Page 234 - CITS - Welder - Trade Theory

WELDER - CITS

Fig 1

papers, disposable diapers and automobile interiors are the largest use for pure water jet cutting. It is interesting
note that in the case of tissue paper and disposable diapers cutting, water jet process produces very low moisture
on the materials. Pure water jet has a very fine stream of 0.1 mm to 0.25 mm in diameter and cut not only thick
but also thin materials. It produces extremely low cutting forces and it does not introduce heat to material. This
process is also able to cut soft and light materials, which may have detailed
Abrasive Water jet Cutting

In the abrasive waterjet, the waterjet stream accelerates abrasive particles and those particles, not the water,
erode the material. Therefore, the abrasive water jet is hundreds of times more powerful than a pure waterjet and
thus, it is able to cut harder materials, such as, ceramics, composites, metals, stone, marble etc.
Abrasive waterjet usually has a stream of 0.5 mm to 1.3 mm and it can also cut geometries with details and it
produces no heat affected zone, mechanical stresses and little burr like pure waterjet cutting. In addition to this,
abrasive water jet cutting process is able cut materials with 250 mm thickness.
Abrasives
The most common abrasive in waterjet cutting is almandine garnet 150-300 μm particle size is common for
cutting most of the materials with a good finish. If particle size is lowered then a better quality is achieved. If
coarser grade is used for cutting, finish quality gets worse while cutting speed increases [4]. When more abrasive
is added to water jet, first, cutting speed increases and after a certain point it starts to decrease. This is also valid
for cost in inverse proportion. When more abrasive is used, first, total cost per inch decreases, then again after a
certain point, total cost starts to increase. Since fastest cutting speed means lowest cost per millimeter, one must
try to achieve highest cutting speed while maintaining cutting quality Moreover, high abrasive flow rate does not
mean that cutting quality would be high. In fact, there is an optimum level for each setting.
Effect of Parameters in Water jet Cutting Some researchers have studied the effects of water pressure, abrasive
flow rate, standoff distance and traverse speed on surface roughness and depth of cut. They found out that
when water pressure gets higher, the depth of cut increases; and when traverse speed gets higher, depth of cut
decreases. High traverse speed also results in higher surface roughness. When abrasive flow rate gets higher,
first, surface roughness decreases and then after a certain point it increases. Similarly, when standoff distance
gets higher gradually, first, surface roughness decreases and after a certain point it increases

Advantages
a Short machine setup times
b Easy automation

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CITS : C G & M - Welder - Lesson 77 - 82 CITS : C G & M - Welder - Lesson 77 - 82