Manufacturing Operations & Technology

ME20026

Technological manufacturing definition

The application of physical and chemical processes to alter the geometry and/or appearance of given starting material to make parts or products; also includes assembly of parts

Alternative manufacturing definition

The transformation of materials into items of greater value by means of one or more processing and/or assembly operations

What do production engineers need to know

Standards, legislation

Technical/business specifications

Product design

Manufacturing system design

Production plan

What are manufacturing industry categories

Primary

Secondary

Tertiary

Primary industries

Those that cultivate and exploit natural resources:

Agriculture/fishing/forestry

Secondary industries

Convert the output from primary industries into consumer and capital goods:

Aerospace/automotive/food processing

Consumer goods

Purchased directly by consumers

Capital goods

Purchased by other companies to produce consumer goods or provide services

Tertiary industries

Provide services rather than tangible goods:

Banking/insurance/education

Activities in manufacturing

Processing and assembly

Material handling

Inspection

Operations management

Operations management

Strategy

Design

Planning and control

Improvement

Low volume production

1-100

Job shop

Medium volume production

100-10,000

Batch

High volume production

>10,000

Mass

Variety and quantity relationship

Inverse correlation

Job shops

Highly flexible production

Multipurpose tools and machines

Customized products

Batch/cellular production

Production in stages

Variety of products from single line

Mass production

Dedicated to standard product

Inflexible

Number of parts

Number of operations

Manufacturing capability

Technical and physical limitations of a manufacturing firm and each of its plants

Technological processing capability

Material

Compatibility

Technical knowhow

Physical product limitations

Size

Weight

Storage

Product capacity

Manning level

Equipment

Speed

Evaluation of processes

Cost

Rate

Quality

Flexibility

Machining definition

Manufacturing processes by which material is removed from raw workpiece

Machining examples

Straight turning

Cutting off

Slab milling

End milling

Straight turning

Workpiece is rotated, cutting tool is moved parallel to remove outer layer

Cutting off

Workpiece is rotated, cutting tool is moved perpendicular inwards to separate parts

Slab milling

Cutting tool is rotated parallel to surface of part, top layer is removed

End milling

Cutting tool is rotated perpendicular to part, removes a cavity

Importance of metal cutting mechanics

Motor selection

Design of structure

Life of tool vs rate of cutting

Merchant 2D model for orthogonal cutting

Shear strain

Velocity diagram

Force circle

Power =

Force x velocity

Merchant’s equation

Tool wear equation

Turning

Causes of tool wear

Stresses

Friction

High temepratures

Design for machining

Access for tools

Long sections cause vibrations

Holes cannot change directions

Curved edges difficult to hold

Outside rounds difficult to achieve

When advanced machining technologies are needed

Material is very strong, hard or brittle

Too much heat is generated

Shape is too complex

Workpiece is too flexible

Special surface finish and dimensional tolerance requirements

Advanced machining technologies examples

Chemical machining

Electrochemical machining

Electrical discharge machining

Laser beam machining

Water-jet machining

Abrasive jet machining

Chemical machining

Laser beam machining

EDM

Economics of advanced machinign processes

Costs of tooling and equipment

Operating costs

Material-removal rate required

Level of operator skills

Casting diagram

Transformative process

Change the shape of materials without removals or additions

Reynold’s number desired in casting to prevent aspiration

<20,000

Chvorinov’s rule

Metal casting definition

Pour molten metal into a mould cavity, let it solidify, remove from mould

Advantages of casting

Complex shapes with internal cavities

Very large parts

Economically competitive with other processes

Near net-shaped process

Scalable

Expendable moulds

Sand casting

Shell mould

Evaporative pattern (lost-foam)

Investment (lost-wax)

Permanent moulds

Permanent mould

Die

Centrifugal

Importance of risers

During solidification, the casting shrinks

True stress

P/A

True strain

ln(l/lo)

Elastic deformation

Deformation disappears when load is removed

Plastic deformation

Deformaiton is permanent

Metal forging definition

Workpiece is shaped by compressive forces applied through dies and tooling

Metal grain in casting

Metal grain in machining from a blank

Metal grain in forging

Cold forging requirements

High forces

Ductility at room temperature

Cold forging advantages

Good surface finish

Dimensional accuracy

Hot forging advantages

Lower forces

Hot forging disadvantages

Less accurate dimensions

Poor surface finish

Forgings require finishing operations such as

Heat treatments

Machining to final dimensions

Open-die forging definition

Solid workpiece between two flat dies, reduced in height by compression

Impression-die forging definition

Workpiece takes shape of die cavity between two shaped dies. Occurs at elevated temperatures to lower required forces and increase ductiility

Parting line location

Largest cross-section of part. Straight for simple shapes.

Flash thickness

3% of maximum thickness of forging

Closed die forging diagram

Length of land

2-5 times flash thickness

To remove forgings

Draft angles are needed

Open die forging diagram

Rolling definition

Rollers reduce the thickness of a strip of metal

Diagram of flat rolling

Velocity of strip during rolling

Slower on left, faster on right, same as roller at no-slip point

Why are there fricitonal forces during rolling

Because the strip moves at a different speed than the rollers

How is friction controlled during rolling

Lubricants

Metal extrusion definition

Cylindrical billet is force pushed through a die

Metal extrusion diagram

Disadvantages of casting

High energy requirements

Inhomogeneous material properties

Costly lead times

Postprocessing often required

Plastic compared to metal forming

Higher viscocity

Lower surface tension

Lower temperatures

Cannot control properties

Injection moulding diagram

Additive manufactuirng definition

Mass is added to the workpiece to achieve the desired component shape

Additive manufacturing advantages

Fast prototyping

No tooling

Complex/optimized/lighter structures

Material savings

Multiple materials

Customization/personalization

Improved supply chain/on demand manufacturing

Simultaneous production of diverse parts

Additive manufacturing examples

Fused filament fabrication

Stereolithography

Selective laser sintering

Electron beam melting

Binder jetting

Laminated object manufacturing

FFF challenges

Anisotropy

Porosity

Residual stresses

Deposition rate

FFF parameters

Temperature

Extrusion force

Viscocity

Speed

Toolpath

FFF diagram

FFF definition

A filament is extruded from a head that moves in two directions, after each layer the table is lowered

SLA diagram

SLA

Liquid polymer is cured selectively to create the component with the use of a UV laser and a vat of polymer

SLS or EBM diagram

SLS/EBM definition

Nonmetallic or metallic powder is melted using a laser to make the component

Difference between SLS and EBM

Mostly used for plastics vs titanium and cobalt-chrome alloys