Erdem Özdemir - 030070307 - 4th Week Definitions

Turret presses

Manufacturing

New – Better Definition

For a part having a number of holes punched in it the diesel will incorporate a number of punches and correspondingly located dies, allowing all the holes to be punched at one stroke of the press. Such a dieset is expensive to manufacture and maintain, and is limited to producing only the part for which it was designed.

To overcome these limitations, and to provide flexibility, the turret press (Figure 3.15) was developed. A number of punches and their corresponding dies are mounted in a turret rotating beneath the ram of the press. A number of strokes will be utilised, moving the workpiece to alternative positions, and rotating the turret to change punch and die as required, to produce the required part. Action is not limited to punching holes: the use of rectangular and shaped punches allows the production of profiles as a series of small steps (termed 'nibbling'). Movement of the part (held by an edge in clamps capable of movement in X and Y axes) beneath the press ram may be manual, controlled by a template, with punch selection being carried out manually, or both may be computer controlled. While the output rate is much slower than a multiple punch dieset, the flexibility offered by turret presses allows for low volume manufacture.

(Principles of engineering manufacture, V. Chiles,Stewart C. Black,A. Lissaman 1996, Pg 79)

Previous

An alternative to the use of dedicated dies for the manufacture of sheet metal parts is the numerically controlled turret press. This is a machine, which contains punches and matching dies in two rotary magazines or turrets. Depending upon the machine size, turrets may contain as many as 72 different dies for a variety of punching operations.

The lower turret rests in the center of the press bed, the surface of ehich is covered with steel balls that freely rotate in spherical sockets and that project just above the bed surface. For this reason the press bed is sometimes referref to as a ball table. A large metal sheet placed onto the press bed can thus slide easily to different positions between the two turret faces. This sliding is accomplished by gripping an edge of the sheet in two clamps attached to linear (X,Y) slideways. The slideways are under numerical control, which allows precise positioning of the sheet under the active punch in the machine turret. The turret is also contolled numerically so that while the sheet is moving to the next punching position, the turrets can be rotated to bring the desired punch and die into play.

(Product Design for Manufacture and Assemble, 3rd Edition, Boothroyd & Dewhurst & Knight, p407)

Cycle Time

Product Management

New-Better Definition

the term cycle time refers to the time frame of so many minutes and so many seconds needed to produce a unit or a piece of product. This is determined by the amount of production and the operating time.

To obtain the cycle time, first divide the quantity required for a month by the number of days of operation to produce the required quantity per day. The daily operating time divided by the required quantity per day becomes the cycle time.

The work procedure must clearly define everything minutely and quantitatively. Everything must be expressed in concrete terms. This will assist the foreman in avoiding waste, unevenness and unreasonableness when determining standard operations. For example, how both hands arc to move, where to place both feet and the general nature of die work must all be clearly stated. Workers must be able to understand the procedure, and it must be standardized. The intent of the person establishing the work procedure must be clearly discernible, as if to say, "This is the way 1 want you to do your work." With that understanding, workers can abide by the work procedure with confidence to make high-quality products safely and quickly.

(Kanban just-in-time at Toyota: management begins at the workplace, David John Lu,Nihon Nōritsu Kyōkai, 1998, Pg 103-104)

Previous

For any production operation, the cycle time is defined as the time that one work unit spends being processed or assembled. It is the time between when one work unit begins processing and when the next unit begins. Cycle time is the time an individual part spends at the machine, but not all of this time is productive In a typical processing operation, such as machining, cycle time consists of actual machining operation time, work part handling time and tool handling time per workpiece. (Mikell P. Groover,Automation,production and computer-integrated manufactoring, Prentice-Hall Pub., 2008, p.49)

Dip Brazing

Manufacturing

New-Better Definition

Dip brazing in molten salt is also referred to as salt-hath dip brazing and molten chemical-hath dip brazing. In this process, the assembly to be joined is immersed in a bath of molten salt, which provides lite heal and may supply [he fluxing action for brazing as well. The bath tem­perature is maintained above the liquidus of the Idler metal but below the melting range of the base metal. Applications of dip brazing of cop­per alloys included waveguides and waveguide hardware, flowmeter hardware, and capillary lube and bellows assemblies. Neutral chloride-base salts arc used. The most commonly used filler metal is BCuP

The support given immersed workpieces by the buoyancy of the molten salt and the rapid and even heating afforded by dip brazing make this process especially useful for joining assem­blies requiring minimum distortion, such as waveguides. When a waveguide assembly has a large number of brazed joints, both external and internal, a sail bath is particularly efficient for simultaneous brazing of all joints in a single immersion in the molten salt. With dip brazing. a flange lilting and the end of a waveguide tube to he joined to it can be brazed by immersing only the joint portion in ihc molten salt bath, as m the example that follows.

(Copper and copper alloys, Joseph R. Davis,ASM International. Handbook Committee, 2001, pg 312)

Dip Brazing

In dip brazing, either a molten salt bath or a molten metal bath accomplishes heating. In both methods, assembled parts are immersed in the baths contained in a heating pot. Solidification occurs when the parts are removed from the bath.

Dip brazing achieves fast heating cycles and can be used to braze many joints on a single part or on multiple parts simultaneously.

(Groover M. P., Fundamentals of modern manufacturing: Materials, processes, and systems ,p. 751)