The Macro Economics of Optimal Material Removal

  • Friday, 21 July 2017 00:00

Many CNC parts manufacturers as well as production and job shops could reduce their overall production costs 15 percent or more by leveraging existing CAM technology that is readily available. By Stas Mylek, applications advisor, CNC Software

Typically, production cost centres are often evaluated independently, whether they be tool costs, raw materials, capital equipment, manpower, or production costs. However, incremental savings in each typically do not add up to significant gains overall.

Our contention is that the areas of cutting tools, CAM, and production, particularly the newer toolpath technologies, along with machine capabilities and investment, be looked at concurrently with the goal of optimisation as they relate to each other. What we are looking for is hitting the optimised sweet spot of all three, referred to as machining effectiveness, to gain significant production cost savings.

Machining Effectiveness

Adoption of this approach pursues a very simple formula:

1. Select optimal cutting tools for the part. This will often be high quality carbide, but can be ceramic, insert tooling, or any other type of tool. The key is optimising to the chosen tool(s).

2. Based on the cutting tool manufacturer’s recommendations, import the correct parameters for consistent chip load machining into toolpaths having this capability.

3. Optimise the cut parameters, if necessary, to match the full capabilities of the machine the job is running on.

4. Repeat for every toolpath process you create using CAD/CAM software where the same tools, material, and machine are used.

Everything begins with the tool, and the calibre and quality of carbide, advances in new ceramics, new grades, coatings, tool geometries, and the design engineering going into today’s tools are far different and more capable today than what was available just five years ago. Full slotting tools capable of going up to four times deeper in not only hardened steels and stainless, but super alloys was unheard of even a short time ago.

Today, it is much more prevalent. These tools promise huge material removal gains, yet also require exact adherence to recommended cut conditions and chip load to gain optimal performance and predictable tool life to address machining effectiveness.

New Toolpath Strategies

Optimal material removal and cutting tool performance occur when CNC machines are programmed using newer, readily available CAD/CAM software technology (Mastercam’s Dynamic Motion technology is one example). This technology continually maintains the cutting tool manufacturer’s recommended cut conditions and chip load, regardless of part geometry. Significantly higher material removal rates, with more predictable and extended tool life, translates into the higher reductions in cycles times and production costs necessary for achieving machining effectiveness.

And the machining effectiveness of the newer toolpath strategies are not limited to just the new breed of cutting tools; improved material removal rates and tool life can be realised with virtually any tool, since these newer toolpath strategies are based on consistent cut conditions.

Over the better part of a decade, since these new toolpath strategies have been available, manufacturers of all types typically report CNC machine cycle time reductions for their roughing operations of between 25 to 70 percent—sometimes much more. Recently, a manufacturer reported that a part with a machine cycle of 32 minutes had been reduced to 12 minutes by implementing a machining effectiveness mindset.

Matching Machining Capabilities

Machining effectiveness gets another cost savings boost when you begin to match machine capabilities to cutting tool performance potential and toolpath strategy.

With a toolpath that always keeps the tool in a safe, cutting condition and does not violate the tool manufacturer’s recommended chip load specs, CNC programmers can apply different methodologies. On faster machines where workholding might be lighter and cutting tool selection more traditional, users might opt for a higher feed rate and small step-over approach to maximise material removal rate and to lower cycle time.

If set up is on a higher horsepower machine, that tops out on feed rate yet where the workholding can be locked down, a company might run the newer, full slotting-capable tools. Matching tool to machine to cutting tool capability, they could run heavy step-overs of 65 to 80 percent at 2x to 3xD or more and see material removal gains increase well beyond 70 to 75 percent over traditional toolpath strategies, resulting in a huge production cost savings. All this is feasible once companies put machining effectiveness into practice.

Time To Adopt

However, adoption of these newer strategies and embracing a machining effectiveness mindset has been slow, yet there are signs they are finally beginning to take hold. Straw polls of CAD/CAM users and industry event attendees indicate that 30-40 percent of programmer/machinists are using these new toolpath strategies with increasing regularity.

But what about the other 60 percent of CAD/CAM users? They frequently report not looking into it because, honestly, they have not had the time, nor given approval to do so.

Exactly how much time are we talking about to implement a demonstrably better cost cutting methodology? Actually, very little. Tool manufacturers’ recommended cut parameters are often provided in available tool libraries and easily imported directly into toolpath operations of the CAD/CAM system when selecting a tool and material. Adjustments are made based on tool capabilities such as whether to use a small or large step-over approach and what limits need to be applied to depth cuts based on the type of tool.

Utilising Your Machine’s Potential

Manufacturers need to evaluate their tool
efficiency to achieve maximum output.

Machine limits relative to spindle speed, feed rate, and horsepower are also considered prior to processing the program. Using toolpaths that maintain consistent chip load and safe cutting conditions, it is simply a matter of taking the program out onto the machine. Machine performance is validated relative to holding the programmed feed rate, ensuring the right workholding setup is in place for strategy, and that spindle load is maintained under the set requirements.

Once the program is running on the machine, it may be necessary to make some minor adjustments to toolpath parameters to make sure the software is taking full advantage of the machine’s capabilities.

Conversely, some machine controller settings may need adjustment to take full advantage of the toolpath. Very often, cutting tool vendors, CAD/CAM resellers, and technical specialists are happy to help you maximise performance and prove out the application.

Cutting Chunks Off A Cycle

Cost breakdown of the manufacturing process.

Once the process and strategy is validated, the approach can be applied every time that tool is used to machine a part made from that material. Benefits can be seen in everything from simple to extremely complex, aerospace and thin wall parts, and more easily machined materials to super-alloys.

For example, a job shop recently took six hours off of a 24-hour cycle for an aerospace part by adopting machining effectiveness methodology. This conversion paid for itself immediately after the first part was produced. Better still, the company had a contract to make six more of them. So the benefits multiplied quickly.

The bottom line is that many manufacturers in many industries are operating far less efficiently than they could be and leaving money—lots of it—on the table by not optimising cutting tool, toolpath, and machine performance and viewing them in an integrated relationship. Cutting costs is necessary to compete and remain profitable. However, there’s a lost opportunity cost for companies, and possibly for entire manufacturing sectors, that don’t leverage everything they can get from inter-related technologies.

Significant Gains

By aiming at that optimised sweet spot called machining effectiveness, the gains company-wide or even for an industry, can be significant. By that, I mean millions.

This seems like a pretty outrageous claim. Can it be justified? I think so. Cutting tool manufacturers are very confident that their best route to justify the benefit of higher quality and cutting tool performance is to show new users improved productivity.

For example, Tom Raun, national milling product manager of Iscar Cutting Tools, maintains that the cost of the tool is really insignificant compared to the benefit of improved machine cycles. Cutting tools amount to about three percent of a typical CNC shop’s total costs. If tool life can be doubled, then that ROI amounts to less than 1.5 percent of the shop’s total costs for cutting tools. Even so, if a shop realises it can reduce its tooling costs by a million dollars by making a simple purchasing decision, it will jump on that opportunity in a heartbeat.

On the other hand, experience has Raun convinced that a 20 percent improvement in material removal efficiency can yield a 15 percent improvement in manufacturing costs per unit.

Think about it: A shop with US$100 million in sales could realise a US$15 million gain by making an average 20 percent across-the-board improvement in machine cycles using mostly existing equipment and software. If parts manufacturers in just the automotive, aerospace, and energy industries embraced this idea, the savings would easily be billions.

Embracing The Effective Viewpoint

Stas Mylek believes the
right tools are essential in
increasing revenue for

So why are we not doing it? It all comes down to a change in viewpoint, finding the time to save time, and making a commitment to get better. Production deadlines are always looming and we all get comfortable with current processes, whether we’re managers or programmers. It takes valuable time and resources to test and evaluate new technologies and methods, or to experiment with the outer boundaries of what is possible.

Yet, with the potential payback and production costs savings of 15 to 25 percent or more, isn’t it worth it? The pressure of a tight deadline could be loosened by the opportunity of getting jobs done faster and with fewer issues or setbacks.

What is needed is a little bit of planning and optimisation targeting better machining effectiveness up-front. This can lessen the impact of tight deadlines as well as down time incurred due to lack of efficiency. It is not uncommon to find initiatives of this sort yielding total manufacturing process cost reductions of 15 to 25 percent or more.

Savings of this magnitude could be used to achieve such worthy objectives as improving profits, capturing more business, and doing the modest amount of training required for more robust workforce development and continuous improvement.

People who are in charge of the day-to-day operations at machine shops are frequently under too many pressures to take the lead in initiating the sort of changes that are required. That sense of urgency also needs to come from the top.

APMEN Machine Tools, July 2017

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  • Last modified on Tuesday, 25 July 2017 04:14
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