Manufacturing Exam

Machining

A process that removes excess material from the surface of a workpiece to produce a desired geometry, including operations like turning, drilling, and milling.

Cutting Speed ($V$)

The constant speed at which the cutting tool travels along the workpiece, typically measured in $m/min$.

Feed Rate ($f$)

The rate at which the tool advances along the workpiece, measured in $mm/rev$ for turning processes.

Shear Plane

The specific plane along which material is sheared to produce a chip during the cutting process.

Continuous Chips

Chips formed with ductile materials machined at high speeds; they produce a good surface finish but can become tangled around toolholders.

Built-up Edge (BUE)

Layers of workpiece material that gradually deposit on the tool tip, changing tool geometry, dulling the edge, and adversely affecting surface finish.

Segmented Chips

Also known as nonhomogeneous or sawtooth-like chips, these occurs with metals having low thermal conductivity and strength like titanium and its alloys.

Discontinuous Chips

Chips consisting of firmly or loosely attached segments that can cause machine vibration (chatter) and affect dimensional accuracy.

Chip Breakers

Devices traditionally clamped to the rake face, or features built into modern tools, designed to break chips intermittently.

Cutting Force ($F_c$)

The force acting in the direction of the cutting speed ($V$) which supplies the energy required for the cutting operation.

Thrust Force ($F_t$)

The force acting in a direction normal (perpendicular) to the cutting force ($F_c$).

Power input in cutting

Calculated using the formula $\text{Power} = F_c \times V$, it is primarily dissipated through shearing and friction.

Primary Shear Zone

A source of heat in machining caused by the work done in shearing the material.

High-speed Machining Benefits

As cutting speed ($V$) increases, more heat is carried away by the chip and less heat enters the tool and workpiece, improving machining economics.

Flank Wear

Tool wear occurring on the relief face due to rubbing against the machined surface, characteristically adhesive or abrasive in nature.

Crater Wear

Wear on the rake face of the tool influenced by the temperature at the tool-chip interface and the chemical affinity between the tool and workpiece.

Nose Wear

The rounding of a sharp tool due to mechanical and thermal effects, which can cause residual stresses on the machined surface.

Direct Tool-condition Monitoring

Observation methods involving optical measurements of wear using microscopes or sensors.

Indirect Tool-condition Monitoring

Observation methods involving the correlation of tool condition with parameters like forces, power, temperature rise, or vibration.

Surface Integrity

The state of material properties such as fatigue life and corrosion resistance that are affected by the nature of the produced surface.

Machinability

A material property defined by surface finish, surface integrity, tool life, force and power requirements, and the level of difficulty in chip control.

Adverse Effects of Temperature Rise

Includes lower tool strength and hardness, uneven dimensional changes in parts, and thermal damage to the machined surface.

Notches (Grooves)

Wear occurring at the depth-of-cut line where the chip is no longer in contact with the tool; deep grooves can lead to gross chipping.

Turning

The process of machining external cylindrical and conical surfaces like shafts, spindles, and pins, usually performed on a lathe.

Straight turning

A process that produces a cylindrical surface by reducing the workpiece diameter to a specific dimension as the tool moves parallel to the axis of workpiece rotation.

Facing

A process that produces a flat surface at the end of the workpiece as the tool moves at a right angle to the axis of rotation.

Taper turning

A process that produces a conical surface as the tool travels at an angle to the axis of rotation.

Contour turning

Also known as profiling, this process uses a single-point cutting tool to reproduce a surface contour from a template.

Form turning

A process used to machine irregular shapes using a cutting tool with the form or geometry of the desired shape advanced perpendicular to the work axis.

Grooving

A turning operation that produces recesses and shoulders on a workpiece.

Parting

The process of cutting off a workpiece into two parts by feeding a thin tool all the way to the axis of the workpiece.

Threading

The process of producing external or internal threads; internal threads are obtained by using tapping tools mounted in the tailstock.

Knurling

A process used to produce a regularly shaped roughness on cylindrical surfaces for applications such as knobs and handles.

Boring

A variation of turning used to enlarge a previously drilled hole or produce internal cylindrical or conical surfaces and grooves.

Material Removal Rate (MRR) - Turning

Calculated as MRR = \text{\pi} D_{avg} d f N = d f V for each revolution of the workpiece.

Cutting time (t) - Turning

The time needed for one pass of the tool, calculated as $t = L / (f N)$, where $L$ is the length of the workpiece.

Drilling

The process of producing holes or enlarging existing ones using a drill bit, which can be mounted in the tailstock of a lathe.

Core drilling

A drilling operation used specifically to make existing holes larger.

Step drilling

A process that produces holes with two or more different diameters.

Counterboring and Countersinking

Operations that produce depressions on the surface around a hole entrance to provide suitable seating for screws and bolts.

Reaming

An operation intended for finishing a previously drilled hole to improve its accuracy and surface finish.

Centre drilling

A process that produces a centre hole to provide a guide for a subsequent drilling operation.

Gun drilling

A process used for drilling deep holes with depth-to-diameter ratios of $100:1$ or higher.

Material Removal Rate (MRR) - Drilling

Calculated by dividing volume removed by cutting time: MRR = (\frac{\text{\pi} D^2}{4}) f N.

Slab milling

Also known as peripheral milling, it generates a horizontal surface where the axis of cutter rotation is parallel to the machining surface.

Face milling

A milling operation where the cutter is mounted on a spindle having an axis of rotation perpendicular to the workpiece surface.

Form milling

Produces curved profiles using special cutters with cutting edges shaped to form the specific cross section required.

Straddle milling

Machining two parallel surfaces simultaneously by mounting more than one cutter on the arbor.

Slotting and Angular milling

The use of a standard cutter to produce rectangular or triangular slots in a workpiece.

Linear speed of the workpiece ($f_m$)

In milling, it is calculated as $f_m = f_t N n$, where $n$ is the number of teeth in the cutter.

Material Removal Rate (MRR) - Slab Milling

Calculated as $MRR = W d f_m$, where $L_A$ is ignored in the calculation.

Machining time (t) - Face Milling ($W \ge D/2$)

Given by $t = (L + D) / f_m$, where an allowance is made for additional relative motion ($L_A = L_O = D/2$).

Nontraditional machining processes

Techniques used when traditional machining is impractical that remove excess material by involving chemical, thermal, electrical or mechanical energy, or combinations of these energies.

Chemical Machining (CM)

The oldest nontraditional machining process where material is selectively removed by exposing a workpiece to a chemical reagent or etchant such as acids or alkaline solutions.

Etchant

A chemical reagent, such as acids and alkaline solutions, used in the Chemical Machining process to remove material.

Maskant

An etch-resistant material used to cover specific areas of the workpiece to protect them while the uncovered areas are exposed to the etchant.

Electrochemical Machining (ECM)

A machining process that removes material by the action of an electrical power source and ion transfer inside an electrolyte fluid, where the tool acts as the cathode and the workpiece acts as the anode.

Electrolyte (ECM)

A pressurized fluid that acts as a current carrier and washes metal ions away from the workpiece to prevent them from plating onto the tool.

Electrical Discharge Machining (EDM)

A process based on the erosion of metals by electrical sparks from a DC power supply discharged across a thin inter-electrode gap between the tool and the workpiece.

Dielectric fluid (EDM)

An electrically non-conducting fluid pumped through the inter-electrode gap to flush out chips in the gap.

Wire EDM

A variation of EDM, also known as Electrical Discharge Wire Machining, where the tool electrode is a wire that travels along a prescribed path at a constant velocity.

Kerf

The constant gap maintained between the wire and the workpiece during the cutting process in Wire EDM.

Electron Beam Machining (EBM)

A process using high-velocity electrons accelerated by voltages between $150$ and $200\text{ }kv$ to melt and vaporize material in a vacuum chamber.

Laser Beam Machining (LBM)

A process using an intensely focused, coherent stream of light (a laser) to heat, melt, and evaporate portions of the workpiece.

Stimulated emission

The process where an energized atom of lasing material is struck by a photon, causing the atom to give off two photons of identical wavelength moving in the same direction.

Water Jet Machining (WJM)

A mechanical machining process that cuts materials via the impact of a water beam ejected from a nozzle opening of $0.05 - 0.1\text{ }mm$ diameter at pressures up to $1400\text{ }MPa$.

Abrasive Jet Machining (AJM)

A technique using abrasives propelled by high velocity gas at pressures of approximately $850\text{ }kPa$ and velocities up to $300\text{ }m/s$ to erode material from a workpiece.

Composite material

A combination of two or more dissimilar materials used together to impart a specific set of characteristics or properties that neither constituent material can achieve on their own.

Specific gravity

Ratio of the mass of a material to the mass of an equal volume of water at $4\,degC$.

Glass fibre (E glass)

An inorganic, isotropic fibre with a modulus of $70\,GPa$ that is strong due to a lack of defects ($>3\,GPa$ as made) but susceptible to environmental attack and fatigue.

Carbon fibre

An inorganic, anisotropic fibre with highly aligned planes of graphite, a modulus from $160-700\,GPa$, and resistance to chemical degradation and fatigue.

Aramid fibre (Kevlar)

An organic, highly anisotropic material strong due to highly aligned linear polymer chains ($>3\,GPa$), with a modulus of about $125\,GPa$ and susceptibility to UV light and moisture.

Phenolic resin

The first modern matrix resin; it is brittle, heat and fire resistant, produces water as it cures, and does not produce toxic gases in a fire.

Polyester resin

The commonest matrix resin in tonnage terms; it cures with catalysts at low temperature, wets out reinforcements very well, but burns easily.

Epoxy resin

The commonest matrix resin in aerospace, typically curing at elevated temperatures with a refrigerated shelf life of up to a year.

Core materials

Materials such as foam or honeycomb used to make sandwich panels to provide stronger and stiffer structures at minimum weight.

Polymethacrylimide (PMI) foam

A core material normally used in aerospace (e.g., Rohacell) with a maximum use temperature of approximately $180\,degC$.

Honeycomb (H/C)

A set of vertical strips of material (often aluminium or Nomex) in a hexagonal array that is stronger and stiffer than foam for a given density but harder to work with.

Direct processes

Manufacturing methods that use separate fibres and resin which are brought together at the point of moulding.

Indirect processes

Manufacturing methods that utilize pre-impregnated fibres (prepregs).

Contact moulding

A direct manufacturing process with very low material costs but poor reliability, poor property flexibility, and high finishing requirements.

Compression moulding

A process with good productivity for larger volumes where mould cycles are short, though tooling costs are expensive and geometrical flexibility is limited.

Vacuum Bagging & Autoclave Cure

A high-reliability manufacturing process for lightweight structures where plant costs for large autoclaves can exceed $£1,000,000$.

Advanced fibre-reinforced composites manufacturing

A unique manufacturing scenario where the material and the structure are created at the same time.

Thermosets

A category of matrix resins for PMCs including Phenolic, Unsaturated polyester, Epoxy, and Vinyl ester.

Thermoplastics

Matrix resins such as PEEK, PEI, and PPS that can be processed and reshaped with heat.

Thermoplastics

Matrices with essentially linear chains held together largely by entanglement.

Thermosets

Matrices where the whole block of resin may effectively be a single three-dimensional molecule; they start with relatively low viscosity and building molecule size through cure reactions.

Condensation Reaction

A chemical reaction occurring in phenolic and polyimide resins where a molecule of water is spat out for each bond produced.

Free Radical Reaction

A reaction used in polyester and vinyl ester resins where a catalyst generates free radicals that catalyze the opening of double bonds leading to cross-link formation.

Ring Opening Reaction

A two-step reaction occurring in epoxy and bismaleimide resins consisting of a ring opening reaction followed by a cross-linking reaction.

Gelation

The point during the cure of a resin when the first chain forms across the whole sample and all flow stops.

Vitrification point

A stage in the cure process after which resin shrinkage is very small but leads to locked-in stress.

Moisture Pick-up Sweeling

The process where resins pick up moisture from the atmosphere and swell, offsetting some of the locked-in stresses from cure shrinkage.

Resin Modulus Requirement

The matrix resin generally needs a Young’s modulus of above $3\,GPa$ to provide good compressive properties in laminates.

FST (Fire, Smoke, and Toxicity)

Selection criteria for aircraft interiors requiring resins that resist ignition and do not produce toxics; phenolic resins are the normal choice as they char rather than burn.

Exotherm

Heat generation on cure which can result in centerline temperatures more than $50^\circ C$ above the tool temperature in thick laminates.

Shop life (Out time)

The time a preimpregnated material can spend at room temperature prior to cure without degrading performance.

Qualification

The non-technical aerospace selection criterion involving a process that can cost >$1\,million$ and take up to $7$ years to generate allowable properties for a new resin.

Binders

Materials used in resin infusion processes to stabilize individual preforms and hold together the assembly, available as powders, fibrils, tacky threads/films, or sprays.