Software strategy slashes programming and rough machining times for molds.

By Patricia L. Smith
managing editor

Rather than programming and processing one toolpath at a time, Surfware's Step Reduction Milling technology simultaneously generates all toolpaths. This method, says Surfware, slashes rough machining time up to 50% and decreases NC programming time as much as 90%.

Moldmakers typically cut molds and dies on machining centers by progressing from larger tools, which handle the bulk of stock removal, to smaller ones that add detail and prepare molds for finish machining, with each tool programmed as an independent operation. But is this the best way to machine molds? Not anymore, says Surfware Inc., Westlake Village, Calif., which has developed a new roughing software strategy that could shake up the world of traditional moldmaking.

Rather than programming and running roughing as series of independent toolpath operations, Step Reduction Milling (SRM) optimizes the machining process as a whole. It allows mold shops to cut rough machining time in half and decrease NC-programming time as much as 90%. These timesavings, in turn, should boost the bottom line for many shops. "For an average shop running four CNC machine tools," speculates Tom Bentley, president of Programming Plus, one of the nation's largest CAM software dealers, " the use of SRM could translate into annual savings of $40,000 to $50,000."

In traditional moldmaking, shops typically employ "rest roughing" practices, in which material is machined in several passes. These passes leave behind steps on the non-vertical or non-horizontal surfaces that smaller tools must clean up.

Because the steps differ in size, they present a significant machining challenge, and the smaller cutters often require considerable time for finish machining. For instance, moldmakers may need 10, 20, even 30 hr or more to machine molds for parts with sweeping freeform profiles such as fender molds, generator covers, lawnmower decks, and stamping and extrusion dies.

In the SRM mold-roughing process, the majority of programming time is spent up front, defining tools and building a tooling database. Once this is set, users specify the cutting tools, in the order in which they're used (from largest to smallest in diameter), and the final step height. The capabilities and limitations of each tool are defined — and stored for later re-use — before the system calculates any tool motion. A First Slice Preview option shows what material will be removed with the selected tool, enabling the user to try "what-if" scenarios to get the best combination of tools prior to toolpath generation.

SRM simultaneously generates all toolpaths for the best possible use of each tool rather than programming and processing one toolpath at a time. This may entail having the same tool tackle two successive toolpaths — the first to make a roughing pass, the second to reduce the size of its own steps — before the system calls on a smaller cutter. The resulting step heights aren't just even; they're also at an optimal height for the next tool.

The subsequent, smaller tool machines only those areas where the previous tool couldn't fit, and only at the Z-axis levels established by the previous tool. In other words, the tool's depth of cut is uniform and never varies, allowing higher spindle speeds and feedrates.

As for SRM's user friendliness, says Bentley, the strategy allows less experienced machinists to run programs with the same efficiency and sophistication as more senior staff. "You let the system know all the specifics about each tool, like the minimum depth of cut and maximum depth of cut. Once that information is stored, it's just a matter of picking your tools. You pick the 4-in. cutter, 2-in. cutter, 1-in. cutter, 3/4-in. cutter, 3/8-in. cutter, and then say 'go.' SRM processes all of the cutter passes simultaneously."

Changing a program is also easy. For example, if programmers want to add, delete, replace, or re-order a tool, SRM automatically recalculates tooling parameters. This capability, claims Surfware, maintains the integrity of the overall process and ensures that tools aren't overtaxed.

An independent review
According to a market survey from CIMdata, an industry analyst organization, "Roughing presents serious challenges to moldmakers in that geometry is often complex and nonmanifold, raw material is expensive, mistakes are costly, and machining cycle times are often long."

Bearing these in mind, Surfware commissioned CIMdata to do an unbiased review of its SRM technology. According to the organization, "[SRM] could minimize or perhaps eliminate the industry's need for rest roughing and/or feedrateoptimization software."

CIMdata also reported that SRM's capability to automate and optimize the rough machining of complex surfaces should make it effective in any application where complex multiple surfaces are machined — particularly in the moldmaking sector.

"A key characteristic of SRM is the consistency in cutting operations that result from the process," reads the survey. "The process is characterized by a constant depth of cut for each tool, constant volume of chip removal for each tool, and a resulting constant load on the cutting tool."

Why use SRM?

While new high-speed machine tools and cutting tools keep moldmaking shops cutting fast, Step Reduction Milling (SRM) further speeds mold production.

"Just a couple of years ago, a 1-in. cutter would remove a certain amount of cubic inches per minute in tool steel," relates Tom Bentley, president of software dealer Programming Plus. "New cutter designs are running on the same piece of equipment and removing something like five-and-a-half times as much material. That's a quantum jump all by itself, but if you combine that with SRM, you will see huge gains."

And whatever machine or tooling used, says Surfware, SRM lets users reap several performance benefits:

Reduce rough machining time for molds 50% or more.

Slash up to 90% off NC programming time for molds.

Obtain uniform step height from one machining pass to the next.

Create one optimal NC program to run an entire set of tools as a single setup process.

Process all cutter paths at the same time.

Make machining more efficient, as each machining pass is programmed with full awareness of which cutter came before it and which cutter comes after it.

Speed cutting as larger cutters remove the bulk of the stock, leaving smaller cutters to remove less.

Minimize wear and tear on smaller cutters, extending their tool life.

Use each tool to remove its optimal amount of stock for high material-removal rates.

Avoid overtaxing tools.