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High stock removal is a technological process with the goal of removing large amounts of material. The quantity of material which can be removed by a specific process depends on the material properties and the machining tool used.
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High stock removal is a technological process with the goal of removing large amounts of material. The quantity of material which can be removed by a specific process depends on the material properties and the machining tool used.
The stock removal rate is largely a function of the material's properties. This is expressed as the machinability of a material: the ease or difficulty of machining a particular material. The machinability of materials varies greatly; for instance, aluminium and magnesium have high machinability compared to titanium and other special metals.
One way of quantifying the machinability of a material is to measure specific energy (e): this is the amount of energy required to cut a given volume of work material (kWh/mm3), and varies with material properties.
New materials are continuously developed to address the extreme demands of market segments such as petrochemical and aerospace. Metallurgical advances have produced a wide range of high-performance materials (e.g. titanium and high-nickel alloys), but a consequence of their attractive properties is often that they are difficult to machine.
The specific cutting energy needed for ‘difficult to machine’ materials can be extremely high. Especially in high stock removal applications, there are problems with thermal load in the work material. An increase of the work material temperature can lead to deterioration of the work material surface integrity, resulting in metallurgical damages like micro-cracks, residual stresses and work hardening. Excessive heat also dramatically shortens tool life.
The energy required to remove large amounts of material depends on the properties of the working material (specific energy) as well as the technological process used.
Several technologies are capable of removing substantial amounts of material. Among them are: sawing, turning, broaching, milling and grinding. Turning and milling are the most popular machining technologies; turning is mainly used for round products (though a specialized variant called whirling can modulate the turning axis to produce non-round shapes), whereas milling has a broad range of applications. Certain ‘difficult to machine’ materials like titanium, stainless steels, and exotic high-nickel alloys can be challenging to process when high stock removal is the goal, due to local heat generation at the cutting edge and the difficulty in removing it. These challenges can be mitigated, however, by strategies such as high-volume flood coolant, specialized cutting tool geometries, optimized speed and feed settings, and tool coatings like AlTiCN which tend to divert heat into the chip, away from the cutting tool.
Traditionally bonded abrasives are used for stock removal. To remove substantial amounts of material in a grinding process, vertical segment grinders are used. These machines work with a rotating disc with abrasive segments, against which the work material is pressed with the aid of a rotating or reciprocating table. These technologies require significantly greater power than other grinding methods, up to 450 hp (340 kW). Some major manufactures of these machines are Blanchard, Mattison, Göckel and Reform.
Grinding with coated abrasives has recently become a viable alternative for high stock removal through developments in machine tool and grinding belt technology.
Belt grinding with coated abrasives can be an attractive process because the large surface area of the recirculating belt tends to carry away heat and prevent local hot spots. The productivity of this technology is, in many cases, three times that of rotary or reciprocating vertical grinders. [ citation needed ] As a result, belt grinding is replacing traditional grinding technologies in the field of the specialty metal processing. [ citation needed ]
Metalworking is the process of shaping and reshaping metals to create useful objects, parts, assemblies, and large scale structures. As a term it covers a wide and diverse range of processes, skills, and tools for producing objects on every scale: from huge ships, buildings, and bridges down to precise engine parts and delicate jewelry.
Machining is a process in which a material is cut to a desired final shape and size by a controlled material-removal process. The processes that have this common theme are collectively called subtractive manufacturing, in contrast to additive manufacturing, which uses controlled addition of material. Exactly what the "controlled" part of the definition implies can vary, but it usually implies the use of machine tools.
A grinding machine, often shortened to grinder, is one of power tools or machine tools used for grinding. It is a type of machining using an abrasive wheel as the cutting tool. Each grain of abrasive on the wheel's surface cuts a small chip from the workpiece via shear deformation.
A grinding wheel is a wheel used for grinding. Grinding wheels are composed of abrasive compounds and are used for various grinding and abrasive machining operations. Such wheels are used in grinding machines.
A grinding dresser or wheel dresser is a tool to dress the surface of a grinding wheel. Grinding dressers are used to return a wheel to its original round shape, to expose fresh grains for renewed cutting action, or to make a different profile on the wheel's edge. Utilizing pre-determined dressing parameters will allow the wheel to be conditioned for optimum grinding performance while truing and restoring the form simultaneously.
Turning is a machining process in which a cutting tool, typically a non-rotary tool bit, describes a helix toolpath by moving more or less linearly while the workpiece rotates.
In the context of machining, a cutting tool or cutter is typically a hardened metal tool that is used to cut, shape, and remove material from a workpiece by means of machining tools as well as abrasive tools by way of shear deformation. The majority of these tools are designed exclusively for metals. There are several different types of single edge cutting tools that are made from a variety of hardened metal alloys that are ground to a specific shape in order to perform a specific part of the turning process resulting in a finished machined part. Single edge cutting tools are used mainly in the turning operations performed by a lathe in which they vary in size as well as alloy composition depending on the size and the type of material being turned. These cutting tools are held stationary by what is known as a tool post which is what manipulates the tools to cut the material into the desired shape. Single edge cutting tools are also the means of cutting material performed by metal shaping machines and metal planing machines which removes material by means of one cutting edge. Milling and drilling tools are often multipoint tools. Drilling is exclusively used to make holes in a workpiece. All drill bits have two cutting edges that are ground into two equally tapered angles which cuts through the material by applying downward rotational force. Endmills or milling bits, which also cut material by rotational force. Although these tools are not made to put holes in a workpiece. They cut by horizontal shear deformation in which the workpiece is brought into the tool as it's rotating. This is known as the tool path which is determined by the axis of the table that is holding the workpiece in place. This table is designed to accept a variety of vises and clamping tools so that it can move into the cutter at various angles and directions while the workpiece remains still. There are several different types of endmills that perform a certain type of milling action.
Knife making is the process of manufacturing a knife by any one or a combination of processes: stock removal, forging to shape, welded lamination or investment cast. Typical metals used come from the carbon steel, tool, or stainless steel families. Primitive knives have been made from bronze, copper, brass, iron, obsidian, and flint.
Belt grinding is an abrasive machining process used on metals and other materials. It is typically used as a finishing process in industry. A belt, coated in abrasive material, is run over the surface to be processed in order to remove material or produce the desired finish.
A diamond tool is a cutting tool with diamond grains fixed on the functional parts of the tool via a bonding material or another method. As diamond is a superhard material, diamond tools have many advantages as compared with tools made with common abrasives such as corundum and silicon carbide.
A diamond blade is a saw blade which has diamonds fixed on its edge for cutting hard or abrasive materials. There are many types of diamond blade, and they have many uses, including cutting stone, concrete, asphalt, bricks, coal balls, glass, and ceramics in the construction industry; cutting semiconductor materials in the IT industry; and cutting gemstones, including diamonds, in the gem industry.
Machinability is the ease with which a metal can be cut (machined) permitting the removal of the material with a satisfactory finish at low cost. Materials with good machinability require little power to cut, can be cut quickly, easily obtain a good finish, and do not wear the tooling much. The factors that typically improve a material's performance often degrade its machinability. Therefore, to manufacture components economically, engineers are challenged to find ways to improve machinability without harming performance.
Abrasive machining is a machining process where material is removed from a workpiece using a multitude of small abrasive particles. Common examples include grinding, honing, and polishing. Abrasive processes are usually expensive, but capable of tighter tolerances and better surface finish than other machining processes
Ultrasonic machining is a subtractive manufacturing process that removes material from the surface of a part through high frequency, low amplitude vibrations of a tool against the material surface in the presence of fine abrasive particles. The tool travels vertically or orthogonal to the surface of the part at amplitudes of 0.05 to 0.125 mm. The fine abrasive grains are mixed with water to form a slurry that is distributed across the part and the tip of the tool. Typical grain sizes of the abrasive material range from 100 to 1000, where smaller grains produce smoother surface finishes.
Grinding is a type of abrasive machining process which uses grinding wheel as cutting tool.
Honing is an abrasive machining process that produces a precision surface on a metal workpiece by scrubbing an abrasive grinding stone or grinding wheel against it along a controlled path. Honing is primarily used to improve the geometric form of a surface, but can also improve the surface finish.
Electrochemical grinding is a process that removes electrically conductive material by grinding with a negatively charged abrasive grinding wheel, an electrolyte fluid, and a positively charged workpiece. Materials removed from the workpiece stay in the electrolyte fluid. Electrochemical grinding is similar to electrochemical machining but uses a wheel instead of a tool shaped like the contour of the workpiece.
Surface grinding is done on flat surfaces to produce a smooth finish.
Flat honing is a metalworking grinding process used to provide high quality flat surfaces. It combines the speed of grinding or honing with the precision of lapping. It has also been known under the terms high speed lapping and high precision grinding.
Grinding wheel wear is an important measured factor of grinding in the manufacturing process of engineered parts and tools. Grinding involves the removal process of material and modifying the surface of a workpiece to some desired finish which might otherwise be unachievable through conventional machining processes. The grinding process itself has been compared to machining operations which employ multipoint cutting tools. The abrasive grains which make up the entire geometry of wheel act as independent small cutting tools. The quality, characteristics, and rate of grinding wheel wear can be affected by contributions of the characteristics of the material of the workpiece, the temperature increase of the workpiece, and the rate of wear of the grinding wheel itself. Moderate wear rate allows for more consistent material size. Maintaining stable grinding forces is preferred rather than high wheel wear rate which can decrease the effectiveness of material removal from the workpiece.