Aprilliano , Francisko, et al. “COMPARISON OF VARIATIONS OF ROBUSTA AND ARABIKA COFFEE GROUNDS BY COMPOSITION (60%: 40%, 50%: 50%, 40%: 60%) TO DETERMINE THE HARDNESS AND CALORIFIC VALUE OF BRICKETS”. Mechanical, Energy and Material (METAL), vol. 3, no. 1, June 2025, pp. 01-07, https://ejournal.widyakarya.ac.id/index.php/metal/article/view/121.