Machine shops that grind metal surfaces flat to remove material or achieve a specific thickness have numerous technology options to improve precision, as well as production speed and control, with advances in technology and greater use of automation.
Today, rotary surface grinders offer sophisticated sensors and controls that can reliably achieve tighter dimensional tolerances, flatness, parallelism, and surface finish, in much less time. The equipment can be used to grind flat metals, alloys, and ceramics to precise dimensions before polishing.
With the new automated grinders, operator control over the process is unsurpassed. The user can enter the specific requirements, for example: 712 RPMs on the spindle, 22 RPMs on the table, with a down-feed rate of 0.003 inches per minute, with a certain dwell cycle. Essentially, the machine can be programmed to meet just about any requirement.
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.
Solving the Skills Problem – Machining metal involves factors such as thickness, parallelism, and surface condition that typically are dictated in the specifications. Grinding is often done to remove significant amounts of material to bring a stock sheet or plate to precise dimensions.
To do this, machine shops primarily use surface grinders with a reciprocating table and a horizontal spindle that turns the grinding wheel, but the process is very slow.
“Reciprocating table grinders are precise, but the material removal rate is slow and multiple passes are required,” said Erik Lawson, Engineering Manager at Winona, MN-based DCM Tech, a designer and builder of industrial rotary surface grinders.
Older rotary surface grinders are another option but can be problematic in the hands of less experienced operators. With limited control of spindle speeds as well as manual controls, the older equipment requires sophisticated operators that can factor in complex calculations. Considerable expertise and experience are required, which can be a challenge as skilled operators retire.
Automated rotary surface grinders – With a modern vertical-spindle, rotary-table surface grinder, 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 facilitates 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,” said Lawson.
Today, surface grinders are designed with much more advanced sensors and controls that automatically maintain very tight tolerances, removing material down to within one ten-thousandth of an inch of the final thickness. Digital technology allows for an interface with easy-to-use touchscreen controls. When combined with automation, surface grinder operators no longer are required to be highly trained individuals.
For example, rotary units such as DCM Tech’s IG 280 SD, with a 24-in. variable-speed table and 20-HP variable-speed grinding spindle motor, make it possible for virtually anyone to operate a unit successfully. One example of innovation available in this model involves automation of the initial contact between the abrasive wheel and the part, which typically had to be finessed by the operator. With this updated option, advanced sensor technology detects vibration and can automatically fine-tune not only the pressure of the spindle motor but how quickly it moves the wheel down onto the part. 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,” according to Lawson.
Regarding production efficiency, the advanced rotary surface grinders also are much faster than reciprocating grinders because the units can get much closer to the required precise dimensions before any finishing steps. This capability can reduce or even eliminate some lapping and polishing steps.
With a conventional surface grinder, if stock with standard thickness needs to be ground down, an operator would stop short of the required removal and leave an unpolished surface. Using another machine was often required to remove the remaining material but this can take excessive time and labor.
“A rotary surface grinder usually will finish the work of a reciprocating grinder in a fraction of the time. For the manufacture of carbide blocks, one OEM was able to document a 14X improvement in cycle time by replacing a reciprocating grinder with a DCM rotary surface grinder,” said Lawson.
The process also consistently achieves high throughput and eliminates variability, which enables machine shops to achieve high-quality final parts, batch after batch.
In addition, programmable Human Machine Interface (HMI) controls allow operators to enter virtually any requirement into a touch screen. This capability enhances shop processing flexibility, so it is easy to adjust any grinding factor to prevent an issue from reoccurring.
For routine processes the use of a variety of grind “recipes” with sets of parameters for specific parts can accelerate production, enhance quality, and aid in quick changeover.
“Different grind recipes can be set for different customers, 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,” Lawson explained.
The grinder also can be programmed to take corrective actions on subsequent passes if the workpiece is a little off on the first pass. There is no need to pick up the workpiece and measure it after every move, as with older machines.
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 does not need to be constantly monitored because it has built-in load monitoring.
“Load monitoring allows a user to set limits, so the machine does not overtax the part being ground or overload the spindle. If something a little unusual happens it can continue without interruption or shutting down,” said Lawson.
He added that automated units also contribute to a safer, cleaner shop environment because the grinding is accomplished under an enclosed shroud that contains the debris and prevents it from entering the work area.
As the tolerances for metal grinding become stricter and production requirements more demanding, machine shops that take advantage of advanced, automated rotary surface grinders will outperform rivals even as experienced operators retire.
“With automated rotary surface grinders, a machinist can be trained to be proficient at operating the equipment by lunch on the first day. It just takes a few hours of training, not decades of experience as with older machines,” Lawson concluded, adding that systems incorporating full automation are now being developed that will use a robot to load, set-up, and run parts without an operator nearby.
Del Williams is a technical writer in Torrance, Calif.
