Tackling the big stuff: Workforce Development & Training

Machining large, heavy workpieces requires more than machine tools massive enough to accommodate oversized production. It also takes machinists with appropriate skills and expertise. Amit Shirsat said his job shop has the needed human and mechanical capabilities to effectively machine big parts. He is owner of Technox Machine & Manufacturing Inc. in Chicago.

The company, which his father, Shamkant, launched in 1976, has a variety of manual and CNC machines, he said. Those include an array of large horizontal boring machines with a maximum work envelope of 3,048 mm × 3,860.8 mm × 1,778 mm (120″×152″×70″); planers and CNC vertical mills for components up to 2,870.2 mm (113″) in length, 8,534.4 mm (336″) in width and 2,133.6 mm (84″) in height; and horizontal, vertical and CNC lathes.

Shirsat said manual machining on some equipment that is now 40 to 50 years old was the norm about 15 years ago.

“The times have changed,” he said, “so now we have more CNCs than we did before.”

To move weighty workpieces, which can weigh up to 13,608 kg (30,000 lbs.), Technox Machine & Manufacturing uses overhead cranes with suitable capacities. But removing workpieces, particularly forgings, from machine tools isn’t as energy-intensive.

“Generally, forgings have a lot of stock to remove,” Shirsat said. “Forging can become much lighter after machining.”

Factors that typically hurt machining accuracy are magnified when parts are larger. Image courtesy of A. Richter

In addition, the machine shop employs about 20 people to run the machines and operates on one full shift five days a week and until noon on Saturday.

“Some of our guys have been here for 40 years,” Shirsat said. “Accidents can happen with (large machine tools), and you have to have knowledgeable people who know what they’re doing.”

Technox Machine & Manufacturing serves customers in various industries, including mining, food processing, power generation, steel processing, textile and automation, and mostly performs 2D machining.

“Every now and then,” Shirsat said, “we’ll do 3D machining of molds and aerospace-type work.”

The main workpiece material is cast ductile iron, but the shop also cuts stainless steel, carbon steel, bronze, chromium, plastics and Ni-Hard, which is a white cast iron alloyed with nickel and chromium for low-impact, sliding abrasion
applications.

“Sometimes we work with nickel-base castings that are hard-turned,” Shirsat said, adding that hardness ranges from 30 to 40 HRC.

Specs for Large

Technox Machine & Manufacturing can achieve tolerances as tight as 0.0127 mm (0.0005″), but Shirsat said that isn’t the case for large parts.

“We can hold plus or minus 0.002″ (0.0508 mm) to 0.003″ (0.0762 mm) on diameter,” he said. “If we’re required to hold five-tenths, we generally leave stock and send it out for grinding.”

The shop outsources cylindrical grinding and performs surface grinding at its grinding facility in Elk Grove Village, Illinois, which has Blanchard and Mattison grinders.

In a company blog post about the challenges of large-part machining, Shirsat said factors that typically hurt machining accuracy are magnified when parts are bigger. This means that careful consideration needs to be placed on monitoring and countering these factors. Temperature is one of the more notable and significant examples of this. The process for machining massive parts generates a lot of heat, so users must compensate for the heat to maintain integrity of the final part. As these parts have larger surface areas, additional quality checks may be required to ensure that parts are being fabricated with reliable repeatability. Taking semifinishing passes and setting aside time to measure between passes before taking one or more finishing passes can be critical to achieving tight tolerances.

Another difference between machining conventionally sized parts and large, heavy ones is longer cycle times.

Technox Machine & Manufacturing’s equipment for machining large, heavy parts includes a King machine tool. Image courtesy of A. Richter

“Some take maybe three days, some take two weeks, and some take longer,” Shirsat said.

However, he said lengthy cycle times don’t involve lights-out machining once a shift ends at the shop’s climate-controlled facility.

“We’ll just stop and restart it the next day,” Shirsat said.

He said the company’s electrician also wears a mechanic’s hat and helps maintain manual machines. If an issue with a CNC machine isn’t overly complex, the shop performs the fix in-house.

“But if it requires more attention,” Shirsat said, “we get the builder involved, and they send their technician out and troubleshoot it.”