To study for the GATE PI (Production and Industrial Engineering) exam, you should primarily focus on the official GATE PI syllabus, referring to recommended textbooks refer these books

-Industrial Engineering- M. Mahajan(Dhanpat Rai & Co.), Statistical Quality Control(Dhanpat Rai & Co.)

-Production Engineering- PC Sharma( Production Engineering), PN Rao (Metal cutting & Machine Tools), NPTEL lectures( For Advance Machining Processes), Meteorology (Dhanpat Rai & Co.)

-General Engineering- PK Nag ( Thermodynamics & HMT), S. Ramamrutham, R. Narayanan or Ratan( SOM), VB Bhandari(TOM), Callister (material science)

-Mathematics & Aptitude- Previous year questions are enough for both Mathematics & Aptitude

Also go for previous year question papers, and taking mock tests.

INDIAN OIL , IOCL, ECIL, ONGC, HPCL, BPCL, NPCIL, BAARC, DRDO, etc. do not recruit Production & Industrial Engg. through gate.so you have to go for alternative options.

Like NTPC, BHEL,GAIL,MDL,VIZAG STEEL,SAIL recruit students of PI provided they appear through ME discipline in GATE.

MOREOVER,Check the latest GATE PI syllabus and exam pattern: before starting your preparation.

1.Focus on conceptual understanding: rather than just rote learning.

2.Regularly practice numerical problems: and solve previous year papers.

3.Stay updated on the latest PSU recruitment notifications: and their respective cutoffs.

GOOD LUCK!!!