Product manufacturing

PRODUT DESIGN TECHNIQUES OF MANUFACTURING

Cutting by abrasionCutting by abrasion An abrasive is a material, often a mineral, that is used to

shape or finish a work piece through rubbing which leads to part of the work piece being worn away.

Tool is often made of hard minerals diamond or corundum, however softer one’s can also be used like calcium carbonate are used as abrasives, such as "polishing agents" in toothpaste.

Abrasive substance is usually granular, gritty and sharp

Mechanics of abrasionMechanics of abrasion These minerals are either crushed or are already of a

sufficiently small size (anywhere from macroscopic grains as large as about 2 mm to microscopic grains about 0.001 mm in diameter) to permit their use as an abrasive. These grains, commonly called grit, have rough edges, often terminating in points which will decrease the surface area in contact and increase the localised contact pressure. The abrasive and the material to be worked are brought into contact while in relative motion to each other. Force applied through the grains causes fragments of the worked material to break away while simultaneously smoothing the abrasive grain and/or causing the grain to work loose from the rest of the abrasive.

FACTORS AFFECTION FACTORS AFFECTION ABRASIONABRASION Difference in hardness between the two

substances: a much harder abrasive will cut faster and deeper

Grain size (grit size): larger grains will cut faster as they also cut deeper

Contact force: more force will cause faster abrasion Loading: worn abrasive and cast off work material

tends to fill spaces between abrasive grains so reducing cutting efficiency while increasing friction

Use of lubricant/coolant/metalworking fluid: Can carry away swarf (preventing loading), transport heat (which may affect the physical properties of the workpiece or the abrasive), decrease friction (with the substrate or matrix), suspend worn work material and abrasives allowing for a finer finish, conduct stress to the work piece

.

EXAMPLESEXAMPLESGrindingGrinding

PolishingBuffing etc

Flame CuttingFlame Cutting Flame cutting is a combustion process. It is not the heating flame

itself that does the actual cutting but an oxygen jet, which burns the material during heat formation and transports the combustion products (slag) away from the cut. 

Before cutting can begin, the steel must be heated to ignition temperature(combustion temperature) by means of a gas flame. The choice of fuel gas affects cut quality and the time used for preheating. When choosing a fuel gas, the thickness of the material must also be considered.

 When cutting, the purity of the oxygen is of huge importance to the cutting speed. The purer the gas, the higher the cutting speed and the better the productivity and cut quality.

The most important part of cutting equipment is the cutting nozzle. The higher the outlet speed of the oxygen jet, the better the output of the nozzle. In turn, the speed depends on the shape of the cutting nozzle. Nowadays, nozzles with an expansion channel are often used, giving the oxygen jet a high velocity.

Parameters Parameters Proper cutting tip selectionProper cutting oxygen pressure

selectionProper preheatProper cutting speedProper selection of the fuel gasA gas supply system (both fuel gas

and Oxygen) that is sufficient to supply the quantity of gas required at the pressure required.

In cutting a kerf Is formedIn cutting a kerf Is formed

Kerf for every process is differentEach cutting process removes a different

amount of material, or kerf. The more precise processes, like waterjet and laser, remove a smaller amount of kerf, which is one of the reasons they can be more precise! A typical example shown here is for 1/2” thick mild steel.

Plasma: 0.150”Oxy-Fuel: 0.045”Waterjet: 0.035”Laser: 0.025”

LASER CUTTINGLASER CUTTINGConcentrated beams of coherent

light(energy) used to cut materials.

Cutting is precise, neat and fast. Laser cutting is best suited to high precision cutting of

thin pieces.The cut quality is so high that the pieces can be used directly, or sent for further processing without the need for post-cut finishing. Laser cutting is extensively used, especially by mechanical engineering companies that serve the automotive industry, as well as in the manufacturing of household equipment, such as dishwashers, washing machines

WORKINGWORKING

The laser beam is a column of very high intensity light, of a single wavelength, or color.

The beam is only about 3/4 of an inch in diameter as it travels from the laser resonator, which creates the beam, through the machine’s beam path. It may be bounced in different directions by a number of mirrors, or “beam benders”, before it is finally focused onto the plate. The focused laser beam goes through the bore of a nozzle right before it hits the plate. Also flowing through that nozzle bore is a compressed gas, such as Oxygen or Nitrogen.

Focusing the laser beam can be done by a special lens, or by a curved mirror, and this takes place in the laser cutting head. The beam has to be precisely focused so that the shape of the focus spot and the density of the energy in that spot are perfectly round and consistent, and centered in the nozzle.

By focusing the large beam down to a single pinpoint, the heat density at that spot is extreme.

The high power density results in rapid heating, melting and partial or complete vaporizing of the material. When cutting stainless steel or aluminum, the laser beam simply melts the material, and high pressure nitrogen is used to blow the molten metal out of the kerf.

Water jet cuttingWater jet cuttingCutting is operated by a

concetrated jet of water, approximately one tenth of a millimetre in a diametre hich is propelled at high pressure ( 5000 to 6000 bars) and great speed(600 to 100 m/s).

The matter does not get wet at all during cutting

AdvantagesAdvantages It is a "cold" cutting process so the material

being cut is not subject to any thermal influence.

The extremely small cutting gap enables optimum material exploitation.

Two- and three-dimensional cutting is possible.

The "waterjet" tool works independent of direction.

All materials including soft material can be cut.

Useful to cut food materials

Water jet cuttingWater jet cuttingTwo types1. Pure water jetAbrasive water jet

While pure waterjet cutting relies on the static pressure of the compact waterjet and the erosive effect of the droplets in order to cut the material, in abrasive waterjet applications there are the solid particles incorporated in the jet which cause micro-cutting action on the material – in this case the waterjet serves merely to accelerate the solid particles.

Abrasive water jet

Pure water jet

Typical waterjet cutting applications are: Foodstuff portioning (frozen food, bread, cakes and pastries,

chocolate, ice-cream) Paper product cutting (nappies, corrugated cardboard) Textile cutting (leather, furniture fabrics, carpets) Trimming of plastic mouldings and carpet shapes for the

automotive industry Cutting of insulation material