Milling is ... Milling tool and procedure description

Milling is a surface treatment method based on the alternate operation of the cutter teeth. There is a huge variety of tools, depending on their functionality, processed materials, characteristics of the parts being manufactured.

Process Features

The milling process, like all existing methods of processing materials by cutting, is based on the main and auxiliary movements. The first is the rotation of the instrument, and the second is feeding it to the working stroke.

Surface milling is usually performed in several consecutive stages:

• Draft - the initial removal of bulk chips to design the necessary general profile, has a low accuracy class. The processing allowance (thickness of the layer to be taken, taking into account all additional factors) can be from 3 to 7 mm, depending on the material of the workpiece.
• The poluchistovoe is the second stage of stripping of the planned milling object, the shavings are smaller, the accuracy of the work is increased and reaches the 4-6th grade.
• Clean - thorough finishing provides high quality of the surface and contours, high accuracy (6-8th grades). The allowance should be 0.5-1 mm.

The implementation of each of the processing stages has its own distinctive requirements for working tools in terms of the nature of their design, material, quantity and quality of the cutting edges. For example, a milling device having a roughing function is characterized by large teeth, while a finishing mill has a fine multi-toothed structure.

Types of milling operations

A wide range of existing mills allows processing materials of varying complexity and configuration, from any angle. All kinds of processes can be divided into several groups:

1. Working with flat surfaces. A roughing and finishing of the non-removable planes having a horizontal, vertical or inclined position is made.
2. Processing of bulk shaped workpieces and parts. A volumetric sweep is performed, giving objects a certain shape.
3. Separation. The parts are divided into several parts, cutting off excess material.
4. Modular finishing. It is based on the formation of the necessary profile of the existing billet, the design of grooves, grooves, teeth, shaped depressions.

For each individual method, a separate milling tool is most often used. Blanks of special complexity are processed using a set of cutters. Thus, milling of wide surfaces is carried out using a set of tools that have multidirectional helical teeth in order to reduce the axial forces.

Varieties of milling cutters depending on the purpose

Several classification characteristics are known, according to which all known milling devices are distributed: according to the material, by the type of knives, in shape, depending on the direction of the working stroke. The main parameter is still the appointment.

1. Cylindrical - machining by milling all horizontal and vertical planes.
2. Edge - finish all planes in any position.
3. End - work of different complexity, the possibility of flat, shaped, modular, artistic milling.
4. Angle and shaped - removing chips from the side surfaces of blanks, profile objects, cleaning conical depressions.
5. Cutting, cutting, spline - separation, cutting teeth on workpieces, forming grooves.

The same type of tools can have differences in diameter, number of knives and their features.

Structural differences of milling cutters

The characteristics of the knives and ways of fixing them are important parameters that determine the purpose of the cutter, in particular, the quality of the treatment.

1. Whole. They are made of tool alloy and high-speed steels. Most often - cylindrical, disk, spline, cutting milling cutters.
2. Compound. There are two options. In the first shank of structural steel is welded to the cutting head - from tool, high-speed steel, less often - from hard alloy. In the second - high-speed or hard-alloy knives are soldered to the body of the device. They are used in end and end cutters.
3. National teams. Knives, most often carbide-tipped, are mechanically connected to the main body.

Integral cutters have a larger number of teeth, which allows for more precise machining. The same possibility is available for composite tools consisting of a carbide-tipped head and a structural shank. Their disadvantage is a high degree of wear. Most often this equipment is used in semi-finishing and finishing stages of chip removal.

Prefabricated cutters are characterized by a high degree of resistance to wear, strength, hardness and sharpness of knives, simplicity of turning and dismantling. However, quantitatively, in relation to one head, they lose considerably. These are mainly involved in roughing.

Machine tools

Required milling operations determine the necessary equipment, including the type of machine on which they will be produced.

Horizontal-milling machines are designed for processing horizontal planes and shaped surfaces, manufacturing gears, processing of certain profile objects. Their device determines the horizontal fastening of the tool, most often a cylindrical, disk or end mill.

The same types of work, but with distinctive features, allows you to perform a vertical machine for milling. A special feature is the vertical fastening of the tool and, consequently, the preferential use of end, end and modular cutters.

Universal milling machines have additional devices for turning the table in 3 planes, which allows working with horizontal, vertical and shaped surfaces.

In the serial production of parts having the same profile, the copying milling units are used, which allow repeating patterns or depressions on the plane with increased accuracy.

The equipment of the future is CNC machines. They ensure the execution of a programmed set of actions, mainly for artistic milling or non-serial production of parts. End, end and modular cutters with different number of cutting edges are used.

Milling is the work on a special cutting machine that provides the working stroke of the tool and the feed of the workpiece.

Effect of cutting modes on the results of work

The results determine not only rationally selected equipment. Their quality depends on how well the milling modes are selected.

1. It is necessary to accurately determine the required diameter of the mill, its design, material, the number of teeth, to establish the relationship between the dimensions of the tool and the thickness of the layer to be removed. It is important for a professional to strive to ensure that the required thickness of metal is removed in a single pass.
2. The tool size determines the speed of its rotation and, accordingly, the speed of work. They are set on the machine by setting the spindle rotation frequency - the fundamental axis for securing the cutter. Too slow or too fast the main working movements of the cutting head result in poor processing quality.
3. An important cutting mode is feed. There is a division in this whole concept. Initially, the cutter feeds one tooth. It is selected according to the directories in accordance with the tool used and the type of working surface. After that, the feed is determined per revolution and per minute, respectively.

The calculation of milling is made on the basis of information about the permissible capacities of the equipment, the type of surface to be treated and the tools selected. There are nominal tables filled with the required and control values. Rational selection and calculation of the main parameters of the work determines its quality.

Accompanying phenomena

Milling is the process of chip removal, which is characterized by increased thermal effects and mechanical influences, which can adversely affect the capabilities of tools and finishes. Some phenomena that affect the results of milling operations:

1. Filling and shrinkage of chips. Slipping of metal on the cutting surface, pressing it spoils the finishing process and the knives themselves. This is more relevant for soft materials.
2. Hardened. Increasing the hardness, reducing the strength and plasticity of the surface layer of the workpiece is a side effect of plastic deformation, which is removed by subsequent heat treatment.
3. Friction, increased heat in the working area, vibration - factors that reduce the efficiency of the cutter.

To prevent side effects, it is necessary to use additional technologies and tools.

Protection of workpieces and tools

To avoid or minimize the negative effects of cutting processes on the tool and the material being processed, the following techniques are used:

1. The use of cooling and lubricating substances and liquids, supplying them directly to the milling zone reduces friction, the formation of work hardening, sticking of chips, and preserves the long service life of the blades.
2. The provided chip removal system eliminates the effect of shrinkage, and a rational choice of cutting regimes for especially soft metals prevents its sticking.
3. Vibration can be reduced by selecting the front and rear corners of the cutting edges, the required speeds and the use of vibration dampers.

Milling with minimal side processes requires high professionalism and experience.

Milling is a complex complex process of finishing a variety of surfaces, the success of which is determined by a rational choice of equipment, tools, cutting modes, lubricants and coolants and additional devices that improve the quality of work.