Mesin Bubut
MESIN PERKAKASMesin BubutBubut merupakan suatu proses pemakanan benda kerja yang sayatannya dilakukan dengan cara memutar benda kerja kemudian dikenakan pada pahat yang digerakkan secara translasi sejajar dengan sumbu putar dari benda kerja. Gerakan putar dari benda kerja disebut gerak potong relatif dan gerakkan translasi dari pahat disebut gerak umpan (feeding).Dengan mengatur perbandingan kecepatan rotasi benda kerja dan kecepatan translasi pahat maka akan diperoleh berbagai macam ulir dengan ukuran kisar yang berbeda. Hal ini dapat dilakukan dengna jalan menukar roda gigi translasi (change gears) yang menghubungkan poros spindel dengan poros ulir (lead screw).Roda gigi penukar disediakan secara khusus untuk memenuhi keperluan pembuatan ulir. Jumlah gigi pada masing-masing roda gigi penukar bervariasi besarnya mulai dari jumlah 15 sampai dengan jumlah gigi maksimum 127. roda gigi penukar dengan jumlah 127 mempunyai ke khususan karena digunakan untuk monversi dari ulir metrik ke ulir inchi.• Prinsip Kerja Mesin BubutPoros spindel akan memutar benda kerja melalui piringan pembawa sehingga memutar roda gigi pada poros spindel. Melalui roda gigi penghubung, putaran akan disampaikan ke roda gigi poros ulir. Oleh klem berulir, putaran poros ulir tersebut diubah menjadi gerak translasi pada eretan yang membawa pahat. Akibatnya pada benda kerja akan terjadi sayatan yang berbentuk ulir.• Bagian-Bagian Mesin BubutMesin bubut terdiri dari meja (bed) dan kepala tetap (head stock). Di dalam kepala tetap terdapat roda-roda gigi transmisi penukar putaran yang akan memutar poros spindel. Poros spindel akan menmutar benda kerja melalui cekal (chuck). Eretan utama (appron) akan bergerak sepanjang meja sambil membawa eretan lintang (cross slide) dan eretan atas (upper cross slide) dan dudukan pahat. Sumber utama dari semua gerakkan tersebut berasal dari motor listrik untuk memutar pulley melalui sabuk (belt).Mesin Freis Freis merupakan suatu proses memakanan benda kerja yang sayatannya dilakukan dengan menggunakan pahat yang diputar oleh poros spindel mesin. Pahat Freis (milling cutter) termasuk jenis pahat bersisi potong banyak (multiple point tool). Mesin Freis dari segi operasionalnya dapat diklasifikasikan sebagai berikut:a Mesin Freis horizontal b Mesin Freis vertikal c Mesin Freis serba guna (universal)d Mesin Freis khusus (special purpose)Jenis-jenis Freis tersebut diatas memiliki prinsip kerja yang sama. Yang membedakan adalah ukuran benda kerja yang dapat dikerja oleh mesin Freis. • Prinsip Kerja Mesin FreisProses pemotongan (penyayatan) dilakukan dengan menggunakan pahat yang diputar oleh arbor yang berhubungan langsung dengan poros spindel mesin. Posisi pahat pada arbor dapat diatur dengan mengatur letak cincin pemisah (spacer). posisi dari poros arbor atau poros merupakan penentu dari jenis apakah mesin Freis ini, apakah jenis mesin Freis horizontal atau pun vertikal. Untuk mengerjakkan benda-benda kerja yang mempunyai bentuk yang rumit dan ukuran yang relatif besar yang tidak mungkin dikerjakan pada mesin-mesin Freis horizontal maupun vertikal maka dibuat mesin Freis khusus (special purpose).• Bagian-Bagian Mesin FreisMesin ini terdiri dari badan atau kolom yang menyangga ram. Pada bagian depan kolom dipasang batang bimbing (guide) slide ways sehingga lutut (knee) yang ditumpu oleh batang ulir bergerak naik-turun secara lurus. Diatas lutut dipasang pelana (sddle) yang bergerak kemuka dan kebelakang sepanjang guide. Diatas pelana dipasangkan meja yang dapat bergerak ke kiri dan ke kanan agar lutut dapat bergerak naik turun, pelana bergerak maju mundur dan meja bergerak ke kiri dan ke kanan. Tujuan dari gerakan-gerakan pada mesin Freis untuk memenuhi gerak umpan (feeding) tetapi juga untuk memudahkan dalam menentukan posisi pahat terhadap benda kerja sebelum proses pemotongan dilakukan.Mesin ScrapScarp merupakan proses pemakanan benda kerja yang sayatannya dilakukan oleh badan mesin (ram) yang meluncut bolak-balik pada Gerak potong pahat pada benda kerja merupakan gerakan lurus translasi. Dalam hal ini benda kerja dalam keadaan diam dan pahat bergerak lurus translasi. Pada saat pahat melakukan gerak balik, benda kerja juga melakukan gerak umpan (feeding). Sehingga punggung pahat akan tersangkut pada benda kerja yang sedang bergerak tersebut. Untuk menghindari gangguan ini, pangkal dudukan pahat diberi engsel sehingga punggung pahat dapat berayun pada waktu balik menyentuh benda kerja.• Prinsip Kerja Mesin Scrap Benda kerja diletakkan dan dijepit pada meja. Posisi meja dapat juga dinaik-turunkan sepanjang pembimbing melalui poros ulir. Dengan memutar poros ulir yang telah dihubungkan dengan roda gigi maka gerakkan suap dari meja sepanjang pembimbing dapat dilakukan. Dimana roda gigi digerakkan oleh tuas pengungkit secara berkala. Gerakkan berkala ini dibuat sedemikian rupa sehingga poros ulir hanya bergerak pada waktu ram melakukan gerak balik membawa dudukan pahat. Gerak putar dari motor listrik diubah menjadi gerak translasi pada ram.• Bagian-Bagian Mesin ScrapDiatas badan mesin terdapat ram yang meluncur bolak-balik pada pembimbing (guide). Didepan ram dipasang leher sehingga dudukan pahat dapat berputar posisi ke kiri dan ke kanan. Tuas pemutar digunakan untuk menurunkan/menaikkan posisi dudukan pahat sehingga ujung pahat posisinya terhadap benda kerja dapat diatur.Mesin Gerinda Mesin gerinda merupakan proses menghaluskan permukaan yang digunakan pada tahap finishing dengan daerah toleransi yang sangat kecil sehingga mesin ini harus memiliki konstruksi yang Bagian badan mesin yangsangat kokoh. • Bagian-bagian Mesin Gerinda biasanya terbuat dari besi tuang yang memiliki sifat sebagai peredam getaran yang baik. Fungsinya adalah untuk menopang meja kerja dan Bagian poros spindel merupakan bagianmenopang kepala rumah spindel. yang kritis karena harus berputar dengan kecepatan tinggi juga dibebani Bagian mejagaya pemotongan pada batu gerindanya dalam berbagai arah. juga merupakan bagian yang dapat mempengaruhi hasil kerja proses gerinda karena diatas meja inilah benda kerja diletakkan melalui suatu ragum ataupun magnetic chuck yang dikencangkan pada meja ini.Mesin GergajiGergaji merupakan alat perkakas yang berguna untuk memotong benda kerja. Mesin gergaji merupakan mesin pertama yang menentukan proses lebih lanjut. Dapat dimaklumi bahwa mesin ini memiliki kepadatan operasi yang relatif tinggi pada bengkel-bengkel produksi. Gergaji tangan biasa digunakan untuk pekerjaan-pekerjaan yang sederhana dalam jumlah produksi yang rendah. Untuk pekerjaan-pekerjaan dengan persyaratan ketelitian tinggi dengan kapasitas yang tinggi diperlukan mesin-mesin gergaji khusus yang bekerja secara otomatik dengan bantuan mesin.Mesin-mesin gergaji memiliki konstruksi yang beragam sesuai dengan ukuran, bentuk dan jenis material benda kerja yang akan dipotong. Adapun klasifikasi mesin-mesin gergaji yang terdapat digunakan adalah sebagai berikut:a Mesin gergaji bolak-balik (Hacksaw-Machine)Mesin gergaji ini umumnya memiliki pisau gergaji dengan panjang antara 300 mm sampai 900 mm dengan ketebalan 1,25 mm sampai 3 mm dengan jumlah gigi rata-rata antara 1 sampai 6 gigi iper inchi dengan material HSS. Karena gerakkan yang bolak-balik, maka waktu yang digunakan untuk memotong adalah 50%. b Mesin gergaji piringan (Circular Saw)Diameter piringan gergaji dapat mencapai 200 sampai 400 mm dengan ketebalan 0,5 mm dengan ketelitian gerigi pada keliling piringan memiliki ketinggian antara 0,25 mm sampai 0,50 mm. pada proses penggergajian ini selalu digunakan cairan pendingin. Toleransi yang dapat dicapai antara kurang lebih 0,5 mm sampai kurang lebih 1,5 mm.c Mesin Gergaji pita (Band Saw)Mesin gergaji yang telah dijelaskan sebelumnya adalah gergaji untuk pemotong lurus. Dalam hal mesin gergaji pita memiliki keunikan yaitu mampu memotong dalam bentuk-bentuk tidak lurus atau lengkung yang tidak beraturan. Kecepatan pita gergajinya bervariasi antara 18 m/menit sampai 450 m/menit agar dapat memenuhi kecepatan potong dari berbagai jenis material benda kerja.
Selasa, 17 Maret 2009
Kamis, 26 Februari 2009
Historical Perspective (material)
The designation of successive historical epochs as the Stone, Copper, Bronze,
and Iron Ages reflects the importance of materials to mankind. Human destiny
and materials resources have been inextricably intertwined since the daw^n of
history; how^ever, the association of a given material w^ith the age or era that
it defines is not only limited to antiquity. The present nuclear and information
ages ov^e their existences to the exploitation of tv^o remarkable elements,
uranium and silicon, respectively. Even though modern materials ages are
extremely time compressed relative to the ancient metal ages they share a
number of common attributes. For one thing, these ages tended to define
sharply the material limits of human existence. Stone, copper, bronze, and
iron meant successively higher standards of living through new^ or improved
agricultural tools, food vessels, and weapons. Passage from one age to another
was (and is) frequently accompanied by revolutionary, rather than evolutionary,
changes in technological endeavors.
It is instructive to appreciate some additional characteristics and implications
of these materials ages. For example, imagine that time is frozen at 1500 BC
and we focus on the Middle East, perhaps the world's most intensively excavated region with respect to archaeological remains. In Asia Minor (Turkey)
the ancient Hittites were already experimenting with iron, while close by to
the east in Mesopotamia (Iraq), the Bronze Age was in flower. To the immediate
north in Europe, the south in Palestine, and the west in Egypt, peoples were
enjoying the benefits of the Copper and Early Bronze Ages. Halfway around
the world to the east, the Chinese had already melted iron and demonstrated
a remarkable genius for bronze, a copper—tin alloy that is stronger and easier
to cast than pure copper. Further to the west on the Iberian Peninsula (Spain
and Portugal), the Chalcolithic period, an overlapping Stone and Copper Age
held sway, and in North Africa survivals of the Late Stone Age were in evidence.
Across the Atlantic Ocean the peoples of the Americas had not yet discovered
bronze, but like others around the globe, they fashioned beautiful work in
gold, silver, and copper, which were found in nature in the free state (i.e., not
combined in oxide, sulfide, or other ores).
Why materials resources and the skills to work them were so inequitably
distributed cannot be addressed here. Clearly, very little technological information
diffused or was shared among peoples. Actually, it could not have been
otherwise because the working of metals (as well as ceramics) was very much
an art that was limited not only by availability of resources, but also by cultural
forces. It was indeed a tragedy for the Native Americans, still in the Stone Age
three millennia later, when the white man arrived from Europe armed with
steel (a hard, strong iron-carbon alloy) guns. These were too much of a
match for the inferior stone, wood, and copper weapons arrayed against them.
Conquest, colonization, and settlement were inevitable. And similar events have
occurred elsewhere, at other times, throughout the world. Political expansion,
commerce, and wars were frequently driven by the desire to control and exploit
materials resources, and these continue unabated to the present day.
When the 20th century dawned the number of different materials controllably
exploited had, surprisingly, not grown much beyond what was available
2000 years earlier. A notable exception was steel, which ushered in the Machine
Age and revolutionized many facets of life. But then a period ensued in which
there was an explosive increase in our understanding of the fundamental nature
of materials. The result was the emergence of polymeric (plastic), nuclear, and
electronic materials, new roles for metals and ceramics, and the development
of reliable ways to process and manufacture useful products from them. Collectively,
this modern Age of Materials has permeated the entire world and
dwarfed the impact of previous ages.
Only two representative examples of a greater number scattered throughout
the book will underscore the magnitude of advances made in materials within
a historical context. In Fig. 1-1 the progress made in increasing the strengthto-
density (or weight) ratio of materials is charted. Two implications of these
advances have been improved aircraft design and energy savings in transportation
systems. Less visible but no less significant improvements made in abrasive
and cutting tool materials are shown in Fig. 1-2. The 100-fold tool cutting speed
increase in this century has resulted in efficient machining and manufacturing
and Iron Ages reflects the importance of materials to mankind. Human destiny
and materials resources have been inextricably intertwined since the daw^n of
history; how^ever, the association of a given material w^ith the age or era that
it defines is not only limited to antiquity. The present nuclear and information
ages ov^e their existences to the exploitation of tv^o remarkable elements,
uranium and silicon, respectively. Even though modern materials ages are
extremely time compressed relative to the ancient metal ages they share a
number of common attributes. For one thing, these ages tended to define
sharply the material limits of human existence. Stone, copper, bronze, and
iron meant successively higher standards of living through new^ or improved
agricultural tools, food vessels, and weapons. Passage from one age to another
was (and is) frequently accompanied by revolutionary, rather than evolutionary,
changes in technological endeavors.
It is instructive to appreciate some additional characteristics and implications
of these materials ages. For example, imagine that time is frozen at 1500 BC
and we focus on the Middle East, perhaps the world's most intensively excavated region with respect to archaeological remains. In Asia Minor (Turkey)
the ancient Hittites were already experimenting with iron, while close by to
the east in Mesopotamia (Iraq), the Bronze Age was in flower. To the immediate
north in Europe, the south in Palestine, and the west in Egypt, peoples were
enjoying the benefits of the Copper and Early Bronze Ages. Halfway around
the world to the east, the Chinese had already melted iron and demonstrated
a remarkable genius for bronze, a copper—tin alloy that is stronger and easier
to cast than pure copper. Further to the west on the Iberian Peninsula (Spain
and Portugal), the Chalcolithic period, an overlapping Stone and Copper Age
held sway, and in North Africa survivals of the Late Stone Age were in evidence.
Across the Atlantic Ocean the peoples of the Americas had not yet discovered
bronze, but like others around the globe, they fashioned beautiful work in
gold, silver, and copper, which were found in nature in the free state (i.e., not
combined in oxide, sulfide, or other ores).
Why materials resources and the skills to work them were so inequitably
distributed cannot be addressed here. Clearly, very little technological information
diffused or was shared among peoples. Actually, it could not have been
otherwise because the working of metals (as well as ceramics) was very much
an art that was limited not only by availability of resources, but also by cultural
forces. It was indeed a tragedy for the Native Americans, still in the Stone Age
three millennia later, when the white man arrived from Europe armed with
steel (a hard, strong iron-carbon alloy) guns. These were too much of a
match for the inferior stone, wood, and copper weapons arrayed against them.
Conquest, colonization, and settlement were inevitable. And similar events have
occurred elsewhere, at other times, throughout the world. Political expansion,
commerce, and wars were frequently driven by the desire to control and exploit
materials resources, and these continue unabated to the present day.
When the 20th century dawned the number of different materials controllably
exploited had, surprisingly, not grown much beyond what was available
2000 years earlier. A notable exception was steel, which ushered in the Machine
Age and revolutionized many facets of life. But then a period ensued in which
there was an explosive increase in our understanding of the fundamental nature
of materials. The result was the emergence of polymeric (plastic), nuclear, and
electronic materials, new roles for metals and ceramics, and the development
of reliable ways to process and manufacture useful products from them. Collectively,
this modern Age of Materials has permeated the entire world and
dwarfed the impact of previous ages.
Only two representative examples of a greater number scattered throughout
the book will underscore the magnitude of advances made in materials within
a historical context. In Fig. 1-1 the progress made in increasing the strengthto-
density (or weight) ratio of materials is charted. Two implications of these
advances have been improved aircraft design and energy savings in transportation
systems. Less visible but no less significant improvements made in abrasive
and cutting tool materials are shown in Fig. 1-2. The 100-fold tool cutting speed
increase in this century has resulted in efficient machining and manufacturing
saint
Authors fear that they may not show sufficient awareness of their debt to
the people who make their books possible. In this vein I hope that I will be
forgiven by the many for citing only the few. Among my colleagues I would
like to thank Professor Edward Whittaker for conscientiously reading and
reviewing several chapters on electronic properties. I am additionally grateful
to Dr. W. Moberly, and Professors W. Carr, D. Smith, and A. Freilich for their
critical comments. However, the bulk of the review process was performed by
many excellent but anonymous reviewers who are the unsung heroes of this
book. They offered encouragement, and much good criticism and advice which
I tried to incorporate. I am solely responsible for any residual errors in my
understanding of concepts and wording of text.
Some very special people to whom I am indebted sent me the beautiful
photographs that elevate and give life to the text. In particular, the contribution
of George Vander Voort must be singled out. This exceptional metallographer
not only provided many excellent micrographs but taught me a bit of metallurgy
as well. I also wish to acknowledge Dr. R. Anderhalt and Mr. Jun Yeh for
their respective scanning electron and optical micrographs.
The software was the result of a multi-man-year team effort in which major
contributions were made by Dmitry Genken, Tom Harris, Dr. Dan Schwarcz,and Eugene Zaremba. Professors W. Carr and D. Sebastian are owed thanks
for evaluating the software.
I am grateful to all of those at Academic Press who had a part in producing
this book including Jane Ellis who encouraged me to undertake its writing,
Dr. Zvi Ruder for his support of this project, and Deborah Moses who so
capably guided and coordinated the complex pubHshing process. Others who
deserve thanks for many favors are Noemia Carvalho, Pat Downes, Dick
Widdecombe, and Dale Jacobson.
the people who make their books possible. In this vein I hope that I will be
forgiven by the many for citing only the few. Among my colleagues I would
like to thank Professor Edward Whittaker for conscientiously reading and
reviewing several chapters on electronic properties. I am additionally grateful
to Dr. W. Moberly, and Professors W. Carr, D. Smith, and A. Freilich for their
critical comments. However, the bulk of the review process was performed by
many excellent but anonymous reviewers who are the unsung heroes of this
book. They offered encouragement, and much good criticism and advice which
I tried to incorporate. I am solely responsible for any residual errors in my
understanding of concepts and wording of text.
Some very special people to whom I am indebted sent me the beautiful
photographs that elevate and give life to the text. In particular, the contribution
of George Vander Voort must be singled out. This exceptional metallographer
not only provided many excellent micrographs but taught me a bit of metallurgy
as well. I also wish to acknowledge Dr. R. Anderhalt and Mr. Jun Yeh for
their respective scanning electron and optical micrographs.
The software was the result of a multi-man-year team effort in which major
contributions were made by Dmitry Genken, Tom Harris, Dr. Dan Schwarcz,and Eugene Zaremba. Professors W. Carr and D. Sebastian are owed thanks
for evaluating the software.
I am grateful to all of those at Academic Press who had a part in producing
this book including Jane Ellis who encouraged me to undertake its writing,
Dr. Zvi Ruder for his support of this project, and Deborah Moses who so
capably guided and coordinated the complex pubHshing process. Others who
deserve thanks for many favors are Noemia Carvalho, Pat Downes, Dick
Widdecombe, and Dale Jacobson.
Rabu, 24 Desember 2008
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