What Precautions Should Be Taken When Grinding Materials With High Ductility

Highly ductile materials such as copper and aluminum are hard to grind because of their ability to deform and smear, which can result in issues including wheel loading, built-up edge, poor surface finish, and excessive heat generation. in order to effectively grind these materials, precautions should be taken when selecting the wheel, optimizing grinding parameters, ensuring machine stability, and much more.

In this blog, we will cover all the common causes and necessary precautions that should be taken when grinding materials with high ductility. 

What is Grinding Materials With High Ductility?

Grinding materials with high ductility refers to the process of using an abrasive grinding wheel to eliminate material from the workpieces that have a considerable capacity to deform due to plastic without breaking.

In other words, it is the process of shaping and finishing components using a grinding wheel that is made of bendable or stretchable metals like copper, aluminum, mild steel, etc.

However, when compared to ductile materials, brittle materials are easier to grind as they are more prone to chipping and breaking. ductile materials, on the other hand, are difficult to grind because they are prone to Generate burrs, Smear, Load the wheel, Deform, and Generate more heat.

Issues When Grinding Materials With High Ductility

There are a number of issues when grinding materials with high ductility that arise due to their natural ability to deform as plastic instead of breaking easily. These problems can impact the quality, efficiency, and cost of the grinding process.

Following are some common issues that occur while grinding materials with high ductility:

• WHEEL LOADING: the ductile material can stick and adhere to the grinding wheel surface causing clogging the pores and decreasing its cutting efficiency. this results in increased heat generation, and poor surface finish and leads to workpiece and wheel damage.

• BUILT-UP EDGE: Built-up edge refers to the tiny pieces of the soft, ductile material that you are grinding, and it get stuck and even welds themselves to the grinding wheel's sharp cutting edges. this built-up edge interferes with the grinding process and results in producing a rough surface finish, increased grinding pressure and inaccurate dimensions.

• POOR SURFACE FINISH: getting a smooth and precise surface finish can be challenging due to plastic deformation and the previously listed problems. this can cause grooving, tearing, and chatter marks on the workpiece.

• HIGH GRINDING FORCES: ductile materials are tough to remove material which leads to increased grinding forces. This will result in vibrations, deflection of the workpiece or machine, and higher energy usage.

• HEAT GENERATION: the friction and the plastic deformation between the workpiece and the wheel produce a certain amount of heat that results in thermal damage and alterations in the material properties of the workpiece.

• CHIP FORMATION & EVACUATION: ductile materials are capable of generating long, stringy chips that can be hard to remove from the grinding zone, which results in poor surface finish and wheel loading.

Precautions To Be Taken When Grinding Materials With High Ductility

The following precautions must be taken to overcome above mentioned issues and to effectively grind materials with high ductility.

1. Selection Of Wheel

Choosing the right grinding wheels is crucial when working with highly ductile materials. The following are the factors to consider while selecting the wheel:

• Wheel with a more open structure: As these materials tend to deform and adhere, a more open structure wheel is usually preferred. As these wheels have wide space between the abrasive grains which will give more chance for ductile chips to be evacuated and eliminate the possibility of wheel loading. Which occurs when material clogs the wheel's pores and reduces its cutting action.

• Selecting a softer grade wheel: A softer grade wheel is also beneficial as these wheels help in releasing dull abrasive grains more easily and revealing fresh and sharp cutting edges. This self-sharpening process helps in preventing the built-up edge formation.

• Using coarser grit sizes: Another precautionary step to be taken while choosing the wheel is to consider using coarser grit sizes. For the surface finish, this may seem strange, but it is sometimes beneficial for chip clearance and lowering wheel loading, mainly for roughing operations. Finer grits, with the right parameters, are highly suitable for finishing jobs.

• Using specialized wheel material: for some applications, using specialized wheel materials, including cubic boron nitride, can be beneficial due to their outstanding hardness and wear resistance while grinding certain ductile metals.

2. Grinding Fluid Application

The grinding fluid application is highly important in grinding ductile materials. This includes:

• Flood cooling: It serves as an efficient coolant making it essential for the grinding process. It helps in spreading the heat produced while preventing thermal damage, distortion and modifications in the workpiece's material properties. This fluid also acts as a lubricant between the grinding wheel and the workpiece, reducing friction, grinding forces, and the ability of material to stick to the wheel, resulting in load on the wheel and the creation of edges. Additionally, the continuous flow of fluid serves as a flushing agent by effectively eliminating long, stringy chips that are typical of ductile materials.

• Type of fluid: using the correct type of fluid is also crucial in grinding ductile materials. For ductile metals like aluminum, water-based coolants with the right additives are perfectly suitable as they have good cooling capability. Oil-based fluids, on the other hand, can be used for other ductile materials, although heat dissipation needs to be carefully considered.

• Ensure proper nozzle placement and flow rate: The fluid's usefulness can be maximized by placing the nozzle and flow rate correctly, which will route the fluid precisely where it is most urgently required for chip evacuation, lubricating, and cooling.

3. Grinding Parameters

Optimizing grinding parameters is crucial to achieving success in grinding ductile materials because of their natural resistance to shearing and ability to bend as plastic; aggressive parameters usually result in excessive heat generation, higher grinding pressures, poor surface finish, and wheel loading.

• Use lower wheel speeds and feed rates: this helps in minimising heat generation and grinding forces. You can try using different combinations to find the best one.

• Increase the depth of the cut cautiously: It is vital to carefully increase the depth of the cut since deeper cuts can result in increasing heat and pressure. Ensure to take incremental cuts, which is a more effective approach.

• Consider using creep-feed grinding: this method includes an extremely slow feed rate and high depth of cut, which can be beneficial sometimes for ductile materials as it produces thicker chips that are simpler to remove.

4. Machine Tool Considerations

The characteristics and condition of the machine tool are crucial in achieving success during operation while grinding highly ductile materials.

• Machine tool is rigid and adequate vibration damping: It is vital to make sure that the machine tool is sturdy and has enough vibration damping abilities, as cutting these materials includes increased grinding forces and the possibility of vibration.  This helps eliminate chatter and enhance the surface finish. 

• Regularly maintain the machine & spindle: Also, it is necessary to regularly maintain the machine and its spindle. A well-maintained spindle provides precise rotation with no excessive runout or vibration, which may affect the grinding process and the quality of the final part. It can be more challenging to grind ductile materials if there is any wear or loose part of the machine.

5. Workpiece Holding

The key to success for any grinding process is securely holding the workpiece, especially when cutting ductile materials. When cutting these materials, the high cutting pressure leads to movement or vibrations of an improperly secured workpiece which results in inaccurate and poor surface finish and also damaging the workpiece as well as the grinding wheel. Therefore, it is crucial to carefully clamp the workpiece by applying proper techniques and fixtures. While grinding ductile materials, stability, the required level of precision, and surface quality are all dependent on a well-thought-out and executed workpiece holding strategy.

6. Wheel Dressing and Conditioning

Because ductile materials have a strong tendency to cause wheel loading and built-up edge, it is very necessary to maintain the grinding wheel's ideal cutting performance when dealing with them. As a result, regular wheel dressing is an essential safety measure. Dressing refers to the process of eliminating any loaded material or dull abrasive grains and altering the wheel's cutting face to restore its sharpness and natural profile. This action helps in revealing fresh, sharp abrasive grains, which is crucial for successful material removal. You can achieve the desired wheel condition with the right dressing tools and techniques.

7. Grinding Strategy 

For highly ductile substances to be machined successfully, a well-considered grinding approach must be developed. Choosing between traditional grinding (up milling) and climb grinding (down milling) is a crucial decision. 

• Climb Grinding: when compared to traditional grinding, climb grinding can generate far better surface finishes when working with ductile materials, but it's necessary to have a stable setup and a machine free of backlash.

• Use Multiple Passes: to obtain the desired surface smoothness and dimensional accuracy, use multiple passes. use roughing passes with more aggressive parameters, then finish passes with finer parameters and softer cuts.

8. Material Preparation

Appropriate material preparation is a basic step that can directly affect the success of grinding highly ductile materials. Make sure that the workpiece material is clean and free from any contaminants like dirt, oxides, machining residues, etc. Can affect the grinding process in many ways. They can cause premature wear of the grinding wheel, increase wheel loading by clogging the abrasive grain spaces, and affect the workpiece's surface finish.

CONCLUSION

By carefully following these precautions and optimizing the grinding process, you can effectively grind materials with high ductility and obtain the required surface finish and dimensional precision. Keep in mind that for the best results with particular materials and applications, it is frequently required to experiment and find the ideal combination of parameters, wheel selection, and grinding fluid.