Insight Into Smoother Boring Processes

By Mike Smith, Product Manager – Reaming and EPB

Boring increases the inside diameter of a drilled or cast hole. Through boring, which includes roughing and finishing operations, you’re able to bring your hole to the desired size and finish as well as achieve hole straightness and concentricity. However, to ensure your boring process goes as smooth as possible, you need to have the right tools for your specific application.  

Typically, boring tools consist of a holder, adapter and cutting unit such as a cartridge or slide. Although, when it comes to roughing versus finishing operations, there are certain boring head characteristics you must take into consideration to achieve the best results.     

A rough boring head, also known as a twin bore, is going to involve two or more inserts (cutting teeth) to quickly remove a lot of material. Such a design proves to work best in shorter-reach, stable applications and those with larger hole diameters. A finish boring head, on the other hand, has a single tooth that removes less material, but provides a better finish as well as reduces cutting forces in longer-reach applications.

You’ll also find there are several different boring head styles on the market to accommodate different hole diameters. This includes cassette style boring heads for hole diameters that are generally over 0.700”. It is a style that allows you to switch between different grades and different chip breaker inserts, depending on your cutting material.

For smaller size diameters, it’s best to use a boring bar style with indexable inserts, similar to what’s used in turning operations. And for really small bores -- down to 0.012" -- non-indexable solid carbide boring bars with ground tips should be used. Keep in mind though, that with such a style of boring bar, it's possible to only go as deep as the bar is sticking out of the boring head. And the smaller the diameter boring bar, the less the tool will extend beyond the head. For example, when boring a 0.012" diameter hole, the boring bar used will not stick out very far, and it's safe to say that the maximum depth capability will be well below 0.047".      

Because vibration is often a problem in boring operations, there are balanceable style boring heads that work well in high RPM and long-reach applications. There are also special vibration dampening systems, such as our Steadyline products, you can use behind the boring head to help reduce the vibrations. These dampening systems work by keeping any vibrations from reaching the machine’s spindle. Dampers prove really effective in large diameter bores that reach out between six and 10 times deep.   

If you’re not using a dampening system and reaching out a long ways, you can experience unwanted chatter due to increased cutting forces. After all, when you put a lot of pressure on something, it tends to flex and create a significant amount of chatter. A twin-style boring head, because it relies on strong cutting forces to do its job, can create chatter in long-reach applications. At which point, you’re probably going to get better results with a single-tooth boring head because it requires less cutting forces.

For deep boring applications (like crank bores), it is a good idea to have a rotary bushing or some type of guide on your tool to stabilize it, preventing the unwanted pushing that occurs when cutting forces become so great.

Lastly, you must pay attention to the interface between your tool and spindle. When trying to determine your boring length-to-diameter ratio, do not factor in the maximum diameter of your boring head, look at the diameter of the shank of the modular connection behind the head.  

Because this is only a snapshot into creating a smoother boring process, please feel free to contact me with any questions you have. Today’s boring heads and inserts are better than ever and there are a lot to choose from, which can be mind numbing. That’s why when you work with Seco, you can rest assured we’ll match you up with the right boring solution for your unique application.

About the Author

Mike is Seco's product manager for reaming 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.

Tips for Tackling the Complexities of Cast Iron Machining

By Todd Miller, Manager, Rotating Products

Today, cast irons are more advanced than they were 20 years ago. They are lighter, stronger and more affordable. In fact, cast iron can be an excellent alternative to steel as you face constant pressures to cut costs. However, several variables and challenges exist when trying to determine the right tooling for your cast iron machining operations. 

First of all, it’s important to understand the different types of cast iron and realize that each one has a different level of strength, cost and machinability. And that for each of these types, there are also several grades with widely different mechanical properties.

TK Insert Grades for Cast Iron Turning

You must also consider the complexities of cast iron metallurgy. The casting process generates microstructures with properties that vary between a part’s surface and its internal body. Cast iron quality also varies from one foundry to the next.  

Here are some of the types of modern cast irons from which to choose:

• Grey cast iron, among the most common and least expensive of all the types, contains carbides in the form of lamellar graphite particles, which gives it excellent vibration damping properties and makes it ideal choice for engine components. It also has the highest level of machinability when compared to other types. 

• Vermicular cast iron, also known as compacted graphite iron, offers greater strength and lower weight when compared to grey cast iron. Because vermicular cast iron is suitable for components subjected to both mechanical and thermal stress, automotive manufacturers are using it more in the production of cylinder heads and brake parts.  

• Silicon alloyed ferritic ductile cast iron is ideal for the production of wheel hubs and axles. Given its high degree of machinability and excellent mechanical properties, the material is becoming increasingly popular within the automotive industry.

• Nodular ductile cast iron, which consists of spheroid nodular graphite particles in ferrite and/or pearlite matrix, possesses high ductility, good fatigue strength, superior wear resistance and a high modulus of elasticity, and hence have been the choice of material for transmission housings and wheel suspension parts within the automotive and heavy equipment industries.

• Austempered ductile iron offers high strength, high fatigue strength, good wear resistance and high values of elongation to fracture, making it a very competitive material in relation to many cast and forged steels. Because of great strength and elastic properties, austempered ductile iron has the lowest level of machinability when compared to the other types of cast iron mentioned here.

MK2050 Insert Grade for Cast Iron Milling

Cutting tool companies, including Seco, are continuously developing new turning and milling products to help overcome the variables and challenges of working with cast iron materials. But this can be a feat in itself because every material, manufacturer and application around the world is unique. However, here are some important tips you should always keep in mind:

• Have your workpiece properties under the best possible control because variations can negatively impact total productivity, either directly or indirectly. When workpiece properties are unclear, you can look to tooling systems and cutting strategies to make up for any material quality shortfalls. The trick, however, is knowing what tools and strategies are the right fit for your application.

• In terms of turning cast iron, everything depends on your specific application. You must determine the number of operations necessary to accomplish your goals. If your workpiece properties are unknown, you may opt to include an extra finishing cut, which impacts product lead times. However, by applying the right tooling for the conditions and requirements of the component, you can reduce the number of operations. 

• When milling cast iron, there’s a lot more complexity involved when compared to turning the material. While the type of insert grade you use is important, it’s even more critical to look at the total cutting solution. You must consider – in addition to insert geometries and grades – cutter body types and the number of cutting edges as related to your component. Furthermore, heat and coolant are not ideal when milling cast iron.

• In terms of selecting the best type of cutter for cast iron milling, there is no real one-size-fits-all answer. But generally speaking, the type of milling cutter that seems to be making a lot of headway these days would be a negative cutter with inserts that have positive rake angles and in a grade that handles both wet and dry conditions.

• While one type of cutter may be able to successfully cut all the different types of cast irons that does not mean it can effectively machine every type of workpiece shape. You must think about the surface you need to cut, and ask yourself: Is it square in form or very long? Are the wall thicknesses thin or thick, weak or stable? And, how secure is workpiece clamping?

• You must consider your machine tool. When machining cast iron materials, there’s a higher dynamic load, so your machine tool must be highly robust as well as provide high power and high stability – all of which puts strain on the machine. However, in these instances, a negative cutter with the positive rake angle can help lower the power requirements of the machine tool and reduce forces on machine spindles as well.

But in the end, with so many variables to consider, if you want to increase the productivity and predictability of your cast iron machining efforts, the best action for you is to work closely with your cutting tool supplier.

About the Author

Todd is the manager of rotating products for NAFTA, responsible for solutions and applications involving face, square shoulder and disc milling. Todd and his team of product experts are dedicated to providing a consistent, high-level of support to Seco customers throughout the United States, Canada and Mexico. In his spare time, Todd likes to bowl and cheer on the University of Michigan football team.