Cutting Processes: Notes

Materials and Processes

Materials:
- Metals (ferrous and non-ferrous)
- Polymers (thermoplastics, thermosets, elastomers)
- Ceramics
- Composites
Technological processes
Quality Control
Specific Processes:
- Casting
- Powder metallurgy
- Polymer Processing (Molding, Injection, Inflation…)
- Forging
- Extrusion
- Rolling
- Bending
- Stamping
- Calendering
- Machining
  - Turning
  - Punching, Drilling
  - Grinding
- Thermal Cutting (Laser, Plasma, Oxy-Fuel, …)
- Welding (MIG, TIG, SER, Laser, SFL…)
- Brazing
- Adhesives
- Mechanical connections (Rivet / Bolts)
- Other processes (Coatings, Prototyping)
TMP: Course Program (3 parts)

Classification of Mechanical Processes

Based on final result:
- Connection Processes (+)
- Cutting Processes (-)
- Deformation Processes (=)
Based on Physical principles:
- Technological Processes (Metals)
  - Mechanical
    - Deformation
      - Friction + Deformation
        On The Plate
        In The Volume
    - Cutting
      - Chip Removal
      - Punching
  - Thermal
    - Fusion + Solidification
      - Welding
      - Casting

Classification based on Primary and Secondary Operations

Primary modeling processes
- Casting (permanent, non-permanent molds, green sand, injected)
- Molding (polymer, glass)
- Plastic Deformation (forging, extrusion, rolling, stamping, calendering)
- Material Powder technology (applied to metallic and ceramic materials)
- Special processes (CVD, electroforming, Hand Lay-up)
Secondary modeling processes
- Cutting (machining, turning, punching grinding)
- Treatments (Thermal) (quench, tempering, aging, mechanical work)
- Connection (welding, brazing, bolted bonding, riveting, adhesives)
Finishing processes
- Finishing (Polishing, Galvanizing, Anodizing, Painting)

Classification in Processing and Connection Operations (M. P. Groover)

Modeling processes
- Casting, Molding…
- Powder technology
- Plastic deformation
Improvement of the Mechanical Properties
- Heat treatments
Surface processing
- Super cleaning and treatments.
- Coatings and deposition
Cutting (material removal)
Permanent Connection
- Welding
- Brazing
- Adhesive bonding
Mechanical connection
- Bolted connection
- Riveted connection

Technological Cutting Processes

Chip removal
- Turning
- Milling
- Drilling
- Saw cutting
- Grinding
- Threading
Punching Processes
Non Conventional and Thermals
- EDM (Electrical Discharge Machining)
- Ultrasonic Machining
- Electrochemical Machining
- Abrasive Blasting Machining
- Thermal Cutting (Laser, Plasma, Oxy-Fuel, …)

Applications of Cutting Processes

Car and truck bodies
Airplane airframes
Train carriage panels
Office furniture
Appliances and kitchen utensils

Chip Removal: Surface Generation

Surface generation process by combining two relative movements between tool and workpiece.
Rectilinear movements generate flat surfaces.
Circular movements generate cylindrical surfaces.

Turning

Turning: Obtaining surfaces of revolution using one or more single-cutting tools.
Cutting movement: Rotation of the machine.
Tool movement: Simultaneous movement of the tool according to a guideline coplanar with the axis.

Types of Turning

Cylindrical Turning: Feed (straight) motion is parallel to the axis of rotation. Can be external or internal.
Facing: Feed motion is perpendicular to the axis of the workpiece.
Conical Turning: Feed movement is concurrent with the rotation axis. Can be external or internal.
Cutoff: Achieving a circular notch or complete cut from the periphery to the center of rotation.

Other Cutting Processes

Boring: Similar to turning, but the rotational movement is given in the tool, the workpiece being fixed.
Drilling: Obtaining cylindrical holes using a multi-cutting tool. The cutting motion can be imposed on the tool or the workpiece.
Reaming: Calibration of holes after drilling, using a tool called a chuck. The tool or workpiece rotates with relative movement between them, parallel to the axis of rotation.
Shaping and Planing: Obtaining flat surfaces generated by an alternate rectilinear movement of the part or tool. The guideline is straight and perpendicular to the generator, with intermittent feed during the tool's return.
Saw Cutting: Sectioning or cutting using thin multi-cutting tools (saw). The movement of the saw can be rectilinear, reciprocating, or continuous.
Grinding: Abrasion machining to obtain surfaces with controlled roughness, providing a good finish to parts previously machined.
Milling: Machining process with varied generate-guideline combinations, generating a variety of surfaces depending on relative movements between the tool and workpiece. Milling cutters are usually multi-die.
Tangential Cylindrical Milling: Surface is flat and parallel to the axis of rotation of the tool.
Front Milling: The milling cutter's axis of rotation is perpendicular to the generated flat surface.
Threading: Obtaining fillets by opening one or more helical grooves of uniform pitch on cylindrical or conical surfaces of revolution. Can be external or internal.

Threading Issues and Solutions

Problem with Thread:
- Only 1-2 threads
- Not reliable
- Thread breaks
Problem with Weld nut:
- Thermal distortion
- Only for plates
Problem with Rivet nut:
- Jam during assembly
- Can twist
- Limited stability
Solution: Flow Drilling

Cutting Parameters

Turning:
- Tool feed (a): Progression or toolpath made in a rotation or duty cycle.
- Depth of Cut (p): Distance between the tool tip and the unmachined surface, perpendicular to the work plane.
- Cutting Speed (v): Instantaneous speed of the reference point of the cutting edge, along the direction and sense of cut.
- $Ac = a * p = b * h$ ; $Ac$ is the tool cutting section
Milling:
- Feed per tooth: Path of each tooth, measured in the direction of the tool's feed between two consecutive cutting surfaces.
- Formula: $a = a_d * Z$ ; Z is the number of teeth

Process Quantification

Requirements:
- Minimization of production costs and increase in quality.
- Minimization of machining time with increased Material Removal Rate (MRR).
Material removal rate:
- Volume of material removed per unit time; represents the flow of material through the cutting area.
- $Zm = Ac * v$ Ac – Cutting area(a × p or b × h)

Material Removal Rate/Specific Cutting Energy

Material removal rate ( $Z_m$ ):
- Volume of material removed per unit time.
Specific Cutting Energy ( $k_s$ ):
- Power required to remove a volume unit.
Cutting power ( $N_m$ ):
- Power required to remove the material.
- $Zm= Ac * v$
- $Nm = ks * Z_m$

Characterization of a Cutting Tool

Elementary tool concept
- Tool with only one cutting edge
- γ – angle of attack
- α – exit angle
- β – Tool edge angle

Physical Mechanisms of Chip Formation

During machining, the tool penetrates the workpiece, repressing a small material element against the leading surface of the tool.
The repressed material deforms plastically, progressively, until shear stresses initiate sliding between it and the workpiece.
Sliding occurs according to the planes of the crystals sliding in a limited region called the cutting or distortion zone.
Continual penetration of the tool separates the material due to slippage.
The deformed material (chips) slips onto the tool's strike surface while a new material element starts deforming., leading to chip formation.

Influence of Parameters

Angle of attack (γ)
- If γ ↑:
  - Thinner chip
  - Less deformation
  - Chip temperature decreases
  - Cutting force decreases
  - More regular cut
  - Frictional force decreases
- It has influence:
  - In friction
  - Tool wear
Exit angle (α)
- It has influence:
  - Tool resistance
  - Heat dissipation
Cutting speed (Vc)
- If Vc ↑:
  - Tool temperature increases
  - Chip Temperature increase
  - Temperature of the part decreases

Geometry of the Orthogonal Chip Start Cut

γ Angle of Attack (γ)
α Exit Angle (α)
Ø Cutting Angle (Ø)
Study Topics Cutting Angle(Ø)
Cutting Ratio
$r = h_c/h = cos(\phi - \gamma)/sin(\phi)$
$tg(\phi) = rcos(\gamma) / (1-rsin(\gamma))$

Forces Acting on the Cutting Edge

Cutting force (Fc)
Feed force (Fa)
Tangent force to attack face (Ff)
Normal force to attack face (Nf)
Tangent Force to Distortion Plane (FS)
Force Normal to Plane Distortion (NS)
$(F_a = R*sin(\beta - \gamma))$
$(F_c = R*cos(\beta - \gamma))$

Forces in the Face of Attack

$Ff = Fc * sin(\beta) + F_a * cos(\beta) = R*cos(\gamma)$
$Nf= Fc * cos(\beta) - F_a * sin(\beta) = R*sin(\gamma)$

Forces in the Plane of Distortion

$Fs = Fccos(\phi − \beta + \gamma) - F_asin(\phi − \beta + \gamma) = R*cos(\beta -\gamma)$
$Ns = Fcsin(\phi − \beta + \gamma) + F_acos(\phi − \beta + \gamma) = R*cos(\beta -\gamma)$

Cutting Angle to Friction and Attack Ratio

Plastic sliding occurs in the plane where shear stresses are maximum
$τs = Fs / A_s = Rcos(φ + β − γ) / (bh)$
$\frac{\partial τ}{\partial φ} = [cos(φ + β − γ)cos(φ) − sin(φ + β − γ)sin(φ)] = 0$
$cos(2φ + β − γ) = 0$
$2φ + β − γ = \frac{π}{2}$
$φ + β − γ = C$
C is the machinability constant of the material

Ernst and Merchant's Theory

Ernst and Merchant's theory allows us to establish a relationship between the angle of cut (Ø), the angle of attack (γ) and the angle of friction (β).
The theory considers that the shear angle (Ø) corresponds to the plane according to which the shear stress is maximum, resulting in: $φ + β − γ = C$