Creep Feed Grinding
Creep Feed Grinding
Creep feed grinding results in high mechanical and thermal loads on the system components, which can be mitigated by adaptive design of the control, grinding wheel, dressing process, machines and coolant.
Unlike surface grinding, creep feed grinding uses a heavier grinding depth. Combined with a slow reverse rate, creep feed grinding generates forms that are higher than typical grinding processes.
Creep Feed Advantages over Conventional Grinding
Creep feed grinding technology has become more popular than reciprocating grinding technology. This is due to increasing consumer demand for productivity. Characteristics for creep feed grinding include:
Lower workpiece speeds and higher cutting depths lead to larger contact between the workpiece and grinding wheel compared to pendulum grinding.
Higher productivity in mass production compared to reciprocating grinding.
High material removal rates from highly porous grinding wheels.
Lower wear in the wheel compared to reciprocating grinding.
Better surface quality than reciprocating grinding.
Applications for creep feed grinding include aerospace flaps, lubrication grooves, teeth grinding, and turbine blades.
Creep Feed Helps to Relocate Heat Treatment
One of the most important characteristics of the creep feed grinding process is a change to the process sequence. In a traditional grinding operation, the part is sent away for heat treatment and then brought back to the shop to continue operations like grinding. This is the standard way to produce parts for manufacturers.
With creep feed grinding, the sequence is reworked. The piece may be heat treated first, reaching its final hardness before any machining work is completed. Creep feed grinding eliminates any interruption and delay associated with shipping parts for off-site work. Matching the MRR milling enables grinding to take larger production roles. In many cases, creep feed grinding promotes better savings.
Use Coolant Effectively
In order to keep creep feed grinding effective, it is important to apply coolant. The long wheel arc means that more heat is being generated from the wheel. Compared to other machining processes, applying coolant to creep feed grinding must be taken seriously.
To ensure that coolant follows with the wheel, the coolant speed must match with the passing point of the wheel. The coolant nozzles are also matched to the profile of a particular grinding wheel. Lastly, coolant collection ramps are placed to collect coolant. This may even be machined to match the profile of the given part.
The Preferred MRR Method is Downgrinding
The only two options for creep feed grinding rotation is either up or down grinding. However, the popular preference is down grinding when wanting high material removal rate. The reason for this preference when material removal rate is high is because of heat.
If the grinding direction were up, the grit would first meet with the material without cutting it. Since these grits result in excess sliding, heat increases due to greater friction. Although down grinding may appear to be more abrupt, it allows for cooler grinding. Up grinding is typically only preferred when an individual needs to extend the life of an abrasive.
Intermittent Dressing Is Possible
Frequent continuous dressing is required for creep feed grinding where the material removal per pass is greater. This issue of continuous dressing can be addressed by using newer grinding wheels that have ceramic grit.
The ceramic wheels continue to stay sharp for longer periods of time, making it possible for intermittent dressing. This means that dressing from a separate wheel is used. When wheels are only dressed as needed, they last longer and eliminate continuous dress capability. This results in better performance on less expensive machines.
Dressing superabrasive wheels with diamond grit is used in cutting manufacturing for many grinding and ceramic tools. Engineers believe that these wheels could possibly grind gamma titanium parts for aerospace as well. The porosity of these wheels allows coolant to successfully infiltrate the wheels.
Depending on the use case of a superabrasive wheel, dressing may not even be required. Some superabrasive wheels have been used for creep feed grinding on milling machines already. These machines use a single-layer superabrasive wheel specifically designed to not require any dressing.
Broaching uses a toothed tool to remove material in a consistent and accurate manner, and is typically used for precision applications and high quality production. Broaching is best used in the production of high volume parts that require accurate, repetitive and complex cuts. Broaching can generate forms much like those of creep feed grinding, although creep feed grinding offers to complete the exact same machining process with a standard machine tool size.
Creep Feed Grinding MRR Matches Milling
When using superalloy grinding applications, creep feed grinding realizes an MRR that is overall equal or better to those that milling cutters provide. Even if that milling cutter is using the same workplace materials.
Creep feed grinding uses high-force processing, but a sharper cutting grit reduces that force. In addition, improved porosity helps improve energy efficiency. The energy demand for creep feed grinding is also comparable to that of a milling machine.
What is Profile Grinding?
Profile grinding is when a grinding wheel is specifically dressed with the profile that is being produced. This can be carried out in both reciprocating and creep feed grinding. This profile is produced using a few possible methods. The most common methods include:
Profile Diamonds - This is the tool with the lowest manufacturing cost.
Forming Rolls - Less production cost, but increased dressing times.
Profile Rolls - The best economical solution for large batch production.
Demand in grinding wheel use is becoming higher. Stock removal rate and tool life are also increasing, which results in adapting dressing tools to the workpiece material. Continuous Dressing grinding has become the most economical solution for profile grinding tasks. Higher feed rates can be completed due to a consistently sharp abrasive grain.
Dressing a Grinding Wheel
Dressing a grinding wheel is most important when a user mistakenly uses incorrect material for that specific wheel. Wheels need to always be inspected before use. This ensures that users are not walking into potentially dangerous work environments.
Dressing a wheel will remove the clogged layer, exposing a fresh layer of grit underneath the wheel. It is best to only dress a wheel when absolutely necessary, because dressing can reduce the size of the wheel. When a wheel is dressed too frequently, the lifespan will shorten. It will be costly to consistently replace grinding wheels. Make sure your grinding wheels are clean and not too worn before use.
Types of Grinding Operations
There are multiple ways to approach the grinding operating process. Creep feed grinding is simply just one way to use abrasive cutting tools. Cylindrical grinding is another common process in abrasive grinding.
The cylindrical grinding process is used to grind surfaces and shoulders of cylindrical pieces. This is completed by mounting the piece on centers, which are then rotated by a center driver. The wheel and piece are rotated by different motors at different speeds. This process creates less vibration than one that uses a regular disk-shaped grinding wheel.
Surface grinding is another example of a different grinding approach. This process uses a grinder composed of an abrasive wheel, a chuck, an electromagnetic vacuum, and a reciprocating table, to produce a finely ground flat surface.
Centerless and Electrochemical grinding processes are less common operations. Centerless grinding is when a piece is supported by only a blad. Two wheels are used to grind the surface and regulate the movement of a workpiece. The types of centerless grinding include internal centerless, plunge, and through-feed grinding. Electrochemical grinding uses positively charged workpieces in a conductive fluid to erod a negatively charged grinding wheel. The resulting pieces are then dissolved into conductive fluid.
What is Conventional Grinding?
Conventional grinding is the process of using a grinding wheel to cut material from a workpiece. This abrasive machining process can be completed by machines such as grindstones, angle grinders, die grinders, and bench grinders. Conventional grinding is a diverse subset in the manufacturing and toolmaking industries. Processes such as creep feed grinding, cylindrical grinding, and surface grinding are all commonly used grinding operations for workpiece material removal.
How to Balance a Grinding Stone
In order for grinding stones to work properly, they must be mounted correctly. If a grinding wheel is incorrectly mounted, hazardous working conditions can be created as a result. Following the proper mounting steps will ensure that a grinding wheel is effective for use.
Install the Grinding Wheel
The grinding wheel should be placed fitting tightly on the grinder. Wrap the grinder with masking tape so the wheel fits snug on the arbor. Guards should not be installed at this point.
Align the Grinding Wheel
Rotate the wheel by hand, identifying the high point on the right side of the wheel. Mark the high point with a pencil, and remove the tightening nut and washer. Then, place masking tape on the washer, positioning the tape so that it is inline with the wheel and center of the arbor.
Then, place a layer of tape on the left side of the wheel, positioned opposite of the tape on the right side of the paper washer. When completed properly, the tape on each side of the wheel is positioned 180 degrees from each other. Reinstall the right side washer and tighten the nut.
Dress the Grinding Wheel
Complete the balancing process by attaching grinder guards. Remember to wear safety glasses when powering on the grinder, and continuously dress the wheel until all high points of the wheel are ground down. Lastly, move the wheel dressed from side to side until the wheel’s face begins to run true.
Creep feed grinding is described as lower workpiece speeds and higher depths of cut. This results in a larger length of contact between the grinding wheel and workpiece compared to reciprocating or pendulum grinding. Coolant and coolant delivery are critical to the creep feed grinding process.