Novel drill geometries for dry drilling of stainless steel

Jou nal o Manu ac u ing P ocesses 92 (2023) 500–520 A ailable online 15 Ma ch 2023 1526-6125/© 2023 The Au ho s. Published by Else ie L d on behal o The Socie y o Manu ac u ing Enginee s. This is an open access a icle unde he CC BY-NC-ND license (h p://c ea i ecommons.o g/licenses/by-nc-nd/4.0/). No el d ill geome ies o d y d illing o s ainless s eel Luk´ aˇ s Pelik´ an a , * , Michal Slaný a , Ondˇ ej S ´ anský a , Libo Be ´ anek a , Zdeˇ nek Pi muc a , Lenka ˇ Cepo ´ a b , ˇ S ˇ ep´ anka D oˇ ´ aˇ cko ´ a c a Depa men o Machining, P ocess planning and Me ology, Facul y o Mechanical Enginee ing, Czech Technical Uni e si y in P ague, 166 00 P ague, Czech Republic b Depa men o Machining and Assembly, Facul y o Mechanical Enginee ing, VSB-Technical Uni e si y o Os a a, 708 33 Os a a, Czech Republic c Facul y o Mechanical Enginee ing, TU Libe ec, S uden ska 2, 461 17 Libe ec 1, Czech Republic ARTICLE INFO Keywo ds: D y machining 17-4 PH s eel S ainless s eel D ill geome y D y d illing Tool op imiza ion ABSTRACT One comple ely new geome y and wo modi ied chip b eake geome ies we e designed o inc ease he s abili y and eliabili y o he s ainless s eel d y d illing p ocess. Expe imen s we e pe o med and he esul s o indi idual ools we e compa ed wi h a con en ional solid ca bide wis d ill Güh ing Ra io wi h a diame e o 5 mm. A ma ix o h ee eed a es (0,03–0,07 mm/ e ) and h ee cu ing speeds (20–30 m/min) was designed o he cu ing condi ions. P ecipi a ion-ha denable s ainless s eel 17-4 PH was chosen as a wo kpiece. Du ing he expe imen , he alues o h us o ce, spindle o que, empe a u e o he ool, su ace oughness, chips mo phology and chips di ision we e eco ded and compa ed wi h he e e ence ool. The esul s showed ha compa ed o he e e ence ool A, he ool C - a mul ipoin d ill wi h g oo es h ough he cu ing edge achie e app oxima ely 4 % lowe alues o h us o ce and 10–15 % lowe alues o spindle o que. Tool D wi h a s ep d ill geome y achie e app oxima ely 17 % lowe alues o h us o ce and 10–15 % lowe alues o spindle o que and he e is no chip clogging in he lu e wi h C and D geome ies. This e ec is con i med by he ac he spindle o que basically does no inc ease wi h he inc easing dep h o d illing. Tool B – new designed geome y achie e app oxima ely 15 % lowe alues o h us o ce and simila spindle o que alues as he e e ence d ill A. Tool empe a u e is a e y impo an ac o when d y d illing. Compa ed o he e e ence d ill A, i was possible o achie e he ool empe a u e educ ion o 20 % wi h he new geome y B, as well as wi h he mul ipoin d ill C educ ion by 26 % and wi h he s ep d ill D educ ion app oxima ely by 30 %. All he modi ied d ills also achie ed a educ ion in he su ace oughness o he d illed holes. By 17 %, 35 % and 48 % lowe su ace oughness Ra was achie ed wi h d ills B, C and D. Chip mo phology was signi ican ly di e en o he es ed d ills. Con en ional wis d ills A and B gene a ed helical sho chips. While C and D wis d ills wi h di ided cu ing edges gene a ed ibbon sna led chips. Thanks o he educ ion o cu ing o ces and empe a u e, i is possible o s ably ope a e he d illing p ocess wi h a highe cu ing speed and eed a e, which leads o an inc ease in he e iciency and eliabili y o he machining p ocess. 1. In oduc ion Ac oss p oduc ion ields, d illing echnology is one o he mos impo an me al cu ing ope a ions. Mo e han ¾ o me al cu ing p o- cesses in ol e d illing ope a ions [1] [2]. The mos widesp ead use o his echnology is in indus ies such as au omo i e and ae ospace. The e is also a high consump ion o cu ing luids in hese a eas, whe he hey a e emulsions o oils. Wo ldwide, his amoun s o se e al million li e s o cu ing luids pe yea . This consump ion ep esen s hund eds o billions o USD in o al global machining cos s, aking in o accoun only he wo ld's la ges economies [3]. The use o cu ing luids in indus y also has a nega i e impac on he en i onmen and on he heal h o machine ope a o s. The high wa e consump ion associa ed wi h he use o cu ing luids is nowadays a undamen al p oblem in many egions, because he ecycling and disposal o used cu ing luids is an ene ge ically and en i onmen ally demanding p ocess [4]. In ela ion o machine ool ope a o s, ae osol inhala ion and skin con ac pose he g ea es isk [5] [6]. Fo hese easons, i is inc easingly p e e able o conside machining wi h mini- mum coolan (MQL), o comple ely d y machining [7]. Howe e , he use o cu ing luids has a signi ican e ec on he cu ing p ocess. App op ia ely applied cu ing luids has a posi i e * Co esponding au ho . E-mail add ess: [email p o ec ed] (L. Pelik´ an). Con en s lis s a ailable a ScienceDi ec Jou nal o Manu ac u ing P ocesses jou nal homepage: www.else ie .com/loca e/manp o h ps://doi.o g/10.1016/j.jmap o.2023.03.006 Recei ed 30 Decembe 2022; Recei ed in e ised o m 3 Ma ch 2023; Accep ed 4 Ma ch 2023 Jou nal o Manu ac u ing P ocesses 92 (2023) 500–520 501 impac on lub ica ion and hus educing ic ion, educing empe a u e, imp o ing chip e acua ion, educing a o ma ion o a build-up edge and imp o ing he opog aphy o he machined su ace [8]. Especially o he me al d illing p ocess, he in luence o he cu ing luid is c ucial. I signi ican ly helps o emo e chips om he cu ing zone, s abilizes he cu ing p ocess and helps o achie e be e quali y o d illed holes in e ms o su ace quali y, dimensions and geome ic speci ica ions [9] [10]. When conside ing d illing wi hou cu ing luids (d y machining), all o he pa ame e s a ec ing he d illing p ocess a e essen ial. We a e mainly alking abou ool geome y, wo kpiece ma e ial, cu ing con- di ions, ool ma e ial and coa ing [11]. Tool geome y is one o he main ac o s ha can be di ec ly in lu- ence o imp o e he d y machining p ocess pa ame e s [12] [13] [14]. This pape deals wi h he no el d ill designs o he needs o s ainless s eel d y d illing. Ma ensi ic p ecipi a ion-ha denable s ainless s eel 17-4PH was chosen as he wo kpiece ma e ial. I is high s eng h, co osion esis an , good weldabili y, and oxida ion esis an s eel [15]. S ainless s eels in gene al a e ega ded as di icul - o-machine ma e ials due o hei high endency o wo k ha den, hei oughness and ela- i ely low he mal conduc i i y [16]. Fo hese easons, he designed ools a e buil on he basis o solid ca bide d ills wi h coa ing. When d y d illing, i is essen ial o o m a sui able chip, he shape o which will allow i o lea e he cu ing zone smoo hly. The goal is o design a d ill geome y ha will gene a e chips capable o lea ing he cu ing zone quickly and wi h minimal esis ance. The d ill will gene a e low cu ing o ces and empe a u e concu en ly. Fo wis d ills, cu ing o ces and chip o ma ion a e signi ican ly in luenced by he geome y o he chisel edge. Ve y low o ze o cu ing speed is achie ed in his a ea. The chisel edge can con ibu e >55 % o he o al h us o ce, while he chisel edge occupies abou 20 % o he cu ing edge o al leng h, depending on he speci ic geome y [17] [18]. Chip o ma ion and i s esul ing shape a e also signi ican ly in luenced by he geome y o he chisel edge o web hinning [19] [20]. Published chisel edge modi ica ions a e implemen ed on HSS d ills and we machining is conside ed. The di e en p ope ies o cemen ed ca bide and he di e en coe icien o ic ion du ing d y machining mus be conside ed. The i s modi ied design (d ill A) ope a es p ima ily wi h he chisel edge modi ica ions. The modi ica ions aim o inc ease he chip ensile s ess in he a ea o he ansi ion be ween he chisel edge and he main cu ing edge and he eby achie e a highe le el o chip cu l. Ano he e ec o he modi ica ions lies in he enla gemen o he a ea o he chips o ma ion and e acua ion om he chisel edge. The e ec o enla ging he chisel edge a ea on he o ma ion and e acua ion o chips is no well desc ibed, unlike he e ec o enla ging he helix on he e acua ion o al eady o med chips [21]. Ano he op ion o di iding chips in o smalle elemen s is d ills wi h a spli cu ing edge. This is ad an ageously used in s ack d illing. By changing he cou se o he h us o ce and dis ibu ing he cu ing o ces o e mul iple cu ing edges, s ep d ills help o educe delamina- ion [22] [23]. The dis ance be ween he i s and second s eps o d ill is usually a ew millime e s in s ack d illing applica ions. The s ep d ill concep is used by some manu ac u e s (Milwaukee, MSTM) o s eel d illing applica ions as well. Howe e , he indi idual s eps a e only a ew en hs o a millime e apa . This concep is no commonly used in combina ion wi h s ainless s eel d illing, o e en d y d illing. Ne e - heless, his concep was chosen as ano he modi ied d ill design (D ill D) because i s abili y o b eak he chip in o smalle elemen s can be bene icial. G oo es o pins on he ace o he d ill a e o en used as ano he a ian s o chip b eake s. A educ ion in cu ing o ces o 5–9 % has been achie ed when machining aluminum alloy using a pin chip b eake [24]. Wi h he g oo e ype o chip b eake , a educ ion o cu ing o ces in he d illing dep h o 3D and mo e has been achie ed when machining low ca bon s eel. A he same ime, ool li e was inc eased due o he educ ion o chip e acua ion o ces [25]. Bo h examples o chip b eake s we e es ed using cu ing luid. Some manu ac u e s (Isca , MSTM) use g oo es in he cu ing edges ha lead h ough he lank. This concep educes he s uc u al s eng h o he cu ing wedge compa ed o chip b eake s on he ool ace. On he o he hand, i b ings lowe empe a- u es in he cu . Due o his ad an age, g oo ed chip b eake design is being conside ed o use in bone d illing [26]. In o de o op imize he d illing p ocess, e alua ion c i e ia mus be de e mined. Th us o ce and spindle o que a e widely used o e alua e he d illing p ocess and ha e a di ec impac on hole quali y, ool wea and p ocess s abili y. The empe a u e has a di ec e ec on ool wea and chip o ma ion, as he plas ici y o he machined ma e ial inc eases, he cu ing empe a u e inc eases [16] [27]. These pa ame e s a e moni o ed in his s udy as key in o ma ion abou he machining p ocess pe o mance. Table 1 Mechanical p ope ies a e hea ea men . UTS [MPa] 0,2 % YS [MPa] Rockwell ha dness [HRC] 1172 1138 38 Table 2 Chemical composi ion o 17-4 PH s eel. Elemen C Mn P S Si C NI Cu Nb Fe W % <0,07 <1 <0,04 <0,03 <1 15–17,5 3–5 3–5 0,15-0,45 emainde Fig. 1. D ill geome y speci ica ions. Table 3 D ill angles. D ill α β γ δ R A, C, D 78◦35◦30◦1◦1.3 B 100◦45◦30◦6◦1.3 L. Pelik´ an e al. Jou nal o Manu ac u ing P ocesses 92 (2023) 500–520 502 D y d illing is la gely sol ed o aluminum alloys [28] [29], i anium alloys [7] [30], o composi es [31] [32]. D y d illing o s ainless s eels is done a ely, due o hei di icul machinabili y. I expe imen s a e ca ied ou , hen wi h AISI 304 s ainless s eel [33] [34]. F om he poin o iew o ool op imiza ion, he published pape s mainly deal wi h poin angle and compa ison o HSS ools [33] [35]. In e ms o long- e m s abili y o he p ocess, howe e , HSS ools a e no able o wi hs and d y d illing condi ions. While changing he poin angle does no b ing a signi ican change in he o ma ion o chips - one o he essen ial ac o s o d y d illing. 17-4 PH s eel is a e y p omising ma e ial. Wi h s anda d ools o s eel d illing, i is e y di icul o implemen d y machining, because he e a e di icul ies wi h he s abili y o he p ocess, o sudden des uc ion o he ool due o high cu ing o ces and high empe a u es. The new geome y is designed o imp o e hese p ope ies, while keeping he classic wis d ill concep . This concep gene a es helical chips ha a e ad an ageous due o packing and he e is no isk o winding on he ool. The o he wo designs a e an al e na i e o he exis ing d ills wi h chip b eake . They a e designed wi h cu ing edge s i ness in mind, as his concep is no commonly used o d ill s ainless Fig. 2. D ill A. Fig. 3. D ill B. L. Pelik´ an e al. Jou nal o Manu ac u ing P ocesses 92 (2023) 500–520 503 s eel. This app oach b ings a signi ican educ ion in cu ing o ces and empe a u e. Howe e , he disad an age is he con inuous chip, which can wind up on he ool and is space-consuming. 2. Ma e ials and me hods 2.1. Wo kpiece The expe imen al s udy was ca ied ou on ma ensi ic p ecipi a ion ha dened s ainless s eel 17-4 PH. This ma e ial can be ound unde he s anda d SAT Type 630, AISI 630 o DIN 1.4542. Specimen dimensions we e 88 mm (leng h) ×72 mm (wid h) ×15 mm ( hickness). The op su ace has been machined o gua an ee i s la ness. The wo kpiece was hea ea ed in he H 1025 condi ion be o e machining. This condi ion including hea ing o 551 ◦C, holding on empe a u e o 4 h and ai cooling below 32 ◦C. Used hea ea men leads o ollowing specimen mechanical p ope ies [36] (Tables 1-2): 2.2. Tools Fo his expe imen , he Güh ing Ra io 2473 d ill wi h a diame e o 5 mm was chosen as he de aul ool. This ool was used wi hou Fig. 4. – D ill A (le ) and D ill B ( igh ) web hinning compa ison. Fig. 5. D ill C. Fig. 6. D ill C geome y speci ica ions. L. Pelik´ an e al. Jou nal o Manu ac u ing P ocesses 92 (2023) 500–520 504 modi ica ions as a e e ence ool unde he designa ion D ill A. Subse- quen ly, 3 a ian s wi h modi ied geome y we e designed. The de aul ool was always he Güh ing Ra io 2473, on which he modi ica ions desc ibed below we e made. Fo he pu poses o his expe imen , he ollowing igu e shows he de ini ion o se e al ool angles ha we e adop ed (Fig. 1). Thei alues a e p esen ed in he Table 3. 2.2.1. D ill A I is a monoli hic ca bide d ill wi h a diame e o 5 mm, a leng h o 3D wi h an poin angle o 140◦and a helix angle o 30◦. Spli poin design is used o web hinning. The ool is equipped wi h a coa ing wi h he ade name nanoFIRE, which is based on TiN-TiAlN (Fig. 2). Fig. 7. D ill D. Fig. 8. D ill D geome y speci ica ions. Table 4 Lis o expe imen al cu ing condi ions. Condi ions 1 2 3 4 5 6 7 8 9 Cu ing speed [m/min] 20 20 20 25 25 25 30 30 30 Feed a e [mm/ e ] 0.03 0.05 0.07 0.03 0.05 0.07 0.03 0.05 0.07 L. Pelik´ an e al. Jou nal o Manu ac u ing P ocesses 92 (2023) 500–520 505 2.2.2. D ill B This ool ea u es a newly designed geome y. I has been modi ied especially in he chisel edge a ea. Web hinning has been modi ied o c ea e mo e space o chip o ma ion om he hinning edge. This caused he chisel edge o hin. The co e igidi y o he d ill is he e o e compensa ed by a smalle inclina ion o he elie (β) (Fig. 3). The ollowing igu es show a compa ison o d ill A and B in he chisel edge a ea. The ed line indica es he cu ing edge o d ill A. In he pho o o d ill B, he enla ged a ea o he o ma ion and e acua ion o chips om he cen e o he ool is highligh ed in yellow (Fig. 4). 2.2.3. D ill C D ill C has he same geome y as d ill A. In addi ion, i was equipped wi h a chip b eake in he o m o g oo es on bo h cu ing edges o he pu pose o di iding he chip in o smalle elemen s. The g oo es on bo h cu ing edges a e in di e en posi ions o compensa e o each o he and no lea e a cu ing edge shape a he bo om o he hole (Fig. 5). The igu e below shows a de ail o he g o es design in he cu ing edges o he d ill (Fig. 6). 2.2.4. D ill D D ill D is a s ep d ill. The i s s ep has he same geome y as he e e ence d ill A. The second s ep is o se by 0.2 mm and has a poin angle o 140◦. The cu ing edge is di ided in o wo sepa a e pa s ( wo s eps) and hus sepa a e smalle chips should be c ea ed (Fig. 7). The igu e below shows a de ail o he s ep d ill geome y (Fig. 8). 2.3. Expe imen al se up The expe imen was pe o med on a e ical milling machine HAAS VF2 wi h maximum spindle speed o 8100 pm and powe ou pu 22.4 kW. The ool was clamped o he spindle using a o a y dynamome e Kis le RCD 9163. I is a 4-componen dynamome e o measu ing o cu ing o ces in x, y and z di ec ion and o ques on he o a ing ool spindle. Th us o ce and spindle o que we e eco ded using he dynamome e . A p o ec i e plexiglass was emo ed on he side o he milling machine and a FLIR T640 he mal came a was secu ely ixed ou side he machining a ea. The empe a u e was measu ed h oughou he machining ime. The peek empe a u e was always eached when he ool was wi hd awn ou o he hole. This poin was always chosen as Fig. 9. Expe imen al se up. L. Pelik´ an e al. Jou nal o Manu ac u ing P ocesses 92 (2023) 500–520 506 he eco ded alue. The su ace oughness o he d illed holes was measu ed using a Ma Su LD 120 machine om he Mah company. Measu emen was pe o med using p obe a m LD B 4–10-27,144 a 5 di e en loca ions. The measu ed da a we e p ocessed using Ma Win so wa e. To e alua e he su ace oughness, he basic wa eleng h λc 0,8 mm was chosen and hus he o al measu ed leng h Ln 4 mm. The su ace scanning speed was 0,5 mm/s. A ull ac o ial design wi h 3 cu ing speeds a 3 eed a es was used o his expe imen . Each expe imen al condi ion was epea ed ou imes o a e aged alues. Howe e , he aim o he expe imen is no o e alua e he dependence o he obse ed alues on he cu ing condi- ions, bu o compa e di e en ly modi ied ools. These 9 combina ions o cu ing condi ions we e chosen because each ool can achie e he bes pe o mance unde di e en cu ing condi ions. To selec cu ing con- di ions, a p elimina y es was pe o med wi h e e ence d ill A. Highe cu ing speeds and highe eed a es we e es ed un il he d ill ailed. The ange o cu ing condi ions was chosen in a sa e window so ha he e is no dange o sudden des uc ion o he d ill (Table 4). Since he expe imen ocuses on he esea ch o d ills sui able o d y d illing, o cou se no coolan was used. Blind holes we e d illed o a dep h o 13 mm in he 15 mm hickness wo kpiece (Fig. 9). 3. Resul s and discussion The measu ed alues we e eco ds o a combina ion o h ee cu ing speeds and h ee eed a es. F om he esul s o h us o ce, spindle o que, and empe a u e, a colo map was c ea ed demons a ing he magni ude o hese alues. The colo anges a e always iden ical o a speci ic da a se , so ha i is possible o easily compa e indi idual ools wi h each o he . 3.1. Th us o ce Th us o ce and spindle o que we e measu ed using he o a y dynamome e . In he ollowing igu e, ypical h us o ce cu es o indi idual ools can be seen. These o que cu es we e measu ed unde condi ions o V c =25 m/s and =0,05 mm/ e (Fig. 10). Du ing he d illing o he en i e dep h o he hole, an almos cons an cou se o h us o ce was obse ed in all expe imen al uns. The median alue om he en i e d illed dep h was used o p ocess he measu ed da a. Fig. 11 shows he dependence o h us o ce on cu ing condi ions o indi idual ools. I can be s a ed ha o all ools he e is an inc ease in h us o ce wi h inc easing eed a e. The e ec o he cu ing speed is p esen ed only by a sligh inc ease in he h us o ce when he cu ing speed inc eases. D ill A achie es he highes alues o h us o ce in he en i e ange o es ed cu ing condi ions. The g aph shows ha he e is a signi ican inc ease in h us o ce wi h inc easing eed a e compa ed o d ill B and D. D ill C also shows a signi ican inc ease in h us o ce wi h inc easing eed a e. The absolu e alues o he eed a e a e app oxima ely 20 N lowe compa ed o d ill A. D ill B and D showed a lowe inc ease in h us o ce depending on he inc easing eed a e. Absolu e h us o ce alues a e also lowe . A a eed a e o 0.07 mm/ e , bo h he B and D d ills achie e a 100 N lowe h us o ce compa ed o he e e ence d ill A (Figs. 12-15). 3.2. Spindle o que Likewise h us o ce, spindle o que was measu ed using a o a y dynamome e . In he ollowing igu e, ypical spindle o que cu es o indi idual ools can be seen. These o que cu es we e measu ed unde condi ions o V c =25 m/s and =0,05 mm/ e (Fig. 16). A simila cou se can be obse ed in he en i e ange o measu ed cu ing condi ions. The e alua ion o he spindle o que ook place on he linea egion on he op o he d illed hole. A signi ican inc ease in o que wi h inc easing hole dep h can be seen o ools A and B. This phenomenon is caused by he clogging o chips in he d ill lu e [37]. Fo d ill B, his e ec is sligh ly less signi ican . Thanks o he modi ied geome y o he cu ing edge, i gene a es smalle chips and he e is a be e di ision o chips and hus easie e acua ion om he cu ing zone. Fo d ills C and D, he o que cu e is essen ially linea du ing d illing o he en i e dep h o he hole. This is due o he o ma ion o a comple ely di e en shape o chips (see chap e 3.5). Long con inuous chips had no endency o clogging in he lu e and we e smoo hly e acua ed om he cu ing zone. Fo compa ison, he g aph in Fig. 17 shows he o que a di e en eed a es a V c =25 m/min o indi idual d ills. The hick ligh e line shows he alue o he linea egion o he o que when d illing a a shallow dep h. The hin da k line shows he maximum o que ha was achie ed when d illing a he la ges d illed dep h o 13 mm. I can be seen om he g aph ha o d ills A and B he e is a signi ican inc ease Fig. 10. Th us o ce eco d - d ill bi s compa ison. L. Pelik´ an e al. Jou nal o Manu ac u ing P ocesses 92 (2023) 500–520 507 Fig. 11. Th us o ce - d ill bi s compa ison. 20 25 30 300 345 390 435 480 525 570 615 660 0.03 0.05 0.07 Cu ng speed [m/min] Th us o ce [N] Feed a e [mm/ e ] D ill A - Th us o ce 300-345 345-390 390-435 435-480 480-525 525-570 570-615 615-660 Fig. 12. Th us o ce - d ill bi A. L. Pelik´ an e al. Jou nal o Manu ac u ing P ocesses 92 (2023) 500–520 508 in o que a a g ea e d illing dep h. Fo d ills C and D, he inc ease in o que is minimal. Howe e , he alue o he maximum o que is only indica i e, as signi ican oscilla ions o he eco ded alue occu . Fo u he e alua ion, alues om he linea ange a e used (Fig. 18). When compa ing he linea ange o spindle o que, i can obse ed ha e e ence d ill A achie es he highes alues. D ill B achie es app oxima ely 0.1 Nm lowe alues in he en i e ange o cu ing con- di ions. Fo d ills C and D, he alues a e e en 0.05–0.1 Nm lowe han in he case o d ill B (Figs. 19-22). F om he pe spec i e o he dependence o spindle o que on cu ing condi ions, an inc ease in o que wi h inc easing eed a e can be seen o all d ills. I is a na i e e ec , as a la ge dep h o ma e ial is being cu . Fo d ills A, B and C, a sligh inc ease in o que can also be obse ed wi h inc easing cu ing speed. In gene al, he opposi e end can be obse ed in machining, as he empe a u e in he cu inc eases wi h inc easing cu ing speed and he mechanical p ope ies o he machined ma e ial dec ease. In his case, wo phenomena may occu : In he case o d y d illing wi h inc easing cu ing speed, he e is an inc ease in ic ion no only be ween he ool and he wo kpiece in a cu ing zone, bu also be ween he chips and he lu e and he wall o he d illed hole [16]. S ainless s eels ha e high oughness and low he mal conduc i i y and easily s ick o he ake ace as he empe a u e inc eases [38]. Fig. 13. Th us o ce - d ill bi B. 20 25 30 300 345 390 435 480 525 570 615 660 0.03 0.05 0.07 Cung speed [m/min] Th us o ce [N] Feed a e [mm/ e ] D ill C - Th us o ce 300-345 345-390 390-435 435-480 480-525 525-570 570-615 615-660 Fig. 14. Th us o ce - d ill bi C. L. Pelik´ an e al. Jou nal o Manu ac u ing P ocesses 92 (2023) 500–520 515 signi ican ly lowe compa ed o con en ional A and B wis d ills. D ill D achie ed app ox. 48 % lowe su ace oughness Ra compa ed o he e e ence d ill A. Unde condi ions o V c =25 m/min and =0.05 mm/ e , i was 1.12 μ m. As wi h ool C, ool D also bene i s om he o ma ion o con inuous chips ha quickly lea e he cu ing zone. Compa ed o d ill C, d ill D shows a lowe su ace oughness Ra unde mos cu ing condi ions. This is ela ed, among o he hings, o he lowe cu ing o ces and lowe o que achie ed by he d ill D. 3.5. Chip o ma ion Chip shape is one o he mos impo an ac o o su icien d illing p ocess. The d illing p ocess can only be s able and eliable i he e is smoo h chip e acua ion [41]. I depends on he shape o he lu e, ic ion coe icien be ween chips, d ill and wall o he hole, bu abo e all on he shape o he chip [42]. Mac oscopic e alua ion o he chips was ca ied ou using an op ical mic oscope (Fig. 31). Fig. 26. Max empe a u e - d ill bi B. Fig. 27. Max empe a u e - d ill bi C. L. Pelik´ an e al. Jou nal o Manu ac u ing P ocesses 92 (2023) 500–520 516 Acco ding o ISO 3685, we can e alua e he shape o he chips as ollows: D ill A gene a ed mos ly helical sho chips. Only a he lowes eed a e o 0.3 mm/ e does he ul ima e ensile s eng h in he chip mo e a ound he c i ical alue. The c i ical alue mus exceed he ul ima e ensile s eng h o he machined ma e ial unde he ac ual condi ions o chip sepa a ion o occu . A =0.3 mm/ e , some chips a e helical sho because he c i ical alue has been exceeded and some chips a e helical sna led because he c i ical alue has no been exceeded. D ill B gene a ed helical sho chips. These chips a e di ided in o indi idual cones. A a eed a e o 0.3 mm/ e , he e is a g ea e de o ma ion o he chips be o e hei sepa a ion. Because o his, he chips a e longe . As he eed a e inc eased, he s i ness o he chips inc eased and his leads o easie b eakage [43]. D ill C gene a ed ibbon sna led chips. The e a e g oo es on he cu ing edge o he ool ha a e deepe han he dep h o he eed a e. Ne e heless, he e was no spli ing o chips in o na ow sepa a e ib- bons. Indi idual chips a e he wid h o he en i e cu ing edge (Fig. 32). On he chip pa e n we can see 2 s ipes om he g oo es in he cu ing edge. In hese a eas, s ong plas ic de o ma ion occu ed, and because o his, he chip emains con inuous ac oss he en i e wid h o he cu ing edge. D ill D gene a ed ibbon sna led chips. E en hough he e a e wo s eps o he d ill and hus he e a e 2 sepa a e cu ing edges on each side, he chips a e wide and con inuous (Fig. 33). The e is no no iceable ansi ion be ween he indi idual cu ing Fig. 28. Max empe a u e - d ill bi D. Fig. 29. Roughness measu emen loca ions in he hole. L. Pelik´ an e al. Jou nal o Manu ac u ing P ocesses 92 (2023) 500–520 517 0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50 20 25 30 Ra [μm] Cung speed [m/min] Su ace oughness Ra = 0.05 mm/ e D ill A D ill B D ill C D ill D 0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50 0.03 0.05 0.07 Ra [μm] Feed a e [mm/ e ] Su ace oughness Ra Vc= 25 m/min D ill A D ill B D ill C D ill D Fig. 30. Su ace oughness Ra - d ill bi s compa ison. Fig. 31. Mac oscopic chips mo phology. L. Pelik´ an e al. Jou nal o Manu ac u ing P ocesses 92 (2023) 500–520 518 edges on he de ail o he chip. These chips a e signi ican ly wide han hose gene a ed by d ill C. The edges o he chips a e mo e agged and he chips a e di ided in o sho e elemen s. All his indica es ha he e is e en mo e plas ic de o ma ion han in he chips gene a ed by d ill C. 3.6. Chip di ision Chip di ision, oge he wi h i s shape, is a e y impo an ac o o smoo h and eliable chip e acua ion. The pieces pe weigh a io me hod was used. In his case, he numbe o chips elemen s pe 1 g o chips is indica ed. Mo e chips pe 1 g means smalle chips elemen s. Di ided small chips p e en ool b eaking, because hey enable hei smoo h e acua ion and he e o e a smoo h d illing p ocess. A he same ime, i imp o es he quali y o he holes and inc eases he ool li e [44]. Howe e , i depends no only on he size o he chips, bu on he com- bina ion o size and shape o he chips [45] (Fig. 34). F om he g aph, we can obse e ha he smalles chip elemen s a e gene a ed by d ill B. Due o he modi ied geome y, especially in he a ea o web hinning, ine chip di ision occu s unde mos condi ions compa ed o he e e ence d ill A. D ill C gene a ed almos exclusi ely long ibbon chips. The e o e, we can obse e he smalles numbe o chip elemen s pe 1 g. D ill D gene a ed signi ican ly sho e ibbon chips ha we e accompanied by sho elemen s. Thanks o his, he numbe o chips eached highe alues compa ed o he d ill C. 4. Conclusion In his s udy, ool geome y modi ica ions we e analyzed when d y d illing o p ecipi a ion ha denable s ainless s eel 17-4PH. Th ee ge- ome ies sui able o d y d illing we e designed and compa ed wi h a con en ional wis d ill design. D ill A is he e e ence ool – a con- en ional monoli hic ca bide wis d ill. D ill B has a modi ied geome y specially adap ed o d y d illing. The o he wo d ills a e equipped wi h chip b eake s, which a e no no mally used o d y d illing. The e o e, he chip b eake s ha e been modi ied wi h ega d o he s i ness o he cu ing edge. D ill C is equipped wi h g oo es in he cu ing edges. D ill D is a s ep d ill wi h wo s eps. The ools we e es ed unde a ious cu ing condi ions in a combi- na ion o 3 cu ing speeds and 3 eed a es. The e ec on h us o ce, spindle o que, ool empe a u e, su ace oughness and chip di ision du ing d illing numbe o holes was analyzed. The ollowing conclusions may be d awn om his wo k: 1. Th us o ce inc eases wi h inc easing eed a e, while cu ing speed has e y small e ec . The p og ess o he h us o ce depending on he d illing dep h was nea ly cons an . D ills B and D achie ed app oxima ely 100 N lowe compa ed o he e e ence ool. 2. Spindle o que inc eases wi h inc easing eed a e and cu ing speed. Wi h inc easing d illing dep h inc eased o que up o +200 % o d ills A and B a a maximum d illing dep h o 13 mm. This is caused by he clogging o chips in he d ill lu e. While d ills C and D show only a small inc ease (10–20 %) in o que depending on he d illing dep h, because hei chip shapes allowed smoo h e acua ion om he cu ing zone. 3. The empe a u e o he ool inc eases wi h inc easing cu ing speed and eed a e. The highes empe a u e alues we e eached by e e ence d ill A, up o 300 ◦C a e being pulled ou o he hole. Modi ied d ills gene a ed an a e age o 20 %, espec i ely 26 % lowe empe a u es and up o 40 ◦C, espec i ely 50 ◦C lowe em- pe a u e a he highes cu ing condi ions o d ill B, espec i ely d ill C. d ill D has a e y di e en empe a u e p o ile depending on he cu ing condi ions. Unde he highes cu ing condi ions, i ea- ches up o 70 ◦C less han d ill A. 4. The su ace oughness dec eases wi h inc easing cu ing speed, while inc easing wi h inc easing eed a e. The e e ence d ill eached su ace oughness om Ra 1.2 μ m o Ra 3.4 μ m, depending on he cu ing condi ions. Modi ied d ills achie ed an a e age o 17 %, 35 %, espec i ely 48 % lowe oughness Ra o d ill B, C, espec i ely D compa ed o he e e ence d ill. 5. The shape o he chips a ied signi ican ly be ween indi idual ools. D ills A and B gene a ed helical sho chips. While d ills C and D gene a ed ibbon sna led chips. Chips gene a ed by he d ill B we e di ided in o he smalles elemen s - up o 200 single elemen s pe 1 g Fig. 32. Chip de ail - D ill C. Fig. 33. Chip de ail - D ill D. L. Pelik´ an e al. Jou nal o Manu ac u ing P ocesses 92 (2023) 500–520 519 o chips. While d ill A eached 180 elemen s pe 1 g. D ill D gene a e >80 elemen s pe 1 g and d ill C only 60 elemen s pe 1 g. As a esul , i can be s a ed he modi ica ions o he d ills led o a educ ion in cu ing o ces and empe a u es and, hanks o his, o an inc ease in he s abili y o he cu ing p ocess, which enables long- e m ope a ion unde highe cu ing condi ions. This was achie ed du ing d y machining o ma e ial 17-4 PH, which is no mally conside ed di icul o machine e en wi h he use o cu ing luid [46]. Tes s o he ool li e and long e m s abili y o he p ocess should be he subjec o u he in es iga ion as well as machinabili y o he wo kpiece ma e ial unde highe cu ing condi ions. 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