Solutions For Hard Milling

Makino demonstrates the latest techniques and technologies for high-speed machining of hardened materials for die or mold applications. Check out tips, tricks, and new technologies you can use to mill the toughest steels, shortening your lead times, lowering your costs, and eliminating bench work.

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Advantages of Diamond Coated Inserts

The metalcutting advantages of diamond are well known. It's not only the hardest substance on earth, but it also has a very low coefficient of friction (less than Teflon) and exhibits thermal conductivity several times better than copper.

Until the CVD diamond process became practical, shops had one type of diamond tool available: polycrystalline diamond (PCD). PCD has been used in metalworking for several years. It consists of diamond crystals in a cobalt binder. Segments of the PCD are brazed on the cutting edge of a carbide insert. Usually only one cutting edge receives a diamond segment, which is precisely shaped by a wire electrical discharge machine to fit a recess in the insert.

The cutting edge geometries of PCD are limited, leading the industry to explore CVD thin-film technology as a complement or even replacement.

Flexibility in insert design is a big advantage of thin-film diamond-coated inserts. As with other coated inserts, chipbreakers and rake geometries are molded into the insert when it is pressed. PCD tools, on the other hand, are limited to very basic geometries with few chipbreaker designs available.

The CVD process "grows" diamond over the entire substrate surface. Depth of cut is not limited by the size of the diamond segment as in PCD tools. Complete surface coverage with CVD thin-film diamond also helps chip flow. Because diamond has a low coefficient of friction, chips move across the various faces of the insert smoothly. When cutting gummy materials, this slippery coating discourages material build up on the cutting edge and insert body.

A diamond insert has multiple cutting edges. Because all edges are coated, the inserts are truly indexable--a triangle has three usable edges, a square has four, and so on.

Performance characteristics of CVD diamond inserts are comparable to PCD. In many applications, CVD diamond inserts can be a direct replacement for PCD. In some cases, the use of chipbreaker geometry allows the machine tool feeds, speeds and depth of cut to be increased over PCD tools without such geometry.

CVD diamond inserts tend to wear evenly. As cutting erodes the diamond film to the point where carbide is exposed, the substrate tends to continue cutting although much less efficiently. This gradual wear-through permits in-process tool monitoring when machines are running lightly tended.

REF: Diamond-Coated Carbide Inserts-Ready, Set, Go By Chris Koepfer

WHAT IS POLYCRYSTALLINE CUBIC BORON NITRIDE (CBN)?

WHAT IS POLYCRYSTALLINE CUBIC BORON NITRIDE (CBN)?

Diamond, cubic carbon, is the hardest, most abrasive resistant material known to man. It is therefore an ideal tool material. Unfortunately, in the presence of heat and iron, nickel or cobalt, diamond transforms to hexagonal form, graphite. This is why ferrous materials are not generally machined with diamond. The second hardest material, Cubic Boron Nitride (CBN), is created by man, using temperatures and pressures similar to those for diamond synthesis, but does not have this inherrant weakness when it comes to the machining of ferrous materials. Used in the correct manner CBN inserts offer cost-effective rapid stock removal and finishing of hardened steels and certain softer ferrous materials.

For more information on CBN Inserts please visit:

David Richards Engineering

Top 20 Tooling Tips For Machining

Gathered from machine shop and application experts' cutting-tool philosophies and trade tricks, here are 20 productivity tips, application insights and general knowledge on how to get an edge in performance and service life.

Machine tool consumption in the United States totaled $3,080.61 million in 2005, up 8.4 percent from the year prior. As machining and tooling obviously still is a key factor in manufacturing, let’s take a look at some general insights and productivity tips regarding cutting-tool philosophy, here via Modern Machine Shop and Modern Application News:

1. The Costs that Count Focus on cost per part, not the cost of cutting tools, as a key target. Because cutting tools account for only three percent of total production costs in metalworking, upgrading cutting tools is likely to yield more overall cost savings.

2. Cutting Tools are a System Keep both hardware (e.g., cutter bodies and toolholders) and software (e.g., indexable inserts) up to date. When looking at an upgrade in insert technology, consider upgrades in toolholders and cutter bodies, and vice versa.

3. Target and Elucidate When engineering a new process or troubleshooting an existing one, target four main areas and set clear, measurable goals for each: cycle time, tool life, part quality and surface finish. Then rank by priority. Share those goals and priorities with your vendors for better answers sooner.

4. Troubleshooting: Process Problem or Tooling Problem? Don’t be too quick to blame the tool. Instead, use the mode of tool failure as a clue to the root problem. Look at machine rigidity, feed, speed, depth of cut, presentation angle, chip clearance and coolant. If it is a tooling problem, changing the tool will fix it. If the problem is a process problem, it probably won’t matter what tool you use.

5. Coatings Aren’t Only for Inserts Coat cutter bodies to get some important benefits that high-tech coatings bring to carbide inserts: hard coatings on cutter bodies resist wear from contact with hot chips moving at high speeds; chips flow more readily through flutes because the coating gives the surface lubricity.

6. Multifunction Tools for Multitasking Machines Added spindles, tool turrets and rotational axes mean tight clearances and a limited number of tool stations, so consider the possibility of having one toolholder with several multipurpose inserts that can do facing, OD turning, drilling, counter drilling and internal threading without a tool change.

7. Modular Thinking is Lean Thinking To keep tool inventory at a more manageable level, consider modular tooling shanks that accept a variety of interchangeable solid carbide heads. As the heads can be replaced or exchanged while the tool is clamped in the machine, setup time can be reduced.

8. Don’t Neglect Power Consumption Besides energy savings, cutting tools that require less power from the machine tool tend to last longer, cause less wear and tear on spindles and ways, and minimize vibration. A 10 percent reduction in cutting forces is likely to result in a 50 percent improvement in tool life.

9. Get Clamping Forces Right When tightening the clamping screws after indexing an insert, DO NOT GUESS about the torque applied. Under-tightening may allow the insert to chatter or prevent the process from holding tolerances, while over-tightening may break the insert or the key. For a simple way to eliminate uncertainty, consider a torque wrench that automatically lights up to signal that proper tightening levels have been reached.

10. Can Your CAM Software Keep Up? When programming for CNC operations, it is important for toolpaths to match the capability of the cutting tools. Not all CAM software allows the programmer to program the moves that optimize the performance of advanced cutting tools.
11. Think Process FirstSometimes taking an unconventional approach is the answer. Especially on larger holes in one-off or short-run work, milling a hole from solid with helical milling often makes more sense than drilling it. Large-diameter drills may be faster, but they’re a lot more expensive and not near as versatile.

12. Understand Cutting-Metal Forces, Use Them to Advantage Cut in a direction that improves rigidity of the setup. Consider reducing the depth of cut to convert radial forces into axial forces. Then increase the feed rate to take advantage of higher axial rigidity. 13. Take Advantage of Tool Geometry This can improve throughput. For instance, on lead-angle cutters, increase the feed rate to achieve maximum recommended chip thickness.

14. Match Tool Geometry to Material Being Cut Especially in job shops handling a variety of workpiece materials, beware of “general purpose” tooling. Take the time to change tools when you change materials. You’ll get more throughput and make more money that way. Again, the price tag on the tooling is the least important part of the process-economics equation.

15. No Vibes Are Good Vibes Minimizing or eliminating vibration is usually a matter of controlling cutting forces so that they are directed to the most stable, most rigid element of the machining system. Upon every proposed change in tooling, examine how vibration is managed. That is the key to prolonging tool life, protecting the spindle and improving surface finish.
16. The True Meaning of “Indexable”To make sure you are getting the full value of the original concept of carbide inserts with indexable edges, look for styles that offer the most in multiple edges and be sure the edges truly are usable.

17. Combining Process and Cutting Your Time in Cut Combining several processes into one makes can increase efficiency and reduce costs. The time required for the separate machining cycles, as well as the time required for tool changes, can be reduced or eliminated. Further, tooling costs can be reduced by reducing the number of tools required for a job. (See also Tip 6.)

18. Understand Heat Know where heat comes from and how it can help or hurt you.
Metalcutting will always generate heat, not all of it from friction. In steel machining in particular, you want only enough heat to soften the workpiece material and form good chips. Avoid heating levels that can trigger hardening reactions in the material, overheat the tool or decarburize (crater) the insert.

19. Maximize Your Liquid Assets For coolant-fed drills, there are two parts to the battle: getting the coolant to the cutting edges and getting the chips out of the hole effectively. Thus, coolant flow and chip flow must be considered equally.

20. Return to School Companies sending their engineers and programmers back to classes often see a fresh return on their investment each time, a return that comes usually within weeks of completing the class. Their people come back excited to apply their new knowledge right away. Some of the excitement may rub off on co-workers. If you’ve tooled a job the same way for more than three years, odds are there’s a better way that will make you more competitive.

Sources
Upgrade Your Cutting Tool Mindsetby Mark Albert Modern Machine Shop, July 2005
Teacher’s Top 10 Tooling Tipsby Dave Eisele Modern Application News, July 2004
Additional
Get an edge on tool performanceby James Benes American Machinist, December 2005

What is the definition of indexable carbide insert drill?

A drill with carbide inserts clamped to a steel body. Indexable carbide drills are among the most cost-effective drills.

What is the definition of carbide insert?

A cutting bit made of hard carbide material that has multiple cutting edges. Once a cutting edge is excessively worn, it can be indexed to another edge, or the insert can be replaced.

Payoffs And Tradeoffs of CBN Inserts

CBN inserts incorporating reinforced, chamfered edges eliminate the edge breakout common when cutting materials harder than 50 RC.

Consider the entire application. Less expensive carbide inserts that can do the job in terms of tolerance and surface finish may be costly when the time spent indexing and replacing inserts is considered. Real productivity results from an understanding of the tradeoffs in throughput, cycle time and insert performance.

In one specialized, low-volume example, a sintered titanium carbide gas turbine blade was milled successfully with coated carbide cutting inserts. At 120 sfm, the carbide cutting edge cut well for just 5 to 10 minutes. Acceptable insert life is typically placed at 15 to 30 minutes in high volume production with difficult materials, but with a low-rate part, the short insert life and frequent tool changes are not major drawbacks. Longer insert life does become important in full production, however, to decrease tool-changing downtime and labor and to increase machine utilization and throughput. Carbide works well for the turbine blade for now, but should the part go to higher volume production, the application may justify harder, more costly inserts made of CBN.

Productivity with advanced material inserts requires adopting the right feeds and speeds. CBN inserts incorporate reinforced, chamfered edges to eliminate the edge breakout common when cutting materials harder than 50 RC. Yet even despite this toughness, CBN inserts demand cutting machine parameters held to tight tolerances. Cutting speeds 10 percent too low or 10 percent too high can dramatically hamper performance.

If faced with the need to machine a difficult material, consider contacting your cutting tool supplier. Suppliers can offer solutions based on how others have approached the same problem. When experimentation is required, careful trial-and-error generally starts with carbide inserts and moves on to harder and more costly cutters. Modern insert geometries, rigid toolholders and refined machining routines often make less costly carbide inserts suitable for tough jobs.