Mehmet Özer, 030070050, 7th Week (07.04.2012)

1. Knurling (Surface Treatment)

Previous Answer

Knurling is the process of impressing a straight or diamond-shaped pattern into a cylindrical piece using special knurling tools. The knurl is formed by forcing the hardened knurling rollers on the knurling tool into the surface of a revolving cylindrical part. The pressure of the knurling tool creates a pattern of straight or diamond grooves as material is forced outward against the knurling rollers.

(Machine Trades Blueprint Reading, 2nd Edition, Taylor, p.194)

New Answer (better)

Knurling is not really a machining (cutting) operation because the knurl is formed, not cut, in the workpiece. Knurling is a common lathe or screw machine operation. The hardened hurling tool rolls against the cylindrical surface of the rotating workpiece with high pressure, causing the surface material of the workpiece to flow into peaks and valleys according to the pattern of the hurling tool. The result is a surface in the finished part that is roughened to a particular pattern, useful to improve the grip if the part must be held or rotated by hand when it is used. Several different patterns are possible. Other uses for the operation are for decoration and to increase the diameter of the part slightly to facilitate a press fit.

(Bralla, J. G., Handbook Manufacturing Processes, How Products, Components and Materials Are Made, pp.88)

Knurling is performed by a knurling tool, consisting of two hardened forming rolls, each mounted between centers. The forming rolls have the desired knurling pattern on their surfaces. To perform knurling, the tool is pressed against the rotating workpart with sufficient pressure to impress the pattern onto the work surface.

(Groover M.P., Fundamentals of Modern Manufacturing: Materials, Processes, and Systems 4^th Edition, pp. 513)

2. Peripheral Milling (Manufacturing method)

Previous Answer

Peripheral milling is a milling method which functions with horizontal tool axis. The cutting edges of the plain milling cutter are located at the tool’s periphery. Peripheral milling is subdividen into up- and down milling.

Up milling:

During up milling (Figure 11.1), the milling cutter rotates in a direction opposite to the feed direction of the workpiece. The feed motion direction (Figure 11.2) is characterised by the feed motion angle φ. If, over the course of a single tooth’s contact with the material (from the moment the tooth comes into contact with the material – tool entry - up to tool exit), φ remains less than 90o, then it is an up milling procedure. During up milling, workpiece material is removed by the resultant force. There is the risk that the workpiece may be pulled out of the mounting or that the milling table will buckle. Specially designed clamping jigs and undercuts in the table guide-ways avoid damage to the workpiece or tool.

Down milling:

During down milling (Figure 11.3), the direction of milling cutter rotation is the same as the workpiece’s feed direction. The milling cutter approaches from the thickest part position of the chip. In down milling, the feed motion angle φ (Figure 11.4) ranges from 90o to 180o. The resultant force presses the workpiece against the base. In cases where the cutter arbour is insufficiently stiff, the milling cutter “climbs” onto the workpiece, and cutting edges break off.

During down milling the resultant force direction coincides with the feed motion direction. Thus, if the feed screw experiences backlash, the resultant force makes the lead-bearing flank at the feed screw changes at each start of the cut. Milling machines for down milling should have a feed drive with no backlash, cutter arbours and frame components of high stiffness.

(Heinz Tschätsch, “Applied Machining Technology”, page 173-174)

New Answer (better)

Peripheral Milling In peripheral milling, also called plain milling, the axis of the tool is parallel to the surface being machined, and the operation is performed by cutting edges on the outside periphery of the cutter. Several types of peripheral milling are shown in Figure 22.18: (a) slab milling, the basic form of peripheral milling in which the cutter width extends beyond the workpiece on both sides; (b) slotting, also called slot milling, in which the width of the cutter is less than the workpiece width, creating a slot in the work—when the cutter is very thin, this operation can be used to mill narrow slots or cut a workpart in two, called saw milling; (c) side milling, in which the cutter machines the side of the workpiece; (d) straddle milling, the same as side milling, only cutting takes place on both sides of the work; and form milling, in which the milling teeth have a special profile that determines the shape of the slot that is cut in the work. Form milling is therefore classified as a forming operation (Section 22.1).

In peripheral milling, the direction of cutter rotation distinguishes two forms of milling: up milling and down milling, illustrated in Figure 22.19. In up milling, also called conventional milling, the direction of motion of the cutter teeth is opposite the feed direction when the teeth cut into the work. It is milling ‘‘against the feed.’’ In down milling, also called climb milling, the direction of cutter motion is the same as the feed direction when the teeth cut the work. It is milling ‘‘with the feed.’’

The relative geometries of these two forms of milling result in differences in their cutting actions. In up milling, the chip formed by each cutter tooth starts out very thin and increases in thickness during the sweep of the cutter. In down milling, each chip starts out thick and reduces in thickness throughout the cut. The length of a chip in down milling is less than in up milling (the difference is exaggerated in our figure). This means that the cutter is engaged in the work for less time per volume of material cut, and this tends to increase tool life in down milling.

The cutting force direction is tangential to the periphery of the cutter for the teeth that are engaged in the work. In up milling, this has a tendency to lift the workpart as the cutter teeth exit the material. In down milling, this cutter force direction is downward, tending to hold the work against the milling machine table.

(Groover M.P., Fundamentals of Modern Manufacturing: Materials, Processes, and Systems 4^th Edition, pp. 524-525)

3. Electrochemical Machining (ECM) (Manufacturing method)

Previous Answer

Application of the electrochemical processes for machining has become one of the most prospective fields for manufacturing. These processes use the principle of metal removal by the electrochemical means and are an enhancement of the chemical machining process. In the electrochemical processes, an electrolytic cell is formed by using workpiece as anode and a cathode of suitable material having the shape of tool in the midst of an electrolyte solution. The well-known Faraday's laws of electrolysis govern the metal removal. The metal is removed in the form of sludge formed by the electrochemical and chemical reactions occurring in the electrolytic cell, which precipitates at the bottom. Hence, these processes are known as electrochemical machining processes.

(Parashar B.S.N., Mittal R.K., Elements of Manufacturing Processes, 2006, pg.335)

New Answer (better)

Electrochemical machining removes metal from an electrically conductive workpiece by anodic dissolution, in which the shape of the workpiece is obtained by a formed electrode tool in close proximity to, but separated from, the work by a rapidly flowing electrolyte. ECM is basically a depleting operation. As illustrated in Figure 26.4, the workpiece is the anode, and the tool is the cathode. The principle underlying the process is that material is depleted from the anode (the positive pole) and deposited onto the cathode (the negative pole) in the presence of an electrolyte bath (Section 4.5). The difference in ECM is that the electrolyte bath flows rapidly between the two poles to carry off the deplated material, so that it does not become plated onto the tool.

The electrode tool, usually made of copper, brass, or stainless steel, is designed to possess approximately the inverse of the desired final shape of the part. An all owance in the tool size must be provided for the gap that exists between the tool and the work. To accomplish metal removal, the electrode is fed into the work at a rate equal to the rate of metal removal from the work. Metal removal rate is determined by Faraday’s First Law, which states that the amount of chemical change produced by an electric current (i.e., the amount of metal dissolved) is proportional to the quantity of electricity passed (current x time).

(Groover M.P., Fundamentals of Modern Manufacturing: Materials, Processes, and Systems 4^th Edition, pp. 633)

4. Hot Rolling (Shaping – Manufacturing)

Previous Answer

Most rolling processes are very capital intensive, requiring massive pieces of equipment, called mills, to perform them. The high investment cost requires the mills to be used for production in large quantities of standard items such as sheets and planets. Most rolling is carried out by hot working, called hot rolling, owing to the large amount of deformation required. Hot-rolled metal is generally free of residual stresses, and its properties are isotropic. Disadvantages of hot rolling are that the product cannot be held to close tolerances, and the surface has a characteristic oxide scale.

(Mikell P. Groover; Fundamentals of Modern Manufacturing Materials, Processes, and Systems 3rd Edition; pg.391)

New Answer (better)
Hot rolling is commonly applied to convert steel ingots to blooms, billets, or slabs, and to make these shapes into salable forms. In the process, heated metal is passed between two rollers whose spacing is less than the thickness of the metal. The rotation of the rollers moves the metal forward, squeezing and elongating it. Fig. 2A1 illustrates the process. The process extends and refines the grain structure of the rolled material. A number of may be required, depending on the thickness desired and the thickness of the entering material.

Reversing rollers are often used to facilitate multiple passes. Thin sheet or foil is best rolled with small-diameter rollers that are backed up with larger rollers to provide the necessary rolling force. As many as twelve rollers in a cluster may be used. Shaped rollers can produce material with various cross sections including those of structural shapes or special cross sections. Low-alloy or plain-carbon steel is heated to about 2200°F. (1200°C) before rolling and after being preheated in a soaking pit. In addition to ferrous metals, aluminum, copper and copper alloys, magnesium, nickel, titanium, and zinc alloys are hot rolled.

(Bralla, J. G., Handbook Manufacturing Processes, How Products, Components and Materials Are Made, pp. 33)

5.Broaches (Cutting Tools)

Previous Answer

Broaches are used for broaching which is one of the most productive of the basic machining processes. The machine tool is called a broaching machine and the cutting tool is called the broach. The broaches compete economically with milling and boring and is capable of producing precision-machined surfaces. The broach finishes an entire surface in a single pass. Broaches are used in production to finish holes, splines, and flat surfaces.

A broach is composed of a series of teeth, each tooth standing slightly higher than the last. This rise per tooth, also known as step or the feed per tooth, determines the amount of material removed. There is no feeding of the broaching tool required. The frontal contour of the teeth determines the shape of the resulting machined surface. As the result of these conditions built into the tool, no complex motion of the tool relative to the workpiece is required and the need for highly skilled machine operators minimized.

(Mikell P. Groover, Fundamentals of Modern Manufacturing, Materials, Processes and Systems, pp. 748)

New Answer (better)

The terminology and geometry of the broach are illustrated in Figure 23.18. The broach consists of a series of distinct cutting teeth along its length. Feed is accomplished by the increased step between successive teeth on the broach. This feeding action is unique among machining operations, because most operations accomplish feeding by a relative feed motion that is carried out by either the tool or the work. The total material removed in a single pass of the broach is the cumulative result of all the steps in the tool. The speed motion is accomplished by the linear travel of the tool past the work surface. The shape of the cut surface is determined by the contour of the cutting edges on the broach, particularly the final cutting edge. Owing to its complex geometry and the low speeds used in broaching, most broaches are made of HSS. In broaching of certain cast irons, the cutting edges are cemented carbide inserts either brazed or mechanically held in place on the broaching tool.

(Groover M.P., Fundamentals of Modern Manufacturing: Materials, Processes, and Systems 4^th Edition, pp. 576)