Diamond Tooling Articles

Material Guide

02 Jun

Learn everything you wanted to know about different materials and methods of working with them

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Understanding the material you will be working with, their unique characteristics and properties is crucial for selecting the appropriate diamond or cbn cutting tools, machining parameters, and processes. Each material behaves differently under machining operations due to its physical, chemical, and mechanical properties. Here’s an overview of what you should know about machining a variety of materials, focusing on metals, composites ceramics, glass, optial glass, semiconductor materials, natural stone, semi precious and precious stone (lapidary), semiconductor materials.

Understanding the physical, chemical, and mechanical properties of materials is fundamental for selecting the appropriate machining strategies, tool materials, and operational parameters. Here’s a more detailed look at these properties:

Physical Properties

Physical properties are those that can be observed or measured without changing the composition of the material. In the context of machining, key physical properties include:

  • Density: The mass per unit volume of a material. It influences the material's weight and stiffness, affecting the choice of machining parameters and tooling requirements.
  • Thermal Conductivity: The ability of a material to conduct heat. High thermal conductivity materials (e.g., copper) dissipate heat more efficiently during machining, affecting tool wear and the need for cooling.
  • Thermal Expansion Coefficient: The rate at which a material expands with temperature. Materials with high thermal expansion coefficients (e.g., plastics) may require adjustments in machining tolerances for operations involving significant heat.
  • Electrical Conductivity: Relevant for processes such as electrical discharge machining (EDM), where the material must be conductive. Materials with low electrical conductivity (e.g., ceramics) are not suitable for EDM.
  • Melting Point: The temperature at which a material changes from solid to liquid. Materials with high melting points can withstand higher machining temperatures but may require specialized cutting tools that can operate effectively at elevated temperatures without losing hardness or strength.
  • Specific Heat Capacity: This property indicates how much heat a material can absorb before its temperature rises. Materials with high specific heat capacities can absorb more heat during machining, potentially reducing thermal-induced stress and deformation but may also necessitate enhanced cooling strategies.

Chemical Properties

Chemical properties describe a material's reactivity with other substances, which can be critical for machining processes involving chemical interactions:

  • Corrosion Resistance: The ability to resist degradation due to reaction with environmental agents. This is crucial for selecting materials for tools and parts intended for corrosive environments.
  • Oxidation Resistance: Important for high-temperature machining operations or applications where the material is exposed to oxygen at elevated temperatures, potentially affecting its integrity and the surface finish.
  • Chemical Stability: The resistance of a material to chemical change. In machining, chemical stability affects the choice of coolants and lubricants, as some materials may react adversely with specific chemical agents.
  • Reactivity with Coolants: Certain materials may react chemically with specific coolants or lubricants, leading to corrosion or material degradation. Selecting chemically compatible coolants is essential to prevent adverse reactions that can affect both the workpiece and the tool life.
  • Surface Chemistry: The chemical composition of a material's surface can influence adhesion, friction, and wear characteristics during machining. For example, certain surface treatments or coatings may be applied to improve surface characteristics or to reduce the tendency for material to weld to the cutting tool.

Mechanical Properties

Mechanical properties determine a material's behavior under various forces or loads. These properties are vital for predicting how materials will respond to machining forces:

  • Hardness:The resistance of a material to deformation, typically measured by scales such as Rockwell, Brinell, and Vickers. Hard materials (e.g., hardened steel, ceramics) require harder cutting tools, such as those made from carbide or diamond.
  • Tensile Strength: The maximum stress a material can withstand while being stretched or pulled before failing. High tensile strength materials are more resistant to cutting forces, demanding more robust machining strategies.
  • Yield Strength: The stress at which a material begins to deform plastically. Knowing the yield strength helps in avoiding excessive deformation during machining.
  • Elasticity and Plasticity: Elasticity is the ability of a material to return to its original shape after deformation, while plasticity is the degree to which it can undergo permanent deformation. Understanding these properties is essential for predicting material behavior under machining stresses.
  • Toughness: The ability of a material to absorb energy and plastically deform without fracturing. Tough materials can withstand high-impact machining processes but may pose challenges in chip formation and control.
  • Wear Resistance: The ability to withstand abrasion and wear during machining. Materials with high wear resistance reduce tool wear but may require more aggressive machining parameters or specialized tool materials.
  • Fracture Toughness: This property measures a material's resistance to crack propagation. Materials with high fracture toughness are less likely to experience catastrophic failure or chipping during machining but may require specific tool geometries to manage chip formation and removal effectively.
  • Ductility: Ductile materials can deform significantly before breaking, allowing for more aggressive machining conditions but also posing challenges in terms of maintaining dimensional accuracy and surface finish. Controlling machining parameters and tool paths is critical for machining ductile materials.
  • Fatigue Strength: The ability of a material to withstand repeated loading and unloading cycles without failing. Understanding the fatigue strength is crucial for parts subjected to cyclic stresses in their operational life. Machining strategies that minimize surface defects can help improve the fatigue strength of the finished part.
  • Modulus of Elasticity (Young’s Modulus): This property measures the stiffness of a material, or its resistance to elastic deformation under load. Materials with a high modulus of elasticity are stiffer, which can influence the selection of machining parameters to prevent deflection or distortion during the cutting process.

Material Debris / Chipping Type

The shape of material debris, or chips, generated during machining operations is significantly influenced by the material properties of the workpiece, as well as the machining parameters such as tool geometry, cutting speed, feed rate, and depth of cut. Understanding the relationship between material properties and chip formation can provide valuable insights into the machinability of the material, the efficiency of the machining process, and the quality of the finished product. Here's how material properties affect chip shapes and what those shapes can indicate about the machining process:

1. Ductility
  • Materials with High Ductility (e.g., most aluminum alloys, mild steels): These materials tend to produce long, continuous chips. Continuous chips are indicative of smooth cutting but can pose problems with chip evacuation and may lead to a wrapped chip around the tool or workpiece, potentially damaging both.
  • Optimization Strategy: Chip breakers, high-pressure coolant systems, or specific tool geometries can be used to control chip formation and facilitate chip breaking or evacuation.
2. Hardness
  • Hard Materials (e.g., hardened steels, titanium alloys, ceramics): Hard materials often result in short, brittle chips. These chips indicate that the material is fracturing ahead of the tool edge rather than undergoing plastic deformation.
  • Optimization Strategy: Adjustments in tool material (e.g., polycrystalline diamond or cubic boron nitride) and cutting parameters can help manage tool wear and surface finish when working with hard materials.
3. Toughness
  • Tough Materials (e.g., nickel-based superalloys, some stainless steels): Tough materials can produce segmented (serrated) chips, which result from a cyclical process of crack initiation, propagation, and fracture due to the material's resistance to shear deformation.
  • Optimization Strategy: Optimizing cutting speed and feed rate, and using tools with reinforced cutting edges can help manage the machining of tough materials.
4. Thermal Conductivity
  • Materials with Low Thermal Conductivity (e.g., titanium, Inconel): These materials tend to retain heat in the cutting zone, affecting chip shape and potentially leading to work-hardening of the surface being machined. Chips may be more difficult to predict but can range from segmented to continuous, depending on the specific conditions.
  • Optimization Strategy: Using coolants effectively to manage temperature and selecting tool materials that can withstand high temperatures can help improve chip formation and surface quality.
5. Brittleness
  • Brittle Materials (e.g., cast iron, some ceramics): Brittle materials typically produce powdery chips or small, fragmented pieces due to their inability to undergo significant plastic deformation before fracturing.
  • Optimization Strategy: Using sharp tools and controlling vibration can help minimize surface damage and improve the quality of the machining process for brittle materials.

Material Machining Parameters

The material machining parameters such as the RPM’s, fee rate, coolant or lubricant to use depends on the material properties

RPM (Revolutions Per Minute)

The RPM setting determines the speed at which the cutting tool or the workpiece rotates. The correct RPM is crucial for achieving efficient cutting, optimal tool life, and the desired surface finish.

  • Material Hardness: Softer materials typically allow for higher RPMs, while harder materials require lower RPMs to reduce tool wear.
  • Tool Material and Type: Diamond tools, due to their hardness and wear resistance, often allow for higher RPMs compared to conventional tool materials.
  • Diameter of Tool: The larger the tool diameter, the lower the RPM, following the principle that cutting speed (measured in surface feet per minute or meters per minute) should remain constant.
Feed Rate

Feed rate is the speed at which the tool moves through the material or the material moves past the tool. It's typically measured in inches per minute (IPM) or millimeters per minute (MM/min).

  • Material Hardness and Toughness: Tougher materials generally require slower feed rates to reduce the risk of tool breakage and to manage force and heat generation.
  • Tool Material and Geometry: The strength and design of the cutting tool dictate how aggressively it can cut. Diamond tools can often support higher feed rates due to their exceptional hardness and wear resistance.
  • Operation Type: Finishing operations usually have lower feed rates than roughing operations to achieve a finer surface finish.
Coolants and Lubricants

Coolants and lubricants serve to reduce heat and friction, flush away chips, and sometimes protect against corrosion. The choice of coolant or lubricant depends on several factors:

  • Material Being Machined: Some materials, such as aluminum, may require water-soluble coolants to prevent overheating, while others, like titanium, might benefit from coolants with extreme pressure additives.
  • Machining Operation: Operations like deep-hole drilling require coolants with excellent chip evacuation capabilities.
  • Environmental and Health Considerations: Regulations and workplace safety standards may influence the choice of coolants, pushing towards the use of safer, more environmentally friendly options.

Material Machining Parameters

The material machining parameters such as the RPM’s, fee rate, coolant or lubricant to use depends on the material properties

  • Material Hardness and Toughness: Tougher materials generally require slower feed rates to reduce the risk of tool breakage and to manage force and heat generation.
  • Tool Material and Geometry: The strength and design of the cutting tool dictate how aggressively it can cut. Diamond tools can often support higher feed rates due to their exceptional hardness and wear resistance.
  • Operation Type: Finishing operations usually have lower feed rates than roughing operations to achieve a finer surface finish.
Coolants and Lubricants

Coolants and lubricants serve to reduce heat and friction, flush away chips, and sometimes protect against corrosion. The choice of coolant or lubricant depends on several factors:

  • Material Being Machined: Some materials, such as aluminum, may require water-soluble coolants to prevent overheating, while others, like titanium, might benefit from coolants with extreme pressure additives.
  • Machining Operation: Operations like deep-hole drilling require coolants with excellent chip evacuation capabilities.
  • Environmental and Health Considerations: Regulations and workplace safety standards may influence the choice of coolants, pushing towards the use of safer, more environmentally friendly options.

Material Comparison Parameters

The material machining parameters such as the RPM’s, fee rate, coolant or lubricant to use depends on the material properties

1. Density (g/cm³)
  • Definition: Density is the mass of a material per unit volume. It's a fundamental physical property that indicates how compactly the atoms or molecules are packed together.
  • Significance: In machining, density affects the weight of the material and can influence the choice of machining parameters, such as feed rates and speeds.
  • Typical Applications: High-density materials are often used in applications requiring significant weight in a small form factor, like aerospace counterweights or in applications requiring high strength and durability.
  • Machining Challenges: Heavier, denser materials may require more power to machine and can lead to increased tool wear.
2. Hardness (Knoop)
  • Definition: Hardness, measured here by the Knoop scale, is a material's resistance to indentation and abrasion. The Knoop hardness test is specifically suitable for brittle materials or thin sheets.
  • Significance: Hardness directly correlates to wear resistance but also to how difficult a material is to machine.
  • Typical Applications: Hard materials are used in cutting tools, wear-resistant surfaces, and components subjected to high stress.
  • Machining Challenges: Hard materials can cause rapid tool wear, necessitating the use of harder tool materials like polycrystalline diamond or cubic boron nitride.
3. Tensile Strength (MPa)
  • Definition: Tensile strength is the maximum stress that a material can withstand while being stretched or pulled before breaking.
  • Significance: It's an important measure of a material's mechanical performance, especially in applications where it is subject to stretching or pulling forces.
  • Typical Applications: Materials with high tensile strength are used in structures under tension, cables, and fasteners.
  • Machining Challenges: Materials with high tensile strength may be tougher to machine and can lead to increased cutting forces and tool wear.
4. Modulus of Elasticity (GPa)
  • Definition: The modulus of elasticity, or Young's modulus, measures a material's stiffness or rigidity. It's the ratio of stress (force per unit area) to strain (deformation) in the elastic deformation phase.
  • Significance: A higher modulus indicates a stiffer material. This property is crucial in applications where deflection must be minimized.
  • Typical Applications: Used in the design of structures and components where precise dimensional control is necessary.
  • Machining Challenges: Stiffer materials can be more difficult to machine due to higher forces required for deformation and potential for tool deflection.
5. Thermal Conductivity (W/m·K)
  • Definition: Thermal conductivity is a measure of a material's ability to conduct heat.
  • Significance: It influences how quickly a material can dissipate heat, affecting temperature control during machining.
  • Typical Applications: Materials with high thermal conductivity are used in heat sinks, thermal insulation, and applications requiring efficient heat transfer.
  • Machining Challenges: Materials with low thermal conductivity can retain heat in the cutting zone, potentially affecting tool life and workpiece integrity. High thermal conductivity materials may require different cooling or cutting strategies to manage heat dissipation.

Advanced Ceramics Materials

Material

Density (g/cm³)

Hardness (Knoop)

Tensile Strength (MPa)

Modulus of Elasticity (GPa)

Thermal Conductivity (W/m·K)

Typical Applications

Machining Challenges

Alumina (Al2O3)

3.9 - 4.2

2000 - 2500

250 - 350

350 - 400

20 - 35

Electrical insulation, wear parts, refractory products

Hard and brittle, requires diamond grinding tools

Silicon Carbide (SiC)

3.1 - 3.2

2800 - 3500

400 - 550

400 - 450

120 - 200

Abrasives, refractory materials, semiconductor devices

Extremely hard, challenging to machine without specialized tools

Beryllia (BeO)

2.85

1000 - 2000

300 - 350

300 - 320

250 - 300

Electronic substrates, thermal management components

Toxic dust, requires handling with safety precautions

Boron Carbide (B4C)

2.52

2750

350 - 400

450 - 470

20 - 30

Armor, abrasive materials, nozzles

Hard and abrasive, difficult to machine and wear on tools

Boron Nitride (BN)

2.1 - 2.3

10 - 20 (Hex)

N/A

20 - 700 (Type dependent)

20 - 600 (Type dependent)

High-temperature lubricants, insulators

Soft in hexagonal form, but machining can be challenging due to layer separation

Graphite

1.5 - 1.8

10 - 20

10 - 50

9 - 15

120 - 140

Electrodes, refractories, lubricants

Brittle and messy, can contaminate if not carefully handled

Piezoelectric Compositions

Varied

Varied

Varied

Varied

Varied

Sensors, actuators, transducers

Material sensitivity requires precise machining methods

Pyrite

4.9 - 5.2

600 - 650

N/A

N/A

0.1 - 0.25

Decorative use, mineral collections

Not typically machined for industrial applications

Sapphire

3.95 - 4.03

2000

400 - 600

345 - 400

25 - 35

Watch crystals, substrates, optical components

Very hard, requires diamond sawing and polishing

Zirconia (ZrO2)

5.5 - 6.0

1200 - 1400

200 - 240

200 - 210

2 - 3

Biomedical implants, cutting tools, oxygen sensors

Tough and wear-resistant, requires diamond or cubic boron nitride (CBN) tools

Steatite

2.7 - 2.8

800 - 850

70 - 100

100 - 120

2.5 - 3.5

Electrical insulators, ceramic mounts

Easier to machine than harder ceramics, but still requires care to prevent chipping

Cordierite

2.5 - 2.8

700 - 900

50 - 100

50 - 100

1 - 3

Kiln furniture, heat exchangers

Low thermal expansion but can be brittle, careful machining needed

Ferrites

4.5 - 5.0

600 - 630

N/A

N/A

5 - 10

Magnetic cores, inductors, transformers

Brittle and magnetic, can be challenging to machine without affecting magnetic properties

Composite Materials

Material

Density (g/cm³)

Knoop Hardness (kg/mm²)

Mohs Hardness

Tensile Strength (MPa)

Thermal Conductivity (W/m·K)

Typical Applications

Machining Challenges

Polymer Matrix Composites (PMC)

Varied

Varied

Varied

Varied

Varied

Aerospace, automotive parts

Cutting may cause delamination; requires special tools.

Metal Matrix Composites (MMC)

Varied

Varied

Varied

Varied

Varied

High-performance automotive and aerospace components

Abrasive on tools, challenging to machine.

Ceramic Matrix Composites (CMC)

Varied

Varied

Varied

Varied

Varied

Aerospace engines, thermal protection systems

Very hard; requires specialized machining processes.

Graphite Carbide

2.1 - 2.2

2500 - 2800

9-10

N/A

120 - 200

High-temperature environments, mechanical seals

Brittle, producing conductive dust during machining.

Honeycomb Structures

Very Low

N/A

N/A

Varied

Very Low

Aerospace and automotive sectors for lightweight structures

Requires precise cutting techniques to prevent crushing.

Fiber (General)

Varied

Varied

Varied

Varied

Varied

Reinforcement materials in composites

Can be difficult to cut without fraying; abrasive on tools.

Resin

1.1 - 1.2

15-30

1-2

55 - 70

0.1 - 0.5

Matrix materials in composites, adhesives

Sticky residue can gum up tools; requires careful curing.

Aramid Fibers

1.44

500-600

2-3

3620 - 4340

0.04 - 0.58

Bulletproof vests, high-strength ropes

Abrasive to cutting tools; challenging to cut cleanly.

Carbon Fibers

1.75 - 2.0

1000-1100

10

3500 - 7000

2 - 5

High-performance composites, sporting goods

Requires diamond-coated tools for clean cuts.

Boron

2.34

3000

9-10

3100 - 3800

27

Aerospace structures, neutron absorbers

Very hard and brittle; difficult to process.

E-Glass

2.54

600

6

3400

1.0

Glass-reinforced plastics, electrical insulation

Wear on tools; handling glass fibers requires care.

S-Glass

2.49

610

6

4570

1.0

Aerospace and military applications for high-strength composites

Similar to E-Glass but with higher wear on tools.

Silicon Carbide (SiC)

3.1 - 3.2

2485 - 2970

9-10

400 - 550

120 - 200

Abrasives, brake discs, high-temperature parts

Extremely hard, requiring diamond tools for machining.

Silicon Nitride (Si3N4)

3.2 - 3.4

1200 - 1500

8-9

600 - 900

15 - 30

Bearings, cutting tools, engine parts

Hard and brittle; specialized equipment needed for machining.

Titanium

4.506

800 - 850

6

900 - 1200

22

Aerospace, medical implants, high-performance automotive

Work hardening and high chemical reactivity with tools.

Diboride (Assuming B4C)

2.52

2800 - 3500

9-10

350 - 400

20 - 30

Armor, abrasive applications

Extreme hardness and abrasiveness to tools.

Construction Materials

Material Category

Density (kg/m³)

Compressive Strength (MPa)

Knoop Hardness (kg/mm²)

Mohs Hardness

Typical Applications

Asphalt

2,300 - 2,500

N/A

N/A

-2

Highways, driveways

Concrete

2,400

20 - 40

N/A

-3

Structural components

Cured Concrete

2,400

20 - 40 (Increases with age)

N/A

-3

Same as concrete

Reinforced Concrete

2,400

20 - 40 (Varies)

N/A

-3

Buildings, bridges

Green Concrete

2,300 - 2,500

20 - 40

N/A

-3

Eco-friendly projects

Masonry

500 - 2,000

2 - 30

Varies

Varies

Walls, partitions

Bricks

1,600 - 1,900

10 - 35

-1000

-6.5

Walls, pavements

Natural Stone

2,200 - 2,700

50 - 200

Varies

2 - 7

Facades, countertops

Artificial Stone

1,800 - 2,400

30 - 100

N/A

-3 - 7

Decorative elements

Abrasive Materials

Varies

N/A

Varies

Varies

Surface treatment

Building Materials

Varies

Varies

N/A

N/A

Construction

Paving

Varies

N/A

N/A

N/A

Walkways, patios

Sidewalks

N/A

N/A

N/A

N/A

Pedestrian paths

Expansion Joints

N/A

N/A

N/A

N/A

Thermal expansion

Glass Materials

Material

Density (kg/m³)

Compressive Strength (MPa)

Knoop Hardness (kg/mm²)

Mohs Hardness

Typical Applications

Machining Challenges

Soda Lime Glass

2500

1000

585

5

Bottles, windows, glassware

Brittle; sensitive to thermal shock

Borosilicate Glass

2230

820

620

6

Lab glassware, cookware, thermal windows

Lower thermal expansion but still requires careful handling

Ceramic Glass

2500

N/A

N/A

N/A

Cooktops, fireplace doors

High hardness and thermal resistance complicate cutting/drilling

Quartz Glass

2200

1100

820

7

High-temperature optics, semiconductor processes

Extreme hardness and brittleness; specialized tools required

Pyrex (Brand)

2230

820

620

6

Cookware, lab equipment

Similar to borosilicate; durable but needs careful machining

Optical Glass

Varies

N/A

Varies

Varies

Lenses, prisms, optical instruments

Requires precision to maintain optical properties

Electronic Glass

Varies

N/A

Varies

N/A

Displays, semiconductors

Thin and fragile; often processed via etching or laser cutting

Technical Glass

Varies

N/A

Varies

N/A

Industrial, scientific applications

Specific challenges depend on glass type; often requires custom processing

Glass Tubing

2500

1000

585

5

Lab glassware, architectural elements

Risk of cracking; requires delicate handling and cutting techniques

Photonics

Varies

N/A

Varies

N/A

Fiber optics, laser technology

Precision cutting and assembly are critical to maintain function

Glass Components

Varies

N/A

Varies

N/A

Varied industrial, commercial uses

Complex shapes demand precise and careful machining

Borofloat Glass

2230

820

620

6

Specialty applications with thermal shock resistance

Similar to borosilicate with added challenges due to size and thickness

Stained Glass

2500

N/A

N/A

N/A

Artistic installations, windows

Requires artistic cutting techniques; fragility is a concern

Art Glass

Varies

N/A

N/A

N/A

Decorative items, artwork

Custom designs necessitate precise and often hand-crafted machining

Glass Assemblies

Varies

N/A

N/A

N/A

Complex components, architectural structures

Assembly precision is key; individual components may have unique challenges

Float Glass

2500

1000

585

5

Windows, mirrors, general building glass

Large sheets require scoring and breaking; risk of sharp edges

Fused Silica/Fused Quartz

2200

1100

820

7

High-precision optics, UV transmission

Very hard and brittle; requires diamond tools for effective machining

Automotive Glass

2500

N/A

N/A

5-6

Windshields, side windows

Laminated and tempered types pose different machining challenges

Flat Glass

2500

1000

585

5

General purpose glass in buildings, vehicles

Similar to float glass; must be cut to size with care
1737F Glass

Varies

N/A

N/A

N/A

Electronic substrates, display glass

Specifically formulated for electronics; machining often involves scribing and breaking

B270/Crown Glass

Varies

N/A

Varies

Varies

Optical applications, high clarity needs

Requires precision machining for optical clarity
Tempered Glass

2500

N/A

620-670

6-7

Safety applications, vehicles, buildings

Cannot be machined after tempering due to risk of shattering

Stone Materials

Material

Density (kg/m³)

Compressive Strength (MPa)

Knoop Hardness (kg/mm²)

Mohs Hardness

Typical Applications

Machining Challenges

Granite

2600-3000

100-250

1400-2000

6-7

Countertops, flooring

Hardness requires diamond tools

Marble

2500-2800

70-100

200-400

3-5

Sculpture, architecture

Softness leads to scratches; acid sensitivity

Limestone

2300-2600

30-250

150-200

3-4

Building facades, flooring

Susceptible to acid erosion

Marble-Limestone

Varies

Varies

Varies

3-5

Decorative interior elements

Combination of marble and limestone challenges

Onyx

2500-2700

70

100-200

6-7

Decorative items, jewelry

Can be brittle; care in cutting required

Quartz

2600

70-90

1200-1300

7

Countertops, decorative items

Hard; abrasive to cutting tools

Porcelain

2400-2600

35-50

800-1000

7-8

Tiles, sanitary ware

Hardness; requires diamond tools for cutting

Sandstone

2200-2700

20-170

200-300

6-7

Building and paving materials

Porosity varies; can wear tools

Serpentine

2500-2600

100-200

150-200

3-6

Countertops, decorative art

Soft, may contain asbestos which poses health risk

Soapstone

2700-3000

40-70

100-200

1

Countertops, carving

Soft; easy to scratch and cut

Flagstone

Varies

Varies

Varies

Varies

Paving, patios

Variability in hardness and porosity

Quarry Tile

2000-2200

30-50

500-800

7-8

Flooring, paving

Hard and durable; abrasive on tools

Slate

2700-2800

50-200

150-300

5-6

Roofing, flooring

Cleavage planes can be a challenge in cutting

Engineered Stone

2400-2500

50-90

1200-1400

7

Countertops, flooring

Consistent but hard; wears tools

Composite Stone

Varies

Varies

Varies

Varies

Construction, decorative uses

Depends on the composite materials; varied challenges

Precious & Semi-precious Stone

Varies

Varies

Varies

7-10

Jewelry, decorative items

Hardness varies; some stones very brittle

Porphyry

2500-2800

150-250

2000-3000

6-7

Paving, columns

Hard and tough; difficult to work

Cantera

2100-2400

15-40

100-200

3-4

Sculpture, architectural elements

Soft; easier to shape but can erode

Black Granite

2900-3100

100-250

1400-2000

6-7

Countertops, memorials

Similar to granite; requires diamond tools

Basalt

2800-3000

150-300

500-600

6

Paving, tiles

Hard and abrasive; tough on machinery

Bluestone

2700-3000

100-200

300-700

5-6

Paving, architectural details

Hard; can vary in composition

Calcarenite

2200-2500

20-70

100-200

3-4

Building materials

Soft and porous; easy to work but less durable

Greenstone

2900-3100

100-250

400-600

5-7

Architectural, ornamental uses

Tough; varies in hardness

Lapidary Materials

Material

Density (kg/m³)

Knoop Hardness (kg/mm²)

Mohs Hardness

Typical Applications

Machining Challenges

Agate

2600

800

6.5-7

Jewelry, decorative items

Hardness requires specialized cutting tools

Ametrine

2650

1050

7

Jewelry

Color zoning can challenge even cutting

Amethyst

2650

750

7

Jewelry, decorative arts

Susceptible to heat damage during cutting

Azurite

3800

N/A

3.5-4

Mineral collections, pigments

Soft, easy to carve but prone to scratching

Cubic Zirconia

5800

1200-1400

8.5

Jewelry (diamond substitute)

Requires diamond-coated tools for cutting

Emerald

2710

1350

7.5-8

High-end jewelry

Inclusions can make cutting and setting challenging

Garnet

3900

1300

6.5-7.5

Abrasives, jewelry

Variability in hardness among types

Gemstones

Varies

Varies

Varies

Jewelry, decoration

Cutting to maximize beauty often requires expertise

Jade

3300

1200

6-7

Carvings, jewelry

Toughness makes carving labor-intensive

Quartz

2650

1200

7

Jewelry, decorative items

Hardness; abrasive to cutting tools

Lapis Lazuli

2500-2800

N/A

5-5.5

Jewelry, decoration

Soft; susceptible to scratching during machining

Meteorites

Varies

N/A

Varies

Collectibles, jewelry

Metal content and structure complicate cutting

Opal

2100-2500

700

5.5-6.5

Jewelry

Fragility requires careful handling to prevent cracking

Onyx

2500-2700

100-200

6-7

Jewelry, decorative items

Can be brittle; care in cutting required

Petrified Wood

2200-2400

N/A

7-8

Decorative items, jewelry

Hardness varies; some pieces can be tough to polish

Rhodonite

3400-3600

N/A

5.5-6.5

Jewelry, carvings

Can show cleavage; careful cutting necessary

Rough Gem Stone

Varies

Varies

Varies

Jewelry (prior to cutting/polishing)

Each stone type presents unique challenges

Ruby

4000

1800

9

High-end jewelry

Hardness requires diamond cutting tools

Tanzanite

3350

700

6.5-7

Jewelry

Risk of thermal shock; careful heating during cutting

Topaz

3500

1350

8

Jewelry

Cleavage planes require careful handling

Tourmaline

3000-3300

1000-1100

7-7.5

Jewelry

Broad color range; some colors more prone to cracking

Tsavorite

3700

1600-1800

7-7.5

Jewelry

Similar to garnet; requires careful cutting due to inclusions

Turquoise

2700-2900

N/A

5-6

Jewelry, decoration

Porous nature makes it sensitive to chemicals and pressure

Optical Glass / Photonic Materials

Material

Density (kg/m³)

Knoop Hardness (kg/mm²)

Mohs Hardness

Typical Applications

Machining Challenges

UV Materials

Varies

Varies

Varies

UV optics, lithography

Material-specific; often require diamond tooling for precision shaping

Excimer Grade Fused Silica

-2200

500-600

7

UV laser systems

Brittle, requiring careful handling; diamond grinding/polishing

UV Grade CaF2

-3180

158-160

4

UV lenses, windows

Soft, cleavage planes present machining challenges

Quartz

-2650

820

7

Optical components, quartz heaters

Hardness requires diamond tooling; prone to thermal shock

BK-7

-2510

610

6

General optical applications

Relatively easy to machine but requires precision polishing

ZKN-7

Varies

Varies

Varies

High refractive index optics

Specific data not widely available; similar challenges to other optical glasses

Pyrex/Tempax

-2230

418

5-6

Lab equipment, cookware

Thermal resistant, but still requires careful thermal management

Various Flint Types

Varies

Varies

Varies

Corrective lenses, prisms

Hard and brittle, varying widely with specific composition

Various Crown Types

Varies

Varies

Varies

Eyeglass lenses, low dispersion optics

Easier to machine than flint types, but precision is key

Various Filter Types

Varies

Varies

Varies

Filters for cameras, telescopes

Machining less of a concern than coating and assembly precision

Borofloat Glass

-2230

620

6

Specialty optics, substrates

Resistant to thermal shock, but machining requires diamond tools

Mirror Substrate Material

Varies

Varies

Varies

Telescope mirrors, laser mirrors

Depends on material; glass substrates require careful polishing

Zerodur

-2530

Varies

-8

Telescope mirrors, precision optics

Very hard and zero expansion; requires specialized equipment for shaping

Ule

-2210

Varies

Varies

Telescope mirrors, metrology components

Very low thermal expansion; machining is specialized and costly

Stainless Steel

-8000

160-500

3-4

Optical system frames

Relatively easy to machine but hardens with work; corrosion-resistant

Aluminum

-2700

250-350

2.5-3

Mirror coatings, mounts

Easy to machine but requires finishing to prevent oxidation

IR Material

Varies

Varies

Varies

IR optics, windows

Specific to material; e.g., Germanium is brittle and requires careful handling

Silicon

-2330

1150

7

Mirrors, lenses in IR systems

Brittle, requiring diamond grinding and careful handling

Germanium

-5323

780

6

IR lenses, windows

Brittle and sensitive to thermal shock; expensive to machine

ZnSe

-5240

120

2.5

CO2 laser optics, IR windows

Soft but toxic dust requires careful handling and machining

ZnS

-4090

210

3

IR windows, lenses

Soft, can be machined but generates hazardous dust

Glass

Varies

Varies

Varies

General optics, windows, lenses

Challenges depend on type; generally requires diamond tooling for shaping

Semiconductor Materials

Material

Density (kg/m³)

Knoop Hardness (kg/mm²)

Mohs Hardness

Typical Applications

Machining Challenges

Silicon (Si)

-2330

1150

7

Brittle, requires diamond cutting tools

Germanium (Ge)

-5323

780

6

IR optics, semiconductor devices

Sensitive to thermal shock, toxic dust

Gallium Arsenide (GaAs)

-5317

750

-6

High-speed electronic devices

Toxicity of arsenic requires careful handling

Gallium Nitride (GaN)

-6150

1300

-9

LED, high-frequency devices

Hard and brittle; difficult to cut

Indium Phosphide (InP)

-4810

580

-6

Telecommunications, photonic devices

Toxic material; requires protective measures

Silicon Carbide (SiC)

-3210

2480

-9-10

Power electronics, high-temperature applications

Extreme hardness; diamond tools necessary

Aluminum Gallium Arsenide (AlGaAs)

-4810

Varies

Varies

Optoelectronics, laser diodes

Similar to GaAs; handling arsenic content

Indium Gallium Arsenide (InGaAs)

-5870

Varies

Varies

NIR detectors, high-speed electronics

Fragile and expensive to produce

Cadmium Telluride (CdTe)

-6240

Varies

-2

Solar panels

Toxic; requires handling in controlled environments

Gallium Phosphide (GaP)

-4070

Varies

-6

LEDs, semiconductor devices

Brittle, similar challenges to GaAs

Silicon Germanium (SiGe)

Varies

Varies

Varies

Heterojunction transistors, RF applications

Handling similar to silicon but with adjusted parameters

Zinc Selenide (ZnSe)

-5240

120

2.5

IR optics, CO2 laser systems

Soft, but toxic dust requires care in machining

Lead Sulfide (PbS)

-7500

Varies

-3

IR detectors, photodetectors

Toxicity of lead and sensitivity to moisture

Cadmium Selenide (CdSe)

-5820

Varies

-2

Quantum dots, optoelectronic devices

Toxicity requires careful environmental controls

Silicon Germanium Carbon (SiGeC)

Varies

Varies

Varies

Electronics, heterojunction bipolar transistors

Specifics depend on the Si/Ge/C ratios

Copper Indium Gallium Selenide (CIGS)

Varies

Varies

Varies

Thin-film solar cells

Complexity in deposition, toxicity concerns

Aluminum Nitride (AlN)

-3260

1200

-9

Electronic substrates, microwave devices

Hard and brittle; diamond tools for machining

Cadmium Sulfide (CdS)

-4820

Varies

-2-3

Photocells, thin-film transistors

Toxic; careful handling required

Silicon Oxide (SiO2)

 -2200

820

7

Optical fibers, microelectronics

Brittle; requires specialized cutting techniques

Zinc Telluride (ZnTe)

-6700

Varies

-2

Solar cells, semiconductor layers

Soft, but care must be taken due to toxicity

Zinc Oxide (ZnO)

-5600

200

4

Varistors, transparent conductors

Abrasive; requires careful machining

Gallium Antimonide (GaSb)

-5900

Varies

-5

IR components, thermophotovoltaic devices

Similar handling to GaAs with additional antimony considerations

Silicon Germanium Tin (SiGeSn)

Varies

Varies

Varies

Electronic and photonic devices

Complex composition adds to machining difficulty

Cadmium Zinc Telluride (CdZnTe)

Varies

Varies

-2

Radiation detectors, solar cells

Toxic and brittle; requires special care

Mercury Cadmium Telluride (HgCdTe)

Varies

Varies

-2

IR detectors

Extremely toxic and sensitive; specialized facilities needed

Metallography Materials

Material

Density (kg/m³)

Knoop Hardness (kg/mm²)

Mohs Hardness

Typical Applications

Machining Challenges

Steel (various grades)

7800-8050

120-700

4-8

Construction, tools

Variability in hardness, depending on alloy and heat treatment

Aluminum (various alloys)

2700

250-350

2.5-3

Aerospace, automotive

Soft, can stick to tools, requires sharp cutters

Copper

8960

210

3

Electrical wiring, plumbing

Soft, malleable, can work harden

Titanium (various alloys)

4500

800

6

Aerospace, medical devices

Hard, reactive to oxygen at high temperatures

Nickel-based alloys (Inconel)

8200-8500

300-550

5-7

Jet engines, chemical plants

Very hard, abrasive, generates heat during machining

Magnesium (various alloys)

1740-1880

N/A

2.5

Lightweight structures, automotive

Flammable as dust, requires careful handling

Cast Iron

6800-7300

210-410

4-5

Machinery parts, cookware

Brittle, can wear tools quickly

Adhesives and Sealants

Varies

N/A

N/A

Joining materials, sealing

N/A (not typically machined)

Stainless Steel (various grades)

7900-8000

250-700

4-6

Kitchenware, medical instruments

Work hardening, requires lubrication and coolants

Brass

8530-8730

200

3

Decorative, musical instruments

Soft, easy to machine but requires sharp tools

Bronze

7700-8900

300

3

Bearings, historical artifacts

Harder than brass, can be tough on tools

Zinc

7140

120

2.5

Corrosion protection coatings

Low melting point, easy to machine

Glass

2200-2500

500-600

5-6

Windows, lenses

Brittle, requires diamond-coated tools for machining

Cobalt-based alloys

8300-8900

300-700

5-7

Medical implants, turbines

Hard and tough, requires advanced machining techniques

Superalloys (Hastelloy)

8000-9000

300-500

5-7

Aerospace, chemical reactors

Difficult to machine, requires specialized tools

Ceramics (alumina, zirconia)

3800-5800

1000-1500

8.5-9

Biomedical implants, cutting tools

Very hard, brittle, requires diamond grinding

Polymers (plastics, elastomers)

900-1400

N/A

N/A

Consumer goods, automotive

Can melt or deform if not machined at correct speeds

Coatings (paints, thermal spray coatings)

Varies

N/A

N/A

Surface protection, decoration

N/A (applied, not machined)

Semiconductor materials (silicon, GaAs)

2330-5317

850-1100

7

Electronics, solar cells

Brittle, requires precision handling

Refractory metals (tungsten, molybdenum)

19250-10280

2000-4000

7-7.5

High-temperature applications

Very hard, high melting points, challenging to machine

Precious metals (gold, silver)

19300-10490

25-70

2.5-3

Jewelry, electronics

Soft, malleable, requires care to avoid deformation

Refractory ceramics (boron nitride)

2000-3500

10-20

1-2

High-temperature insulators

Soft in one direction, hard in another, challenging to shape precisely

Electronic materials

Varies

Varies

Varies

Electronics, PCBs

Specific to material; e.g., PCBs require etching, not machining

Biomaterials (biodegradable polymers)

1100-1400

N/A

N/A

Medical devices, tissue engineering

Sensitive to heat and moisture, can be difficult to process

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