Question

1. Which of the following description is not correct for injection molding:
   1. it is better to avoid depressions (undercuts) on the inner surfaces
   2. threads are hard to be made
   3. sharp corners should be replaced by round corners
   4. a draft angle should be designed

1. The high temperature of a cutting tool during turning process is mainly because:
   1. shear deformation of the workpiece material
   2. friction of the tool with machined surface
   3. friction of the tool with chips                        
   4. vibration of the machine too
      
      Which one is an important characteristic/advantage of AM processes that is also a source of defects in some finished products?
      1. Cost per unit part
      2. Layer by layer fabrication
      3. Using powders in some processes
      4. Uncontrolled grain growth

Answer 1

1) sharp corners should be replaced by round corners is not correct for injection molding.

2) During machining process heat is generated at the cutting point from three sources, as
indicated in Fig.1. Those sources and causes of development of cutting
temperature are:
• Primary shear zone (1) where the main a part of the energy is
converted into heat
• Secondarily deformation zone (2) at the chip – tool interface where
further heat is generated thanks to rubbing and / or shear
• At the wiped out flanks (3) thanks to rubbing between the tool and therefore the
finished surfaces.

3 Vt VC Fig. 2.7.1 Sources of heat generation in machining

The heat generated is shared by the chip, cutter and therefore the blank. The generation of sharing that heat depends upon the configuration, size and thermal conductivity of the tool – work material and therefore the cutting condition. Fig. 2 visualises that maximum amount of warmth is over excited by the flowing chip. From 10 to twenty of the entire heat goes into the tool and a few heat is absorbed within the blank. With the rise in cutting velocity, the chip shares heat increasingly.

100 blank CHIP tool JOB Share of heat % TOOL chip Vc O > 100 m/min Cutting velocity, Vc →

Fig-2: Generation of heat between tool, chip and blank

3). Cost per unit part is an important characteristic/advantage of AM processes that is also a source of defects in some finished product.