Stock removal
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High stock removal is a technological process with the goal to remove large / substantial amounts of material. The quantity of material, which can be removed in a specific process, depends on the material properties and the machining tool used.
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[edit] Materials
The stock removal rate or the possible removal of material in a specific time period is depending on material properties. This is expressed by the machinability of a material: the ease or difficulty to machine a particular material. The machinability of materials varies greatly, for instance, aluminium and magnesium have a high machinability ratio compared to titanium and other special metals.
[edit] Specific energy
One way of qualifying the machinability is the specific energy (e). This is the amount of energy required to cut a volume of work material (kWh/mm3). Specific energy is depending on material properties. This makes that stock removal is related to specific energy.
[edit] New materials
There is a continuously development of new materials to fulfil the extreme demands of market segments like, Petrochemical, Power/Energy and Aerospace. Metallurgical changes have improved a large range of these materials (titanium, nickel). But by making the materials harder tougher, less heat sensitive and/or more resistant to corrosion and fatigue, this also make these new developed materials hard to machine.
[edit] Temperature rising
The specific cutting energy needed for ‘difficult to machine’ materials are extremely high. Especially in the high stock removal applications there are problems with the temperature rising of the work material surface. An increase of the work material temperature leads to deterioration of the work material surface integrity. Resulting in metallurgical damages like micro cracks, residual stresses and work hardening.
[edit] High stock removal machine tools
Not only the material properties determine the energy required to cut a volume of material (specific energy). The needed energy also depends on the technological process used to process the work material.
[edit] Technologies
A lot of technologies are capable of removing substantial amounts of material. Among them are: sawing, turning, broaching, milling and grinding. Turning and milling are conventionally the most popular machining technologies. Turning is mainly used for round products, milling has a broad range of applications. Conventional methods like milling do have problems to keep up with the developments of the ‘difficult to machine’ materials. These methods generate locally too much heat. The special materials in particular require a cool cutting process.
[edit] Grinding
Traditionally bonded abrasives are used for stock removal. To grind large products, with a substantial material removal, vertical segment grinders are used. These grinding machines work with a rotating disc with abrasive segments. The work material is pressed against those segments with the aid of a rotating or reciprocating table. These technologies are using significantly greater horsepower (up to 450 Hp!) than other grinding methods. Some major manufactures of these machines are Blanchard, Mattison, Göckel and Reform.
[edit] Belt grinding
Recently grinding with coated abrasives has become a viable alternative for high stock removal by some major developments in the field of the machine tool and grinding belt. High stock belt grinding is a cool cutting process. The amount of friction energy is significantly lower compared to other (bonded) grinding techniques. The reason is that the amount of rubbing and ploughing energies are greatly reduced due to special configuration of machine components, machine settings, and wide belt grinding tools. The productivity of the abrasive belt grinding technology is in most cases three times that of the rotary or reciprocating vertical grinders. As a result of this belt grinding is replacing the conventional technologies in the field of the speciality metals. As an example the world biggest titanium manufactures are using the belt grinding techniques. Site of wide belt manufacturer
