Increasing Die Throughput

Corner correction capability rounds tool paths to avoid sharp transitions in corners and other difficult-to-reach part features.

Still strong despite what some are calling the worst automotive downturn in history, Exco Engineering of Newmarket, Ont., has found its niche in the market for producing large, high-pressure die casting dies.

The company has been a tooling supplier to the worldwide automotive industry for more than 50 years, with its experience being in the design of large dies for engine blocks, transmission cases, and instrument panels.  

Exco is housed in a 150,000-sq.-ft. plant that includes a foundry with a 3,500-ton high-pressure die cast machine. The company’s engineering and CAM departments have received patents on two tooling methodologies.

To ensure the accuracy and functionality of its dies, Exco has invested in the latest design and manufacturing software and makes use of CNC machines, including machining centers, large boring mills, as well as coordinate measuring machines (CMMs). 

Recently Exco management moved to further upgrade the company’s responsiveness and ability to deliver dies more rapidly. It wanted to:

• Increase the flexibility in the CAM department
• Reduce the amount of input required to define a tool path to speed up programming.
• Increase shop floor machining efficiency by 20 percent.
• Allow operators to program at the machine.
• Decrease programming time to improve throughput and lower mold cost.
• Reduce the amount of time spent on tool path verification.
• Reduce machining time.
• Read CAD data directly into the software without having to use a translator.
• Improve machining strategies to aid in the goal of reducing the time to complete dies.

Exco uses software to generate all tool paths for creating complex cavities in the H-13 steel dies - the most time-consuming programming task in the shop, which also assembles and tests the dies it produces. The die machining process generally is to rough it, heat treat it, and finish it; however, the company’s management team determined that the time frame for machining had to be reduced to help improve competitiveness.

Over a period of six months the company’s NC programmers tested many different CAM tools to evaluate how they could help them achieve these goals. At the end of this process the company chose PowerMILL CAM software from software supplier Delcam.

Gaining popularity 10 years ago as a stand-alone CAM system for shop floor programming, PowerMILL combines a range of machining strategies with gouge and collision checking. This functionality is one of the reasons Exco chose it.

The software also includes a range of five-axis strategies for both roughing and finishing, three-axis swarf machining, and parametric surface finishing. According to the company, it is the reduced calculation time and improved point distribution that are contributing to Exco’s ability to produce complex molds quickly and accurately.

Rough Machining

Five-axis roughing reduces the number of setups needed to machine many components. It also can be used to give a more efficient cutting angle that allows more material to be removed with each pass.

Using automatic verification along with the stock model enables Exco Engineering to rough out additional areas of insert with a shorter tool assembly.

Using a spiral tool path for roughing allows the overall machining time for mold components to be reduced by minimizing the number of air moves. In addition, a more consistent load can be applied to the cutter, limiting wear and reducing the chance for tool damage.

The collision avoidance options allow Exco’s operators to “cascade down” with a shorter tool assembly, allowing more area to be cut without the need for a longer tool. This feature allows the company to complete roughing in a day, when previously many components could take up to a week to program.

Another available roughing strategy, Raceline Machining, lets Exco take full advantage of cutter designs in which the side of the tool is used to make deeper cuts.  Roughing passes are progressively smoothed out as the tool paths move farther from the main form. The resulting paths minimize sudden changes in direction and allow faster machining with less wear on the cutter and lower stress on the machine tool.

Since in all roughing operations the software orders tool paths so that air moves are reduced, this also makes the ordering of rest roughing tool paths more efficient. The rest tool paths completely remove material left by a previous, larger tool, allowing only areas that require smaller cutters to be remachined, and greatly reducing milling times.

Finish Machining

This new software package also gives Exco’s programmers strategies for finish machining, including parametric offset machining, three-axis swarf machining, and interleaved constant Z.

In parametric offset machining, the number of tool paths used over a surface of varying width is kept constant. Instead of stopping and starting some paths, the step-over between the tool paths is varied within preset limits. According to Delcam, this approach gives a better finish by avoiding sudden changes of direction that can leave marks on the surface.

Three-axis swarf machining is used to finish vertical walls with the side of the tool, resulting in a smoother surface finish than cutting the wall in a series of operations at different Z levels. Also, corner machining is improved. Previously, long tools would get into a corner and be unable to machine smoothly through it.

The graphical icons and representation of the tool paths help the company’s CNC programmers to think of different strategies. According to Delcam, another helpful tool for programmers is the template creation option that lets them process multiple tool paths on similar part configurations unattended, saving time in programming. And when programmers want to edit paths, they can do it quickly simply by picking any part of a tool path and deleting it, while still having the rest of the tool path intact.

For more information, visit www.delcam.com and www.excocorp.com.