Inserts Show Their True Colors

April 1999 It’s not hard to understand why insert buyers are confused. They may be thinking they are simply buying a box of pressed carbide chips, and how hard can that be?

But, as Karl Katbi, director of global R&D for WidiaValenite Inc., Madison Heights, MI, says, they are really buying a complete system. Each of the insert’s features, including its substrate material and coating, its chipbreaker, its shape, and its edge preparation, was chosen from a host of possibilities to perform in a certain way in concert with all the other features.

Selecting the right tool is easier now with systems that lead the user step by step to the insert designed for the job.

The number of different inserts available from a toolmaker is equal to the product of all the variations offered for each feature. Thus, if a toolmaker offers 10 grades, 12 chipbreakers, five nose radii, and six shapes, the total number of products in its line will be 10x12x5x6, or 3600 inserts. And this is a simplified example.

In reality, there are a number of other features that could be thrown into the mix to multiply the number of possibilities well into five digits. When the number of possibilities rises to this level, selecting the best combination becomes more a matter of luck than skill.

In recent years, toolmakers have tried to even the odds by introducing tool-selection systems that increase users’ chances of finding the right insert for the job. These systems lead users through the selection process step by step, helping them use what they already know about the application—such as the workpiece material, the type of operation, and the depth of cut (DOC)—to methodically find their way to the one insert that will provide the best performance. These systems break down the toolmakers’ insert lines into smaller groups, so that the user is no longer choosing an insert from thousands of possibilities but from just those that were designed for a certain class of materials or a certain type of operation.

Often these smaller groups are arranged in a matrix. Users follow along the row that corresponds to some attribute of the job, typically the workpiece material, until they reach the column that corresponds to another job attribute, typically the type of operation. The insert grade and chipbreaker to use for the job will be listed where the row and column meet.

Toolmakers have simplified the process even further by adding color codings and symbols to identify the subgroups into which they’ve divided their product lines. The markings are a visual aid to help users find the right section of the selection guide and, when printed on labels or embossed on the inserts themselves, they help users quickly identify the tools in their inventory.

Like any technical system with a simple user interface, the selection systems hide a significant amount of development work behind their easy-to-understand facades. To group tools into categories that make sense to users, toolmakers have had to carefully examine how cutting tools are used and determine which factors have the greatest influence on tool selection. Once the categories have been established, the next step is to laboriously test each workpiece material and tool to determine which category it fits into.

The Material World
Most selection guides group insert grades by the materials they are designed to cut. At first glance, these designations seem to follow the categories established by the International Organization for Standardization (ISO). Like ISO, the toolmakers divide their products into inserts for steels, stainless steels, and cast irons. Most selection systems even use the same color and letter codes to identify these categories: blue and the letter P for steel, yellow and M for stainless steel, and red and K for cast iron. But the criteria that toolmakers have used to determine the scope of each category differ from ISO’s criteria.

ISO’s groupings were based on the type of chip that was produced when the material was machined. This criterion led the organization to include tools for nonferrous materials, such as aluminum, with the cast irons. “We decided to extend our selection system to six material groups based on what happens to the insert and what cutting tool materials are used to machine these materials,” says Terry Ashley, product manager for carbide turning inserts at Kennametal Inc., Latrobe, PA. Using these criteria, it doesn’t make sense to group aluminums with cast irons, Ashley says, because the predominant tool material for cutting aluminum is polycrystalline diamond, not carbide. To group tools according to the way they are actually used, Kennametal has established distinct categories for hardened steels and irons, nonferrous materials, and heat-resistant alloys.

According to Alan Godfrey, vice president of marketing for Sandvik Coromant Co., Fair Lawn, NJ, his company believes that shops machining niche materials such as high-temperature alloys have little in common with shops machining more conventional materials. Therefore, Sandvik would prefer to develop specialized selection guides for these users rather than include these materials in one of its standard guides.

A fair amount of research was necessary to determine which workpiece materials and tool grades should be grouped together. “We’re machining 180 tons of chips a year in development,” says Godfrey. As they observe the results of these tests, the toolmakers use tool life as their principle measure of success. Ashley says Kennametal’s tool designers use the customer’s expectations for tools in a particular material as their benchmark. When the company says this is the tool to use, it means that it will offer the expected tool life. Godfrey says Sandvik’s target is 15 minutes of tool life, but performance in terms of speed and feed rate is also a key criterion.

The toolmakers also rely on field reports to pinpoint the tool materials and chipbreakers that work and to determine where the boundaries between categories lie. For instance, by noting the increases in feed rate or workpiece hardness that prompt users to change tool materials or geometry, the toolmakers can learn where roughing stops and semiroughing begins or where inserts for a particular type of steel belong on the selection matrix.

Within each workpiece category, the toolmakers have subdivided their products by chipbreaker, grouping them according to application. The standard categories are roughing, semiroughing, and finishing. These three chipbreaker categories, crossed with the three grades for various workpiece materials, form the basis for the Secolor 353 selection matrix developed by Carboloy Inc., Warren, MI (Figure 1).

Figure 1: Carboloy's Secolor selection system groups its three grades and three chipbreakers into a nine-cell grid.

Sandvik has tried to make the selection process more precise by adding another three categories that correspond to the difficulty of the job, creating, in effect, a 3x3x3 matrix. Its guide uses the workpiece material to determine the tool material needed. The insert geometry is still determined by the type of operation, and the insert grade is determined by whether the application conditions—such as the presence of interruptions and forging scale and machining speed—are good, average, or difficult.

Middle-of-the-Road Selections
Equipped with the grade and chipbreaker needed, the user is ready to dive into the toolmaker’s catalog to find the insert with the right shape for the job. The selection guides carry their color-coding scheme throughout. This allows users with cast-iron workpieces, for instance, to limit their search for the right insert to those pages in the guide with a red color scheme. Robert Goulding, Carboloy’s stationary-tooling manager, says the recommended cutting data that his company’s guide supplies gives users a safe starting point. “We’re saying, ‘Mr. Customer, if you choose this operation and this insert, you will get a reliable solution. You can rely on it to work for you.’”

While these selection systems were designed to present users with safe, reliable, middle-of-the-road choices, none of the toolmakers guarantee that they will locate the optimal tool choice. They do believe their selection processes will satisfy 75% to 80% of their customers. As Godfrey says of Sandvik’s CoroKey system, the selection process was designed “to cover the majority of machining requirements in an average workshop where they’re machining a reasonable range of materials.”

The toolmakers understand that some jobs will warrant the time and expense it takes to fine-tune the operation. For these situations the selection systems offer guides that lead the user further along toward an optimal choice. Goulding says users of Carboloy’s system “come out of the grid into an optimization table.” For example, if the basic recommendation was for an ABC grade with a 123 chipbreaker, but the user wants a little more wear resistance or a little faster machining speed, the optimization guide would recommend an ABC insert with higher hardness. If, on the other hand, the user finds that the steel he’s working with is softer than expected, the guide would suggest an insert with a different chipbreaker than that of the first-choice tool. All of these tools will still fall within the same family of products as the first choice.

Katbi says these selection systems have made it so easy to locate the right tool that optimizing is a relatively simple process. After running some tests to see how the first-choice insert performs and how it fails, the user has the information needed to look up the tool that is specifically tailored to the application. “The selection process will get you 85% to 90% there,” Katbi says. “If you want to go that extra 10% to 15%, there are a couple pages in the catalog that will help you do that.”

A Guide for Toolmakers, Too
For some toolmakers, their selection system isn’t just a convenient way to sort out their current product line. It also provides a road map for future development efforts. Some see their tool matrix as a guide for product consolidation. Their goal is to find inserts that will cover as broad a range of applications as possible. This would simplify the selection process even further by reducing the number of inserts needed to the absolute minimum. Carboloy has been at the forefront of this effort. Goulding says his company’s selection guide started with six grades and 12 chipbreakers. But by developing products that spanned more than one category, the company has been able to reduce its offering to the three grades and three chipbreakers listed in its current selection matrix.

Others have their doubts that broad-range tools can be truly useful. According to Katbi, manufacturing trends actually make it difficult to develop cutting tools that can be used in a wide variety of applications. With automakers and aerospace builders seeking light, high-performance materials with unique properties, the market is demanding more niche tools designed for a select few applications rather than tools that can provide satisfactory performance cutting a variety of conventional materials.

Rather than develop broad-range tools, some toolmakers have used their selection matrix to guide them in the development of tools for particular application conditions. Sandvik is one of the toolmakers moving in this direction. Godfrey says the company has retired most of its older products in favor of inserts developed for specific cells in its matrix. But even so, Sandvik continues to be wary of overwhelming the user with choices. To give users some help in finding improved tools for established applications, the company gives its new tools the same names as the tools they replace. And to help users locate the right tool in their own inventory, Sandvik permanently marks a wealth of data about the tool, including its geometry, nose radius, and grade, directly on the insert. The insert’s identification codes and recommended speed, feed, and DOC also are printed on the box label.

All of the toolmakers say users have welcomed their selection guides with enthusiasm. “One good sign is that we distributed more than 150,000 copies in the last year alone,” says Katbi. The guides also have been embraced by the toolmakers’ in-house sales staff and the tool distributors who carry their products. In the past few years, color-coded selection guides seem to have sprouted up everywhere. While each scheme has its own quirks, all have imposed some sense of order on the insert-selection process.