Shop Solutions: Quick-Change Tooling Primes Pump Production
Long job changeover times and setup scrap constantly hindered drive-shaft machining operations at Bosch Rexroth Corporation’s drives and controls plant in Fountain Inn, SC. The shop desperately needed to reduce setup scrap and the almost 60 minutes of downtime that occurred every time it switched from one hydraulic pump drive-shaft job to the next on its twin-spindle/twin-turret turning machines.
The facility produces drive shafts in high volumes. The shafts go into its axial piston hydraulic pumps and motors used for mobile hydraulics and in the agriculture, construction, mining, and material handling industries, among others. Pumps are classified according to displacement, and Bosch Rexroth manufactures a range of pump sizes/series, and each series can encompass several different shaft part numbers.
Each drive shaft features a customer-specified interface type that can be a keyway or one of many spline variations. The interface is the end of the shaft that adapts to a customer’s system, while the opposite end is inside the pump and never changes. All these interface variations constitute a different part number. And these myriad part numbers within each of the different pump series mean that Bosch Rexroth is faced with frequent job changeovers.
To streamline turning machine changeovers, the shop developed one CNC program that would accommodate all of the different shaft part numbers. However, it realized that tooling up its turning machine turrets was a huge time constraint. So the goal was to optimize the turrets, load them with as much tooling as possible and be able to machine all the different part numbers within a shaft/pump series size with minimal, if any, tool changeover.
To optimize its turning tools, Bosch Rexroth worked with Seco Tools Inc. (Troy, MI) and incorporated cutting inserts, custom holders and Seco-Capto quick-change tooling. The Seco tooling helped Bosch Rexroth boost its tool capacity by 20% for each of the turrets in the three multitasking turning centers producing drive shafts. The shop can now load up turrets with all the tools needed for a single pump size and all its associated drive shaft part numbers to reduce changeover times to less than five minutes. Plus, the tools are preset offline in the shop’s toolcrib, a practice that further speeds changeovers for operators. But more importantly, it reduces setup scrap by about 60%.
Additionally, the Seco tooling allows Bosch Rexroth to run its turning operations more aggressively—in some instances with speed and feed increases of 15%. Doing so has lopped a minute off of each shaft-machining cycle time without sacrificing tool life. The Seco-Capto quick-change tooling also provides the critical repeatability needed for tooling to go directly from offline presetting operations into machine turrets so operators no longer have to perform time-consuming gage cuts that can potentially generate numerous scrapped parts.
Hydraulic pump drive shafts are made from stainless steel bar stock that can be tough to cut. For the shafts, Bosch Rexroth uses a mixture of Seco turning inserts, including the company’s Duratomic type in its Seco-Capto quick-change tooling—a combination that lets the shop easily hold the ±20 µm required shaft tolerances.
At the onset of the tooling project, Holger Werz, manufacturing engineer/group leader at Bosch Rexroth, recognized that most shaft machining problems stemmed from having operators perform their own tooling changes. And when it came to setup scrap, most of that occurred when exchanging finish turning inserts.
“Once we determined the problems were at the machines, we decided to set tools offline and let the highly skilled experienced machinists in the toolcrib handle the task,” said Werz. “They could ensure tools were set properly. However, offline setup required quick-change tooling with high repeatability, for us that was at least 10 µm, and Seco’s system easily meets that requirement.”
Prior to the toolcrib decision, operators would have to change out four or five turning inserts at a time. And for each, said Werz, they had to rotate the machine’s turret to be able to see the insert, clean it, index the insert or remove it if broken or its seat was damaged. A damaged insert seat also meant installing a new holder.
Additionally, inserts were often improperly secured in holders, so they would move and generate at least four or five scrapped parts before being detected. The movement was slight and hard to notice, but it was enough to cause scrap. With Seco-Capto, operators can quickly and easily swap out a worn or damaged insert by removing that cartridge/insert assembly and replacing it with a new preset one from a tooling cart next to the machine.
While quick-change tooling made changeovers faster and more accurate, Bosch Rexroth still needed to get more tools on its turrets, said David Casey, manufacturing engineer and current shaft-machining project leader at Bosch Rexroth. The shop had to have room for hobs, end mills, drills and taps used to generate the required customer-specific shaft features. Unfortunately, turning is the predominant shaft operation, so the majority of turret positions had to house turning inserts.
Seco’s Custom Tools Division provided the solution with special square-body, double-shank tooling that delivers extra clearance in the turret while accommodating two inserts located one on top of the other. The tooling essentially doubles the capacity of an individual turret station. In each of its turrets, Bosch Rexroth can now load four turning tools and take up only two turret positions, thus freeing up two pockets for additional tooling for special features.
Another benefit of the Seco-Capto quick-change tooling, according to Casey, is that it helped streamline Bosch Rexroth’s point-of-use tool inventory. And it provided more control of that inventory.
“Ever since we switched from our old-style holders to the new Seco-Capto quick change, we now have basically one type of turning toolholder in our machine turrets. Before this, we had three left-hand holders and three right-hand ones. But with the Seco tooling, there’s only one holder, and every tool we need for turning can go in one base holder. As a result, we have far less tooling at each machine.”
He estimated that Bosch Rexroth has reduced toolholder inventory by about 50%. Plus, moving the tooling responsibility to the tool crib also practically eliminated tooling discrepancies.
Prior to doing so, the shop had virtual toolcribs at the machines. Operators were tasked with tracking tool use, but often tool barcodes were scanned incorrectly which generated discrepancies between the inventory numbers in the system and what tooling was actually on hand. This greatly skewed the tool inventory forecasting process—often resulting in over or under ordering. When unexpected outages happened, the shop had to adapt different tools to keep production going or shut down a machine or machines until the tooling arrived. The shop now has accurate tool data because the toolcrib handles everything.
Casey said that changeovers are critical to not only maintain seamless production from one product family to the next, but also to accommodate the company’s varying order lot sizes. He said that they always try to run just-in-time (JIT) production, but other processes will influence that, such as heat treating, a process that can only be done so fast.
“In such a manufacturing environment as ours, what differentiates us from the competition is the complexity of our manufacturing equipment,” said Casey. “Most companies are unwilling to invest in advanced multiprocess technology. We try to complete parts in single machines with fewer clampings and less part handling. This reduces the risk of error and thus makes for higher precision parts. And thanks to the agility and flexibility of the machines and our quick-change tooling, we now have three machines with basically the same setups that let us quickly and easily switch between completely different parts numbers.” ME
For more information from Seco Tools Inc., go to www.secotools.com/us, or phone 248-528-5200.
This article was first published in the August 2014 edition of Manufacturing Engineering magazine. Click here for PDF.
Published Date : 8/1/2014