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CRITICAL TO QUALITY (CTQ)

"Critical to quality" (CTQ) is a term widely used within the field of Six Sigma activities to describe the key output characteristics of a process. An example may be an element of a design or an attribute of a service that is critical in the eyes of the customer.

A CTQ tree helps the team to derive the more specific behavioural requirements of the customer from his general needs.

A CTQ tree is a useful tool during the data collection stage (define) of an improvement project. Once the project team has established who their customers are, the team should then move towards determining the customer needs and requirements. The need of a customer is the output of a process. Requirements are the characteristics to determine whether the customer is happy with the output delivered. These constitute what is "critical to quality" and a CTQ tree helps to identify these CTQs in a systematic way.

( Basu R.,Implementing quality:a practical guide to tools and techniques : enabling the power of operational excellence, page 59)

VIBRATORY BALL MILLING

The use of vibratory ball mills for MA has been promoted predominantly by Kuhn. The vibratory ball mill is a long closed tube containing grinding balls and powder. The mill agitates the charge in three mutually perpendicular directions. Impact forces acting on the powder in a vibratory mill are a function of rates of milling, amplitude of vibration and mass of the milling medium. High energy milling forces can be obtained by using high frequency and high amplitude of vibrations. These mills normally operate at frequencies of the order of 200 Hz and a high amplitude of about 12 mm. It is estimated that the maximum acceleration of the grinding balls work out to be 24 g, where g is the gravitational force.

(Soni P.R.,Mechanical Alloying: Fundamentals and Applications, page 9 )

ELEVATED TEMPERATURE MACHİNİNG

To overcomethe strain-hardening problem and reduce force and power requirements, many forming operations are performed at elevated temperatures. There are two elevated temperature ranges involved , giving rise to the terms warm working and hot working.

Warm working: Because plastic deformation properties are normally enhanced by increasing workpiece temperature, forming operations are sometimes performed at temperatures somewhat above room temperature but below the recrystallization temperature. The term warm working is applied to this second temperature range. The dividing line between cold working and warm working is often expressed in terms of the melting point for the metal.

Hot working: Hot working (also called hot forming) involves deformation at temperatures above the recrystallization temperature. The recrystallization temperature for a given metal is about one-half of its melting point on the absolute scale. In practice, hot working is usually carried out at temperatures somewhat above one-half of its melting point, thus enhancing the advantage of hot working above this level. However, the deformation process itself generates heat, which increases work temperatures in localized regions of the part. This can cause melting in these regions, which is highly undesirable. Also, scale on the work surface is accelerated at higher temperatures.

(Groover M.P.,Fundamentals of Modern Manufacturing: Materials, Processes, and Systems, page 388 )

METAL INJECTİON MOLDING

Metal injection molding (MIM) is the process of mixing elemental or alloyed powders with thermoplastic binders. The binders are selected to deliver the optimum flow characteristics to facilitate uniform distribution of the material in the mold.

Under moderate pressures and temperatures, the material is extruded into a mold. The material hardens as it cools and is removed from the mold in what is called "green" condition. At this point, the part is larger than the desired shape by the amount of binders used in the mixture. These binders are preferentially and selectively extracted from the "green" part. Generally, a low-temperature furnace treatment slowly evaporate the binder over a 1-3day period. The parts are then sintered in a high- temperature furnace under controlled atmospheric conditions, and a temperature profile is selected to remove the remaining binders and present a finished part with the desired physical properties. Obviously, the entire process lends itself admirably to microprocessor control.

(Brown J.A.,Modern manufacturing processes, page 1 )