In abrasive jet machining (AJM) process, fine abrasive particles entrained in gas stream are allowed to strike the work surface at high velocity (100 – 300m/s) to gradually erode material. Mechanism of material removal is nothing but impact erosion. Eroded material in the form of solid tiny particles and used abrasive grits are moved away from machining zone by the carrier gas. Reuse of these abrasive particles is not recommended because of following two reasons.
- Abrasives get contaminated by wear debris (removed work material).
- Abrasives lose its sharp edges and thus reduced cutting ability.
Reason-1: Contamination by wear debris
When abrasive particles are made to strike the work surface, they erode material in the form of solid tiny particles and both get mixed up. The mixture of wear debris and abrasives is subsequently taken away from the machining zone by pressurized carrier gas. Size of the removed tiny particles is usually similar to the size of abrasives grits (both in the range of 10 – 100µm). In this condition, it becomes very difficult to separate one from another. In fact, the cost of 100% separation of abrasives from mixture becomes higher than the cost of abrasive itself. On the other hand if metal particles are not completely separated from mixture then it will agglomerate and will tend to chock the pipeline. Thus it is not economical to reuse abrasive particles in abrasive jet machining.
Reason-2: Loose of cutting ability
After the first impact, abrasive particles lose its sharpness. Sharpness is one of the desired properties of abrasive particles as it helps easy and efficient cutting (eroding). So reuse of abrasive particles may result low material removal rate (MRR) and poor surface quality.
What will happen if abrasive particles are reused?
If abrasive particles are reused for abrasive jet machining, the following unintended results are likely to occur.
- Presence of agglomerated coarse particles within the abrasive jet.
- Choking in the pipelines.
- Faster erosion of nozzle (reduced nozzle life).
- Unbalanced mixing ratio and flow rate.
- Fluctuation of striking velocity of abrasive jet (because of jamming in pipeline).
- Lower material removal rate (MRR).
- Poor surface quality.
- More embedded abrasive grits on machined surface.
- Book: Nonconventional Machining by P. K. Mishra (Narosa Publishing House).
- Book: Unconventional Machining Processes by T. Jagadeesha (I. K. International Publishing House Pvt. Ltd.).