Chapter 25: Machining Centers, Machine Tool Structures and Machining Economics

Transcription

1 Manufacturng Engneerng echnology n SI Unts, 6 th Edton Chapter 25: Machnng Centers, Machne ool Structures and Machnng Econocs Copyrght 200 Pearson Educaton South Asa Pte Ltd

2 Chapter Outlne 2 Introducton Machnng Centers Machne-tool Structures Vbraton and Chatter n Machnng Operatons Hgh-speed Machnng Hard Machnng Ultraprecson Machnng Machnng Econocs Copyrght 200 Pearson Educaton South Asa Pte Ltd

3 Machnng Econocs 3 Ltatons of achnng/ateral reoval operatons:. Wasted ateral (although ay be sall) 2. Longer te (vs. forng/shapng): cuttng/non-cuttng 3. Requre ore energy (vs. forng/shapng) 4. Adverse effects on surface qualty / propertes of product Iportance of achnng (despte above):. Producng coplex workpece shapes (e.g. nternal features) 2. Hgh densonal accuracy / surface fnsh

4 Machnng Econocs 4 Costs/factors nvolved wth achnng:. Machne tools, work-holdng devces, fxtures and cuttng tools 2. Labor and overhead 3. Settng up te (achne for operaton) 4. Materal handlng and oveent (e.g. loadng blank, unloadng achne part) 5. Gagng for densonal accuracy and surface fnsh 6. Cuttng tes and non-cuttng te

5 Machnng Econocs 5 Mnzng Machnng Cost per Pece Iportant n all anufacturng processes to nze: Machnng cost per pece, C p Machnng te per pece, p Varous approaches exst (usng software) Iportant: nput data ust be accurate and up to date to be relable We show here sple/popular ethod of analyzng achnng cost n turnng operaton

6 Machnng Econocs 6 Cont. Mnzng Machnng Cost per Pece otal achnng cost per pece, C p, n turnng s C = C C C C p s l t Followng sldes: dscuss each of these costs n ore detal

7 Machnng Econocs 7 Cont. Mnzng Machnng Cost per Pece Machnng cost per pece, C, s gven by: C = L : achnng te per pece L : labor cost of producton personnel per hour B : burden rate (aka overhead charge), ncludng: Deprecaton Mantenance Indrect labor, etc. ( B ) C = C C C p s l C t he setup cost, C s,s fxed aount (n $) per pece

8 Machnng Econocs 8 Cont. Mnzng Machnng Cost per Pece C = C C C C Loadng/unloadng, achne-handlng cost, C l, per pece: ( L B ) C = l l p s l t l : te requred to, load/unload part change speeds change feed rates, etc. L and B : see last slde

9 Machnng Econocs 9 Cont. Mnzng Machnng Cost per Pece he toolng cost, C t, per pece: C = C C C p s l C t C t = N c L B D N f L B N : nubered of parts achned per nsert N f : nubered of parts that can produced per nsert face c : te requred to change the nsert : te requred to ndex the nsert D : deprecaton of nsert (n $)

10 Machnng Econocs 0 Cont. Mnzng Machnng Cost per Pece he te requred to produce one part s c p = l N N : calculated for each partcular operaton Exaple: for turnng: L = fn L: length of cut πld = fv f: feed N: angular speed (rrr) of the workpece D: workpece daeter V: cuttng speed (note, approprate unts ust be used) f

11 Machnng Econocs Cont. Mnzng Machnng Cost per Pece Fro the aylor tool-lfe equaton, : te () to reach a certan flank wear (before regrndng/changng nsert) = C V / n he nuber of peces per nsert face: Nuber of peces per nsert: : nuber of faces actually used Note, : not necessarly nuber of faces per nsert Reason: not all faces are used before nsert s dscarded Cobnng and n N : N = f N = N = N f fc πldv / = (/ n)

12 Machnng Econocs Cont. Mnzng Machnng Cost per Pece We now seek to deterne optu V (V o ) and ( o ) Frst we fnd V o and o for n. cost, C p We dfferentate C p wth respect to V and set t to zero, = 0 V C p ( ) ( ) [ ] ( ) n c n n B L D B L n B L C V = 0 ( ) [ ] ( ) c B L B L D B L n = 0 2

13 Machnng Econocs Cont. Mnzng Machnng Cost per Pece Agan we seek to deterne optu V (V o ) and ( o ) Now we fnd V o and o for ax. prod on,.e. n. p We dfferentate p wth respect to V and set t to zero, = 0 V p n c n C V = 0 = c n 0 3

14 Machnng Econocs 4 Cont. Mnzng C p per Pece Qualtatve plot of C p /pece Note, C p also depends on req. surface fnsh: better S.F. hgher C p Note, V o = p, Qualtatve plot of p /pece (.e. producton rate) Note, V o = p, Range bet. wo V o s s: hgh-effcency achnng range

15 Machnng Econocs 5 Cont. Mnzng Machnng Cost per Pece Fnal notes Iportant to have accurate data, snce sall changes n V greatly affect C p, and p, (see last slde) Prevous analyss can be done for all anufacturng processes: E.g. Cost/part n sand castng uses E.g. Cost/part n powder etallurgy, etc.