CNC Machining Part 3

Literature Review

The important of CNC machine are

1. Accuracy

2. Repeatability

3. Programming capability

The biggest CNC machine called Conventional-CNC machining. It is a combination both Conventional and CNC function and put in single machine. This type of machine has large amount of cutting tools. This makes this machine complete to do all type of manufacturing process including combination Lathe and milling works.

This machine can do several types of process like Lathe, milling, turning, boring, cutting and finishing. The common cutting materials are coated carbide, ceramic and uncoated carbide. It depends on how strong the workpiece is. The good cutting material is stronger than the work piece to prevent from the tools break. There are 2 types of machine cutting tool which are:

• The workpiece moving while the cutting tool in static position
• The workpiece stay static and moving cutting tools

Mechanism and Theoretical Background

As the name is Computer Numerical Control, CNC has a control system that can control the machine by a specific program. By doing the programming on CNC machine, the machine then read the instruction and performs the series of motion.

CNC machines have a specific range of motion–typically between 2 to 5 linear and rotational axes. Each direction of motion of a CNC Machine is called an axis. It is simply a direction of motion under the influence of the CNC controller. It can either be linear or rotary. For machine movement two types of motor are used either stepper motor or servo motor.

For trainer machine use a small machine. It just for training purpose and no large quantity of product has been produced. There are possibility to have large amount of defect on product because no expertise in skill. It is for skill development purpose.

For production machine it cost a big cost and also big amount of quantity of product in a short period. The defect of product is less since the machine is conducted by professional. Usually the machine used in production is bigger than the machine used for trainer.

Typical usage and Application

The entire machine component must be rigid and very strong material. The spindle should be high strength, sustain a high temperature and supported by large bearing. The clamp system should be strong enough to hold work piece as the machine facing a moveable part during the manufacturing process. In addition clamping system should be efficiently moved fast in clamping or unclamp the work piece with fast movement during the process. The importance of choosing cutting tools is important in order to make sure it will not break when cut the work piece.

Attached to the side of the machine usually collections of cutting tools. This also called a tools magazine. The machine will take a fast time to change the suitable cutting tools following what the machine is programmed. The range of time to change the cutting tool is between three to ten seconds depending on the machine. The bigger machine may have up to 60 cutting tool putting inside the tool magazine. Each will loading automatically follow the instruction of the programming.

The place that holds the work piece while machining is called a bed or work table. It consists of hard steel named “ways” which is usually covered by flexible guards. The worktable can flexibly move with required angle depends on what kind of process. For example process like turning and finishing sometimes need work table to stay on an angle so that the cutter can cut with required shape of the design work piece. Cast iron or Meehanite used to be the material of choice for metal working machines. Today, most machines make liberal use of weldments of hot-rolled steel and wrought products such as stainless steel to reduce cost and allow fabrication of more intricate frame designs.

Adopting in CNC machine technique is easy for large amount of production. CNC is using automated machines that work as what the machine is program and controlled. The essential part that user must know before conducting CNC machine:

• Spindle
• Work table
• Cutting tools
• Controller
• Computer programming
• Safety management