Grinding machine

12 de Aug de 2020

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Grinding machine

  1. GRINDING MACHINE Department of Mechanical Engineering University of Engineering & Technology Lahore Machine Tools & Machining
  2. Table of Contents:  Grinding Machine  Working Principle  Specifications  Purpose of Grinding  Types of Grinding  Parts of Grinding Machine  Labelled Diagram  Grinding Machine Operations  Calculating Wheel Sized or Shapes  Coolant  Affecting Factors  Precautions
  3. Grinding Machine  The grinding machine is a kind of tool which is used for grinding work pieces.  Grinding machine it makes use of an abrasive wheel in the form of a cutting tool.  The rough surface of the abrasive wheel shreds away small pieces of the work piece as needed. Each grain of abrasive on the wheel's surface cuts a small chip from the workpiece via shear deformation.
  4. Working Principle  Work piece is fed against the rotating abrasive wheel. Due to action of rubbing or friction between the abrasive particles and work piece material is removed.
  5. Specifications  Grinding wheels (super abrasive wheels) can be applied to various specifications by combining 1. abrasive grain (abrasive grain type) 2. grain size (abrasive grain size) 3. bond strength 4. degree of concentration (grain concentration in bond) 5. bond type (bonding material).
  6. Purpose of Grinding  To keep the working tool in proper conditions and reduce costs of the purchase of a new tool  The working tool is in fact any cutting tools including knives, scissors, joiner´s and other tools having similar properties and functions.  Grinding systems of this type have to be of good quality, reliable and easily operable.
  7. Types of Grinding  There are four major types of grinding machine; 1. Surface Grinding 2. Cylindrical Grinding 3. Centerless Grinder 4. Tool & Cutter Grinder
  8. Types of Grinding | 1: Surface Grinder  The surface grinding machine is used for grinding flat surfaces.  The workpiece is supported on a rectangular table which moves back and forth and reciprocates beneath the grinding wheel.  A surface grinder consists of an abrasive wheel, a chuck (a workpiece holding device), and a rotary table.  The chuck is used to hold the material in place while the wheel and object are rotated to produce a smooth finish.
  9. Types of Grinding | 2: Cylindrical Grinder  A cylindrical grinder is used for shaping the outside of a workpiece.  These machines accept workpieces in a variety of shapes as long as they can be rotated through a central axis.  In a cylindrical grinder, both the workpiece and grinding wheel are simultaneously rotated.  Outside diameter grinders, internal diameter grinders, and centerless grinders are all types of cylindrical grinders.
  10. Types of Grinding | 3: Centreless Grinder  A centerless grinder is a type of cylindrical grinder which uses two rotary wheels to secure the workpiece in place.  Unlike a centered grinder, a centerless grinder does not make use of a spindle.  The speed of the rotation of the wheels determines at what rate the material is removed.
  11. Types of Grinding | 4: Tool & Cutter Grinder  A tool and cutter grinder makes use of a CNC machine tool with up to 5 axes and multiple grinding wheels.  These devices are used for sharpening and producing milling cutters such as drills, endmills, and step tools.  It is also widely used for producing the tools needed in the woodworking and metal cutting industries.
  12. Parts of Grinding Machine:  A grinding machine consists of following parts: 1. Base or Bed 2. Tables 3. Headstock 4. Tailstock 5. Wheel head 6. Crossfeed
  13. Grinding Labelled Diagram
  14. Standard types of Grinding Wheels:  Grinding wheels come in many different sizes, shapes, and abrasives. Some off the various types are listed below 1. Straight 2. Cylinder 3. Tapered 4. Straight Cup 5. Flaring Cup 6. Dish 7. Saucer
  15. Standard shapes of Grinding Wheels Faces:  Following figure illustrates standard shapes of grinding wheel faces.  The nature of the work dictates the shape of the face to be used.  For instance, shape A is commonly used for straight cylindrical grinding and shape E for grinding threads.
  16. Grinding Machine Operations:  Some Grinding operations are discussed in the following: 1. Surface Grinding Operation: It is used to make a flat surface, the rotating grinding wheel removes the material from the top surface of the work-piece gives a flat look. 2. Cylindrical Grinding Operation: This type of grinding operation is performed only for cylindrical jobs. The cylindrical grinding operation is two types: External cylinder grinding Internal Cylinder grinding
  17. Grinding Machine Operations: 3. External Cylinder Grinding Operation: When we need to remove the excess material from the outer surface of the work-piece then we performed an external grinding operation. 4. Internal Cylindrical Grinding Operation: This operation is done for smoothening the internal surface of a hole or any cylindrical work-piece.
  18. Grinding Machine Operations: 5. Centerless Grinding Operation:  In this type of grinding operation two grinding wheels are fitted parallel with a little 5-10 degree angle, this angle is provided to get a longitudinal motion of the work-piece.  A cylindrical rod is entered between the two grinding wheel due to the tilted angle the work-piece is automatically pass through the wheels, and we got a smooth surface. 6. Form Grinding Operation:  In this type of grinding process, the grinding wheel is maintained exactly the same shape as the final product.  When the job is passing through it automatically the pre-determined shape is formed on the work-piece.
  19. Grinding Machine Operations: 7. Wet and Dry Grinding Operation: Although there are two methods of doing a grinding operation, one is wet grinding and the second one is dry grinding. Wet Grinding: In wet grinding, during the grinding operation, we sprayed coolant generally water or any coolant to cool the surface so that the longevity of the grinding wheel increases and also we get a fine surface finish. Dry Grinding: In this type of grinding process coolant is not used. Dry grinding is not preferable, in this process grinding wheel wear is more plus we get an uneven surface finish.
  20. Calculating Wheel Sized or Shape:  Both cutting speeds in SFPM and rotational speed in RPM must be known to determine the size wheel to be used on a fixed-speed grinding machine. To determine the grinding wheel size, use the following formula:
  21. Coolants:  Most grinding machines are equipped with coolant systems.  The coolant is directed over the point of contact between the grinding wheel and the work.  This prevents distortion of the workpiece due to uneven temperatures caused by the cutting action.  In addition, coolant keeps the chips washed away from the grinding wheel and point of contact, thus permitting free cutting.
  22. Factors Affecting the Grain Size: Grain size to be chosen when selecting a grinding wheel depends upon the factors described below. The softer and more ductile the material, the coarser the grain size. The larger the amount of stock to be removed, the coarser the grain size. The finer the finish desired, the finer the grain size.
  23. Factors Affecting the Grade of Hardness: The factors described below will determine the proper grade of hardness of the grinding wheel. The harder the material, the softer the wheel. The higher the work speed with relation to the wheel speed, the milder the grinding action and the harder the grade should be. The better the condition of the grinding machine and spindle bearings, the softer the wheel can be
  24. Factors Affecting the Structure: The structure or spacing of the abrasive grains of wheel depends upon the four factors described below. The softer, tougher, and more ductile the material, the wider the grain spacing. The finer the finish desired, grain spacing should be. Surfacing operations require open structure (wide grain spacing). Cylindrical grinding and tool and cutter grinding are best performed with wheels of medium structure (medium grain spacing).
  25. Safety Precautions:  Wear goggles for all grinding machine operations.  Check grinding wheels for cracks before mounting.  Never operate grinding wheels at speeds in excess of the recommended speed.  Use proper wheel guards on all grinding machines.  Never adjust the workpiece or work mounting devices when the machine is operating  Do not exceed recommended depth of cut for the grinding wheel or machine.  Remove workpiece from grinding wheel before turning machine off.  On bench grinders, adjust tool rest 1/16 to 1/8 inch from the wheel.