Going Back to Q School

Sacrificing tool life can increase metal removal rates, reduce costs

Cutting tools

Cutting tools must help to ensure the machinist receives maximum performance and metal removal rate, as well as maintainable and predictable tool life.

Editor's Note: This article is based on a presentation by Iscar Tools Marketing and Sales Manager Gidi Drori at the November 2014 comprehensive customer seminar in Tefen, Israel.

In many machining processes, increasing tool life typically is the goal of both machinists and their tooling suppliers. Recently, however, a new school of thought is taking over. Increasing productivity by increasing the cutting data—to reduce cycle time, not extend tool life—can have a more dramatic effect on overall cost per part (CPP).

According to Gidi Drori, marketing and sales manager for Iscar Tools, being highly productive today depends on the tooling and machining strategy that is applied to the process. In this very competitive world, manufacturers continuously try to increase their productivity, and this ongoing challenge requires removing more metal.

To enact this strategy, shops must:

  1. Boost feed rate parameters.
  2. Increase depth of cut.
  3. Maximize cutting speeds.

To achieve all three, metal cutting strategies must be managed properly, applied in the most effective way, and include the latest cutting tool technology.

The Bottom Line on Tooling

Cutting tools play an important role in the machining process. Although cutting tools account for only 3 percent of total production cost, when properly chosen and used they can deliver savings up to 15 percent of overall costs. This is achieved by improving machining productivity.

Total Investment
Building and
associated costs
21 percent
Machines 26 percent
Labor 28 percent
Raw materials 22 percent
Cutting tools 3 percent

Source: Iscar Tools

Reducing investment in any of these areas shown in the table isn’t necessarily the best way to reduce overall CPP either.

Iscar Tool’s engineers

Iscar Tool’s engineers design new tools to meet the challenges of today’s shops, including high-speed and high-feed milling.

By raising machining performance 15 to 20 percent, through increased cutting data, a shop can realize substantial gains in productivity. This will directly contribute to a higher level of profitability. According to Drori, these objectives can be achieved only by combining innovative cutting tools with an advanced CNC machine tool and smart CAD/CAM software.

Improving productivity, not tool life, should be the goal of modern chipmaking operations.

By taking the tool life increases that are created and returning that benefit to production, cycle time is reduced and, therefore, overall per-part cost.

For example, if a shop that is currently getting 50 pieces per insert can improve that rate to 75 pieces by increasing the spindle speed, feed rate, depth of cut, or a combination of all three, a more dramatic cost benefit is realized.

The reason for this is based on a simple equation: Total investment/ Total parts = CPP.

Because tooling accounts for only about 3 percent of the total cost of the piece, reducing cycle time will be much more cost-effective for the process than any improvement in tool life. Even in the best-case scenario, doubling tool life, only a 1.5 percent saving to the total cost of the part will be realized. The reduction in cycle time increases the number of total parts produced, thereby reducing CPP.

Improving Chip Volume

Reducing cycle time also reduces labor, machine cost, and overhead costs of each job. But, this is not the only way to increase the volume of material removed. Other ways include:

  • Run 24/7. Most shops today would like to operate their machines as close to 24 hours per day as they can. To do this, they have to have reliable tools in the magazine.

    According to Iscar, the main aim of cutting tools is to ensure the user receives maximum performance to increase profitability. This goal can be reached only by providing tools that boost metal removal rate and simultaneously feature reasonable, maintainable, predictable tool life.

  • Reduce setup time. Reducing setup time equals more profit. One way to help reduce setup time is to choose tools with inserts that can be swapped out without switching the tool body.

  • Reduce vibration. The two main factors that contribute to a high volume of metal removal in a milling operation with minimum energy consumption are a helical cutting edge geometry and variable-pitch flute configuration. Tools with variablepitch flute configuration have patterns that eliminate harmonic vibration, known to be the main source for chatter.

    Previously, solid-carbide end mills with an uneven angular pitch of flutes were employed to reduce chatter by providing stable cutting in a range of applications. Now, based on the same design principle, chatter-free milling can be achieved via indexable cutting. New one-sided inserts have two cutting edges with different inclinations of the insert bottom. According to Iscar, this asymmetry generates a varying axial rake angle, improving the tool’s dynamic characteristics.

  • Evacuate the chip. Poor chip evacuation can limit speeds and feeds, especially in a drilling operation. Combining improved performances of shearing mechanism, accuracy, and efficient distribution of cutting forces, while eliminating vibration and facilitating easy chip evacuation, all lead to a substantial reduction in power consumption, as well as higher productivity.

    Also, using tools that require less power allows more feed to be used.

  • Use advanced cutting motion. High-speed machining, for example, requires that a specific grade be used for each material. Selecting the right cutting tools and machining parameters can reduce cycle time, even at high speeds, and therefore reduce total energy consumption per piece. This fast metal removal process not only provides high productivity, but saves energy. In broad terms, the shorter the engagement of the tool with the cut, the more productivity is achieved and more power is saved. This feature can further be enhanced by utilizing an advanced CAD/CAM system to define the shortest path for the tool, coupled with optimized machining conditions.
  • Drori concluded that designing more innovative cutting tools is a key factor in maximizing productivity.

    A high level of productivity—as measured by material removal—can be achieved by using the optimal tooling with the appropriate machining strategy.

    Implementing efficient machining strategies will contribute to the reduction of cutting forces, distribute these forces effectively, eliminate vibration, facilitate chip evacuation, and ultimately lead to a higher volume of metal removal.

    www.iscar.ca