Piston

Extrusion or Stock Channel

Machine from Solid

Casting

Welded Assembly

Sheet Metal

Injection Mold

Piece-part costs

Tooling costs

Production Volume: Recurring Costs versus Non-Recurring Costs


Design for assembly dfa fewer parts generally means lower overall mfg cost
Design for Assembly (DFA) standard times and empirical models (e.g. Boothroyd and Dewhurst)Fewer Parts generally means lower overall mfg.cost

Number of Parts: 24 8 4 2

Assembly Time (s): 100 38 10 3


Feature Based Costing (FBC) Research standard times and empirical models (e.g. Boothroyd and Dewhurst)

  • CAD-integrated feature recognition and extraction methodology to provide engineers with accurate real-time cost feedback during design.

  • Industry/University Collaborative research project: Started in 1992 with

  • UIUC / John Deere Collaboration - now commercialized www. aPriori.com*

aPriori

1. Cost Scripting Language

2. Parameterized machine, material, tooling and labor Database

Supplier

In-House

Virtual Production Environments

feature extraction algorithms

Physics Based Mechanistic Manufacturing

Process Models

(cycle times -> cost)

CAD Solid

Model

Geometric Cost Drivers

Routing Engine

Times and Costs

Non-Geometric Cost Drivers

User

Optimum manufacturing sequence automatically derived from CAD Solid Model based on deterministic routing logic and Genetic Algorithms

real-time cost feedback loop

* Philpott, M.L., “Integrated Real-Time Feature Based Costing (FBC),” U.S. Patent No. 7,065,420, June 20, 2006


Cost Accounting standard times and empirical models (e.g. Boothroyd and Dewhurst)

Insights and Cost Reduction Opportunities


Mechanistic Cost Models standard times and empirical models (e.g. Boothroyd and Dewhurst)Eg. Laser Process Model


Laser Cycle/Labor Time standard times and empirical models (e.g. Boothroyd and Dewhurst)

LaserCycleTime = Cutting Time + Piercing Time + Rapid Traverse Time + Scrap Cut Time

LaserLaborTime = LaserCycleTime * LaborStandard


Sheet metal process group
Sheet Metal standard times and empirical models (e.g. Boothroyd and Dewhurst)Process Group


Sheet Metal – Common Production Processes standard times and empirical models (e.g. Boothroyd and Dewhurst)

Soft Tooling - general purpose programmable machines with low-cost expendable tooling

Typical Routings: (as in aPriori)

Sheet Stock

[Bend Brake]

Laser cut

Sheet Stock

[Bend Brake]

Plasma cut

Sheet Stock

[Bend Brake]

Oxy Fuel

Sheet Stock

[Bend Brake]

Turret Press

Hard Tooling (aka Stamping) - Processes requiring custom made high-cost molds or die sets

Standard Press

Sheet Stock

Production Rate

Stage Tooling (aka Tandem die)

Sheet Stock

Large Stampings (eg car Body Panels)

Sheet Stock

Transfer Press

Progressive Die

Coil Stock

Small Stampings


Hard Tooling standard times and empirical models (e.g. Boothroyd and Dewhurst)

Sheet Metal - Progressive Die Set

Progressive Die Tool – a tool custom designed and built to produce stamped metal parts at high speed on a Progressive Die Press (a reciprocating press)


Progressive Die in Operation – 30 ppm standard times and empirical models (e.g. Boothroyd and Dewhurst)


Progressive Die in Operation – 100 ppm standard times and empirical models (e.g. Boothroyd and Dewhurst)

Used for Small High-Volume Stampings


Stamping die i e tooling example
Stamping Die standard times and empirical models (e.g. Boothroyd and Dewhurst)(i.e. Tooling)Example


Transfer Press in Operation standard times and empirical models (e.g. Boothroyd and Dewhurst)

Used for Large High-Volume Stampings


Standard press manual presses operated in batch mode typically low to medium volume applications
Standard Press standard times and empirical models (e.g. Boothroyd and Dewhurst)- manual presses operated in batch mode, typically low-to-medium volume applications


Stage Tooling standard times and empirical models (e.g. Boothroyd and Dewhurst)– manual presses organized in a production line with manual transfer of parts between presses (popular in low labor cost countries, non-automotive)


Progressive Die standard times and empirical models (e.g. Boothroyd and Dewhurst)– coil fed, automatic, high-speed single press with multiple stations; coil strip transfers the part


Tandem Die standard times and empirical models (e.g. Boothroyd and Dewhurst)- manual or automatic presses organized in a production line manual or robotic transfer of parts between presses (often a mix of manual or robotic)


Transfer Press standard times and empirical models (e.g. Boothroyd and Dewhurst)– sheet fed, single press action with multiple dies attached to platen and transfer mechanism


Sheet Metal – Common Production Processes standard times and empirical models (e.g. Boothroyd and Dewhurst)

Soft Tooling - general purpose programmable machines with low-cost expendable tooling

Typical Routings: (as in aPriori)

Sheet Stock

[Bend Brake]

Laser cut

Sheet Stock

[Bend Brake]

Plasma cut

Sheet Stock

[Bend Brake]

Oxy Fuel

Sheet Stock

[Bend Brake]

Turret Press

Hard Tooling (aka Stamping) - Processes requiring custom made high-cost molds or die sets

Standard Press

Sheet Stock

Production Rate

Stage Tooling (aka Tandem die)

Sheet Stock

Large Stampings (eg car Body Panels)

Sheet Stock

Transfer Press

Progressive Die

Coil Stock

Small Stampings


Turret Press Process standard times and empirical models (e.g. Boothroyd and Dewhurst)‘Soft Tooling’ for straight bends – No Custom Tooling (ie no Hard Tooling)

Turret Press


Bend Brake Process standard times and empirical models (e.g. Boothroyd and Dewhurst)‘Soft Tooling’ for straight bends – No Custom Tooling (ie no Hard Tooling)

Bend Brake (aka Press Brake)


Bend Brake – safety! standard times and empirical models (e.g. Boothroyd and Dewhurst)


Plastic Molding standard times and empirical models (e.g. Boothroyd and Dewhurst)Injection Molding: Standard IM, Structural Foam Molding, Reaction Injection Molding (RIM)


Structural foam molding thick parts inch 6mm
Structural Foam Molding standard times and empirical models (e.g. Boothroyd and Dewhurst)Thick parts => ¼ inch (6mm)


Blow molding and rotational molding
Blow Molding and Rotational Molding standard times and empirical models (e.g. Boothroyd and Dewhurst)

Blow molding

Bottles and small disposable containers

Rotational molding

larger hollow shapes.


Injection Molding standard times and empirical models (e.g. Boothroyd and Dewhurst)

1. Mold Closes

2. Inject Plastic

3. Cooling

4. Mold Opens

Labor Cost = (Mold Close time + Injection Time + Cooling Time + Mold Open time) * $/hr rate


The Mold standard times and empirical models (e.g. Boothroyd and Dewhurst)

(Tooling)

Tooling Cost = Cost to design and build this mold tool


Moving Side Cores or ‘Slides’ standard times and empirical models (e.g. Boothroyd and Dewhurst)


Moving Internal Cores or ‘Lifters’ standard times and empirical models (e.g. Boothroyd and Dewhurst)


Avoiding Moving Side Cores and Lifters (1) standard times and empirical models (e.g. Boothroyd and Dewhurst)


Avoiding Moving Side Cores and Lifters (2) standard times and empirical models (e.g. Boothroyd and Dewhurst)


Polypropylene (1.5¢/cu. in): standard times and empirical models (e.g. Boothroyd and Dewhurst)Outstanding resistance to flex and stress cracking. Excellent chemical resistance and electrical properties., Good impact strength above 15ºF. Good thermal stability, light weight, low cost. Some grades can be electroplated.

Common Thermoplastic Materials (1)

4

Polyethylene - HDPE & LDPE (1.2¢/cu. in)

Lightweight, easy to process, low cost material. Poor dimensional stability and heat resistance. Excellent chemical resistance and electrical properties.

LDPE

2

HDPE

5

PP

Polystyrene (1.7¢/cu. in): Low cost, easy to process, rigid, crystal-clear, brittle. Low moisture absorption, and heat resistance. Poor outdoor stability.

6

PS


PVC (2.2¢/cu. in): standard times and empirical models (e.g. Boothroyd and Dewhurst)Rigid grades are hard, tough, and have excellent electrical properties, outdoor stability, and resistance to moisture and chemicals. Flexible grades are easier to process but have lower properties. Heat resistance is low, and low cost.

Common Thermoplastic Materials (2)

3

V

ABS (2.9¢/in3): Very Tough, hard, and rigid. Fair Chemical resistance. Low Water absorption and good dimensional stability. High abrasion resistance. Some grades are easily electroplated.

Acrylic (3.1¢/cu. in) Hard , glossy surface and high optical clarity. Fair Chemical resistance. Excellent resistance to outdoor weathering. Available in brilliant, transparent colors. Excellent electrical properties.


Acetal (5.8¢/cu. in) standard times and empirical models (e.g. Boothroyd and Dewhurst)

Very Strong, stiff, and low tendency to stress crack. High resistance to chemicals. Retains most properties when immersed in hot water. Exceptional dimensional stability. High abrasion resistance. Low coefficient of Friction.

Common Thermoplastic Materials (3)

PETE (4.9¢/cu. in)

Crystal clear and hard. Used widely for shampoo bottles. Good moisture, and chemical resistance. Good dimensional stability.

1

PETE

7

Other

Polyurethane (6.1¢/cu. in)

Tough, extremely abrasion and impact-resistant. Good electrical properties and chemical resistance. UV exposure causes brittleness, lower properties, and yellowing.


Nylon (6/6-5.9 ¢/cu. in;6/12 - 9.0 ¢/cu. in; +glass -16.3¢/cu. in): Family with outstanding toughness and wear resistance. Low Coefficient of Friction. Excellent chemical resistance and electrical properties. Hygroscopic; dimensional stability is poor. Some grades are electroplatable.

Common Thermoplastic Materials (4)

Polycarbonate (6.3 ¢/cu. in): Highest impact resistance of any rigid, transparent plastic. Excellent outdoor stability and resistance to creep under load. Fair chemical resistance. Some aromatic solvents cause stress cracking.

Fluoroplastics (30 - 65¢/cu. in): PTFE, FEP, PVDF etc. Family of high cost, low-to-moderate strength. Excellent chemical resistance. Low Friction. Outstanding stability at high temperatures.


Rapid prototyping process group
Rapid Prototyping +glass -16.3¢/cu. in): Process Group


Rapid prototyping principles
Rapid Prototyping +glass -16.3¢/cu. in): Principles

SLA

3D Printing

SLS


StereoLithography (STL) +glass -16.3¢/cu. in):

Selective Laser Sintering (SLS)

Fused Deposition Modeling (FDM)

Laminated Object Manufacturing

Polyjet

Hot Plot

Solid Ground Curing

Light Sculpting

Solid Creation System

Solid Object Ultra-Violet Laser Plotting

Computer Operated Laser Active Modeling

Electro-Optical Systems - Stereos

Rapid Prototyping Systems


Rapid Prototyping at BMW +glass -16.3¢/cu. in):

Cool video (click on pics)


Rapid Prototyping +glass -16.3¢/cu. in):

MechSE Ford Lab


Stereo-Lithography Apparatus (SLA) +glass -16.3¢/cu. in):


Polyjet Process +glass -16.3¢/cu. in):


SLS - Sintered Laser System +glass -16.3¢/cu. in):


EOS – Direct Metal Laser Sintering +glass -16.3¢/cu. in):


3D Scanning & +glass -16.3¢/cu. in):

FDM – Fused Deposition Modeling


STL Format: +glass -16.3¢/cu. in): B-rep, solid object

  • An STL file is saved with the extension “.stl," case-insensitive.

  • STL is a triangular facet based representation that approximates surface and solid entities only. Entities such as points, lines, curves, and attributes such as layer and color will be ignored during the output process

  • An STL file consists of a list of facet data.

  • Each facet is uniquely identified by a unit normal (a line perpendicular to the triangle and with a length of 1.0) and by three vertices (corners).

  • The normal and each vertex are specified by three coordinates each, so there is a total of 12 numbers stored for each facet.


BLOCK +glass -16.3¢/cu. in):

facet normal 0.000000e+00 -1.000000e+00 0.000000e+00

outer loop

vertex 0.000000e+00 0.000000e+00 -1.000000e+00

vertex 1.000000e+00 0.000000e+00 0.000000e+00

vertex 0.000000e+00 0.000000e+00 0.000000e+00

endloop

endfacet

facet normal 0.000000e+00 0.000000e+00 1.000000e+00

outer loop

vertex 1.000000e+00 1.000000e+00 0.000000e+00

vertex 0.000000e+00 0.000000e+00 0.000000e+00

vertex 1.000000e+00 0.000000e+00 0.000000e+00

endloop

endfacet

facet normal -1.000000e+00 0.000000e+00 0.000000e+00

outer loop

vertex 0.000000e+00 1.000000e+00 0.000000e+00

vertex 0.000000e+00 0.000000e+00 -1.000000e+00

vertex 0.000000e+00 0.000000e+00 0.000000e+00

endloop

endfacet

facet normal 0.000000e+00 0.000000e+00 1.000000e+00

outer loop

vertex 1.000000e+00 1.000000e+00 0.000000e+00

vertex 0.000000e+00 1.000000e+00 0.000000e+00

vertex 0.000000e+00 0.000000e+00 0.000000e+00

endloop

endfacet

facet normal 0.000000e+00 -1.000000e+00 0.000000e+00

outer loop

vertex 0.000000e+00 0.000000e+00 -1.000000e+00

vertex 1.000000e+00 0.000000e+00 -1.000000e+00

vertex 1.000000e+00 0.000000e+00 0.000000e+00

endloop

endfacet

facet normal 1.000000e+00 0.000000e+00 0.000000e+00

outer loop

vertex 1.000000e+00 1.000000e+00 -1.000000e+00

vertex 1.000000e+00 0.000000e+00 0.000000e+00

vertex 1.000000e+00 0.000000e+00 -1.000000e+00

endloop

endfacet

facet normal 1.000000e+00 0.000000e+00 0.000000e+00

outer loop

vertex 1.000000e+00 1.000000e+00 0.000000e+00

vertex 1.000000e+00 0.000000e+00 0.000000e+00

vertex 1.000000e+00 1.000000e+00 -1.000000e+00

endloop

endfacet

facet normal 0.000000e+00 0.000000e+00 -1.000000e+00

outer loop

vertex 0.000000e+00 1.000000e+00 -1.000000e+00

vertex 1.000000e+00 0.000000e+00 -1.000000e+00

vertex 0.000000e+00 0.000000e+00 -1.000000e+00

endloop

endfacet

facet normal 0.000000e+00 0.000000e+00 -1.000000e+00

outer loop

vertex 1.000000e+00 1.000000e+00 -1.000000e+00

vertex 1.000000e+00 0.000000e+00 -1.000000e+00

vertex 0.000000e+00 1.000000e+00 -1.000000e+00

endloop

endfacet

facet normal -1.000000e+00 0.000000e+00 0.000000e+00

outer loop

vertex 0.000000e+00 1.000000e+00 -1.000000e+00

vertex 0.000000e+00 0.000000e+00 -1.000000e+00

vertex 0.000000e+00 1.000000e+00 0.000000e+00

endloop

endfacet

facet normal 0.000000e+00 1.000000e+00 0.000000e+00

outer loop

vertex 1.000000e+00 1.000000e+00 -1.000000e+00

vertex 0.000000e+00 1.000000e+00 -1.000000e+00

vertex 0.000000e+00 1.000000e+00 0.000000e+00

endloop

endfacet

facet normal 0.000000e+00 1.000000e+00 0.000000e+00

outer loop

vertex 1.000000e+00 1.000000e+00 0.000000e+00

vertex 1.000000e+00 1.000000e+00 -1.000000e+00

vertex 0.000000e+00 1.000000e+00 0.000000e+00

endloop

endfacet

endsolid BLOCK

An Example STL File – Block.stl


The density of triangle facets change according to the geometry

And it Changes with Chord Height affecting final surface resolution


STL Format: geometryB-rep, solid object

  • There are two storage formats available for STL files, which are Ascii and Binary. ASCII file is human-readable but larger than binary

  • Each facet is part of the boundary between the interior and the exterior of the object. The orientation of the facets (which way is "out" and which way is "in") is specified redundantly

  • First, the direction of the normal is outward. Second, which is most commonly used now-a-day, list the facet vertexes in counter- clockwise order when looking at the object from the outside (right-hand rule).


Vertex to geometryVertexRule

Each triangle must share two vertices with each of its adjacent triangles. In other words, a vertex of one triangle cannot lie on the side of another.

  • to check:

    • F must be even

    • E must be a multiple of three

    • 2*E must equal 3*F

      F, E, V, and B are the number of faces, edges, vertices, and separate solid bodies.

A violation of the vertex-to-vertex rule.


“Leaky” Models geometry

Two facets crossed in the 3D space.

The triangulated edge of two surface patch do not match, thus produce gaps between faces.

All facets in a STL data file should construct one or more non-manifold entities according to Euler's Rule for legal solids:

F-E+V=2B

F, E, V, and B are the number of faces, edges, vertices, and separate solid bodies.

If the relation does not hold, we say that the STL model is 'leaky'. When a 'leaky' STL file is processed by slicing algorithms, the result produces slice boundaries that are not fully closed.


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