For nearly 50 years, Takoma Gears (Parkano, Finland) has specialized in prov iding largescale gears and gear components to customers, mainly in its domestic market. Concentrated heavily in the marine industry, the company prides itself on minimizing lead times and costs while meeting extremely strict quality requirements. Dedication to maintaining these standards leads the company to constantly evaluate its operations and track developments in technology that can lead to process improvement.
Traditionally, Takoma has used HSS hobs for the cutting of gear teeth. In 2009, the company purchased several new machines for the production of large gear components for use on ships. Slewing rings with an outer diameter of approximately 2 meters (6.56 feet) are produced from 42CrMo4 steel and require high dimensional tolerances. Takoma initially began machining the slewing rings’ teeth with a specialized gear cutter that provided acceptable quality levels, but was expensive and required lead times of up to 12 weeks to receive. Feeling that a better option must exist, the company contacted a provider of tooling used in many of the secondary operations of its parts.
“We have worked with representatives from Sandvik Coromant for over 30 years in regards to drilling, milling and turning tools,” says Jyrki Koitto, production manager at Takoma Gears. “We knew that they were increasing their focus on tooling for cutting gear teeth, so we asked if they had or would be interested in developing a tool that would perform this application for us.”
After consulting closely with Koitto and other employees at Takoma,Sandvik Coromant engineers spent several months designing and testing a custom tool optimized for the process. The gear cutting tool that resulted from these efforts was brought to Takoma for multiple tests and runoffs and then implemented with Sandvik Coromant’s assistance. It achieved very similar results to the original tool, but with a slightly reduced cost. More importantly, turnaround times for delivery were less than a week, compared to 12 weeks for the old tool. This allowed Takoma to maintain much more flexibility in responding to customer needs. Additionally, while working on this project with Sandvik Coromant, Takoma was exposed to the CoroMill 170, a new cutter for gear milling that the company felt held potential for some of its other applications.
The CoroMill 170 was developed to optimize milling applications in large gears, module 12–22, an area traditionally covered by indexable inserts and HSS tools. The tool provides robust performance through design focus on its shape and providing secure insert seats. Takoma chose to apply a 300 mm (11.81 inch) version of the tool to a marine ring gear measuring approximately 2.5 meters (8.2 feet) in diameter. The part was machined from 34CrMo4 steel.
Takoma had previously used a 230 mm (9.06 inch) HSS hob to cut teeth on the ring gear. Running at a speed of 25 meters/min (82 feet/min) and feed rate of 0.12mm/rev (0.0047inch/rev), the operation took 1,260 minutes per component. Upon applying the CoroMill 170, Takoma was able to increase cutting speed and feed rate to 126 meters/min (413 feet/min) and 0.20 mm/rev (0.0079 inch/rev), respectively. This reduced cycle time by nearly 60 percent, to just 510 minutes per component.
“We are now using the CoroMill 170 all of the time and saving a significant amount of time,” says Koitto. “By shortening our machining time, it also allows us to reduce turnaround to our customers. Instead of taking five weeks to process an order and provide finished parts, we can now provide customers with the same service in four weeks.”
In addition to allowing faster service to their customer, productivity gains from implementation of the CoroMill 170 have resulted in annual cost savings of 20,000 euros.
