Friday, April 18, 2014

3 Strategies for Working With ISO S Materials


By Don Graham, Manager of Education and Technical Services

As a result of healthy aerospace, energy and medical industry segments, the consumption of machined components from the ISO S category (superalloys and titanium-based alloys) is increasing.

Nickel and cobalt-based superalloys have outstanding hot hardness and strength properties, especially when compared to more traditional structural alloys such as steel and cast iron. Titanium alloys have excellent strength-to-weight ratios, making them particularly attractive when weight and fuel savings are important.

Unfortunately, the very properties that make these alloys attractive for critical applications also make them more difficult to machine. Consequently, it’s important to understand the machinability factors of these alloys to ensure reliable, consistent and relatively economical part processing.

Machinability, which describes a material’s response to the machining process, includes four basic factors: mechanical force, chip formation and evacuation, heat generation and transfer, and cutting tool wear and failure. Difficulties in any or all of these factors can cause a material to be deemed “difficult to machine.”

Manufacturers using the same tools and machining techniques with ISO S materials as they were with iron and steel will find themselves battling issues with tool life, process time, reliability and overall part quality. Therefore, it’s important to rethink outdated machining techniques and make use of new cutting tools and strategies.

Below are three strategies to consider when working with ISO S materials:

#1 – The traditional approach to machining difficult materials is to proceed cautiously and use less-aggressive cutting parameters, such as reduced feed rates, depths-of-cut and speeds. However, many cutting tools made specifically for ISO S materials are meant to run at increased depths-of-cut and feed rates. The tools engineered to handle these more aggressive parameters include fine-grained carbide grades with good high-temperature edge strength, deformation resistance and wear resistance. The most common failure mode encountered when machining superalloys is notching at the depth-of-cut and depth-of-feed areas. This is usually caused by a work-hardened surface. Utilizing heavier depths-of-cut and feed rates will minimize the amount of contact time between the work piece and the cutting edge.

#2 – Compared to machining steel or cast iron, there’s a major difference when it comes to heat generation and dissipation. Heat-resistant materials are poor conductors of heat, meaning heat builds up in the tool and workpiece and, in turn, causes shorter tool life and part deformation. Thereby, manufacturers should use sharp-edged cutting tools. While generally considered weak, these sharp tools – when used on machines with sufficient power, stability and vibration resistant – cut the material more than deform it, reducing heat and temperature buildup. 

#3 – Nickel- and titanium-based alloys exhibit greater strength hardening tendencies than steel. Thereby, it becomes important to minimize the number of cutting passes, when possible. For instance, instead of removing 0.4" of material with two 0.2"-deep cutting passes, it’s better to use one pass at 0.4" depth-of-cut. With single-pass machining, however, machinists need to rethink the finishing process, which traditionally involves multiple passes at small depths-of-cut and light feed rates. They should look for possibilities to increase the machining parameters as much as possible because doing so can improve tool life and surface finish. Finding the optimum balance between aggressiveness and caution is key.

At Seco, we’ve developed several advanced products and strategies that address ISO S machinability – and will continue to do so as progress with these high-performance workpiece materials continues. If you have any questions or would like more information on how our tools and machining strategies for ISO S materials can bring you increased success, please don’t hesitate to contact me.

About the Author
Don is the manager of education and technical services for Seco, responsible for all educational activities for the NAFTA market, new product testing and various other technical functions. Outside of work, he enjoys making maple syrup, restoring antique tractors and farming. 

Thursday, March 20, 2014

Tooling and Strategies for Holemaking


By Mike Smith, Product Manager – Reaming, Boring and EPB

Holemaking is a fundamental manufacturing process, consuming nearly a third of all the time spent in metalcutting operations. Manufacturers make holes in a nearly an infinite number of sizes and levels of quality, ranging from loose-specification clearance holes to highly-toleranced holes engineered for critical applications.

Holes most often are made to accommodate mating parts, fasteners or shafts. The fit between the parts can be grouped in three very general categories: sliding or clearance fits, tight and secure interference fits, and transition fits in which a shaft is held securely but not so tightly so it cannot be removed from the hole.

Standards for quantitatively determining the class of fit for a hole cover nine characteristics, namely straightness, circularity, cylindricity, parallelism, perpendicularity, positioning, concentricity, diameter/dimensions/tolerances, and surface finish. For each characteristic, the hole’s actual dimensions are compared to a theoretical cylinder or standard dimension.

To produce the desired hole size and quality in the most cost efficient and productive way, it is crucial to apply the most appropriate tooling and machining strategies.

The selection process for holemaking tooling begins with determining a hole’s basic requirements, including its diameter and depth, whether it is a blind or through hole, its geometry in relation to the part, where the hole is positioned on the part, the desired surface finish and whether the hole includes steps or chamfers. Also influencing tool choice are the machinability characteristics of the workpiece material, the production volume required, machine tool and fixturing capabilities, and the availability of coolant.

The part manufacturer’s priorities play a large role in tool selection, including such issues as minimizing hole cost and tooling cost per part, speeding cycle times, and matching production requirements with shop capacity.

Different hole characteristics require different tooling configurations. For simple holes in solid material, drills are usually the first choice. Existing holes can be enlarged via turning and rough boring. Milling processes are often the most appropriate way to make complex or large holes. Depending on the quality desired, final dimensions and finish are produced via reaming and finish boring.


Crownloc Plus
Available holemaking tooling includes a wide variety of alternatives. When considering drills, for example, solid carbide versions enable efficient production of small diameter, accurate holes when applied on suitable machines. Solid carbide drills also can be reconditioned, reducing tool costs. For medium-diameter holes, “replaceable end” drills, such as Seco’s Crownloc® tools, provide high accuracy while offering the convenience of a replaceable drill point. When making larger diameter holes, inserted drills like Seco’s Perfomax® drill can be fitted with different insert grades to provide optimal performance in differing workpiece materials.

Hole finishing systems offer similar variety. To maximize hole quality in terms of class of fit, rough and fine boring heads such as those in the Seco A750 system offer high positioning accuracy. For control of hole geometry, boring heads provide the best results in regard to straightness. When surface finish is a major consideration, hole finishing tooling like Bifix®, Precifix™, Xfix™ reamers from Seco represent excellent solutions.

In many cases, production volume dictates the selection of holemaking tooling and process strategies. If a manufacturer’s goal is to minimize cost per hole in a high-volume situation, the focus will be on machine utilization, productivity, reduction of cycle times, and operational security of the long-running job. Those goals can be obtained by fine tuning cutting parameters and process steps with CNC programming written to produce the holes in the most efficient way. In choosing tooling, selection of drilling and reaming tools chosen for and dedicated to the particular job will provide reliable operation.

On the other hand, in small batch holemaking the emphasis is on flexibility. Tooling such as center-cutting endmills can provide versatility to handle a wide range of part configurations and workpiece materials. Advanced programming techniques including helical interpolation can enable a single milling tool to produce a variety of hole sizes and configurations. After the hole is milled, adjustable boring tools can provide the required tolerances and finishes.

In situations where a holemaking operation represents a bottleneck in the production flow, selection of the right tooling and procedures can overcome slowdowns that result from slow cycle times, poor chip control, less-than-rigid tooling, fixturing and machining equipment. Effective management of cutting speeds and feeds is essential in reducing cycle times while also avoiding vibration that can affect surface finish. High-performance holemaking tooling tailored to create specific hole requirements and provide top performance in certain workpiece materials will contribute as well.

Though not strictly a tool or a strategy, coolant delivery is a key element in nearly any holemaking operation. Coolant flow has three major functions. It enhances chip evacuation, always a crucial issue in holemaking. It also cools the tool and workpiece, which is essential because the heat of metalcutting in holemaking is concentrated deep in the hole. Finally, sufficient coolant flow lubricates the drill land margins, which are in direct contact with the wall of the hole and generate additional heat through friction. 

To channel the fluid directly to the drill cutting edges and margins and push the chips back out of the hole, it is always best to utilize holemaking tools with internal through-coolant capability. Where internal coolant delivery is not possible, the coolant flow should be directed parallel to the drill to ensure that as much of it as possible enters the cutting zone. It may be necessary to reduce cutting speeds by 20 percent compared to drilling with internal coolant.

The selection of the best tools and strategies for holemaking operations will facilitate productivity and boost cost efficiency in what is metalcutting’s most widely-used process.

About the Author
Mike is Seco's product manager for reaming, boring and EPB tool holders, which includes EPB’s line of rough and finishing boring heads. In his spare time, Mike enjoys spending time with his wife and two daughters as well as running when he gets a chance. Contact Mike at msmith@secotools.com.

Tuesday, February 4, 2014

Finish Turning Tactics in Depth (of cut)


By Chad Miller, Product Manager – Turning and Advanced Materials

A common approach to finish turning involves the use of light depths of cut. In many cases, however, heavier depths of cut can help optimize finishing processes.

When improving a finishing operation, changing feed rate is rarely an alternative. Feed often is tied to a surface finish (Ra/Rz) requirement, following cutting tool makers’ charts that list specific combinations of nose radius and feed rate needed to achieve desired surface finish. However, even if feed rates are essentially fixed, altering the depth of cut can help overcome the special issues of finish turning.

Seco MF2 Chipbreaker
Because finishing operations often generate thin, hard-to-control chips, the first consideration is choosing a chip groove geometry. The geometries are designed for different applications. Seco, for example, offers MF2 and M3 chipbreakers for fine and light-to-medium duty cuts in steels.  Every chip control geometry has an optimal working window and it is important to use cutting parameters that fit. For example, if the working area of the insert’s chip groove is 0.011" - 0.020" depth of cut, but finishing is performed at 0.010" depth of cut, chip control won’t be as effective as it could be.

Even with the correct chip groove, surface finish may be unsatisfactory. The cause can be premature insert wear resulting from the combination of a light depth of cut and a large nose radius.

When turning with a very light (for example, 0.010") depth of cut and a large (e.g. 0.031") nose radius, chips roll over the nose radius and onto the land area at the periphery of the insert edge. In a high-carbon steel, that contact can promote crater wear on the land and thereby decrease the insert’s ability to produce a smooth finish.

A heavier depth of cut will form the chip beyond the nose radius. With a 0.031" nose radius, for example, using a 0.040" depth of cut will direct the chip over the flank of the insert and cause it to make contact with the tool in the gullet behind the land, where crater wear is more acceptable.

An overly light depth of cut will produce uncontrolled chips that will form stringers or a nest that can wrap around the tool and scratch the workpiece. A heavier depth of cut tends to help chips roll up and break, but most shops don’t finish at a 0.040" depth of cut with a 0.031" nose radius. The answer can be use of a smaller nose radius for finishing applications. A shop may use a CNMG 432 (1/32" or 0.03125" nose radius) in roughing and then a CNMG 431 (1/64" or 0.01562" nose radius) for finishing. The smaller nose radius paired with a lighter depth of cut will direct the chip to the insert flank because the depth of cut is larger than the tangency of the nose radius.

Manipulating depth of cut can also control cutting forces and help minimize chatter. There are three categories of cutting force in a turning operation. Axial force is generated when feeding along the z-axis towards the machine chuck. The force is into the strongest areas of the machine and workpiece and is an element of a stable cut. A second force, called tangential force, is the pressure on the top rake of the insert as it is cutting. The force increases as the part spins faster and generally is not a problem.

The third force is radial force. It involves x-axis pressure and the insert pushing off the part or the part pushing off the insert. Radial force can promote chatter or vibration and generate a wavy finish.

The goal is to maximize axial force and minimize radial force. If the tool is rigid and the part is large in diameter and well supported, the negative effect of radial force is small. But the situation is different when turning, for example, a 16"-long, 1"-diameter shaft. With a slender, long part that is not well supported in the center, the beginning of the cut near the tailstock and the end of the cut near the chuck are fairly rigid and solid, but vibration occurs in the center because there is no support. Radial forces really come into play in that scenario. For example, with a 0˚ or -5˚-lead angle insert that has a 0.015" nose radius, turning at a 0.012" depth of cut over a 2.5" length of cut will produce a taper of roughly 0.0004" per inch. However, increasing the depth of cut to 0.022" generates negligible taper because the depth is 0.007" past the tangency line of the nose radius. The nose radius is out of the cut and doesn’t generate significant radial force. In other words, the axial force is greater than the radial force. Summing it up, as depth of cut decreases, radial force at the nose radius grows. To reduce chatter, generally use the smallest nose radius possible and increase the depth of cut.

About the Author
Chad manages Seco's turning and advanced materials product lines, including all CBN and PCD products. When he's not helping customers implement advanced metalcutting solutions, you can find him training for and running 5K, 10K and 1/2 marathon races and triathlons. 

Tuesday, December 10, 2013

Optimize Your Parting-Off and Grooving Operations

By Don Halas, Product Manager – Threading & MDT

Parting-off and grooving processes involve tight, narrow cutting zones that create singular challenges regarding tool strength and rigidity as well as chip control. Therefore, tool manufacturers are employing innovative tooling designs and advanced coolant delivery strategies that meet the special requirements of these processes. 

X4 Multi-edged Tangential Tool
Consider our new X4 series of slender, highly robust tangential inserts with four cutting edges. The series minimizes material consumption in parting-off operations and enables precise grooving of small and medium-sized complex parts. These inserts provide narrow cutting widths from .031” to .94” and cutting depths between 0.20” and 0.52”. 

Keep in mind, however, narrower-style inserts can produce instability in the cut. Therefore, holding the insert with the shortest blade possible and clamping it in the largest tool shank that does not interfere with the workpiece will help control vibration.

The good news for X4 users is that it is available in several tool shank sizes and the tangential inserts direct the cutting forces into the holder to maximize rigidity, stability and productivity. Furthermore, all of the insert types fasten into the same easy-to-load toolholder for increased flexibility and a reduction in tooling inventory. 

The limited cutting zone space in parting-off and grooving operations creates chip control problems. The workpiece material surrounds the cutting tool on both sides while it is in the cut, restricting the chips’ path of escape. An uncontrolled continuous chip can jam in the cut, mar the workpiece and endanger the operator. However, the X4 can apply an MC chipbreaking geometry that will bend the chips and break them if possible.

Another method for chip control is the application of coolant, which can flush away chips that otherwise might clog the cutting zone. However, traditional flood coolant usually has insufficient pressure to reach the cutting zone in parting-off and grooving applications. It is also difficult to position flood coolant nozzles for optimum placement of the coolant stream. An alternative to flood coolant is coolant applied at high pressure and as close to the cutting edge as possible. 

Consequently, our new Jetstream Tooling® Duo technology, which is incorporated with the X4 toolholders, delivers direct, high-pressure coolant from two outlets. In addition to upper jets that are directed to the optimal point of the rake face, the new Duo technology uses an additional coolant jet to flush the clearance surface. The cutting edge receives high-press coolant from opposite directions – above and below – maximizing the control of the chip flow as well as cooling the cutting zone. 

As you can see, modern parting-off and grooving tools and technology play a big role in optimizing this specialized but important group of machining processes. If you are interested in learning more about how the X4 can improve your operations, please don’t hesitate to contact me

Watch the X4 in action.

About the Author
As product manager for threading and grooving at Seco, Don is responsible for threading, threadmilling, cut-off, grooving and oil field chasers. In his spare time, he enjoys restoring old motorcycles. Contact Don at dhalas@secotools.com.

Friday, November 1, 2013

Tips for HRSA Machining with Ceramic Inserts


By Chad Miller, Product Manager – Advanced Materials

CS100 ceramic grade
Our new CS100 ceramic grade provides excellent rough machining performance in heat-resistant super alloys (HRSA), including Inconel, MAR, RENE, Nimonic and Waspaloy. We designed this grade to reduce machining time and increase productivity by allowing for higher cutting speeds. In fact, the high-speed capabilities of ceramic result in metal removal rates that are four to eight times greater than carbide.

However, to effectively utilize the CS100 at high speeds, your workpiece set up and machining conditions need to be as stable as possible to prevent chipping of the grade. Here are some important tips to keep in mind before utilizing this sialon-based solution.

Toolholders

It’s best to use a toolholder that’s intended for securely holding ceramic inserts. You can gain improved stability by choosing a toolholder with a large shank size, such as boring bars made from heavy metal or carbide. 

As with any machining process, it’s important to keep your tool overhang as short as possible. However, when long overhangs are unavoidable, such as in boring applications, it’s best to avoid negative inserts due to high radial cutting forces. Instead, go with a positive insert geometry and tool holder combination with a 90-degree angle between the leading edge of the insert and the machining surface.  

When machining high-temperature materials, you can improve tool life by using toolholders with large lead angles, as those less than 15 degrees will leave you unsuccessful. A large lead angle will thin out your chips and possibly increase your cutting parameters. 

Inserts

You should utilize the strongest insert geometry possible for your application. A round insert works best in roughing operations, and you’ll want to keep its arc of engagement low (not to exceed 45 degrees) to prevent chatter and slippage. However, if a round insert isn’t an option, then choose an insert with the largest possible radius. Also, the thicker the insert the more strength and predictable tool life you’ll have. 

Insert geometry strength from highest to lowest:
• Round
• 100-degree corner of 80-degree diamond
• 80-degree diamond
• Trigon
• Triangle
• 55-degree diamond
• 35-degree diamond

Having the correct edge prep for your workpiece material is also an important consideration. A chamfered edge with a hone is preferred for applications that involve the roughing of high-temperature materials.   

Coolant

Concentration-level controlled flood coolant is important when machining with ceramic tooling – and you’ll want plenty of it, as an intermittent coolant supply will make for a disastrous situation. The coolant should also be clean because any contamination will shorten your tool life. 

You should not use high-pressure or high-velocity coolant (1000 + psi) during the machining process. Doing so reduces the temperature of the cutting zone and keeps the material from softening, thereby increasing cutter forces and accelerating tool wear. High-pressure coolant also causes erosion that will, in turn, decrease tool life. You also don’t want to use oil as a cutting fluid as that becomes a fire and smoke hazard.  

Application of Inserts

Insert geometry and radius size influence what feed rate you can effectively run in your machining operations. For instance, the weaker your geometry and the smaller your radii, the lower your feed rate must be. When possible, you should use larger radius sizes when machining components with large diameters. If smaller radii are absolutely necessary, then you must reduce your feed rate. 

These are just a few items to consider when machining with ceramic tooling, so if you’re interested in learning more, please don’t hesitate to contact me. I’d also be glad to go into detail on how the new CS100 can decrease your cost per part and improve your overall machining performance. 

About the Author
Chad manages Seco's advanced materials product lines, including all CBN and PCD products. When he's not helping customers implement advanced metalcutting solutions, you can find him training for and running 5K, 10K and 1/2 marathon races and triathlons. Chad can be reached at cmiller@secotools.com.