3. Mekanisme Pembentukan dan Geram

Mekanisme Pembentukan Geram

Proses Pemesinan

Material Removal Processes

M. Oktaviandri

Mulanya diperkirakan geram terbentuk karena adanya retak mikro (micro crack) timbul pada benda kerja tepat di ujung pahat pada saat pemotongan dimulai.

Dengan bertambahnya tekanan pahat, retak tersebut menjalar ke depan sehingga terjadilah geram (Gambar 3.1).

Sebenarnya dapat dijelaskan dengan analogi tumpukan kartu (Gambar 3.2)

Komponen Gaya Pembentukan Geram

Teori Merchant  model pemotongan sistem tegak (ortogonal system),

dengan asumsi:

-Mata potong pahat sangat tajam sehingga tidak menggosok atau menggaruk benda kerja

-Deformasi terjadi hanya dalam dua dimensi

Ada tiga cara menentukan gaya total 1.Ditinjau dari deformasi material 2.Dengan dinamometer

Chip Formation

The types of chips produced significantly

influences surface finish and integrity, as well as

the overall cutting operation. Types of chips

commonly produces are:

– Continuous chips;

– Built-up edge;

Continuous chips

Continuous chips are usually formed at high rake

angles and/or high cutting speeds. Continuous

chips are less likely to form if the workpiece is

brittle. A good surface finish is generally produced.

However, continuous chips are not always

desirable, particularly in automated machine tools,

because they tend to get tangled around the tool,

and the operation has to be stopped to clear away

the chips. This problem can be alleviated by using

Built-up edge chips (BUE)

Discontinuous chips