ME302 Introduction to Engineering Design and Graphics

Lecture Notes: Materials and Manufacturing Processes

Contents

What is Manufacturing

Process of converting raw materials into products

Manufacturing a Product: Paper Clip

Criteria for Selecting Manufacturing Processes

Types of Manufacturing Processes

Casting Processes

Forming and Shaping Processes

Sheet-Metal Forming Processes

Machining Processes

Joining Processes

Manufacturing Processes for Plastics

Reference: Kalpajian, S., ``Manufacturing Processes for Engineering Materials'', 1991.

Manufacturing a Product

Thought processes and procedures involved in designing and manufacturing common products.

Example: Paper Clip

Must meet its basic functional requirement: hold pieces of paper together with sufficient clamping force so that the papers do not slip away from each other.

Design based on strength of materials and mechanics of solids, dealingwith the stresses and strains involved during manufacturing and during normal use of the product.

Material selected must have certain stiffness and strength: Force to open the clip too high? Not enough clamping force on the paper? Permanent bend during use due to low yield stress?

Manufacturing a Product

Other considerations:

Style, appearance, surface finish or texture of clip

Corrosion properties: rust marks on paper

Production concerns:

Bending of selected material during manufacturing without cracking or breaking

Cutting the wire from a long piece without excessive wear

Cutting the wire with a smooth edge

The most economical way of manufacturing the clip to make a profit

Consider the design, material selection, and processing methods involved in manufacturing a jet engine!

Criteria for Selecting a Manufacturing Process

Shape of the final product and raw material

Type of material and its basic properties:

Brittle and hard materials cannot be formed easily, but they can be cast or machined.

Manufacturing process often alters the properties of the materials: metals that are formed at room temperature become stronger, harder, and less ductile than prior to processing.

Design requirements

Additional Criteria

Dimensional and surface finish requirements:

Size, thickness, and shape complexity: parts with thin cross-sections cannot be cast properly; complex parts cannot be formed easily.

Tolerances and surface finish: better in hot-working vs. cold-working; dimensional changes, warpage, surface oxidation at elevated temperatures.

Additional operations: grinding, polishing (better finish but more expensive!)

Operational and Cost considerations:

Design and cost of tooling

Lead time required to begin production

Effect of workpiece material on tool and die life

Expensive materials: minimize scrap (e.g., machining produces too much scrap)

Availability of machines and equipment

Number of parts or products required and desired production rate

Environmental concerns

Manufacturing Processes for Metals

Casting: expendable mold and permanent mold

Forming and Shaping: rolling, forging, extrusion, drawing, sheet forming, powder metallurgy, molding

Machining: turning, boring, drilling, milling, planing, shaping, broaching, grinding, ultrasonic machining, chemical machining, electrical discharge machining (EDM), electrochemical machining, high-energy beam machining

Joining: welding, brazing, soldering, diffusion bonding, adhesive bonding, mechanical joining

Finishing Operation: honing, lapping, polishing, burnishing, deburring, surface treating, coating, plating 

Choosing Methods of Production

Casting Processes

Among the oldest methods of manufacturing: used to make arrowheads, ornaments, about 4000 B.C.

Introduction of molten metal into a mold cavity; upon solidification, metal conforms to the shape of the cavity

Capable of producing intricate shapes, with internal cavities, in a single piece

Very large, very small, and hollow parts can be produced economically

Typical cast products: engine blocks, crankshafts, pistons, valves, railroad wheels

 

Expendable mold casting: molds made of sand, plaster, ceramics, investment casting

Permanent mold casting : molds, made of metals, can be re-used; pressure casting, die-casting, centrifugal casting

 

 

 

Forming and Shaping Processes

Bulk deformation processes induce shape changes by plastic deformation under forces applied by tools and dies

Take cast metal and roll it down into general shapes such as slabs, plates, billets, then forge it into near-net shape

Forging: plastic deformation carried out by compression into a die (e.g., crankshafts, connecting rods, turbine disks, gears, wheels, bolt heads, hand tools,...)

 

Rolling: reducing the thickness or changing the cross-section of a long workpiece by compression through a set of rolls (e.g., plates for ship hulls, bridges, machine structures, nuclear vessels; sheets for automobile bodies, appliances, containers for food and beverages, ...)

Extrusion: forcing a billet through a die opening by compression, hot or cold

Drawing: reducing the cross-section of a bar by pulling it through a converging die by tension (rods used for small components;wires used for cables, springs, musical instruments, fencing, shopping carts)

Sheet-Metal Forming Processes

Producing thin sheets of metal at room temperature (metal desks, appliance bodies, aircraft panels, beverage cans, car bodies)

Shearing: cutting a sheet metal by subjecting it to shear stress, between a punch and a die

Bending: used to form flanges, curls, seams, corrugations

Deep drawing: a flat sheet-metal blank is formed into a cylindrical or box-shaped part by means of a punch that presses the blank into the die cavity

Spinning: forming assymetric parts over a rotating mandrel with the use of rigid tools or rollers
 
 

Machining Processes

Material removal from a workpiece: cutting, grinding, nontraditional machining processes

Finishing operations that remove small amounts of material

Pros: improves dimensional accuracy, can create hard-to-obtain features (e.g., sharp corners), can control surface finish

Cons: expensive, generates waste, can have adverse effects on surface quality and properties of product

Cutting to produce round shapes (e.g., shafts, pistons, cylinders, gun

Drilling: making holes

Turning: removing material while part turns (e.g., shafts, spindles, pins, handles, and various machine components)

Facing, boring, parting

Cutting to produce various shapes:

Milling: cutting with a multi-tooth tool which rotates

 

 

Broaching: cutting with a multi-tooth tool which makes progressively deeper cuts (e.g., holes of circular, square, or irregular section, keyways, teeth of internal gears, ...)

Planing, shaping, sawing, filing

Workpiece material is too hard or brittle, or its shape is difficult to produce with sufficient accuracy by cutting

Grinding: cutting with a rough wheel to finish a surface

 

Surface grinding, cylindrical grinding, internal grinding, centerless grinding

 

 

Joining Processes

Includes welding, brazing, soldering, adhesive bonding, mechanical joining

Reasons for importance:

Product is impossible to manufacture as a single piece

Product is easier and more economical to manufacture as individual components

Products may have to taken apart for repair or maintenance

Transporting the product in individual components and assembling them later may be easier and less costly

Manufacturing Processes for Plastics

Plastics are shipped to manufacturing plants as pellets or powders and are melted just before the shaping process. Polymers melt at relatively low temperatures and, unlike metals, are easy to handle and require less energy to process.

Plastics can be molded, and formed, as well as machined and joined, into many shapes with relative ease and with little or no additional operations required.

Extrusion: Raw powder is placed into a hopper and fed into the extruder barrel; the barrel has a screw that blends and conveys the powder down the barrel; the powder is heated and liquefied; the molten plastic is then forced into a die.

Injection Molding: the powder is melted inside a heated chamber; the melt is forced into a split-die chamber either by a hydraulic plunger or by a rotating screw (cups, containers, knobs, toys,...)

Blow Molding: a tube is extruded and clamped into a mold cavity and then blown outward to fill the mold (e.g., hollow containers)

Thermoforming: a sheet is heated to the softening point and placed over a mold and pulled against the mold through the application of vacuum (e.g., advertising signs, packaging, panels for shower stalls,...)

Compression Molding: a preshaped part or premeasured amount of powder is placed directly in a heated mold cavity; forming is done under pressure with a plug (e.g., dishes, handles, fittings, container caps,...)