Turning is a frequently occurring metal cutting operation in manufacturing. It is a relatively straightforward process, in most cases performed with a single-edge cutting tool. How, then, can turning be improved to the extent that it has any noticeable effect on productivity? With costs being central to the issue of productivity, surely the lowest tool costs in the form of the cheapest inserts and largest discounts will have the best effect? The problem is: a machine tool will only perform as good as the cutting tools with which it is equipped. Furthermore, today, it is more often the case that a machine shop, even company, will not perform better than the tooling and services with which it is being supplied. The next few paragraphs indicate the typical productivity factors for turning operations and how they are affected by new means and methods
Doing more machining in the same production time
The number of parts per hour is probably the most common manufacturing requirement and gauge of productivity. For the subcontractor, this is what decides if he will get the job done in time and how large the profit margin will be. For the mass-production company, it is volume and competitiveness. If output is the critical factor, it is ways of increasing the speed of machining that will count. The main influence on the time it takes to perform a turning operation is the feed: the length turned per minute or revolution of the part. If the feed can be doubled, the cutting time is halved and almost twice as many components are made in the same time. There are turning inserts available with a modified nose radius that permits very high feeds instead of conventional rates, while providing the same surface finish, during a similar tool-life. Wiper inserts are innovative high-productivity inserts for semi-finish and finish turning that are being used increasingly by all types of industry. These are inserts where the nose-radius and cutting geometry have been modified. Improvements in machining are put in place simply by changing from one indexable insert to another and applying it correctly.
Maintaining production security with predictable tool-life
Breakdowns sabotage productivity. Machine stoppages are unproductive time, during which no parts are being machined and the money invested in production resources is seeing no payback. Unfortunately, machine downtime due to tool or equipment breakdown unnecessarily represents an excessively large proportion of non-machining time. An increasingly important productivity factor for machine shop is to be sure of producing a set amount of parts during the available production time. For many, to be able to rely on a batch being completed, within the set quality parameters and on time, is top priority. Dedicated grades last longer and make machining in specific workpiece materials safer. Dedicated insert geometries provide the right cutting action and chipbreaking. Basic, but essential to safe machining P-line, M-line and K-line inserts have been developed for high-security, high-performance turning operations in modern production environments, capable of wet and dry machining. Sharp cutting edges, smooth chip formation, combined with balanced wear resistance and toughness for the cutting edge strength needed throughout the insert application areas provide a basis for accurate predictability of tool-life. New-type toolholders such as the T-Max PRC toolholder provide high reliability in insert retention by giving cutting edges uncompromising stability.
Quality consistency - without continuous supervision and adjustments
Maintaining quality levels go hand in hand with production security. Having predictable tool-life in finish turning is the same as being able to machine to close tolerances and low Ra-values while the insert is in the toolholder. The most suitable steel insert-grade applied with right cutting speed determines the tool-life, where a coated cemented carbide or cermet may compete for selection depending upon operational factors. The positive, sharp cutting edges of a stainless steel insert geometry combined with the right dedicated GC2000 insert grade, developed to withstand the higher cutting temperatures, minimise the typical material-related risks during machining. Burrs, smearing material on cutting edges and deformation hardening on the workpiece surface are typical quality risks.
Cast-iron inserts minimise cutting forces through positive cutting geometries for finishing, providing added capability for keeping within close tolerances and not deflecting thin-walled parts during machining. GC3000 grades have high degree of abrasive wear resistance thanks to thick coatings of ceramic-hard aluminium oxide. Placed in the RC-type toolholder, these inserts make a formidable cutting tool for maintaining quality in any conditions. Modern cermet and ceramic insert grades complement these areas in providing levels of consistency of high quality in machining in new applications.
Selecting cutting tools more easily
One of the straightest paths to high productivity is choosing the right tool and applying it correctly. But there are thousands of different tools and inserts, a lot of which could be seen to be candidates for the operations at hand. Picking the tool and making the programme for a component to be turned from a drawing can be demanding without experience and guidance. And the consequences of the wrong or outdated choice of tool type, insert shape, geometry, grade, nose radius, cutting speed, feed, cutting depth, etc always have an important impact on productivity. The CoroKey concept includes a carefully selected range of tools and first choice options with variation according to machining factors. Workpiece materials vary considerably in machining characteristics and need dedicated insert geometries and grades to perform to sufficiently high standards. Steel (P), stainless steel (M) and cast-iron (K) are by far the most commonly used materials and as such a good base on which to establish the family of inserts needed. The type of application, such as finishing, medium or rough turning leads to a choice of three inserts, as regards geometry and grade. The assessed machining conditions, ranging from good, normal and difficult, will pinpoint the best insert choice for that operation.
Minimising tool inventory - and having the right tool when needed
Tools in stock represent tie-up capital. Having to choose between a lot of different tools in the crib takes time. Chasing tools in the machine shop is unproductive time as it is often done by the operator of the machine. It does not take long for the contents of a tool crib to grow and for many items to become unnecessary. Tools and inserts become outdated or operations change and soon a number of shelf-warmers are established. At the same time, it is vital for a machine shop to have the right tools at hand when they are needed, often double up for security. Rightly planned, the inventory will make use of todays quick tool delivery services. Most machine shops should be able to make use of the Direct Distribution of Sandvik Coromant, where a standard tool ordered by a certain time one day, will be delivered the next morning. Productivity improvement and rationalisation programmes, carried out with machine shops by Sandvik Coromant sales engineers and specialist and the CoroKey concept of selecting tools are two means by which tools inventory and selection are improved. Tool management products such as Auto Tas can complement further. Modern P, M, K inserts lend themselves to far-reaching rationalisation with their balance of dedication and versatility.
Productivity solutions - for predicting performance and results in turning
In todays machine shops, productivity factors usually go hand in hand and many look towards achieving as much as possible in respect to all of them. Continual lowering of production costs is a priority for maintaining competitiveness whatever the type of manufacturing by making sure the machine shop has access to the best tools and services, one is making sure of maximising the manufacturing potential through:
1. Output and quality being maximised,
2. Turning performance and security being optimised,
3. Tools selected and applied being fewer and better and
4. Tool inventory and handling being minimised.
Performance and results in turning can be improved over-night through modern means such as:
· P, M and K inserts, dedicated high performance to suit operations and conditions.
· Wiper inserts, high productivity finishing inserts and secure RC-toolholders, with Coromant Capto tooling, where needed
· CoroKey, selection and application concept supported by the services of Sandvik Coromant Sales engineers and distributors.