Erdem Ozdemir 030070307 - 1st Week Answers

Transfer Machines

Manufacturing

New – Better Answer

Transfer-type production machines, frequently designated as automated machines, complete a series of machining operations at successive stations and transfer the work from one station to the next. They are in effect a production line of connected machines that are synchro­nized in their operation so that the workpiece, after being loaded at the first station, progresses automatically through the various stations to its completion.

"Transfer machines" perform a variety of machining, inspecting, and quality control func­tions. They drill, mill, hone, and grind, as well as control and inspect the operations.

Types of Transfer Machines

Transfer machines are of the following three types :

1.   Rotary indexing table transfer machines.

2.   In-line transfer machines.

3.   Drum type transfer machines.

1. Rotary indexing table transfer machines :

In rotary transfer system the workpieces are held in fixtures on a continuous rotating table. The rotating table brings the workpieces under different machines

Owing to the problems of rigidity and maintenance of proper accuracy, the table size is always limited and, hence, is the number of stations fixed on this type of machine. Usually, such a machine carries 6 or 8 sta­tions around it, although for smaller workpieces this number can be as high as 16. The components size and required number of work stations are the main factors which affect the determination of table size and the number of stations.

•    This method is quite compact and permits the workpiece to be loaded and unloaded at a sin­gle location without having to interrupt the machining.

•   This type of arrangement is best suited for automatic assembly of a product.

2. In-line transfer machines :

In this arrangement the workpiece is held in a fixture or special 'pallet". The fixtures are located and clamped in proper position. A schematic diagram of an In-line transfer machine is shown in Fig. 15.2.

"Palletized" work holding fixtures secure the transmission during all operations. Pallets are often carried in conveyors which are indexable.

Following are the functions of an in-line transfer machine : (0 Transfers workpiece to the first station and then from station to station, (ii) Locates and clamps the work at each station, (iti) Rapid approach of the tools to the work.

(iv) Feed the tools through the cutting cycle.

(v)  Retract the tools clear of the work and guide bushes

(vi) Unclamp the workpiece at various stations ready for further transfer.

3. Drum type transfer machines :

In these types of machines work fixtures are fastened to the outside surface or periphery of the drum and work stations are positioned radially around the circular path at equal intervals.

As the work hangs from the fixture, the clamping arrangement must be fool proof and efficient. Like circular indexing arrangement, this too cannot be big in size.

•    Solution of transfer machines depends on the following factors : (t) Product size and machining requirements.

(u) Handling systems used, (tit) Floor space available.

•        Transfer machines range from comparatively small units having only two to three stations to long straight line machines with more than 100 stations.

•        These machines are used primarily in the automobile industry. Products processed by these machines include cylinder blocks, cylinder heads, refrigeration compressor bodies and similar parts.

Constructional Features of a "Transfer Machine"

The principal constructional features of a Transfer machine' consists of the following main parts and mechanisms :

1.  Central bed.

2.  Machining heads.

3.  Automatic work holding and Transfer mechanisms.

4.  Locating and clamping devices.

5.  Cooling supply mechanisms.                                                                     ^

6.  Chip disposal devices.

7.  Control systems.

Advantages and Disadvantages of Transfer Machines Following are the advantages and disadvantages of transfer machines :

Advantages :

1.  Higher production rates are achieved.

2.  Higher accuracy is obtained.

3.  Less floor space is required.

4.  Heavy workpieces can be easily handled.

5.  The quality of products is considerably improved.

6.  Complex shaped components can be conveniently machined.

7.  The length of production cycle is reduced.

8.  Less number of operators are required.

9.  Increased tool life (resulting in further reduction in production cost).

Disadvantages :

1.  High initial investment.

2.  A breakdown of one machine means stoppage of whole of the production line.

3.  Complex control systems are required.

4.  Much time is required to change over the machine to handle a different shaped components.

5.  Very high overhauling and maintenance costs of transfer lines, specifically when reshuf­fling is required.

(A textbook of manufacturing technology, R. K. Rajput, Pg 688-670)

              

               Previous:

                   Typically consisting of two or more powered units, these machines can be arrange on the shop floor in linear, circular, or U-shape patterns. The weight and shape of the workpieces influence the arrangment selected, which is important for continuity of operation in the event of tool failure or machine breakdown in one or more of the units. Buffer storage features are corporated in these machines to permit continued operation in such an event.

(Kalpakjian S., Schmid S.R.,Manufacturing Engineering and Technology, 5th Edition, pg.1150)

Metin Atmaca - 030080007, 1st week definitions

     

1. Affinity Diagram (Organization- Management)

Previous Definition:

The purpose of affinity diagram is to organize large groups of information to meaningful categories. The affinity diagram helps break old patterns of thought, reveal new patterns, and generates more creative ways of thinking. The affinity diagram helps organize team's thoughts most effectively when:the issues seem to large and complex;you need to break out of old,traditional ways of thinking; everything seems caotic; or there are many customer requirements. The affinity diagram helps tonaturally group ideas or your customer's valid requirements and showthe relationship between items and groups. The affinity diagram helps you gather and group large amounts of language (e.g., needs, wants, wishes, ideas, amd opinions) into natural relationships.

(Soleimannejed F., Six Sigma, Basic Steps & Implementation , p. 94)

New Definition (Better):

The affinity diagram organizes a large number of ideas into their natural relationships. This method taps a team’s creativity and intuition. It was created in the 1960s by Japanese anthropologist Jiro Kawakita.

When to Use an Affinity Diagram

·        When you are confronted with many facts or ideas in apparent chaos

·        When issues seem too large and complex to grasp

·        When group consensus is necessary

Typical situations are:

·        After a brainstorming exercise

·        When analyzing verbal data, such as survey results.

Affinity Diagram Procedure

Materials needed: sticky notes or cards, marking pens, large work surface (wall, table, or floor).

1.    Record each idea with a marking pen on a separate sticky note or card. (During a brainstorming session, write directly onto sticky notes or cards if you suspect you will be following the brainstorm with an affinity diagram.) Randomly spread notes on a large work surface so all notes are visible to everyone. The entire team gathers around the notes and participates in the next steps.

2.    It is very important that no one talk during this step. Look for ideas that seem to be related in some way. Place them side by side. Repeat until all notes are grouped. It’s okay to have “loners” that don’t seem to fit a group. It’s all right to move a note someone else has already moved. If a note seems to belong in two groups, make a second note.

3.    You can talk now. Participants can discuss the shape of the chart, any surprising patterns, and especially reasons for moving controversial notes. A few more changes may be made. When ideas are grouped, select a heading for each group. Look for a note in each grouping that captures the meaning of the group. Place it at the top of the group. If there is no such note, write one. Often it is useful to write or highlight this note in a different color.

4.    Combine groups into “supergroups” if appropriate.

Affinity Diagram Example

The ZZ-400 manufacturing team used an affinity diagram to organize its list of potential performance indicators. Figure 1 shows the list team members brainstormed. Because the team works a shift schedule and members could not meet to do the affinity diagram together, they modified the procedure.

Figure 1 Brainstorming for Affinity Diagram Example

They wrote each idea on a sticky note and put all the notes randomly on a rarely used door. Over several days, everyone reviewed the notes in their spare time and moved the notes into related groups. Some people reviewed the evolving pattern several times. After a few days, the natural grouping shown in figure 2 had emerged.

Notice that one of the notes, “Safety,” has become part of the heading for its group. The rest of the headings were added after the grouping emerged. Five broad areas of performance were identified: product quality, equipment maintenance, manufacturing cost, production volume, and safety and environmental.

Figure 2 Affinity Diagram Example

 (Nancy R. Tague, The Quality Toolbox, Second Edition, p. 96.)

2. Computer-Aided Process Planning (CAPP) (Manufacturing)

Previous Definition (Better):

Process planning is concerned with selecting methods of production: tooling, fixtures, machinery, sequence of operations and assembly. All of these diverse activities must be planned, which traditionally has been done by process planners.

When done manually, this task is highly labor-intensive and time-consuming and relies heavily on the experience of the process planner. Computer-Aided Process Planning (CAPP) accomplishes this complex task by viewing the total operation as an integrated system, so that the individual steps involved in making each part are coordinated with others anda re performed efficiently and reliably.

(manufacturing engineering and technology-Serope kalpakjian, page 1204-1205)

New Definition:

An efficient CAPP system has a key role to integrate the design and manufacturing or assembly systems properly considering available resources and design constraints. It has been found that 15% of the process planner’s time is spent on technical decision making  while  remaining time is spent equally between gathering data, calculating and the preparation of documentation. Investigation shows that an efficient CAPP systems could result in a total reduction of the manufacturing cost by up to 30% and time in the manufacturing cycle and the   total engineering time could also be reduced by up to 50%.

(Younis, M.A. and Wahab, A.M.A., 1997,”A CAPP Expert System for rotational components”, Computers and Industrial Engineering, pp. 509-512)

3. Net-Shape Manufacturing (Manufacturing Process)

Previous Definition:

A particular manufacturing process may not produce a finished part, and thus additional operations may be necessary. For example, a forged part may not have the desired dimensions or surface finish; as a result, additional operations such as machining or grinding may be necessary. Likewise, it may be difficult, impossible, or uneconomical to produce a part with holes in it by using single manufacturing process, and thus a subsequent process may be required, suc as drilling or producing the hole using various advanced methods, such as chemical pr electrical means. Furthermore, the holes produced by a particular manufacturing processs may not have the proper roundness, dimensional accuracy, or surface finish, and thus they may require an additional operation, such as honing.

(Kalpakjian S., Schmid S.R.,Manufacturing Engineering and Technology, 5th Edition, pg.31

New Definition (Better):

The formation of strong, dense metal parts is the goal of many innovative approaches to three-dimensional manufacturing and repair of advanced components and structures. Laser rapid prototyping of complex shapes and designs has been in use since the 1980’s. This includes stereolithography, selective laser sintering, and mold-shape deposition casting. However, these processes have largely been limited to nonmetallic. In the last ten years or so, several companies in the United States and abroad have focused on techniques of metal powder fusion to provide dense metal parts.

(Joshua Rabinovich, Advanced Materials & Processes, Volume 161, Issue 1, January 2003 (ASM International) p. 47)

4. Ball Milling (Manufacturing):

Previous Definition (Better):

The ball mills can be divided into 2 types : centrifugal and planetary mills.
In a centrifugal ball mill, a single bowl fastener is merely horizontally and eccentrically driven while not rotating itself.In spite of this, the velocity of the grinding balls in this case is still six times that of the grinding balls in the gravity ball mills.
In planetary ball mills 2 or 4 bowl fasteners ,each of which accommodates one grinding bowls and supporting disc rotate in opposite directions, so that 2 different centrifugal forces act on the bowl contents.
(Powder metallurgy technology first edition 2002 p.34)

New Definiton:

Ball mills, which use steel or ceramic balls, are mainly used for fine grinding and are divided into two types:

-          Tube mills, which usually have a high length: diameter ratio (~6:1) and two compartments separated by a partition

-          Single-compartment mills, which have a small length: diameter ratio (~1.5:1). Single-compartment ball mills are the best-known form of tumbling mills.

(Alban J. Lynch, Chester, A. Rowland, The history of grinding, p. 95)

5. Visual sensing (Manufacturing):

Previous Definition:

In visual sensing, cameras optically sense the presence and shape of the object. A microprocessor then processes the image (usually in less than one second), the image is measured, and the measurements are digitized (image recognition). There are two basic systems of machine vision: linear array and matrix array.

(Kalpakjian S., Schmid S.R.,Manufacturing engineering and technology, 5th Edition, p 1173)

New Definition (Better):

Industrial robots are designed for tasks as pick and place, welding, grinding, parts assembly and painting, where repeated work is needed and the robot path is programmed previously. Consequently, if the working condition is changed and deviates from the programmed parameters, the robot may not be able to function properly. To ensure that the robot adapts to new tasks without reprogramming, sensing technology is integrated to the robot system to enhance the robot’s capability to work in a dynamic environment. It makes the robot system easy-to-use for the end user and yet operative with a human. Vision sensing is a vital sensing technology where the robot mimics human vision to guide itself through the complex process.

(Zhongxue Gan, QingTang, Visual Sensing and its Applications, preface)

Erdem Ozdemir 030070307 - 1st Week Answers

Laser Interferometer Measuring System

Measurement

New – Better Answer

The laser interferometer measurement system is a highly precise instrument used to measure changes in the height of the product surface in a UST. The laser interferometer system consists of two elements: a laser interferometer mounted on a rugged adjustable stand, and two brass lubes inside of which are positioned floats containing comer-cube beam reflectors. The signal from the two interferometer channels is shown on two local displays which are in rum connected to a data acquisition computer so that long-term testing can be conducted. In operation, the laser measures changes in float position with respect to the interferometers mounted on the stand. The reference standard for these distance measurements is the wavelength of the laser light, which is very tightly reguluied.

Product-level changes are measured simultaneously in both tubes, with one opened and one closed to the product in the tank. Product-level changes in the tube open to the tank are identical to the product-level changes in the tank, and thus are affected by all sources of noise and simulated leaks. Product-level changes in the closed rube ire theoretically affected only by the thermal expansion or contraction of the product and by evaporation or condensation of the product.

Because the hear generated by the laser head and electronics is separated from the interferometers, the height measurements are very precise. The resolution and precision of the laser interferometer (according to its manufacturer's specification) are 0.025 and 0.043 u,m. respectively. The laser is re-zeroed each time the power is turned on or off, or each lime the laser display units are reset. As a consequence, the system is used to measure product-level changes but is not used to measure the depth of product in the tank. The product-level data are sampled at 200 Hz (200 samples/s), with a special-purpose data acquisition program (LIDAS) (261. written in Hewlett-Packard (HP) Basic, on an HP 9836 computer system that collects, downsamples. stores, and displays the data tn real time. The data are transferred between the laser display units and the computer system via two binary-coded decimal (BCD) interface cards and two specifically designed 64-pin connecting cables.

(Volumetric leak detection methods for underground fuel storage tanks, J. W. Maresca, Pg:142)

Previous:

Presently lasers are used as length measuring devices. They are commonly used for positional accuracy measurements. They are also used as length measuring machines of high accuracy (accuracy of the order of 0.01 micrometer). The feedback of this can be used for positioning of the machine and also for computation of measurements. Nowadays it has become a common practice to use laser-measuring system for the calibration of CNC machines.

Using laser-measuring system the measurements performed are reliable, accurate and faster compared to conventional methods. The laser interferometer can be directly interfaced with a computer. This makes it easy for the operator to evaluate the results as per the evaluation procedures mentioned in various standards like AMT, AFNOR, VDI, MTTA, and JIS etc. Using different attachments laser interferometer is also used for other measurements like straightness, flatness, squareness, velocity, pitch, yaw etc.

(Radhakrishnan P., Subrahmanyan S., Raju V., CAD/CAM/CIM, 3rd Edition, p. 513 )

Erdem Ozdemir 030070307 - 1st Week Answers

The Glass Transition Temperature, T_g

_{Material Property}

_{New – Better Answer}

The glass transition is a phenomenon observed in linear amorphous poly­mers, such as poly(siyrene) or poly(methyl methacrylate). It occurs al a fairly well-defined temperature when the bulk material ceases to be brittle and glassy in character and becomes less rigid and more rubbery.

Many physical properties change profoundly at the glass transition tem­perature, including coefficient of thermal expansion, heat capacity, refractive index, mechanical damping, and electrical properties. All of these are dependent on the relative degree of freedom for molecular motion within a given polymeric material and each can be used to monitor the point at which the glass transition occurs. Unfortunately, in certain cases, the values obtained from these various techniques can vary widely. An example is the variation found in the measured values of T_f for poly(mcthyl methacrylate). which range from 110 °C using dilatometry (i.e. where volume changes are moni­tored) to 160 °C using a rebound elasticity technique. This, though, is an extreme example; despite the fact that the measured value of T_s does vary according to the technique used to evaluate it, the variation tends to be over a fairly small temperature range.

The glass transition is a second-order transition. In this it differs from gen­uine phase changes that substances may undergo, such as melting or boiling, which arc known as first-order transitions. These latter transitions arc char­acterised by a distinct volume change, by changes in optical properties (i.e. in the X-ray diffraction pattern and the infrared spectrum) and by die exis­tence of a latent heat for the phase change in question. By contrast, no such changes occur at the glass transition, though the rate of change of volume with temperature alters at the T_$, as illustrated in Figure 3.5.

V

The glass transition can be understood by considering the nature of the changes that occur at the temperature in question. As a material is heated to this point and beyond, molecular rotation around single bonds suddenly becomes significantly easier. A number of factors can affect the ease with which such molecular rotation takes place, and hence influence the actual value that the glass transition temperature takes. The inherent mobility of a single polymer molecule is important and molecular features which cither increase or reduce this mobility will cause differences in the value of 7_?. In addition, interactions between polymer molecules can lead to restrictions in molecular mobility, thus altering the 7* of the resulting material.

T

Figure 3.5 Plot of volume against temperature for a typical polymer passing through its glass transition.

Briefly, the following features are known to influence the glass transition temperature:

(a)  The presence of groups pendant to the polymer backbone, since they increase the energy required to rotate the molecule about primary bonds in the main polymer chain. This is especially true of side chains or branches.

(b)  The presence of inherently rigid structures in the backbone of the mole­cule, e.g. phenylene groups.

(c)        Crosslinking.

(d)  Hydrogen bonds between polymer chains.

(e)  Relative molar mass, which influences 7_g because higher molar mass polymers have less case of movement and more restrictions in their overall molecular freedom than polymers of lower molar mass.

if) The presence of plasticisers. These are discussed in detail in the next section of this chapter.

(The Chemistry of Polymers, John W. Nicholson, Pg:48,49)

Previous:

The glass transition temperature (Tg) is a key parameter in thermosetting polymers, not only from the product performance point of view, but also from the processing point of view, since it may strongly affect the reaction kinetics. The glass transition temperature marks the boundry bbetween the glassy, rigid state of a polymer and the soft, flexible (or fluid) state of the polymer. Below the glass tranition temperature, the available energy is insufficient to allow the molecules coordinated mobility (although there may be some localized motion), so the material is rigid; above the glass transition, the molecules can flow past each other above the glass transition temperature - the polymer is a "melt". In the case of thermoset polymers above the glass transition temperature, the chemical crosslinks prevent the molecules from flowing, but there is enough mobility for molecules to cooperatively relax, and the polymer becomes flexible and "rubbery".

(Cheng S.Z.D., Handbook of thermal analysis and calorimetry: applications to polymers and plastics, 2002, pg.315,316)

Erdem Ozdemir 030070307 -1st Week Answers

Error-Proofing

Better Answer – Manufacturing Management

New:

Error-proofing is another lean manufacturing technique that also supports ISO 9000. Its basic premise is that anything that requires human intervention and judgment to prevent mistakes is a mistake waiting to happen. Dr. Shigeo Shingo introduced this technique to Japan as baka-yoke (fool-proofing). He changed it to poka-yoke because workers inferred from baka-yoke that management perceived them as stupid (Shingo 1986, 45).

Here is an example of poka-yoke. "While the welding operation is in progress, fan-shaped plates, operated by cams, cover in turn all operating buttons except the one needed for the next move. It is impossible for the operator to go wrong" (Ford 1930, 198). Gilbreth's (1911) advice to color-code objects to facilitate proper orientation also is a form of error-proofing. Color-coded wires and matching connection points are an example of this, but keep in mind that some people are color-blind.

Another error-proofing technique is designing keys into parts to pre­vent improper assembly. The large and small prongs on a polarized electri­cal plug, with matching openings in the electrical outlet, are an example. It is impossible to insert the plug backward.

Gages and automatic sorters that prevent the use of substandard parts also are a form of error-proofing. Nonconforming raw materials or compo­nents that enter the constraint can cause downtime, scrap, or rework.⁸ It is therefore very worthwhile to keep such items out of the constraint. Down­stream incorporation of bad parts into good units from the constraint also can be devastating, since post-constraint scrap is irreplaceable.

The concept of error-proofing also applies to workplace safety. The basic principle at Ford's River Rouge plant was, "can't is better than don't." That is, set up the equipment and the job so workers can7 injure themselves instead of telling them, for example, "Don7 monkey with the buzz saw." The System Company (191 la. 114) cites the latter instruction as "one of New England's colloquial proverbs, to which too many four-fingered men call attention " Even Henry Ford's production chief, Charles Sorensen, lost two fingertips when he made wooden patterns for iron casting molds. Interlocks, guards over moving parts, and lockout-tagout are examples of accident-proofi ng.

(Lean enterprise: a synergistic approach to minimizing waste, William A. Levinson, Raymond A. Rerick Pg:77-78)

Previous:

It is a basic principle of manufacturing process design that any mistake whose prevention relies on operator vigilance is sure to occur sooner or later. If a job can be done wrong, it eventually will. This is the concept behind error proofing, or poka-yoke. Error-proofing devices and self-check systems support the lean manufacturing principle: "Don't take it (poor quality), don't make it, don't pass it on." Self-check systems can be treated as a special class of error proofing devices that, instead of actually preventing mistakes, catch them before they can cause significant harm. 
(Beyond the Theory of Constraints, William A. Levinson, p 122)