::. FOR REFERENCE

MACHINE ACCESSORIES FOR MILLING

Milling is a cutting work process performed by means of basic circular motion (cutting) and any feed-motion perpendicular to the tool rotation axis. Milling represents a discontinuous operation of metal removing; rhythmic interrupts in metal removing and cutting force alterations require good dynamic properties of milling machines and accessories. Permissible cutting modes for workpiece processing are determined by the weakest component in ‘machine – accessory – tool – part’ force loop. Milling of inclined, flat, raised and concave surfaces and high repetition accuracy in positioning require high geometric relationship of machines and accessories.

Milling machines fall into following types:

-vertical milling knee-type machines
-horizontal milling knee-type machines
-milling machines with crossed motion table
-super universal milling machines
-contour-milling machines
-planer-type milling machines
-rotary milling machines
-keyseat-and-slot milling machines

Since milling is a processing method, which often shows high cutting forces, clamp mechanisms design is of special importance. Four major tasks are met in installing and securing workpieces: positioning, securing, attaching additional supports and cushioning. To position a workpiece properly, following methods are used:

-applying workpiece to a specific permanent stop block installed on a fixed cam or finger
-positioning in two-way special stoppers mounted on plates, v-blocks, profiled cams or elbows
-centering in one or two directions, either secure or not etc.

Clamp mechanisms must be engaged with machine by means of keys and stop bars (with force closure). Clamp force is created by components like screws, jib members, eccentrics, levers, cams, springs and hydraulic and pneumatic cylinders. These clamp devices are driven either manually or by hydraulic and pneumatic mechanisms.

Depending on number of processed parts and required automation degree, various types of clamp mechanisms can be utilized, thus providing operational comfort. Machine vice is an all-purpose device. It is used for processing parts, which vary in shape and dimensions. Vice has permanent parts (body, movable and fixed jaws, clamp mechanism) and removable parts used for securing workpieces of various sizes. Vice can have one or two movable jaws, or floating jaws. Following clamps are used in vice: manual, screw, eccentric, motorized, pneumatic, hydraulic and pneumo-hydraulic clamps. Most widely spread is screw clamped vice and hydraulic boosted vice. Depending on clamp force direction applied to movable jaw, vice can be divided into pulling and pushing clamp force types. Vice can be non-rotational, one-axis turning, or turning in two or three mutually perpendicular planes (two-axis and three-axis). Machine vice must be stiff, fast in operation and easy to use. Turning or non-rotational normal accuracy machine vice and precision vice are chosen depending on required processing precision. Vice can be installed either on a milling machine table, or in intermediate devices like tilting table. There are also vice equipment made of two separate units (divided vice), which allows to secure large workpieces. To clamp a large-sized part, one can use several vices, which secure the workpiece in several points. In this case precision vice with body height close tolerance are used. Machine vice, which allow to secure multiple workpieces, vice installed on side surfaces of the foot and vice installed on multipiece stands are more and more widely used. Advanced stiffness vice (the so-called compact vice) are used in CNC machines. Milling machines can be equipped with some types of sine vice. Various plates are used for securing workpieces in required positions: parallel plates, angle templates, removable and attachable jaws etc.

Turning dividing tables and dividing equipment of diverse types are used for milling of angled surfaces. They are necessary because of the fact that many products have vast number of rotation bodies, which require lathing and smooth finishing together with milling. Machines with horizontal axis allow to secure workpieces between centers at the side of divider and deadhead. It is possible to use a holder installed in divider coupled with center of the opposing deadhead. Chucks are used in dividing mechanisms with vertical axis position. Some dividing mechanisms allow to install chucks either vertically or horizontally. Manual dividing mechanisms have single spindle, as a rule.

Conical bores with taper rate of 7:24 or Morse cones are used for installing mill securing appliances onto milling machines.

Mandrels for different arbor-type milling cutters (frontal, slotted, disk-shaped or angular) with a cylindrical seating hole, are equipped with shanks with taper rate of 7:24 or Morse cones. The mill is seated on a cylindrical flange, its longitudinal slot is engaged with parallel key. The mill is secured by a flat-head screw. Mandrels with Morse cone shanks are installed into 7:24 taper rate spindle slots by means of adapter sleeves. Adapter sleeves with outer cone 7:24 and frontal groove are used for installing various mill mandrels and chucks, which have their shank designed with Morse cone and flattened surfaces. Central mill mandrels are designed for installing attachable cylindrical, disc, profiled, slitting and other mill saws into horizontal milling machines. One end of a central mandrel is secured in machine spindle slot, the other end is installed in arbor support bearing secured at machine’s overarm support. Spacer rings allow milling saws to be positioned at a predefined distance from each other and from the mandrel shank flange.

Adapter sleeves for shank-type end mills with conic shanks have Morse cones and taper rate of 7:24. Sleeve kits allow to install mills with Morse cones 1 to 6 into metal cutting machine spindles.

Shank-type end mills with cylindrical shanks require collet holders.

Quick-operating chucks are used for jobs that involve frequent tool change. Chucks allow to change tools without using draw-in bolt, which reduces tool change time 2-3 times.