Examining a cutting tool’s performance values, not just its cost, reveals the true efficiency of machining processes.
Question: “How long should this cutting tool last?” Answer: “How long do you want it to last?”
Answering a question with a question is fair in this case, as it forces a shop to examine its cutting tool expectations and requirements by taking into account the factors impacting the mold machining environment. These factors include cutting tool geometries, coatings, sizes, brands, surface footage, depth of cut, width of cut, feed per tooth, dry or wet machining, horsepower consumption, and rigidity. Manipulating these variables can lead to vastly different outcomes, so a shop’s approach to machining costs is key.
For example, many shops only look at price when selecting their cutting tools and toolholders. This narrow view often results in very poor machine efficiency, which can lead to substantial hidden costs, including longer cycle times, poor tool life, inaccurate profile tolerances and so on. The average mold shop can spend between 2 and 4 percent of its total operating costs on cutting tools and toolholders. If a shop were to find a tool that is half the cost of the one it is currently using, it could theoretically reduce tooling expenses to 1 to 2 percent of operating costs. However, a more expensive tool that can get parts out of the machine twice as fast would double the shop’s potential revenue. Which scenario would you prefer? The answer to this question can be difficult in real-world machining environments, and most shops’ situations fall somewhere in between the two extremes.
Consider these three performance values of the cutting tool to determine machining costs and identify the appropriate machining solution for a shop:
1. The time required for the cutting tool to get parts through the machine.
2. Cutting tool life, as defined by either the number of cutting tools per part or the number of parts per cutting tool.
3. Cost of the cutting tool used.
As you can see, the actual cost of a cutting tool is only one of three factors in the equation, so if that is the only value taken into account, the shop is ignoring the two other essential considerations. To maximize productivity, a shop needs to get parts off the machine as fast as possible at the lowest cutting tool cost with the best possible cutting tool life.
Comparing these key considerations against each other in real-life applications requires some basic math (see chart below). For example, the cost of cutting tool per part plus the shop rate divided by the number of parts per hour. The cost of the cutting tool per part is typically a very small part of the total cost of production. Although using a much less expensive tool initially looks very attractive for reducing part costs, very often that cost savings is only a small part of the total cost reduction. The larger cost savings for most shops comes from getting parts off of the machine more quickly.