Selection of the appropriate abrasives for automobile industry grinding applicationsPhilip Hipol | April 30, 2020
Abrasive grinding operations are used extensively in the automotive industry for machining of several driveline, suspension, body and chassis components. For example, driveline components, such as engine block cylinders, cylinder heads, valves, crankshafts, camshafts, bearings and gears require highly precise, smooth and polished surfaces in order to reduce friction and wear, ensure proper sealing, or enable smooth, noise-free operation.
Body components, which are welded and brazed, require grinding operations to remove sharp edges and obtain smooth and polished surfaces suitable for high gloss painting (Figure 1). The various automotive grinding applications may require different types of abrasives in different configurations, which can have a significant impact on part quality, production speed, maintenance downtime and cost. This article describes some of the challenges presented by automobile industry grinding applications, and how these challenges affect the selection of the appropriate grinding abrasives.
Perhaps the biggest challenge presented in automobile manufacturing pertains to the volume of vehicles produced. In 2019, U.S.-based automobile manufacturing exceeded 17 million vehicles, with each vehicle containing hundreds of machined components, translating into thousands of surfaces per vehicle that required finishing with abrasive grinding. In order to maintain the large production volumes, high throughput rates are needed, resulting in higher grinding speeds. These high speeds cause additional wear on grinding tools and higher operating temperatures, which reduce the life of the abrasives. Frequent tooling changes may therefore be required, which translate into higher production costs. One of the current trends in the automobile industry is to use harder steels with smoother surface finishes to improve wear and lifetime. These harder surfaces make grinding more difficult, and, in some cases, require specialized abrasives. The abrasives must therefore be carefully matched to the materials being ground, the speed of the grinding operation and the desired surface finish of the parts being machined.
The different types of grinding operations employ sheets, discs or wheels, where abrasive particles are bonded together, coated onto a substrate or incorporated into non-woven abrasives. Bonded abrasive wheels (Figure 2) consist of abrasive particles that are pressed and bonded together into a round, solid shape by a cementing matrix. Coated abrasives consist of abrasive materials that are bonded onto belts, sheets, discs or rolls with an adhesive (Figure 3). Non-woven abrasives consist of three-dimensional strands of flexible fibers, onto which abrasive grains are bonded, that are pressed together to form sheets, discs or cylinders (Figure 4). The choice of the type of abrasive particles used, and whether they are incorporated into a bonded versus a coated versus a non-woven abrasive in grinding operations depends on numerous factors, such as the type and hardness of the work piece, the amount of material that needs to be removed, the shape of the work piece, the surface finish desired, the speed of the grinding operation, and the contact temperature between the work piece and abrasive.
Grinding operations in the automotive industry use abrasives that fall into two general categories: conventional abrasives and superabrasives. Conventional abrasives include aluminum oxide (Al2O3) ceramic alumina, silicon carbide and zirconia alumina, which are the most widely used and least expensive. The ceramic abrasives are generally harder than aluminum oxide and consist of sharp grains with aggressive shapes. Superabrasives, such as diamond or cubic boron nitride (cBN), may cost more than 50 times as much as their conventional abrasive counterparts. These abrasives, however, may be used to grind 100 times the number of parts that a conventional abrasive may grind. Superabrasives can grind the hardest of steels while exhibiting very little wear, and thus, may be well-suited to grinding operations where the tools are not changed frequently. An added benefit of cBN is that these materials conduct heat more readily than conventional or ceramic abrasives, enabling cooler operating temperatures during grinding.
In summary, the main considerations for selecting an appropriate abrasive for automotive industry grinding operations include the type, design and configuration of the components to be ground, the material to grind (including type of heat treatment, hardness or grinding stock), the finish requirements (for example, roughness, straightness or size tolerance), the machining or grinding cycle time allowed for the operation, and the grinding equipment available (for example, hand held, manual machine or robotic). These factors will help define several important aspects of the abrasive(s), such as the grit size, the configuration of the abrasive (wheel, disc or cylinder), and the type and hardness of the abrasive (conventional versus superabrasives). These factors will also define the grinding process, such as the type of grinding machine, its configuration, horsepower, grinding speed and pressure, and grinding process cooling or lubrication requirements.
About Norton | Saint-Gobain Abrasives
Norton | Saint-Gobain Abrasives is the world leader in abrasive products that provide a unique portfolio of grinding, cutting, blending, finishing and polishing solutions for a wide array of markets, materials and applications. Their abrasive products are engineered and manufactured with the highest degree of quality to ensure superior and consistent performance. Norton’s experienced sales and product support teams can provide their customers with up-to-date technical information on their stock (off-the-shelf) products and assist them in selecting the correct product for grinding operations. For applications requiring special considerations, Norton’s technical and engineering teams can assist customers by developing made-to-order products that are custom-engineered to meet the most stringent of customer requirements. Whatever the specific need, Norton products provide the superior finish with a total brand solution of product and competitive pricing at any level to get the job done right. More information about Norton | Saint-Gobain Abrasive products and services can be found on their website.