Views: 18 Author: Site Editor Publish Time: 2018-07-11 Origin: www.fuchun-casting.com
When choosing the tool angle, we need to consider the influence of many factors, such as workpiece material, tool material, processing properties (rough, finishing) and so on, we must choose reasonably according to specific conditions. Generally speaking, the tool angle refers to the marking angle used in manufacturing and measuring. In practical work, the actual working angle and the marking angle are different, but the difference is usually very small, because of the different installation position of the tool and the change of cutting direction.
Tool materials must be of high temperature hardness and wear resistance, necessary bending strength, impact toughness and chemical inertia, good workmanship (cutting, forging and heat treatment, etc.) and not easily deformed.
Usually, when the material is of high hardness, the wear resistance is also high, and the impact toughness is high when the bending strength is high. However, the higher the hardness, the lower the flexural strength and impact toughness. Because of its high bending strength, impact toughness and good machinability, high speed steel is still the most widely used tool material in modern times, followed by cemented carbide.
Pcbn(Polycrystalline cubic boron nitride)is suitable for cutting hardened steel and hard cast iron with high hardness; polycrystalline diamond is suitable for cutting iron-free metals, and alloys, plastics and FRP, etc. Carbon tool steel and alloy tool steel are now used only for tools such as files, plate teeth and taps.
The cemented carbide indexable inserts have been coated with TiC, TiN, Alumina or composite hard layers by chemical vapor deposition (CVD). The developing physical vapor deposition method can be used not only for cemented carbide tools, but also for high speed steel tools, such as drills, hobs, taps and milling cutters. Hard coatings act as barriers to chemical diffusion and heat conduction, slowing down tool wear during cutting, and prolonging the life of coated inserts by more than 1-3 times compared with uncoated inserts.
Due to the high temperature, high pressure, high speed, and working in corrosive fluid medium, more and more difficult-to-machine materials are used, the level of automation in cutting and the requirement of machining accuracy are higher and higher. In order to adapt to this situation, the development direction of cutting tools will be the development and application of new tool materials; further development of tool vapor deposition coating technology, deposition of higher hardness coating on high toughness and high strength substrate, better solve the contradiction between tool material hardness and strength; further development of indexable tool structure; Improve the manufacturing accuracy of cutting tools, reduce the difference of product quality, and optimize the use of cutting tools.
According to the cutting motion mode and the corresponding blade shape, the cutting tool can be divided into three types. General-purpose cutting tools, such as turning tools, planers, milling cutters (excluding formed turning tools, forming planers and forming milling cutters), boring tools, drills, reamers and saws; forming tools, such as cutting edges with the same or close to the section of the workpiece being processed, such as forming lathes, forming planers, forming milling cutters, drawing cutters, etc. Cutters, bevel reamers and various thread cutting tools, etc. Generating cutters are used to process the tooth surface of gears or similar workpieces by generating methods, such as hobs, shapers, shavers, bevel gear planers and bevel gear cutters.
The structure of various knives is made up of clamping part and working part. The clamping part and working part of the integral structure cutter are all made on the cutter body; the working part of the toothed structure cutter (cutter tooth or blade) is mounted on the cutter body.
The clamping part of the cutter has two kinds: the hole and the handle. The tool with hole is mounted on the spindle or mandrel of the machine tool by the inner hole, and the torque is transmitted by the axial key or the end face key, such as cylindrical milling cutter, sleeve face milling cutter, etc.
The tool with handle usually has three kinds: rectangular handle, cylindrical handle and conical handle. Turning tool, planer, etc. are generally rectangular shank; taper shank * bears axial thrust and transfers torque with the aid of friction; cylindrical shank is generally suitable for smaller twist drills, end milling cutters and other cutters, cutting with the aid of friction generated by clamping torque transmission. Many tool shanks with shanks are made of low alloy steel, while the working parts are butt welded with high speed steel.
The working part of the cutter is the part that produces and processes chips, including the knife edge, the structure that breaks or curls the chips, the space for discharging or storing the chips, the channel of cutting fluid and other structural elements.
Some cutting tools work part is the cutting part, such as turning tool, planer, boring and milling cutter, etc. Some cutting tools work part includes cutting part and calibration part, such as drill, reamer, inner surface broach and tap. The function of the cutting part is to cut the chip with the cutting edge, and the function of the calibration part is to trim the machined surface and guide the cutting tool.
The working parts of the cutting tool are of three types: the integral type, the welding type and the mechanical clamping type. The overall structure is to make cutting edges on the blade body; the welding structure is to braze the blade to the steel blade body; the mechanical clamping structure has two kinds, one is to clamp the blade on the blade body, the other is to clamp the brazed blade on the blade body. Cemented carbide tools are generally made of welding structure or mechanical clamping structure; porcelain tools are mechanical clamping structure.
This is where a batch of steel meets more than one specification or grade. It is a way of allowing melting shops to produce stainless steel more efficiently by restricting the number of different types of steel. The chemical composition and mechanical properties of the steel can meet more than one grade within the same standard or across a number of standards. This also allows stockholders to minimise stock levels.
For example, it is common for 1.4401 and 1.4404 (316 and 316L) to be dual certified - that is the carbon content is less than 0.030%. Steel certified to both European and US standards is also common.
There are many different types of surface finish on stainless steel. Some of these originate from the mill but many are applied later during processing, for example polished, brushed, blasted, etched and coloured finishes.
The importance of surface finish in determining the corrosion resistance of the stainless steel surface cannot be overemphasised. A rough surface finish can effectively lower the corrosion resistance to that of a lower grade of stainless steel.
Various types of stainless steel are used across the whole temperature range from ambient to 1100 deg C. The choice of grade depends on several factors:
In the European standards, a distinction is made between stainless steels and heat-resisting steels. However, this distinction is often blurred and it is useful to consider them as one range of steels.
Increasing amounts of Chromium and silicon impart greater oxidation resistance. Increasing amounts of Nickel impart greater carburisation resistance.
Austenitic stainless steels are extensively used for service down to as low as liquid helium temperature (-269 deg C). This is largely due to the lack of a clearly defined transition from ductile to brittle fracture in impact toughness testing.
Toughness is measured by impacting a small sample with a swinging hammer. The distance which the hammer swings after impact is a measure of the toughness. The shorter the distance, the tougher the steel as the energy of the hammer is absorbed by the sample. Toughness is measured in Joules (J). Minimum values of toughness are specified for different applications. A value of 40 J is regarded as reasonable for most service conditions.
Steels with ferritic or martensitic structures show a sudden change from ductile (safe) to brittle (unsafe) fracture over a small temperature difference. Even the best of these steels show this behaviour at temperatures higher than -100 deg C and in many cases only just below zero.
In contrast austenitic steels only show a gradual fall in the impact toughness value and are still well above 100 J at -196 deg C.
Another factor in affecting the choice of steel at low temperature is the ability to resist transformation from austenite to martensite.
It is commonly stated that “stainless steel is non-magnetic”. This is not strictly true and the real situation is rather more complicated. The degree of magnetic response or magnetic permeability is derived from the microstructure of the steel. A totally non-magnetic material has a relative magnetic permeability of 1. Austenitic structures are totally non-magnetic and so a 100% austenitic stainless steel would have a permeability of 1. In practice this is not achieved. There is always a small amount of ferrite and/or martensite in the steel and so permeability values are always above 1. Typical values for standard austenitic stainless steels can be in the order of 1.05 – 1.1.
It is possible for the magnetic permeability of austenitic steels to be changed during processing. For example, cold work and welding are liable to increase the amount of martensite and ferrite respectively in the steel. A familiar example is in a stainless steel sink where the flat drainer has little magnetic response whereas the pressed bowl has a higher response due to the formation of martensite particularly in the corners.
In practical terms, austenitic stainless steels are used for “non-magnetic” applications, for example magnetic resonance imaging (MRI). In these cases, it is often necessary to agree a maximum magnetic permeability between customer and supplier. It can be as low as 1.004.
Martensitic, ferritic, duplex and precipitation hardening steels are magnetic.