NIMS Core Grinding Skills 251

“NIMS Core Grinding Skills 251” covers skills necessary for the Grinding competency within the NIMS Level 1 Machining standard. This course covers grinding safety and setup topics, including grinding fluids, refractometers, wheel guarding, wheel mounting, dressing, and truing.

Taking this course in conjunction with the other listed requirements for the NIMS Level 1 Machining standard will prepare users for certification in Grinding.

Class Details

Class Name:
NIMS Core Grinding Skills 251
Version:
2.0
Difficulty:
Intermediate
Number of Lessons:
19

Class Outline

  • The Importance of Safety
  • Grinding Fluids
  • Refractometer Readings
  • Waste and Residue
  • Wheel Guards
  • The Importance of Wheel Guards
  • Automatic Safeguards
  • Automatic Safeguards in Action
  • Preparing for Grinding
  • Mounting the Wheel
  • Truing
  • Wheel Balance
  • Manufacturer Balancing
  • Detecting Wheel Imbalance
  • Balancing Methods
  • Dressing
  • Dressing and Truing Tools: Stationary Dressers
  • Using a Single-Point Diamond Dresser
  • Dressing Tools: Rotary Dressers

Objectives

  • Describe the importance of safety during grinding.
  • Describe methods for safely using grinding fluids.
  • Describe a refractometer.
  • Identify appropriate methods for disposing of waste and residue.
  • Describe the importance of wheel guards.
  • Identify types of automatic protections built into certain grinding machines.
  • Describe grinding wheel preparation steps.
  • Describe the wheel mounting process.
  • Describe truing.
  • Describe wheel balance.
  • Describe how grinding wheel manufacturers ensure wheel balance.
  • Describe how to detect wheel imbalance.
  • Describe different methods for balancing a grinding wheel.
  • Describe dressing.
  • Describe common stationary dressing and truing tools.
  • Explain how to use a single-point diamond dresser.
  • Describe rotary dressers.

Job Roles

Certifications

NIMS
  • Grinding Skills-FastTrack

Glossary

Vocabulary Term Definition
abrasive grain A small, hard particle that forms chips during grinding. Abrasive grains are held together by bond material to create grinding wheels and other abrasive tools.
American National Standards Institute ANSI. A private, nonprofit organization that administers and coordinates voluntary standards and systems for products, services, and systems in the United States. American National Standards Institute sets forth safety guidelines for the care and usage of grinding wheels.
ANSI B7.1 A standards document published by the American National Standards Institute that establishes guidelines regarding the safe use and care of grinding wheels and grinding machines. ANSI B7.1 includes requirements on wheel guards, wheel mounting, and flanges.
auto-balancing unit A precise, computerized device that detects vibration and corrects wheel imbalance. Auto-balancing units use counterweights, gases, or liquids to restore balance.
automated system A grinding wheel dressing system that operates without human action or intervention. Automated system settings are prepared during machine setup and require little in-process attention.
axis An imaginary straight line that passes through the center of an object. The axis of rotation of a grinding wheel after it has been properly trued is parallel with the machine spindle's axis of rotation.
balanced wheel A grinding wheel that has an equal distribution of weight about its dynamic center of rotation. A balanced wheel's center of rotation should be aligned with the wheelhead spindle's axis of rotation.
balancing The process of ensuring that a grinding wheel has equal weight about its center of rotation. Balancing a grinding wheel helps to achieve accurate grinding results.
balancing stand A frame-like device with two equal points that can hold a mounted grinding wheel. A balancing stand is often used to check the static balance of a grinding wheel.
bearings A friction-reducing device that allows one moving part to glide past another moving part without excess wear or friction. Bearings in the wheelhead spindle on a grinding machine help to support the grinding wheel.
blotters A pair of paper or cardboard rings that help prevent the flanges from damaging the bond material in a vitrified bond grinding wheel. Blotters are only required for grinding wheels with vitrified bonds.
bolts An externally threaded, cylindrical fastener with a head at one end and a threaded blunt end at the other. Bolts are designed to fit into nonthreaded holes to join parts and are assembled with a nut.
bond material The adhesive substance in a grinding wheel that holds the abrasive grains together. Bond material determines the grinding wheel's hardness.
bonded abrasive An abrasive tool made from a combination of abrasive grains and bond material. Bonded abrasives are typically in the form of grinding wheels but also include dressing sticks.
bore The interior diameter of a cylindrical object. The bore on a grinding wheel is its center hole.
Brix scale A system used for measuring the concentration of a substance that has been mixed with water. The Brix scale is used in conjunction with a refractometer to determine the concentration of a fluid.
calibration The comparison and adjustment of a device with unknown accuracy to a device with a known, accurate standard. Calibration eliminates any variation in the device being checked.
carat A unit of weight for precious stones. Carats can be used to measure the weight of diamonds.
centerline An imaginary line that defines the theoretical center of an object. The vertical centerline on a grinding wheel is a reference point when performing a ring test.
chatter marks A type of surface flaw on a workpiece that looks like waves or lines. Chatter marks are often the result of vibrations from an out-of-balance or out-of-true wheel.
clearance An intentional amount of space left between two components. Clearance between the bottom of the grinding wheel bore and the spindle is provided by wheel manufacturers.
CNC computer numerical control. A type of programmable automation, directed by mathematical data, which uses computers to carry out various machining operations. Computer numerical control is a self-contained system that executes program instructions to guide machine tool components, perform processes, and manufacture parts.
combustible Capable of igniting and burning. Combustible liquids require special storage and labeling.
computer numerical control CNC. A type of programmable automation, directed by mathematical data, which uses computers to carry out various machining operations. Computer numerical control is a self-contained system that executes program instructions to guide machine tool components, perform processes, and manufacture parts.
concentrate The chemical mixture that is diluted with water to create a suitable cutting fluid. Concentrate must be checked regularly to ensure optimal cutting fluid performance.
concentric Having a common center or sharing the same axis with another object. A concentric grinding wheel is aligned with the spindle's axis of rotation.
continuous dressing A dressing process that requires a rotary dresser to maintain constant contact with the grinding wheel during grinding. Continuous dressing is performed using diamond roll dressers.
control unit A component of a computer's central processing system that directs its operation. A control unit on an auto-balancing unit directs counterweight movement to restore dynamic wheel balance.
conventional abrasive The category of abrasive materials that includes the most commonly used, inexpensive abrasives. Conventional abrasives include aluminum oxide and silicon carbide.
coolant Fluid applied to prevent damage to a tool or workpiece by absorbing heat from an operation and by lubricating operation components. Coolants can be mixtures of water, oil, and synthetic fluids.
counterweights A weight that provides balance against something of equal weight. Counterweights are used with an auto-balancing unit to restore the dynamic balance of a grinding wheel.
cover plate A hinged lid on a refractometer that covers the prism surface. The cover plate is transparent to allow light into the device.
crush roll A hard rotary dresser used under pressure to form a profile into the operating surface of a grinding wheel. Crush rolls are often made of tungsten carbide or tool steel.
cylindrical grinder A machine used to grind round, tapered, or angled features on a cylindrical workpiece. Cylindrical grinders can be automatic or manual.
diamond The hardest known substance. Diamond is both a naturally occurring and a manufactured superabrasive.
diamond roll dressers A hard rotary dresser that is used for continuous dressing. A diamond roll dresser is typically used to dress superabrasive wheels.
dressing The process of removing swarf, dull grains, and excess bond material from a grinding wheel by fracturing away the wheel surface. Dressing also conditions the wheel.
dressing stick A rectangular abrasive tool used to remove swarf and dull grains from the operating surface of a grinding wheel. Dressing sticks are bonded abrasive tools.
dynamic The state of an object in motion. A dynamic balanced wheel will be able to come to rest only when the grinding wheel loses momentum.
dynamic balance The ability of a grinding wheel to come to rest only when it loses momentum. The wheel is mounted on a mandrel and rolled along a balancing stand.
electroplated A superabrasive bond type created by immersing a metal wheel in an electrically charged chemical bath that contains metal particles. Electroplated wheels have a single layer of superabrasive material.
fasteners A device that holds two or more objects together. Common fasteners include bolts and screws.
finishing A grinding process that achieves the required size and surface finish of the part. Finishing operations require precisely balanced wheels.
fire flashback The explosion of a container caused by a fire that occurs outside the container. Fire flashback occurs when flame enters the container through the flammable or combustible liquid's vapors.
fire-suppressant gas A gas, typically carbon dioxide, which displaces oxygen to smother fires. In grinding, fire-suppressant gas is used to extinguish fires caused by friction between a grinding wheel and workpiece.
flame arrester A mechanical device designed to prevent the buildup of flammable vapors and quickly extinguish a fire in a flammable liquids container. Flame arresters are made of double mesh wire and extend inside the container from its nozzle.
flange A flat or raised metal disc that clamps down on the top and bottom sides of a grinding wheel. A flange should be at least one-third the diameter of the grinding wheel.
fracture The breaking apart of an abrasive grain into two or more pieces as a result of stress. Fracturing can occur when individual grains break away from the wheel bond or when very small pieces of a grain break off.
friction A force that resists motion between components in an operation. Increased friction raises the heat in an operation and can cause damage.
grinding The use of an abrasive to cut the surface of a workpiece and change its shape. Grinding operations commonly use abrasive grains bonded into the shape of a wheel.
grinding fluid A liquid used to cool and lubricate the grinding wheel and workpiece during grinding. Grinding fluids can be composed of water, oil, or synthetic compounds, depending on the needs of the process.
grinding wheels A round cutting tool made of abrasive grains held together with a bond material. Grinding wheels cut tiny chips from a workpiece for a fine surface finish.
imbalance An uneven distribution of weight around a rotating object. Imbalanced grinding wheels can cause machine vibration.
interlocking doors A set of doors that engage with one another by overlapping or fitting together to form a tight lock. In grinding, interlocking doors cover a grinding area to protect the operator from flying debris and fluid splashes.
kilometers per hour kph. How far an object travels, in kilometers, in one hour. In grinding, the velocity of a wheel's periphery is typically 129 kilometers per hour.
lockout/tagout A method of protecting employees by preventing accidental machine startup through proper locking and labeling of machines during maintenance. Lockout/tagout is the common term for OSHA's Control of Hazardous Energy Standard.
lubricates Reduces friction between components in an operation. Grinding fluids lubricate the machine, prolonging tool life and part quality by reducing heat damage.
machine guards A shield or cover over hazardous areas on a machine to prevent accidental contact with body parts or to prevent debris, such as chips, from exiting the machine. In grinding, machine guards include wheel guards and interlocking doors.
magnetic chuck A workholding device that holds a workpiece or tool during grinding. Magnetic chucks can be permanent or electromagnetic.
mass The amount of matter in an object. Mass gives an object weight when it is acted upon by gravity.
material removal rate The amount of material removed from a workpiece in a given amount of time, measured in cubic inches per minute or cubic millimeters per second. Material removal rates fluctuate depending on the type of abrasive in the grinding wheel, speed settings, and other factors.
meters per second m/s. A measurement of speed that describes the distance in meters that a point on a grinding wheel travels in one second. Meters per second depends on the spindle rotates per minute and wheel circumference.
miles per hour mph. How far an object travels, in miles, in one hour. In grinding, the velocity of a wheel's periphery is typically 70 miles per hour.
mounting A process that uses flanges to prepare a grinding wheel for placement on the wheelhead spindle. Mounting occurs after an operator inspects a grinding wheel for damage.
nut A fastener containing a hole and internal threads that mates with a screw or bolt. A nut may be used to secure a flange to a grinding wheel.
Occupational Safety and Health Administration OSHA. The federal agency that enforces safety and health legislation. Occupational Safety and Health Administration helps employers reduce injuries, illnesses, and deaths in the workplace.
oily waste cans A container used for disposing rags soaked in flammable and combustible liquids. The oily waste can features a self-closing lid.
operating surface The outer edge of a grinding wheel. The operating surface, or periphery, of a grinding wheel is usually the portion that contacts the workpiece.
operators A person trained to operate a piece of machinery. Grinding operators oversee and perform grinding operations.
OSHA Occupational Safety and Health Administration. The federal agency that enforces safety and health legislation. OSHA helps employers reduce injuries, illnesses, and deaths in the workplace.
out-of-balance wheel A grinding wheel with an unequal distribution of weight about its dynamic center of rotation. An out-of-balance wheel's center of rotation is not parallel or concentric with the spindle's axis of rotation.
out-of-true The state in which a grinding wheel has lost its initial shape due to frequent use. An out-of-true wheel causes excessive vibrations and chatter marks on a workpiece.
parallel Two lines or objects that are equidistant from each other and will never intersect. The workpiece and grinding wheel being parallel assures grinding accuracy in surface grinding.
periphery The outer edge of the grinding wheel. Typical grinding operations take place on the grinding wheel's periphery.
personal protective equipment PPE. Safety equipment that machine operators wear or use to prevent injury in the workplace. Personal protective equipment includes safety glasses and safety boots.
pores An opening or void in a material. The pores in a grinding wheel facilitate effective grinding fluid application.
porosity The relative number of openings or voids in a material. The porosity of a grinding wheel can be filled in by the wheel manufacturer when balancing the wheel.
pressure Physical force applied continuously to an object. Too much pressure can damage machines and workpieces and present danger to operators.
prism surface The surface on which fluid is placed in a refractometer. The prism surface is located underneath the cover plate.
profile A workpiece feature created by a specialized grinding wheel. The shape on a grinding wheel has to be precisely dressed so the profile can be ground into a flat or cylindrical workpiece.
radially Movement that is perpendicular to the workpiece centerline. A radial feed of a crush roll into a grinding wheel is used to form a grinding wheel for profile grinding.
refractometer An optical instrument used to measure the chemical or oil concentration in a water-miscible fluid. A refractometer uses a Brix scale to assess the amount of concentrate in a cutting fluid.
relieved flange A flange that is recessed on one side to take pressure away from the center hole of the grinding wheel. Relieved flanges can be used with many different wheel types.
resin bond A type of grinding wheel bond material made from synthetic plastic resins. Resin bond grinding wheels with superabrasives require separate truing and dressing processes.
retrofitted To modify a machine or tool with a new part. Retrofitting manual grinding machines with rotary dressers allow them to form complex or highly accurate profiles into grinding wheels.
ring testing Performing a manual test used to detect damage in bonded grinding wheels. Operators suspend a wheel loosely and tap it with a tool. Wheels that emit a ringing sound are likely undamaged.
rotary dresser A very precise dressing and truing tool that turns as it conditions a grinding wheel or alters its shape. Rotary dressers can form an entire profile onto a grinding wheel in one short plunge operation.
rotary dressers A very precise dressing tool that turns as it conditions or alters the shape of a grinding wheel. Rotary dressers are often motorized.
roughing A type of material removal process with a high material removal rate. Roughing processes grind a workpiece close to its finished size but without regard for surface finish.
safety disposal can A container used for safely storing and disposing of up to five gallons (19 liters) of industrial waste. Safety disposal cans are often used for flammable and combustible liquids.
safety venting An opening that helps prevent the contents of a container from reaching temperatures that would cause them to explode. Safety vents are found on most OSHA-approved containers for flammable and combustible liquids.
self-dressing A method of wheel dressing where pressure or feed during grinding forces abrasive grains to break off the bond material in varying degrees. Self-dressing reveals a sharper abrasive grain.
sensors A device that detects changes in physical conditions such as heat or pressure. A sensor alerts operators to hazardous conditions or engages automatic safeguards.
setup The series of tasks necessary to prepare for processing a workpiece. Setup includes preparing machines, adjusting workholding devices or tooling, and safeguarding machine elements to ensure proper and safe operation.
single-point diamond dresser A dressing and truing tool that contains an individual, industrial-grade diamond embedded on one end. Single-point diamond dressers are common stationary dressing and truing tools.
sleeve flange A flange that consists of two differently shaped parts that fit around a grinding wheel to deflect mounting pressure. Sleeve flanges are generally used with larger and wider grinding wheels used for precision grinding.
sparks A tiny fragment of the grinding wheel or workpiece made incredibly hot from the friction of the grinding process. Sparks can burn an operator or ignite oil-based grinding fluid.
spindle A rotating component of a machine tool. The spindle on a grinding machine wheelhead holds the mounted grinding wheel.
spindle nut A fastener containing a hole and internal threads that mates with a screw or bolt. Spindle nuts are used to secure the grinding wheel assembly to the machine spindle.
static The state of an object at rest. A static object may be working while causing no movement.
static balance The ability of a grinding wheel to remain at rest in any position when placed on a balancing stand. Static balance means that a grinding wheel has no heavy side.
stationary dresser A dressing tool that has a single fixed point or multiple fixed points. Stationary dressers include single-point diamonds and abrasive dressing sticks.
structure The spacing of the grains and bond material in a grinding wheel. Structure depends on the method used to create the porosity within the grinding wheel.
superabrasive A group of relatively expensive but effective materials possessing superior hardness, abrasion resistance, and thermal conductivity. Superabrasives used in grinding wheels are cubic boron nitride and diamond.
surface feet per minute sfm. A measurement of speed that describes the distance in feet that a point on a grinding wheel travels in one minute. Surface feet per minute depends on the spindle rotates per minute and wheel circumference.
surface finish The texture of a part after it has gone through the grinding process. Surface finish is key to the performance of a completed part.
surface grinder A grinding machine used to finish workpiece surfaces or grind parts to accurate size. Surface grinders may have vertical or horizontal machine spindles.
swarf The gritty combination of chips, abrasive grains, and worn bond material produced during grinding. Swarf can clog a grinding wheel and cause it to function improperly.
tailstock A component on a cylindrical grinder located opposite the headstock that supports the far end of the workpiece. The tailstock holds the stationary diamond dresser.
tile dresser A metal stationary dressing and truing tool with a thin blade saturated with diamonds. A tile dresser lasts longer than a single-point diamond dresser.
tolerances The allowable deviation from a given dimension that will still allow the part to perform its desired function. Tolerances indicate the allowable difference between a physical feature and its intended design.
tool steel A specialized type of alloy steel that exhibits excellent strength, toughness, and wear resistance. Tool steels can be used to make crush roll rotary dressers.
traverse rate The speed at which the dressing tool travels across the periphery of a grinding wheel. The traverse rate during dressing is critical in order to achieve the desired surface condition for the grinding wheel.
truing The process of removing material from a grinding wheel to make the wheel periphery perfectly round. Truing a wheel makes the wheel periphery run true to the axis of rotation of the grinding machine spindle.
tungsten carbide A sintered compound of tungsten and carbon bound together in a cobalt binder. Tungsten carbide is used to make crush roll rotary dressers.
velocities The combination of an object’s speed and direction of motion. Unlike speed, velocity always implies a direction.
vitrified bond A clay or ceramic grinding wheel bond material characterized by its strength, rigidity, and resistance to oils, water, and temperature changes. Vitrified bonds have qualities similar to glass.
washers A flat, thin disc used with a threaded fastener to relieve friction or distribute pressure. A plastic washer is often used between a vitrified bond grinding wheel and a flange.
waste drum A container used for storing and disposing of large amounts of flammable and combustible liquid waste. Waste drums can commonly hold up to 55 gallons (208 liters) of liquid.
water-miscible fluid A fluid that can be mixed with water and is at least partially composed of water. Water-miscible cutting fluids include soluble oils, chemical fluids, and semi-chemical fluids and provide lubrication and cooling during the metal cutting process.
wheel glazing The formation of a smooth, flat surface on the periphery of a grinding wheel. Wheel glazing can occur when grinding a hard workpiece with a hard grinding wheel.
wheel guard A protective cover secured over a grinding wheel to protect workers from broken wheels or debris. Wheel guards are required by OSHA.
wheel infeed The depth of the grinding wheel into the workpiece. Wheel infeed is a grinding variable that can significantly alter the surface condition of a wheel.
wheel speed The speed of the periphery, or edge, of the grinding wheel as it rotates. Wheel speed changes depending on the wheel type and grinding operation.