Srinivas School of Engineering, Mukka, Mangalore

VII Semester B. E - (A, B)I-IA Test- Scheme of Evaluation

Tool Design (07ME62)Duration: 1 hour Date: 5/09/2015Staff: Mr Vishwas, Mr Raghavendra E H Max Marks: 25

Note: Answer any ONE full question from each part.

PART – A

1. List the ejection methods and explain any one with a neat sketch. (10 marks)

Ans. Ejection system: (2)

Parts of ejector plate:

i. Ejector plateii. Ejector rod

iii. Retaining plate iv. Ejector rod bush

Ejector plate assembly is that part of the mould in which ejector element

Ejector plate assembly

Ejector plate assembly is the part of the mould in which ejector element is attached one end of ejector rod is threaded and screwed into the ejector plate.

Ejection methods:

Depending on the shape and size of the moulding the various ejection methods are as follows: (2)

Pin ejection Sleeve ejection Bar ejection Blade ejection Air ejection Stripper ejection

Pin ejection method: (6)

This is the simplest method of ejecting the moulding. Moulding is ejected by the application of a force by a steel rod called ejector pin.

The location of an ejector pin elements and number of ejector pins used depends on shape of the component. The ejector pin should be so located that the moulding is pushed off evenly from the core.

Shouldered pin

Pin ejection method by using multi-pins

2. Explain compression moulding with a neat sketch and list out its advantages and disadvantages.

(10 marks)

Ans. Compression Moulding: (1)Compression moulding process is one of the low cost moulding methods as compared to

injection moulding and transfer moulding. It is a high pressure forming process in which the molten plastic material is squeezed directly into a mould cavity by the application of heat and pressure to conform to the shape of the mould.

Working Principle (5)In this process, the predetermined amount of charge of plastic material is placed in the lower

half of a mould cavity. The plastic material is preheated before inserting into the mould cavity. The mould cavity is closed with upper movable half mould and pressure is applied to compress the material in to the mould cavity. This causes the raw material to be squeezed out to take the shape of the mould cavity. The application of the heat and pressure increases the polymerization process. Hence, plastic material is cured. The temperature of the mould cavity is usually in the range of 130- 200°C. Generally, the hydraulic pressure is required in the range of 7-25 MPa to squeeze the plastic material. The mould cavity is then cooled for sometimes so that moulded plastic part gets solidified. The mould cavity is then opened and the final product is taken out with the help of ejector pin. The moulded part may require the finishing operation.

In compression moulding, the charge of plastic material may be inserted into the mold cavity either as a powder, granules or as a preformed. The manufacturing cycle time (heating, cooling, and part ejection) may be long (about 1-6 minutes). For high production rate, it is desirable to have multi cavity molds. Compression mold cavity can also be available in a wide variety of shapes and sizes; therefore plastic products can be manufactured into different shapes and sizes.There are four important factors to be considered before compression molding process:

Amount of plastic material (charge) Heating time and melting temperature of plastic material Pressure required to squeeze the material in to the mold cavity Cooling time

Two different types of moulding compounds i.e. bulk moulding compound (BMC) and sheet moulding compound (SMC) are commonly used in compression molding process.

In bulk moulding compound, the plastic materials are blended with fillers and short fibers and placed into the mold cavity. In SMC, the long fiber sheet is usually cut according to the mold cavity and placed into the mold surface. The resin is placed on the fiber sheet. It is a layer by layer making process. The process is completed until desired thickness is obtained. The long fiber sheet results in better mechanical properties as compared with the bulk molding compound products. In both the molding compounds (BMC and SMC), the plastic materials are conformed to the mold cavity, with the application of heat and pressure.

Compression moulding setup

Applications (1)Compression moulding process is used for manufacturing electrical and electronic equipments

(electrical wall receptacles, circuit breakers, television cabinets, radio cases, electric plugs and sockets, electrical switch, fuse box, electricity meter housing), brush and mirror handles, trays, cookware knobs, clothes dryer blower fan blade, cooking utensils, milling machine adjustment wheel, water testing equipment buttons, dinnerware, appliance housings, aircraft main power terminal housing, pot handles, dinnerware plates, automotive parts (such as hoods, fenders, scoops, spoilers, gears), flatware, buttons, buckles, and large container. Compression moulding is also suitable for heavy moulding applications.

Advantages (3) The advantages of the compression moulding process are as following:

Low initial setup costs and fast setup time Heavy plastic parts can be moulded Complex intricate parts can be made Good surface finish of the moulded parts Wastes relatively little material as compared with other methods the moulding process is cheaper as compared to injection moulding Best method for holding close tolerance More uniform density of moulded parts are achieved

DisadvantagesThe disadvantages of the compression moulding process are as following:

Low production rate Limited largely to flat or moderately curved parts with no undercuts

PART – B

3. Define injection moulding and explain the process of working with a neat sketch (ram type). (10

marks)

Ans. Injection moulding : (1)

It is a manufacturing process for producing parts by injecting material into a mould. Injection moulding can be performed with a host of materials, including metals, glasses, elastomers, confections, and most commonly thermoplastic and thermosetting polymers. Material for the part is fed into a heated barrel, mixed, and forced into a mould cavity, where it cools and hardens to the configuration of the cavity.

Injection moulding machine: (4)Injection molding machines consist of two basic parts, an injection unit and a clamping unit.

Injection molding machines differ in both injection unit and clamping unit. The name of the injection molding machine is generally based on the type of injection unit used.

Elements or parts of injection moulding machine: (2)

1. Injection unitThe injection unit melts the polymer resin and injects the polymer melt into the mold. The unit may be: ram fed or screw fed.2. Feed hopperThe container is holding a supply raw molding material to be fed. The hopper located over the barrel and the feed throat connects them.3. Injection ramThe ram or screw that applies pressure on the molten plastic material to force it into the mold cavities.4. BarrelBarrel is a major part that melts resins transmitted from hopper through screws and structured in a way that can heat up resins to the proper temperature. A band heater, which can control temperatures in five sections, is attached outside the barrel. Melted resins are supplied to the mold passing through barrel head, shot-off nozzle, and one-touch nozzle.5. Clamping unitThe clamping unit holds the mold together, opens and closes it automatically, and ejects the finished part. The mechanism may be of several designs like mechanical, hydraulic or hydro-mechanical.

6. Injection moldThere are two main types of injection molds: cold runner (two plate and three plate designs)

and hot runner.

7. Injection platensSteel plates on a molding machine to which the mold is attached. Generally, two platens are

used; one being stationary and the other moveable, actuated hydraulically to open and close the mold. It actually provide place to mount the mould. It contains threaded holes on which mould can be mounted using clamps.

Principle of Injection Moulding: (3)The injection moulding system consists of three main components:1. Mould2. Plasticising system3. System for mould clamping

For the injection molding cycle to begin, four criteria must be met: mold open, ejector pins retracted, shot built, and carriage forward. When these criteria are met, the cycle begins with the mold closing. This is typically done as fast as possible with a slow down near the end of travel. Mold safety is low speed and low pressure mold closing. It usually begins just before the leader pins of the mold and must be set properly to prevent accidental mold damage. When the mold halves touch clamp tonnage is built. Next, molten plastic material is injected into the mold. The material travels into the mold via the sprue bushing, and then the runner system with the help of plunger movement and delivers the material to the gate. The gate directs the material into the mold cavity to form the desired part. This injection usually occurs under velocity control. When the part is nearly full, injection control is switched from velocity control to pressure control. This is referred to as the pack/hold phase of the cycle. Pressure must be maintained on the material until the gate solidifies to prevent material from flowing back out of the cavity. Cooling time is dependent primarily on the wall thickness of the part. During the cooling portion of the cycle after the gate has solidified, plastication takes place. Plastication is the process of melting material and preparing the next shot.

Shot is a term used to describe the total amount of material that has been injected into the mould in one cycle including component to be made, runner, gates and sprues.

The basic injection cycle is as follows: Mold close – injection carriage forward – inject plastic – metering – carriage retract – mold open – eject part(s) Some machines are run by electric motors instead of hydraulics or a combination of both. The water-cooling channels that assist in cooling the mold and the heated plastic solidifies into the part. Improper cooling can result in distorted molding. The cycle is completed when the mold opens and the part is ejected with the assistance of ejector pins within the mold.

4. Explain 2 plate and 3 plate mould with a neat sketch.(10 marks)

Ans. Types of Injection moulds (6)There are many types of injection moulds and tooling in use today, such as two-plate, three-

plate and stack moulds. Two and three-plate moulds are more commonly used for heavy wall and non-packaging products. Both cold and hot-runner systems are used for two and three-plate moulds. Each mould component must be machined and finished to exact dimensions with very tight tolerances and must be heat-treated to be able to withstand very high injection and clamp pressures.

TWO PLATE MOLD THREE PLATE MOLD

A two-plate mould has only one parting line. If a runner is used, it is connected to the moulded product and requires manual removal and separation after the part is ejected. This type of mould is the least expensive to make and is commonly used for parts with relatively simple geometries. Three-plate moulds have two parting lines, one for the runner system and one for the moulded product. When the mould opens, the runner is automatically separated from the product to allow separate handling. This eliminates the need for manual separation and removal and the sprue and runner system may be fed directly to a recycling system. This type of mould is more expensive than the two-plate mould. (4)

PART – C

5. Explain cooling system in injection moulding with a neat sketch. (5 marks)

Ans. Mould Cooling: (2)The operating temperature of a mould depends on the following factors:

Type of plastic material used for the process Wall section of the moulding Length of flow within the impression Length of feed system.

Mould cooling process: (3)

Mould cooling process accounts for more than two-thirds of the total cycle time in the production of injection moulded thermoplastic parts. An efficient cooling circuit design reduces the cooling time, and in turn, increases overall productivity of the moulding process.

Moreover, uniform cooling improves part’s quality by reducing residual stresses and maintaining dimensional accuracy and stability.

The mould itself acts as heat exchanger, in which the heat from the hot polymer or thermo-plast melt is taken away to the coolant circuit.

The molten plastic must be cooled rapidly to harden plastic, to yield minimum production time.

The lower the mould temperature, the faster the cycle time. Rapid cooling increases residual stress and molecular orientation. To maintain the requires temperature difference between the mould and plastic material water

or some other fluid is circulated through the holes or channels within the mould and these holes or channels are called as flow ways.

Complete system of flow ways or water ways are called as circuit.

Integer cavity plate cooling system using water circulated through holes

6. Explain forming process and list out the types of forming process.(5 marks)

Ans. Forming Processes: (2)Forming processes are particular manufacturing process which make use of suitable stresses

(like compression, tension, shear) to cause plastic deformation of the materials to produce required shapes.

During forming processes no material is removed, i.e. they are deformed and displaced.Primary Metal Forming Processes (3)

Rolling Forging Extrusion Tube and wire drawing and Deep drawing Although Punching and Blanking operations are not metal forming processes however these

will be covered due to similarity with deep drawing process.