Machining die-cast aluminum components

As lightweighting efforts force more automakers and suppliers to get comfortable with aluminum, the use of die-cast parts is growing rapidly. The North American Die Casting Association predicts that demand for small, near-net shape aluminum parts will grow faster than the economy and the automotive industry throughout the next several years. Following a 7.3% growth in aluminum automotive die castings in 2014, the association predicts a 5.1% increase this year. By 2025, the group expects companies to ship 16.4 billion die-cast aluminum parts worldwide to original equipment manufacturers (OEMs), up from fewer than 9 billion parts in 2012.

That increase in parts production – expected to take place in the United States and abroad – forced engineers at Makino Inc. to rethink their approach to tapping and other finishing operations for the small pieces that are typically covered in features that need to be machined. David Ward, horizontal product line manager for the company, recently sat down with Today’s Motor Vehicles to discuss the a40, a machining center created for die-cast parts at the company’s new Automotive Technologies Center near Detroit.
 

Today’s Motor Vehicles: Makino sells several general purpose machining centers, most notably the a51nx, used by die casters. Why the need for such a specific machine?

David Ward: There just wasn’t a machine out there for die-cast parts. Automotive makes up 44% of the die-cast market, so we’re dealing with auto market economics.

The OEMs were really pounding on the die-cast parts people to reduce their per-piece costs, and those costs were generally a factor of the machining time, especially in powertrain where there are many holes to be tapped and small features to be machined.

We observed the machining process on a lot of these parts, and we saw that the actual machining time wasn’t the problem. More than one-third of the time was spent moving from feature to feature, not on the cutting.

TMV: Typically, when you tell a machine maker you need to cut cycle times, the response is to speed up rapid traverse rates or the spindle. Why did Makino cut the spindle speed on the a40 from the a51nx?

DW: For some applications, the a51 was the right solution. But for smaller die-cast parts, we saw room to improve. There were two factors for improved profitability – higher reliability and lower cycle time.

The biggest part was rapid positioning time, but even there, the challenge was different from what we see with other components. The features on the parts are very closely aligned, so this wasn’t a matter of moving the spindle long distances. The challenge was accelerating quickly to cover very small distances. That’s the time that we need to optimize.
 

TMV: Some of your rivals post rapid-traverse rates on their machines that are higher than the a40’s. Is that a problem for Makino?

DW: For a lot of machines, that higher figure is generally only when you’re moving more than 300mm. With these die-cast parts, sometimes you’re only moving 20mm. So you’re never taking advantage of the higher speed capabilities. To cut down on those short, rapid traverses, you have to rethink designs.

Using more force and adding bigger motors is an expensive solution to the problem, and it really doesn’t help much for those small distances. From a linear perspective, the only thing that affects inertia is mass. The systems responsible for the linear motion required a purposeful redesign, one that reduced weight while maintaining the necessary stiffness and rigidity. The more that we reduce the inertia, the quicker we can accelerate the spindle positioning movements. Short, rapid positioning moves that are common when moving between features on a part have been reduced by approximately 14% in X/Y and 20% in Z.

One of the key decisions was going to a 12,000rpm spindle (down from 14,000rpm on the a51nx). But power wasn’t the problem in die cast; speed was the problem. By dramatically reducing inertia on the spindle, acceleration from 0rpm to 12,000rpm is 0.45 seconds. The a40 spindle has the speed and agility performance typically seen on drill tap centers but with the robustness of a 40-taper spindle.

Cycle time for common tap sizes such as M6 are reduced by 0.5 seconds to 0.8 seconds per hole, compared to other horizontal machining solutions. We’re only talking seconds or fractions of seconds, but when you’re producing at high volumes, that adds up quickly.
 

TMV: As you’ve mentioned, this is a very price-sensitive industry, so what does the return on investment (ROI) look like for the a40?

DW: When you run through the spreadsheet for a high-volume run of die-cast parts, the increases in non-cutting speeds, the faster tool-changes and tapping times, you get to the point where you can handle the job with fewer machines.

The a40 includes cyclonic coolant filtration. We showed how a superior coolant filtration system can reduce coolant tank maintenance requirements. We have an example where a five-machine installation is projected to reduce annual coolant cleaning tank costs by $115,000.

When you put it all together, the lower machine count means elimination of fixtures, a tool set, labor, floor space, and potentially automation costs. We ran a scenario showing a 10% price premium for the Makino versus other machines, and you still come out ahead because of the lower operating costs and the lower number of machines.

Makino Inc.
www.makino.com

About the author: Robert Schoenberger is the editor of TMV and can be reached at 216.393.0271 or rschoenberger@gie.net.