Optimizing Tools for High-Volume Deep Drilling

July 5, 2023
An automotive supplier found the best quality and most productive deep-boring performance results from a solid-carbide drill modified with a PCD cutting tip.

The Schlote Group opened a new specialty machining operation in Harzgerode, Germany, in 2017, to handle a single type of automotive aluminum diecastings – clutch housings – with all Mapal Group supplying all of the cutting tools for the processes.

The Harzgerode operation is a joint-venture with Trimet Aluminium, whose aluminum operation supplies the diecastings for machining at rates topping 4,000 units per day. The finished housings are delivered to various major automakers, mostly to be installed in vehicles with two-liter engines. The bell housing connects the transmission to the engine. While the transmission side is the same on all the clutch housings, the other side is adapted to the respective manufacturer’s engine. The differences are mostly small, so the bell housing construction is “99 percent identical for all of the car manufacturers,” as detailed by Schlote.

Schlote Harzgerode GmbH exhibits a very high degree of automation. Around the clock, five days per week, 120 employees work there, and production can be expanded to six or seven days a week if necessary.

The automotive industry, of course, places very high quality standards. “The part is not only an adapter flange, but also the back of the transmission. The bearing seats thus require the highest degree of precision,” explained Sebastian Swiniarski, work-preparation team leader at Schlote Harzgerode. The diecasting requires multiple bores with different tolerances, for which precision is required down to the thousandth of a millimeter.

Mapal and Schlote have cooperated effectively for several years, which is why Mapal was entrusted with supplying PCD milling cutters (which create the defined rough surfaces on which sealant is applied), tap drills, reamers, and a diverse selection of drilling tools. “We offer our customers comprehensive solutions including the development of entire processes,” according to Stefan Frick, Mapal’s technical advisor to Schlote.

Successful improvement process

From the start of the project there was careful scrutiny of the tools to be implemented there. Since Harzgerode started up in 2017, ongoing analyses have been performed to find possible weak points and optimize manufacturing. Within the context of this continuous improvement process, Schlote and Mapal have managed to achieve longer tool lives, lower tool expenditures, and higher production quantities. While 3,600 parts were produced at most per day in the beginning, the limit has been raised now to 4,500 parts – without the need for further machines.

The newest optimization involves deep drilling for oil channels used to change gears in the automatic transmission. “We evaluate every month with our tool-management system which tools have to be exchanged how often,” Swiniarski reported. “Time and again, the deep drills have proven to be particularly sensitive. As these drills are relatively cost-intensive, we have concentrated on them to cut our tool costs further.”

Finished-part quality is also affected by tool wear: a blunt drill produces burrs at the bore exit. In this particular case, two of five deep bores are involved with a diameter of 8 mm and cutting depths of 180 mm and 141 mm. They run through the part from the side up to the bearing seat in the middle.

Solid-carbide tools were used for this process up to now, which is standard for deep bores. Schlote was able to achieve a tool life of 2,500 parts in this way.  Load monitoring on the machine had already registered tool wear starting at 2,000 parts though, and burrs could be seen at the bore exit.

Longer tool life with PCD

When it came to optimizing the deep bore, plant manager Tino Lucius (formerly a Mapal associate) suggested PCD variants. And so, working together Mapal and Schlote developed the idea to deploy a PCD tip for the deep drills.

There was a lot to consider during the implementation, Frick related: “It is not possible to construct this type of drill entirely out of PCD. Besides the high costs, the brittleness of the material is a problem. There is also always the danger of chipping of the cutting edges during interrupted cuts. Good cooling must also be ensured as PCD is heat sensitive.”

Mapal started the new tool design with the existing solid-carbide drill and inserted a PCD cutting edge at its tip. The tool’s structure is reminiscent of a concrete drill with a carbide tip.

The manufacturers in Harzgerode are very happy with the PCD deep drill’s tool life. While the solid-carbide drill’s tool life ends after 2,500 parts, the PCD version keeps going reliably up to 15,000 parts.

There is further scope for improvement in machining challenges, such as blowholes in the material and varying casting quality. The partners are currently working on this together. “We have occasionally been able to achieve a tool life of 40,000 parts. Naturally, we want to make this ultra-long tool life the norm,” Frick stressed.

The cutting data is the same as that of the solid-carbide drill at a spindle speed of 8,700 rpm, a feed of 0.3 mm/rev, and a cutting speed of 218 m/min. The new drill’s potential lays in its considerably longer tool life, the resulting lower tool costs, and the higher process reliability. Fewer tool changes also means less machine downtime.

Production at Schlote in Harzgerode involves a total of 10 manufacturing cells. Each cell has three CNC machines manufactured by SW – two W06 double-spindle machines and a One6 single-spindle machine. The parts are machined in three clamping set-ups, whereby the double-spindle machines handle the first two set-ups and finishing takes place during the third.

An electric future

Clutch housing manufacturing at the site was planned to continue at least eight years with a peak output of 1.1 million parts per year. This peak was surpassed in 2020. Production has been ongoing for five years, with 900,000 parts produced per year.

Due to continuously improving productivity and the lower production quantities, there has been time to address future trends and produce different parts, and the Harzgerode factory is already being modified for this purpose. The first of two new projects involves manufacturing six different parts that Schlote is to produce for a hybrid model from a sports car manufacturer.

In the other project, Schlote’s expertise as a clutch housing manufacturer will be put to use for a new electric vehicle. For a new EV model with a three-speed transmission, the connection between engine and transmission is to be produced in Harzgerode. Half of the factory capacity is currently being converted, and production of parts for internal-combustion engines is to be ramped down to 50 percent.

In future, hybrid cars will account for 10 percent of the output, and EVs will account for 40 percent. Schlote has already produced the first parts for the new projects.