Published 12/19/2011

Reaming Application Illustrates True Cost of Cutting Tools

Cutting tools have two costs: purchase price and combined cost of all time, effort and extra steps required for a particular tool.

Peter Zelinski

Editorial Director, Modern Machine Shop

The “Bayo T-Ream” is a reaming system featuring a quick-change carbide head and a steel shank.

But then comes the second price, which is the combined cost of all of the time, effort and extra steps that this particular tool requires. This second price is invisible without careful analysis, even though it generally contributes much more to the total cost of the tool. The most cost-effective production plants tend to be those that are the very best at tracking the true, total cost of each tool.

Cutting tool supplier Iscar recently shared an example of an auto-industry manufacturer that performed precisely this analysis on the tooling in a crucial boring operation. Iscar’s national deep-hole drilling and reaming product manager Tom Edler says that even though the price differences seem extreme in this analysis, the numbers actually offer a fairly typical picture of how far high-performance tooling can go to deliver savings. Based on the analysis, the customer chose to abandon a tool with a price of less than $5 per insert in favor of a tool with a price of around $200 per insert. The secondary cost savings made the new tool the clear cost leader, even though the purchase price was 40 times more.

The specific application involved a blind bore machined in an injector body on a CNC turning machine. The workpiece material made gummy chips. These chips would pack into the hole and would sometimes get caught between the hole and the boring bar. Without warning, the part could fail to meet specifications, so the plant had to inspect every piece.

Iscar proposed replacing the boring bar with a very different tool. The company’s “Bayo T-Ream” is a reaming system with an interchangeable carbide head and a steel shank with a quick-change bayonet mechanism. Internal coolant holes direct fluid onto each of the head’s six cutting edges. This fluid, in combination with the geometry of the flutes, forces material to flow up and out of the cut. The design of this reaming head is complex compared to a single-point boring insert, accounting for the higher price. But the manufacturer discovered the cost savings to be even higher still.

The first area of savings was in the quantity of inserts purchased, Iscar says. Tests demonstrated that one reaming head delivered five times the tool life of a boring insert in terms of the number of workpieces machined.

Further savings came from the various secondary cost factors mentioned above, including time, effort and extra steps. Specifically:

• Time. The reaming head has six flutes, whereas the boring tool cuts with just one edge. For the same chip load, feed rate could be increased by a factor of six. The operation is now performed in one-sixth the time.

• Effort. Shorter tool life meant the process had to be stopped more frequently so the insert could be changed—particularly since the full life of the boring insert involves an index from one cutting edge to another. The reaming system reduced both tool setups and the frequency of reordering tools.

• Extra steps. The reaming system is so effective at controlling the gummy chips that the bore now consistently meets spec. The extra step of inspecting every piece—a step necessary entirely because of the previous boring system—has now been eliminated.

“Productivity is the great equalizer,” Mr. Edler says. This principal is even larger than cutting tools. At all levels, companies that base manufacturing decisions on purchase prices are seeing most of those prices increase. The key to overcoming these quoted prices is to find all of the unquoted cost savings that come from having a more productive process.

One caveat is that this search for savings often requires a change of thinking. Previously, the injector body manufacturer saw the critical hole as a boring application. The savings came when the company saw it as a reaming application instead. Something similar frequently occurs in milling work, Mr. Edler says. Many facilities can double their metal-removal rate in milling, but doing so requires the counterintuitive step of switching to a high-feed milling tool design that mandates a light depth of cut—lighter than what the shop is taking now. Running this tool at a substantially higher feed rate can more than overcome the lighter cut to save overall cost. In applications such as these, he says, the cost-effective approach often looks very different from the way that a given part or feature has historically been machined.

Cost Analysis

This cost analysis for machining the blind hole does not include the savings from eliminating 100-percent inspection. Even without these savings, total cost per piece was reduced by 60 percent, despite the fact that the winning tool had the higher pricetag.