Abrasive wheel advances

Whenever a Norton application engineer collaborates with a customer to assist with process improvements and propose the best abrasives technology, it’s important to start by determining the customer’s goal, says Arianna Smith, corporate application engineer, Norton | Saint-Gobain Abrasives.

“Most of the time, objectives will fall into one or more of the following categories: reduce cycle time (improve productivity), increase wheel life (increase parts per wheel), or improve part quality (reduce scrap rate),” Smith says. “It’s key to analyzing the application to determine what solution will provide the most value for the customer’s goal.”

If a customer is at capacity, can’t make parts fast enough, or has a high overhead cost, reducing cycle time to increase throughput may be the priority. In this case, Smith explains, part quality is satisfactory and wheel life isn’t as critical, so reducing cycle time will increase part production and revenue, and save costs due to optimizing the process.

As another example, a customer may want to reduce costs, but is experiencing a bottleneck during a secondary operation after the grinding process. “Even if they cut their cycle time in half to save costs, the parts are just going to stall out at the next process step, so any gains in cycle time reduction are lost. In this case, assuming part quality is sufficient, increasing wheel life will be the best solution to save costs.”

In a third example, a customer is grinding an exceedingly difficult-to-machine alloy where they are experiencing burn, inconsistent size, poor part finish, and, as a result, an extremely high scrap rate. “In this scenario, the cycle time and wheel life may not be as critical as the capability to make good parts, so the goal would be to improve part quality,” Smith explains.

The first case study (OD grinding) illustrated below shows improved wheel life, the second case study (ID grinding) shows an improved material removal rate.

Micro grains

The case study results Norton | Saint-Gobain Abrasives offers are due to its Quantum Prime product and how it leverages its unique micro-grain structure.

According to Smith, Quantum Prime satisfies a variety of critical grinding challenges. “It works extremely well on difficult-to-grind materials, such as complex alloys or gummy metals, materials sensitive to heat generation, parts that require accurate profiles and form holding, and in processes where fast cycle times, longer wheel life, lower machine power draw, and better part quality are essential.

“It’s excellent on difficult-to-grind materials due to the friability of its proprietary nano-crystalline ceramic grain. This grain micro-fractures, breaking down into much smaller, sharper fragments at lower pressures compared with other ceramic grains.”

Other ceramic grains may release larger sections, increasing wheel wear. Also, other grains may be too durable to break down at the right time with the necessary forces, resulting in more rubbing than cutting. Smaller fragments are critical because as difficult material begins to stick to the grains, the Quantum Prime grain will shed a very small layer to release the metal capping and continue cutting, minimizing friction. The grain’s sharp shape also allows efficient penetration and material removal before metal capping begins.

Quantum Prime leverages its micro grains to reduce cycle times, increase wheel life, and/or improve part quality. Because the grain micro-fractures, the friction, rubbing, and forces imparted onto the workpiece are much lower. Therefore, spindle load is decreased and overall power draw is reduced.

“Different applications experience varying amounts of improvements, but with OD grinding, we’ve seen up to 70% lower power draw compared to previous generation ceramic grains,” Smith says. Users can choose to grind with these power savings or can increase material removal rates to match the original spindle load, allowing lower cycle time at the same power usage.

In addition, the grain is strong enough to withstand faster feed rates and increased depths of cut, resulting in faster cycle times. The strength, shape, and sharpness of the grain allow for higher material removal rates without an increase in breakdown, so longer wheel life can be expected. Because of the grain’s friability, Quantum Prime resharpens itself as it’s used, reducing the need for additional dressing, and lowering dress compensation.

Using proper dressing tools with optimized programs can help customers maximize their grinding wheels and positively affect the quality of the parts they’re grinding. Depending on the strength and makeup of the grinding wheel, some applications require specific types of dressing tools. Quantum Prime can be used with stationary or rotary dressing tools.

Due to its ability to micro-fracture, it has also shown merit in materials where heat generation is a concern. “Instead of needing to use the same grain surface which dulls as it continues cutting, adding to the heat concern, Quantum Prime’s ability to shed very tiny pieces produces consistently sharp edges, provides a cooler cut, and significantly reduces the frictional forces in the grind zone,” Smith notes. While the grain micro-fractures at lower pressures, the overall strength is high. “Due to its strength, it satisfies the need for accurate profiles and is great at form-holding even complex shapes,” she adds.

Advanced bonding

Smith says Norton’s Vitrium3 advanced bonding technology allows Quantum Prime to wear more consistently, for improved part quality, geometry, and finish even at high material removal rates. Vitrium 3 offers increased bond strength at a lower bond-to-abrasive ratio compared to other vitrified bonds. This lower bond amount creates more pores in the grinding wheel for the same amount of abrasive.

“This porosity allows for a cooler cut in multiple ways. The decrease in bond reduces the amount of friction between the bond and part that is being ground. Also, because the bond posts are smaller, more abrasives are stuck to each one, increasing the surface area of the abrasive, which in turn, increases cutting action,” Smith states.

Additionally, the porosity allows swarf to fall out of the wheel more easily and more coolant to enter. The increased strength of the bond also allows for a decrease in bond breakdown under pressure resulting in longer wheel life, improved and longer lasting wheel form, and more accurate shape and corner holding – all resulting in less wheel dressing. The strong bond also holds the grains longer, not releasing them before their full life, allowing them to withstand faster grinding and improved cutting rates.

Applications

A few applications where Quantum Prime is frequently used include OD, ID, surface, creepfeed, gear, centerless, flute, and disc grinding. Because it can be blended with a variety of aluminum oxide and silicon carbide secondary abrasives in various percentages, it can be customized to customer needs, industries, material types, and applications.

“To specify a made-to-order wheel, we recommend a customer works with their local Norton sales representative” Smith advises. “The representative will gather information on the application, material(s), grind and dress parameters, issues they are facing, and goals for the new wheel.” The sales representative then works with the Norton application engineering and product management teams to produce the specification best suited for the application.

Grinding or machining?

Due to Quantum Prime’s micro-fracturing capability and grain composition, Q’ (specific material removal rate) values are higher than with previous generation ceramic grains, and in some cases can begin to rival those of conventional machining, especially in applications with significant material removal requirements, Smith says. Also, the micro-fracturing, resharpening, and abrasive hardness benefits of it allow the wheels to stay sharp and continue cutting longer compared to conventional machining steel and carbide cutting tools that will need to be replaced once worn. In addition, because it has more cutting edges than conventional cutting tools used in machining applications, friction is minimized and heat generation is lower, offering better part quality internally and externally. Smith emphasizes Quantum Prime’s increased cutting points produce better surface finishes and more accurate profile shapes – critical in precision grinding applications, especially those with very tight tolerances. “Norton’s team of application engineers based throughout North America can assist both virtually or onsite to support customers by offering solutions to complex grinding problems and/or process optimization, including dressing parameter updates and recommendations,” she says.