ADVANCED METHODS OF MANUFACTURING LAB

Course Code: BTM 821 Credit Units: 01

Experiment no: 1-

Study of G and M codes for NC Machine Tools.

A g-code program consists of a collection of statements/blocks to be executed in a sequential

manner. Each statement comprises a number of wordsa letter followed by an integer

number. The first word in a statement is the block number designated by the letter N followed by

the number of the block (e.g., N0027, for the 27th line in the g-code program). The next word is

typically the preparatory function designated by the letter G (hence, the letter g in g-code)

followed by a two-digit number. Several examples of G words are given in Table 1.

TABLE 1 Some G Words

Code Function Code Function

G00 Point-to-point motion

G01 Linear-interpolation motion

G02 Clockwise circular-interpolation

G03 Counterclockwise circular interpolation motion

G20 Imperial units

G21 Metric units

G32 Thread cutting motion

G98 Per-minute feed rate

G99 Per-revolution feed rate

The preparatory function is followed by dimensional words designated by axes letters X, Y, and

Z with corresponding dimensions, normally expressed as multiples of smallest possible

incremental displacements (e.g., X3712 Y-47000 Z12000; multiples of 0.01 mm) or in absolute

coordinates (e.g., X175.25 Y325.00 Z136.50). The feed rate and spindle speed words are

designated by the letters F and S, respectively, followed by the corresponding numerical values

in the chosen units. Next come the tool number word designated by the letter T and the

miscellaneous function word designated by the letter M (Table 2).

A typical g-code program block is

N0027 G90 G01 X175:25 Y325:00 Z136:50 F125 S800 T1712 M03 M08;

TABLE 2 Some M Words

M00 Program stop (during run)

M02 End of program

M03 Spindle start clockwise

M05 Spindle stop

M08 Coolant on

M11 Tool change

M98 Call a subprogram

M99 Return to main program

Experiment no: 2-

Study of Robots for material handling. Material handling is defined by the Materials Handling Institute as the movement of bulk

packaged and individual goods, as well as their inprocess and postprocess storage, by means of manual labor or machines within the boundaries of a facility. Material handling does not add value to the product but only cost. Thus the objective of material handling is the efficient movement of goods for the on-time delivery of correct parts in exact quantities to desired locations in order to minimize associated handling costs.

Material handling equipment can be classified according to the movement mode: above-floor transportation (e.g., belt conveyors, trucks, etc.), on-floor transportation (e.g., chain conveyors), and overhead transportation (e.g., cranes). INDUSTRIAL TRUCKS Industrial powered trucks are the most versatile and flexible material handling devices in manufacturing. They can transport small or large loads over short distances in a plant with minimal restrictions on their movements. Powered trucks are generally classified into two broad categories: lift trucks and tow tractors. Lift Trucks

Powered (lift) fork trucks are the most common industrial trucks used in the manufacturing industry for the transportation of parts placed on pallets. The basic elements of a fork truck are

1) the mast assemblya one-stage or multistage mechanism that lifts the forks, most commonly, through hydraulic power;

2) the fork carriagea carriage that is mounted on the mast, to which the forks are attached, with a primary objective of preventing loads from falling backward once they have been lifted off the ground; and,

3) the forksthe two forks can be of fixed configuration or with variable horizontal distance to accommodate varying load sizes. On most trucks, the mast assembly, including the forks, can be tilted backwards (4 to 12) for increased security during motion.

Tow Tractors

A variety of wheeled vehicles are utilized in the manufacturing industry for towing (pulling) single- (or multi-)trailer cart attachments. Most tractors (like forklift trucks) are battery operated for maintaining clean-air environments within closed plants. The load carried can be palletized or (manually) placed directly on the trailer. The typical load-carrying capacity of electric powered tow tractors ranges from 5,000 to 25,000 kg. As with forklift trucks, the primary disadvantage of tow tractors is their dependence on human drivers. In the following subsection, automated guided vehicles will be presented as a potential answer to this disadvantage.

Automated Guided Vehicles The Materials Handling Institute defines an automated guided vehicle (AGV) as a

driverless vehicle equipped with an on-board automatic guidance device (electro-optical or electromagnetic) capable of following preprogrammed paths. The path information can be uploaded onto an onboard computer through (radio-frequency, RF) wireless communication or through a temporary (physical) connection to the plants computer network. Reprogrammability of AGVs is their primary asset. Occasionally, AGVs are referred to as mobile robots owing to their reprogrammabilty. This is an erroneous classification, since AGVs mostly do not include a robotic manipulator arm capable of interacting with the environment.

Navigation guidance: Navigation guidance for AGVs can be in two forms: passive or active tracking of a guidepath. Both methods rely on noncontact tracking of a guidepath installed on or in the floor of the manufacturing plant. Optical passive tracking is the most economical and flexible method, where the guidepath is defined by a painted or taped-on strip. An optical detection device mounted underneath the vehicle follows the continuous guidepath (a collection/network of branched paths) and guides the vehicle to its destination (Fig. 4). Naturally, such a method can only be employed if the painted/taped-on guidepaths can be maintained reasonably well for prolonged periods of time. Load carrying capacity: Most unit-load carrying AGVs have been designed to cope with weights in the range of 500 to 1,000 kg, though some custom-made vehicles can carry up to 50,000 kg. Tractor-type AGVs have been commonly designed to pull weights of up to 20,000 kg. AGVs can achieve typical speeds of up to 2 to 4 km/hr.

CONVEYORS

Conveyors are a broad class of material handling (conveying) equipment capable of transporting goods along fixed paths. Although conveyors are the least flexible material handling equipment (owing to their path inflexibility), they provide manufacturers with a cost-effective and reliable alternative. Conveying equipment is generally classified as above-floor conveyors versus on-floor or overhead tow-line conveyors. Both classes allow horizontal and inclined conveying, while tow-line type conveyors also allow vertical conveying (e.g., bucket elevators). In the following subsections, several examples of conveyors will be discussed with the emphasis being on conveying for manufacturing. Above-Floor Conveyors

Above-floor conveyors have been also classified as package handling conveyors owing to their primary application of transporting cartons, pallets, and totes. On the factory floor, they are utilized to transport (palletized/fixtured) workpieces (e.g., engine blocks, gearboxes, household items) from one assembly station to another. In a networked environment, where branching occurs, automatic identification devices must be utilized to route parts correctly to their destination along the shortest possible path. Roller Conveyors Powered roller conveyors are line-restricted conveying devices comprising a set of space rollers mounted between two side frame members and elevated from the floor by a necessary distance (Fig. 6). Rolling power can be achieved by having a moving flat belt underneath the rollers or a set of drive belts rotating the rollers individually, yielding speeds of up to 30 to 40 m/min. Belt Conveyors The early use of belt conveyors can be traced back to late 1800s in the mining industry. Today, the flat-belt version of such conveyors (versus the ones used in bulk-material transfer with side-inclined rollerstroughing idlers) are commonly used in the manufacturing industry for the transfer of individual (unpalletized) workpieces, as well as cartons/bins/etc. The highly durable, endless belt is placed in tension between two pulleys and normally operated in uni-directional motion. The belt is the most important and expensive component of a belt conveyor. A carcass, enclosed between top and bottom covers, provides the tensile strength necessary for conveying and absorbs the impact forces by workpieces being loaded onto the belt. The top cover protects the carcass against tear and wear and against high temperatures when needed (up to 200C). Steel is commonly used in the construction of the carcass for high tension applications.

INDUSTRIAL ROBOTS Robotics is a multidisciplinary engineering field dedicated to the development of

autonomous devices, including manipulators and mobile vehicles. In this section, our focus will be on robotic manipulators developed for industrial tasks. These devices are reprogrammable and multifunctional manipulators of goods and tools. The word robot has been often traced to the Czech word for forced labor mentioned by Karel Capek in his science fiction play Rossums Universal Robots around 1921. The modern concept of industrial robotic manipulators was only

introduced in late 1950s by G. C. Devol (U.S. Patent 2988237) and later championed by J. Engelbergeroriginators of the first industrial robot by Unimation Inc. in the 1959. The first installation of the Unimate robot for loading/unloading a die-casting machine at GM was in 1961. Today industrial robots can be found in almost all manufacturing applications, ranging from machine servicing to welding to painting. Mechanical Design

An industrial robotic manipulator is typically an open-chain mechanism (fixed at one end to a base and free at the other end with an attached endeffector), whose mobility is defined by the number of independent joints in its configuration. As can human arms, these robotic mechanisms can manipulate objects/tools within a workspace defined by the geometry of the arm, via the end effector/gripper attached to the last link of the arm. The mobility of the end-effector is formally defined by the number of degrees of freedom (dof ) of the robotic arm.

Classification of industrial robots is carried out according to their configuration based on the geometry of their workspace, primarily, defined by the first three joints: Rectangular-geometry robots: There exist two primary robot configurations that belong to this group: Cartesian and gantry. Both configurations employ three linear joints assembled orthogonally for best achievable repeatability. The gantry type configuration is reserved for increased payload capacity due to its better structural stiffness and for better workspace utilization (e.g., electronic components assembly). Rectangular-geometry robots can have up to three additional (closely located) rotary joints following the first three linear joints for a total of six-dof mobility. Cylindrical-geometry robots: There exist two primary robot configurations that belong to this group: cylindrical and SCARA. The former has a sequence of rotary-linear-linear joints assembled orthogonally, while the latter has a sequence of rotary-rotary-linear joints. The cylindrical robot configuration was originally developed for fast periphery access with good repeatability (due to the linear joints).

The SCARA (selective compliance assembly robot arm) configuration, on the other hand, was developed in the late 1970s for vertical insertion of small parts (e.g., watch components) placed on a plane, thus requiring a maximum of four dof. SCARA robots provide manufacturers with complete three-dof mobility in the part-placement plane and one-dof (vertical motion) linear mobility to reach the plane, for a total of four-dof mobility. In contrast, most cylindrical robots would have three additional (rotary) dof at their configuration end for a total six-dof mobility necessary for an arbitrary motion in three-dimensional space. Spherical-geometry robots: There exist several robot configurations that yield spherical workspace geometries: spherical and articulated (anthropomorphic, human-like) types are the most common (Figs. 12a, 12b). The former (the first commercial robot configuration) has a sequence of rotaryrotary- linear joints assembled orthogonally to provide manufacturers with a fast reach-in/at capability along simple trajectories (e.g., machine loading/ unloading). The latter articulated robot configuration provides maximum reachability among all available manipulator geometries (e.g., reaching into automobile bodies for spray painting) with a sequence of three rotary joints.

Experiment no: 3-

Tool planning and selection for Turning Centre & Machining

Centre. The basic difference between milling and turning is that in milling the cutter is being

rotated and the part is being feed into the path of the cutter, in turning the part is being rotated and the tool is being feed along or perpendicular the center of rotation. The most basic lathe (turning) operations are: facing, turning, grooving, parting, drilling, boring, reaming threading. Because of the nature of turning some additional tools are being used.

Facing operation involves cutting the end of the material such that the resulting end is perpendicular to the centerline of the rotation. Turning involves removal of material from the outside diameter of rotating material. Different profile shapes can be created including, cylinders, tapers, contours, shoulders. The toll shapes for facing and turning are very similar, with facing tools having less side clearance.

Grooving requires the tool to be fed into the work in a direction perpendicular to the work centerline. The cutting edge of the tool is on its end.

Parting involves cutting off the part from the main bar stock. This operation is done with a cutoff tool that has some clearance on the sides while the cutting is done with the front of the tool. The tool is fed into the part perpendicular to the center of rotation.

Threading on a CNC lathe is done with a tool which has a 60 included angle insert. This operation involves cutting of helical grooves on the outside or inside surface of a cylinder or cone.

It is important to mention the materials used in turning. Cemented carbides are formed by using tungsten carbide sintered in a cobalt matrix. Some grades contain titanium carbide, tantalum carbide or some other materials as additives. To increase the wear resistance, cemented carbides are coated. Coating materials include titanium carbide or aluminum oxide. Both coatings offer excellent performance on steel, cast irons and nonferrous materials. Another type material used is ceramic. It is a very hard material formed without metallic bonding. It displays exceptional resistance to wear and heat load. The most popular material used in ceramics is aluminum oxide. Where everything else fails we turn to diamonds. There are two types of diamond cutting materials. The first is a single crystal natural diamond. It has an outstanding wear resistance but low shock resistance. The other type diamond consists of smaller synthetic diamond crystals fused together at high temperatures and pressure. This material displays good resistance to shock loading. Diamond tools offer substantial improvement over carbides.

Experiment no: 4-

Tool Design for a plastic processing. The first step in designing a plastic product is the selection of an appropriate polymer (and reinforcing material, when needed). Factors in choosing a material for a specific application include mechanical properties, thermal and chemical properties (for example, resistance to ultraviolet sunlight), hazards (e.g., toxicity, flammability), appearance (e.g., transparency), and

economics (including manufacturing costs). For the automotive parts industry, for example, engine parts must be resistant to automotive fluids and high temperatures. Similarly, body panels must be resistant to high paint-oven temperatures or, when not painted, they must have extra resistance to water absorbtion and UV light. Ski bindings, on the other hand, must be resilient to low temperatures and be very rigid.

From a manufacturing perspective, since most parts are fabricated in molds, part design strongly impacts on mold design and thus manufacturability. The filling of the mold as well as the cooling of the part within the mold can be simulated using computer-aided engineering (CAE) analysis tools for better part design. Such analyses will remind designers to refrain from using sharp corners and/or sudden wall thickness changes that would disrupt the uniform flow of the resin in the cavities. Changes in wall thicknesses also result in additional shrinkage problems, such as stress concentrations, warpage, and even sink marks. Sink marks predominantly occur opposite to ribs, flanges, and bosses, which are used for increasing stiffness and strength without adding weight to the part. Thus a rule of thumb is to have their thickness be 50 to 75% of the wall thickness they are reinforcing.

Shrinkage problems are of major concern in the design of thermoset plastics. Mold design should accommodate for significant shrinkages in the curing of such materials. The problem is further complicated for composite parts, where fiber wetting as well as uniform fiber volume distribution are major concerns. A list of design guidelines for thermoset plastics and composites, which is also be applicable to thermoplastic parts, is given here:

Wall thicknesses must be kept as uniform as possible with gradual changes between sections through the use of fillets, tapers, etc.

Tapers should be used for ease of removal from the mold. Side holes and/or undercuts should be avoided for low-cost molds. Holes must not be placed too near to edges/faces to avoid fracture. Fine screw threads should be avoided in composite part design, since even short fibers

(less than 3 mm in length) would not be present at the threads. Raised letters can be manufactured more easily (through engravings in the mold cavity).

Experiment no: 5

Pattern design for a casting components: Cope, Drag and Gating

design. A pattern is a model or the replica of the object (to be casted). It is embedded in molding

sand and suitable ramming of molding sand around the pattern is made. The pattern is then withdrawn for generating cavity (known as mold) in molding sand. Thus it is a mould forming tool. Pattern can be said as a model or the replica of the object to be cast except for the various al1owances a pattern exactly resembles the casting to be made. It may be defined as a model or form around which sand is packed to give rise to a cavity known as mold cavity in which when molten metal is poured, the result is the cast object. When this mould/cavity is filled with molten

metal, molten metal solidifies and produces a casting (product). So the pattern is the replica of the casting. OBJECTIVES OF A PATTERN

1) Pattern prepares a mould cavity for the purpose of making a casting. 2) Pattern possesses core prints which produces seats in form of extra recess for core

placement in the mould. 3) It establishes the parting line and parting surfaces in the mould. 4) Runner, gates and riser may form a part of the pattern. 5) Properly constructed patterns minimize overall cost of the casting. 6) Pattern may help in establishing locating pins on the mould and therefore on the casting

with a purpose to check the casting dimensions. 7) Properly made pattern having finished and smooth surface reduce casting defects.

FACTORS EFFECTING SELECTION OF PATTERN MATERIAL The following factors must be taken into consideration while selecting pattern materials.

1) Number of castings to be produced. Metal pattern are preferred when castings are required large in number.

2) Type of mould material used. 3) Kind of molding process. 4) Method of molding (hand or machine). 5) Degree of dimensional accuracy and surface finish required. 6) Minimum thickness required. 7) Shape, complexity and size of casting. 8) Cost of pattern and chances of repeat orders of the pattern

TYPES OF PATTERN The types of the pattern and the description of each are given as under.

1) One piece or solid pattern 2) Two piece or split pattern 3) Cope and drag pattern 4) Three-piece or multi- piece pattern 5) Loose piece pattern 6) Match plate pattern 7) Follow board pattern 8) Gated pattern 9) Sweep pattern 10) Skeleton pattern 11) Segmental or part pattern

Cope and drag pattern In this case, cope and drag part of the mould are prepared separately. This is done when the complete mould is too heavy to be handled by one operator. The pattern is made up of two halves, which are mounted on different plates.

Gated pattern In the mass production of casings, multi cavity moulds are used. Such moulds are formed

by joining a number of patterns and gates and providing a common runner for the molten metal, as shown in Fig. 10.7. These patterns are made of metals, and metallic pieces to form gates and runners are attached to the pattern. FACTORS CONTROLING GATING DESIGN The following factors must be considered while designing gating system.

1) Sharp corners and abrupt changes in at any section or portion in gating system should be avoided for suppressing turbulence and gas entrapment. Suitable relationship must exist between different cross-sectional areas of gating systems.

2) The most important characteristics of gating system besides sprue are the shape, location and dimensions of runners and type of flow. It is also important to determine the position at which the molten metal enters the mould cavity.

3) Gating ratio should reveal that the total cross-section of sprue, runner and gate decreases towards the mold cavity which provides a choke effect.

4) Bending of runner if any should be kept away from mold cavity. 5) Developing the various cross sections of gating system to nullify the effect of turbulence

or momentum of molten metal. 6) Streamlining or removing sharp corners at any junctions by providing generous radius,

tapering the sprue, providing radius at sprue entrance and exit and providing a basin instead pouring cup etc.