Plastic moulding methods

-Introduction:

-Large number of method used for processing of plastic. This method is depend upon type of plastic, softening temperature, geometry, size of finished product.

-Following are plastic moulding processes:

1. Compression moulding.

2. Injection moulding.

3. Blow moulding.

4. Vacuum forming.

5. Extrusion.

6. Calendaring.

-Above plastic moulding processes are discuss in detail one by one.

1. Compression moulding:

Compression molding is similar process of closed die forging process. It is mostly used for thermosetting plastic. In this process plastic is put on heated mould and compress under suitable pressure and temperature.

-Process consist following step:

1. Use moulding material loose powder and  granules into heated die cavity. Temperature varies  between 150°C to 180°C.

2. Close the split mould between press plate. Pressure around plate is 30 N/mm2 to 60 N/mm2.

3. Open the split mould. Eject product from the mould manually or  automatically.

4.blow out the tool for remove particle left behind the previous moulding.

5. Lubricate for next moulding.

6. Repeat the process again.

Fig. Compression moulding process.

-Advantage:

1. Lower cost tolling.

2. No gate and sprue or runner required.

3.good for small production.

-Disadvantages:

1. Greater Waste.

2. High labour cost.

3. Slow process time.

4. Not suitable for complex path.

-Application:

Application of compression moulding toilet seat , cup and plate, covers, dishes, electrical switches etc.

2. Injection moulding.

-injection moulding machine can be used for mass production. In this process melted plastic is forced into mould cavity. After cooling mould  can be removed.

-this process is commonly used mass production and prototyping of product.

-Process consists following step:

1. Basic process is  simple. Thermoplastic material supply in pallet form, are dry when necessary, melted injected into mould under pressure and allowed to cool.

2. Then open the mould, and close it for next cycle. The process is repeated again and again

3. Melting the plastic and injected into mould is function of plastifying and injection system.

4. Rate of injection and pressure in the mould achieve by hydraulic system. Injection pressure range form 100-150 Mpa.

5. In this process temperature varies between 150°C to 300°C.

Fig.Injection moulding.

  

-Advantage:

1. Very high production rate.

2. Complex part threads and difficult shape       can produce.

3. Part after process no require further    machining .

-disadvantage:

1. Process is limited to thermoplastics.

2. Die and cylinder should be non corrosive.

-Application:

 Typical applications include plumber fitting, housings ,cups, container, toys, knobs, house ware buckets, telephone receiver, washing machine part and car component.

(Next remaining process are we will discuss in next blogs)