Page 1. Module. 3. Machinability. Version 2 ME IIT, Kharagpur. Page 2. Lesson. Failure of cutting tools and tool life. Version 2 ME IIT, Kharagpur. Page 3. Recommended materials for machinability. Parts made from both ferrous and non -ferrous material can be machined. However, materials like plastics (with or. Page 1. Version 2 ME, IIT Kharagpur. Module. 3. Machinability. Page 2. Version 2 ME, IIT Kharagpur. Lesson. Cutting Tool Materials of common use. Page 3.

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Diamond turning is turning with diamond as the cutting machinabiluty. It is a process of mechanical machining of precision elements using lathes or derivative machine tools e. The term single-point diamond turning SPDT is sometimes applied, although as with other lathe work, the “single-point” label is sometimes only nominal radiused tool noses and contoured form tools being options. The process of diamond turning is widely used to manufacture high-quality aspheric optical elements from crystalsmetalsacrylicand other materials.

Plastic optics are frequently molded using diamond turned mold inserts. Optical elements produced by the means of diamond turning are used in optical assemblies in telescopesvideo projectorsmissile guidance systems, lasers, scientific research instruments, and numerous other systems and devices.

Diamonds also serve in other machining processes, such as milling, grinding, and honing. Diamond turned surfaces have a high specular brightness and require no additional polishing or buffing, unlike other nptrl machined surfaces.

Diamond turning is a multi-stage process. Initial stages of machining are carried out using a series of CNC lathes of increasing accuracy. A diamond-tipped lathe tool is used in the final stages of the manufacturing process to achieve sub- nanometer level surface finishes and sub- micrometer form accuracies.

The form accuracy is measured as a mean deviation from the ideal target form. Quality of surface finish and form accuracy is monitored throughout the manufacturing process using such equipment as maachinability and laser profilometerslaser interferometersoptical and electron microscopes. Diamond turning is most often used for making infrared optics, because at longer wavelengths optical performance is less sensitive to surface finish quality, and because many of the materials used are difficult to polish with traditional methods.

Temperature control is crucial, because the surface must be accurate on distance scales shorter than the wavelength of light. Temperature changes of a few degrees during machining can alter the form of the surface enough to have an effect. The main spindle may be cooled with a liquid hptel to machinabioity temperature deviations.


The diamonds that are used in the process are incredibly strong in the vertical downward direction but very weak in the upward and sideways directions. For best possible quality natural diamonds are used as single-point cutting elements during the final stages of the machining process. The granite base is placed on air suspension on a solid foundation, keeping mqchinability working surface strictly horizontal.

Manufacturing Processes – II NPTEL

The machine tool components are placed on top of the granite base and can be moved with high degree of accuracy using a high-pressure air cushion or hydraulic suspension. The machined element is attached to an air chuck using negative air pressure and is usually centered manually using a micrometer.

The chuck itself is separated from the electric motor that spins it by another air suspension.

The cutting tool is moved with sub-micron precision by a combination of electric motors and piezoelectric actuators. As with other CNC machines, the motion of the tool is controlled by a list of coordinates generated by a computer. Typically, the part to be created is first described using a CAD model, then converted to G-code using a CAM program, and the G-code is then executed machinabilitg the machine control computer to move the cutting tool. Alternative methods of diamond machining in practice also include diamond fly cutting and diamond milling.

Diamond fly cutting can be used to generate diffraction gratings and other linear patterns with appropriately contoured diamond shapes. Diamond milling can be used to generate aspheric lens arrays by annulus cutting nachinability with a spherical diamond tool.

Diamond turning is specifically useful when cutting materials that are viable as infrared optical components and certain non-linear optical components machinabiity as KDP.

KDP is a perfect mafhinability in application for diamond turning, because the material is very desirable for its optical modulating properties, yet it is impossible to make optics from this material using conventional methods. KDP is water-soluble, so conventional grinding and polishing techniques are not effective in producing optics. Diamond turning works well to produce optics from KDP.

Generally, diamond turning is restricted to certain materials.

Materials that are readily machinable include: The most often requested materials that are not machinavility machinable are: Ferrous materials are not readily machinable because the carbon in the diamond tool chemically reacts with the substrate, leading to tool damage and dulling after short cut lengths. Several techniques have been investigated to prevent this reaction, but few have been successful for long diamond machining processes at mass production scales.


Tool life improvement has been under consideration in diamond turning as the tool is expensive. Hybrid processes such as laser-assisted machining have emerged in this industry recently. Machinabiility all the automation involved in the diamond turning process, the human operator still plays the main role in achieving the final result.

NPTEL Video Course : NOC:Introduction to Machining and Machining Fluids

Quality control is a major part of the diamond turning process and is required after each stage of machining, sometimes after each pass of the cutting tool. If it is not detected immediately, even a minute error during any of the cutting stages results in a defective part.

The extremely high requirements for quality of diamond-turned optics leave virtually no room for error. The SPDT manufacturing process produces a relatively high percentage of defective parts, which must be discarded. As a result, the manufacturing costs are high compared to conventional polishing methods. Even with the relatively high volume of optical components manufactured using the SPDT process, this process cannot be classified as mass production, especially when compared with production of polished optics.

Each diamond-turned optical element is manufactured on an individual basis with extensive manual labor. From Wikipedia, the free encyclopedia. This article needs additional citations for verification.

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