Machine Dynamics, Machining, and Mechanical Systems

Machine Dynamics and Mechanical Systems

A machine is a physical system that uses energy to apply forces and control movement to perform an action. Dynamics is the part of physics that studies the motion of objects and their response to the forces acting on them. It relates the concepts of force, mass, and acceleration. The principles of dynamics are Newton’s laws:

  • First Law of Newton: Principle of Inertia
  • Second Law of Newton: Principle of Force
  • Third Law of Newton: Principle of Action and Reaction

Work is the energy transferred to or from an object by applying force along a displacement. The SI unit is the joule. Energy is the quantitative property that is transferred to a body or a physical system, recognizable in the performance of work and in the form of heat and light. It is the capacity of bodies to perform work and produce changes in themselves or other bodies.

Kinematics and Machining Processes

Kinematics is a subfield of physics and mathematics that studies motion without considering the causes that produce it (forces), limiting itself to the study of the trajectory as a function of time. It relates the concepts of space, velocity, acceleration, and time. The fundamental types of motion are:

  • Linear motion
  • Accelerated linear motion
  • Circular motion

Machining is a manufacturing process in which a desired shape or part is created by the controlled removal of material, usually metal, from a larger piece of raw material by cutting. It is a form of subtractive manufacturing that uses machine tools.

  • Turning: A machining process in which a cutting tool describes a helix toolpath by moving more or less linearly while the workpiece rotates.

  • Boring: The process of enlarging a hole that has already been drilled (or cast). Boring is used to achieve greater accuracy of the diameter of a hole and can be used to cut a tapered hole.

  • Milling: Uses a rotating cutting tool to bring cutting edges to bear against the workpiece. This is the most versatile tool and technique used in a machining workshop.

  • Reaming: A process that uses a rotary cutting tool to smooth an existing hole in a workpiece. This is a cutting process that removes material, and its primary purpose is to even out the walls of a hole.

  • Drilling: Creates a new hole or refines an existing hole using a rotating cutter. Drilling is most commonly done using drill presses, but sometimes drilling tools will be attached to compatible lathes or mills to create holes.

Mechanical Systems and Motion Transmission

Mechanisms (and, by extension, mechanical systems) consist of the following basic elements:

  • Drive system or input system: Receives the input energy, which will be transformed or transmitted. In a car, this would be the engine.

  • Transmission system: Allows the energy or movement provided by the drive system to be modified. In a car, this system would be composed of transmission shafts, clutches, gearboxes, etc.

  • Receiver system or output system: Performs the work with the output provided by the transmitter system and is the objective of the mechanical system. In a car, this system would be composed of the drive wheels.

Motion Transmission Systems

The driving system and the receiving system have the same type of movement.

  • Linear transmission: Rectilinear movements (pulleys, levers). The fundamental application of these mechanisms lies in the transformation of forces so that the force required to carry out a certain action is less than that which would be required if the mechanism were not used.

    • The lever: Consists of a rigid bar that is articulated at the so-called fulcrum, which enables the bar to rotate.

    • A pulley: Is a disk that can rotate around its axis and has a groove on its edge through which a rope, cable, or belt is passed. The function of a fixed pulley is to modify the direction of the applied force.

  • Circular transmission: Rotational movements (belt transmission, with chains, gears). The aim of this type of mechanism is to increase or reduce the speed of rotation of a shaft as much as desired.

Motion Transformation Systems

The motor system and the receptor system have different types of movement.

  • Rack and pinion: This mechanism transforms the rotary movement of an axle, on which a pinion is mounted, into rectilinear movement by meshing the teeth of the pinion with the teeth of a prismatic bar (rack) that moves longitudinally. This type of mechanism is reversible. It is used to open and close doors on guides and in car steering.

  • Screw-Nut: Its operation is based on the fact that if the nut is kept fixed, the rotary movement of the screw produces the longitudinal displacement of the screw and vice versa. This system converts the circular movement of the screw into the rectilinear movement of the nut.

  • Rod-crank: The system consists of a rotating element called a crank, connected to a rigid bar called a connecting rod, so that when the crank turns, the connecting rod is forced to advance and retreat successively. This creates a reciprocating motion of the connecting rod.

  • Crankshaft: The crankshaft is an axis with elbows and counterweights that, applying the principle of the crank-connecting rod system, transforms the rectilinear alternative movement into rotary movement or vice versa.

Brakes and Clutches

BRAKES: Their main function is to stop or progressively reduce the speed of a mechanical element, normally an axle, shaft, or drum, or to keep it immobilized when stopped.

CLUTCHES: The clutch is the mechanism that must allow the motor and driven shafts to be easily decoupled completely or partially according to the needs of the process.

Lubrication in Mechanical Systems

Lubrication plays a critical role in the longevity and efficiency of machinery in industrial settings. Proper lubrication:

  • Reduces friction between moving parts, which decreases energy consumption and wear.
  • Minimizes heat generation due to friction, preventing overheating and potential equipment failure.
  • Prevents corrosion by forming a protective layer on metal surfaces.
  • Improves reliability and reduces unplanned downtime, leading to more consistent production.
  • Saves costs in maintenance and replacements by prolonging the lifespan of components.

Types of Lubricants

  • Oils: Commonly used for high-speed applications. Ideal for situations where easy reapplication or circulation is needed. Do not use when the machine part is dirty or dusty.

  • Greases: Thicker than oils and adheres to surfaces well, making it ideal for components like bearings, gears, and joints. Suitable for applications where the lubricant needs to stay in place for long periods. Do not use grease on delicate or fast-moving machine parts.

  • Dry lubricants: Made of fine particles that make them more slippery. Used when components cannot tolerate oils or greases due to contamination risks. Do not use when the application is exposed to solvents or liquids that can wash away the remaining lubricant.

Methods of Lubricant Application

  • Manual Lubrication (Hand Greasing)
  • Automatic Lubrication Systems
  • Centralized Lubrication Systems
  • Spray (Mist) Lubrication
  • Oil Bath or Splash Lubrication

Impact of Lubrication on Mechanical Wear and Tear

  • Increased Friction
  • Surface Fatigue
  • Corrosion
  • Abrasive Wear