Diamond tool
A diamond tool is a cutting tool with diamond grains fixed on the functional parts of the tool via a bonding material or another method. As diamond is a superhard material, diamond tools have many advantages as compared with tools made with common abrasives such as corundum and silicon carbide.
History
In Natural History, Pliny wrote "When an adamas is successfully broken it disintegrates into splinters so small as to be scarcely visible. These are much sought after by engravers of gems and are inserted by them into iron tools because they make hollows in the hardest materials without difficulty."Advantages
Diamond is one of the hardest natural materials on earth; much harder than corundum and silicon carbide. Diamond also has high strength, good wear resistance, and a low friction coefficient. So when used as an abrasive, it has many obvious advantages over many other common abrasives.Advantages of diamond grinding tools
Diamond can be used to make grinding tools, which have the following advantages:- High grinding efficiency, Low grinding force: Less heat will be generated by the hole in the grinding process. This can decrease or avoid burns and cracks on the surface of the workpiece, and decrease the equipment's wear and energy consumption.
- High wear resistance: Diamond grinding tools' change in dimension is small. This can lead to good grinding quality and high grinding precision.
- Long lifespan, Long dressing period: This can greatly increase the work efficiency, and improve the workers' labor environment and decrease the product's labor intensity.
- Low comprehensive cost: The processing cost of each workpiece is lower.
Categories
Categories by manufacturing method
According to their manufacturing methods or bond types, diamond tools can be categorized to the following way:- Metal-bonded diamond tools: The tool's bonding material is sintered metal containing diamond grit. The functional parts of the tool are usually diamond segments. These tools include metal-bonded diamond saw blades, diamond grinding cup wheels, diamond core drill bits, etc. For metal-bonded diamond tools, the bond is one of the prime factors when selecting which tool to use for cutting or grinding a specific material, depending on how hard or abrasive the material is. The bond used dictates the rate at which the metallic powders wear down and expose new diamond crystals at the surface, thereby maintaining an abrasive cutting surface. Different bond strengths are achieved by the alloy mix of metallic powders chosen and how much heat and pressure are applied to the sintered segment. The reference material has historically been cobalt, thanks to high diamond retention, ease of processing by hot pressing and adjustable wear rate by admixed bronze or tungstene carbide powders. Due to its high and unstable price and to environmental concerns, alternative systems have been developed based on iron-copper alloys or mixtures, with further metallic and non metallic additions.
- Resin-bonded diamond tools: The tools' bonding material is mainly resin powder. An example of this kind of tool is the resin-bonded diamond polishing pads used in the construction industry.
- Plated diamond tools: These tools are made by fixing the diamonds onto the tool's base via electroplating method or via CVD method. They can usually be made to good processing precision.
- Ceramic-bonded diamond tools: The tools' bonding material is usually glass and ceramic powder. This tool usually has the features of good chemical stability, small elastic deformation, but high brittleness, etc.
- Polycrystalline Diamond : They are normally made by sintering many micro-size single diamond crystals at high temperature and high pressure. PCD has good fracture toughness and good thermal stability, and is used in making geological drill bits.
- Polycrystalline Diamond Composite or Compacts : They are made by combining some layers of polycrystalline diamonds with a layer of cemented carbide liner at high temperature and high pressure. PDC has the advantages of diamond's high wear resistance with carbide's good toughness.
- High-temperature brazed diamond tools: This tool is made by brazing a single layer of diamonds onto the tool via a solder at a temperature of over 900 °C. using vacuum brazing or atmosphere-protected brazing. This tool has several advantages: the solder can hold the diamonds very firmly, the single layer of diamonds' exposed height can be 70%–80% of their sizes, and the diamonds can be regularly arranged on the tool.
Categories by use
Applications
Applicable materials
Diamond tools are suitable to process the following materials:- Carbide alloy
- Hard or abrasive non-metallic materials, for example, stone, concrete, asphalt, glass, ceramics, gem stone and semiconductor materials.
- Non-ferrous metals such as aluminium, copper and their alloys, and some soft but tough materials such as rubber and resin.
Applied domains
Diamond tools are used in the following domains:- Geological or project exploration: Diamond geological drill bits, diamond oil drill bits and diamond thin-wall drill bits are often used. The main application of PCD drilling bits is in the oil and natural gas industries and the mining industry.
- Stone processing: Diamond circular saw blades, diamond gang saws, diamond band saws are used to saw marble, granite and other stone blocks. Diamond wire saws are used in stone quarries to exploit raw stone blocks. Shaped diamond tools are used to process stone to a particular shape. Resin-bonded diamond polishing pads are used to polish stone.
- Construction: Medium or small sized diamond saw blades, diamond core drill bits and some diamond grinding or polishing tools are often used in repairing roads, remodeling buildings, and processing building materials.
- Woodworking: Composite laminate flooring is widely used. It is wearable as stone. PCD circular saw blades, profiling cutter, twist drill bits and other diamond tools are used in its processing.
- Auto spare parts processing: PCD and PCBN cutting tools are used to meet the high efficiency and low deviation processing requirements in this domain.
- IT and home appliance products processing: High-precision super-thin diamond cutting wheels are used to cut silicon slices. Resin-bonded diamond grinding wheels are used to process ceramics in optical fiber industry.
- Engineering ceramics processing: Engineering ceramics are widely used in many industries. They have the properties of high toughness, high hardness, high-temperature resistance. High-toughness and durable diamond grinding wheels are developed to process them.
- Carbide tools and other mechanical tools processing: Diamond tools are used to gain high processing precision and efficiency.
Apart from its use as an abrasive due to its high hardness, diamond is also used to make other products for its many other good properties such as high heat-conductivity, low friction coefficient, high chemical stability, high resistivity and high optical performances. These applications include coatings on bearings and CDs, acting as lens and thermistors, making high-voltage switches and sensors, etc.
Some examples of diamond tools
Diamond dressing tools
Diamond dressers consist of single-point or multipoint tools brazed to a steel shank, and used for the trueing and dressing of grinding wheels. The tools come in several types, including: grit impregnated, blade type, crown type, and disc type. The advantages of multipoint over single-point tools are:- The whole diamond can be used; in a single-point tool, when the point is blunt the diamond must be reset, and after few resettings the diamond is replaced.
- Multipoint tools have higher accuracy, especially in form grinding, where blade types are used. Blades consist of elongated diamonds. The thickness is controlled and blades are available in thicknesses from.
- Grit-type tools are of a tough grade, and can be used for bench grinders.
- Since small points are used, the diamonds have a cutting edge with natural points, unlike single-point tools, which have brutted points.
- The cost of multipoint tools is lower, since smaller, less expensive diamonds are used.
PCD cutting tools
Most wafers are polished to a mirror finish, then cut with an electrical discharge machining tool into smaller, workable segments that are then brazed onto the sawblade, reamer, drill, or other tool. Often they are EDM machined and/or ground an additional time to expose the vein of diamond along the cutting edge. These tools are mostly used for the machining of nonmetallic and nonferrous materials.
The grinding operation is combined with EDM for several reasons. For example, according to Modern Machine Shop, the combination allows a higher material removal rate and is therefore more cost effective. Also, the EDM process slightly affects the surface finish. Grinding is used on the affected area to provide a finer final surface. The Beijing Institute of Electro-Machining attributes a finer shaping and surface geometry to the combination of the two processes into one.
The process itself is accomplished by combining the two elements from each individual process into one grinding wheel. The diamond graphite wheel accomplishes the task of grinding, while the graphite ring around the existing wheel serves as the EDM portion. However, since diamond is not a conductive material, the bonding in the PCD work piece must be ample enough to provide the conductivity necessary for the EDG process to work.
Polycrystalline diamond tools are used extensively in automotive and aerospace industries. They are ideal for speed machining in tough and abrasive aluminum alloys, and high-abrasion processes such as carbon-fiber drilling and ceramics. The diamond cutting edges make them last for extended periods before replacement is needed. High volume processes, tight tolerances, and highly abrasive processes are ideal for diamond tooling.