28523 - Foundations of Mechanics Applied to Machines T-2

Learning outcomes

Basics on functioning and realization of mechanical systems.

Course contents

1.Elements of engineering drawing

Sizes and layouts of drawing sheets

Types of lines and examples of their applications.

Projection methods. Orthogonal projections: first dihedral and third dihedral methods. Views.

Scales

Reference arrows method.

Sections. One cutting plane. Two or more cutting planes: Parallel and contiguous planes. Cylindrical surface sections with a given directrix. Unsectioned elements. Half section view. Rotated and subsequent sections. Section hatching.

Special conventional representations. Contiguous parts represented by reference. Outline of elements before or after processing. Real and imagery intersections. Local views. Flat faces. Symmetrical object view. Interrupted views, partial and local sections. Repetitive elements. Detail drawing. Light inclination and curvature.

2. Dimensioning

Characteristics and scope

Leader and dimension lines; arrows. General rules and examples

Partial and actual view dimensions

Angles, arcs and chords

Dimension writing methods

End-product, manufacturing, assembly drawings

Direct and indirect dimensions. Alternative dimensioning

Choice of the dimensioning system according to the type and purpose of the drawing

Functional and manufacturing dimensioning

Dimensioning techniques. Chain and auxiliary dimensioning. Parallel and superimposed dimensioning. Combining dimensioning and dimensioning by coordinates (Cartesian or polar).

Special standards for dimensioning. Diameter (Ø), Radius (R) and Spheres (SØ or SR), Bevels and chamfers. Repeated features.

3. Dimensional tolerancing

Geometric and dimensional errors. Functional dimensions. Adjustment.

Nominal dimensions. Limit dimensions (maximum and minimum). Deviations (upper and lower).

Dimensional tolerance

Shafts and holes

Interference and clearance. Couplings with interference, transition and clearance fit.

Dimensioning influence on tolerancing

Tolerancing indications. Direct method. Tolerance classes. The ISO tolerance system.

4. The ISO tolerance system

Shaft / hole couplings

Ranges of nominal dimensions

Normalized degree of tolerance

Tolerance position. Zero line. Fundamental deviation.

Standard and recommended couplings.

Shaft/hole basis system.

Dimensioning with the ISO system.

5. Dimensional testing

The vernier caliper and gages

6.Normal numbers

7.Special representations

Threads and threaded parts. Dimensioning. Unscrewing systems.

Keys. Retaining rings (Seeger), nuts, washers.

Spline couplings

Gears

8.Surface roughness

Surface, undulation and roughness profile. Cut-off. Sampling length.

Measurement and calculation. Representation on drawings.

Relation to the manufacturing processes.

Recommended roughnesses and costs

9. Elements of mechanics of materials

Mechanical characteristics: elasticity and plasticity, fragility

Stresses and tensions : internal and at a point state of stress, the Cauchy’s stress tensor and theorem, normal and shear stresses, Indefinite equations of equilibrium, Principal stresses and directions.

Deformations. Local field of displacement. Affinity. Transformation components. Strain tensor. Principal strains and directions. Congruence equations. Physical meaning of the tensor components.

Stress-strain relation: Constitutive equations. Elastic, linear and isotropic body. Elastic constants and physical meaning.

Elastic equilibrium: equation system, boundary conditions, equation solution, de Saint-Venant method

Assumptions of the de Saint-Venant’s problem

Tension or compression: tensions and deformations; tensile testing; typical curves.

Bending: Linear bending. Neutral axis. Biaxial flexure. Tensions and deformations.

Torsion: Tensions and deformations in a circular section.

Shear: Tensions (the approximate method); rectangular and circular section.

Internal loads.

The de Saint-Venant’s problem applied to engineering beams .

Calculation of internal loads in a transmission shaft.

10.Surface hardness

Description, advantages and disadvantages of the Brinell’s, Rockwell’s and Vickers’ hardness tests.

Microhardness

11.Classification of materials

12.Cast Iron

Production: blast furnace, coke

Graphite

Gray, ductile and white cast iron. Malleable cast iron (whiteheart and blackheart)

13.Steel

Production: Bessemer converter; Martin -Siemens furnace; EAF furnace, LD process.

Main alloying elements (Cr, Mn, Ni, Si) and their effects. Harmful elements. Minimum contents of the alloying elements.

Designation system.

Mainheat treatments :normalization; hardening, tempering, reclamation, annealing, surface hardening, cementation fuel.

14.Aluminium(Al) and its alloys

Characteristics. Effects of the alloys. Designation system

15.Copper(Cu) and its alloys

Characteristics. Designation system

Brass(Zn <= 40%); Bronze(Sn <= 10%);Cupro-nickel(Ni<= 30%); Aluminum bronze(Al<= 10%)

16.Magnesium(Mg) and its alloys

Characteristics. Designation system. Ultralight alloys(Al, Mn, Zn)

17.Titanium (Ti) and its alloys

Characteristics.

18.Non-metallic materials

Plastics: characteristics, thermoplastics, thermos setting materials, additives.

Ceramic materials: characteristics and main applications.

Composite materials: structure (reinforcement and matrix), characteristics and main applications

19. Foundry

Metal alloys casting

Molding; Flasks

Patterns. Pattern drawn and rapping. Cores. Pattern shrinkage allowance. Functionality (pattern plate). Materials.

Foundry sands

Dry and green sand molding

Casting Sprues. Riser. Blowholes, Pull air bubbles

Chilled casting

Die-casting (hot room and cold room)

Investment casting

20.Hot and cold deformation processing

Ductility, malleability, plasticity

Forging (press and hammer)

Rolling. Ingots. Continuous casting. Semi-finished. Rolling trains

Extrusion

Die -drawing

Sheet metal machining: Cutting and punching, flame cutting, bending, cylindering, deep drawing.

21. Machining

Chip formation; cutting angles and parameters

Cutting motions.

Choice of machine tools

Rotary Cutting machines: characteristics, types, tools, motions. Lathe. Milling Machine. Drill (sensitive, Automatic, radial). Drilling, core drilling, countersinking, reaming processes. Boring machine.

Linear Cutting machines: characteristics, types, tools, motions and machinings. Shaper. The Fairbairn’s guide. Slotting, planer and broaching machines.

Grinding and grinding wheels

Numerical controls

22.Welding

Base and filler material.

Protection from oxygen and cinders

Autogenous weldings by fusion . Electric arc weldings (with coated electrode , MIG, MAG,TIG and submerged arc ). Gas (torch, oxyacetylene) welding. Plasma, laser; electron beam, aluminothermic weldings.

Autogenous weldings by pressure: spot, seam, contact and ultrasonic weldings

Brazing : strong, soft and braze welding.

Coupling Types.

Drawing representation

23. Machining Cycles

Description

Positioning of a body, of a plane, of a straight line, of an axis.

Fixing. Flattening, turning, puncturing. Direct and indirect systems. Knuckles.

Guides and equipments.

Examples of machining cycles. Machining cycles sheet. Sheet analysis operation.

24. Rolling Bearings

Characteristics and mounting.

Types. Deep groove ball bearings. Self-aligning ball bearings. Angular contact ball bearings (O, X, in tandem mounting; resultant of the forces). Cylindrical roller bearings. Needle roller bearings. Spherical Roller bearings. Single row tapered roller bearings.

Thrust ball bearings. Thrust Cylindrical and needle roller bearings. Spherical roller thrust bearings.

Load capacity and life. Wear and surface fatigue. Basic rating life. Basic dynamic and static load rating. Life calculation (equivalent load and examples)

Friction and speed. Bearing systems. Selection. Conventional representation in technical drawings.

25 Ball and roller linear guides.

26. Recirculating ball screws

Characteristics. Internal and external recirculation. Threads shape. Speed of the rolling elements;. Loads and performance. Inverse motion. Life. Stiffness and preload.

27.Roller screws

Characteristics and functioning.

28. Linear translational motion

29.Kinetoelastodynamics Modeling

30. Couplings

Introduction to transmissions.

Shaft permanent connections.

Misalignments and related motions. Types of misalignments.

Classification and selection of couplings.

Rigid couplings: sleeve couplings (simple, precision, Sellers), shell coupling, disc and flange couplings.

Torsionally rigid flexible couplings. Lamellar, beam, chain, gear couplings.

Flexible couplings. Characteristics and influence on the system dynamic behaviour. Equation of motion of the output shaft and motor torque. Transmissibility. Helicoidal peripheral springs couplings. Bibby, Rotex Periflex and Giubo couplings. Couplings with rungs.

Mechanism Couplings. Spline coupling. Simple and Double Universal joint. Homokinetic balls joint. Rzeppa's , Oldham's and Schmidt's joints.

Torsional vibrations of the Universal joint. Secondary effects in homokinetic joints.

31. Clutches

Description and classification.

Dog clutches: clutches with rungs, with front and radial teeth.

Friction clutches

Flat clutches . Types, control, pressure distribution and torque. Lubrication. Selection and calculation. Industrial and automotive clutches. Torsional vibration damper.

Cone clutches. Characteristics, pressures and torques. Examples

Synchronizer clutch.

Centrifugal action automatic clutches

32. Freewheels

Description , classification and use

Ratchet clutch. Theoretical and real constraints. The overrunning. Non-return devices. Backlash reduction.

Friction Freewheels : Examples and applications. Roller freewheels. Clamp freewheels.

33. Intermittent mechanisms

Intermittent motions characteristics and alternative solutions.

The Maltese cross mechanism. Characteristics of motion according to slots number. Outline on speed and acceleration of the output link.

Intermittors: Cycloid motion, peripheral and front pins, applications.

34. Hydraulic joint

Description , functioning, advantages.

Transmission ratio. Slip. Efficiency and power dissipation. Transmitted power and torque. AC motor coupling. Torque converter (outline).

35.Brakes

Description, classification and types of control.

Mechanical brakes

Clasp brakes . Pressure distribution with translating shoe. Optimal wrap angle. Rotating brake shoe. Contact pressure resultant: model, circumference and points of Romiti; simplified model. Brake shoe functional characteristics, balance. Simple and double solutions. Industrial solution: description and brake blocks' balance. The balanced brake.

Drum brakes: Characteristics and types.

Band brakes. Characteristics, the Eithelwein's formula , braking torques and decelerations.

Disc brakes. Characteristics. Full and partial brakes. Single-disc and multi-disc brakes. Floating and fixed discs and brackets. Contact pressures and transmitted torques.

Braking motors

Brake selection and verification: useful design parameters

36. Braking

Shaft motion equation

Effective braking conditions

Braking time, deceleration, braking stopping distance, power and energy dissipation approximate calculation.

Braking calculation of a plant (example)

Teaching methods

The course is composed of two modules. The first one (60 hours) provides main theoretical and practical knowledge and it mainly consists of lectures and exercises. Exercises at the laboratory of Mechanics are also provided. The second module (30 hours) provides the basics for the proper use of CAD and it mainly consists of interactive lectures at the computer laboratories of the School of Engineering.

Assessment methods

Written and oral examination.
Written examination consists of three questions:
One question on engineering drawing to be held by hand or by a ruler (other drawing instruments are not allowed). Examples of possible exercises: orthogonal projection, representation of a mechanical component, drawing of a detail extract from an assembly, dimensioning, tolerances, drawing of coupling and mounting systems (as reported in the final programme of the course).

Two theoretical questions about the topics covered in Module 1 of the Course.

Oral examination includes a CAD practical test.

Teaching tools

Course Slides.

Office hours

See the website of Nicola Sancisi

See the website of Francesco Vai