MSE 257: INDIGENOUS METHODS OF MATERIALS PROCESSING

Dr. Emmanuel Kwesi Arthur

Department of Materials Engineering,

Kwame Nkrumah University of Science and Technology, Kumasi, Ghana

Email: ekarthur2005@yahoo.com

Phone #: +233541710532

Course Code: MSE 257

Lecture Four

Investment casting (lost wax casting)

Molten metal solidifies in a ceramic cast made by coating a wax pattern with liquid slurry, then dried.

Wax is melted out and ceramic mold is destroyed after part solidifies.

Material: alloy of aluminum, zinc, magnesium, brass, steel, stainless steel.

Economic production quantity: less than 10,000 pieces

Beads Casting

The Ghanaian glass beadmaking tradition is one of several regional glass beadmaking traditions in West Africa, and all of these traditions evolved over many centuries in the context of long-distance trade.

Transcontinental trade over the Sahara from the eighth century bc and ocean-going trade from the 1480s transferred finished beads as well as raw materials for glass bead production and introduced knowledge of various methods of working beads and glass.

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Materials In Ghana, some of the materials used

for making glass beads are pieces of glass, firewood for fuelling the kilns, metal mortar, pestle, grinding stone, bodkin, bead holder, bricks and cassava leaf stalk.

Materials and other resources required are mainly bottles of a specific make that is compatible to the other composite materials like ceramic and other powdered pigments when they are subjected to high temperatures

Among the local resources are the ceramic or powdered pigment and fire-wood to fuel the kiln. The kiln is usually constructed from local materials4

Bottles for making glass beads

Kiln for firing beads

Mould Making

To prepare the mould for casting glass beads, clay is collected from a clay pit at a river side.

The clay is allowed to dry completely. It then becomes easier to remove large particles of unwanted matter such as roots, leaves, wood and pebbles.

The next process is to pound the clay into fine powder and to sieve the pounded clay to get rid of small bits of unwanted materials, using a wire mesh.

A lump of clay is formed and kneaded to remove the air bubbles trapped in it.

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Mould Making

a slab of standard thickness is moulded taking into consideration the size of the beads to be produced. A rectangular or circular object is placed on the slab and traced to get the outline.

A sharp knife is used to cut the drawn shape or outline from the clay slab. The cut shape is allowed to dry up to the leather hard stage. While the shaped clay pieces are setting, a piece of wood is shaped leaving a small projection at the tip

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“Foa” which is a piece of shaped wood is used to make cavities in the clay mould into which powdered glass would later be poured.

The tool is pushed into the slab carefully to create a pit.

The projection at the tip of the tool created an extended pit.

Mould Making

Clay solution with a light consistency is prepared.

The moulds are then immersed into the clay solution and allowed to dry.

The activity is repeated to make sure that all pores in the mould are sealed off.

When the moulds are dry, the cassava leaf stalks are cut into pieces of the same size.

The stalks are put into each of the lower pits in the larger pits in the mould.

Care was taken to secure the stalks in the small pits

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the mould contains several bowl shaped forms.

A piece of the leaf stalk of cassava is fixed to the centre of the bowl-shaped depression to create the threading hole in the glass bead

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Mould For Bead Casting

Mould for bead casting

(Note the small, extended pits at the base of the larger pits)

Pieces of cassava stalks for creating holes in beads

Preparation of Glass Powder

Fine glass powder is the main material for the making of glass beads.

broken bottles or louvre blades are grouped into various colours of powder for designing the beads.

After this, each colour is put separately in a metal mortar and pounded with a metal pestle into fine powder.

The pounded glass is sieved to get the finest for casting.

As a safety measure, the nose and mouth are covered during pounding to prevent inhaling the glass dust. Goggles are put on to protect the eyes.

Various grades of mesh were used to sieve the glass powder starting from course to fine grade and then the glass powder was put into a plastic container and covered very well

9 Metal mortar and pestle

Broken pieces of glass and bottles

The moulds are filled with the glass powder with a simple manual technique and the use of a small container.

Also layers of coloured glass powder are filled into the holes to create patterns.

A pin is used to pinch the side of the holes to allow various layers of colour to flow into each other

The mould is well shaken to make sure that the cavities were firmly filled. More powder is added to top the fillings where necessary.

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Pin with a wooden handle

The filled moulds are packed carefully in the kiln in the brick-laying formation to avoid breakage

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Packed mouldsMoulds filled ready for firing

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kwadjo Gomerdo of cedi beads industry firingbeads in a kiln constructed of termite-mound clay,odumase krobo, Ghana, 1999.

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Packaging mould into kiln

The newly cast beads in their moulds

The cast beads are removed gradually and put in a water container for washing

With the help of a needle and thread, the beads are put together to form necklaces, bangles and pendants.

Other items such as earrings are also made from the beads Cast beads removed from mould

Finished beads, necklaces, bracelets and earrings

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Sheet Metalworking

The permanent deformation of thin metal sheets by bending and shearing forces produced by mechanical or hydraulic forces.

Often called stamping forces. Produces parts of moderate complexity. Size: less than 24x24inches Economic production quantity: more than 10,000 Material: alloys of steel and aluminum Bending Blanking Drawing Punching Shearing Spinning

Shearing : cutting or separating sheet metal along a straight line.

Blanking: shearing of a smaller, shaped piece, called a blank, from the stock.

Punching: produces slots, notches, extruded holes, and holes.

Embossing: forming plastic indentations to form ribs, beads, or lettering on the surface of metal.

Sheet metal drawing

Punch plastically deforms a blank sheet material into a die, forming cupped-, box-, or hollow-shaped parts

Products: soda cans, ammunition cartridge casings, and pots and pans.

BlankDrawn part

Clamp force

Blank holder

Die

Punch

Punch ram

Machining

The removing of material from the workpiece by a sharp cutting tool that shears away chips of material to create a desired form or features.

It is a subtractive process that produces manufactured waste and can, therefore be expensive.

Often used as a secondary process to true-up critical dimensions or surfaces or to smooth the surface finish.

Often used for low-volume production.

Machining processes

ExtrusionForgingRollingBar drawingWire drawing

Deformation

CentrifugalDie castingInvestmentPermanent moldSand casting

Casting

BendingBlankingDrawingPunchingShearingSpinning

SheetMetal

Blow moldingCastingCompression moldingExtrusionInjection MoldingThermoformingTransfer molding

PolymerProcesses

BoringDrillingFacingGrindingMillingPlaningTurningSawingECM, EDM

Machining

AnodizingHoningPaintingPlatingPolishing

Finishing

AutomatedBondingBrazingManualRivetingSolderingWelding

Assembly

ManufacturingProcesses

Machining – removal of material…

Sawing –using a toothed blade. Milling – from a flat surface by a rotating cutter tool. Planing – using a translating cutter as workpiece feeds. Shaping - from a translating workpiece using a stationary cutter. Boring - increasing diameter of existing hole by rotating the

workpiece. Drilling- using a rotating bit forming a cylindrical hole. Reaming – to refine the diameter of an existing hole. Turning - from a rotating workpiece. Facing - from turning workpiece using a radially fed tool. Grinding - from a surface using an abrasive spinning wheel. Electric discharge machining (EDM) - by means of a spark.

Machining process considerations

sawing, turning, boring, milling, drilling, grinding, ECM

material removed solid material machining

hardness, strength of materialshear forces = strong jigs & fixtures tool/bit wear, replacementsize of workpiece, fit machine?volume removedrate of removal, hp neededtolerances operator skill, CNCcosts (materials, tooling, processing)Add to your

notes

Finishing

Preparing the final surface for aesthetics and protection from the environment.

Cleaning: wire brushing is used to remove grit and scale, and chemical solutions, including acid baths, are used to remove oily films

Protection: polymers and ceramics requires little protection from the environment. Metals, however, require some surface treatment with oil-and-water based painting providing the least expensive coating. Steels are often plated with chrome, cadmium, or zinc). Aluminum alloys are usually anodized (a chemical surface treatment).

Finishing processes

ExtrusionForgingRollingBar drawingWire drawing

Deformation

CentrifugalDie castingInvestmentPermanent moldSand casting

Casting

BendingBlankingDrawingPunchingShearingSpinning

SheetMetal

Blow moldingCastingCompression moldingExtrusionInjection MoldingThermoformingTransfer molding

PolymerProcesses

BoringDrillingFacingGrindingMillingPlaningTurningSawingECM, EDM

Machining

AnodizingHoningPaintingPlatingPolishing

Finishing

AutomatedBondingBrazingManualRivetingSolderingWelding

Assembly

ManufacturingProcesses

protection?