Tuesday, July 22, 2014

Best Practices for Austenitic Stainless Steel (ISO M) Machining

By Don Graham, Manager of Education and Technical Services
Austenitic stainless steel, an iron-chromium-nickel alloy, provides enhanced strength and corrosion resistance for a wide variety of today’s demanding component applications. The benefits of this ISO M material, however, come with a downside. The alloy’s nickel content, which boosts its corrosion-resistance capability, also makes the material harder and therefore more difficult to machine. Fortunately, there are strategies that address this problem and help manufacturers significantly boost productivity in austenitic stainless steel machining operations. 
Milling Stainless Steel
Here are some of the most effective strategies:
Use sharp tools with carbide substrates. Traditionally, machinists assumed that because the austenitic stainless steel alloys were stronger, mechanical cutting forces would be higher, necessitating the application of stronger, negative-geometry tools at reduced cutting parameters. That approach, however, resulted in shorter tool life, longer chips, frequent burrs, unsatisfactory surface roughness and harmful vibration.  In reality, the mechanical cutting forces involved in cutting austenitic stainless steel aren’t much higher than those typical when machining traditional steels. Most of the extra energy consumption required to machine austenitic stainless steels is due to their thermal properties and work hardening characteristics. 
Metalcutting is a deformation process, and when deformation-resistant austenitic stainless steel is machined, the operation generates excessive heat. Evacuating that heat from the cutting zone is of primary importance. Unfortunately, in addition to being resistant to deformation, austenitic stainless steel also has low thermal conductivity. Because of this, the workpiece and chips generated during machining absorb very little heat, so, excess heat transfers directly into the cutting tools to severely shorten their working lives. 
Carbide tool substrates, on the other hand, combat this problem and provide hot hardnesses that endure the elevated temperatures when machining austenitic stainless steel. Paired with sharper cutting edges, carbide substrate tools actually cut the stainless steel – as opposed to deforming it – to reduce the amount of generated heat.
Take large depths-of-cut at aggressive feedrates. With austenitic stainless steel, the bigger the chip the more heat it can carry away from the cutting zone. The most effective way to generate big chips is through large depths-of-cut and aggressive feedrates. Larger depths-of-cut will also reduce the number of cutting passes required to complete a part – an important consideration because austenitic stainless steel tends to progressively strain harden during lengthier machining operations. 
There are practical limitations to these aggressive machining tactics, however. For instance, the power available from the machine tool, as well as the strength of the cutting tool and the workpiece, will ultimately determine how aggressive the cutting parameters can be. In addition, machinists should rethink the finishing process, which traditionally involves multiple passes at smaller depths-of-cut and light feedrates. The most effective strategy is to maximize machining parameters whenever possible, as this can improve tool life and workpiece surface finish.
Use appropriate coolant, applied under high pressure. Due to the problematic thermal properties of austenitic stainless steels, the application of coolant during machining operations is almost always crucial for favorable machining results. The coolant must be of high quality, with at least eight or nine percent oil content in an oil/water emulsion – compared with the three or four percent oil content typical for many machining operations. The higher the pressure at which coolant is delivered to the cutting zone, the better it will do its job. Specialized delivery systems, such as Seco’s Jetstream Tooling, that delivers a high-pressure stream of coolant directly to the cutting zone are even more effective. 
At Seco, we’ve developed several advanced products and strategies that address ISO M austenitic stainless steel machinability – and will continue to do so as the use of these high-performance workpiece materials grows. If you have any questions or would like more information on how our tools and machining strategies for austenitic stainless steels can boost your productivity, 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. 

Friday, June 6, 2014

Resolving Opposing Concepts in Production Economics

By Patrick de Vos, Corporate Technical Education Manager, Seco Tools AB
To gain maximum productivity and economic benefits in your metal cutting operations, it’s essential to evaluate the processes in light of overall production economics. The goal is to ensure reliability of the machining process while maintaining high productivity and low production costs. Achieving those goals involves an examination of several opposing concepts.

Macro Versus Micro
The traditional approach to maximizing metal cutting results involves a narrow-perspective micro model based on 1:1 optimization of one tool in one operation. Macro models, however, consider manufacturing processes from a broader perspective. These models focus on the total floor-to-floor time required to produce a given workpiece. 

The macro perspective considers the interrelation of all the steps in a manufacturing process. A simplified example involves two machines employed in series to produce a component. If machine tool A is optimized to boost its output but the results from machine B can’t be improved, parts from the first machine will sit waiting for the second as semi-finished inventory, increasing costs. In this case, simply optimizing cutting costs (rather than output) on the first machine would lower machining cost overall while maintaining output. 

On the other hand, in a situation where machine B sits idle waiting to process parts from machine A, increasing the output of the first machine will increase total output. Much depends on whether the shop organizes production flow in a line, batch, or parallel sequence. 

Cost Versus Productivity
After evaluating the process from a macro viewpoint, shops can optimize operations on an individual basis with the goal of achieving high metal removal rates at the lowest possible cost. The process involves selecting tooling best suited to machine the part’s features and then employing the largest depth of cut and highest feed rate possible. Those parameters, of course, are subject to constraints regarding available machine power and torque, and the stability of workpiece fixturing and tool clamping. 

Shop personnel then can use cutting speed to fine-tune the machining process to achieve minimum cost, maximum productivity or a compromise result. Initially, machining time drops and productivity rises with increasing cutting speeds. After a certain point, however, costs again start to rise. Above a certain cutting speed, tool life becomes so short that the cutting edge requires frequent replacement. At that point, the decrease of the machining time cost has a smaller beneficial effect than the increasing cost of tools and changeover time. Somewhere between the extremes there is a cutting speed where the two costs balance to result in a minimum total cost.

Quality Versus Productivity
Standards for part quality continually become stricter, but the quest for quality sometimes is overdone. Pursuing unnecessary high quality wastes money. Manufacturers can drastically reduce costs and dramatically increase productivity just by fulfilling the given requirements for part precision. 

Productivity Versus Reliability
Similarly, focusing entirely on maximum productivity in terms of lower cycle times can negatively affect the reliability of a metal working process. A process that is run constantly at the limit may exceed that limit at a cost of scrapped workpieces and lost time. Understanding tool wear and failure modes is essential. Wear-related phenomena generally are gradual and predictable, while other failure modes, such as tool breakage, lack the predictability required to maintain a reliable cutting process.

Individual Factors Versus Overall Results
Typically, more than 50 to 70 individual factors can have an appreciable effect on product quality, production time, and cost. Typical factors that should be analyzed include tools/tooling systems, workpiece configuration and materials, equipment process capabilities and data, human factors, peripheral equipment and maintenance issues. Environmental factors such as energy consumption and disposal or recycling of worn tools and machining waste must also be examined, in addition to employee safety considerations. 

Universal Versus Specialized Tooling
An accepted way to increase productivity in an individual operation is to engineer specialized tooling for that specific process. Spending the time and money involved in such an effort may be worthwhile when the expense can be amortized over a long production run. However, balancing productivity, reliability and tool cost considerations in the small-batch situations that have become more frequent today requires versatile “universal” tooling that offers flexibility over a broad window of application. These tools reduce downtime by minimizing the time needed to switch in a new tool when the workpiece changes. They also eliminate the need to set up and test run a new tool. 

In summary, the choice of tooling and machining parameters for a single operation is dependent on how that operation fits into the total manufacturing picture. The choice should be biased toward what is desired in terms of productivity, cost efficiency and reliability, and what best fits a broad view of the production process.

About the Author 
Based in Sweden, Patrick is the corporate technical education manager for Seco Tools AB with global responsibilities for the technical education activities that help train Seco employees and customers worldwide. He led the creation of the Seco Technical Education Program (STEP) and since its launch more than 145,000 people worldwide have participated in the program. He has been with the Seco organization for more than 30 years, and during that time he has trained more than 50,000 people in over 55 countries. He is also the author of the book “Metal Cutting, theories in practice.”  

Friday, May 16, 2014

Productive Tradeoffs in Rough Turning

By Chad Miller, Product Manager – Turning and Advanced Materials 

Maximizing productivity in rough turning operations requires a balance of tradeoffs between the properties of the cutting tool substrate as well as the characteristics of its chipbreaker geometry. 

Seco M6 Roughing Geometry
A tool’s cutting edge must be harder than the material it cuts. High hardness, especially at elevated temperatures generated in high speed machining, will prolong tool life. A harder tool, however, is also more brittle. Uneven cutting forces encountered in roughing, especially in interrupted cuts involving scale or varying depths of cut, can cause a hard cutting tool to fracture. Instability in the machine tool, fixturing, or workpiece can also precipitate failure. 
On the other hand, boosting a tool’s toughness by including a higher percentage of cobalt binder, for example, will enable a tool to resist impact. But at the same time, reduced hardness also makes a tool subject to rapid wear and/or deformation in higher-speed operations. The key is to balance tool properties in light of the workpiece being machined. 
For example, Seco’s TP0500 grade is engineered for maximum hardness and wear resistance and trades off some impact resistance or toughness for faster speed capabilities. It is best suited for higher-speed roughing on workpieces without interruptions and on stable machining setups. The TP3500 grade, on the other hand, is designed to provide long, predictable tool life in unstable conditions. To gain toughness, the grade trades off some heat resistance and high-speed capability. 
Incidentally, Seco’s Duratomic coating enhances the performance of both grades. The aluminum and oxygen in the coating’s outer layer are arranged on the atomic level to maximize hardness, toughness, and lubricity, allowing cut material to flow freely minimizing heat buildup.
While the substrate material and coating of a cutting tool provide a foundation for roughing operations, the tool’s chipbreaker geometry enables fine-tuning of tool performance.
Seco TP0500 Grade

Just as with tool materials, tradeoffs are involved in the engineering of tool geometries. A positive cutting geometry and sharp cutting edge reduce cutting forces and maximize chip flow. However, a sharp edge is not as strong as a rounded one. 
Geometric features such as T-lands and chamfers can be manipulated to strengthen the cutting edge. A T-land – a reinforcing area behind the cutting edge – set at a positive angle can provide sufficient strength to handle specific operations and workpiece materials and minimize cutting forces as much as possible. A chamfer squares off the weakest part of a sharp cutting edge, at the price of increased cutting forces. 
“Hard” chip control geometries guide the chips through a relatively acute angle to curl and break them immediately. These geometries can be effective with long-chipping materials but place extra load on the cutting edge. “Soft” chip control geometries put less load on the cutting edge, but generate longer chips. 
Good examples of differences in roughing geometries are the M5, M6, and MR7 designs from Seco. Listed basically in the order of their capability to handle increasing DOC and feed rate in roughing operations, the inserts are negative in overall geometry in that they have perpendicular flank faces and are engineered for two-sided use. 
Seco M5 Roughing Geometry
The M5 geometry combines high edge strength with comparatively low cutting forces. At the insert nose, the tools have a 0.30 mm wide, 5˚ positive T-land followed by a 20˚ transition area to the insert’s rake face. The rest of the cutting edge has a 1˚ negative chamfer preceding a 0.31 mm-wide, 5˚-positive T-land before an 18˚ transition to the rake face. The chamfer boosts edge strength, and an open chip groove facilitates the flow of ductile long-chipping alloys. The M5 geometry suits a variety of workpiece materials including steel, stainless steel, cast iron and superalloys.
The MR7 geometry, in comparison, is engineered to handle heavy interruptions and tough applications such as roughing forgings/castings with skin and oxide scale in steel, cast iron, and stainless steel. To maximize edge strength, the tools have a wider 0.35 mm, 0˚ T-land at both the nose and the cutting edge with a shallower, 17˚ transition to the insert’s rake face. While the wider, flat T-land and shallower transition angle provide increased strength, they also generate higher cutting forces because the tool overall is less sharp. Together, the geometry features provide strength comparable to that of single-sided inserts for heavy roughing operations.
A combination of geometric features places the performance of the new M6 geometry between, and overlapping, that of the M5 and MR7 tools. The 4˚-positive T-land at the nose is 0.25mm wide, not as wide as the M5 or MR7 tools, and there is a 19˚ transition to the rake face. The 0.30 mm-wide, 0˚ T-land on the cutting edge is followed by a 21˚ transition to the tool’s rake face. This chip-control configuration combines strength and a wide chip control groove to expedite flow of the cut material. 
Although the three geometries differ in details and areas of application, they share an engineering strategy aimed at protecting the cutting edge, minimizing cutting forces and maximizing efficiency of chip evacuation. The tools illustrate how tradeoffs and combinations of geometric features can positively affect the final results of roughing operations. 
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. 

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.