Automated Grinding Machines Yield Tighter Tolerances and Save Resources

Located in East Dundee, Illinois, National Tool & Manufacturing Co. (National) is a family-owned business deeply rooted in the steel and moldmaking industries. The company supplies mold and die customers with both raw and highly processed holder plates and also functions as a one-stop-shop source for mold base steel needs.

On the mold base side, National services customers within industries such as medical, consumer goods, automotive, packaging and pharmaceuticals. In particular, the packaging and pharmaceutical customers require tight tolerances due to molded material type, volume and critical dimensioning. The company has seen mold base tolerance demands shrink from the already tighter than standard ±.0005" to a near zero tolerance of ±.0001".

National's steel division is a leading supplier of steel holder plates for mold bases. That division uses rotary grinders as well as planer mill technology and steel inserts to precision cut the surface plates. The VR Stainless plates distributed by National are regularly used in tight tolerance applications, not achievable by these processing options.

According to National’s President, Eric Sandberg, the future lies heavily in its customizable steel services to meet the specific needs of its customers. Roughly 90% of the company’s customers are moldmakers — the majority of whom are requesting more and more aggressive processing options. In the future, this will include more detailed work in the mold base (tighter tolerances and more features), meeting tighter deadlines.

“The more accurate we are, the more lead time is shaved off for our customers’ purposes,” says Matthew Grassel, production manager for National.

With little to no room for error with tight-tolerance jobs, the company began searching for an automated grinding solution that would yield the required tolerances and simultaneously provide a more user-friendly, lights-out approach to free up its skilled workers for other jobs throughout the shop floor.

The solution manifested in the form of two Ziersch machines. Purchased through YCM Alliance in the U.S., these machines served as the link to precision and repeatability for National as it can now achieve the tight tolerances its customers require.

Trend Toward Tighter Tolerances

For surface grinding operations, National specializes in Class 101 and 102 molds, maintaining total flatness and parallelism tolerances within 0.0005 inches (half a thousandth) with abilities to hold .0001 if need be. Class 101 molds are built for high-volume production. Grassel says that flatness varies and is dependent on the operator, in terms of having a good, clean setup. If this isn’t the case, flatness will be off.

On the other hand, parallelism has everything to do with the machine. Factors such as whether the machine is perfectly squared and leveled, or if there’s too much way-lube pressure or not (as this could cause the table to float or the head to float) all come into play.

Sandberg gives an example for this tight tolerance challenge, discussing the different kinds of injection molds and even more specifically, the plates. On larger molds with less critical features in the base or carved into a large block, the parting line tolerance is open and less critical. For many mold builders, a milled parting line is acceptable. 

“However, our customer base is seeing a greater need for tighter tolerance, smaller work for mold bases. Therefore, the location where the plates stack up is extremely critical as the tolerance on flatness as well as thickness becomes tighter and tighter and tighter,” Sandberg explains.

The company has seen instances where it had small mold bases in terms of length and width, but these still required a large number of plates stacking up. According to Sandberg, with a high number of plates, a small defect on accuracy is multiplied. For example, a .0005 off on each plate out of 11 plates turns into over .005's total — unacceptable for the most critical applications.

“We knew we needed to start looking into grinding equipment that would enable the tolerances our customers need to satisfy demand, but that wouldn’t take all day to achieve this,” Grassel says.

Originally, the company had always relied on the skill of its employees (like Grassel) as well as some of its grinders in the steel shop to take on these tougher tolerance jobs. These individuals were essentially utilizing manual machines — specifically four Mattison Brand surface grinders — to achieve these tolerances. Having its technicians fight the consistency on these machines proved an unsustainable practice as National continued to receive an influx in need for tightened tolerances.

Therefore, the company found itself at the brink where these jobs could no longer be accurately completed on its manual grinding machines. “When using these older, manual machines, the operator would have to mic the plates for measurement purposes. Before taking the plates off the machine, operators would need to rely on their micrometers and depth mics,” adds Grassel.

“Tolerance-wise, this method can be difficult, especially when one person is dedicated to keeping their eye on the machine to ensure no mistakes are made (for example, in grinding too much or too little),” Sandberg says.

Originally, National Tool’s mold base division had two dedicated (attended operators) shifts devoted to grinding (eight hours each), plus overflow at its steel division. With the Ziersch grinders, this is now achievable in less than two attended shifts.

Automated Grinding Machines to the Rescue

Fortunately, while Sandberg was attending a trade show in Germany back in 2019, he happened by Ziersch’s booth and connected with the company’s owner, Frank Ziersch. 

After connecting at the show, Sandberg says he also received good feedback and references from some of National’s moldmaking customers which prompted him to take the plunge with Ziersch grinding machines.

Originally, National purchased a large, single-column grinder, also called an over-arm grinder (1,500 × 800 mm; 59 × 31 inches) and had this installed in December 2019. Impressed by its benefits, in December 2023, the company decided to purchase a double-column grinder (2,000 × 1,700 mm; 79 × 67 inches) to further bolster its tolerance work and grinding capabilities.

The Z715 (the smaller of the two machines) proved to be useful for most workpieces, while the Z1520 (a giant bridge machine) handled the larger workpieces to provide optimal tolerances.

Sandberg says the installation process went smoothly as National has a collaborative relationship with the Ziersch team. National’s team was very much involved in setting up the machines for its application.

According to Philipp Ziersch, export manager at Ziersch and factory representative to YCM Alliance, both of the machines National purchased can be used universally for a variety of jobs and are also well-suited for processing a wide range of materials, such as steel, glass, carbide, ceramics, plastic, alloys, aluminum and more. This flexibility across the complete line of Ziersch grinding solutions, which includes surface grinders, rotary table grinders and cylindrical grinders, is key for mold and die jobs and virtually all machining applications requiring ultrahigh precision.

Additionally, the Ziersch machines offer Heidenhain encoders. This feature lends itself to an electro-permanent magnet that functions to inhibit heat, ensuring there is no distortion of material thickness during the grinding process.

According to Grassel, who taught himself how to operate these two grinding machines, the touchscreen controls were very intuitive and easy to learn how to use. He went on to teach four other operators in the shop how to use the equipment.

“With these grinders, you’re able to program depth of cuts, and depending on the material, the type of wheel you are using and how much of an open dress you have, this will directly affect the finish,” Grassel says.

“The automated dressing cycle enables the operator to set up a plate, select the designated amount of material for the machine to remove and then repeat this process until that specific amount of material has been completely removed from the plate,” Grassel adds.

This function enables the operator to set up the machine at the start of the job and walk away without worry. This frees up employees to check on other machines or take on additional responsibilities on the shop floor.

Ziersch also has a proprietary system which offers a chuck equipped with gundrill lines that enable air release in the plate.

“Grinding can often cause plates to get stuck, making this feature very useful. It enables the plates to move more easily on the chuck, similar to an air hockey table. This makes it much easier to remove center plates or larger plates without lift holes,” Grassel says.

Additional benefits of the Ziersch machines include a manual grinding option with open door (as noted above), a fully automatic grinding cycle with dressing cycles (divided into roughing/finishing), various grinding cycles: surface grinding, multiple plunge grinding, plunge grinding (up to 20 grooves), roughing/finishing/sparking out and profile grinding.

The machines also offer an automatic vertical infeed with compensation of the dressing amount, warmup program and night shutoff and grinding wheel management.

Ultimately, according to Ziersch, these machines enable drive powers of up to 32 kW and the use of grinding wheels with dimensions of up to 600 mm × 150 mm (which can achieve much tighter tolerances than traditional grinders). In addition to the corundum grinding wheels, diamond and CBN grinding wheels can also be used, and cutting speeds of up to 50 m/sec. are possible. 

Tight Tolerances: Conquered; Resource and Cost Savings: Activated

The benefits of having two Ziersch machines were quickly noticeable on the company’s shop floor and not only in terms of achieving tight tolerances. “The Ziersch surface grinders were well-suited for repeatable and unmanned operation. In our scope of precision work, surface grinding remains an integral step in production. The surface grinding operation is always completed after significant work goes into a plate (steel preparation, gundrilling, rough machining). Errors at this stage are a significant in terms of cost and delay. These grinders have increased our output while reducing the risk of errors, a double win for us,” Sandberg says.

“We have lowered our scrap rate because we are no longer fighting parallelism. We can achieve perfect parallelism where on the older machines this would be much more of a challenge, as sometimes you could accumulate errors up to 0.0005 inches (half a thousandth) across the surface,” Grassel says. 

With the addition of the Ziersch machines, National has since reduced its original, traditional grinder count from four to two.  

The company also saw a 40%  reduction in attended hours for grinding at its mold base facility. Prior to utilizing the Ziersch machines, the day and night shift employees needed to dedicate a lot more time during their eight-hour shifts to monitor and handle the old grinding machines to ensure precision and control for tight tolerances were being met (16 hours total time per day when combining day and night shifts).

Currently, National alternates operations between assembly and grinding. This change has enabled the company to reduce overhead costs, as it no longer needs to pay an employee to operate a single machine. Grassel has one employee who is managing tasks in two departments while operating two machines, while also working in an additional department.

With the Ziersch grinding machines, National has not only been able to successfully secure the tight tolerance and precision work to satisfy customer demand but it has been able to create more time and opportunities for its team to focus elsewhere on the shop floor. Lesson learned? Work smarter, not harder.