1 Unstructured data for injection molding* Finding information with - - PDF document

SLIDE 1

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ME 474-674 Winter 2008 Slides 7 -1

More info: “Materials Selection in Mechanical Design”, Chapters 7 and 8

Process Selection

Processes and their attributes Screening by attributes Selecting shape-forming processes Selecting joining processes Selecting surface-treatment processes Case study + demos

ME 474-674 Winter 2008 Slides 7 -2

Manufacturing processes

The text book classified manufacturing processes into three broad

categories

• Shaping
• Joining
• Surface treatment

Each has many sub-categories, which may then be further subdivided

into individual processes

Many processes are used in combination with others

• Manufacturing process selection involves identifying which will

work best for a particular application

ME 474-674 Winter 2008 Slides 7 -3

Examples of processes

Sand casting

Shaping

Blow moulding

Shaping

Fusion welding

Joining

Induction hardening

Surface treating

ME 474-674 Winter 2008 Slides 7 -4

Each family has attributes that differ. Family

Joining Shaping Surfacing

Data organization: the PROCESS TREE

Kingdom

Process

data-table Class

Casting Deformation Molding Composite Powder Rapid prototyping

Member

Compression Rotation Injection RTM Blow

Attributes

Process records

RTM

Material Shape Size Range

• Min. section

Tolerance Roughness Economic batch Documentation

• - specific
• - general

RTM

Material Shape Size Range

• Min. section

Tolerance Roughness Economic batch Documentation

• - specific
• - general

Blow molding

Material Shape Size Range

• Min. section

Tolerance Roughness Economic batch Documentation

• - specific
• - general

Blow molding

Material Shape Size Range

• Min. section

Tolerance Roughness Economic batch Documentation

• - specific
• - general

Injection molding

Material Shape Size Range

• Min. section

Tolerance Roughness Economic batch Documentation

• - specific
• - general

Injection molding

Material Shape Size Range

• Min. section

Tolerance Roughness Economic batch Documentation

• - specific
• - general

Difficult !

ME 474-674 Winter 2008 Slides 7 -5

Shape classification

Wire drawing, extrusion,

rolling, shape rolling: prismatic shapes

Casting, molding,

powder methods: 3-D shapes

Stamping, folding,

spinning, deep drawing: sheet shapes

Some processes can make only simple shapes, others, complex shapes.

ME 474-674 Winter 2008 Slides 7 -6

Structured data for injection molding*

INJECTION MOULDING of thermoplastics is the equivalent of pressure die casting of metals. Molten polymer

is injected under high pressure into a cold steel mould. The polymer solidifies under pressure and the molding is then ejected.

Injection molding (Thermoplastics)

*Using the CES EduPack Level 2 DB

Process characteristics

Discrete True Prototyping False

Economic Attributes

Economic batch size 1e+004 - 1e+006 Relative tooling cost high Relative equipment cost high

+ links to materials

Shape

Circular Prism True Non-circular Prism True Solid 3-D True Hollow 3-D True

Physical attributes

Mass range 0.01- 25 kg Roughness 0.2 - 1.6 µm Section thickness 0.4 - 6.3 mm Tolerance 0.1 - 1 mm

Cost modeling

Relative cost index

fx fx Typical uses

Injection molding is used ……….

Key physical factors in choosing a shaping process (economics always important)

SLIDE 2

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ME 474-674 Winter 2008 Slides 7 -7

Unstructured data for injection molding*

Design guidelines. Injection moulding is the best way to mass-produce small, precise, plastic parts with complex shapes. The surface finish is good; texture and pattern can be moulded in, and fine detail reproduces well. The only finishing operation is the removal of the sprue. The economics. Capital cost are medium to high; tooling costs are high, making injection moulding economic only for large batch-sizes (typically 5000 to 1 million). Production rate can be high particularly for small mouldings. Multi-cavity moulds are

• ften used. The process is used almost exclusively for large volume production. Prototype mouldings can be made using

cheaper single cavity moulds of cheaper materials. Quality can be high but may be traded off against production rate. Process may also be used with thermosets and rubbers. Typical uses. The applications, of great variety, include: housings, containers, covers, knobs, tool handles, plumbing fittings, lenses, etc. The environment. Thermoplastic sprues can be recycled. Extraction may be required for volatile fumes. Significant dust exposures may occur in the formulation of the resins. Thermostatic controller malfunctions can be extremely hazardous. The process. Most small, complex plastic parts you pick up – children’s toys, CD cases, telephones – are injection moulded. Injection moulding of thermoplastics is the equivalent of pressure die casting of metals. Molten polymer is injected under high pressure into a cold steel mould. The polymer solidifies under pressure and the moulding is then ejected. Various types of injection moulding machines exist, but the most common in use today is the reciprocating screw machine, shown schematically here. Polymer granules are fed into a spiral press like a heated meat-mincer where they mix and soften to a putty- like goo that can be forced through one or more feed-channels (“sprues”) into the die. Heater Screw Granular Polymer Mould Nozzle Cylinder No.8-CMYK-5/01 *Using the CES EduPack Level 2 DB ME 474-674 Winter 2008 Slides 7 -8

Finding information with CES

Browse Select Search Toolbar Print Search web

File Edit View Select Tools Find what? Which table?

SLS Processes RTM

Joining Shaping Surface treatment

ProcessUniverse

+ + + Table: ProcessUniverse Table: ProcessUniverse Subset: Edu Level 2 Subset: Edu Level 2

ME 474-674 Winter 2008 Slides 7 -9

Process Selection

Like materials selection, process selection also has the same 4 basic steps Once a material is selected, it becomes one of the constraints in process

selection Step 2 Screening: eliminate processes that cannot do the job Step 3 Ranking: find the processes that do the job most cheaply Step 4 Supporting information: explore pedigrees of top-ranked candidates Step 1 Translation: express design requirements as constraints & objectives Because there are thousands of variants of processes, supporting information plays a particularly important role

ME 474-674 Winter 2008 Slides 7 -10

Shape

Circular prismatic Non-circular prismatic Flat sheet etc

Physical attributes

Mass range kg Tolerance mm Roughness μm Material Ceramic Hybrid Metal Polymer

Ferrous Non-ferrous

B1 > B > B2

Batch size B

Selection by series of screening stages

Browse Select Search

• 1. Selection data

Edu Level 2: Processes - shaping Edu Level 2: Processes - shaping

• 2. Selection Stages

Graph Limit Tree

Results

X out of 60 pass

Process 1 Process 2 Process 3 Process 4 Process 5

……….. 0.2 100 0.5 0.3

ME 474-674 Winter 2008 Slides 7 -11

Example of the Translation step

Example: Casing for a capacitance pressure sensor for use as a traffic sensor Function

Casing for road-pressure sensor

Constraints

Material: Al alloy Shape: non-circular prismatic Minimum section: 2 ± 0.025 mm

Objectives

Minimize cost

Free variable

Choice of process The sensor lies across the road, covered by a rubber mat. Vehicle pressure deflects top face, changing capacitance between top face and copper conducting strip.

ME 474-674 Winter 2008 Slides 7 -12

Spark-plug insulator: translation

Mass

0.05 kg

Section

3 - 5 mm

Tolerance

< 0.5 mm

Roughness

< 100 μm

Batch size

>2,000,000

Material class

Alumina

Shape class

3-D, hollow

Constraints Free variable

Choice of process

Body shell Insulator Central electrode

Make 2,000,000 insulators from alumina with given

shape dimensions tolerance and surface roughness

Design requirements

Insulator

Translation of design requirements Function

SLIDE 3

3

ME 474-674 Winter 2008 Slides 7 -13

3 Economic attributes Physical attributes

Mass range Range of sect. thickness kg

• Tolerance

Roughness

Shape

mm mm μ m

• Hollow, 3 D

Economic batch size

• Materials

Ceramics Alumina Hybrids B-carbide Metals Silicon Polymers W-carbide

2

Spark-plug insulator: screening

Body shell Insulator Central electrode

Translation Select Level 2: Shaping processes

1

Mass

0.05 kg

Section 3 – 5 mm Tolerance < 0.5 mm Roughness < 100 μm Batch size >2,000,000 Material class Alumina Shape class 3-D, hollow

Constraints

b

0.06 0.04 3 5 0.5 100 2e6

ME 474-674 Winter 2008 Slides 7 -14

Rank on Processes based on batch size

Desired Batch Size

Economic batch size (units) 1 10 100 1000 10000 100000 1e6 1e7 1e8

Pressing and sintering Powder injection molding ME 474-674 Winter 2008 Slides 7 -15

The selection: two shaping processes

Powder pressing and sintering Powder injection molding

ME 474-674 Winter 2008 Slides 7 -16

Data organization: joining processes

Gas welding

Material Joint geometry Size Range Section thickness Relative cost ... Documentation

Gas welding

Material Joint geometry Size Range Section thickness Relative cost ... Documentation

Gas welding

Material Joint geometry Size Range Section thickness Relative cost ... Documentation

Gas welding

Material Joint geometry Size Range Section thickness Relative cost ... Documentation

Gas welding

Material Joint geometry Size Range Section thickness Relative cost ... Documentation

Gas welding

Material Joint geometry Size Range Section thickness Relative cost ... Documentation

Attributes

Adhesives Welding Fasteners Braze Solder Gas Arc e -beam ...

Class Member Family Kingdom

Surface treatment Joining Shaping

Processes

• Lap
• Butt
• Sleeve
• Scarf
• Tee

Joint geometry

ME 474-674 Winter 2008 Slides 7 -17

A joining record*

Gas Tungsten Arc (TIG)

Tungsten inert-gas (TIG) welding, the third of the Big Three (the others are MMA and MIG) is the cleanest and most precise, but also the most

• expensive. In one regard it is very like MIG welding: an arc is struck

between a non-consumable tungsten electrode and the work piece, shielded by inert gas (argon, helium, carbon dioxide) to protect the molten metal from contamination. But, in this case, the tungsten electrode is not consumed because of its extremely high melting

• temperature. Filler material is supplied separately as wire or rod. TIG

welding works well with thin sheet and can be used manually, but is easily automated.

Physical Attributes

Component size non-restricted Watertight/airtight True Demountable False Section thickness 0.7

• 8

mm

Economic Attributes

Relative tooling cost low Relative equipment cost medium Labor intensity low

Typical uses

TIG welding is used ………. *Using the CES EduPack Level 1 DB

+ links to materials

Joint geometry

Lap True Butt True Sleeve True Scarf True Tee

True

Materials

Ferrous metals

Key physical factors in choosing a joining process

Documentation

ME 474-674 Winter 2008 Slides 7 -18

Selection of Joining Processes

Joining -- the most important criteria are:

The material(s) to be joined The geometry of the joint

Apply these first, then add other constraints

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ME 474-674 Winter 2008 Slides 7 -19

Data organization: Surface treatment

Family Kingdom

Surface treatment Joining Shaping

Processes Class

Heat treat Paint/print Coat Polish Texture ...

Member

Electroplate Anodize Powder coat Metallize...

Attributes

Process records

Anodize

Material Why treatment? Coating thickness Surface hardness Relative cost ... Documentation

Anodize

Material Why treatment? Coating thickness Surface hardness Relative cost ... Documentation

Anodize

Material Why treatment? Coating thickness Surface hardness Relative cost ... Documentation

Anodize

Material Why treatment? Coating thickness Surface hardness Relative cost ... Documentation

Anodize

Material Function of treatment Coating thickness Surface hardness Relative cost ... Documentation

Anodize

Material Function of treatment Coating thickness Surface hardness Relative cost ... Documentation Thermal insulation Electrical insulation Color Texture Decoration …. Increased hardness Wear resistance Fatigue resistance Corrosion resistance Oxidation resistance

Function of treatment

ME 474-674 Winter 2008 Slides 7 -20

A surface-treatment record*

Induction and flame hardening

Take a medium or high carbon steel -- cheap, easily formed and machined -- and flash its surface temperature up into the austenitic phase-region, from which it is rapidly cooled from a gas or liquid jet, giving a martensitic surface

• layer. The result is a tough body with a hard, wear and fatigue resistant,

surface skin. Both processes allow the surface of carbon steels to be hardened with minimum distortion or oxidation. In induction hardening, a high frequency (up to 50kHz) electromagnetic field induces eddy-currents in the surface of the work-piece, locally heating it; the depth of hardening depends

• n the frequency. In flame hardening, heat is applied instead by high-

temperature gas burners, followed, as before, by rapid cooling.

Economic Attributes

Relative tooling cost low Relative equipment cost medium Labor intensity low *Using the CES EduPack Level 2 DB

+ links to materials Key physical factors in choosing a surface treatment

Physical Attributes

Curved surface coverage Very good Coating thickness 300

• 3e+003

µm Processing temperature 727

• 794

K Surface hardness 420

• 720

Vickers

Typical uses

Induction hardening is used …..

Function of treatment

Fatigue resistance Friction control Wear resistance Hardness

Documentation

ME 474-674 Winter 2008 Slides 7 -21

Selection of Surface Treatment Processes

Surface treatment -- the most important criteria are:

The purpose of the treatment The material to which it will be applied

Apply these first, then add other constraints

ME 474-674 Winter 2008 Slides 7 -22

The main points

• The structure allows easy searching for process data
• Select first on primary constraints
• Shaping:

material, shape, and batch size

• Joining:

material(s) and joint geometry

• Surface treatment: material and function of treatment
• Then add secondary constraints as needed.

Documentation in CES, and http://matdata.net

• Processes can be organized into a tree structure containing records for

structured data and supporting information

ME 474-674 Winter 2008 Slides 7 -23

The Process – Material matrix

A given process can shape, or join, or finish some materials but not

• thers.

Process – Material charts have a red dot to indicate that the pair are

compatible.

Processes that cannot shape the material of choice are non-starters.

ME 474-674 Winter 2008 Slides 7 -24

The Process – Material matrix

Figure 7.16

SLIDE 5

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ME 474-674 Winter 2008 Slides 7 -25

The Process – Shape matrix

Shape is the most difficult attribute to characterize. Many processes involve rotation or translation of a tool or of the work-piece.

These processes make parts that have axial symmetry, or translational symmetry.

• Turning creates axisymmetric (or circular) shapes;
• Extrusion, drawing and rolling make prismatic shapes, both circular and

non-circular.

Sheet-forming processes make flat shapes (stamping) or dished shapes (deep

drawing, bending).

Certain processes can make 3-dimensional shapes, and among these some

can make hollow shapes whereas others cannot.

The process-shape matrix displays the links between the two. If the process

cannot make the desired shape, it may be possible to combine it with a secondary process to give a process-chain that adds the additional features: casting followed by machining is an obvious example.

ME 474-674 Winter 2008 Slides 7 -26

Shape classification

Wire drawing, extrusion,

rolling, shape rolling: prismatic shapes

Casting, molding,

powder methods: 3-D shapes

Stamping, folding,

spinning, deep drawing: sheet shapes

Some processes can make only simple shapes, others, complex shapes. Figure 7.18

ME 474-674 Winter 2008 Slides 7 -27

The Process – Shape matrix

Figure 7.17

ME 474-674 Winter 2008 Slides 7 -28

The Process – Mass - range chart

The bar-chart on the next page shows the typical mass-range of components

that each processes can make.

Large components can be built up by joining smaller ones. Therefore the

ranges associated with joining are also shown.

In applying a constraint on mass, we seek single shaping-processes or

shaping-joining combinations capable of making ia part and reject those that cannot.

ME 474-674 Winter 2008 Slides 7 -29

The Process – Mass - range chart

Figure 7.19

ME 474-674 Winter 2008 Slides 7 -30

The Process – Section thickness chart

The bar-chart on the next page allows selection to meet constraints on section

thickness.

Surface tension and heat-flow limit the minimum section of gravity cast

shapes.

• The range can be extended by applying a pressure or by pre-heating the

mold, but there remain definite lower limits for the section thickness.

Limits on rolling and forging-pressures set a lower limit on thickness

achievable by deformation processing.

Powder-forming methods are more limited in the section thicknesses they can

create, but they may be the only ones available for ceramics and very hard metals that cannot be shaped in other ways.

The section thicknesses obtained by polymer-forming methods – injection

molding, pressing, blow-molding, etc – depend on the viscosity of the polymer; fillers increase viscosity, further limiting the thinness of sections.

Special techniques, which include electro-forming, plasma-spraying and

various vapor – deposition methods, allow very slender shapes.

SLIDE 6

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ME 474-674 Winter 2008 Slides 7 -31

The Process – Section thickness chart

Figure 7.20

ME 474-674 Winter 2008 Slides 7 -32

The Process – Tolerance chart

No process can shape a part exactly to a specified dimension.

• Some deviation Δx from a desired dimension x is permitted
• This is referred to as the tolerance, T, and is specified as mm, or as

mm x

• r

mm x

1 . 05 .

50 1 . 100

+ −

= ± =

ME 474-674 Winter 2008 Slides 7 -33

The Process – Tolerance chart

Figure 7.21

ME 474-674 Winter 2008 Slides 7 -34

The Process – Surface roughness chart

The surface roughness R, is measured by the root-mean-square

amplitude of the irregularities on the surface.

It is specified as

• R<100μm (the rough surface of a sand casting) or
• R<0.01μm (a highly polished surface).

The bar chart on the next page allows selection to achieve a given

surface roughness.

ME 474-674 Winter 2008 Slides 7 -35

The Process – Surface roughness chart

Figure 7.22

ME 474-674 Winter 2008 Slides 7 -36

The Process – Economic batch-size chart

Process cost depends on a large number of independent variables. The

influence of many of the inputs to the cost of a process are captured by a single attribute: the economic batch size.

A process with an economic batch size with the range B1 – B2 is one

that is found by experience to be competitive in cost when the output lies in that range.

SLIDE 7

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ME 474-674 Winter 2008 Slides 7 -37

The Process – Economic batch-size chart

Figure 7.24