Reducing Prep Work With Precision Blanks

For many manufacturers, the first step in a machining operation is to square off the blanks before moving on to machining part features. Keeping the workpieces in a production line as similar as possible is vital, as variances in dimensions can lead to machining errors or automation failures. This is a time-consuming, but necessary process that ensures precision machining can take place. But squaring blanks can also be a bottleneck that demands valuable machining time and slows down throughput.

One solution to avoid this bottleneck is precision blanks machined and ground by a supplier. So we wondered: If machine-ready, precision blanks represent a time-consuming challenge for machine shops, what prevents them from representing the same challenge to a supplier?

To find out, we asked TCI Precision Metals.

Machine-Ready Blanks

TCI Precision Metals is a material supplier that deals in steel, stainless and aluminum — all of which are warehoused at TCI — as well as nickel alloys, tool steel, titanium and plastic on request. While much of its precision blanks are flat, TCI also supplies blanks for prismatic parts. The company uses precision saws and waterjet machines to cut the blanks to a basic shape, then grinds or mills them (in most cases) to a tolerance within 0.002 inches or tighter all around, including flatness. Additionally, the company can hold dimensional tolerances as tight as 0.0005 inches. “Our shop is designed to efficiently produce square, flat material at tight tolerances pre-machined to customer specifications,” says President and COO Ben Belzer. Machine-ready blanks arrive ready to go directly from receiving to machining.

TCI has an array of Blanchard and double-disk grinding machines, as well as duplex mills. The company chose these machines because they can easily achieve the required tolerance while minimizing stress on the parts. Once the blanks are cut or ground to final tolerance, TCI deburrs them and measures to ensure tolerance, employing portable CMMs as well as feeler gauges to check flatness. Additionally, the company can coordinate heat treatment and and coating of parts according to customer needs.

Belzer sees TCI’s niche as simplifying the production process for high-production milling work, especially in automated machining cells. “The more machining time a shop has dedicated to prepping parts,” he says, “the better our value offer is.” By switching to precision blanks, he argues shops with machines dedicated to prepping work can dramatically increase throughput.

Heavily automated machine cells can see especially good results. Robot and cobot arms rely on workpieces being precisely the same shape to reliably transport each part into the machine. Precision blanks guarantee that the parts are within the required specifications without any prep work on the part of the shop. “We see a lot of success with lights-out machining,” Belzer says. “When you set up a lights-out cell, you want to reduce variance as much as possible, and precision blanks can do that without adding any more work for the shop.”

High-Production, Low Automation

TCI performs most of its grinding operations using  machine tools older than most of its workers. “Some of our best machines are over 50 years old,” Belzer says. “We have updated them with CNC technology, and they are very good at what they do.” The company has to keep these machines running in excellent shape, as replacements are not readily available. Not many companies make custom grinding machines large enough for TCI’s purposes, which means using older, well-maintained machines that can still reliably hit their 0.002-inch goal.

“Our most important area of expertise is in producing flat blanks, especially thin ones less than 0.5 inches thick,” Belzer says. With thicker workpieces, stresses in a small area are unlikely to cause a crack or deformation along the entire part, but flat parts are a different story. Internal material stress built up from the forging process can cause parts to bend or bow like a potato chip during finish machining, resulting in parts being scrapped. Deformation is most prevalent with thin parts with larger surface areas, as the width can provide stressed sections with leverage, while the thickness means there is less mass to resist movement. As part of the production process, machine-ready blanks are stress relieved to help prevent movement.

Belzer says that there are two major benefits to using a double-disk grinder when producing precision blanks: the ability to grind both the top and bottom at once — a process that helps reduce residual stress in the material. “Double-disk is just that,” Belzer explains. “The material floats between two grinding discs with material removed from the top and bottom equally.” The process releases material stress during the grinding process, resulting in a material that is flat and — because the stress has been released intentionally — has a propensity to stay flat.

The Blanchard grinders are primarily used for flat blanks that are too wide for double-disk grinding. For these large parts, the company uses vacuum workholding developed in-house to prevent deformation on especially thin blanks and to allow grinding access to 100% of the surface. The raw material for TCI’s blanks can exceed 120 pounds per piece — or even over 1,000 pounds — providing a significant downward force that helps keep the workpieces in place. The Blanchard grinders are suited for this task because they have large abrasive surfaces that can quickly achieve the desired flatness over a large area. However, unlike the double-disk grinders, blanks machined on a Blanchard require separate setups for each flat surface.

Somewhat ironically for a process that helps shops automate production, the grinding process at TCI is not heavily automated. While the company produces tens of thousands of blanks per month, it relies on the experience of its employees to maintain production levels. The machinists and grinding specialists at TCI need to be experts in identifying which machines are best for which parts, as well as knowing the grit and feed rate required.

Dovetailing Into Milling

In addition to its grinding machines, TCI uses duplex mills for machining prismatic, six-sided blanks. For example, the company uses an Amada THV800 for machining large prismatic blanks up to 31 inches in length and width, and 9 inches thick. The machine has a rotary table that enables the company to mill both length and width in a single setup, further improving the speed of production.

“We use the duplex mills because that’s really the fastest way to machine six-sided blanks that are 1 inch or thicker, and the duplexes can easily hit our tolerance,” Belzer says. The company also uses duplex milling to stack multiple, thin, flat blanks and mill them to length and width before surface grinding.  “Volume cutting, milling and grinding are efficient and allow us to provide increased value to our customers,” Belzer says. 

TCI also provides blanks with added features to further assist its customers. “This can be a small feature or a hog-out,” Belzer says, “but lately we are getting a lot of requests for dovetails.”

Dovetail fixturing has become very popular in five-axis machining, and Belzer sees precision blanks becoming more popular in that realm. “It’s really the same value proposition as anywhere else,” he explains. “Do you want an experienced machinist spending valuable time cutting dovetails into the bottom of a workpiece, or do you want them machining complex parts?”