Machine Shops that grind ceramic workpieces flat to remove material or achieve a precise thickness now have “endless possibilities” to improve their capabilities with more advanced, automated equipment.
Ceramics are used in a range of industrial, commercial and consumer products. With ceramics, some of which can be quite hard, grinding is an essential process to achieve closer tolerances. The extreme hardness, as well as strength of some ceramics, makes it difficult to grind. Due to the material’s exceptionally hard, dense and brittle characteristics, ceramics need specialized precision grinding to achieve required tolerances.
However, due to the brittleness of ceramics, particular care must be taken to avoid surface damage, edge chipping and pitting, as well as microcracks and fissures that can render a workpiece useless.
Modern rotary surface grinders offer sensors and controls that can contribute to achieving tighter dimensional tolerances, flatness, parallelism and surface finish in much less time. The equipment can be used to planarize ceramic materials to close tolerance dimensions prior to lapping. Unlike traditional grinding, ceramic grinding involves using a metal-bonded diamond grinding wheel to remove stock from the surface of the material.
Operator control over the process is unsurpassed with the new automated grinders. The user can enter the specific machine parameters, for example: 712 rpm on the spindle and 22 rpm on the table, with a down-feed rate of .003 inches (0.076 mm) per minute and certain dwell times in seconds. Essentially, the machine parameters are infinitely variable.
Compared to traditional grinding equipment with manual controls that require experienced machinists familiar with the nuances of each machine, these automated units consistently produce higher quality parts in less time. As a result, a growing number of machine shops are installing new grinders that can be operated by less experienced personnel while still achieving the desired results.
In machine shops that work with ceramic workpieces, factors such as thickness, parallelism and surface condition are specified on a drawing. Grinding is utilized to remove stock to bring a workpiece to the stated dimensional specifications.
The use of older rotary surface grinders is a method for grinding ceramic that can be problematic in the hands of less experienced operators. With limited control of spindle speeds and manual controls, the older equipment requires experienced operators. The situation is exacerbated as skilled operators retire.
In modern rotary-table surface grinders, the table rotates with the workpiece held firmly in place underneath a vertical spindle. The grinding is not performed by the peripheral edge of the wheel but by the entire diameter of the abrasive surface, which improves grinding performance and consistency.
“With rotary table surface grinders, the entire part passes through the wheel, which is more efficient than reciprocating table grinders that may have workpieces wider than the grinding wheel,” says Erik Lawson, engineering manager at Winona, Minn.-based DCM Tech, a designer and builder of industrial rotary surface grinders.
Today, surface grinders are designed with much more advanced sensors and controls that automatically maintain tolerances via 0.0001" (0.0025 mm) of machine Z-axis feed resolution. Digital technology allows for an interface with easy-to-use touchscreen controls that, teamed with automation, means operators are no longer required to be seasoned technicians.
For example, rotary units such as DCM Tech’s IG 282 SD, with a 24" (610 mm) variable-speed table and a variable-speed, 20-hp grinding spindle motor, make it possible for virtually anyone to successfully operate a unit. One innovative approach available in this model is the automation of initial contact between the abrasive wheel and the part, which typically had to be finessed by the operator. When the machine senses the abrasive wheel has contacted the part, it automatically begins the grind cycle.
“Automatic part detection eliminates the need for the operator to do time-consuming, error-prone ‘manual touch offs,’ where they would manually feed the grinding machine until it just touches the surface of the part before backing off and restarting it,” Lawson says.
With regard to production efficiency, the advanced rotary surface grinders are also much faster than reciprocating grinders because the units can get closer to the required thickness dimensions prior to lap and polish operations. This capability can reduce or even eliminate lap and polish times.
“A rotary surface grinder will usually finish the work of a reciprocating grinder in a fraction of the time,” Lawson asserts.
The rotary grinder process also consistently achieves high throughput and can reduce variability, which enables machine shops to predictably generate targeted workpiece specifications. In addition, programmable human-machine-interface controls allow operators to easily enter machine operation parameters via fixed fields of entry on a thin-film-transistor LCD touchscreen.
For routine processes, the use of a variety of grind “recipes” can be saved on the control memory, which provides process repeatability for differing but recurring jobs on the machine.
“Different grind recipes can be named for different customer jobs, material types or even part numbers so complex programming or data does not need to be entered at the start of each job. A new recipe can be created for job variations, such as a different finish or number of parts on the table,” Lawson explains.
The grinder can also be programmed to make subsequent passes if the workpiece is not to size on the first pass. There is no need to touch off on the workpiece on subsequent grind sequences because the machine recalls the position from the previous grind sequence and picks up where it left off.
According to Lawson, the automation provided by advanced rotary grinders allows operators to set up the machine and then attend to other tasks. The machine doesn’t need to be constantly monitored because it has built-in load monitoring.
“Load monitoring allows the user to set limits to pause the auto-feed motion if the selected spindle load limit value is met during the grinding process. During the auto-feed pause, the spindle load will typically drop due to the wheel breaking down or material removal from the workpiece. When the load drops below the programmed load limit, the auto-feed will automatically resume at the programmed feed rate,” Lawson explains.
He adds that the automated units also contribute to a safer, cleaner shop environment because the grinding is accomplished inside an enclosed shroud that contains the debris and prevents it from entering the work area.
As the tolerances for ceramic grinding become tighter and production requirements become more demanding, machine shops that take advantage of advanced, automated rotary surface grinders can meet or beat current productivity levels. This is especially critical as experienced operators retire.
“With automated rotary surface grinders, a machinist can be trained to be proficient at operating the equipment by lunchtime on their first day on the machine. It just takes a few hours of training, not decades of experience as with older machines,” Lawson concludes.
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