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Design for Manufacture

Manufacturing Processes

Review

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Handle

Join

Insert

Fasten

Inspect

ManufacturingManufacture

Shape forming

Handle

Primary manufacturing

Shape forming

Inspect

Shape change

Handle

Secondary manufacturing

Machining

Inspect

Finish

Handle

Tertiary manufacturing

Coating, treatment

Inspect

Assembly

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Process PlanningGiven the engineering drawing:

– Drawing interpretation– Material evaluation, Production volume and

rate, Tolerance and surface finish, and process selection

– Selection of machine and tooling– Setting process parameters– Tooling and fixtures– Selecting quality assurance methods– Costing

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Combined Routing Sheet / Operation List

Part No.: Part Name: Revision: Page No.:

Matl.: Size: Planner: Date:

No.

Operation Dept. M/C Tooling Gauges

Setup Time

CycleTime

10 Face; rough & finish turn to360.075 dia. and 300.1 length; Face shoulder to 80.05 and finish turn to 450.05 dia.

L 325 G856 1.0h 6.12m

20 Reverse: face to 1200.1 dia. length; finish turn to 450.05 dia.; Drill 25 +0.15 -0.05 dia. hole

L 325 0.5h 3.10m

30 Drill & Ream 3 radial holes at 9.50.05 dia D 114 F512 0.3h 2.50m

40 Mill 120.1 wide x 9.50.075 deep slot M 240 F321 0.3h 1.80m

50 Mill 180.1 wide x 9.50.075 deep flat M 240 F322 0.3h 1.45m

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Primary Manufacturing Processes

• Casting

• Molding

• Powder Metallurgy

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Sand Casting – Pros & ConsPros:

• Produce parts with complex geometries, both internally and externally.

• Possible to net shape with no further manufacturing required.

• Large parts can be produced.

• Wide choice of metals.

• Suitable for mass production.

Cons:

• Poor dimensional control for some processes

• Poor surface finish for some processes

• Limitation on mechanical properties

• Safety hazard

• Environmental hazard

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Expendable Mold Casting -Shell Mold

Pros:– Smoother surface finish than sans casting.– Surface finish of 2.5 m can be obtained.– Good dimensional accuracy 0.25 mm on small

to medium size parts.– No further machining is needed.– Capability for automation lowers the cost for larger

quantities.

Cons:– More expensive metal pattern, especially for small

batch.

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Expendable Mold Casting -Vacuum Mold

Sand held together by vacuum pressure.

Pros:– Sand can be recovered unlike shell mold.– No chemical binder, and therefore no special

treatment for the sand.– No water mixed with the sand and therefore no

moisture related problems

Cons:– Relative slow– Not readily adaptable to mechanization.

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Expendable Mold Casting -Expanded Polystrene Mold

Pros:– Pattern need not be removed.– No cope /drag is needed, all features are built

into the pattern.– Possibility for automated production.

Cons:– The pattern is not reusable.

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Expendable Mold Casting -Investment Casting

Pros:– Capability to cast parts with great complexity and

intricacy.– Close dimensional control ( 0.076 m tolerance).– Good surface finish.– Wax can be recovered and reuse.– Additional machining normally not required.

Cons:– Normally cater for smaller parts.– Relatively expensive.

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Expendable Mold Casting -Plaster Mold and Ceramic Mold

• Similar to sand casting in terms of process.

• Plaster mold is for lower temperature alloys while ceramic mold is for higher temperature alloys.

Pros:– Good surface finish and dimensional control.– Capability to make thin cross sections.

Cons:– Curing takes too long to render it unsuitable for

volume production.

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Permanent Mold Casting - Basic Permanent Mold

Pros:– Good surface finish and close dimensional

control.– More rapid solidification, finer grain structure,

stronger castings.

Cons:– Generally limited to lower melting point metals.– Simpler part geometries as mold is permanent.– Mold cost is expensive and thus cater for volume

production.

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Permanent Mold Casting - Die Casting

Pros:– High production rates are possible.– Economical for large quantities.– Close tolerances are possible ( 0.076 mm).– Good surface finish.– Thin sections are possible (down to 0.5 mm).– Rapid cooling, fine grain, high strength.

Cons:– melting point of metals.– shape restriction.

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Casting

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Molding

• Tolerances

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Powder Metallurgy - Pros• Net shape manufacturing• Minimum wastage of material• Production of porous parts, typically for self-

lubricating applications• Produce parts from material difficult to

process• Produce parts with special alloying content• Good dimensional control• Can be automated for economic production

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Powder Metallurgy - Cons

• High tooling and equipment cost.

• Expensive raw material.

• Difficulty with storing and handling of powder.

• Limiting in geometry as the powder does not flow readily in die.

• Inhomogeneity of produced part.

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Powder Metallurgy Design Considerations

• Large batch size to make it cost effective, typically over 10,000.

• Controlled porosity parts.

• Special alloying elements parts.

• Limited geometry to allow die opening.

• Built-in chamfers and radii.

• Minimum wall thickness of 1.5 mm and minimum hole diameter of 1.5 mm.

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Secondary Manufacturing ProcessesMachining

• Turning, Boring

• Drilling

• Reaming

• Milling

• Shaping

• Broaching

• Sawing

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Tertiary Manufacturing Processes• Grinding and Abrasive Processes

– Grinding– Honing, Lapping, Super-finishing, Polishing

and Buffing

• Non-traditional Machining and Thermal Cutting Processes– Mechanical Energy Processes– Electrochemical Machining Processes– Thermal Energy Processes– Chemical Machining

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Surface Roughness Values

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Tertiary Manufacturing Processes Application Considerations

Very small holes below 0.125 mm diameter. (Laser beam machining, LBM)

Holes with large depth-to-diameter ratio, d/D>20. (ECM or EDM)

Holes that are not round (ECM or EDM)

Narrow slots in slabs or plates (ECM, LBM, EDM, water jet, abrasive jet)

Micromachining (PCM, LBM, EBM)

Shallow pockets and surface details in flat parts (Chemical machining)

Special contoured shapes for mold and die applications (EDM or ECM)

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Special shapes for which the non traditional processes are appropriate (a) very small diameter holes, (b) holes with large depth-to-diameter ratios, (c) nonround holes, (d) narrow, non-straight slots, (e) pockets, and (f) die sinking

Tertiary Manufacturing Processes Application Considerations

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Tertiary Manufacturing Processes Materials Consideration

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Tertiary Manufacturing Processes Machining Characteristics

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Case Study

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Product Specification

• Final product specification will be issued after:– Prototyped is designed, fabricated, and tested– Cost analysis after trail batch es

• Dimension – specified in the drawing

• Material – Grey cast iron

• Maintenance – the bolting arrangement should incorporate standard parts.

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Product Specification

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Product Specification

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Drawing Interpretation• Review the part drawing to determine the

primary manufacturing process: casting or forming – Casting – tooling fabrication– Forming – tooling fabrication or direct stock

purchase

• Secondary manufacturing process: machining – Overall stock size and material– Tolerance & surface finish requirements

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Material Evaluation

• Light weight

• Hard with good wearing resistance

• Low cost

• Good casting properties

• Good machinability

• Batch size - 350

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Manufacturing Considerations• the 100 mm and 50 mm bores cannot deviate from the nominal size by more than

0.01mm;

• the 100 mm diameter bore must also be perpendicular to the flange face within 0.1 mm tolerance zone;

• the 100 mm and 50 mm bores must be machined to a surface finish of 0.1m;

• the flange face and centreline of the 12 mm hole must be parallel to each other to within a tolerance zone of 0.1mm;

• the flange face must be machined to a surface finish of 0.8m;

• the 12 mm hole must be perpendicular to the component centreline within a 0.01 mm tolerance zone;

• all holes must not deviate by more than 0.1 mm of the nominal size;

• all holes must have a surface finish of 1.6m;

• all spotfaces must not deviate by more than 0.1 mm of the nominal size;

• all spotfaces must have a surface finish of 0.8m;

• all fillets are R7 unless otherwise stated;

• the general dimensional tolerance is 0.5mm;

• the general surface finish is 12.5m.

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Process Selection

• Suitable for grey cast iron (sand casting / investment casting)

• Meet general dimensional tolerance of ±0.5 mm

• Meet general surface finish of 12.5 µm

• Produce economically 350 per batch

• Meet the tolerance specifications stated in the drawing

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Process Selection

• Investment casting

• Holes assumed to be drilled with the help of drill jigs.

• Processes:– Turning – for the flange face– Drilling – for the holes and spotfacing– Grinding – for the 100 mm and 50 mm

bores

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Process Sequencing• Stock produced by investment casting with 2 mm

machining allowance– Wax pattern, flasking, bake, mold, stock removal

• Machine the flange face by turning– Rough facing with 0.2 mm left for fine finishing

• Machine spotfaces by drilling

• Machine holes by drilling

• Machine bores by grinding– Internal grinding each 100 mm and 50 mm holes

in four passes

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Tooling and Fixtures

• Turning/facing tool – facing

• Spotfacing - 20 mm and 25 mm spot drills

• Drilling - 10 mm and 12 mm twist drills

• Grinding - 20 mm internal grinding wheel

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Tooling and Fixtures