Plastic injection moulding machine ,
Advantages & disadvantages
Advantages:
No heating required
Better surface finish
Superior dimensional contro , die cast molds .
Better reproducibility and interchangeabilit , plastic housing .
Directional properties can be imparted into the metal
Contamination problems are minimized
The increase in strength due to strain hardening is comparable to that of heat treating. Therefore, it is sometimes more economical to cold work a less costly and weaker metal than to hot work a more expensive metal that can be heat treated, especially if precision or a fine surface finish is required as well. The cold working process also reduces waste as compared to machining, or even eliminates with near net shape methods. The material savings becomes even more significant at larger volumes, and even more so when using expensive materials, such as copper. The saving on raw material as a result of cold forming can be very significant, as is saving machining time. Production cycle times when cold working are very short. On multi-station machinery, production cycle times are even less. This can be very advantageous for large production runs.
During cold working the part undergoes work hardening and the microstructure deforms to follow the contours of the part surface. Unlike hot working, the inclusions and grains distort to follow the contour of the surface, resulting in anisotropic engineering properties.
Disadvantages:
Greater forces are required
Heavier and more powerful equipment and stronger tooling are required
Metal is less ductile
Metal surfaces must be clean and scale-free
Intermediate anneals may be required to compensate for loss of ductility that accompanies strain hardening
The imparted directional properties may be detrimental
Undesirable residual stress may be produced
Due to the large capital costs required to setup a cold working process the process is usually only suitable for large volume productions.
Intermediate annealings may be required to reach the required to continue cold working a workpiece, otherwise it may fracture if the ultimate tensile strength is exceeded. An anneal may also be used to obtain the proper engineering properties required in the final workpiece. Also, the distorted grain structure that gives the workpiece its superior strength can lead to residual stresses.
Cold worked items suffer from a phenomenon known as springback, or elastic springback. After the deforming force is removed from the workpiece the springs back slightly. The amount a material springs back is equal to Young’s modulus for the material from the final stress.
Processes
Squeezing
Rolling
Swaging
Extrusion
Forging
Sizing
Riveting
Staking
Coining
Peening
Burnishing
Hubbing
Thread rolling
Bending
Angle bending
Roll bending
Draw and compression
Roll forming
Seaming
Flanging
Straightening
Shearing
Slitting
Blanking
Piercing
Lancing
Perforating
Notching
Nibbling
Shaving
Trimming
Cutoff
Dinking
Drawing
Tube drawing
Wire drawing
Spinning
Embossing
Stretch forming
Sheet metal drawing
Ironing
Superplastic forming
References
Notes
^ a b c d e Degarmo, p. 375.
^ a b Degarmo, p. 378.
^ Degarmo, p. 376.
^ a b c d Degarmo, p. 408.
Bibliography
Degarmo, E. Paul; Black, J T.; Kohser, Ronald A. (2003), Materials and Processes in Manufacturing (9th ed.), Wiley, ISBN 0-471-65653-4 .
Categories: MetalworkingHidden categories: All articles to be merged | Articles to be merged from October 2008
