Manufacturing Practices (BT-106) Unit 1 Notes

How unit 1 is examined

This unit surveys the workshop trades: manufacturing methods, CNC and 3D printing, fitting, electrical work, carpentry, plastic moulding, casting and welding. No question has been asked recently, so every topic is short but complete.

Manufacturing Methods: casting, forming, machining, joining, advanced methods

Not asked since 2022

Definition. Manufacturing is the conversion of raw material into a finished useful product through a sequence of processes.

Key points.

Casting pours molten metal into a mould cavity, where it solidifies into the shape of the cavity.
Forming (forging, rolling, extrusion, drawing) changes shape by plastic deformation without removing material.
Machining (turning, milling, drilling, shaping) removes excess material with a cutting tool.
Joining (welding, brazing, soldering, riveting) attaches parts; advanced methods (CNC, 3D printing, laser, EDM) use computers or non-conventional energy.
Casting suits complex shapes, forming gives strong grain flow, machining gives close tolerance and finish, and joining builds assemblies.
Advanced methods such as EDM, laser beam machining and ultrasonic machining cut hard materials that ordinary tools cannot.

CNC machining, Additive manufacturing

Definition. CNC (Computer Numerical Control) machining uses a programmed computer to control tool movement, while additive manufacturing builds a part layer by layer from a 3D model.

Key points.

A CNC machine follows a part program written in G-codes (motion) and M-codes (miscellaneous functions such as spindle on or coolant on).
CNC gives high accuracy, repeatability and quick production of complex shapes with little operator skill.
Additive manufacturing (3D printing) starts from a CAD model, slices it into layers and deposits material layer by layer, for example by FDM using melted plastic filament.
It wastes little material and makes complex parts, but it is slow and unsuited to mass production.
The main CNC parts are the machine control unit (MCU), the input device, the drive system with servo motors and the feedback system with sensors.
Typical CNC operations are turning on a CNC lathe and milling, drilling and boring on a machining centre.
Other additive processes are SLA (resin cured by laser) and SLS (powder fused by laser), and the sequence is CAD model, STL file, slicing, printing, post-processing.

Fitting operations & power tools

Definition. Fitting is the assembly of machine parts by filing, cutting, drilling and finishing them to fit each other without machine-tool production.

Key points.

Basic fitting operations are marking, sawing, filing, chipping, drilling, reaming, tapping and threading.
Common hand tools are the bench vice, hacksaw, files, chisel, scriber, try square, steel rule, surface plate and vernier calliper.
Power tools such as the electric drill, angle grinder, power hacksaw and impact wrench do the same work faster and with less effort.
Safety rules include wearing goggles, clamping the job firmly and keeping guards in place.
Filing removes small amounts of metal with a file, chipping removes metal with a cold chisel and hammer, and tapping cuts internal threads with a tap.
Reaming finishes a drilled hole to an accurate size with a reamer, and a die cuts external threads on a rod.

Electrical & Electronics

Definition. Electrical work covers wiring and the installation of circuits, while electronics work covers assembling and soldering small components on circuit boards.

Key points.

Wiring uses insulated copper or aluminium wire, switches, fuses, MCBs and earthing for safety.
Tools include the wire stripper, cutter, tester, multimeter and pliers.
Soldering joins components with a low-melting tin-lead alloy melted by a soldering iron, using flux to clean the joint.
Common components are the resistor, capacitor, diode and transistor, assembled on a PCB (printed circuit board).
A good soldered joint is bright and smooth; a dull, grainy joint is a dry joint that conducts poorly.
Series connection gives one path for current, while parallel connection gives each load full supply voltage; house wiring is parallel.
Earthing carries leakage current to the ground and protects the user from shock.

Carpentry

Definition. Carpentry is the craft of cutting, shaping and joining wood to make furniture, doors and other structures.

Key points.

Marking and measuring tools are the try square, marking gauge, steel rule and bevel.
Cutting and shaping tools are the rip saw, tenon saw, chisel, plane and mallet.
Common joints are the lap joint, mortise and tenon joint, dovetail joint, dado joint and butt joint.
Seasoned timber is used because it shrinks and warps less than green wood.
The mortise and tenon joint is strong and used for frames and doors, and the dovetail joint resists pulling apart and is used for drawers.
Steps in making a joint are marking, sawing, chiselling, planing and fitting the pieces together with glue or nails.

Plastic moulding, glass cutting

Definition. Plastic moulding shapes heated plastic in a mould cavity, and glass cutting scores a glass sheet and breaks it along the score line.

Key points.

In injection moulding, molten plastic is forced under pressure into a closed mould, cooled, and the part is ejected.
Other methods are compression, blow and extrusion moulding; thermoplastics soften on heating and can be remoulded, while thermosets cannot.
Glass is cut by scoring one line with a diamond or carbide wheel cutter against a straight edge.
Light pressure under the score then breaks the sheet cleanly along the line.
Injection moulding suits mass production of items such as buckets, toys and switch bodies with high accuracy.
The glass cutter wheel should be oiled and used in a single firm stroke, because a second pass along the score spoils the break.

Metal casting

Definition. Metal casting is the process of pouring molten metal into a mould cavity made in sand and letting it solidify to get the desired shape.

Key points.

A pattern is a replica of the part, made slightly larger to give a shrinkage allowance, and it also carries a draft allowance for easy withdrawal from the sand.
The mould has a cope (top half) and drag (bottom half) in a moulding box, with sprue, runner, gate and riser for metal flow and feeding.
Steps: make the pattern, ram the sand around it, remove it, add cores if needed, pour the metal, cool, and remove the casting.
Defects include blowholes, shrinkage cavities and misruns.
Pattern materials are wood, metal, plastic and wax, and pattern types include the single-piece, split and match plate patterns.
Moulding sand needs porosity, strength, refractoriness and permeability so that gases escape and the mould keeps its shape.
A core is a sand shape placed in the mould to form a hollow cavity in the casting.

Welding (arc welding & gas welding), brazing

Definition. Welding permanently joins metal parts by melting the joint edges, usually with a filler metal, so they fuse on solidifying.

Key points.

In arc welding, an electric arc between the electrode and the job produces heat of about 3,000 to 4,000 degrees Celsius that melts the joint.
Gas welding burns oxyacetylene at the torch to produce a flame of about 3,200 degrees Celsius, and a filler rod is added.
Brazing joins parts using a filler metal (such as brass) that melts above 450 degrees Celsius but below the melting point of the base metal, which stays solid.
Welders must wear a helmet with a filter glass, gloves and an apron to protect against arc rays, sparks and heat.
The three oxyacetylene flames are neutral (equal gases, for general welding), carburising (excess acetylene) and oxidising (excess oxygen).
Arc welding uses a flux-coated electrode whose coating shields the molten pool from air, and an AC transformer or DC generator supplies current.
Common welding defects are porosity, cracks, undercut and incomplete penetration.

Last-minute revision

Casting pours molten metal into a mould, forming changes shape by deformation, and machining removes material.
CNC is programmed with G-codes and M-codes.
3D printing (additive manufacturing) adds material layer by layer from a CAD model.
Fitting operations are marking, sawing, filing, drilling, reaming and tapping.
Soldering uses a low-melting tin-lead alloy and flux.
Carpentry joints include lap, mortise and tenon, dovetail and dado.
Injection moulding forces molten plastic into a closed mould.
A sand mould has a cope on top and a drag below.
A pattern carries shrinkage and draft allowances.
Oxyacetylene flame is about 3,200 degrees Celsius.
Brazing filler melts above 450 degrees Celsius and below the base metal.

Memory hooks

Casting, forming, machining, joining is "CFMJ": pour, press, cut, connect.
Cope is on top, drag is dragged along the bottom.
G is for going (motion) and M is for miscellaneous.
Brazing: the base metal never melts; welding: it does.

Coverage checklist

Manufacturing Methods- casting, forming, machining, joining, advanced manufacturing methods: no past questions.
CNC machining, Additive manufacturing: no past questions.
Fitting operations & power tools: no past questions.
Electrical & Electronics: no past questions.
Carpentry: no past questions.
Plastic moulding, glass cutting: no past questions.
Metal casting: no past questions.
Welding (arc welding & gas welding), brazing: no past questions.

Account

Manufacturing Practices (BT-106) - Unit 1 Short Notes

How unit 1 is examined

Manufacturing Methods: casting, forming, machining, joining, advanced methods

CNC machining, Additive manufacturing

Fitting operations & power tools

Electrical & Electronics

Carpentry

Plastic moulding, glass cutting

Metal casting

Welding (arc welding & gas welding), brazing

Last-minute revision

Memory hooks

Coverage checklist