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Seco provides manufacturers with cast iron solutions
Seco provides manufacturers with cast iron solutions
Seco provides manufacturers with cast iron solutions

Seco provides manufacturers with cast iron solutions

Added to MTDCNC by MTDCNC on 31 May 2013

According to Seco Tools (UK), manufacturers looking to improve quality, increase productivity and control costs need more than a superficial knowledge of cast iron in order to select cutting tools and insert geometries and grades best suited to meet their specific manufacturing requirements.

Cast iron is used in a wide variety of industries with the automotive and heavy equipment sectors being primary end users. Products such as brake disks (manufactured in large volumes) and large pumps (manufactured in short production runs) are just two examples of its application.

Cast iron types have come on leaps and bounds in recent years. They are lighter, stronger, have better wear resistance and are cheaper than ever before. They can be used for complex-shaped components, and have high machinability. (However, these ‘qualities’ and characteristics are not consistent between cast iron types, and the casting process itself generates micro-structures that differ between a casting’s surface and its internal body/core.

Take grey cast iron for example. Its machinability is affected by variations in the surface and by other near-surface conditions, such as mould residues or free ferrite (the latter of which is iron in its purest form).  Residues create harder and randomly-located zones, whilst free ferrite results in softer areas in the work-piece. Such variations create unpredictability when machining the material.

It is important therefore that manufacturers control all their means and methods of production - from casting to storage to machining - to ensure they have consistent work-piece batches that are large enough for their applications.

When work-piece properties are unclear, manufacturers can look to tooling systems and cutting strategies to make up for any material quality shortfalls. However, the trick is to know what tools and strategies work best.

Cutting tool companies are continuously developing new turning and milling solutions that can help overcome the variables and challenges manufacturers face when working with cast iron materials. But this can be a feat in itself because every material, manufacturer and application around the world is different. So whilst a cutting tool company may have product solutions with wide application potential for cast iron, much depends on an individual customers and the machining strategy or methods they employ.

While some manufacturers are willing to spend money on a wide variety of insert types and grades to optimise every application, others choose a limited selection of inserts and grades (an almost one size fits all approach) to make their processes easier to manage even if this means making some compromises on the results achieved.

Turning considerations

Consider insert grades for turning. In the past, cutting tool companies offered numerous insert grades. Today things are different with the emphasis being on creating fewer high-performance ‘universal’ solutions for a wide range of cast iron materials.

Some cutting tool companies are using advanced coating processes to create two- and three-grade strategies for customers. Seco Tools, for example, has a two-grade turning strategy made possible via its exclusive Duratomic® coating technology where the aluminum oxide coating is manipulated at the atomic level to create inserts with exceptional toughness that are abrasion resistant and that maintain surface integrity.

As far as actual cast iron turning operations are concerned, everything is application specific. Manufacturers need to determine the number of operations necessary to accomplish their objectives. If the work-piece properties are unknown, a manufacturer may opt to include an extra finishing cut, even though this will impact on product lead times. However, by applying the right tooling in the first instance manufacturers can reduce the number of machining operations required.

A more specific turning operation scenario might involve a manufacturer machining components within a just-in-time supply chain. In such situations, batches of as-cast work-pieces can sometimes be out of specification in terms of near-surface conditions, but must still be machined despite an increased cost per part caused by reduced tool life and lower productivity. In these instances a manufacturer must carefully decide between different types and grades of inserts, and this might include selecting either cemented carbide and/or polycrystalline cubic boron nitride (PCBN) tooling. However, if the foundry supplying the grey cast iron can provide a consistent quality level, manufacturers can achieve unbeatable productivity levels using PCBN tooling.

Milling considerations

When it comes to milling cast iron there is a lot more complexity involved. While the type of insert grade used is important, it is even more critical to look at the total cutting solution.

A manufacturer must also consider, in addition to insert geometries and grades, cutter body types and the number of cutting edges being used. as related to the component being machined.

Today’s cutting tool companies are trying to simplify the selection process by providing solutions that are easier to apply and that perform better for as many types of materials and applications as possible. For example, because heat and coolant are not ideal when machining cast iron, especially in milling operations cutting tool companies are creating high-performance grades for milling in both dry and wet conditions.
 
These companies are also looking to help manufacturers reduce machining times through cutting solutions that can effectively rough and finish in one pass.
 
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 most headway is a negative cutter with inserts that have positive rake angles and that are supplied in a grade that can handle both wet and dry machining.
 
By having a positive cutting rake angle in a negative cutter, manufacturers benefit in multiple ways (e.g. free and flexible cutting action as well as reduced power consumption and heat generation resulting in longer tool life and an increase in usable cutting edges)
 
For example, consider face milling an engine block with numerous cavities. When the cutter machines each cavity corner, a primary objective is to avoid chipping these cavity edges. If the manufacturer is using a worn cutter in conjunction with high cutting forces, there is an increased risk of chipping out sections of the work-piece material — whereas a negative cutter with a positive rake angle will help avoid this from occurring.
 
However, whilst one type of cutter may be able to successfully cut all different types of cast iron it doesn’t necessarily follow that it can effectively machine every work-piece shape. For that reason, cutting tool companies offer different shaped cutters, from square shoulder mills to face mills and everything in between. Manufacturers need to think about the surface being machined and ask themselves the following questions:

• Is it square in form or very long?
• Are the wall thicknesses thin or thick, weak or stable?
• How secure is the work-piece clamping?

 
Furthermore, manufacturers also need to consider the type of machine tool they are using in their operations. When machining cast iron there is a higher dynamic load involved therefore machine tools must be robust as well as being powerful and stable.  (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).
 
With so many variables to consider it’s not surprising that manufacturers, looking to increase productivity and achieve predictability in results when machining cast iron, are increasingly turning to cutting tool suppliers to help create and deliver be-spoke machining solutions.
 
Seco, through the experience and expertise of its engineers and its ability to work in partnership with its customers to conceptualise, design and manufacture custom tools, is a natural choice for manufacturers looking to improve their performance when machining cast iron.


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