“Reducing mass is an effective way to reduce a vehicle's emissions,” according to the International Council of Clean Transportation (ICCT)’s Fact Sheet: Europe report. The onus is on automotive manufacturers to produce more weight-efficient components. Yet heavy cast-iron and forged steel remain popular, and manufacturers must design/engineer these “heavy” metals to be weight-efficient. I asked Sangram Dash, Product Application Manager for Indexable Milling at Sandvik Coromant, to explain why lighter and closer-cutting shoulder milling and face milling are the answer. His comments are included here.
Further to the ICCT’s findings, McKinsey & Company’s Lightweight, heavy impact report offers in-depth calculations on how lighter vehicles emit fewer CO2 emissions: “Lightweight measures can help reduce CO2 emissions to a certain extent (approximately 0.08g CO2 reduction per kilogram saved).” The report continues: “If an original equipment manufacturer (OEM) manages to reduce the vehicle weight by 100kg, it saves approximately 8.5g CO2 per 100km.”
In response to findings like these, automotive manufacturers are turning to “lightweighting,” which involves building cars and trucks that are less heavy to achieve better fuel efficiency and handling. Lighter metals, such as aluminum and magnesium, can help in this regard. But lightweighting is about more than simply choosing whichever material weighs less ꟷ especially when heavier materials, such as forged steels, cobalt chrome, Inconel or gray and nodular cast irons (NCIs), are still widely used in vehicle manufacturing.
Rather, manufacturers must design engineer these “heavy” metals to offer a weight-efficient and strong alternative to lighter metals. This means producing more complex, near-net shaped parts based on more complex designs. which is tough when producing ISO-K materials that are more difficult to machine. What’s more, all cast irons contain Silicon carbide (SiC), which is highly abrasive to the cutting edge. A further challenge for OEMs is to manufacture these more-complex components to the highest quality, with high productivity and a low cost per part.
Where there is a need to produce a variety of components, and for large amounts of material to be removed quickly from the workpiece, shoulder milling is the best approach. The basic yet versatile milling application ensures a lighter cutting action which, in turn, minimizes the impact on the tool and ensures that the component stays in shape. With shoulder milling, the tool creates a plane and shoulder surface simultaneously.
To achieve this, it is essential to use the correct angle to avoid unwanted offsets between the cutter and workpiece. A 90-degree angle is preferable, but other angles can be used depending on the application.
A ‘Light Touch’
There are a number of shoulder milling tooling inserts on the market designed for a near-90-degree milling angle. Generally, these inserts have eight edges ― four on the front and four on the back to produce the shoulder and plane simultaneously ― or, in some cases, six. Nevertheless, Sandvik Coromant felt there was room for a new shoulder milling concept; one that would offer greater productivity, tool life advantages and economic benefits for OEMs.
In response to the above challenges, Sandvik Coromant developed its CoroMill® MF80 family of inserts. Designed for automotive milling applications in ISO-K and ISO-P materials, the inserts have eight cutting edges, chip protection and optimized micro geometry. In particular, the tools are designed to be ideal for thin-walled components and machine setups with limited stability. The cutting edge is inclined for a smooth cutting action and low cutting forces. This improves security and chip evacuation, and provides a wiper edge for a superior surface finish.
The CoroMill® MF80 is not entirely new, and is based on a technology platform similar to Sandvik Coromant’s existing CoroMill® 345. This new milling concept offers a 40% lighter cutter body with shim protection and a high number of inserts for secure and stable machining, even in vibration-prone overhang applications.
With shoulder and face milling applications, cutting tools with 90-degree lead angles are generally preferred because they generate radial cutting forces and, importantly, transfer more cutting energy away from the part. This is especially ideal when machining parts with thinner walls or near-net-shapes. The CoroMill® MF80 actually offers an 89.5 degree approach angle, allowing the multi-edge cutter to work even closer to the fixture while machining.
The near-90-degree angle also reduces axial forces for improved milling on thin wall components and weak fixtures, without vibration and chatter. Key advantages include improved accuracy and machine utilization, as well as longer tool life with less scrap.
Let’s look at the performance of the CoroMill® MF80 when machining ISO-K and ISO-P materials.
In one case, the CoroMill® MF80 was run against a competitor’s mill in a rough shoulder milling application to produce pump and valve components from an ISO-P carbon steel (DIN 1.0619) workpiece. The mills were run with identical cutting data ― an n of 500 rpm, a vc of 125 m/mm, ae of 15/50 mm, ap of 5 mm and fz of 0.15 mm ― with one exception, the vf. The competing mill was run at 375 mm/min and the CoroMill® MF80 was run at 600 mm/min.
In the end, the CoroMill® MF80 boosted productivity by 60%. The competing mill produced nine components while the CoroMill® MF80 produced 15. In terms of the tool life, after 40 minutes of machining time, only chipping wear was visible on the CoroMill® MF80, which increased the tool life by 67%. The key advantage for the customer is that the mill’s shim protection and the high number of insert edges can lower the cost per part in roughing or shoulder milling applications.
In another test, the CoroMill® MF80 and a competing insert were used in a roughing application on an ISO-K workpiece. The mills were used to produce carriers and supports from an ISO-K spheroidal graphite (SG) iron (GJS400/K3.1.C.UT) workpiece. Again, both tools were run with the same cutting data, including a 20-80 mm radial depth of cut (ae) and 2-3 mm axial depth of cut (ap). Each mill was run at a spindle speed (n) of 1000 revs per minute (rpm), a cutting speed (vc) of 250 meters per minute (m/min) and a table feed (vf) of 1200 millimeters per minute (mm/min). There was a slight difference in the feed per tooth (fz), 0.24 mm for the competitor’s mill and 0.3 mm for the CoroMill® MF80.
The end result was that the customer achieved a 54% increase in the tool life with Sandvik Coromant’s mill. While the competitor’s mill produced ten components in 55 minutes before showing signs of wear, the CoroMill® MF80 ran for 82 minutes and produced 15 components in that time.
The CoroMill® MF80 offers significant benefits for OEMs’ lightweighting applications, with longer-lasting and more productive performance when machining heavier materials, such as ISO-K NCIs, Inconel or gray irons, forged steels and cobalt chrome. These advantages can also prove essential in helping manufacturers produce vehicles that meet stringent CO2 emission regulations while maintaining a lower cost per part and ensuring that, in the words of the ICCT’s report, “Reducing mass is an effective way to reduce a vehicle's emissions.”