Square shoulder milling, a universal solution

By Niraj M Wanikar, Chief Editor, CNCTimes.com, 2014-02-20 08:52:22

By Patrick De Vos

Square shoulder milling is a commonly used milling operation using a cutter with a 90° entering angle. With square shoulder milling, it is possible to have a universal solution for different milling applications. These include contouring, ramping, circular, helical and trochoidal interpolation milling, copy milling, plunging and slotting.

A square shoulder milling cutter has to offer a number of bene?ts, namely economy, ?exibility and reliability. We know that the customers are seeking economical, high performance solutions that increase productivity and that cost per component is a key element. With square shoulder milling, they want to achieve true 90° and ?at walls. Sometimes they use an 88° cutter with multi-edge inserts for reasons of economy, but then one more operation is needed in order to get the 90° square shoulder.

Rejected components cost money. Some competitor multiple-edge tools are noisy with high vibration levels, and the result is often poorly ?nished components. A square shoulder milling cutter can be used for several different milling operations. Our customers want a reliable, cost-effective, universal solution for all general milling applications and most importantly, an experienced and knowledgeable partner. They sometimes lack detailed information and knowledge of the key parameters of milling operations, i.e. average chip thickness, compensation factors for feed rates, cutting speeds, the radial engagement ratio and axial depth of cut.

The 90° entering angle of a square shoulder milling cutter presents us with some speci?c considerations. A 90° entering angle implies increased impact forces. If not compensated for by carefully selected carbide grades and edge geometry, these impact forces could result in broken edges and vibrations.

A maximum of 30% of the diameter of a square shoulder cutter should be in cut (radial cutting depth). When using a square shoulder cutter for slotting, the cutter is used over its full width. This could result in vibrations as well as chip evacuation problems. Careful consideration also has to be given to the number of teeth, axial depth of cut and feed rate.

The direction of the feed force should be comprehensive and versatile solution for the full range of square shoulder milling requirements. From Nano Turbo, with 5 mm depth of cut, to Power Turbo with 17 mm, Seco has a Turbo solution for every operation in every material. All Turbo cutters deliver free-cutting, next generation performance in square shoulder operations. They also have the capability to perform ramping, slotting, contouring, plunging, pocket milling and can handle circular, helical and tro choidal interpolation.

In both mass production and batch production, it is important to know how the component is produced. If the machining conditions are good and stable, depth of cut is not too high, and materials like steel (SMG 2-4), cast iron or stainless steel (SMG 8) are to be machined, the Square 6 range is an interesting alternative. It offers a multi- edge solution that improves production/economy.

Square 6, with its six cutting edges per insert, offers a low cost per cutting edge. The positive cutting edge on the insert makes the cutting rake angle positive, ensuring high performance. By reducing operating costs and improving performance, Square 6 can boost productivity and increase production economy.

Left: Application areas for the Turbo and Square 6 milling cutters. Above: Square shoulder and slot milling are comparable operations but both deserve careful consideration when selecting the correct milling cutter and cutting conditions as the load on the cutting edge is completely different and this needs to be compensated for.

The Turbo range offers performance. Application areas can include deep pocket milling and slotting in soft and sticky materials. Unstable cutting conditions can also be handled. Depths of cut can be high (max. 17 mm) and other strategies, like ramping and helical interpolation are also possible. Square 6 offers economy. Applications are mainly contouring in cast iron and steel. Cutting conditions must be stable and depths of cut are medium (maximum 7.5 mm). Face milling and plunging are possible.

CONSIDERATIONS

Square shoulder milling, as face milling, is a basic milling operation. In face milling, the operation allows for most optimised milling cutter concepts. In square shoulder milling, the 90° entering angle is a limiting element. A well selected strategy and cutter, together with correctly selected cutting conditions have to compensate for that. But in doing so, it is possible to perform square shoulder milling operations with high production economy.

The optimum combination of cutting conditions (high security and productivity and low production costs) is big depths of cut and feeds combined with moderate cutting speeds. When the machine is overloaded, the cutting depth must be reduced. This is preferable to reducing the feed. Radial depth of cut should be limited to 30% of the cutter diameter (for security). Axial depth of cut can be equal to the cutting edge length (if security is important it’s wise to limit to 80%) in case of a radial depth of cut smaller than 30% of the cutter diameter. When the radial depth of cut is more than 30%, the axial depth of cut should be limited to 30% of the cutting edge length.

If depths of cut and/or feeds are limited due to operational constraints (dimensions of component, power of machine tool, stability of component or cutting tool), increasing the cutting speed can be used in the search for productivity. Use the average chip thickness and speed factors to optimise the opera- tion, especially when radial depth of cut is small compared with the cutter diameter (less than 30%).

Cutter and cutting edge (carbide grade, geometry and dimensions) selection should be done in line with the selected combination of cutting data. Clamp the cutter as short as possible and as tightly as possible and always select the largest possible cutter diameter that is compatible with the task.

Close pitch cutters have less room for chip removal, but are more stable and allow for higher table feeds. When radial depth of cut is smaller than 30% of the cutter diameter, the best selection is a close pitch cutter. For slotting operations a coarse or normal pitch cutter is the best selection.

If the surface ?nish is less important, the table feed should be as high as possible. High feed is required in order to avoid surface hardening of the material, especially when milling stainless steels and super alloys and titanium alloys). However, the maximum feed per tooth (point geometry) must not be exceeded.

Patrick De Vos is Seco’s Chief Technical Education Manager. Born in Belgium in 1959, he has a Masters degree in Mechanical and Electrical Engineering (specialised in Production Technology). From 1981 to 1983, he was post graduate lecturer and researcher (research subject optimizing strategies for metal cutting processes and production economics) at the university. From 1983 till 2006, he was employed by Seco Tools Benelux in several technical, commercial, marketing and management positions and was member of several international council groups in the company. Since 2006, he is Corporate Technical Education Manager for Seco Tools AB. In the last 30 years, he has trained more than 50,000 people in more than 55 countries worldwide. He has also authored a book, “Metal Cutting, theories in practice”

He can be contacted on: patrick.de.vos@secotools.com

• Follow @CNCTimes