NC Modules

In this unit, we discuss the kind of machining modules that can be carried out on a CNC milling machine. Depending on the softwares that is being used, the name of these modules varies. As we are using Pro/NC as our demonstration software, we will also identify the name used under Pro/NC. We will discuss 3 modules in detail and introduce to you what is needed to work in these modules. 1. Profile Milling Other softwares may call this contour milling. Under this module, the software need to know how you want to approach/retract from the workpiece. How much you want to leave behind (or overcut, if needed), and how many rounds that you want to loop. 2. Pocket Milling Pro/NC has a powerful module called Volume Milling, and it has also a Pocketing module. We are using the Volume Milling to create Pocket Milling. Regardless of the name, what is required include, approach point, cutting method, cutting direction and how deep you want to cut. We will also discuss about the problems arises from the inclusion of an island. 3. Cycles Pro/NC called this module, Holemaking. As the name suggests, it is mainly in the making of holes, countersink hole, tap hole ream hole, deep hole, etc. What the module requires include the initial height, retract height, depth of the hole, peck drilling parameters etc.

Machining and Tooling Parameters

To machine efficiently, we need to specify parameters that are required by the individual machines. Furthermore, depending on the process that is being performed, the parameters may vary. Some parameters have special meaning when applied to certain toolings. For example, step over distance for a ball endmill need to be much smaller than a flat endmill. Zig zag or spiral tool path need to be specified when we are removing material inside a cavity. Profile increment need to be specified when finishing and roughing need to be done in profile milling. This chapter aims at explaining these parameters one by one.

Calculating of step over distance and scallop height

Whenever there is an area to be cut, the cutter need to traverse back and forth in order to cover the whole area. Most of the time the surface area to be cut is much bigger than the diameter of the cutter. As such, the cutter need to "Step Over" in order to cover the whole area. At the same time, the "Step Over" must be smaller than the diameter of the cutter in order not to leave a ridge of uncut material behind. Further complication is the use of a ball end mill, which can affect the surface roughness when the area is being machined. The waviness of the surface can be defined by the term "Scallop Height". With all these considerations, a set of mathematical procedure has been developed to help us to calculate the appropriate values. The video below is supposed to illustrate that. REMEMBER, when you are watching the video you can always pause it for you to think and absorb the detail.

NC Motion Control

NC control system can be categorized into the following:
1. Point to point system
2. Straight cut control system
3. Contouring control system

Contouring, being more complicated, can also be divided into 3 subsystems.
3.1 2D Contouring system
3.2 2½D Contouring system
3.3 3D Contouring System

In order to cut along the contour, the computer need to run an utility called an interpolator.

There are 5 types of interpolators:
1. linear interpolator
2. circular interpolator
3. helical interpolator
4. parabolic interpolator
5. cubic interpolator

Introduction to PC-CAD/CAM

As manufacturing continues to go for more sophistication, parts are getting smaller and more complex. Modern design also incorporates fancy, curvy shapes into their products. Conventional machining processes can no longer be used to achieve the kind of precision and fanciness that modern parts require. In order to assist manufacturers to deliver their products timely, accurately with the fancy look, softwares are used to turn computer-designed parts into machine codes, and subsequently, the codes are used in CNC machines to machine the intricate parts. By integrating the design and machining process, the process becomes faster and less-prone to error. Before the codes are used in actual production, the machining process could be simulated on screen to make sure that the code actually delivers the final product that the designer has dreamed of. Please refer to Unit 1 in the handout and complete the tutorial at the end of the unit. You can now view the answer to the tutorial from the following slide.


Additional assignment:
Write your comment and suggest what the world could be like if there were no computers to help us to design and manufacture. Look around you and suggest something that could not even exist if there were no computers to help.